南水北调对密云水库水位变幅带土壤磷释放量的影响

南水北调来水引起的水位上涨可能会导致密云水库水位变幅带土壤中磷的释放.过量的磷可能会引起水体富营养,因此,研究水库变幅带磷释放风险对密云水库水质安全保障具有科学指导意义.本研究采用连续浸提法测定密云水库变幅带土壤及沉积物中弱吸附态磷(NH_4ClP)、铁磷(BD-P)、铝磷(NaOH-P)及钙磷(HCl-P)等4种不同形态磷含量,探讨其分布特征;并在室内进行了磷释放模拟实验,估算了南水北调来水引起水库水位上升所致的易释放磷的释放量.结果表明,NH_4Cl-P、BD-P、NaOH-P、HCl-P广泛地分布于密云水库变幅带土壤及沉积物中.在白河、内湖及潮河3个库区,磷形态分布具有一致规律,即HCl-PNaOH-PBD-PNH_4Cl-P.因密云水库变幅带为中国典型的北方碱性土壤,变幅带无机磷主要为钙磷.NH_4Cl-P在3个库区变幅带土壤中含量相差不大,在受水动扰动力影响较小的内湖库区BD-P含量略高于其它2个库区.在3个不同库区中,潜在活性磷NH_4Cl-P和较稳定的NaOH-P在岸上和水陆交界面土壤及水下沉积物中含量相差不大,受氧化还原条件影响较大的BD-P在沉积物中的含量略高于岸上和水陆交界面土壤.磷释放模拟实验及释放量估算结果表明,水库水位上涨3 m的情况下,白河、潮河和内湖库区淹没变幅带土壤分别释放1.02、0.80、0.37 mg·m~(-2)易释放磷.白河和内湖库区变幅带被水淹没土壤中磷释放的风险可能更高,需加强防护.

Impact of south-to-north water diversion project on phosphorus release from water level fluctuating zone at Miyun reservior

South-to-north water diversion project may lead to increased water level, thereby releasing phosphorus from water level fluctuating zone at Miyun reservoir and causing eutrophication. Investigating on phosphorus release from water level fluctuating zone of Miyun reservoir has scientific guidance for phosphorus release risk. In this study, the distribution characteristics of loosely absorbed phosphorus (NH₄Cl-P), Fe-bound phosphorus (BD-P), Al-bound phosphorus (NaOH-P) and Ca-bound phosphorus (HCl-P) were measured with continuous extraction method. The phosphate release characteristics were simulated in the lab and the release flux resulted from water level in the reservoir were calculated. Results showed that NH₄Cl-P, BD-P, NaOH-P and HCl-P were widespread in soils and sediments in water fluctuating zone of Miyun reservoir. The contents of four fractions were presented with the consistent trends in areas of Baihe, Neihu and Chaohe, i.e. HCl-P > NaOH-P > BD-P > NH₄Cl-P. Obviously higher contents of HCl-P were mainly due to the alkaline soil characteristics of soils in the Miyun reservoir. The contents of NH₄Cl-P did not appear with much difference in three different reservoir areas. However, the contents of BD-P were slightly higher in Neihu area less effected by hydraulic agitation. The contents of potential activity phosphorus NH₄Cl-P and stable NaOH did not appear with obvious difference in soils in land, land-water interfaces, and sediments at three different reservoir areas, while BD-P contents at land-water interfaces were slightly higher than those in lands and sediments. The results of P release simulated experiments and release flux calculation showed that when water level increased by 3 m, the water fluctuating zone of Baihe, Chaohe, and Neihu areas could release 1.02, 0.80 and 0.37 mg·m^-2, respectively. Additionally, the water fluctuating zones of Baihe and Neihu areas may increase the P release risk after water fluctuation and hence these two areas should be protected with higher attention.