长江中游滨岸带水体氨氮循环速率及影响因素

氨氮(NH_4~+)是大多数浮游生物优先利用的氮源,其在水体中的再生过程(REG)和潜在吸收过程(U_(pot))影响水体初级生产力和生物群落的生长。以长江为研究对象,采用同位素稀释法对长江中游滨岸带水体的NH_4~+循环速率进行研究。结果显示:长江中游滨岸带水体NH_4~+再生速率为0.12～1.62μmol/(L·h),潜在吸收速率为0.21～2.35μmol/(L·h),生物群落NH_4~+需求(CBAD)为0.08～0.75μmol/(L·h)。NH_4~+再生速率、潜在吸收速率和生物群落NH_4~+需求均随水流方向自宜昌至鄱阳湖湖口呈现显著的下降趋势(p0.05)。统计分析表明,化学需氧量(COD)(p0.01)和悬浮物浓度(SS)(p0.05)是影响长江中游水体NH_4~+循环速率的主要因素。长江中游水体NH_4~+再生速率占潜在吸收速率的43.1%～76.0%,均值为58.5±8.5%,表明NH_4~+再生是长江中游水体中生物群落NH_4~+吸收过程的主要NH_4~+来源。估算得到的NH_4~+再生量是长江中游水体TN负荷的2倍,表明水体NH_4~+再生在支持水体初级生产力和维持氮素内循环方面具有重要作用。

Ammonium Recycling and Its Influencing Factors Along the Littoral Zone of the Middle Reaches of Yangtze River

Ammonium(NH4+) is the preferred nitrogen form for plankton, its regeneration(REG) and potential uptake(Upot) are related to primary productivity and growth of organisms in water ecosystems. In this study, NH4+ recycling rates in the littoral zone of the middle reach of the Yangtze River were studied by using the isotope dilution method. Results showed that the REG rates in the middle reach of the Yangtze River were 0.12-1.62 μmol/(L·h), the Upot rates were 0.21-2.35 μmol/(L·h), and the community biological NH4+ demand(CBAD) rates were 0.08-0.75 μmol/(L·h). Moreover, along with the flow direction of Yangtze River, NH4+ recycling rates showed significant decreased trend from Yichang to Poyang Lake estuary(p<0.05). Statistical analyses showed that chemical oxygen demand(COD) and suspended solids(SS) are the main factors influencing the NH4+ recycling rates in the middle reach of the Yangtze River. During the study area, the REG rates accounted for 43.1%-76.0% of the Upot rates, with a mean value of 58.5%±8.5%. This indicated that REG is the main source of NH4+ in the process of Upot by the biological communities in the middle reach of the Yangtze River. NH4+ produced by REG process is 2 times higher than that of water column TN loads, indicating that REG plays an important role in supporting primary productivity and maintaining nitrogen internal circulation.