长江大通站溶解有机氮生物可利用性潜力及输入通量

根据2012~2013年度隔月对长江大通站的6次调查,分析了长江水体中溶解态总氮(TDN)的构成,包括溶解无机氮(DIN)及溶解有机氮(DON)中的尿素、自由态氨基酸(DFAA)、结合态氨基酸(DCAA)的构成和丰度,并评价了DON的生物利用性潜力,估算了不同形态氮的输入通量.结果表明,受稀释作用和悬浮颗粒物吸附影响,长江水体中DON浓度呈现出春冬季高、夏秋季低的变化特征,平均浓度为(33.28±21.35)μmol/L,占TDN比例平均为20.05%±13.53%;DON中组分尿素、DFAA和DCAA占DON的氮摩尔占比分别为21.94%±19.89%、0.84%±0.52%、3.68%±2.61%.其中,尿素浓度受季节性施肥灌溉影响,与径流量呈现出明显的正相关.总溶解态氨基酸(TDAA)占溶解有机碳(DOC)的碳摩尔分数和氨基酸降解指数均表明长江水体中DON具有较高的生物可利用性,且呈现出春夏季高、秋冬季低的变化趋势.DON的年输入通量为42.04万t,约占TDN年输入通量的17%.其中,具有高生物可利用性的尿素、DFAA、DCAA分别占DON年通量的15.50%、0.64%、2.80%.上述结果表明,长江输入的DON具有相当高的生物可利用性,对长江口及其邻近海域富营养化的贡献不可忽视.

Potential bioavailability and flux of dissolved organic nitrogen at the Datong station of the Yangtze River

Based on the bimonthly investigation at the Datong station in the Yangtze River during 2012 to 2013, the concentrations and compositions of total dissolved nitrogen (TDN) including dissolved inorganic nitrogen (DIN) and dissolved organic nitrogen (DON) and its important compositions urea, dissolved free amino acids (DFAA) and dissolved combined amino acids (DCAA) were analysed. On the other hand, the bioavailability of DON was evaluated and the fluxes of different nitrogen forms were calculated. The concentration of DON in the Yangtze River showed a seasonal variation tendency, which were higher in spring and winter and were lower in summer and autumn, due to the dilution of Yangtze River and the adsorption of suspended particulate matter to DON. The average concentration of DON was (33.28±21.35)μmol/L, accounting for 20.05%±13.53% of TDN; and the concentration of urea, DFAA and DCAA accounted for 21.94%±19.89%、0.84%±0.52% and 3.68%±2.61% of DON, respectively. The concentration of urea presented a positive correlation with the river runoff, which attributed to the seasonal fertilization in the Yangtze River basin. The carbon-normalized of total dissolved amino acids (TDAA (%DOC)) and the degradation index of TDAA both indicated that the DON in the Yangtze River had high bioavailability and presented a seasonal variation, which was higher in spring and summer and was lower in autumn and winter. The flux of DON was 42.04′104t/a, approximately accounted for 17% of TDN. Accordingly, the flux of urea, DFAA and DCAA accounted for 15.50%、0.64% and 2.80% of DON flux, respectively. In conclusion, the DON in the Yangtze River had high bioavailability and constituted the important nutrients for eutrophication in the Yangtze Estuary and its adjacent areas.