The Wetland Book pp 1555-1562 | Cite as

USA Wetlands: NWI-Plus Classification System

  • Ralph W. Tiner
Reference work entry


The original classification system used to inventory and map US wetlands was based on the Cowardin system with its descriptors based on soil, vegetation, hydrology, and water chemistry. This system was extended with hydrogeomorphic descriptors (the LLWW descriptors: landscape position, landform, water flow path, and water body type) to enable functional assessment of wetlands. The resulting system, the NWI+ database, is used to classify wetlands according to both Cowardin and LLWW types and can predict function for the wetlands in a watershed. The 11 functions predicted routinely are surface water detention, coastal storm surge detention, streamflow maintenance, nutrient transformation, sediment and other particulate retention, carbon sequestration, bank and shoreline stabilization, provision of fish and aquatic invertebrate habitat, provision of waterfowl and waterbird habitat, provision of habitat for other wildlife, and provision of habitat for unique, uncommon, or highly diverse wetland plant communities. The LLWW descriptors can also help to predict the impact of change on wetland functions. Results of assessments are published in reports, and an online mapping tool is available.


Wetland classification Wetland descriptors NWI+ Hydrogeomorphic classification USA wetlands Wetland function 


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Copyright information

© Springer Science+Business Media B.V., part of Springer Nature 2018

Authors and Affiliations

  1. 1.U.S. Fish and Wildlife Service (retired)HadleyUSA
  2. 2.Institute for Wetlands and Environmental Education and Research, Inc. (IWEER)LeverettUSA

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