| Due to the strong influence of anthropogenic activities,soil acidification in the Taihu watershed has become increasingly severe in recent decades,a process that has facilitated the accelerated loss of Bioavailable Silicon(BSi)from the land and into the water column.To reveal the loss characteristics of BSi in watershed soils and the response characteristics of lakes under the influence of long-term anthropogenic acidification,four typical land use soils,two typical lake sediments,river and lake water samples were collected for testing,and historical data on lake water chemistry(1993-2019),historical data of BSi in soils(1980s)and socio-economic data(2017-2021)were collected for this study,the effects of anthropogenic activities on the distribution and migration transformation of BSi in watershed soils and lake sediments were analyzed.In addition,the main driving factors and processes that accelerate the loss of BSi from soil to sediment were elucidated by means of influencing factors and Si/Al and PHREEQC models.The results showed that:(1)In the land,the order of BSi content in the soil was forest land>wetland>vegetable land>wheat-rice land,the BSi in the surface(0-15 cm)of forest,vegetable and wheat-rice land was significantly lower than that in the deeper(p<0.05),except for wetland;in the further analysis in Dapu town(soil parent material was consistent),the order of BSi content in the soil was wetland>vegetable land>wheat-rice land,and the BSi content in the wheat-rice surface soil was significantly lower than that in the wetland and the vegetable land(p<0.05),the BSi content in the wheat-rice surface soil was significantly lower than that in the deeper(p<0.05),due to as a result of the strong anthropogenic activities(acid deposition and enhanced nitrogen fertilization and anthropogenic harvesting)in the wheat-rice.(2)In the lake,BSi content of the lake sediment profile shows an increasing trend from 14 cm upwards;spatially,the BSi content in the sediments of the northwest lake area is significantly higher than that of the southeast lake area(p<0.05).This reflects the accelerated loss of BSi in the soil and the collection of deposits in sediment at the last 40 years.(3)In the comparison of land and lake,the concentration of dissolved silicon in river water was significantly higher than that in lake water(p<0.05);the BSi content in soils was significantly lower than in and sediments(p<0.05)and showed opposite trends from the surface to the bottom in soils(0-45cm)and sediments(0-14 cm)in the profile.These indicated a gradual increase in the characteristics of sources and sinks of BSi in soils and sediments at the last 40 years.(4)Anthropogenic acidification is the main driver of accelerated loss of BSi from soil to sediment,the analysis showed that soil pH was positively correlated with BSi content(p<0.05)and acidification of soils has accelerated in recent decades due to anthropogenic activities,particularly in wheat-rice land;while it was not correlated with BSi in sediments(p>0.05).In addition,organic matter(OM)in the surface soil causes soil acidification,which accelerates the loss of BSi and its accumulation in the sediment,as evidenced by a negative correlation between OM and BSi content in the surface soil(p<0.05)and a positive correlation with BSi content in the sediment(p<0.05).(5)The comparative results of Si/Al in soils and sediments and evidence of Si/Al changes in the sediment profile demonstrate that increased anthropogenic activity at the last 40 years led to soil acidification and accelerated the flow of BSi from the soil to the lake;the current levels of BSi in the soil are significantly lower than in the 1980s,the dissolved silicon centration in Lake Taihu water has gradually increased at the last 30 years,and the PHREEQC model results indicate that the SI(SiO2)in the lake water has gradually increased and reached supersaturation,suggesting that the accelerated flow of BSi to the lake is entering the sediment through natural deposition. |
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