基于数值模拟的排水沟渠营养盐滞留机制解析

Analysis of in-stream nutrient retention mechanism based on numerical simulation

现有溪流沟渠营养盐滞留研究对滞留机制精细化的描述或刻画相当不足,难以满足小流域水环境管理和沟渠营养盐滞留环境生态功能提升的需要.针对此问题,本文首先对传统的营养螺旋指标概念进行拓展,提出了面向水文过程、生物吸收和物理化学吸附作用的营养螺旋指标,并给出了量化指标内在关系的计算模式.在此基础上,利用OTIS模型及数值模拟技术,定量估算水文过程、生物吸收和物理化学吸附作用的营养盐滞留贡献率及其相对贡献水平,从而解析排水沟渠营养盐滞留机制.案例分析表明,在排水沟渠NH_(4)^(+)和PO_(4)^(3-)滞留中,水文过程占据绝对主导地位,生物吸收和物理化学吸附滞留贡献较小.其中,水文过程、生物吸收和物理化学吸附对NH_(4)^(+)滞留率变化范围分别为7.91%~13.07%、0.09%~0.27%和0.31%~0.58%,相对贡献水平变化范围分别为91.75%~95.29%、1.07%~2.00%和3.64%~6.26%;对PO43-滞留率变化范围分别为7.82%~12.94%、0.06%~0.35%和0.18%~0.57%,相对贡献水平分别为92.36%~97.09%、0.69%~2.60%和2.22%~4.88%.案例分析结果验证了营养螺旋指标拓展及其内在关系度量对精细刻画排水沟渠营养盐滞留机制的适用性和有效性.

In-stream nutrient retention is an important ecological function of aquatic ecosystems,yet the underlying mechanisms are still unclear in streams and ditches.In this study,the traditional concept of nutrient spiraling metrics were extended with three parts,including hydrological process,biotic uptake and physicochemical adsorption,and a novel model was introduced to quantitatively describe the internal relationship between such metrics.On this basis,we used the OTIS(one-dimensional transport with inflow and storage)model and numerical simulation method to quantitatively calculate the nutrient retention contribution rate and relative contribution level of all three metrics to investigate the nutrient retention mechanism in drainage ditches.Results of a case study showed that the hydrological process was the dominant metric in both NH_(4)^(+)and PO_(4)^(3-)retention in a drainage ditch,while the contributions of biotic uptake and physicochemical adsorption were inappreciable.The contribution rates to NH_(4)^(+)of hydrological process,biotic uptake and physicochemical adsorption were 7.91%~13.07%,0.09%~0.27%and 0.31%~0.58%,respectively,and the relative contribution levels varied 91.75%~95.29%,1.07%~2.00%and 3.64%~6.26%,respectively.For PO43-retention,the contribution rates were 7.82%~12.94%,0.06%~0.35%and 0.18%~0.57%,respectively,and the relative contribution levels were 92.36%~97.09%,0.69%~2.60%and 2.22%~4.88%,respectively.The results verified that the extended nutrient spiraling metrics and the measurement of their internal relationship were applicable and effective to finely described the nutrient retention mechanism in drainage ditches.