Abstract
Phytoplankton density can be influenced by a wide range of factors whereas the role of suspended particulate matter (SPM) are not clear in river that annually subjected to hydrodynamics shift. Here, spatial-temporal variation of environmental parameters and phytoplankton density were studied from January 2013 to December 2014 in Yulin River, a tributary of the Three Gorges Reservoir, China. Laboratory experiments were conducted to elucidate the key parameter and interpret how it impacted phytoplankton density. SPM is negatively correlated with phytoplankton density. Despite SPM in Yulin River revealed weaker NH3-N, NO3-N and PO4-P adsorption capabilities in comparison to that in other aquatic ecosystems, increase of water velocity from 0.1 to 0.8 m/s led to approximately 6.8-times increase of light attenuation rate. In experiments evaluating the aggregation of Chlorella pyrenoidosa upon SPM, floc size showed 7.4 to 22% fold increase compared to the SPM or algae itself, which was due to the interaction between SPM and phytoplankton extracellular polymeric substances. Our results suggest that SPM could contribute to the variation of phytoplankton density through the integrated process including light attenuation, nutrient adsorption and algae aggregation. This is the first evaluation of the multiple processes underlying the impact of SPM on phytoplankton.
Highlights
Phytoplankton communities are key components in determining ecosystem stability in aquatic environments and contributes nearly half of global primary production
The total phosphorus (TP) concentration showed maximum 10-fold increase when the Three Gorges Reservoir (TGR) altered from flood season to dry season, in addition, the dissolved PO4-P contributed little to TP concentration, indicating TP may predominately maintained in suspended particles
The correlation matrix showed that in the estuary, phytoplankton density was strongly correlated with total nitrogen (TN), NO3-N, PO4-P, DO, TP, NH3-N, velocity, suspended particulate matter (SPM), temperature, and illumination (Fig. 1a)
Summary
Phytoplankton communities are key components in determining ecosystem stability in aquatic environments and contributes nearly half of global primary production. Layers while increasing the mobile P content in water column[4], which may favor phytoplankton growth This was supported by the outcomes of studies regarding the nutrient transports in Huanghe basin, China[5]. Since the initial filling of the Three Gorges Reservoir (TGR) in June 2003, algal blooms begin to occur annually in the reservoir and in some upstream tributaries, and intense phytoplankton blooms have been observed in some tributary backwaters even in winter[8] Both the frequency of phytoplankton blooms and the numbers of tributaries involved have increased as the normal high water level has shifted upwards. Previous studies have revealed that wind-induced and tidal currents can cause frequent sediment re-suspension, resulting in high SPM values of the water column[10] and, increased light attenuation, which inhibits phytoplankton growth[1]. A number of studies have evaluated SPM levels in shallow lakes, little information is available on the impact of SPM on the density of phytoplankton in river-type reservoirs as well as on the underlying mechanism
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