沉积物生源要素对水体生态环境变化的指示意义

受人类活动影响,输入到湖泊、河口中的营养盐剧增,导致水体富营养化、食物链结构改变、底质季节性缺氧等生态环境变化。这些环境变化会在沉积物中留下记录,沉积物中生源要素及其稳定同位素的变化是指示水域古生产力、营养盐水平的有效指标。总结归纳了沉积物中生源要素(碳、氮、磷、硅)指标对水体环境中初级生产力、物质来源、营养盐水平3方面变化的指示作用。沉积物中TOC、TN、δ13C、CaCO3和BSi可以反映水体沉降有机质含量和浮游植物的生长状况,是指示水域初级生产力水平的有效指标。根据不同类型植物来源的有机质中δ13C、δ15N和C/N的差异,可以追踪沉积物中有机质的来源。有效地区分有机质来源对于研究人类活动对水体环境的影响及水体富营养化具有重要的价值。沉积物中TN、δ15 N、TP和非磷灰石磷(NAIP)含量的升高直接反映了陆源输入氮、磷的增加。BSi在指示浮游植物生长状况的同时,还反映了水体溶解硅浓度水平和富营养化状况。水体中的生源物质在沉降和埋藏的过程中,会受到早期成岩作用、水动力搬运等众多因素的作用,使沉积物记录的环境变化信息发生改变,从而干扰其对水体环境演变的重建作用。因此综合分析各生源要素指标反映的环境变化信息及其可能的干扰因素,方能正确地反映水域的环境变化过程。

Indicative significance of biogenic elements to eco-environmental changes in waters

The increasing input of nutrients to lakes and estuaries by the anthropogenic activities has resulted in the aquatic eco-environment changes,such as the change of food chain,eutrophication and frequently seasonal hypoxia in bottom waters,which can be recorded in sediments.The biogenic elements and their stable isotopes in sediments are effective proxies to reflect the paleoproductivity and nutrient level in waters.The indicative significance of biogenic elements(C,N,P,Si) to the change of primary production,material sources and nutrient levels was reviewed in this paper.TOC,TN,δ13C,CaCO3 and BSi in sediments reflecting the content of organic matter and the growth of phytoplankton,can be used as effective proxies to indicate the primary production level.Source identification of organic matter by the differences of δ13C,δ15N and C/N values between different types of plants has important value to study the influence of anthropogenic activities on the aquatic environment and eutrophication.The increasing trend of TN,δ15N,TP and non-apatite phosphorus(NAIP) in sediments reflects the increasing input of terrestrial nitrogen and phosphorus to coastal waters.BSi can reflect the phytoplankton growth,and further indicate the Si concentration variations and eutrophication in waters.Biogenic elements are influenced by many factors in their deposition and burial,such as diagenesis and hydrodynamic conditions,which can disturb the sedimentary records of biogenic elements and then hinder the proper indication of environmental changes by these proxies.Consequently,in order to exactly understand the aquatic environmental changes,it is essential to comprehensively analyze the information of environmental changes provided by multiple biogenic element proxies and to fully consider the potential interference factors for the paleoenvironmental reconstructions.