Modeled sensitivity of Lake Michigan productivity and zooplankton to changing nutrient concentrations and quagga mussels
Modeled sensitivity of Lake Michigan productivity and zooplankton to changing nutrient concentrations and quagga mussels
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模拟密歇根湖生产力和浮游动物对营养物浓度和斑驴贻贝变化的敏感性
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发表时间：
2017
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通讯作者：
E. Reavie
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作者：
D. Pilcher;G. McKinley;J. Kralj;H. Bootsma;E. Reavie
最近密歇根湖生产力的下降通常归因于入侵斑驴贻贝的过滤器喂养，但一些研究也暗示了全湖营养物质浓度的减少。我们使用一个3-D耦合水动力-地球化学模型来评估改变营养盐浓度和斑鳖贻贝过滤对浮游植物生产和浮游植物和浮游动物生物量的影响。敏感性实验用于单独和一致地评估每种变化的净效应。斑驴贻贝被发现有最大的影响，在等温混合期间，而营养物质有最大的影响，在热分层。斑驴贻贝还可以增强空间异质性，特别是在近岸-近海区域之间。这种效应导致近岸-近海生产力梯度的逆转：从prequagga湖相对较高的近岸生产力到quaggas之后相对较低的近岸生产力。这两个过程的综合影响导致浮游植物和浮游动物生物量大幅减少，并对地表水pCO 2的季节性产生重大影响，特别是在贻贝放牧全年持续的近岸地区。这些结果支持了人们日益关注的问题，即浮游植物和浮游动物的大量损失将导致较高营养水平的同时损失。观察到的生产力的比较表明，斑驴贻贝过滤和较低的全湖总磷是必要的，以准确地模拟最近在密歇根湖的初级生产力的变化。
The recent decline in Lake Michigan productivity is often attributed to filter feeding by invasive quagga mussels, but some studies also implicate reductions in lakewide nutrient concentrations. We use a 3‐D coupled hydrodynamic‐biogeochemical model to evaluate the effect of changing nutrient concentrations and quagga mussel filtering on phytoplankton production and phytoplankton and zooplankton biomass. Sensitivity experiments are used to assess the net effect of each change separately and in unison. Quagga mussels are found to have the greatest impact during periods of isothermal mixing, while nutrients have the greatest impact during thermal stratification. Quagga mussels also act to enhance spatial heterogeneity, particularly between nearshore‐offshore regions. This effect produces a reversal in the gradient of nearshore‐offshore productivity: from relatively greater nearshore productivity in the prequagga lake to relatively lesser nearshore productivity after quaggas. The combined impact of both processes drives substantial reductions in phytoplankton and zooplankton biomass, as well as significant modifications to the seasonality of surface water pCO2, particularly in nearshore regions where mussel grazing continues year‐round. These results support growing concern that considerable losses of phytoplankton and zooplankton will yield concurrent losses at higher trophic levels. Comparisons to observed productivity suggest that both quagga mussel filtration and lower lakewide total phosphorus are necessary to accurately simulate recent changes in primary productivity in Lake Michigan.