近百年来我国西南地区酸沉降背景下湖泊环境变化——来自四面山龙潭湖沉积硅藻证据

Lake environmental changes in response to acid deposition in Southwest China over the last century:Evidence from sedimentary diatoms in Lake Longtan of the Simian Mountains

大气酸沉降会导致地表水体酸化和富营养化,同时气候变暖也会影响湖泊水体环境,湖泊生态系统如何响应二者相互作用是全球变化研究的热点之一.我国西南地区是全球酸沉降负荷最高的地区之一,然而目前对酸沉降影响下地表水环境变化规律知之甚少.本文以重庆四面山龙潭湖为研究对象,通过沉积岩芯的210 Pb测年和硅藻分析,并结合流域历史资料数据,揭示龙潭湖过去近百年来水环境变化及其主要驱动因子.结果表明,1926-1968年,龙潭湖以Achnanthidium minutissimum和Encyonema silesiacum占优势;随后,Lindavia bodanica快速增加至峰值后逐渐减少,伴随Aulacoseira alpigena和Aulacoseira ambigua含量上升.硅藻组合中以适应中性和弱碱性水体的属种为主,嗜酸性属种含量很少,表明目前水体总体维持弱碱性,这得益于当地紫色砂页岩和森林土壤对于酸沉降的缓冲作用.尽管目前龙潭湖仍维持弱碱性,1980s以来硅藻推导水体酸碱度下降、中富营养种增加,表明酸沉降降低水体碱度并提高营养水平.气候变暖加剧水体热力分层和营养富集,导致适应扰动、贫营养环境的L.bodanica减少.2010年以来,中富营养属种略有减少反映湖泊富营养化有所减缓.

Atmospheric acid deposition leads to surface water acidification and eutrophication;meanwhile,climate warming also influences lake water environment.The response of lake ecosystems to their interactive interaction is one of research hotspots in global environmental changes.Southwest China is one of the regions with the highest acid deposition loading all over the world.However,there is a paucity of information on how aquatic environments respond to acid deposition.This study investigated historical documents and diatom communities in a 210 Pb-dated sediment core collected from Lake Longtan of the Simian Mountains in Chongqing City,to explore aquatic environmental changes and major underlying driving forces during the past century.The results showed that Achnanthidium minutissimum and Encyonema silesiacum were dominant species in Lake Longtan from 1926 to 1968.Subsequently,Lindavia bodanica increased sharply to a peak and then decreased gradually,concurrent with the increases of Aulacoseira alpigena and Aulacoseira ambigua.Taken together,the dominance of circumneutral and alkaliphilous diatoms with few acidophilic species indicated that water column maintained weakly alkaline in Lake Longtan.One potential explanation is that local bedrock(i.e.purple sand shale)and forest soils have strong ability to buffer against the effects of acid deposition.Although water column in Lake Longtan is slightly alkaline at present,diatom-inferred alkalinity loss and the increase of mesotrophic species after the 1980s indicated that acid deposition had caused a decrease in alkalinity but an increase in nutrient level.Warming-driven thermal stratification and nutrient enrichment probably resulted in a decrease in L.bodanica,a taxon preferring mixing and oligotrophic environment.Recent decreases in meso-and eu-trophic diatoms reflected eutrophication alleviation in Lake Longtan.