重庆梁滩河表层沉积物氮形态时空特征及影响因素

为研究流域快速城市化背景下浅水河流表层沉积物氮赋存形态时空格局特征及潜在环境风险,选择重庆主城区的梁滩河为研究对象,于2014年12月和2015年6月采集干、支流主要断面水样及表层沉积物样进行分析。结果表明:梁滩河干、支流表层沉积物总氮(TN)含量变化为2.63～8.12 g/kg,离子交换态氮(IEF—N)、弱酸可提取态氮(WAEF—N)、强碱可提取态氮(SAEF—N)和强氧化剂可提取态氮(SOEF—N)含量分别为190～1 764,119～1 139,208～2 039,159～2 829 mg/kg,受流域污染源分布格局影响,沉积物各形态氮含量空间变化幅度均较大;梁滩河沉积物TN、WAEF—N、SAEF—N、SOEF—N含量上游至下游均逐渐降低,而活性最高的IEF—N则在城市河段出现明显峰值,外源污染强度和建设用地面积对不同形态氮的空间变异性具有较高的解释量,表明流域内污染格局及人类活动强度对沉积物氮形态分布具有重要影响;沉积物中可转化态氮(TF—N)含量占TN比例的52.9%～72.3%,且在城市河段IEF—N占比均显著高于非城市段,呈现较高的氮释放风险,表明城市污染进一步促使沉积物氮的活化;大部分断面总氮及各形态氮冬季略高于夏季,但变化幅度不大;统计分析表明,各形态氮之间具有较强的相互转化的联系,而且与水体pH、DO、DOC等环境参数呈显著相关关系,沉积物中氮形态分布特征受外源有机碳输入及水体污染的影响。综上,受流域城市发展过程中形成的不同污染源格局的影响,梁滩河表层沉积物氮形态空间变异性大,特别是城市区河段内源污染风险较大,如何调控内源氮释放是未来治理河流的关键。

Temporal and Spatial Characteristics and Influencing Factors of Nitrogen Morphology in Surface Sediments of Liangtan River, Chongqing

Urban rivers pollution is a serious issue facing the world today. With the controlling progressively for most of the urban point source pollution, endogenous release of nitrogen and phosphorus from sediments, which could continuously pollute river water, became the greatest challenge for the remediation of urban river. The purpose of this study was to examine the spatial and temporal characteristics and risks of nitrogen forms in surface sediments of the river with basin rapid urbanization. Liangtan River, which is a typical urban river and has been greatly polluted due to the rapid development of the city and industry on the basin of wastewater, was selected to carry out a seasonal investigation of nitrogen forms and water environment parameters. The results showed that the range of total nitrogen (TN) concentrations in surface sediment of Liangtan River and its tributary (Huxi River) were 2.63~8.12 g/kg, and contents of the ion exchange nitrogen focusing (IEF-N), weak acid leaching nitrogen (WAEF-N), alkali leaching (SAEF-N) and strong oxidant may leach nitrogen (SOEF-N) contents were 190~1 764, 119~1 139, 208~2 039 and 159~2 829 mg/kg, respectively. The high variability of such N forms was attributed to the distribution pattern of the pollution sources (such as urban, industry, and farming) in the basin. The contents of TN, WAEF-N, SAEF-N and SOEF-N in sediments decreased gradually from the upstream to the downstream of Liangtan River, while the IEF-N with the highest activity showed different peaks in the urban reach, indicated that the spatial distribution of the N forms in river sediments was dominated by the watershed anthropogenic activities and pollution types. Meanwhile, the transferable nitrogen (TF-N) accounted for 52.9%~72.3% in TN, with higher IEF-N percentage in urban reach than these in non-urban reach, showing the higher release risk of N in urban river. Seasonal pattern of the majority N forms in surface sediment of Liangtan River showed the winter were significantly higher than summer. The statistical analysis showed that sediment different N forms parameters had significant correlations with each other, indicating that their closely mutual transformation connection; in addition, the contents of different N forms were significantly and positively associated with pH, DO, and DOC in surface water, indicating that exogenous water pollution hand a positive impact on sediment nitrogen release. Overview, N forms in the surface sediment of Liangtan River showed a great variability in spatial as the results of the pollution sources pattern in the process of urban development. There was a high release risk in the urban reaches due to the small molecular carbon input and higher exogenous pollution loading. The regulation of endogenous nitrogen release was the key point for river management in the future.