龙感湖沉积物中人类活动导致的营养盐累积通量估算*

通过LL-4孔沉积环境指标研究表明,近100年来龙感湖地区人类活动加强,导致营养元素磷、碳、氮以及铁在沉积物中的浓度均呈增长趋势,特别是1950年以来,随着大量人口的迁入,围湖造田、破坏湖滨湿地等造成水土流失加剧,沉积物质量累积速率加快,同时营养元素累积量急剧增加。根据营养元素与参比元素Al, Fe和Ti之间的关系,以及不同营养元素之间的相互关系,人类活动引起的累积量得以从自然背景上区分出来,结合沉积物质量累积速率计算,人类活动引起的磷、有机碳和氮的累积通量分别在151.0~889.4mg/m²a,4.3~149.0g/m²a和0.5~18.6g/m²a间变化。碎屑物质的累积稀释了沉积物中营养盐的富集浓度,龙感湖草型湖泊的特点,使湖泊沉积环境易于呈氧化环境,生物和地球化学作用,也削弱了人类活动累积营养盐的变化幅度,使沉积中营养盐呈平稳上升的趋势。

ESTIMATE OF ANTHROPOGENIC NUTRIENT ELEMENT FLUXES RECORDED IN LACUSTRINE SEDIMENTS:A CASE STUDY IN LONGGAN LAKE

The steady sedimentary environment and an accurate geochronological analysis make it possible to estimate the anthropogenic nutrient element fluxes in a catchment area. A 63cm sediment core (the LL-4 core) was drilled using a gravity corer at the northwest bay of the Longgan Lake. 137 Cs,210 Pb,and spheroidal carbonaceous particles (SCP) were measured to establish the time sequence and obtain the mass accumulation rate of the LL-4 core. Grain-size composition indicates that the sedimentary environment at the sampling site has been steady in the past century which provides an ideal field to estimate anthropogenic nutrient accumulation fluxes recorded in lake sediment. Total organic carbon and total nitrogen content of sediment were calculated using CE440 elemental analyzer after inorganic carbon was removed using 5% HCl. Total phosphorus (TP),aluminum (Al),iron (Fe) and titanium(Ti) concentrations were calculated using inductively coupled plasma-atomic emission spectrometry (ICP-AES) with standard solution SPEX TM from the US as the standard after samples were digested by mixed acid (nitric acid,hydrofluoric acid,and perchloric acid). The recorded phosphorus (P),organic carbon (OC) and nitrogen (N) contents increased concomitantly with increased human activity in the region and are intensively enhanced since 1950 when a large population migrated to the lake catchment. Based on the relationships among different nutrient elements and geogenic tracer elements (Al,Fe,Ti),the background values of P,OC and N were estimated. Anthropogenic nutrient element accumulation fluxes were then obtained by subtracting background from measured value. During the past century,the accumulation fluxes of anthropogenic P,OC and N increased considerably from 151.0mg/m 2 a to 889.4mg/m 2 a,from 4.3g/m 2 a to 149.0g/m 2 a,and from 0.5g/m 2 a to 18.6g/m 2 a,respectively. Results of this work can be used to lake restoration. Detrital input can dilute anthropogenic nutrient concentration in sediment. Under oxidized condition,biogeochemical processes can also reduce the total nutrient concentration in the sediments.