Table of Content

10 March 2018, Volume 37 Issue 3

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Advances in studies on nitrous oxide (N₂O) emission in the reservoirs under the background of river impoundment.

Lü Xin, LIU Xiao-long, LI Jun, BAI Li, LI Si-liang, WANG Bao-li, WANG Fu-shun, WANG Zhong-liang

2018, 37(3):  613-623. 

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Most of rivers over the world are impounded. The effects of the impoundment on greenhouse gas emission have attracted much attention in recent years. Studies on production and emission of nitrous oxide (N₂O) are important for better understanding of nitrogen biogeochemicalcycling in reservoirs and impounded rivers and important for assessing the emission fluxes of N₂O from reservoirs. However, the knowledge on N₂O emissions and related mechanisms is still limited, especially on key processes, emission fluxes, and driving factors. Here, we reviewed theresearches on nitrogen biogeochemical cycling and N₂O emissions worldwide and proposed future research trends for further research and the unresolved key questions, aiming to accurately evaluate the emission fluxes of N₂O in river reservoir systems under impoundment.

Silicon cycle in lake-watershed system and its effects on carbon and nutrient cycles.

YANG Wei-hua, HAO Qian, XIA Shao-pan, MA Nan, SONG Zhao-liang

2018, 37(3):  624-633. 

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Silicon, with the abundance of 28.8%, is one of the most abundant elements in the earth’s crust. It is a beneficial element for the growth of most plants. In ecosystems, silicon cycle is closely related to the cycles of carbon and other nutrient elements. Most researches of silicon cycle are focused on marine or terrestrial ecosystems. Few studies focused on the processes of silicon cycle and their effects on carbon and nutrient cycles in lake-watershed systems. This review summarized the speciation and distribution of silicon in lake-watershed systems, elaborated the basic processes of silicon cycle in lakewatershed systems, and illustrated the underlying mechanisms for the controlling of silicon cycle on carbon and nutrient cycles. We suggest that futureresearch should analyze silicon sources of lakes and quantify the amount of carbon sequestered by phytoliths and diatoms in lake sediments. It is necessary to strengthen the study on the stoichiometric relationships of nitrogen, phosphorus and silicon in lakes and to build ecosystem models coupled with silicon carbon-nutrient cycles for lake-watershed system. This review is helpful for fully understanding silicon cycle and its effects on carbon and nutrient cycles, and provides reference for mitigating the eutrophication of lake-watershed systems and the impacts of global climate change.

Effects of mercury mobilization in reservoirs on mercury accumulation in fish: A review.

YU Yang, WANG Yu-chun, QU Xiao-dong, ZHANG Min, ZHANG Hai-ping, XIE Ying, ZHOU Huai-dong

2018, 37(3):  634-641. 

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Mercury concentration in fish tends to elevate in new hydroelectric reservoirs because of increased rates of converting mercury in the environment into methyl mercury, which is known as “reservoir effect” of mercury. The “reservoir effect” is worldwide, though its duration and strength would be reservoir specific. We reviewed the progress of research on mercury concentrations in fish after impoundment of reservoir, as well as the reservoir features and environmental factors related to “reservoir effect”. For a better understanding of the underlying mechanism, we gave a detailed discussion about the sources of mercury in reservoir and bioavailablity, and the traits of bioaccumulation and biomagnification. We also analyzed the mercury methylation reactions in reservoirs in China, which are distinguished from those in Europe and America. This paper provides a theoretical basis for prevention and control of mercury contamination inreservoir fish.

Runoff and sediment variations in the upstream of Wujiang River Basin and the influences of hydropower station construction.

WU Xiao-ling, ZHANG Xin, XIANG Xiao-hua, CHEN Xi, WANG Chuan-hai, LI Xiao-dong

2018, 37(3):  642-650. 

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The upstream of Yachihe Hydrologic Station is the main sediment area in Wujiang River Basin. The sediment movement to the downstream has important influence on sediment status in the whole basin. The characteristics of rainfall, runoff, sediment yield, and sediment transport have greatly changed since 1959. Based on longterm hydrology data, we analyzed the characteristics of runoff and sediment variation in the Yachihe River Basin and summarized the causes of such changes. The results showed that there was no significant variation in rainfall, but runoff showed a significant downward trend. In general, the sediment quantity was positively correlated with runoff quantity. However, there were great changes in sediment quantity of Yachihe Hydrologic Station and HongjiaduHydrologic Station after 1994 and 2004, respectively. The sediment quantity of Yachihe Hydrologic Station was reduced by 98.8%, and that of Hongjiadu Hydrologic Station was close to zero. The variation of runoff was mainly caused by human activities. Especially, the sudden change of runoff in 2002 was closely related to the construction of HongjiaduHydropower Station. The change of sediment yield was mainly caused by the change of the underlying surface due to human activities, whereas sediment transport was mainly blocked by dams in the river. Sediment deposition amount in cascade reservoirs was about 261.4 million tons between 1994 and 2014, and that in Hongjiadu Reservoir was about 33.8 million tons between 2004 and 2014.

The cycle and coupling effect of carbon and sulfur in cascade reservoirs: A case study of Jialing River.

YANG Meng-di, CUI Gao-yang, LI Qin-kai, HUANG Jun, LI Si-qi, ZHANG Jun, TAO Yue-le, LI Xiao-dong

2018, 37(3):  651-660. 

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Damming on the rivers has important effects on biogeochemical cycles of carbon,nitrogen and sulfur. To clarify the responses of C and S elements under the influence of cascade reservoirs, four representative cascade reservoirs in Jialing River were selected as the research objects. Samples of inflow, outflow, and stratified water in four cascade reservoirs were collected in winter (January) and summer (July) of 2016. Dissolved inorganic carbon (DIC) concentration, SO₄^2- concentration and isotopic compositions of δ¹³C_DIC and δ³⁴S were analyzed. The results showed that: (1) Water chemistry was mainly controlled by carbonic acid balance. At the same time, H₂SO₄, derived from pyrite and atmospheric SO₂ oxidation, was widely involved in regional carbonate weathering; (2) DIC was mainly affected by soil CO₂ and carbonate. SO₄^2- was mainly controlled by precipitation and pyrite oxidation process; (3) Significant correlations (P<0.05) existed among paired characters of reservoir water DIC concentration, SO₄^2- concentration, δ³⁴S value and δ¹³C_DIC value, indicating that the spatial and temporal dynamics of C and S elements in reservoir were affected by similar processes (physical, chemical, and biological). After intercepting of the dam, the river water environment and nutrient cycle had undergone great changes. The use of C and S double isotopes can effectively track the limnetic evolution of reservoirs.

Characters and sources of dissolved inorganic carbon isotope in channel reservoir: A case of Wanan Reservoir.

CHENG Tian-yu, ZHOU Tao, QIN Yong, Waiwai Phoye, WANG Fu-shun

2018, 37(3):  661-666. 

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In this study, Wanan Reservoir was investigated with four seasonal samplings from September 2014 to June 2015, to understand the characters and sources of dissolved inorganic carbon (DIC) and its carbon isotope (δ¹³C_DIC). Nine sampling sites covering the reservoir were included in the field survey. Results showed that the concentration of DIC in water was lower in summer and autumn than that in other seasons. The value of δ¹³C_DIC was more positive in winter and spring. From upstream to downstream, DIC concentration showed a decrease trend, whileδ¹³C_DIC become more positive gradually. Photosynthesis and organic matter decomposition playedimportant roles in controlling the variation of δ¹³C_DIC in the surface water. Along the water column in the central reservoir, in situ parameters such as water temperature had no significant difference, indicating a weak thermal stratification in reservoir. However, DIC concentrations had an increase trend downwardly, while δ¹³C_DIC gradually become more negative from surface water to deep water. Based on massbalance calculation, about 57% of DIC derived from soil CO₂ at the reservoir entrance, while this value was 49% at the site of reservoir discharge. This result means that river damming could change the weathering information contained in the chemical composition of river water.

