Yao Zhang1, Chunlei Song2, Lei Ji3, Yuqian Liu4, Jian Xiao5, Xiuyun Cao6, Yiyong Zhou7. 1. Center for Environment and Health in Water Source Area of South-to-North Water Diversion, School of Public Health and Management, Hubei University of Medicine, Shiyan 442000, PR China. 2. Key Laboratory of Algal Biology, State Key Laboratory of Freshwater Ecology and Biotechnology, Institute of Hydrobiology, the Chinese Academy of Sciences, 7# Donghu South Road, Wuhan 430072, PR China. Electronic address: clsong@ihb.ac.cn. 3. College of Life Science, Huaibei Normal University, Huaibei 235000, PR China. 4. Yellow River Water Resources Protection Institution, Zhengzhou 450004, PR China. 5. Key Laboratory of Algal Biology, State Key Laboratory of Freshwater Ecology and Biotechnology, Institute of Hydrobiology, the Chinese Academy of Sciences, 7# Donghu South Road, Wuhan 430072, PR China; University of Chinese Academy of Sciences, Beijing 100039, PR China. 6. Key Laboratory of Algal Biology, State Key Laboratory of Freshwater Ecology and Biotechnology, Institute of Hydrobiology, the Chinese Academy of Sciences, 7# Donghu South Road, Wuhan 430072, PR China. Electronic address: caoxy@ihb.ac.cn. 7. Key Laboratory of Algal Biology, State Key Laboratory of Freshwater Ecology and Biotechnology, Institute of Hydrobiology, the Chinese Academy of Sciences, 7# Donghu South Road, Wuhan 430072, PR China. Electronic address: zhouyy@ihb.ac.cn.
Abstract
To explore the relationship and cause and effect between eutrophication and the nitrogen (N)/phosphorus (P) ratio, samples from 38 lakes in Wuhan City, China, with differing degrees of eutrophication, were collected for nutrient levels and extracellular enzyme activities (EEA) in the water column from July 2011 to November 2011. The phosphorus fraction, abundance and potential denitrification rate (PDR) as well as community composition of nirS-type denitrifier in sediments of five typical lakes were further analyzed. A higher trophic level index (TSI) corresponded to a lower N/P ratio, which can be attributed to a loss of N and an increase in P. Specifically, in more eutrophic lakes, the enrichment of total organic carbon and all forms of P in sediments could fuel PDR by shaping community composition and increasing the abundance of nirS-type denitrifier as evidenced by correlation and redundancy analysis, ultimately resulting in a loss of N. Meanwhile, iron-bound phosphorus release induced by anoxia and the hydrolysis of organic P accounted for the observed increase of P in the water column. The lower N/P ratio facilitated the production of leucine aminopeptidase, which was unexpectedly induced by high P but not by low N. Similarly, alkaline phosphatase was induced by high N but not by low P. These findings indicate a mutual coupling and interplay between N and P cycling and confirm our hypothesis that P accumulation accelerates N loss in the process of eutrophication.
To explore the relationship and cause and effect between eutrophication and the n class="Chemical">nitrogen (N)/n class="Chemical">phosphorus (P) ratio, samples from 38 lakes in Wuhan City, China, with differing degrees of eutrophication, were collected for nutrient levels and extracellular enzyme activities (EEA) in the water column from July 2011 to November 2011. The phosphorus fraction, abundance and potential denitrification rate (PDR) as well as community composition of nirS-type denitrifier in sediments of five typical lakes were further analyzed. A higher trophic level index (TSI) corresponded to a lower N/P ratio, which can be attributed to a loss of N and an increase in P. Specifically, in more eutrophic lakes, the enrichment of total organic carbon and all forms of P in sediments could fuel PDR by shaping community composition and increasing the abundance of nirS-type denitrifier as evidenced by correlation and redundancy analysis, ultimately resulting in a loss of N. Meanwhile, iron-bound phosphorus release induced by anoxia and the hydrolysis of organic P accounted for the observed increase of P in the water column. The lower N/P ratio facilitated the production of leucine aminopeptidase, which was unexpectedly induced by high P but not by low N. Similarly, alkaline phosphatase was induced by high N but not by low P. These findings indicate a mutual coupling and interplay between N and P cycling and confirm our hypothesis that P accumulation accelerates N loss in the process of eutrophication.