Functional Responses of Phytoplankton Assemblages to Watershed Land Use and Environmental Gradients

Xue Du,Le Wang,Huibo Wang,Dan Song,Jingshuang Yang,Tangbin Huo,Xing Jin,Kun Ming,Hui Liu,Chen Zhao

doi:10.3389/fevo.2021.819252

Abstract

Watershed land-use changes have been identified as major threats to lake fauna, subsequently affecting ecosystem functioning. In this study, the functional-based approach was used to examine the effects of land use and environmental changes on phytoplankton communities in four selected lakes in Northeast China. We also identified the sensitive functional traits as indicators of environmental stressors. The integration of RLQ analysis with the fourth-corner approach significantly identified five of 18 functional trait categories, including flagella, filamentous, unicellular, mixotrophic, and chlorophyll c, as potential indicators to changes in watershed land-use intensity and environmental gradients. Significant relationships between traits and land use and water quality highlighted the consequential indirect impact of extensive agricultural and urban development on phytoplankton via allochthonous nutrient inputs and various contaminants. In addition, the functional richness of phytoplankton assemblages generally increased along with surface area and forests, but decreased along with intensive agricultural and urban land use, implying that functional homogenization may cause a reduction in ecosystem productivity and reliability to land-use intensity. Given the superior performance of the functional-based approach, our findings also highlighted the importance of the application of both the biological traits and functional diversity index in monitoring programs for lake ecosystems.

Highlights

Agriculture and urbanization have drastically transformed complex natural ecosystems into simplified managed ecosystems in many locations (Flynn et al, 2009; Hooke and Martín-Duque, 2012)
The first two axes of the principal component analysis (PCA) performed on phytoplankton functional traits explained 26.11 and 20.07% of the variation, respectively (Figure 2)
The RLQ analysis revealed that land use and environmental gradients influence the distribution of phytoplankton species with specific traits and that the composition of phytoplankton assemblages is dependent on the land use and environmental gradients of studied lakes and influenced by species traits

Summary

Introduction

Agriculture and urbanization have drastically transformed complex natural ecosystems into simplified managed ecosystems in many locations (Flynn et al, 2009; Hooke and Martín-Duque, 2012). Sediment, nutrient, and organic matter loading (Williamson et al, 2008), land-use changes have far-reaching consequences for aquatic ecosystems (Foster et al, 2003). Intensive and extensive agricultural practices, and the application of fertilizer or manure within watersheds, are strongly responsible for lake eutrophication (Bennett et al, 2001; Carpenter, 2005), in conjunction with the proliferation of harmful algal blooms, decrease in dissolved oxygen (DO) levels, and loss of aquatic biodiversity (Carpenter et al, 1998), while watershed urban development is associated with several environmental consequences, including nutrient pollution, and sewage, pathogen and other contaminants (Bai et al, 2018). Functional trait-based approaches can be informative for understanding the biotic communities in response to environmental gradients (Mouillot et al, 2013)

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Conclusion