Hydrochemical characteristics and chemical weathering processes in Chishui River Basin.

XU Sen, LI Si-liang, ZHONG Jun, SU Jing, CHEN Shuai

2018, 37(3):  667-678. 

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Chishui River, the only tributary without the dam in the upper reaches of YangtzeRiver, is of importance for better understanding solute transportation in rivers and the chemical weathering processes. In this study, we investigated the hydrochemical characteristics of the mainstream and major tributaries and its major driving factors in Chishui River Basin. Mass balance and forward model approach were applied to calculate the contribution of different endmembers, the chemical weathering rates, and the atmospheric CO₂ consumption rates in the river. Theresults showed that cations of the rivers were dominated by Ca²⁺ and Mg²⁺. The contributions of cations derived from atmospheric input, human activities, silicate weathering, and carbonate weathering were 12%, 3%, 9% and 77%, respectively. The anions of the rivers were dominated by HCO₃^- and SO₄^2-. The Chishui River water had higher SO₄^2- and lower HCO₃^- concentrations compared with Yangtze River and Wujiang River. The weathering rates and CO₂ consumption rates of silicate were estimated to be 7 t·km^-2·a^-1 and 1.7×10⁵ mol·km^-2·a^-1, respectively, which were similar to those in other rivers located in karstic areas of southwest China. The weathering rates and CO₂ consumption rates of carbonate were estimated to be 57.6 t·km^-2·a^-1 and 4.52×10⁵ mol·km^-2·a^-1 after excluding the impacts of sulfuric acid in weathering reactions, respectively. The weathering rates increased to 74.6 t·km^-2·a^-1 and CO₂ consumption ratesdecreased to 1.74×10⁵ mol·km^-2·a^-1 when considering the sulfuric acid as a carbonate weathering agent. The results suggested that the carbonate weathering rates increased by 30% due to the involvement of sulfuric acid. Due to higher concentration of SO₄^2- and lower concentration of HCO₃^- in water, CO₂ consumption rates were lower in the Chishui River compared to other rivers in karstic areas of southwest China.

Effects of dam interception on hydrogen and oxygen isotope compositions in cascade reservoirs: A case of Jialing River.

ZHANG Jun, CUI Gao-yang, LI Qin-kai, HUANG Jun, TAO Yue-le, YANG Meng-di, LI Si-qi, LI Xiao-dong

2018, 37(3):  679-687. 

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River damming alters natural attributes of rivers, with consequences on water cycle in the river catchment. In this study, water samples including stratified water from four cascadereservoirs in the Jialing River basin were collected in January, April, July, and October in 2016. The hydrogen and oxygen isotopic compositions and their spatial and temporal variations wereanalyzed to assess the impacts of dam interception on water cycle in the river basin. The results showed that the δ¹⁸O and δD values of the surface water were generally turning positive along with the flow path due to the latitude effect and the dam interception. The δ¹⁸O values of the water samples were more positive in January and October than those in April and July, which should be resulted from the variations in the amount and sources of precipitation. In the summer stratification period, the range of¹⁸O value in the reservoir with thermal stratification (Tingzikou reservoir) was larger than that in other seasons. In contrast, it was not the case in other reservoirs. Moreover, reservoir stratification led to divergence in hydrogen and oxygen isotopic compositions between the discharged water and the surface water near dam. The existence of cascade reservoirs enhanced watershed evaporation, which might be responsible for the greater deviation of thehydrogen and oxygen isotope compositions of the river water from the local meteoric water line. The evaporation in the summer (July) was the strongest in the study area, followed by the spring (April) and the weakest in the winter and autumn (January and October).

 

Chemical weathering and CO₂ consumption flux in Tibetan Plateau: A case of NiyangRiver catchment.

LIU Xu, ZHANG Dong, GAO Shuang, WU Jie, GUO Jian-yang, ZHAO Zhi-qi

2018, 37(3):  688-696. 

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Tibetan Plateau is an ideal place to study the relationship between tectonic uplift,surface weathering and climate change. Here, the role of sulfuric acid in carbonate and silicate weathering and its effects on the corresponding CO₂ consumption flux and climate change were investigated in Niyang River catchment using hydrochemical method and forward model. The results showed that: (1) The hydrochemical type of Niyang River was characterized by HCO₃·SO₄Ca·Mg and HCO₃·SO₄Ca. The cations in river water were mainly derived from weathering of carbonate and silicate, contributing to 79.4% and 11.7% of the total water cation, respectively. (2) There was substantial chemical weathering of sulfide minerals in the catchment, with weathering rate (13.5 t·km^-2·a^-1) being three times as high as that of the silicate mineral weathering (4.46 t·km^-2·a^-1). (3) The net CO₂ emissions during chemical weathering of carbonateresulted by sulfuric acid, to a large extent, could offset the CO₂ consumption caused bycarbonate silicate mineral weathering in Niyang River catchment.

Hydrogeochemical characteristics and controlling factors in Jiulong River (Fujian Province) during the flood season.

LI Xiao-qiang, HAN Gui-lin, DONG Ai-guo, LIU Man, YANG Kun-hua

2018, 37(3):  697-706. 

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To understand the environmental status of Jiulong River basin, water samples from the river were collected in July 2017. The pH value of water ranged from 6.7 to 7.9, with an average of 7.2, indicating slightly alkaline. The average value of total dissolved solids (TDS) was 90.9 mg·L^-1, lower than the global mean value of the rivers. The average value of electrical conductivity and dissolved oxygen was 116.5 μS·cm^-1 and 7.5 mg·L^-1, respectively. Ca²⁺ was the dominant cation, accounting for 47.9% of the total cations, whereas K⁺ and Na⁺ together accounted for 29.6% of the total cations. HCO₃^- and SO₄^2- were main anions, which together accounted for 68.6% of the total anions. Those results suggested that the hydrogeochemical type of Jiulong River was HCO₃SO₄Ca. The forward method was used to estimate the contribution of each end member, the results of which showed that carbonate and chemical weathering of silicate contributed to 50.6% and 30.7% of the total cations, respectively. Precipitation had an obvious influence on the water chemistry, presenting a contribution of 12.9% to total cations. The influence of anthropogenic input could not be ignored, especially for the contents of SO₄^2- and NO₃^-. The water chemistry of North River was heavily affected by industrial production due to the industrial and agricultural layout, while that of West River and South River were affected by agricultural activities. Therefore, the discharge of wastewater from industrial production as well as urban sewage should be strictly controlled in North River. In addition to urban sewage, the use of fertilizers also should be strictly controlled in West River and South River.

Nitrogen and phosphorus retention in cascade reservoirs along the upper reaches of Wujiang River.

ZHOU Tao, CHENG Tian-yu, YU Ning-xiao, WANG Fu-shun

2018, 37(3):  707-713. 

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Rivers are generally facing the interception by dams all over the world, leading to the conversion of rivers from natural state into “impounding river”. The transport fluxes and retention of nitrogen and phosphorus in the river system are key issues for evaluating the water environmental impact of reservoirs. In this study, three cascade reservoirs (Hongjiadu, Dongfeng and Wujiangdu) along the upper reaches of Wujiang River basin were investigated to understand the distribution patterns, transport fluxes and retention of nitrogen and phosphorus in these reservoirs. The annual retention rates of total nitrogen (TN) of Hongjiadu, Dongfeng and Wujiangdu reservoirs were 20.2%, 36.0%, and -21.1%, while that of total phosphorus (TP) were 5.4%,56.5% and -84.9%, respectively. The three reservoirs had different retention effects and spatiotemporal patterns due to differences in hydrologic conditions, reservoir running time and anthropogenic factors. The annual retention rates of TN and TP in Wujiangdu Reservoir were negative due to the influence of cage fishery. However, Dongfeng Reservoir showed obvious nutrient retention. The nutrient retention in Hongjiadu Reservoir was weaker than that in Dongfeng Reservoir because of the degradation of plants previously buried in Hongjiadu Reservoir.

