Jäger Christoph G, Borchardt Dietrich
Helmholtz Centre for Environmental Research - UFZ, Department of Aquatic Ecosystems Analysis and Management, Brückstraße 3a, 39114 Magdeburg, Germany.
J Theor Biol. 2018 Apr 7;442:66-78. doi: 10.1016/j.jtbi.2018.01.009. Epub 2018 Jan 11.
In riverine ecosystems primary production is principally possible in two habitats: in the benthic layer by sessile algae and in the surface water by planktonic algae being transported downstream. The relevance of these two habitats generally changes along the rivers' continuum. However, analyses of the interaction of algae in these two habitats and their controlling factors in riverine ecosystems are, so far, very rare. We use a simplified advection-diffusion model system combined with ecological process kinetics to analyse the interaction of benthic and planktonic algae and nutrients along idealised streams and rivers at regional to large scales. Because many of the underlying processes affecting algal dynamics are influenced by depth, we focus particularly on the impact of river depth on this interaction. At constant environmental conditions all state variables approach stable spatial equilibria along the river, independent of the boundary conditions at the upstream end. Because our model is very robust against changes of turbulent diffusion and stream velocity, these spatial equilibria can be analysed by a simplified ordinary differential equation (ode) version of our model. This model variant reveals that at shallower river depths, phytoplankton can exist only when it is subsidised by detaching benthic algae, and in turn, at deeper river depths, benthic algae can exist only in low biomasses which are subsidised by sinking planktonic algae. We generalise the spatial dynamics of the model system using different conditions at the upstream end of the model, which mimic various natural or anthropogenic factors (pristine source, dam, inflow of a waste water treatment plant, and dilution from e.g. a tributary) and analyse how these scenarios influence different aspects of the longitudinal spatial dynamics of the full spatial model: the relation of spatial equilibrium to spatial maximum, the distance to the spatial maximum, and the response length. Generally, our results imply that shallow systems recover within significantly shorter distances from spatially distinct disturbances when compared to deep systems, independent of the type of disturbance.
在河流生态系统中，初级生产主要在两种生境中进行：一是在底栖层由固着藻类进行，二是在地表水层由向下游输送的浮游藻类进行。这两种生境的相关性通常会随着河流的连续变化而改变。然而，到目前为止，对河流生态系统中这两种生境中藻类的相互作用及其控制因素的分析非常少见。我们使用一个简化的平流 - 扩散模型系统结合生态过程动力学，来分析区域到大规模理想化溪流和河流中底栖藻类与浮游藻类以及养分之间的相互作用。由于许多影响藻类动态的潜在过程受深度影响，我们特别关注河流深度对这种相互作用的影响。在恒定环境条件下，所有状态变量沿着河流趋近稳定的空间平衡，与上游端的边界条件无关。由于我们的模型对湍流扩散和水流速度的变化具有很强的鲁棒性，这些空间平衡可以通过我们模型的简化常微分方程（ode）版本进行分析。该模型变体表明，在较浅的河流深度下，浮游植物只有在由脱离的底栖藻类提供补贴时才能存在，反之，在较深的河流深度下，底栖藻类只能以低生物量存在，且由下沉的浮游藻类提供补贴。我们使用模型上游端的不同条件来概括模型系统的空间动态，这些条件模拟了各种自然或人为因素（原始源头、水坝、污水处理厂的流入以及例如支流的稀释），并分析这些情景如何影响完整空间模型纵向空间动态的不同方面：空间平衡与空间最大值的关系、到空间最大值的距离以及响应长度。一般来说，我们的结果表明，与深系统相比，浅系统在空间上不同的干扰后能在显著更短的距离内恢复，与干扰类型无关。
