wise use of mires and peatlands - Peatland Ecology Research Group

82 VALUES AND FUCTIONS OF MIRES AND PEATLANDSfast aerobic decay. Under these conditions,carbon and nutrients are not longeraccumulating, but are released from the peat.Mires and peatlands have diverse effects onthe chemical composition of the water in acatchment depending on their position withinthe catchment, the wetland water balance, thewater source, and the related biological,chemical and physical processes 203 . Miresreceive water of different quality fromdifferent sources. Water pathways includerainwater, surface run-off, lower groundwater,deeper groundwater, or river water inflow dueto over-flooding.Bogs by definition derive their water only fromprecipitation. Bog mires act as sinks forcarbon and nutrients by accumulatingcarbon, nitrogen and other nutrients in theirpeats. The water flowing out of bogs ischaracterised by low pH and highconcentrations of humic substances andammonia 204 . Bogs therefore act as localsources for carbon and nitrogen in acatchment. The concentrations of humicsubstances, nitrogen and phosphorus in therun-off water can rapidly increase after bogdrainage depending on land use practice, e.g.fertilisation, chalking, agriculture, forestry.Groundwater-fed fens like spring mires orpercolation mires have a high potential forthe transformation of inflowing substancestransported with the groundwater. At theinterface between mineral substrate and peatdenitrification leads to a decrease in the nitrateconcentration of the inflowinggroundwater 205 . Additionally, the inflowingnutrients are partly stored through peataccumulation. Groundwater fed fens are ableto improve the water quality in a catchment.Drainage and agricultural intensification bothin the fen and in the catchment affect thisfunctioning. Due to increased nutrientconcentrations in the groundwater followingfertiliser application in the catchment, thetransformation potential can be over-used,resulting in an increased nutrient availabilityin the fen and decreased biodiversity.Drainage activities change the waterpathways and therefore the mixing of differentwater sources. As a result, groundwaterinfluence decreases and rainwater influenceincrease which affects the vegetationcomposition in the fen.In flood mires and many terrestrialisation 206mires, freshwater inflow is the main watersource. These mire types foster processeswhich reduce chemical concentrations, suchas denitrification, sedimentation or plantuptake. These wetlands act as sinks fornutrients in the catchment when theoutflowing load has decreased compared tothe inflowing load 207 . In the nitrogen cycle,denitrification is quantitatively the mostimportant transformation pathway. Theefficiency of such fen types in removingchemicals is related to the hydraulic retentiontime (the length of time the water is retainedin the mire) and the inflowing water quality.High ammonia or N orgconcentration will notbe reduced significantly in small wetlands withlow detention time. In some wetlands theinflowing nitrate, which is removed bydenitrification, is replaced in the outflow bymobilised ammonia concentration. The netquantification of nitrogen and phosphorusretention in wetlands is therefore still acomplex task. In addition to assessing theinflow and outflow concentrations ofchemical substances it requires anexperimental approach for the quantificationof internal nutrient transformation rates 208 .Mires and peatlands have diverse effects onthe hydrochemistry of a catchment. Miresreceive water of different quality fromdifferent sources, including rainwater, surfacerun-off, lower groundwater, deepergroundwater, or river water inflow due to overflooding.Specific regulation functions ofcertain mire types include:● Bog mires which derive their water onlyfrom precipitation act as sinks for carbon