Abstract: The replenishment of fish with different species compositions at the beginning of the year was used to remediate and maintain the ecological environment of Maoli Lake, Changde. We monitored the characteristics of lake plankton and environmental factors in the summer of two years. The effects of fish control measure were analyzed from the aspect of community diversity and ordination. We further discussed the practicability of implementing this technology in lake ecological remediation and maintenance. The mass ratio of silver carp (Hypophthalmichthys molitrix), bighead carp (Aristichthys nobilis), block carp (Mylopharyngodon pieces), crucian carp (Carassius auratus) was 15∶60∶15∶10 (by weight) in 2016. The mass proportion of silver carp, bighead carp, block carp, crucian carp, culter fish (Culter aburnus), yellow-head catfish (Pseudobagrus fulvidraco) and mandarin fish (Siniperca chuats) was 25∶50∶10∶5∶5∶3∶2 in 2017. The results showed that water quality of the whole lake was enhanced to the level of Class Ⅲ following environmental quality standards within the two years. The mean chemical oxygen demand (COD) was decreased by 16% from 4.12 mg·L^-1 in 2016 to 3.47 mg·L^-1 in 2017. The mean levels of transparency, pH, dissolved oxygen, chlorophyll, total nitrogen and total phosphorus of the lake were not significantly changed (P>0.05). The mean density of the phytoplankton was decreased by 4.8% from 518 ×10⁴ ind·L^-1 in 2016 to 493×10⁴ ind·L^-1 in 2017, while that of the zooplankton was increased by 9.6% from 3283 ind·L^-1 in 2016 to 3597 ind·L^-1 in 2017. The green algae were dominant, the miniaturization of the zooplankton appeared, and the abundance of the large zooplankton was low. The Margalef indices of phytoplankton, zooplankton and plankton were increased by 6.2%, 15.5%, and 13.6% respectively, while the Shannon index of the zooplankton was increased by 8.3%. Water depth, chlorophyll level and total nitrogen concentration were the key factors controlling the plankton community structure across the two years. The factor weight of COD effect on the community ordination decreased from 0.68 in 2016 to 0.20 in 2017. The COD became the minimum factor affecting community ordination in 2017. The community similarity, plankton population correlation, and the relation of community diversity to environmental factors among nine sites in 2017 weredeclined compared with those in 2016. In all, the fish population manipulation for raising functional group diversity and trophic levels of fish in the lake ecosystem could maintain the lakewater quality to the Class Ⅲ under the national groundwater environmental standards, improve the community diversity, and drive a uniform distribution of plankton species in the lake.

Key words: karst, rocky desertification control, soil organic carbon, land use type, soil organic carbon component