The direct and indirect effects of land use and water quality on phytoplankton communities in an agriculture-dominated b
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The direct and indirect effects of land use and water quality on phytoplankton communities in an agriculture-dominated basin Zhiming Zhang & Junfeng Gao
&
Yongjiu Cai
Received: 11 July 2020 / Accepted: 3 November 2020 # Springer Nature Switzerland AG 2020
Abstract Understanding the factors that control biodiversity in rivers is challenging due to the variety of potential sources, linkages, and processes. This research assesses the effects of land use on phytoplankton communities across water quality gradients. By employing abiotic and biotic datasets of 149 catchments in Lake Chaohu basin, China, and a structural equation model (SEM), the direct and indirect effects of land use and water quality on phytoplankton dynamic were analyzed. Both land use and water quality had statistically significant direct effects on phytoplankton community attribute and diversity, although these effects differed among these indices. For instance, farmland was found to positively affect the abundance and diversity indices, while total nitrogen (TN) had significant positive effects on species richness and abundance. Importantly, the average indirect effects strengthened the effects of land use (e.g., built-up land and woodland) up to 82.4% mainly through nutrients, while the average indirect effects weakened the effects of land use (e.g., farmland) by as much as 49.9% mainly due to nutrients, thus Z. Zhang : J. Gao (*) : Y. Cai Key Laboratory of Watershed Geographic Sciences, Nanjing Institute of Geography and Limnology, Chinese Academy of Sciences, 73 East Beijing Road, Nanjing 210008, China e-mail: [email protected]
Z. Zhang e-mail: [email protected] Y. Cai e-mail: [email protected]
indicating the prevailing role of the effects of land use on phytoplankton based on nutrient concentrations. The results suggest that nutrients can regulate the effect of land use on phytoplankton community attribute and diversity indices. This study highlights the advantages of using an SEM because the potential linkages for phytoplankton diversities are more likely to be identified with this method than with a classical linear regression model. Therefore, SEM has wide application prospects in the field of the conservation of biodiversity in freshwater rivers. Keywords River . Farmland . Eutrophication . Nutrients . Structural equation model . Biodiversity
Introduction Eutrophication has caused a wide range of ecological and environmental problems in freshwater ecosystems, such as degraded water quality, reduced biodiversity, and disruptions to ecological balance (Smith 2003; Tett et al. 2007; Hiley et al. 2010; Hayes et al. 2015; Wei et al. 2018; Russo et al. 2019). Therefore, eutrophication is considered a major threat to freshwater ecosystems (Le Bagousse-Pinguet et al. 2012). The main performance index of eutrophication in freshwater ecosystems is phytoplankton overgrowth (Carpenter et al. 2011), which is influenced by a series of complex factors. For example, excessive nutrients (e.g., phosphate and nitrate) are considered a major dri
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