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扩散。在不同生态系统中的许多研究表明，压力往往同时发生，并相互作用，就其对生物体的影响。然而，大多数研究都是在局部尺度上进行的，使局部斑块与其空间背景脱钩，这可能会影响生态结果。事实上，生态系统是通过景观矩阵中的资源和个人的交换而相互联系的，这对河流网络尤其如此。在河流生态系统中，压力源往往发生在当地（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。这最终会改变流动并补贴河流网络下游部分的无机或有机材料的数量和质量。因此，当地压力源可以直接（即压力源向下游转移）和间接（即通过向下游转移的资源和生物的数量和质量的变化）在下游地区引发级联效应。到目前为止，可能是出于实际原因，大多数多重压力源的研究都集中在压力源引入的地方。据我们所知，只有少数压力相关的研究已经考虑了河流网络结构，这些主要是基于模拟或小规模的微观世界。当涉及到解开多个压力源的影响时，操纵性围隔研究具有明显的优势，可以通过受控和复制的实验单元来隔离压力源的影响，同时提供高度的环境现实主义。在这个项目中，我们将遵循一个中生态系统的方法，但不是采用孤立的实验单位，我们将创建简化的空间网络连接水槽。然后，我们将操纵两个不同的压力源的空间传播，一个是化学压力源，直接传输到下游河段和一个非化学压力源，即夜间光污染，这是不直接传输。我们将结合联合收割机传统技术与分子方法在一个完整的析因设计，以检查压力对无脊椎动物和藻类群落和食物网结构的影响。然后，我们将通过记录漂移来测量上游和下游河段之间的个体交换，并通过析因实验来推断压力源对下游斑块的空间效应。最后，我们将评估压力源和河流网络结构如何影响资源同化跨营养级通过分析的能量通量和化学计量生态位。我们预计，在上游河段的压力源的空间传播将增加在下游社区的效果大小，防止任何救援效果。

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.