Sulfate sources and its impacts on chemical weathering in water of the upper reaches of Xijiang River.

LIU Jing, LI Si-liang, ZHONG Jun, DING Hu

2018, 37(3):  714-722. 

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Mineral weathering by sulfuric acid plays an important role in chemical weathering in the catchment, with consequences on global carbon cycle. Highfrequency sampling and analysis can accurately assess the sources and biogeochemical processes of dissolved solutes in the river. However, few studies have focused on the temporal variation of sulfate in rivers and rock weathering by sulfuric acids. Here, a monthly sampling campaign was conducted in the Nanpan, Beipan and Hongshui rivers along the upper reaches of Xijang River during a whole hydrological year (October 2013 to September 2014). The seasonal variation of riverine sulfate was affected by the monsoon climate in the upper reaches of the Xijang River basin. Heavy isotopes were generally enriched in sulphate during the dry season compared to that in the wet season. The isotopicevidence showed that the riverine sulfate was mainly derived from sulfide oxidation, whereas evaporite dissolution could be an important source during the dry season. Mine drainage would be an important source of sulfate to those rivers during the wet season, mainly due to the responses of the fast surface flow to frequent heavy rain in monsoonal climate regions. A relatively highproportion of HCO₃^- was derived from rock weathering by sulfuric acid during the wet season compared to that during the dry season. Approximately 1/4 of the HCO₃^- in the Hongshui River originated from carbonate weathering by sulfuric acid, which derived from the oxidation of sulfide. In all, information from the specific dual isotopic characteristics of riverine sulfate throughout a hydrological year can provide unique evidence for understanding the temporal dynamics of sulfate concentrations and weathering processes in the rivers.

Characteristics of sulfur and oxygen isotopes of dissolved sulfate in response to water sediment controlling in the Yellow River.

ZHANG Dong, LIU Song-tao, ZHANG Yong-ling, ZHAO Zhi-qi

2018, 37(3):  723-733. 

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To elucidate how the water-sediment controlling process affects element cycling in the Yellow River Basin, water samples were collected during water-sediment controlling in 2012, and then sulfur and oxygen isotopes were analyzed. The results showed that sulfur and oxygen isotope values of river water samples in Sanmenxia station varied from 7.9‰ to 12.5‰ (with an average of 10.1‰) and from 4.8‰ to 8.4‰ (with an average of 7.1‰), respectively. Sulfur and oxygen isotope values of river water samples in Xiaolangdi station ranged from 8.5‰ to 9.1‰ (with an average of 8.6‰) and from 5.6‰ to 7.4‰ (with an average of 6.6‰), respectively. Sulfur and oxygen isotope values of river water samples in Huayuankou station varied from 8.7‰ to 12.0‰ (with an average of 10.0‰) and from 6.5‰ to 8.5‰ (with an average of 7.7‰), respectively. Sulfur and oxygen isotope values of sulfate in river water decreased with the increases of siltcontents in the river water samples, indicating that the “newly produced sulfate” was mainlyderived from oxidation of sulfide and organic sulfur during water-sediment controlling, especially in Sanmenxia station and Xiaolangdi station. However, such differences of sulfate isotopes were not significant in Huayuankou station due to the mixing processes impacted by the tributaries of Yiluo River and Qinhe River. The range of sulfate isotopes suggested that dissolved sulfate in river water was mainly controlled by dissolution of gypsum, oxidation of sulfide and organic sulfur and sewage water. Watersediment controlling process affected sulfur cycling in Yellow River, in that it can release sulfate by oxidation of sulfide and organic sulfur in sediment, and thus increases sulfate flux to the downstream. The proportion of sulfate released into river by water sedimentcontrolling was about 24.2% in Sanmenxia Reservoir and 8.8% in Xiaolangdi Reservoir, respectively. The results improved our understanding of water-sediment controlling on the riverineelement cycling in the Yellow River Basin.

Chemical composition and heavy metal distribution in surface water of typical inlandrivers in Qinghai.

WANG Yi-han, LIU Yin-xu, LIU Hai-hong, LIU Xiao-long, LU Zhan-kui, LI Jun

2018, 37(3):  734-742. 

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To reveal the hydrochemical composition and the distribution of heavy metals in the surface water of typical inland rivers in Qinghai, water samples were collected from the Bayin River, Golmud River and Xiao Qaidam Lake during July-August 2015. The concentrations ofmajor ions and twelve heavy metal elements were analyzed, and the water quality was assessed. The results showed that the chemical composition of surface water in rivers and lakes were primarily dominated by the rock weathering and evaporation crystalization processes, respectively. The concentrations of most heavy metals in lakes were higher than those in rivers, due to the enrichment and crystallization of heavy metals caused by lake water chemistry and evaporation. Principal component analyses (PCA) showed that the heavy metals mainly came from rock weathering and were less affected by human activities. The concentrations of heavy metals in river waters met grade I water quality according to the standard of Surface Water Environmental Quality Standard of China (GB 3838-2002).

Response of nitrogen dynamic change to heavy rainfall events during summer in Haihe River of Tianjin City.

XIA Yan-meng, LI Cai, LI Si-liang, DI Chong-li, YUE Fu-jun, PENG Hui

2018, 37(3):  743-750. 

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Climate change is an important factor affecting material transport in the basin. Annual rainfall has increased significantly in recently years in the North China. The environmental impact of material transport should be considered during the construction of sponge city. In this study, river water samples in four important sections of the Haihe River and samples from city roadrunoff were collected during rainy season to explore the effects of heavy rainfall events on the dynamics of nitrogen pollution in Haihe River in Tianjin. The rainfall data were taken from the relevant hydrological stations. The results showed that NO₃^--N concentrations of all the studied sections sharply increased after the heavy rainfall events and recovered to pre-rainfall levels after one week. However, δ¹⁵NNO₃^- and δ¹⁸ONO₃^- first decreased and then increased. Integrated analysis suggested that mixing effects, biogeochemical processes and different responses to rainfall affected the dynamics of nitrogen pollution of the Haihe River in Tianjin. The substantial increases of nitrogen load during the rainfall period indicated that the factitious pollution during rainevents was very serious, which led to elevated nitrogen pollution in urban rivers. In summary, the material transportation in urban river during the rainfall period did not follow the dilution effect. Controlling of urban point source pollution should be given priority in the management of urban water environment quality.

Iron and manganese cycling and vertical distribution of heavy metals in sediments of Aha Lake and Hongfeng Lake.

KANG Ting, SONG Liu-ting, ZHENG Xiao-di, HUANG Ying, YANG Jie, TENG Yan-guo

2018, 37(3):  751-762. 

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Aha Lake and Hongfeng Lake are two adjacent lakes on the Yunnan-Guizhou Plateau, the sedimentary environments of which are different. The sedimentary environment of Aha Lake is weakly oxidizing to reducing whereas that of Hongfeng Lake is oxidizing. To compare the enrichment, migration, and transformation characteristics of heavy metals in lakes with different sedimentary environments, contents and vertical distributions of heavy metals in sediments as well as pore waters were investigated in Aha Lake and Hongfeng Lake. The results showed that contents of Co, Ni and Zn were relatively high with moderate to heavy pollution levels in the sediments of Aha Lake. For Hongfeng Lake, while the contents of As and Zn were relatively high,  other heavy metals were unpolluted or slightly polluted. The characteristics of the cycling of Fe and Mn in two lakes were significantly different. In contrast to that in Hongfeng Lake, Fe and Mn cycling was extremely intense and the reduction zoning was more distinct in the sediments of Aha Lake, due to higher Fe, Mn, and S contents and Mn/Fe ratio. Based on those findings, we constructed a conceptual model of early diagenesis of Fe and Mn cycling process in the sediments of Aha Lake and Hongfeng Lake. Following terrigenous correction and correlation analysis, results showed that the cycling of Fe and Mn played an important role on the distributions, migrations and transformations of heavy metals. The migrations and transformations of Co, Ni, Zn and As were mainly influenced by Mn cycling, while that of Cu was mainly influenced by Fe cycling in Aha Lake. In contrast, the migrations and transformations of Co, Ni, Cu, Zn, Cr, As and Pb were influenced by Fe cycling in Hongfeng Lake.

