The fluid definition of the ‘waters of the United States’: Non‐uniform effects of regulation on US wetland protections

Abstract

Recent revisions to the definition of the ‘waters of the United States’ (WOTUS) have considerably altered how wetlands are federally regulated under the Clean Water Act. The two most recent modifications to WOTUS, the Clean Water Rule (CWR) and the Navigable Waters Protection Rule (NWPR), represent two opposing approaches to the federal wetland policy. The impacts of these two rules on the regulation of wetlands have as of yet been poorly characterized at broad spatial scales. Using New York State (NYS) as a case study, we evaluated the jurisdictional statuses of more than 253 000 wetlands under the CWR and the NWPR to assess the landscape‐scale effects of WOTUS re‐definitions. We found that statewide and within each of NYS's hydrologic regions, the NWPR protects fewer wetlands and less total wetland area than the CWR. The efficacy of the two regulations varied considerably in space across NYS, highlighting the need for comprehensive, nationwide assessments of wetland policy outcomes. We also observed that both rules produced non‐uniform patterns in jurisdiction across a range of landscape positions and wetland sizes, preferentially protecting large wetlands close to the stream network. This effect was particularly pronounced under the NWPR, which excludes all geographically isolated wetlands from protection. Our findings in NYS emphasize the existence of unique patterns in protected wetlands across spatial scales, highlighting the value in applying geospatial analyses to evaluate environmental policy.

Patterns of Wetland Hydrologic Connectivity Across Coastal‐Plain Wetlandscapes

“…Likewise, slow subsurface hydrologic connectivity extends residence times that enabled further biogeochemical processing (Marton et al., 2015) including landscape nutrient retention (Cheng & Basu, 2017; Cheng et al., 2022). In short, the heterogeneity in connectivity within and between wetlandscapes documented here impacts a multitude of functions considered under the Clean Water Act (Creed et al., 2017; Lane et al., 2018; Sullivan et al., 2020; Wade et al., 2022; Ward et al., 2023). Given the evidence for both surface and shallow subsurface wetland connectivity, the collective impacts of wetlands across coastal plain wetlandscapes on the physical, chemical, and biological functions of downstream waters seems clear.…”

“…For example, variability of wetland surface connectivity is a factor influencing chloride accumulation (Thorslund et al., 2018), and a strong regulator of landscape nutrient retention (Cheng & Basu, 2017; Cheng et al., 2022). However, because surface connectivity between depressional wetlands and adjacent water bodies is not persistent, these “geographically isolated wetlands” have been assumed to lack meaningful contributions to the hydrological and biogeochemical functions of downstream “waters of the United States”, with crucial implications for shifting U.S. Federal protections under the Clean Water Act (Creed et al., 2017; Sullivan et al., 2020; Wade et al., 2022; Ward et al., 2023). While the presence or duration of surface connectivity is not, nor should not be, the sole criterion for defining a “significant nexus,” it is clear that understanding the spatial and temporal patterns of wetland connectivity along both surface and subsurface flowpaths is relevant across scientific and regulatory discussions (Leibowitz et al., 2008).…”

Changes in water age during dry-down of a non-perennial stream

“…Repeated disagreement over how to define "significant connections" persists (Alexander, 2015), as seen in policy that extends protections to adjacent waters on a case-by-case basis if they have a "significant nexus" (Clean Water Rule, 2015) or if they contribute continuous flow to downstream perennial waters (Navigable Waters Protection Rule, 2020). Both of these rules have since been repealed or vacated, with US federal protections returning to those codified by the US EPA andACE in 1986 (US DOD, 1986;Wade et al 2022). These policy changes and debate suggest an urgent need to quantify the influence of non-perennial streams on both local and downstream water quantity and quality (Koundouri et al, 2017;Stubbington et al, 2020).…”