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Guide
to National Wetlands Inventory Types and Functions |
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We have recently established the Montana Wetland and Riparian Mapping Center that will use the National Wetland Inventory (NWI) classification system to map wetlands. However, while NWI maps will increasingly become available, there was no detailed information available on NWI type vegetation, management, and ecological functions. We examined wetlands in the Gallatin Valley and reference literature to link the common NWI types to National Vegetation Classification System types, other vegetation types (Hansen et al. 1995), and Hydrogeomorphic (HGM) wetland functions. While the HGM approach is useful due to its focus on the functions of wetlands, there is no HGM mapping. Since NWI maps are available our goal is to associate HGM functions with NWI types to improve assessment and mitigation of wetlands in Montana. In the NWI classification, most Montana wetlands are in the Palustrine System which includes any wetlands not within a stream or river channel (Riverine System) or within bodies of water > 20 acres (Lacustrine System). There are nine Classes possible in the Palustrine System; four were common and sampled in the Gallatin Valley. One Riverine System was described. See a complete NWI legend here. |
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Palustrine System, Unconsolidated Bottom Class (PUB) and Aquatic Bed Class (PAB) Palustrine System Emergent Wetland Class (PEM) Palustrine System Scrub-Shrub Wetland Class (PSS) Palustrine System Forested Wetland Class (PFO) Riverine
System, Lower Perennial Unconsolidated Shore (R2US) |
The Hydrogeomorphic (HGM) Approach (Brinson 1993) was developed to evaluate impacts on wetland functioning as part of the permitting procedure required by Section 404 of the Clean Water Act. It is based on the three fundamental factors that create and maintain specific wetland functions: 1) landscape position, such as depression or riverine; 2) water source and transport, such as precipitation or groundwater; and 3) hydrodynamics, such as the unidirectional flow of a sloping drainway or the vertical flow in a depression. The HGM method recognizes that different types of wetlands perform different functions, and that some wetlands perform certain functions better than others. For example, a depression wetland high in a watershed will better perform the function of water storage than a floodplain wetland. |
| Montana State Library, 1515 East Sixth Ave., Helena, MT 59620-1800 • 406-444-5354• fax 406-444-0581 • email: mtnhp@mt.gov | |||
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