Ammonium and phosphate enrichment across the dry–wet transition and their ecological relevance in a subtropical reservoir, China

Abstract

Small river reservoirs are widespread and can be ecologically sensitive across the dry-wet transition under monsoon climate with respect to nutrient loading and phenology. Monthly sampling and high-frequency in situ measurements were conducted for a river reservoir (southeast China) in 2013-2014 to examine the seasonal pattern of nutrients and phytoplankton. We found that nutrient concentrations were runoff-mediated and determined by watershed inputs and, in some cases, by internal cycling depending on hydrology and temperature. Ammonium and phosphate were relatively enriched in February-March (a transitional period from dry/cold to wet/hot climate), which can be ascribed to initial flushing runoff from human/animal waste and spring fertilizer use. A phytoplankton bloom (mainly Chlorophyta) occurred during April after a surge of water temperature, probably due to the higher availability of inorganic nutrients and sunlight and suitable hydraulic residence time (medium flow) in the transitional period. The concentration of phytoplankton was low during May-June (wet-hot climate) when the concentrations of total suspended matter (TSM) were highest, likely owing to the "shading" effect of TSM and turbulence of high flow conditions. Nutrient-algae shifts across the dry-wet season and vertical profiles suggested that algal blooms seem to be fueled primarily by phosphate and ammonium rather than nitrate. Current findings of a strong temporal pattern and the relationship between physical parameters, nutrient and biota would improve our understanding of drivers of change in water quality and ecosystem functions with dam construction.

Surface water quality assessment in the Bach Dang river basin, Vietnam: using water quality index and geographical information system methods

“…This is because, during the dry season, the river's water flow is often reduced, which reduces the diluting effect of pollutants such as the ammonium and phosphate, resulting in higher concentrations. According to a previous report, the concentrations of ammonium and phosphate were higher during the dry season than the rainy season [55][56][57]. This is also due to a combination of causes, including initial flushing runoff from human and animal waste and spring fertiliser application [57].…”

Microbial Communities and Nitrogen Transformation in Constructed Wetlands Treating Stormwater Runoff

“…Water level fluctuations is one of the key characteristics of CWs that can cause shifts in microbial communities as microbial composition, structure, and function are sensitive to the depth, frequency, and duration of fluctuations. The dynamics of wetland hydrology not only alter the response of wetland systems, but also alter the microbial genes responsible for N removal pathways (Bambauer et al, 1998;Fritsche et al, 1999;Kämpfer et al, 1999;Doronina et al, 2010;Drury et al, 2013;Eichmiller et al, 2013;Liu et al, 2013;Chen et al, 2014;Mo et al, 2016;Isabwe et al, 2018). Systems with high water levels contained significantly higher DO concentrations in their bed sediment which can change the microbial community structure and composition (Han et al, 2020;Huang et al, 2020).…”

“…Periodic drying and wetting conditions can cause changes in microbial community dynamics (Huang et al, 2018;Kan, 2018;Rose et al, 2018). Previous studies have investigated the processes of microbial assembly and dynamics under wet and dry condition within CWs, creek, and watershed (Bambauer et al, 1998;Fritsche et al, 1999;Kämpfer et al, 1999;Doronina et al, 2010;Drury et al, 2013;Eichmiller et al, 2013;Liu et al, 2013;Chen et al, 2014;Mo et al, 2016;Huang et al, 2018;Isabwe et al, 2018;Kan, 2018;Rose et al, 2018).…”

Spatiotemporal Variations in Nitrogen and Phosphorus in a Large Man-Made Lake and Their Relationships with Human Activities

“…Unfortunately, approximately 3 million ha of forests or wetlands were converted into croplands per year from 1995 to 2002 throughout the world [21], which led to greater nutrient losses to the local water bodies. Furthermore, a large number of hydroelectric dams were constructed around the world for hydropower generation, flood control, agricultural irrigation, tourism, and drinking water supply [22]. However, these hydroelectric dams greatly change the hydrometeorological conditions, sediment retention, and nutrient cycling, leading to water eutrophication [22][23][24].…”