Temporal and Spatial Characteristics of Dissolved Silicon,Nitrogen and Phosphorus Concentrations and Ecological Stoichiometry in the Hanfeng Lake of the Three Gorges Reservoir
Clarifying the typical nutrient components of silicon(Si),nitrogen(N)and phosphorus(P)in water and their temporal and spatial changes of ecological stoichiometry is helpful to explore the degree of eutrophication and the limiting state of phytoplankton nutrition.In this study,seven sampling sites were set up in Hanfeng Lake of the Three Gorges Reservoir.The temporal and spatial variation characteristics of concentrations of soluble silicate(DSi),soluble total nitrogen(DN),soluble total phosphorus(DP),chlorophyll a(Chl-a)and other indicators were measured via sampling from May 2020 to April 2021.The phytoplankton nutrient restriction status in water was assessed through the establishment of ecological stoichiometry relationship of Si,N and P.The results showed that the monthly average concentration of DSi was 18.80 mg/L with the lowest value in August and the highest in November.At the seasonal scale,this value was the lowest in summer and the highest in autumn.The monthly mean concentrations of DN and DP were 1.57 mg/L and 0.09 mg/L,respectively.The seasonal variations of DN and DP were similar,with high concentrations in winter and spring and low concentrations in summer and autumn.The monthly average concentration of Chl-a was 4.48 μg/L,with the highest in summer and the lowest in autumn,showing an opposite to the seasonal variation of DSi concentration,and a significant negative correlation.In space,the concentrations of DSi,DN and DP in Nanhe section were all higher than those in other sections.A small part of DSi might come from the release of sediment decomposition,and a large part of DSI was supplemented from land to water body via surface runoff.The mean value of the ratio of DSi/DN for the whole year was 6.47,with the lowest value in February and the highest in November.The ratio of DN/DP was the lowest in January and the highest in July,with an annual average of 47.76.The results indicated that the main limiting factor of phytoplankton growth in Hanfeng Lake was element P.
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