Temporal And Spatial Distribution Characteristics Of Silicon In Reservoirs With Different Nutritional Status In Karst Area

As an important element in diatom's life activities,silicon plays an irreplaceable role.Diatom,as the representative of primary productivity in water body,is the main source of BSI in sediment,while the sediment in Lake is the sink of Lake silicon,which plays an important role in the silicon cycle of lake.It can be used as an indicator to characte-rize eutrophication pollution.Therefore,it is very important to understand the temporal and spatial distribution characteristics of dissolved silicon,particulate biogenic silicon and sediment biogenic silicon.Because of its rich resources and unique karst landscape,plateau lakes in Guizhou Province play an important role in the study of lake system in China.Early research on deep-water lakes in Guizhou Plateau found that the reservoirs with high level of nutrition are prone to silicon limitation,but there is no systematic Study and Analysis on the migration and transformation process of silicon forms in lakes with different age and nutrition status in karst areas of Guizhou Plateau.In this study,three typical deep-water reservoirs of Hongfeng Lake and Pingzhai reservoir in the Wujiang River Basin of Guizhou Plateau,with different age and nutritional status,were taken as the research objects.The contents of DSi,PBSi,TOC,and TP in lakes with different nutrient status were studied,and the spatial and temporal distribution characteristics of silicon in lakes and its circulation were clarified Ring process.The main results are as follows:(1)There are seasonal thermal stratification in Hongfenghu reservoir,Puding reservoir and Pingzhai reservoir.The seasonal difference of DSi content is obvious,and the DSi content is uniform in winter mixing period.The order of dissolved silicon content from high to low is:Pingzhai reservoir>Puding reservoir>Hongfenghu reservoir in spring;Pingzhai reservoir>Hongfenghu reservoir>Puding reservoir in summer;Pingzhai reservoir>Puding reservoir>Hongfenghu reservoir in autumn;Pingzhai reservoir>Puding reservoir>Hongfenghu reservoir in winter.The dissolved silicon content in the bottom water of Hongfenghu reservoir is the highest in summer,and the dissolved silicon content in the upper and lower water bodies is lower in winter;the dissolved silicon content in the surface water of Puding reservoir is lower than that in the middle and lower layers;the dissolved silicon content in the middle and lower layers of Pingzhai reservoir has little change,and the surface layer content is low.The change of dissolved silicon content is closely related to the change of bio silicon,and is consistent with the eutrophication level of lake.(2)The content of particulate BSi in Hongfenghu reservoir and Puding reservoir was the highest in autumn,and low in winter and spring,which indicated that the increase of precipitation promoted the input of exogenous silicon material,resulting in the significant increase of suspended particulate biogenic silicon content.The content of particulate BSi in Pingzhai reservoir is higher in autumn than in winter,and higher in middle and lower layers in winter than in autumn,indicating that there is more exogenous silicon input in the surface layer in autumn,and the content of particulate BSi in middle and lower layers in winter mixing period is higher than that in autumn.(3)The vertical distribution of biogenic silicon content in the sediment column of lakes with different nutritional status is complex,and there are significant differences in the vertical profile of biogenic silicon content.For Hongfenghu reservoir with eutrophication level,the content of bio silicon near point F of Beihu dam is relatively high in summer,which fluctuates from 4.04%to 16.33%,with an average of 10.11%.The content of bio silicon at point B of South Lake is between 5.75%to 10.84%,with an average of 8.09%.However,the content of bio silicon in Puding reservoir is between 2.78%and 4.91%,with an average of 3.95%.The content of bio silicon in point C in front of dam is between 2.93%and 6.90%,with an average of 4.26%.On the whole,the content of bio silicon in the sediments of Hongfeng Lake reservoir is higher than that of Puding reservoir,and there is a high value near the dam in Hongfeng Lake Reservoir and Puding reservoir,indicating that the interception effect of the dam is obvious.The content of BSi in the two reservoirs indicates the process of decreasing the primary aquatic productivity from the upper layer to the lower layer.(4)Through the inversion of eutrophication process of Hongfenghu reservoir and Puding reservoir,it is found that the content of biogenic silicon and organic carbon in Hongfenghu reservoir is higher than that in Puding reservoir,and the eutrophication level is consistent with the accumulation of nutrients.The contents of BSi,TOC,TP in sediments were determined BSi:TOC,TOC:TN correlation analysis was carried out,it was found that the BSi content in Hongfeng Lake was significantly affected by carbon and phosphorus activation,and the BSi content in Puding reservoir was significantly affected by organic matter sources.