长江口海域表层水体颗粒有机物δ^(15)N的分布特征

THE DISTRIBUTION OF δ^(15)N IN PARTICULATE ORGANIC MATTER IN SURFACE WATER OF THE CHANGJIANG RIVER ESTUARY

提要以长江口海域2005年4个季度的现场调查为基础,测定了不同季节表层水体中悬浮颗粒有机物的δ15N值(δ15Np),初步分析了δ15Np的时空分布特点以及表层水体中δ15Np指示水体富营养化的可行性。结果显示,长江口海域表层水体中平均δ15Np偏低,δ15Np离散程度较大,农业化肥、大气沉降对该海域氮来源贡献较大,陆源氮输入变化及氮分馏作用程度较大。δ15Np的空间分布具有季节性差异,陆源氮输入变化及氮分馏作用导致的长江口近岸海域δ15Np的季节变化是其主要原因。5月份δ15Np与DIN具有显著正相关性,一定程度上δ15Np可以指示海域氮富营养化程度。

To determine the sources of nitrogen entering the Changjiang （Yangtze） River estuary and understand eutrophication mechanisms in regional areas, nitrogen isotope of suspended particulate organic matter （δ^15Np） was measured in 2005. Results show that the average value of δ^15Np in surface water of the estuary was lower in a wider range than those of others in the world. Vertical variation of δ^15Np from surface to bottom changed clearly in season. In the maximum turbid zone and biologically active areas of the estuary, δ^15Np values were higher and more complicated than those in adjacent areas. The δ^15Np values varied positively with salinity in February and September, and negatively in May and November. In May, the average of δ^15Np in the estuary was higher, followed by September, November and February, reflecting seasonal rainy-dry change. Also, the level of δ^15Np concentration was more fluctuated stationwise in May, during which δ^15Np was linearly-correlated to DIN in surface water significantly. Air precipitation and agriculture discharge were the major nitrogen sources into the estuary with biogeochemistry and fractionation processes that should be considered. As the seasonal variation of the δ^15Np in nearshore area was more variable than that in open sea, in May, land-derived nitrogen sources, biogeochemistry processes, and fractionation varied very dynamically. Therefore, the δ^15Np values could be used to indicate the DIN level in the surface water to some extents.