Impact of the Water–Sediment Regulation Scheme on the phytoplankton community in the Yellow River estuary

Abstract

The Water–Sediment Regulation Scheme (WSRS) transports large amounts of water, sediment, and nutrients to the Yellow River estuary (YRE) in a very short time, which significantly changes the ecological environment of the estuary area in summer (wet season). The influence of these changes on the distribution and abundance of phytoplankton communities in the YRE are still inadequately understood. We studied the spatial distribution of environmental factors, zooplankton abundance and biomass, and phytoplankton abundance and community in the YRE at different WSRS stages during 2018 (WSRS year) and compared with corresponding durations in 2017 (non–WSRS year). Our results demonstrate that the WSRS (1) promoted phytoplankton growth in estuarine areas at the pre-stage and decreased phytoplankton abundances in the entire study area during the inter-stage, (2) decreased phytoplankton biodiversity and increased abundance and proportion of Synedra sp., and (3) led to a temporary rapid increase in zooplankton abundance and biomass. Bottom–up effects dominated phytoplankton variability at the pre- and end-stages of the WSRS, while top–down effects dominated the inter-stage. Redundancy analysis indicated that phytoplankton assemblages were primarily influenced by nitrate and the ratio of nitrogen to phosphorus at the pre-stage, by zooplankton abundance and biomass at the inter-stage, and by ammonium and dissolved silica at the end-stage. Our findings provide essential information for understanding and predicting the changes in the phytoplankton community due to increases in hydrodynamics, nutrients, and turbidity conditions in river estuaries.