Biogeochemical characteristics of nitrogenous species in sediments of Baihua Lake.

SI Xia-li, YUE Fu-jun, WANG Zhong-Jun, ZENG Jie, JIA Guo-dong, ZHONG Jun, LI Si-liang

2018, 37(3):  763-770. 

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Deep lakes experience alternate oxidation and reduction environment, which mayaffect the biogeochemical processes of nitrogen. Lake sediments generally have a unique reduction environment with complicated biogeochemical processes of nitrogen. In the present study, vertical sediments were collected from a typical plateau deep lake, Baihua Lake, during summer stratification. The concentration of nitrogenous species in pore water, watersoluble, adsorptionsoluble, and particle organic nitrogen (PON) with δ¹⁵NPON in the different depths of sediments were analyzed. The results showed that the concentration of total nitrogen (TN) in the pore water,ranging from 6.9 to 42.8 mg·L^-1, was mainly composed of NH₄⁺-N, ranging from 6.6 to 25.6 mg·L^-1, and dissolved organic nitrogen. The concentrations of nitrate and nitrite were underdetection line, indicating that the nitrate was used by denitrification or the potential dissimilatory reduction. The concentration of adsorptionsoluble NH₄⁺-N was higher than that of watersoluble NH₄⁺-N. The concentration of PON in the sediment ranged from 0.22% to 0.60%. Meanwhile, its variation tendency was well fit to the exponential decay pattern, suggesting that the variation of PON concentration in the sediment may be due to the diagenetic effect and mineralization. The δ¹⁵NPON value above 31 cm depth decreased with depth, ranging from 3.4‰ to 10.0‰ and with an average of 6.4‰. It showed a more decrease tendency above 10 cm depth, which may be caused by the microbial degradation activity and the water exchange between pore water and lake water. The trend of δ¹⁵NPON value below 31 cm depth was opposite to that of the surface, which may be the result of diagenesis at early stage. TN in pore water had higher δ¹⁵N value than did watersoluble and adsorptionsoluble N. TN in watersoluble and adsorptionsoluble N had similar δ¹⁵N value, which was higher than the δ¹⁵NPON. The results suggested that the increases of NH₄⁺-N concentration in pore water may be related to the dissimilatory reduction process.

Effects of macrophytes on gaseous nitrogen emissions and nitrogen removal from sediments in a shallow eutrophic lake.

XING Tao, LI Jun-xiong, LI Bin-bin, SUN Yi-qi, LI Wei-ping, LIANG Xia

2018, 37(3):  771-778. 

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Anthropogenic nutrient enrichment in lakes and subsequent increases of greenhouse gas emission are major global problems affecting the ecosystem function of lakes. In this study, laboratory experiments were carried out to investigate the effects of diel dynamics of dissolvedoxygen (DO) cycles, induced by macrophyte photosynthesis and respiration, on nitrous gaseous emissions and nitrogen removal from sediments of a macrophytesdominated eutrophic lake. We found that macrophytes significantly enhanced the diurnal fluctuation of DO in water andincreased sediment oxygen levels. The fluxes of N₂O and N₂ showed substantial diurnal variation with the fluctuation of DO. Moreover, macrophytes dominated sediments were characterized by significantly  higher potential nitrification and denitrification compared to non-vegetated control sediments. The concentrations of TN and NH₄⁺-N in macrophytes sediments were significantly lower than those in controls. Based on the evaluation of N transformation pathways, we found that nitrogen uptake by macrophytes and N₂ emissions were the dominant pathways for N removal from macrophytes dominated sediments. The results provide scientific basis for the ecological restoration of eutrophic lakes.

Distribution and bioavailability of soil phosphorus at the riparian zone of Lanlingxiwatershed in the Three Gorges.

WU Qi-xin, HAN Gui-lin

2018, 37(3):  779-785. 

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The fluctuations of water level can lead to the changes of the concentration and forms of phosphorus (P) in the riparian zone. In this study, we investigated the changes of forms and bio-availability of P in different elevations of riparian zone of Lanlinxi catchment in Three Gorges Reservoir. The mean concentration of total P was 508.48 mg·kg-1, which is lower than that of the background soil, suggesting that the submerging led to P release in the riparian zone. Detrital apatite P and occluded P were the main forms of P in Lanlinxi riparian zone. The concentrations of various forms of P were following the order: detrital apatite P > occluded P > Fe bound P > Albound P > organic P > authigenic apatite P > loosely adsorbed P. The mean concentration of bio-available P was 204.12 mg·kg^-1. Phosphorus would be released to the water body when riparian zone was submerged.

Composition characters of mercury and fatty acids in cultured fish from Wujiangdu Reservoir.

LIN Dan, LIN Jing, DING Li, YANG Guang-hong, YAN Hai-yu

2018, 37(3):  786-792. 

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To evaluate the nutrient value and estimate the mercury concentration and fatty acids composition in the cultured fishes of Wujiangdu Reservoir, we randomly collected 120 samples of 10 dominant fish species. The concentrations of THg, MeHg and polyunsaturated fatty acids (n6/n3 PUFA) and DHA and EPA (speciation of fatty acids) in fishes were analyzed. The results showed that the concentration of THg in cultured fishes varied from 3.50 to 185.05 ng·g^-1, with an average value of 23.90 ng·g^-1. The concentration of MeHg varied from 0.16 to 49.09ng·g^-1, with an average value of 7.78 ng·g^-1. The concentrations of THg in cultured fishes were low, and did not exceed the limit of provisions of China’s edible standards of contaminants in aquatic products. Furthermore, the content of EPA + DHA in n3 PUFA, the essential fatty acids to human body, was the highest in crucian carp, and the lowest in carnivorous catfish. After analyzing the ratio of n6/n3 PUFA of samples, we found that the fishes enriched with n6 PUFA as well as EPA and DHA. In conclusion,Parabramis pekinensis, Hypophthalmichthys molitrix, Ctenopharynodon idellus, Mylopharyngodon piceus, and Tinca tinca are fishes with higher concentration of EPA and DHA and lower concentration of MeHg, being better dietary for human health.

Mercury distribution of aquatic plants and its response to mercury in sediments in Caohai wetland, Guizhou Province.

HE Tian-rong, ZENG Ling-xia, XU Yi-yuan, LI Zhen-ji

2018, 37(3):  793-800. 

