What Is a Wetland Functional Assessment?

Wetlands perform many ecological functions that have value to society. These functions (sometimes called ecological services) include groundwater recharge, storm water retention, stream bank stabilization, and fish and wildlife habitat. The USFWS’s (United States Fish and Wildlife Service) LLWW (Landform, Landscape, Waterbody, Water Flow Path) classification system is used to describe the physiographic context within which wetlands, as mapped by the NWI (National Wetland Inventory) and other systems, are located.

For example: 

A wetland located within a riverine floodplain may likely provide functions in stormwater retention, stream bank stabilization, and fish and wildlife habitat. According to LLWW, this wetland is located in a lotic (riverine) landscape position, has a basin (depressional) landform, and is in a through-flow area where surface water may flow for some time each year or during high water events. The LLWW and NWI systems, called NWIPlus when used together, provide land managers and other interested parties with an overview of wetland distribution and the types of wetland functions across large areas. Wetlands could also be "ranked" according to their potential to provide a given function, helping managers understand where wetlands are performing particular functions and at what level (moderate or high). This information may be useful for determining what current wetlands might be of high priority for preservation.

Douglas County, WI

Douglas County, found in Northwest Wisconsin, funded their Lake Superior Watershed Framework for Assessment of Wetland Services through a National Oceanic and Atmospheric Administration (NOAA) National Estuarine Research Reserve System Science Collaborative Grant. The county was concerned about area flooding, turbidity, and sedimentation problems, while the citizens were showing interest in wetland mitigation policy and management. NOAA and Douglas County enlisted GSS in August 2013 to provide the wetland data and GIS analysis products that can then inform local decisions regarding wetlands and surface water.

This includes mapping and describing present-day wetlands as well as identifying potentially restorable wetlands using GIS. The image here shows an aerial view of an agricultural field prior to restoration activities, with the following GIS layers: 1) modeled surface flow lines created from a 10m DEM using a 200 cell contributing area threshold (yellow/green to blue lines indicating increasing flow accumulation - flow direction is to the southwest); 2) Compound Topographic Index (CTI) raster (blue, purple, pink pixels or cells) (a catchment analysis of a 10m DEM) where blue is low, purple is moderate, and pink is a high CTI; and 3) SSURGO soil map units (polygons) with a Soils Water Regime Rank 2 (yellow-shaded polygons) (in this case, these are “somewhat poorly drained soils”).

Santa Fe National Forest, NM

In collaboration with Amigos Bravos, a statewide water conservation organization located in New Mexico, GSS utilized NWIPlus (NWI and LLWW) wetland data to identify and characterize important wetlands or wetland complexes (also known as Wetland Jewels) inside the Santa Fe National Forest. These Wetland Jewels provide several important ecological functions to the landscape inside the national forest and can ultimately be targeted for preservation, restoration, and/or enhancement.

Along with identifying the Wetland Jewels inside the Santa Fe National Forest, an Esri Story Map was developed to highlight these important wetlands and be used as an educational outreach tool for Amigos Bravos.

Kodiak

The United States Fish and Wildlife Service (USFWS) Region 7 NWI Program funded a pilot project with GSS to develop wetland spatial data for Kodiak National Wildlife Refuge at a finer scale than what is available through the traditional NWI. Additional wetland descriptive metrics (e.g., connectivity to perennial streams, location relative to natural barriers to fish migration) were correlated with each entry in the NWI database, so that each wetland is tagged with a list of functional attributes defining the ecological function a particular wetland is predicted to perform. This performance prediction is based upon each wetland's position in the landscape and some habitat characteristics. This also allows for a comparison of the importance of each wetland relative to other wetlands in the surrounding area. At Kodiak, one important function is the provision of habitat for salmon spawning, rearing, and migration. The data and information produced by this project will serve as a valuable source for resource planning within the National Wildlife Refuge and for stakeholders throughout the Kodiak Borough.