References is a Moving Target in Sea-Level Controlled Wetlands

Abstract

Central to the restoration of wetlands is the concept of reference.Wetlands are grouped within a reference domain of the samehydrogeomorphic subclass and compared to reference standards of theleast impacted members of the subclass. Restoration decisions can bebased within this context. Sea-level controlled wetlands, including saltmarshes, provide a challenge to establishing reference standards becausethey progressively change in response to rising sea-level and associatedstressors. The natural progression of change is distinct from thatinduced by human activities. We review geomorphic classifications forsea-level controlled wetlands to identify a spatial scale appropriatefor restoration. This scale encompasses an ecosystem state change modelwhich accounts for the natural progression. We emphasize the importanceof more proximal causes of change than sea-level rise itself(e.g.,access to fresh and sea water, sediment, and space for transgression).Through examples from several marshes, we highlight the consequences ofmovement, note distinctions between low and high marshes, and describethe transition between them. These distinctions are made for hydrologyin an intertidal and nontidal portion of a marsh and for nitrogencycling in a northern and a southern marsh on the Atlantic coast of theUSA. Further, we describe the nature of one change in state as the turfof a high marsh becomes unstable, producing a hollow and hummock patternthat is expected to transform into low marsh. Recognition of theconsequences of movement to more explicit, hydrogeomorphology-basedreference systems helps place restoration in a perspective which willimprove both project design and probability of success.