Abstract: The destruction of riverine habitats and the decline in the integrity of aquatic functions is a problem in the Pearl River due to over-exploitation and over-utilization of water resources. To protect river habitats and maintain the integrity of river ecosystems in the Pearl River, we need to know how different carbon sources contribute to the aquatic food web. The potential basal carbon sources and dominant consumers were sampled in three typical sections of the Pearl River in March and August 2015, with the δ¹³C and δ¹⁵N of potential carbon sources and dominant consumers being then determined. The IsoSource estimation results showed that, in the wide-open water upstream habitats, C₃ plants contributed more than 50% (within the 50% confidence level) to the dominant consumers. The downstream habitats were covered by large areas of submersed plants, which contributed almost, or more than 50% (within the 50% confidence level) to local consumers. In the downstream habitats, submersed plants became the dominant source to most consumers, while C₃ plants were the secondary carbon source. In the bifurcation section, phytoplankton contributed nearly or more than 40% (within the 50% confidence level) to the local consumers and became the dominant source supporting many consumers, while both submersed plants and C₃ plants were secondary sources. Therefore, the primary contribution sources to local consumers varied in different river sections with different habitats, which may be related to the proportion of different carbon sources and their availability to consumers. Our results suggest that the conservation of multiple habitats is essential for maintaining the functional integrity of aquatic ecosystems of the Pearl River.

Key words: nitrogen addition, community structure, forage yield, plant functional group., forage quality