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Dominant plant species were collected from the deepwater area and shallowwater area of Caohai Lake, a National Nature Reserve of China. The distribution of mercury and methyl mercury in aquatic plants were analyzed, and the risk of mercury pollution was evaluated. Theresults showed that the total mercury concentrations in those species ranged 5.18-40.06 ng·g^-1 with an average of 12.78 ng·g^-1, which was comparable to the findings from other naturalreserves. The mercury concentration was higher in stems and leaves ofAlternanthera philoxeroides, Najas marina, and Polygonum hydropiper. Methyl mercury concentrations in those species ranged from 0.04 to 2.47 ng·g^-1, with an average of 0.34 ng·g^-1. Methyl mercury concentrations in leaves and stems were positively correlated with total mercury in those tissues (r=0.38,n=46,P<0.01). The concentrations of total mercury and methyl mercury in plants from the shallowwater area were significantly higher than those from the deepwater area. Such a pattern was consistent with the distribution of methyl mercury in sediments, but was opposite to that of total mercury in sediments. Our results suggested that methylation and the bioavailability of mercury in sediments from the shallowwater area were higher than those from the deepwater area in Caohai Lake. The difference in organic matter concentrations of the sediments and the wetdry alternation (flooding recedingflooding) in the surrounding shallow marshes would associate with the relatively higher concentrations of mercury and methyl mercury in aquatic plants in the shallowwater area. The underlying mechanism is needed to be uncovered in further studies.

Effects of nitrogen and phosphorus supply on plant community structure of coastal wetland in the Yellow River Delta.

LIU Xiao-ling, WANG Guang-mei, YU Jun-bao, RAN Yue-nan, GUAN Bo, HAN Guang-xuan, WANG An-dong, ZHAO Ya-jie

2018, 37(3):  801-809. 

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Human activities have significantly altered the environmental N and P status through changing both supply level and ratio, with consequences on ecosystem structure and function. To explore the effects of N and P supply on plant community structure of coastal wetland in the Yellow River Delta, a field manipulation experiment combined three supply levels and three N:P supply ratios (5:1, 15:1, 45:1) was conducted in 2015 and 2016. The results showed that the amount of N and P supply had significant effects on species diversity, while N:P supply ratio had neither significant main effects nor interactive effects. Species richness and Shannon index was highest at medium nutrient level, while Pielou index was maximal at low nutrient supply. Dominant species responded differently to the variation of relative supply of N and P. Neither supply level nor N:P supply ratio significantly affected the importance values of Tripolium vulgare,Cynanchum chinenseandPhragmites australis. In contrast, supply level had significant effects on the importance values ofSuaeda glaucaandSuaeda salsa.With the increases of supply level, the importance value ofS. glaucaincreased while that of S. salsadeclined. Under different N and P supply treatments,S. glaucashowed strongest impacts on species diversity, followedbyS. salsa, while P. australias had little influence on species diversity. Meanwhile, the responses of theimportance values of dominant species and species diversity to changes of N and P supply were different between 2015 and 2016, suggesting that the effects of N and P supply condition on plant community structure of coastal wetland would be mediated by air temperature, precipitation and other natural conditions.

Habitat selection of wintering crane in Shengjin Lake wetland.

WANG Cheng, DONG Bin, ZHU Ming, HUANG Hui, ZHAO Kang-kang, Lü Dian, CUI Yu-huan, GAO Xiang

2018, 37(3):  810-816. 

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Shengjin Lake National Nature Reserve is one of the most important wetlands in the world and an important habitat for wintering cranes in China. Environmental factors of wetland ecosystems influence habitat selection of cranes. In this study, we analyzed data of land use types and winter bird observation in Shengjin Lake during the period from 1986 to 2015. Grey relevancy model was adapted to examine the relationship between crane population and land use types, with the aim to get the main habitat types of cranes. Principal component analysis was used to analyze the main factors influencing habitat selection of cranes. The results showed that reed beach land was the main habitat type for four species of overwintering cranes. The main factors affecting the habitat selection of cranes were water level, planktonic biomass, and residential distance. Within those factors, the relative weight of water level was the highest, followed by planktonic biomass and residential distance.

 

Time budget and behavioral rhythm of wintering Tundra Swans in a lotus pond reclamation area around Poyang Lake.

SHAO Ming-qin, ZHANG Cong-min, DAI Nian-hua, XU Ning, ZHI Yi-jin, LU Ping

2018, 37(3):  817-822. 

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The scan sampling technique was used to examine the winter behaviors of Tundra Swans (Cygnus columbianus) from December 2016 to March 2017 in a lotus pond reclamation area around Poyang Lake, Jiangxi Province, China. Resting (45.93%) and feeding (30.52%) were the main behaviors. Grooming, flying and vigilance behaviors of adults were significantly higher than those of young birds. The locomotion budget at temperatures of 10-15 SymbolpB@C was significantly higher than that at other temperatures. Grooming behavior in shallowwater area was significantly higher than that in deepwater area. With respect to daily behavioral rhythm, small resting peaks occurred in 07:00-07:59 and 13:00-13:59, with nadirs occurring in 09:00-09:59 and 17:00-17:59. Resting behavior was dominant in each period, suggesting a survival strategydominated by resting. Feeding behavior peaked in 17:00-17:59 and with no obvious nadirs, probably to gain energy to compensate overnight consumption by increasing  feeding time. The resting curve fluctuation of adults was less than that of young birds, indicating that the resting behavior of young birds was more random. Moreover, the feeding curve fluctuation of adults was less than that of young birds, indicating adult feeding behavior was stable, with an evening peak to deal with cooler conditions. Fluctuations in feeding and resting curves were smaller in deepwater area than shallowwater area, indicating that deep waters would be more suitable for bird survival.

Effects of soil properties on plant community structure in a semi-arid grassland.

FU Zhi-yuan, JIANG Hong, WANG Guo-qiang, A Ying-lan, XUE Bao-lin, WANG Hong-qi

2018, 37(3):  823-830. 

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Data of vegetation and soil physicochemical properties were collected from 55 quadrats in a typical semi-arid grassland in Ewenke Tribe Autonomous Qi (Flag), Hulunbuir, easternInner Mongolia, China. The effects of soil physicochemical properties on the spatial distribution of vegetation community were analyzed by canonical correspondence analysis (CCA). With respect to its spatial distribution, the vegetation was slightly degraded. The degraded communities showed the characteristics of high biomass and low diversity. The transitional communities showed the characteristics of high diversity and low biomass, and the original communities showed an intermediate state. Soil physical properties, such as particle composition and bulk density, had little spatial variation. In contrast, there were substantial spatial variation in the contents of soil organic matter, total phosphorus, total nitrogen, and soil moisture. The horizontal change of plantcommunity structure was mainly driven by soil moisture, total phosphorus, organic matter andtotal nitrogen contents, with soil moisture being the most important factor. The moisture of surface soil (0-20 cm) was the most important factor affecting community structure (with a contribution rate of 38%), followed by the moisture of deep soil (60-80 cm) (with a contribution rate of 36.4%). Such a result indicated that plant community structure was affected not only by shortterm precipitation but also by longterm climate. In conclusion, soil moisture was the most important factor driving the spatial variation of plant community structure in the semi-arid grassland, followed by soil organic matter, total nitrogen  and total phosphorus contents.

Impacts of nitrogen application and legume-grass mixed planting on grassland community and soil respiration.

TANG Xue-juan, XU Li-jun, PANG Huan-cheng, YANG Yun-hui, WANG Di, LI Da, BAI Ke-yu

2018, 37(3):  831-839. 

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Legumegrass mixed planting is an important way to improve conservation and useefficiency of water and soil resources, restore degraded land, and maintain soil health. Five types of pastures (Medicago sativa, Bromus inermis,Leymus chinensis, M. sativa and B. inermis mixed planting, andM. sativa and L. chinensis mixed planting) were established in HulunbuirGrassland Station, with different nitrogen fertilization levels being applied. Aboveground biomass,photosynthetic characteristics and soil respiration were measured, aiming to understand the impacts of nitrogen application and legumegrass mixed planting on the characteristics of grassland community and the dynamics of soil respiration and thus provide theoretical basis for pastureestablishment and optimal utilization in eastern Inner Mongolia. Results showed that mixed planting did notsignificantly increase the total biomass of pasture as expected under drought condition. The netphotosynthetic rate (P_n) of the three species was in the order of:M. sativa <B. inermis<L. chinensis. Mixed sowing with alfalfa significantly improved the P_n of grasses. Nitrogen application increased the soil respiration intensity under each planting type. Moreover, mixing with alfalfa improved soil respiration intensity, with perk values occurring at 10:00-12:00.

