基于沉积物中总氮和总磷垂向分布与吸附解吸特征的白洋淀清淤深度

针对白洋淀清淤示范区2种主要水体类型：开阔淀和鱼塘，采用沉积物总氮（TN）和总磷（TP）的垂向分布拐点法和吸附解吸平衡浓度法，开展了清淤深度确定研究.根据沉积物TN和TP含量垂向分布拐点法与吸附解吸平衡浓度分别确定的清淤深度是一致的.南刘庄示范区淀水体清淤深度为（50±10）cm，南刘庄示范区鱼塘水体清淤深度为（30±10）cm，采蒲台示范区鱼塘水体清淤深度为（30±10）cm.沉积物对NH₄⁺-N吸附/解吸平衡浓度（ENC₀）与交换态NH₄⁺-N含量和TN含量显著正相关；沉积物对溶解态活性磷（SRP）吸附/解吸平衡浓度（EPC₀）与沉积物交换态SRP含量和TP显著正相关.沉积物TN和TP含量可以预测沉积物对上覆水体释放氮、磷的风险.南刘庄和采蒲台清淤示范区沉积物有向上覆水释放氮、磷的趋势，沉积物是水体营养的来源.建议判别清淤深度TN控制值为750mg·kg^-1、TP控制值为500mg·kg^-1，沉积物剖面TN含量大于750mg·kg^-1、TP含量大于500mg·kg^-1，可设计为清淤层.

Identification of Dredging Depths Based on Sediment Vertical Distribution Profiles of Total Nitrogen and Total Phosphorus and Their Adsorption-desorption Equilibria

A dredging demonstration project in the Baiyangdian Lake included open waters and fishing ponds to reduce the internal release of nitrogen and phosphorus from bottom sediments. The dredging depth design was determined by both the sediment vertical distribution profile of total nitrogen and phosphorus, and the sediment adsorption-desorption equilibrium method. The determined dredging depths were very similar and coincident. The dredging depth for the demonstration area of open waters in Nanliuzhuang was identified as(50±10) cm; and the dredging depths for fishing ponds were(30±10) cm in both the Nanliuzhuang and Caiputai demonstration areas. The equilibrium nitrogen(NH₄⁺-N) and phosphorus(SRP) concentrations at zero net sorption or desorption(ENC₀ and EPC₀) were significantly positively correlated with both exchangeable and total nitrogen and phosphorus in the sediments. The total nitrogen and phosphorus in the sediments were also used to predict the risk of their release from the bottom sediments to the overlying water column. The sediment layers with ENC₀ and EPC₀ values greater than the NH₄⁺-N and SRP in the overlying water column indicated the sediments act as a source of dissolved nitrogen and phosphorus to the overlying water column in the Nanliuzhuang and Caiputai demonstration areas. Accordingly, the sediment layers with both total nitrogen concentrations greater than 750 mg·kg^-1 and total phosphorus concentrations greater than 500 mg·kg^-1 should be identified as dredging layers.