The two classification systems presented this week were the Hydrogeomorphic (HGM) wetland classification system (first introduced by Brinson in 1993) and the Cowardin Classification System (Cowardin et al., 1979; also deemed as the National Wetlands Classification Standard).HGM classification defines wetland classes and subclasses based on the components of geographic setting, water source, and hydrodynamics (Brinson, 1993). This system focuses on the evaluation of the functions of wetlands.
HGM classification depends on the landscape context, and not just morphological characteristics within the wetland. It emphasizes two abiotic controls, hydrology and geomorphology, in maintaining wetland functions, rather than using a system that is limited to biotic characteristics. Hydrology controls the amount, source, and season of the water entering the wetland, while geomorphology controls where the water comes from and if and/or how it leaves (Brinson, 1993). Using HGM classification can help to envision how a wetland functions.Cowardin Classification is hierarchical and places an emphasis on the physical characteristics of vegetation (Cowardin et al.
, 1979). In this system, wetlands are defined by hydrology, substrate, and non-specific structures of the dominant vegetation. Water regimes and man-made alterations are additional attributes used (Cowardin et al., 1979). This system classifies both wetland and deepwater habitats, which are often treated separately in other classifications. Using the Cowardin system can help to envision what a wetland looks like.HGM is used by the U.
S. Army Corps of Engineers and other agencies to assess wetland functions and classify jurisdictional wetlands (Brinson, 1993). It can assist in estimating the amount of wetland area and corresponding functions that are lost with development or interference activities, which can influence wetland mitigation strategies.
The Cowardin Classification System is used by the U.S. Fish and Wildlife Service for the National Wetlands Inventory program for wetland mapping. The Cowardin system can have some limitations for regulation and management, as it neglects some important factors, such as differences in morphometry and landscape position (Brooks et al., 2013). Wetlands might support similar habitat and be put into the same category per the Cowardin system, but each might function in a different manner (which can be separated using HGM classification). This can influence and limit the efforts for wetland restoration, wetland delineation, and assessments of wetland function. On the other hand, HGM classifications may be limited for scientific research, as they are not designed to be sensitive to species of vegetation (Adamus, 2001).
This may be concerning from the perspective of biodiversity and conservation of rare plant and animal communities. Classification using the Cowardin system can also be easier to utilize and possibly less costly. This classification system could be considered more straightforward because it is based on vegetation structure that is easily identified, often from aerial photography.
In addition, water regimes can often be inferred by knowledge of regional or local conditions. Classification using HGM can be more involved, and usually involves onsite inspection and data gathering along with knowledge of regional and local conditions (Brinson, 1993).No single classification, without being extremely complex and expensive, can address all needs. Both classification methods discussed have uses depending on the application, and an integration of HGM and Cowardin classification systems would be useful to characterize observed differences in structure and function, providing more information for scientific research and management. Works CitedAdamus