When is Aquatic Resource Type Conversion Appropriate: A Framework for Cleaning Sand out of the Gears and a Case Study for McInnis Marsh

Abstract

Wetland and stream restoration projects may sometimes involve converting one “type” of aquatic habitat to another “type” (e.g., managed salt ponds into tidal marshes, depressional wetlands into streams, marsh into transition zone habitat). This “type conversion” may be necessary and beneficial in the context of addressing watershed plans or regional restoration goals, or in achieving resiliency to climatic changes (Goals Project 2015). Conversion can also occur through other large-scale, complex actions (e.g., mitigation banking initiatives). Whether driven by habitat restoration goals or compensatory mitigation needs or both, regulatory oversight typically governs the process. Holistically assessing such conversion through the regulatory lens is challenging for permitting programs. The challenge stems from how to accurately determine the overall value of an aquatic resource based on site-specific ecological properties and in the context of larger regional ecosystem management and goals. This is further compounded when assessing aquatic habitats that provide intrinsically different functions and services. Assessments must also account for the fact that wetlands and streams are not static ecosystems, but rather dynamically changing through time due to natural and anthropogenic factors, many of which are difficult to control or even accurately assess (e.g., sea level rise). These challenges are further exacerbated due to urbanization, conflicting human-environment goals, and the evolving state of habitat restoration science. Type conversion (i.e., replacing one aquatic type with a different aquatic habitat type) is recognized by agencies as a “sand in the gears” problem that can stymie planning and permitting because such actions typically require multiple agency authorizations (which may or may not be consistent with internal policies), habitat resource trade-offs, and consensus on ecosystem goals. The lack of consistent, defensible analysis based on transparent evaluation has been shown to impede critically needed habitat restoration (Bourgeois 2018; SFBRA 2022). To address this challenge, an interagency team of federal and state regulators and resource managers in California developed a structured and transparent approach for evaluating the appropriateness of aquatic resource type conversion. The resulting framework can support project planning and inform regulatory evaluation by helping to answer: 1) what loss or gain of function is expected from various aquatic resource type conversions, and 2) whether conversion might be ecologically (or functionally) appropriate. The framework is not intended to inherently value one type of aquatic resource over another, nor to supersede regulatory mandates. Rather, the intent is to support agencies’ technical and regulatory decisions by providing a standardized, transparent set of tools and approaches that can inform discussions between agencies and with project proponents during the project evaluation phase, with a goal of ensuring that projects are not only permittable, but environmentally beneficial. The framework consists of three modules that can be done either sequentially or in parallel. Together they can be used to assess the feasibility/suitability, functions, and regional context of a proposed type conversion project (Figure 1).