Assessing potential impacts of multiple stressors on riverine phytoplankton community by integrated models

Increasing pressures from both natural disturbance and anthropogenic activities challenge river ecosystem resilience. A better understanding of the ecological balancing of structure under multiple stressors is thus critical for sustainable future as well as human wellbeing. Phytoplankton are one of the important autotrophs in the river ecosystem. They are sensitively reflecting multiple filters. However, studies on how flow regime, land-use pattern, physicochemical condition and spatial factors overall affect the lotic phytoplankton community are still scarce. This study aims to examine riverine phytoplankton community structure in relation to combined abiotic gradients, and to consider the potential responses under changing status. Study area is located in a lowland catchment Treene, Germany. We establish an integrated modelling framework in combination of hydrological model with ecological models. The investigations show high spatial and temporal variations of phytoplankton community. Benthic diatom is dominant in most of the study area. Euglenophyta show higher existence percentage in the headwaters and exhibit a strong positive correlation to the share of agricultural land-use. Microcystis has found with high abundance downstream of a lake. Higher phosphorous concentration directly causes the increase of Microcystis population. Both species and traits composition more relate to hydrological and local physicochemical heterogeneity than to species dispersal, which confirm the suitability of lowland phytoplankton-based bioassessment in the study area. Due to the importance of flow regime in shaping pelagic algal community, it is necessary to include hydrological variables in biodiversity conservation. The shares of forest land-use area have outstanding explanation to the variation of species richness. Our findings emphasize the significance of preservation of forest area in protecting the aquatic algal biodiversity for maintaining the river ecosystem functioning.



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