太湖沉积物孔隙水无机氮空间变化特征

Spatial variation of porewater inorganic nitrogen in Lake Taihu,China

采集太湖不同生态类型湖区(草型湖区胥口湾;风浪大、水华较少的湖心区和水华较严重的梅梁湾)沉积物柱状样,研究沉积物理化性质以及孔隙水无机氮浓度垂直变化特征。结果显示,各点含水率、有机质、总氮均随深度增加而降低,而梅梁湾含量最高,湖心区最低。沉积物溶解氧随深度增加而降低,胥口湾最高,梅梁湾最低。孔隙水NH_4^+-N随深度增加而增大,NO_3^--N、NO_2^--N均随随深度增加而减小。比较表层0-5cm沉积物孔隙水和上覆水无机氮浓度,发现各湖区NO_3^--N和NO_2^--N释放风险小,胥口湾(草型湖区)和梅梁湾(藻型湖区)NH_4^+-N释放风险较大,湖心区较小。

Sediment cores were collected in different areas with different ecological states in Lake Taihu to observe vertical variation in physicochemical characteristics of sediments and porewater inorganic nitrogen. The three areas were Xukou Bay dominated by macrophytes, Central Lake with strong wave and less algal bloom, Meiliang Bay with severe algal bloom. The results showed that water content, organic matter, and TN decreased with increasing sediment depth in the three sampling sites, with the highest values observed in Meiliang Bay while the lowest values in Central Lake. Meanwhile, dissolved oxygen within sediments decreased with increasing sediment depth, and the highest concentration was found in Xukou Bay and the lowest in Meiliang Bay. Porewater ammonium concentration increased dramatically downward in the sediments, in contrast to nitrate and nitrite concentrations. A comparison of inorganic nitrogen concentration from within top 5-cm sedimentary porewater and the overlying water suggested that release risk of nitrate and nitrite was low in all three areas; both Xukou Bay and Meiliang Bay had a relatively high risk for ammonium release into overlying water, while the risk was low in Central Lake.