Water use strategy of poplar (Populus alba) in different growing seasons based on isotopic analysis.

LI Xue-song, JIA De-bin, QIAN Long-jiao, FENG Yun

2018, 37(3):  840-846. 

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Carbon, hydrogen and oxygen isotope tracer techniques were used to analyze theseasonal dynamics of water sources and water use efficiency of poplar (Populus alba) in Zhenglanqi, with direct judgment method and multivariate mixed linear model. The results showed that there was obviously seasonal dynamics in poplar’s water sources. In early and late stages of growing season (April-May, October), poplar used both shallow soil water (0-50 cm) and deep soil water or underground water under 150 cm. In middle stage of growing season (June to September), poplar primarily used precipitation which infiltrated to 0 to 150 cm soil. Water use efficiency of poplar was relatively higher, with 35.90, 13.90, 20.65, 28.93 and 63.88 mmol C·mol^-1 H₂O from May to September, respectively. Poplar could use deep soil water and increase water use efficiency when shallow soil water could not satisfy its water requirement in rainy season. When there was enough precipitation, poplar use soil water from the top layer, and water use efficiency decreased gradually as well. These results indicated that poplar had higher water use efficiency due to its ability to use alternative water sources and controlling its water use rate in semiarid area. These strategies assist poplar to reach the greatest water use efficiency favoring their growth.

DBH and stand density regulate intraspecific competition of Larix gmelinii in eastern Inner Mongolia.

LIU Yi-qing, TIAN Yu-hong, SONG Han-zhang, HUANG Wei-lin

2018, 37(3):  847-853. 

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Competition is one of the main drivers for forest decline and restoration. In this study, we investigated 293 target trees in aLarix gmeliniiplantation in a semiarid area of eastern Inner Mongolia. We used Heygi individual competition index model to quantify the competition intensity at both individual and plot levels and analyzed the determinant factors. Results showed that the competition intensity ofL. gmeliniidecreased with the increases of diameter at breast height (DBH). Their relationship followed the power function. Results from Pearson’s correlation analysis indicated that individual competition index was negatively correlated with tree height and crown width, and positively correlated with tree decline index. A multiple linear regression model analysis demonstrated that the competition intensity at the plot level was mainly influenced by stand density. Our results had implications for uncovering the mechanism for the forest decline in eastern Inner Mongolia.

Biomass and nutrient storage of logging residues ofPinus massoniana plantation.

LI Hua, ZHENG Lu, LI Zhao-ying, LU Li-hua, MING An-gang, NONG You, SUN Dong-jing

2018, 37(3):  854-860. 

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To understand soil productivity maintenance and provide reliable scientific basis for plantation management, biomass and nutrient allocation in different components of logging residues were examined in the clearcutting land of a 31-year-oldPinus massoniana plantation. We measured biomass and nutrient concentration of logging residue’s components, and then calculated nutrient storage. The results showed that the total biomass of logging residues was 39.1t·hm^-2, and the storage of carbon, nitrogen, phosphorus, potassium, calcium and magnesium was 18303, 101.2, 8.3, 73.4, 96.0 and 24.7 kg·hm^-2, respectively. Among different components, the biomass and carbon storage were in the order of sprig (accounting for 25.3% and23.3% of total biomass and carbon storage, respectively) > branch (21.7% and 21.1%) and taproot (17.1% and 18.5%) > coarse root (11.5% and 12.4%) and leaf (9.2% and 9.1%). Nitrogen, phosphorus, potassium, calcium and magnesium were mainly stored in sprig, branch, and leaf (the sum of those components were 70.5%, 76.5%, 72.2%, 76.2% and 72.6%, respectively), followed by taproot and coarse root. The middlesized root, small root and fine root had the lowest biomass and nutrient storage. The biomass and nutrient storage of logging residues were enormous, especially in branch and leaf. Therefore, retaining logging residues during forest regeneration is important for forest productivity maintenance.

Growth and biomass allocation of Sophotora flavescens andCatsia tora seedlings beneath moso bamboo forest in response to moso bamboo density.

GAO Ping-zhen, CHEN Shuang-lin, GUO Zi-wu, YANG Qing-ping

2018, 37(3):  861-868. 

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To explore the suitable stand density of moso bamboo (Phyllostachys edulis) in the agroforestry systems of bamboo-Sophotora flavescens and bamboo-Catsia tora, we investigated the growth and biomass of two nitrogenfixing species, S. flavescensandC. tora, under three moso bamboo densities, D1 (1600±200 stems·hm^-2), D2 (2400±200 stems·hm^-2) and D3 (3200±200 stems·hm^-2) with the same site conditions and management levels. The results showed that plant height, basal diameter, tissue biomass and total biomass of both species all decreased with the increases of moso bamboo density. The decreased amplitude followed the order of D3>D2>D1. The biomass proportions of leaf and bean of S. flavescensshowed an inverted V shaped pattern, while the root biomass proportion and root/shoot ratio varied with a Vshaped pattern, and the stem biomass proportion decreased linearly with the increases of bamboo density. Except for the stem, the biomass proportions of other organs had no significant differences (P>0.05) among three bamboo densities. With the increases of moso bamboo density, stem biomass proportion, root biomass proportion and root/shoot ratio ofC. tora seedlings showed a similar trend to that of theS. flavescensseedlings. The proportions of leaf biomass and bean biomass showed an increase trend, with the values in D1 being significantly higher than that of D2 and D3 (P<0.05).Results from the principal component analysis and Rtype factor analysis showed that the comprehensive scores of growth and biomass allocation of bothS. flavescens and C. tora followed the order of D1>D2>D3. Our results indicated that the bamboo density had negative effects on the growth and biomass allocation ofS. flavescens andC. tora seedlings. D1 (1600±200 stems·hm^-2) would be the suitable bamboo density for the management of both agroforestry systems.

Effects of light quality on leaf chlorophyll fluorescence parameters and antioxidant enzyme activities of Schima superba andCunninghamia lanceolataseedlings.

LIU Qing-qing, MA Xiang-qing, HUANG Zhi-jun, LI Yan-juan, ZHUANG Zheng, ZHU Chen-xi, LIU Bo

2018, 37(3):  869-876. 

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This study explored the effects of different light qualities (red, blue, and white) on chlorophyll fluorescence parameters and antioxidant enzyme activities in leaves of Schima superba andCunninghamia lanceolata seedlings. The results showed that original fluorescence (F_o), maximal fluorescence (F_m), variable fluorescence (F_v) and steady state fluorescence (F_t) ofS. superba seedling leaves were the highest under the white light. The photochemical efficiency (F_v/F_m), potential activity (F_v/F_o) and antenna transfer efficiency (F_v′/F_m′) of PSII reaction center under different treatments followed trend: white light > blue light > red light. Compared to the white light, the blue light significantly increased the activity of superoxide dismutase (SOD). The red and blue light decreased the activity of catalase (CAT) but increased the activities of peroxidase (POD) and the content of malonaldehyde (MDA).F_oand F_t ofC. lanceolata seedlings were the highest under the red light.F_m andF_v were the highest under the white light.F_v/F_m,F_v/F_o andF_v′/F_m′ratios were the highest under the white light, followed by the blue and red light treatments. Light quality had no significant effect on SOD activity, CAT activity and MDA content ofC. lanceolata seedling leaves, while it had significant effects on POD activity, with a highest value under the white light. In short, light quality would regulate the seedling growth of both tree species examined here. The potential vitality of S. superba andC. lanceolata seedlings decreased under red and blue light treatments due to light stress and unbalanced antioxidant enzyme system. Consequently, red and blue light would be unfavorable for seedling growth.

