The U.S. Fish and Wildlife Service is the principal Federal agency that provides information to the public on the extent and status of the Nation's wetlands. Through the National Wetlands Inventory, the agency has developed a dataset featuring wetlands and deepwater habitats. These data have been used extensively to make resource management decisions at the federal, state and local government levels.
The goal of the National Wetlands Inventory is to provide the citizens of the United States and its Trust Territories with current geospatially referenced information on the status, extent, characteristics and functions of wetland, riparian, deepwater and related aquatic habitats in priority areas to promote the understanding and conservation of these resources.
The wetland geospatial data layer provides on-line information for all of the conterminous U.S., Hawaii, Puerto Rico, the Virgin Islands, Guam, the major Northern Mariana Islands and over 35% of Alaska. This has been accomplished by working with numerous public and private cooperators. Currently, efforts are underway to complete, update and maintain the seamless digital wetlands data set for the Nation. This effort constitutes the Wetlands Data Layer of the National Spatial Data Infrastructure, and is a National Geospatial Data Asset as identified by The Federal Geographic Data Committee (FGDC).
As of May 2016 the NWI dataset has been updated to Version 2, a more comprehensive version which characterizes all surface water features on the landscape. It stems from the need to represent all surface waters and wetlands as polygons in a single geospatial dataset, which facilitates accurate area calculations and consistent standardized ecological classifications. These features allow the dataset to be used for adaptive management, geospatial summaries, and modeling.
The NWI Version 2 dataset was created by retaining the wetland and deepwater polygons that composed the original NWI digital wetlands spatial data layer and are classified according to the Cowardin et al. (1979) nomenclature that provides ecological descriptors of habitat types. These wetlands and deepwater features were supplemented by reintroducing any linear wetland or surface water features that were orphaned from the original NWI hard copy maps and converting them to narrow polygonal features. The NWI wetland classification is retained for these narrow features. Additionally, the data are supplemented with hydrography data as a secondary source for any single-line stream features not mapped by the NWI and to complete segmented connections. These features are assigned a Cowardin classification to conform to federal wetland classification standards and buffered to become polygonal features. A geoprocessing model addresses geospatial overlaps by incorporating a hierarchical clipping logic based on source data and wetland classification and also updates all existing NWI classifications to current standards. The resultant dataset is a more complete depiction of all surface waters and wetlands.
Due in part to how wetlands were mapped in the past, coupled with improved geospatial processing techniques, the NWI Version 2 dataset is a departure from the legacy NWI data in several ways. It depicts all surface water and wetland features in a single database; it applies the Cowardin et al. (1979) system to provide consistent ecological descriptors intended to address wetlands and water bodies.
The NWI Version 2 dataset provides a substantially more comprehensive inventory of wetland and associated water bodies. The difference between these two datasets has important implications for past wetland data summaries and modeling that has been generated using the legacy NWI map data.
The following webinar was presented at the 2016 Association of State Wetland Managers (ASWM) State/Tribal/Federal Coordination Meeting as part of a Wetland Mapping Consortium breakout session. This presentation provides a complete description of the NWI V2 dataset; what it is, why it was developed and how is was made. View the 30 min webinar here:
There are many opportunities to apply NWI Version 2 data to assist in resource management, planning, and strategic habitat conservation efforts. Applications include various geospatial analyses, tracing contaminant pathways through aquatic systems, identifying and prioritizing habitat restoration opportunities, examining continuity or dissection of habitat corridors, quantifying aquatic and wetland resource types, and facilitating ecological modeling. Modeling changes at the community level (e.g., species richness, diversity, cover, and biomass) are often linked to the hydrologic characteristics of wetlands or the surface water bodies adjacent to wetlands. Current hydrography that attempts to trace surface water flow is often incomplete or misleading because it lacks one or more of the landscape-level components that make up surface water features. The NWI Version 2 dataset provides more complete geospatial data on surface waters and wetlands than has been available in the past and will provide a more efficient means to make determinations of flow and water movement in surface water basins and channels, as well as in wetlands.