Disconnected: integrating spatial complexity in multiple stressor research

人类活动大大增加了对生态系统施加压力的压力源的多样性和传播性。不同生态系统中的许多研究表明，应激源经常在其对生物体的影响方面共存并相互作用。然而，大多数研究是在局部尺度上进行的，将局部斑块从其空间背景中分离出来，这可能会影响生态结果。实际上，生态系统是通过交换景观矩阵中的资源和个体而连接在一起的，这一点对河流网络尤其适用。在河流生态系统中，应激源通常发生在当地(如废水输入、田间或城市径流)，并影响该河段的生物群落，包括当地食物网中的生物量分布。这最终改变了无机或有机物质的数量和质量，这些物质将流动并补贴河网的下游部分。因此，局部应激源可以直接(即应激源向下游输送)和间接(即通过向下游输送的资源和生物体的数量和质量的变化)在下游位置触发连锁效应。到目前为止，想必是出于实际原因，大多数多应激源的研究都集中在压力源引入的地方的影响。据我们所知，只有少数与应激源相关的研究考虑了河网结构，这些研究主要是基于模拟或小规模的微观世界。当谈到解开多个应激源的影响时，操纵性中观研究在通过受控和重复的实验单位分离应激源效应方面具有明显的优势，同时提供了高度的环境现实主义。在这个项目中，我们将遵循中观方法，但我们将创建连接的水槽的简化空间网络，而不是使用孤立的实验单元。然后，我们将操纵两个不同压力源的空间传播，一个是直接输送到下游的化学压力源，另一个是不直接输送的非化学压力源，即夜间的光污染。我们将结合传统技术和分子方法进行完全析因设计，以考察压力源对无脊椎动物和藻类群落和食物网络结构的影响。然后，我们将通过记录漂移来测量上游和下游之间的个体交换，并通过析因实验推断应激源对下游斑块的空间效应。最后，我们将通过对能量通量和化学计量生态位的分析，评估应激源和河网结构如何影响营养水平之间的资源同化。我们预计，上游地区应激源的空间扩散将增加下游社区的影响规模，从而阻止任何救援效果。

Human activities have strongly increased the diversity and spread of stressors that exert pressure on ecosystems. Many studies in different ecosystems have shown that stressors often co-occur and interact with each other regarding their impact on organisms. However, most studies were conducted at local scale, decoupling local patches from their spatial context, which can influence the ecological outcomes. Indeed, ecosystems are connected through the exchange of resources and individuals in the landscape matrix, which holds in particular for the riverine network. In river ecosystems, stressors often occur locally (e.g. wastewater input, field or urban runoff) and affect the biotic community in this reach including the biomass distribution in the local food web. This ultimately changes the quantity and quality of the inorganic or organic material that will flow and subsidize downstream sections in the river network. Hence, local stressors can, directly (i.e. stressor is transported downstream) and indirectly (i.e. through changes of quantity and quality of resources and organisms transported downstream), trigger cascading effects in downstream locations. So far, presumably for practical reasons, most of the multiple stressor research has focused on the effects of stressors at the place of their introduction. To our knowledge only a few stressor-related studies have considered the river network structure and these have mainly been based on simulations or small scale microcosms. When it comes to untangling the effect of multiple stressors, manipulative mesocosm studies have a clear advantage to isolate stressor effects through controlled and replicated experimental units while providing high environmental realism. In this project, we will follow a mesocosm approach but, instead of employing isolated experimental units, we will create simplified spatial networks of connected flumes. We will then manipulate the spatial spread of two different stressors, one chemical stressor that is transported directly to downstream reaches and one non-chemical stressor, i.e. light pollution at night, that is not transported directly.We will combine traditional techniques with molecular methods in a full factorial design to examine effects of stressors on the invertebrate and algal communities and food web structure. We will then measure the exchange of individuals between upstream and downstream reaches by recording the drift and infer the spatial effect of the stressors on the downstream patches via a factorial experiment. Finally, we will evaluate how stressors and river network architecture influence the resource assimilation across trophic levels through an analysis of the energy fluxes and stoichiometric niches. We anticipate that the spatial spread of stressors in the upstream reaches will increase the effect size in downstream communities, preventing any rescue effect.