ESTIMATE OF ANTHROPOGENIC NUTRIENT ELEMENT FLUXES RECORDED IN LACUSTRINE SEDIMENTS:A CASE STUDY IN LONGGAN LAKE
龙感湖沉积物中人类活动导致的营养盐累积通量估算*

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.