Lu Ting, Chen Nengwang, Duan Shuiwang, Chen Zhuhong, Huang Bangqin
Key Laboratory of the Coastal and Wetland Ecosystems, Coastal and Ocean Management Institute, College of the Environment and Ecology, Xiamen University, Xiamen, 361102, People's Republic of China.
Department of Geology and Earth System Science Interdisciplinary Center, University of Maryland, College Park, MD, 20742, USA.
Environ Sci Pollut Res Int. 2016 Dec;23(23):24166-24177. doi: 10.1007/s11356-016-7397-3. Epub 2016 Sep 19.
Many coastal rivers have a system of cascade reservoirs, but the role of these reservoirs in regulating nutrient transport from watershed to coast is still unknown. In this study, phosphorus (P) in surface water and top sediment was investigated along the North Jiulong River (southeast China) under three hydrological conditions (high flow, medium flow and low flow) in 2012-2013, and P dynamics in a cascade reservoir (Xipi Reservoir) were studied on a monthly scale. Results showed that the concentrations of dissolved reactive phosphorus (DRP) consistently decreased longitudinally in the upper river with the lowest values observed in the section of cascade reservoirs, likely due to tributary inputs and in situ uptakes. The decrease was most rapid during base flow when DRP was highest in the free-flowing river section and lowest in cascade reservoirs. Results from monthly monitoring on the Xipi Reservoir showed general downriver decreases in DRP, total particulate phosphorus (TPP) and total phosphorus (TP) in the riverine zone and transition zone. Mass balance results on an annual basis suggest that the Xipi Reservoir (lacustrine zone) was an overall sink for TPP (6 % retention) but somewhat a source of DRP (-0.3 %) with TP retention (1 %). Even scaled up to the whole cascade reservoir system, P retention was low compared with worldwide reservoirs, which we ascribe to the high P loading and short hydraulic residence time. Nevertheless, major processes controlling P retention in coastal rivers with cascade reservoirs varied from sedimentation in the dry-cold season to biotic transformation in the wet-warm season, thereby affecting loading and composition of P from watershed to the coast. This study highlights the hydrological controls on the role of cascade reservoirs in regulating P retention and downriver fluxes in different seasons.
许多沿海河流都有梯级水库系统，但这些水库在调节从流域到海岸的养分输送方面所起的作用仍不明确。在本研究中，于2012 - 2013年在三种水文条件（高流量、中流量和低流量）下，对中国东南部九龙江北部地表水和表层沉积物中的磷进行了调查，并按月尺度研究了一座梯级水库（溪口水库）中的磷动态。结果表明，溶解态活性磷（DRP）浓度在上游河流中沿纵向持续下降，在梯级水库断面观测到最低值，这可能是由于支流输入和原位吸收所致。在基流期间下降最为迅速，此时DRP在自由流动河段最高，而在梯级水库中最低。对溪口水库的月度监测结果显示，在河流区和过渡区，DRP、总颗粒磷（TPP）和总磷（TP）总体上沿下游方向减少。年度质量平衡结果表明，溪口水库（湖泊区）总体上是TPP的汇（保留率6%），但在一定程度上是DRP的源（-0.3%），TP保留率为1%。即使扩大到整个梯级水库系统，与全球范围内的水库相比，磷的保留率也较低，我们将其归因于高磷负荷和短水力停留时间。然而，控制具有梯级水库的沿海河流中磷保留的主要过程在干冷季节为沉积，在湿热季节为生物转化，从而影响从流域到海岸的磷负荷和组成。本研究强调了水文条件对梯级水库在不同季节调节磷保留和下游通量作用的控制。
