埃及Burullus潟湖沉积生源要素变化:百年来人类活动影响

Changes of Nutrient Salts Deposited in the Burullus Lagoon,Egypt:Effects of Human Activity over the Past Century

Burullus是尼罗河河口高封闭性潟湖,其生源要素主要来源于尼罗河,是研究Aswan大坝建成以来流域变化如何影响河口湖泊环境的最佳区域。研究通过对Burullus潟湖B1岩芯的210Pb测年、粒度、以及TOC、TN、TP、BSi生源要素的测试分析,结合历史资料,试图揭示Aswan建坝前后河口湖泊营养盐的差异变化,以及这些变化对生态环境的影响。结果表明:1)沉积物中TOC、TN和TP含量自下而上总体增加,表明尽管Aswan大坝导致营养盐通量急剧减少,但由于下游人类排放N、P通量大大增加,导致下游湖泊N、P浓度并没减少;且沉积TN/TP均小于16,表明湖泊仍为P限制。2)但BSi和BSi/TOC自下而上总体呈减少趋势,表明Aswan大坝引起的水沙减少导致湖泊中硅藻的生物量及其总初级生产力占比都在减少,潟湖水体生态环境将趋于恶化。

Burullus Lagoon is a a high,closed lagoon at the mouth of the Nile River,whose nutrients were mainly from the Nile.It is a critical area for studying how the changes in the Nile Basin has affected the lake environment of the Nile estuary after the Aswan Dam was built.This study investigated the changes of 210Pb dates,grain size,total organic carbon(TOC),total nitrogen(TN),total phosphorus(TP)and biogenic silica(BSi)in the B1 core from Burullus Lagoon,combined with historical data,to reveal the changes of nutrient salts in estuarine lakes and the impact of these changes on the ecological environment following construction of the Aswan Dam.The results showed that:(1)The content of depositional TOC,TN and TP increased from bottom to top,indicating that although the Aswan Dam led to a sharp decrease in nutrient flux,the TN/TP concentration in the downstream lakes did not decrease due to the greatly increased TN/TP flux discharged by human activity downstream of the dam.Also,TN/TP was less than16,indicating that the lake was still P-restricted.(2)However,BSi and BSi/TOC generally decreased from bottom to top,indicating that the reduction of water and sediment caused by the Aswan Dam has led to a decrease in the biomass of diatoms and the ratio of total primary productivity in the lake.The ecological environment of the lake tends to be deteriorating.