Abstract

Abstract. An approach to assess estuarine environmental flow based on phytoplankton preference, including the complex relationships between hydrological modifications and ecosystem biomass, was developed in this study. We initially established a relationship between biomass requirements for primary and higher nutritional level organisms based on the ecosystem nutritional energy flow principles. Subsequently, diagnostic pigments were employed to represent phytoplankton community biomass, which indicated competition between two groups of phytoplankton in the biochemistry process. Considering empirical relationships between diagnostic pigments and critical environmental factors, biomass responses to river discharge were established by simulating distributions of critical environmental factors under action of river discharges and tide currents. Consequently, environmental flows were recommended for different fish biomass requirements. We used the Yellow River estuary as a case study; and May and June were identified as critical months for maintaining environmental flow. Temporal variation in natural river flow dynamics, which was used as a proxy for environmental flow, should be carefully examined in artificial hydrological regulation strategies, particularly during high-amplitude flood pulses, which might result in negative effects on phytoplankton groups, and subsequently higher aquatic species biomass.

Highlights

  • Estuaries are semi-enclosed coastal transition zones, where freshwater inflow from rivers mixes with tidal action saline water from the sea

  • Canonical correspondence analysis (CCA) was used to illustrate the relationships between diagnostic pigments and different environmental variables under different seasons based on field data

  • CCA identified salinity as the most influential environmental factor affecting diagnostic pigments, and empirical relationships between salinity and diagnostic pigments were determined based on these observed results

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Summary

Introduction

Estuaries are semi-enclosed coastal transition zones, where freshwater inflow from rivers mixes with tidal action saline water from the sea. Variation in freshwater inflow can result in negative or deleterious consequences for many aquatic species by reducing or altering available aquatic habitat (Attrill et al, 1996; Sun et al, 2013). This problem might be exacerbated by climate change (Cai et al, 2011a, b; Sun and Feng, 2013). Three seagrass species sensitive to salinity changes were selected as indicators to determine the minimum required freshwater inflow for the Caloosahatchee Estuary (Doering et al, 2002). Arhonditsis et al (2007) examined spatial and temporal patterns in phytoplankton communities to report ecosystem variation influenced by river flow fluctuations in the Neuse River estuary

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