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Wetlands • Wetland – “those areas that are inundated or saturated by surface or groundwater at a frequency and duration sufficient to support, and that under normal circumstances do support, a prevalence of vegetation typically adapted for life in saturated soil conditions. Wetlands generally include swamps, marshes, bogs and similar areas.” --- EPA Clean Water Act enforcement definition
Wetlands • Emergent macrophytes (vegetation)effectively define wetlands. • Marsh = dominated by non-woody vegetation. • Swamp = dominated by trees. • Aquatic Marginal Wetlands = emergent macrophytes can grow around a body of surface water (lake, stream, ocean). – presence depends on substrate and water conditions (Can emergent macrophytes grow there?) -Fringe wetlands – almost always wet -Flood wetlands – seasonally or less frequently wet
Wetlands • Mires = where emergent macrophytes can grow BUT are not around an open body of water and are permanently waterlogged. –depend on groundwater and/or reliable runoff -Fens – “fed” by groundwater and runoff; nutrient rich -Bogs – “fed” runoff (above the water table); nutrient poor; mosses of the genus Sphagnum.
Wetland Conditions • Waterlogged soils less/low/no oxygen (decomposition uses + low diffusion) Usually low in Nitrate (N) because of effects of low oxygen on bacteria. If organically rich, anaerobic bacteria create hydrogen sulphide (H2S). • If flooded and dried or f ringing and subject to water motion conditions usually have more oxygen and nitrate in the soil.
Wetland Primary Production • Primary production in some tropical fringing marshes equals that in tropical rainforests. • Primary production in some polar fens and bogs is very low (equivalent to tundra). • Few organisms consume the emergent macrophytes directly (only some mammals), most energy in the system relies on detritus. • Many terrestrial and aquatic organisms depend upon wetlands as “visitors.”
Wetland Human “Benefits” • Riparian flood wetlands reduce flow variation and intensity of flood events. (Katrina & New Orleans) • Ocean flood wetlands (salt marshes) reduce the effects of storm surge. (Katrina & New Orleans) • Serve as areas of groundwater infiltration. (Florida aquifers) • Fringing and flood wetlands remove sediments and nutrients from water flowing through them.
Wetlands: Human Impacts • Development – Many drained and then built upon or used for agriculture. Some have been removed for mosquito control. • Water diversion – Many wetlands have been eliminated because their water sources have been diverted for other use. • Sediment starvation – some salt marshes off New Orleans lost due to reduced sedimentation after Mississippi alteration. • Peat/Sphagnum mining – Many mires damaged or removed.
