重庆园博园龙景湖新建初期内源氮磷分布特征及扩散通量估算

采集重庆园博园龙景湖不同区域沉积物样柱,分析沉积物上覆水和孔隙水中氮磷垂直分布特征,并利用一维孔隙水扩散模型(Fick定律)来估算氨氮和正磷酸盐的扩散通量和年负荷贡献量.结果表明,龙景湖沉积物-水界面氨氮从上覆水到孔隙水在垂直剖面上总体都呈现出增大趋势;表层(0~5 cm)沉积物孔隙水中氨氮平均浓度为6.13 mg·L-1±3.07 mg·L-1,是上覆水氨氮平均含量10倍.正磷酸盐垂直分布特征总体表现为先增大再减小,在表层孔隙水出现极大值;沉积物孔隙水中正磷酸盐平均浓度为2.01 mg·L-1±1.05 mg·L-1.所有区域氨氮均表现为由沉积物向上覆水释放,新增淹没区库湾区域氨氮扩散通量低于6.0 mg·(m2·d)-1,龙景沟水库、龙景湖主湖原有湖区氨氮扩散通量分别高达47.19 mg·(m2·d)-1、40.29mg·(m2·d)-1.原有湖区正磷酸盐表现为由沉积物向上覆水释放,扩散通量仍以龙景湖主湖及龙景沟水库最大,为7.89mg·(m2·d)-1、6.13 mg·(m2·d)-1.新增淹没区的河道、库湾及赵家溪部分区域正磷酸盐却表现为由上覆水向沉积物中扩散,扩散通量为-1.93~-2.78 mg·(m2·d)-1.整个湖区氨氮年负荷贡献量为3.95 t·a-1,新增淹没区贡献率为85%;正磷酸盐年负荷贡献量为0.357 t·a-1,新增淹没区贡献率为72%.

Distribution of Nitrogen and Phosphorus in the Sediments and Estimation of the Nutrients Fluxes in Longjinghu Lake, Chongqing City, During the Initial Impoundment Period

Sediment cores from a newly formed urban lake (Longjinghu Lake in China's Chongqing City) were selected to study the vertical distribution characteristics of both nitrogen and phosphorus from the overlying water to porewater, and then fluxes of ammonia (NH₄⁺-N) and orthophosphate (PO₄^3--P) from different areas of the lake were calculated using a one-dimensional transport-reaction model based on the Fick's First Law. The results showed that the mean ammonia concentrations in porewater of surface layers (0-5 cm) was 6.13 mg·L^-1±3.07 mg·L^-1, higher by a factor of 10 compared with that in the overlying water. While orthophosphate contents tended to increase downwards, reaching a peak in surface sediment porewater, and then decreased in downcore, with a mean concentration of 2.01 mg·L^-1±1.05 mg·L^-1. Based on the porewater diffusion model, ammonia were released from sediments to overlying water, which indicated potential internal nutrient releasing risk. Although the flux of ammonia in the "initial lake area" was higher than that in the "newly submerged area", the annual load contribution from the "newly submerged area" was 85% (3.95 t·a^-1). Similar to ammonia, orthophosphate was also released from sediments to overlying water in the "initial lake area", with the highest fluxes in the former Longjinghu Lake and Longjingou Lake Reservoir, reaching 7.89 mg·(m²·d)^-1 and 6.13mg·(m²·d)^-1, respectively. However, in a portion of the "newly submerged area", orthophosphate in the overlying water was transported to the sediments, resulting in negative fluxes ranging from -1.93 to -2.78 mg·(m²·d)^-1. The annual load of orthophosphate from the whole sediments was 0.357 t·a^-1, with 72% contributed by the "newly submerged area".