2.0 Methods
To date, few studies have investigated how the regulatory shift from the CWR to the NWPR has impacted US watersheds (Meyer & Robertson, 2019; Walsh & Ward, 2019; Walsh and Ward, In Review). We take NYS as a case study (Figure 1), providing an assessment in the northeastern US that spans multiple ecoregions and drains to multiple endpoints (including the Great Lakes, Susquehanna and Delaware River basins, and the Atlantic Ocean). The approach used in this study, following prior work of Walsh & Ward (2019, In Review) and Meyer & Robertson (2019), leverages several publicly available datasets to classify the jurisdictional status of wetlands in New York. We quantified the federal protections of more than 373,000 non-marine wetlands present in the US Fish and Wildlife Service’s National Wetland Inventory (NWI), covering over 876,000 ha across the state of New York (U.S. Fish and Wildlife Service, 2021). We excluded wetlands classified as estuarine or marine in NWI records. Wetlands smaller than 0.01 ha in size were also omitted from further analysis. We selected this threshold to minimize the inclusion of small wetland fragments adjacent to larger contiguous wetland polygons. We summarize wetland protection statuses state-wide and at a smaller regional scale (defined by USGS HUC–6 basins; Figure 1). Given that most investigations of wetland policy are performed at the watershed scale, our analysis allows for an evaluation of policy outcomes across a range of broader spatial scales.
As the jurisdictional status of wetlands primarily stems from their proximity to streams, the identification of the location of the stream network is a key task in the evaluation of WOTUS protections. Previous approaches (e.g., Walsh & Ward, 2019) used topographically-based flow accumulation methods to estimate the spatial extent of the stream network. We instead chose to define the stream network using the USGS National Hydrography Dataset (NHD; 1:24,000 scale, Model Version 2.2.1), as we could not ensure the reliability and accuracy of a topographically-generated network at the geographic scale of NYS (U.S. Geological Survey, 2020). While the NHD may underestimate stream network extent (Elmore et al., 2013), the NHD does provide a consistent and validated record of the location of streams within our study area and across most regions in the US (Meyer & Robertson, 2019). We used NHD waterways as the basis for the location of the stream network in both the CWR and NWPR scenarios. This may result in a conservative estimate of the jurisdictional stream network under the CWR as the version of the NHD used here only maps perennial and intermittent streams in NYS (U.S. Geological Survey, 2020). Thus, we assume the NHD network is representative of the network with flow during a typical year for the NWPR scenario and serves as a conservative lower bound for the stream network in the CWR scenario.
To define the protection status of each wetland within NYS, we translated the regulatory procedures of the CWR and NWPR into a set of geospatial analysis steps within ArcGIS Pro (Version 2.6.0). Using this process, we classified each NWI wetland as jurisdictional, non-jurisdictional, or requiring the application of the significant nexus test (abbreviated as ‘significant nexus’) for each regulation based on the spatial relationships of each wetland to the stream network. Under the CWR, wetlands located (1) within 100 ft (30.5 m) of a jurisdictional water, (2) within both 1500 ft (457.2 m) of a jurisdictional water and the 100-year floodplain, or (3) within 1500 ft (457.2 m) of a traditionally navigable waterway are considered jurisdictional by rule. As US wetland regulations are based around imperial system units, we report these values first, followed by SI units in parentheses. We applied a spatially continuous floodplain map (Woznicki et al., 2019) to estimate the location of the 100-year floodplain in our study area, as the commonly used Federal Emergency Management Agency (FEMA) floodplain dataset was incomplete across NYS. To identify the extent of traditionally navigable waterways, we used publicly available streamflow information and channel geometry from the USGS to create discharge-depth regression relationships across New York State. We defined ‘traditionally navigable’ waterways as those receiving at least a median of 0.30 m of inundation per year (following Walsh and Ward, 2019). All wetlands that do not satisfy the aforementioned jurisdictional criteria but are located within 4000 ft (1219.2 m) of another jurisdictional water are subject to the significant nexus test under the CWR. Given the challenge in applying the case-by-case significant nexus test to broad spatial scales, we were unable to determine the precise extent of jurisdictional wetlands when evaluating the CWR. Instead, depending on the results of site-specific significant nexus determinations made by the USEPA and USACE, the percentage of jurisdictional wetlands under the CWR may vary considerably. Wetlands located further than 4000 ft (1219.2 m) away from a jurisdictional water are considered non-jurisdictional by rule and are afforded no protection by the CWR. While not directly assessed in this study, the CWR also considers the impacts of ‘similarly situated waters’, effectively assessing aggregate impacts from several wetlands.
In contrast to the buffering approach used by the CWR, the NWPR defines protections based on a surface-water connection between wetlands and the jurisdictional stream network. The rule eliminates the significant nexus test, instead classifying wetlands as either jurisdictional or non-jurisdictional. For the NWPR scenario, wetlands were considered jurisdictional only if they directly intersected the jurisdictional stream network, simulating a surface-water connection. While we acknowledge that this intersection approach does not necessarily guarantee federal jurisdiction based on the NWPR, as we cannot confirm a continuous surface connection at the scale of this analysis, we take this as a reasonable estimate for protection.