Forecasting the combined effects of urbanization and climate change on stream ecosystems: from impacts to management options

Abstract

Summary 1.Streams collect runoff, heat, and sediment from their watersheds, making them highly vulnerable to anthropogenic disturbances such as urbanization and climate change. Forecasting the effects of these disturbances using process-based models is critical to identifying the form and magnitude of likely impacts. Here, we integrate a new biotic model with four previously developed physical models (downscaled climate projections, stream hydrology, geomorphology, and water temperature) to predict how stream fish growth and reproduction will most probably respond to shifts in climate and urbanization over the next several decades. 2. The biotic submodel couples dynamics in fish populations and habitat suitability to predict fish assemblage composition, based on readily available biotic information (preferences for habitat, temperature, and food, and characteristics of spawning) and day-to-day variability in stream conditions. 3. We illustrate the model using Piedmont headwater streams in the Chesapeake Bay watershed of the USA, projecting ten scenarios: Baseline (low urbanization; no on-going construction; and present-day climate); one Urbanization scenario (higher impervious surface, lower forest cover, significant construction activity); four future climate change scenarios [Hadley CM3 and Parallel Climate Models under medium-high (A2) and medium-low (B2) emissions scenarios]; and the same four climate change scenarios plus Urbanization. 4. Urbanization alone depressed growth or reproduction of 8 of 39 species, while climate change alone depressed 22 to 29 species. Almost every recreationally important species (i.e. trouts, basses, sunfishes) and six of the ten currently most common species were predicted to be significantly stressed. The combined effect of climate change and urbanization on adult growth was sometimes large compared to the effect of either stressor alone. Thus, the model predicts considerable change in fish assemblage composition, including loss of diversity. 5. Synthesis and applications . The interaction of climate change and urban growth may entail significant reconfiguring of headwater streams, including a loss of ecosystem structure and services, which will be more costly than climate change alone. On local scales, stakeholders cannot control climate drivers but they can mitigate stream impacts via careful land use. Therefore, to conserve stream ecosystems, we recommend that proactive measures be taken to insure against species loss *Correspondence author. E-mail: kanelson@umd.edu Re-use of this article is permitted in accordance with the Creative Commons Deed, Attribution 2·5, which does not permit commercial exploitation. or severe population declines. Delays will inevitably exacerbate the impacts of both climate change and urbanization on headwater systems.

Australia's Murray - Darling Basin: freshwater ecosystem conservation options in an era of climate change

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“…In the literature on freshwater ecosystem services modelling, many studies have focused on fish populations: for example Boughton and Pike [52] studied the impacts of altered storm patterns on fish migration windows, Bouska, et al [53] studied the impact of environmental changes on fish species distributions, Downing, et al [54] focused on the effect of lake management on the stock of fish, Nelson, et al [55] studied the impact of sediments, water flows and temperature on fish assemblages, and van Poorten, et al [56] studied the effects of stocking management on the fish population. However, the fish dynamics depend mainly on the availability of food.…”

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