Cumulative effects in a riverscape across scales: thresholds of disturbance in ecosystem integrity

生态系统正逐渐因发展（城市化、农业、林业等）而丧失。对于为下游提供水、营养和物质以维持栖息地、供水和生态系统服务的小支流来说，栖息地的丧失尤为明显。虽然我们知道，在许多河流网络中，支流会逐渐改变，但我们还无法预测下游对水质、生物多样性和生态系统服务的影响。我们对这些损失如何影响对水源物种本身至关重要的栖息地保护知之甚少。保护自然环境的机构努力寻找保护河流生态系统的方法，包括保护上游和下游环境。由于多种压力源对大流的累积影响的评估存在许多问题，特别是包括非常大的尺度问题、稀释效应、滞后时间、非加性和非线性效应。对于水源专家来说，累积效应也发生在整个景观的栖息地丧失规模上。源头流提供了一个很好的起点，可以将经验和模型研究结合起来，了解累积效应的影响，以及如何最好地预测和测量源头流损失对下游条件的贡献。我们的建议包括四个目标。1. 利用两个独特的数据集和额外收集的数据，我们将研究黄河上游和较大河流的群落结构的时空格局

Ecosystems are being lost incrementally to development (urbanisation, agriculture, forestry, etc.) across the landscape. Habitat loss is especially obvious for the small tributary streams that provide the water, nutrients and materials to sustain habitats, water supply and ecosystem services downstream. Although we know that tributaries are cumulatively altered in many stream networks, we are not yet able to predict downstream consequences on water quality, biodiversity, and ecosystem services. And we know very little about how such losses impact conservation of habitats critical to headwater species themselves. Agencies that protect our natural environments struggle with ways to conserve stream ecosystems, both in the headwaters and to protect downstream environments. Assessment of cumulative effects from multiple stressors on large streams is problematic for many reasons, but especially including the very large scaling issues, dilution effects, lag times, and non-additive and non-linear effects. Cumulative effects also occur at the scale of habitat loss across a landscape for headwater specialists. Headwater streams provide an excellent place to begin to combine empirical and modelling studies to understand the impacts of cumulative effects and how best to predict and measure the contribution of losses of headwater streams to downstream conditions. Our proposal includes four objectives. 1. Using two unique datasets, and additional data to be collected, we will study the spatial and temporal patterns of the community structure of headwaters and larger streams in nested catchment designs. This will also use landscape context, e.g., the degree of alteration of neighbouring headwaters, as an environmental gradient affecting persistence of local headwater communities. We will also add measures of select ecosystem functions to the field studies. 2. We will use detailed, process-based models to generate predictions of how changes might scale across catchment sizes as one progresses downstream. 3. We will use data to test the model predictions downstream at nested scales through fluvial networks. 4. We will develop GIS-based decision tools to assist evaluation of risks associated with the loss of headwater streams.