珠江口三维水质与底泥耦合模型的验证及应用

基于一维河网与三维河口耦合水动力模型,建立了可描述珠江口水体-底泥中营养盐动态变化的三维水质-底泥模型,利用1999年和2006年夏季观测数据对模型进行了验证,在此基础上,模拟分析了珠江口主要水质因子和底泥营养盐通量的分布特征,以及底泥通量对珠江口营养盐输入的贡献.验证结果表明,模型能较好地反映出水体和底泥中的营养盐及溶解氧浓度的时空分布特征,各水质因子的模拟值与观测值的相对误差均小于38%;另外,底泥营养盐通量的模拟值与文献报道的实测结果较为接近,表明模型能合理地刻画出底泥主要生化过程及通量变化特征.模拟结果显示,夏季珠江口氨氮(NH_4~+-N)和活性磷酸盐(PO_4~(3-)-P)通量主要从底泥向水体输送,底泥是水体氮磷元素的源,而硝态氮和亚硝态氮(NO_3~-+NO_2~-,NO23)的通量输送方向则与之相反,底泥呈现“汇”的效应;底泥营养盐通量主要从河口向外海递减,伶仃洋NH_4~+-N、NO23、PO_4~(3-)-P的通量变化范围分别为0.24~8.88、-10.06~-0.14、-0.37~0.41 mmol·m~(-2)·d~(-1),珠江口近海的通量变化范围分别为-0.01~4.14、-1.45~0.68、-0.12~0.09 mmol·m~(-2)·d~(-1).整体而言,底泥营养盐通量对珠江口营养盐输入有明显贡献,夏季经底泥释放进入水体的NH_4~+-N和PO_4~(3-)-P最大相当于陆源总氮、总磷输入量的12%和22%.

Validation and application of a three-dimensional coupled water quality and sediment model of the Pearl River Estuary

We developed a 3D water quality-sediment model, which depicts the dynamic changes of nutrients in water column and sediments of the Pearl River Estuary (PRE), based on a coupled 1D-3D hydrodynamic model. The proposed model was validated using observations collected during summer in years 1999 and 2006 and then it was applied to simulate the distribution of water quality and sediment nutrient fluxes in the PRE and to quantify the contribution of sediment fluxes to nutrient inputs. Validation results show that our model simulates the spatio-temporal distributions of nutrients and dissolved oxygen concentrations successfully both in water column and sediments, with relative model/data errors less than 38%. In addition, the simulated sediment nutrient fluxes match the observed ones reported in published literatures, suggesting that our model reasonably reproduces the key sediment biochemical processes and flux characteristics. Our model results indicate that NH₄⁺-N and PO₄^3--P fluxes are mainly directed from sediments to water column during summer in the PRE, which means that sediments are the source of nitrogen and phosphorous to water column. With respect to NO₂^--N+NO₃^--N (NO23), it is transported from water column to sediments, which act as the sink of NO23. The sediment nutrient fluxes mainly decrease from the inner estuary towards offshore; the fluxes are estimated 0.24~8.88,-10.06~-0.14, and-0.37~0.41 mmol·m^-2·d^-1 at Lingdingyang for NH₄⁺-N, NO23, and PO₄^3--P, respectively, and estimated-0.01~4.14,-1.45~0.68,-0.12~0.09 mmol·m^-2·d^-1 at the coastal sea, respectively. In general, the sediment fluxes have notable contributions to nutrient inputs in the PRE and the sediment fluxes of NH₄⁺-N and PO₄^3--P during summer can reach as high as 12% and 22% of terrestrial TN and TP inputs, respectively.