RETENTION OF SEDIMENT AND OTHER PARTICULATES


Many wetlands owe their existence to being located in areas of sediment deposition. This is especially true for floodplain and estuarine wetlands. This function supports water quality maintenance by capturing sediments with bonded nutrients or heavy metals as in and downstream of urban areas (e.g., Gambrell 1994). Estuarine and floodplain wetlands plus lotic (streamside) and lentic (lakeshore) fringe and basin wetlands including lotic (in-stream) ponds are likely to trap and retain sediments and particulates at significant levels. Terrene throughflow basins should function similarly. Vegetated wetlands will likely favor sedimentation over nonvegetated wetlands and therefore they received a high rating versus moderate for the nonvegetated types. Lotic flat wetlands are flooded only for brief periods and less frequently than the wetlands listed above due to their elevation; they are classified as having moderate potential for sediment retention. Throughflow (in-stream) ponds and associated fringe and basin vegetated wetlands are rated as high, since they occur within the stream network where they trap water-borne sediments. Stormwater treatment ponds are designed specifically to perform this function, so they are rated as high. Other ponds and terrene basins may be locally significant in retaining such materials, and are therefore designated as moderate. However, commercial, industrial, residential, sewage treatment, golf, and mining ponds were not rated as significant since many are isolated diked impoundments. Terrene flats are not rated as potentially significant because they are level landscapes that do not appear to trap substantial amounts of sediment from surrounding areas.


For this function, the following relationships are used:

High

Estuarine vegetated (not floating mats), Lentic vegetated (not Flat and not floating mats), Lotic vegetated (not Flat, not Floodplain-flat, and not floating mats), Throughflow Ponds and Lakes (in- stream; designated as PUB... on NWI) and associated vegetated wetlands, Bidirectional-tidal Ponds and associated vegetated wetlands, Terrene Throughflow Basin, Stormwater Treatment Ponds






Moderate

Estuarine nonvegetated (excluding rocky shore), Lotic nonvegetated, Lotic Flat, Lotic Floodplain-flat, Lentic Flat, Marine Fringe (excluding rocky shore), Marine Island (excluding rocky shore), Other Terrene Basins, Terrene wetlands associated with ponds (excluding some types of ponds - commercial, industrial, sewage treatment, and mining), Other Ponds and Lakes (classified as PUB... on NWI) and associated wetlands (excluding some types of ponds – commercial, industrial, sewage treatment, and mining and slope wetlands)



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