大冶湖沉积物氮磷形态分布特征及生态风险评价

Distribution characteristics of nitrogen and phosphorus forms and ecological risk assessment of sediment in Daye Lake

为探究城市湖泊的内源污染环境现状,以黄石市大冶湖为研究对象,开展其冬夏季沉积物氮磷形态分布特征解析及生态风险评估.结果表明:沉积物中总氮(TN)的平均含量为3491 mg·kg^(-1),处于国内各湖泊中上游水平;而可转化态氮(TTN)的平均含量较低,为761.0 mg·kg^(-1).分析氮的赋存形态可知,相比于IEF-N(离子交换态氮)、SAEF-N(强碱可浸取态氮)、WAEF-N(弱酸浸取态氮),夏冬季4种形态的TTN均以SOEF-N(强氧化剂态氮)为主,说明沉积物中有机氮的含量较高;沉积物中总磷(TP)平均含量为622 mg·kg^(-1),生物可利用磷(BAP)年均含量处于国内各湖泊中间水平,为253.6 mg·kg^(-1).从磷形态来看,夏季4种无机磷形态的含量排序为HCl-P(钙结合态磷)>金属氧化物结合态磷(NaOH-P)>可还原态磷(BD-P)>弱吸附态磷(NH_(4)Cl-P),而冬季为BD-P>NaOH-P>HCl-P>NH_(4)Cl-P,说明沉积物磷形态与季节关联性较大.相关性结果表明:夏季WAEF-N、SAEF-N与TP、NH_(4)Cl-P、BD-P、NaOH-P均呈现出明显的正相关性(p<0.01),相关性系数(R^(2))普遍超过0.6,推测大冶湖沉积物中氮形态与磷形态可能存在同源性.沉积物与上覆水、间隙水氮磷的相关性热图显示,大冶湖水体中的氮污染主要来自于外源氮的输入;而磷污染受控于沉积物的内源释放,且季节差异影响明显,夏季磷的内源释放风险更高.生态风险评价表明,大冶湖的狭长型形态导致不同区域的氮磷污染风险存在较大差异,其沉积物磷污染较氮污染明显,属于轻度污染,污染风险整体呈现西高东低的趋势.

In this work,the seasonal distribution patterns of nitrogen and phosphorus in sediments of Daye Lake,along with an ecological risk assessment,were studied to gain insight into the endogenous pollution of urban lake sediment.The results showed that the average content of total nitrogen(TN)in sediments was 3491 mg·kg^(-1),higher than that of most lakes,while the average content of transformable nitrogen(TTN)was low at 761.0 mg·kg^(-1).Among the various nitrogen forms,strong oxidant extractable form nitrogen(SOEF-N)was the mian component of TTN in both seasons,indicating a high content of organic nitrogen in the sediments.In contrast,the average content of total phosphorus(TP)in sediments was 622 mg·kg^(-1),and the bioavailable phosphorus(BAP)was at an intermediate level with a value of 253.6 mg·kg^(-1).The contents of inorganic phosphorus forms were in the following order:calcium-bound phosphorus(HCl-P)>metal oxide-bound phosphorus(NaOH-P)>reducible phosphorus(BD-P)>weakly adsorbed phosphorus(NH_(4)Cl-P)in summer,while in winter was BD-P>NaOH-P>HCl-P>NH_(4)Cl-P.This indicated that the phosphorus form in sediments is closely related to the seasonal variations.Correlation analysis results revealed significant positive correlations(p<0.01,R^(2)>0.6)between WAEF-N and SAEF-N with TP,NH_(4)Cl-P,BD-P and NaOH-P in summer,suggesting that the nitrogen morphology has a strong homology with phosphorus morphology in sediments of Daye Lake.Further correlation analysis of N and P among sediments,overlying water and interstitial water indicated that the nitrogen pollution in Daye Lake is mainly due to the exogenous inputs,while the phosphorus pollution stemmed predominantly from endogenous sediments release.Importantly,the effect of seasonal variation on the phosphorus pollution was pronounced,with a high risk of endogenous release in summer.The ecological risk assessment showed that the narrow and long shape of Daye Lake led to obvious differences of nitrogen and phosphorus pollution risks in different regions.Sediments were found to be more seriously polluted by phosphorus compared to nitrogen.While Phosphorus pollution was catagerized as light pollution and the overall ecological risk exhibited a distinct spatial pattern of“high in the west and low in the east”across Daye Lake.