Effects of different nitrogen forms on photosynthesis, energy allocation and activities of antioxidant enzymes in the leaves ofTetrastigma hemsleyanum.

ZHANG Qiang, LONG Min-hui, SONG Yun-xian, SHU Liang-zuo, WU Xiao-min, ZHOU Xiu-jie, WANG Bing-xuan, BAO Wan-qing, HAN Chun-miao

2018, 37(3):  877-883. 

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To provide theoretical basis for rational nitrogen (N) fertilizer management of an endangered medicinal plant, Tetrastigma hemsleyanum Diels et Gilg, the effects of two different N forms (NO₃^--N and NH₄⁺-N) on photosynthesis, energy allocation and activities of antioxidant enzymes in the leaves of T. hemsleyanum seedlings grown under shading conditions (30% of full sunlight) were investigated. The results showed that two different N forms had no significant effects on leaf area, specific leaf weight, chlorophyll content, superoxide dismutase activity, catalase activity and energy allocation pattern. The photosynthetic parameters (net photosynthetic rate, stomatal conductance, and transpiration rate) were significantly higher and peroxidase activity and malondialdehyde content were significantly lower in the leaves of T. hemsleyanum under NO₃^--N supply than that under NH₄⁺-N supply. Our results indicated that  the application of NO₃^--N is more conducive to the growth of T. hemsleyanum.

Relationship between seed germination indices and seedling’s chilling tolerance of tomato rootstocks.

HAN Min, LI Ming-ming, CHEN Chen, ZHANG Zhi-huan, XU Kun

2018, 37(3):  884-890. 

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To obtain the convenient indices for identifying the chilling tolerance of tomato rootstocks and to screen out tomato rootstocks with strong chilling tolerance, we examined the effects of different temperatures (28, 20, 15 ℃) on the seed germination and the changes of seedling’s chilling injury of 40 tomato rootstocks under low temperature stress (10 ℃/3 ℃), and analyzed the correlation between seedling chilling injury index and seed germination indices. There was no significant difference in germination rate, germination index and vigor index among the different rootstock’s seeds at 28 ℃, but the germination related indices at 15 and 20 ℃significantly differed with those at 28 ℃. There were significant differences in the chilling index among the seedlings of different rootstocks under the low temperature of 10 ℃/3 ℃ (day/night). The chilling index of the seedlings was significantly correlated with the germination indexes under the low temperature, with the correlation coefficient at 20 ℃ being higher than that at 15 ℃. The regression model of seedling’s chilling injury index was established by multiple stepwise regression analysis. The relative germination rate and relative germination index at 20 ℃ were selected, and the determination coefficient of the model was 0.984 (P<0.001). According to the results ofclustering analysis, the rootstocks could be divided into cold-tolerant, cold-sensitive, and intermediate types. There were six cold-tolerant materials and five cold-sensitive materials. The clusteranalysis by using the two factors selected by the chilling index regression model found that the classification of 39 out of 40 materials was the same as that from the cluster analysis ofseedling’s chilling injury index, except that one material was classified into the cold-sensitive type rather than into the intermediate type. In all, our results showed that the relative germination rate and relative germination index of the seeds at 20 ℃ could be used as convenient indices for identi fying tomato chilling tolerance at seedling stage.

Effects of planting density on canopy structure, dry matter accumulation and yield of summer maize in a hilly region of central Sichuan Province, China.

MA Xiao-jun, LU Ming-yuan, LI Lan, LI Qiang, WU Ya-wei, LIU Xiao-lin, WANG Xing-long, JIN Rong, YUAN Ji-chao, KONG Fan-lei

2018, 37(3):  891-897. 

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Five planting densities (4.50×10⁴, 5.25×10⁴, 6.00×10⁴, 6.75×10⁴ and 7.50×10⁴ plants·hm^-2, designated as T1, T2, T3, T4 and T5, respectively) were set up to explore the effects of planting density on canopy structure, dry matter accumulation and yield of summer maize, aiming to provide theoretical basis and technical support for highyield cultivation ofsummer maize in the hilly area of central Sichuan, China. The results showed that with the increase of planting density, leaf area index (LAI) of maize was significantly increased, whereas the stem diameter, the angle between stem and leaf, and the transmittance were significantlydecreased. With the planting density increasing by 1×10⁴ plants·hm^-2, the stem diameterdecreased by 1.4 mm in 2015 and 1.3 mm in 2016, the first leaf angles uppermost and underneath ear reduced by 3.601° and 1.440°, and the bottom transmission at silking and midfilling stages reduced by3.73% and 2.82%, respectively. The dry matter accumulation of individual maize was significantly decreased, while the dry matter increased with the increase of planting density. Compared with T1, the dry matter accumulation of per individual in T5 decreased by37.13% (2015),25.95% (2016) at the maturity stage, and the dry matter accumulation at communitylevel of 2016 increased by 26.72%, 23.41% in 7 days after silking and at the maturity stage, respectively. With the increase of planting density, the yield of summer maize firstincreased and then decreased, with the highest value being found at 6.00×10⁴ plants·hm^-2. At such a density, the group and individual function of maize reached a synergistic gain and maize yield compositions (effective panicle number, grains per spike and grain weight) were coordinated, which accounted for the increase of maize yield.

Comparison of the light response models of photosynthesis in leaves ofMagnolia sinostellataunder different light intensity and moisture conditions.

YU Qin, WANG Qian-ying, LIU Zhi-gao, ZHANG Ming-ru, ZHANG Shou-zhou, SHEN Ya-mei

2018, 37(3):  898-905. 

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Five light response models of photosynthesis (exponential, rectangular hyperbolic, non-rectangular hyperbolic, quadratic function, and modified rectangular hyperbola) were applied to analyze the light response curves ofMagnolia sinostellata seedlings under different light intensity and moisture conditions. The results showed that: (1) The fitting accuracy of those models followed the order: exponential > modified rectangular hyperbola > rectangular hyperbola > non-rectangular hyperbola > quadratic function. (2) The light response parameters in fitting effect indicated that the exponential model could result in more accurate maximum net photosynthetic rate (P_nmax) and light saturation point (LSP). The rectangular hyperbolic model was the best one at figuring out light compensation point (LCP). The non-rectangular hyperbolic model was more reasonable to figure out dark respiration rate (R_d). (3)M. sinostellata seedlings could adapt to the environment with weak light and flowing water, but not for strong shading and waterlogging environment.

Distribution pattern and impact factors of chlorophyll a of size-fractionated phytoplankton in winter in the sea near Zhangzidao Island.

WU Wen-guang, ZHANG Ji-hong, LIU Yi, WANG Wei

2018, 37(3):  906-913. 

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We investigated the distribution of chlorophyll a of size-fractioned phytoplankton in the sea near Zhangzidao Island in January, 2016. Correlations of the concentrations of chlorophyll a and multiple environmental factors were explored to determine the main impact factors. Ourresults showed that, in the surface layer, the concentrations of chlorophyll a of total phytoplankton, microplankton, nanoplankton and picoplankton ranged 0.24-0.92, 0.15-0.58, 0.09-0.46 and0-0.03 μg·L^-1, respectively, with averaged concentrations being 0.69, 0.36, 0.33 and 0.002 μg·L^-1. Contributions of microplankton, nanoplankton, and picoplankton to total chlorophyll a were 51.72%, 48.01%, and 0.26%, respectively. In the bottom layer, picoplankton was not found. The concentrations of chlorophyll a of total phytoplankton, microplankton and nanoplankton in the bottom layer ranged 0.29-1.77, 0.12-1.45, 0.17-0.50 μg·L^-1, respectively, with mean concentrations being 0.78, 0.43, and 0.34 μg·L^-1. Contributions of chlorophyll a of microplankton and nanoplankton to total chlorophyll a were 52.97% and 47.03%, respectively. There was no significant difference in the concentrations of chlorophyll a of total phytoplankton, microplankton and nanoplankton between the surface and bottom layers (all P<0.01, pairedttest), indicating a homogeneously vertical distribution. Horizontal distributions of chlorophyll a of total phytoplankton, microplankton and nanoplankton also showed a homogenous pattern, with concentrations all gradually decreasing from the northwest to the south. Results from the redundancyanalysis showed that temperature, salinity, dissolved oxygen, particulate organic matter, NO₂^--N and NH₄⁺-N were main impact factors driving the distribution of chlorophyll a of phytoplankton.

