Citation:

Cohen, M., I. Creed, L. Alexander, N. Basu, A. Calhoun, C. Craft, E. D'Amico, E. DeKeyser, L. Fowler, Heather E. Golden, J. Jawitz, P. Kalla, L. Kirkman, Charles R. Lane, M. Lane, Scott G. Leibowitz, D. Lewis, J. Marton, D. McLaughlin, D. Mushet, H. Raanan-Kiperwas, M. Rains, L. Smith, AND S. Walls. Do Geographically Isolated Wetlands Influence Landscape Functions? PROCEEDINGS OF THE NATIONAL ACADEMY OF SCIENCES. National Academy of Sciences, WASHINGTON, DC, 113(8):1978-1986, (2016).

Impact/Purpose:

Geographically isolated wetlands (GIWs), those surrounded by uplands, are an important wetland resource, constituting most of the wetlands in many North American landscapes. A recent EPA technical report supporting the new Waters of the US rule reviewed more than 1,200 peer-reviewed papers and concluded that additional research focused on the frequency, magnitude, timing, duration, and rate of change of fluxes from non-floodplain wetlands – including GIWs – to downgradient waters is needed. This manuscript begins to fill in these research gaps on GIWs. This paper synthesizes evidence for hydrological, biogeochemical and biological connectivity between GIWs and their surroundings, including downstream waters. Because the geography of GIWs is integral to understanding how landscape functions arise from the continuum of wetland connectivity, and because this information was unavailable in the literature, the paper also presents a novel analysis of the geometry and distributions of GIWs in archetypal wetland landscapes. This analysis reveals the relative contribution of GIWs to total wetland number, perimeter and area. The analysis and synthesis suggest that wetlands connect to traditional navigable waters along a continuum of connectivity, from permanent to transient, from fast to slow, and from principally surface to subsurface flow paths, and that these connections vary in time as well as space. It is equally clear that landscape functions arise from the cumulative effects of connections that vary in mode and strength. It follows that selectively eliminating some connective pathways and preferentially protecting others can have important long-term effects on these functions. In short, wetlands with weaker, slower or less obvious connections provide functions that other wetlands do not. As such, realizing the full complement and magnitude of landscape ecosystem services requires the entire distribution of connectivity. This manuscript is an extra product of SSWR 1.1B that emerged from a November 2013 “Isolated Wetlands Research Workshop” that was held at the Joseph W. Jones Ecological Research Center.

Description:

Landscape functions such as flow generation, nutrient and sediment retention, and biodiversity support depend on the exchange of solutes, particles, energy, and organisms between elements in hydrological and habitat networks. Wetlands are important network elements, providing hydrological, biogeochemical and biological functions that vary in time and space along a continuum of connectivity with nearby and downstream waters. Geographically isolated wetlands (GIWs), those surrounded by uplands, are an important wetland resource, constituting most of the wetlands in many North American landscapes. Because they are generally small, they also represent a disproportionately large fraction of total wetland perimeter, where hydrological, biogeochemical and biological functions can be significantly enhanced. While GIWs lack persistent surface water connections, geographic isolation does not imply the absence of connectivity to other waters. Indeed, while hydrological and biogeochemical connectivity to other waters may be episodic or slow (e.g., via groundwater) and biological connectivity may require overland dispersal, limited material or organism exchange is, in many cases, precisely what enables important, sometimes unique, wetland functions. Further, GIWs often exist within complexes of similarly situated waters, creating spatial heterogeneity in the timing and magnitude of network connectivity that is critical to cumulative landscape functions. However, legal protections for GIWs are weak, leading to preferential losses from many landscapes, and now unlikely in the United States unless a “significant nexus” with traditional downstream waters can be demonstrated. Here we argue that sustaining the portfolio of wetland services that enable important landscape functions requires conserving the entire continuum of wetland connectivity.

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