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Cowardin Water Regime Modifiers The purpose of water regime modifiers is to provide a better description of the variations in hydrology that occur in wetlands on a seasonal and annual basis. These descriptions are general in nature because wetland hydrology is extraordinarily dynamic. Hydrology is the most variable component of wetlands and can vary substantially within a single basin weekly, monthly, seasonally, annually and over decades. Extraordinarily wet or dry periods, whether short or prolonged, do have dramatic effects on the presence or absence of water in any given wetland. Whether a wetland has naturally occurring hydrology or whether it is partially or completely drained affects its behavior as a component of the landscape, its appearance, the vegetation that inhabits it, and the effectiveness of the functions that it performs. Wetlands may also have artificially induced hydrology due to stormwater inputs or interconnections to other wetlands via ditch or tile drain systems. Careful consideration of each wetland within the overall context of the landscape is necessary to understand which water regime best fits along with the special modifiers that describe alterations to wetlands. � One special modifier class that is missing is the "stormwater pond" category. This is a commonly occurring condition in urban landscapes and should be added. Stormwater ponds may have been specifically constructed for that purpose or, in the past, previously existing wetlands were used to treat stormwater and now function as stormwater ponds rather than "natural" wetlands. Descriptions of the modifiers are taken from Cowardin et al (1979, pgs 21 — 22) and from Santos and Gauster(1993, pgs 30— 32). Descriptions within the parentheses are terms used on the NWI key and the longer description is the one used by Cowardin et al. (1979). Where a parenthetical term is excluded, the two terms are the same. Modifier "A" Temporarily Flooded (Temporarv) Surface water is present for brief periods during the growing season but the water table usually is well below the soil surface for most of the season. Temporarily flooded wetlands usually have plants that are characteristic of both uplands and wetlands. This modifier description is most appropriately assigned to Type 1 and 1 L wetlands but clearly does not fit the Type 7 Hardwood Swamp wetland type. Table 4 (Cowardin et al 1979, pg 28) is inconsistent by including this regime in the Type 7 category. Modifier "B" S aturated Soil saturation occurs to the surface for extended periods during the growing season but surface water is seldom present or evident. Many sedge and rush wetlands fit into this category. This modifier also aptly fits the water regime that occurs in the hardwood swamps that are present in parts of Minnesota in hardwood swamps such as black ash swamps and in coniferous swamps such as white cedar, tamarack, and black spruce swamps. This modifier also describes Type 2 wetlands as described above and includes fens and sedge/rush dominated wetlands.