The impacts of simulated climate change on seed dispersal distance by wind for six dandelion species in northeast China.

WU Jian-guo, XU Tian-ying

2018, 37(3):  914-928. 

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To understand the effect of climate change on the seed dispersal process by wind, the effects of climate change on the seed dispersal distance ofTaraxacum antungense, T.ohwianum,T. asiaticum, T.junpeianum,T.coreanum, and T.mongolicum in Fengcheng of LiaoningProvince, Changchun of Jilin Province and Muling County of Heilongjiang Province from May to October were monitored, based on climate change scenarios of RCP2.6, RCP4.5, RCP6.0 and RCP8.5 generated by the global climate model of NorESM1-M, and by using the seed winddispersal model of WINDISPER-L Lagrangian wind profile. The results showed that, under future climate change scenarios, air temperature would increase, the annual precipitation wouldincrease or decrease with obvious fluctuations, and wind speed would increase with obviousfluctuations in the three regions. The seed dispersal distances of those species by wind were about 1 m with high fluctuations from May to October in the period 2001-2050. Under different climate change scenarios, the seed dispersal distance of these dandelion species would decrease compared with that under baseline scenarios in most years from 2001 to 2050, whereas it wouldincrease in some exceptional years. The results suggest that the seed dispersal distance of these dandelion species would decrease, and such changes would be dependent on plant species identity, time, and location.

Assessment for factors affecting urban water resource utilization in Chongqing based on POET model.

HAN Wen-yan, CHEN Xing-peng, ZHANG Zi-long

2018, 37(3):  929-936. 

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Water is one of the crucial natural resources for human survival and social development. The rational and efficient utilization of water is strategically significant for sustainable development of human beings. At present, many structural factors affect water utilization at urban and national scales. Based on Duncan’s ecological complex (POET) model and the multipleregression analysis method, we investigated the effects of the structural factors of water resourcesutilization on the total amount and intensity of water consumption in Chongqing City, in terms of different dimensions of population, social organization, environment and technology. The results showed that in terms of population dimension, the growth of total population and the proportion of population aged 15-64 years in the total population promoted the increase of the total amount and intensity of water utilization in Chongqing. In terms of social organization dimension, the increases of urbanization rate and the proportion of secondary industry GDP accelerated the increase of the total amount and intensity of water utilization. However, the increases of per capita GDPreduced both parameters. From the aspect of environment dimension, the growth of the ratio of actual use of foreign investment to GDP increased the total amount and intensity of water utilization of Chongqing, while rising water price helped control water consumption and decrease theintensity of water utilization. Finally, the increase of the sewage treatment rate reduced the total amount and intensity of water utilization in terms of the technical dimension.

 

Potential propagation path of sudden oak death in southeast China.

JIANG Hou-zhi, CAO Chun-xiang

2018, 37(3):  937-942. 

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Sudden oak death (SOD) could result in large area of host vegetation to die in a short time. To examine the spread of SOD spores, the Hysplit forward trajectory model and meteorological data were used to simulate their trajectory in July of 2007, 2011 and 2015, in California, USA. Overlay analysis of the simulation results and SOD outbreak points in the next year showed that the region with a track frequency >10% would have higher point density of the new occurrence of SOD. The simulated results and the next year’s SOD outbreak points were highly fitted. Finally, we used the same method to simulate the trajectory of four hypothetical outbreak points of Zhangzhou Port in Fujian, China for a month (April 2016). The results showed that the SOD would spread from Zhangzhou Port to Zhejiang, Jiangxi and Guangdong. The areas with track frequency >20% mainly distributed in the coastal areas of Fuzhou to Xiamen.

Effects ofSpartina alterniflora invasion on benthic faunal community in saltmarsh and mangrove wetland.

FENG Jian-xiang, HUANG Qian, CHEN Hui, SHEN Qian-qian, HUANG Jian-rong, LI Zu-fu

2018, 37(3):  943-951. 

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Coastal wetlands such as saltmarsh and mangrove support high biodiversity and complex food web, in which the benthic invertebrate communities play pivotal roles in energy transfer. The composition of benthic community could be easily disturbed by the exterior environmental changes, with consequences on biodiversity, nutrient cycling, and energy flow. As one of the most serious threats to the coastal wetlands in China, the invasion of Spartina alterniflora on the benthic community and trophic relationship deserve more concerns. There is no consensus on the effects of S. alterniflora invasion on the benthic community structure and food web relationship as such effects were determined by different factors. In this review, we discussed the factors influencing the invasive effects of S. alternifloraon the benthic community structure, including original vegetation type, invasive period, the growth characteristics of S. alterniflora and the taxonomic status of benthic invertebrates. We further focused on the change of trophic relationship of benthic invertebrate under the invasion o S. alterniflora and its underlying mechanism. The deficiencies of existing research were pointed out and suggestions on the management of coastal wetlands were proposed.

Response of wetland plant functional traits to hydrological processes: A review.

LI Ya, YU Xiu-bo, LIU Yu, ZHANG Guang-shuai, ZHANG Quan-jun, DUAN Hou-lang

2018, 37(3):  952-959. 

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Hydrological processes play essential roles in driving the growth, development, reproduction and distribution of wetland plants, with consequences on ecosystem functioning of wetlands. Here, we reviewed the research of the functional traits of wetland plants and elaborated that the research on the wetland plant functional traits is conducive to understand the distribution characteristics of wetland plant in different environments. We could forecast the responses of plants to the environmental changes based on the connection between plant traits and the environment. Many hydrological factors, such as water table, wetting and drying alternation, water depth, water table fluctuation and flooding, may influence plant functional traits in wetlands. To adapt to environmental changes, wetland plants alter functional traits such as plant height, leaf and biomass allocation according to the dominating factors of hydrological processes. Plant phenotypic plasticity is a key trait in determining plant viability under different environments. However, few studies have examined the belowground traits of wetland plants. Future studies should strengthen the research in belowground traits of wetland plants, with emphasis on appliedresearch of the growth and distribution of wetland plants controlled by water level.

Status, problems and perspectives on the systematic biology of genusLigia: A review.

HUANG Zi-qian, ZHAO Li, SUN Jing-xian, ZHANG Peng

2018, 37(3):  960-966. 

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The genusLigia belongs to the most primitive terrestrial isopods with biggest body size, and is known as the intermediate form between marine and strictly terrestrial isopods. There are 42 species in the genus worldwide based on the traditional taxonomic classification. Most of those species are coastal species, with only eight species dwelling in inland. Molecular systematic analysis revealed high level of intraspecific genetic divergence, suggesting limited migrationability ofLigia. Geographical isolation affected the gene flow among different populations, consequently resulting in the species differentiation and formation. On the basis of molecular phylogeny researches, this study defined three research hotspots, including PanCalifornia Peninsula group, Hawaii Islands group and China JapanKorea East Asia group. Although some progresses have been achieved, there are still some problems, including lack of basic biological description of statistical samples, deficient fundamental ecological researches and low-level academic research in underdeveloped regions. Therefore, it is important for the scientific communities to enhance the comparability of data, encourage fundamental researches, conduct international collaboration, and construct an open database.