The Role of Top-Down and Bottom-Up Control for Phytoplankton in a Subtropical Shallow Eutrophic Lake: Evidence Based on
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The Role of Top-Down and BottomUp Control for Phytoplankton in a Subtropical Shallow Eutrophic Lake: Evidence Based on Long-Term Monitoring and Modeling Zhigang Mao,1 Xiaohong Gu,1* Yong Cao,2 Min Zhang,1 Qingfei Zeng,1 Huihui Chen,1 Ruijie Shen,1 and Erik Jeppesen3,4,5 1 State Key Laboratory of Lake Science and Environment, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, East Beijing Road 73, Nanjing 210008, Jiangsu Province, China; 2Illinois Natural History Survey, Prairie Research Institute, University of Illinois, Champaign, Illinois 61820, USA; 3Department of Bioscience, Aarhus University, 8600 Silkeborg, Denmark; 4 Sino-Danish Centre for Education and Research, Beijing 100049, China; 5Limnology Laboratory and EKOSAM, Department of Biological Sciences, Middle East Technical University, 06800 Ankara, Turkey
ABSTRACT Lake ecosystems are exposed to a range of anthropogenic pressures, particularly eutrophication, and in some cases also stocking and/or overfishing of top-predator fish species, all factors that have implications for the food web structure and which could lead to dominance of nuisance cyanobacteria. Restoration of degraded lakes demands insight into the relative role of top-down for bottom-up regulating forces. While knowledge about these forces in temperate lakes is extensive, comparatively little is known of their role in subtropical lakes where the importance of herbivorous and benthic feeding fish is higher. Here, we analyzed a long-term monitoring data set on subtropical, shallow Lake Taihu, China, and applied
Received 27 August 2019; accepted 9 January 2020 Electronic supplementary material: The online version of this article (https://doi.org/10.1007/s10021-020-00480-0) contains supplementary material, which is available to authorized users. Author Contributions ZGM, XHG and YC conceived and designed the study; YC and MZ contributed new models; QFZ, HHC, and RJS performed research; ZGM and EJ wrote the paper. *Corresponding author; e-mail: [email protected]
random forests regression to examine how phytoplankton was related to environmental variables and biotic assemblages. Our results indicate that the biomass and density of phytoplankton increased with increasing biomass of benthivorous and zooplanktivorous fish and decreased with increases in ammonium concentrations, the nitrogen to phosphorus ratio, and zooplankton biomass, while the response to climate fluctuations and changes in the biomass of piscivores was weak. Effects of higher trophic levels explained as much of the variance in phytoplankton biomass as did nutrients and climatic factors. Moreover, the remarkably reduced ratio of zooplankton to phytoplankton biomass and the decline in cladoceran individual biomass emphasized the increasing importance of top-down control in regulating the phytoplankton following extensive stocking. Our findings offer insight into how fish management may be combined with catchment-level restoration measures to conserve and enhance water quality. Key words: Bottom-up; Top-dow
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