Assessing the relative vulnerabilities of Mid-Atlantic freshwater wetlands to projected hydrologic changes

Wetlands are known to provide a myriad of vital ecosystem functions and services, which may be under threat from a changing climate. However, climate change effects may not be homogenous across ecosystem functions, wetland types, or ecoregions. Therefore, it may not be appropriate to apply the same management techniques broadly across regions or wetland types. Here, we provide a relative vulnerability framework that can be used at multiple scales to assist in identifying potential management strategies. The framework uses the Vulnerability Scoping Diagram (VSD) approach, separating the concept of vulnerability into three components: exposure, sensitivity, and adaptive capacity. We identify relevant processes and measures of exposure and sensitivity as they pertain to the attributes of wetland extent and community composition, and populate them with data for three primary Hydrogeomorphic (HGM) wetland types (riverine, slope, and depression) in seven small watersheds across four ecoregions (Ridge & Valley, Piedmont, Unglaciated Plateau, and Glaciated Plateau) in the Susquehanna River watershed in Pennsylvania. We used data generated from the SRES A2 emissions experiment and MRI-CGCM2.3.2 climate model as input to the Pennsylvania Integrated Hydrologic Model (PHIM) to simulate future exposure to altered hydrologic condition in our seven watersheds, as expressed in two hydrologic metrics: % time groundwater levels occur in the upper 30 cm (rooting zone) during the growing season, and median difference between Spring and Summer mean water levels. We examined effects between different ecoregions, wetland types, and wetland type by ecoregion across the Mid-Atlantic. Overall, we found find that relative differences in exposure persisted at a very fine grain. For temporal scale, relative differences in exposure occurrsed at the scale of seasonal results, and were are not as strong in the annual ones; at a seasonal scale we found find a magnification of summer dry-down and winter wet periods becoming wetter. Exposure also shows significant relative differences at the following spatial grain sizes: between ecoregions; between HGM wetland types; for a single HGM type between ecoregions; and between watersheds within an ecoregion. These results indicate that building a national framework for wetland vulnerability will have to be built done from the bottom up, as ecoregion and wetland-type play a large role in response to climate change effects on hydrology. To aid others in developing their own wetland relative vulnerability assessments, we provide a universal generalized framework that other regions can use to construct “look-up tables” – containing documentation of responses of selected wetland attributes to hydrologic alterations from climate change – to support evaluation of relative vulnerabilities of wetlands functions and associated services. A comparison between historical changes in hydrology due to anthropogenic disturbance and anticipated hydrology under climate change indicates potential shifts in hydrologic patterns that are far beyond our management experience.

Impact/Purpose

Wetlands are a familiar and important feature of our environment, providing a portfolio of ecosystem services that are deemed critical for human health and well-being (Millennium Ecosystem Assessment 2005, Mitsch and Gosselink 2015). The name captures their defining and unifying characteristic—they are “wet,” described as transitional habitats between upland and aquatic habitats (Cowardin et al. 1979, Brinson 1993a, Burkett and Kusler 2000). Wetlands are aquatic ecosystems of national importance. They are one of the major natural ecosystems that provide services to people (e.g., see [de Groot et al. 2002, Zedler and Kercher 2005, Keddy et al. 2009], including biogeochemical cycling of CO2 [Bonneville et al. 2008, Langley et al. 2009], water storage and groundwater recharge [Acharya 2000, McCarthy 2006], and nutrient cycling [Zhao et al. 2004]). Managers seek to preserve these valued services through the protection and restoration of wetlands (Pitchford et al. 2012). From the perspective of the U.S. Environmental Protection Agency (EPA), wetlands are a key aquatic resource (among streams, rivers, and lakes) covered under Section 404 of the Clean Water Act (CWA), which attempts to ensure that wetland impacts are avoided or minimized, or, when unavoidable, compensated for. Impacts are not solely derived from activities directly inside the wetland boundary, such as dredging or filling; a number of studies have shown that anthropogenic activities in the surrounding landscape, such as agriculture, deforestation, and urban development, to name a few, have impacts on wetlands and the services they provide (Kentula et al. 2004, Brooks et al. 2006, Wardrop et al. 2007, Whigham et al. 2007), via changing hydrologic patterns, sedimentation, and nutrient enrichment (Wardrop and Brooks 1998, Mahaney et al. 2004, 2005).

Citation

Wardrop, D., A. Hamilton, M. Nassry, J. West, AND A. Britson. Assessing the relative vulnerabilities of Mid-Atlantic freshwater wetlands to projected hydrologic changes. ESA Journals, 10(2):e02561, (2019). [DOI: 10.1002/ecs2.2561]

DOI: Assessing the relative vulnerabilities of Mid-Atlantic freshwater wetlands to projected hydrologic changes