wise use of mires and peatlands - Peatland Ecology Research Group

VALUES AND FUCTIONS OF MIRES AND PEATLANDS81Only mire types of which the peat layer canshrink and swell with changing water supply(such as percolation mires and to a lesserextent schwingmoor mires - see §2.3), or thatcombine a large storage co-efficient with alimited hydraulic permeability (such asacrotelm mires and patterned surflace flowmires including aapa mires) have a “buffering”effect on catchment hydrology.Other mire types, such as immersion, waterrise, and flood mires and most types ofsurface flow mires, do not bring about similareffects. The fact that flood mires in rivervalleys may play an important role in floodmitigation 194 , is not related to their peatlandor wetland character but to the fact that theylie in or near the valley. Mineral wetlands ordry land with similar topography wouldfunction in exactly the same way.After drainage the water movement andstorage characteristics of peatlands changeconsiderably. Generally they start to resembledrier mineral soils: peak discharge is stronglyreduced because the peat layer is no longercompletely saturated and the dynamic storagecapacity is increased 195 . In other cases, opendrainage – as associated with afforestationand agriculture – increases peak charge rates,because the increased storage capacitywithin the peat afforded by the lowering ofthe water table is of lesser importance thanthe higher density of open channels in thedrained areas 196 . Similar effects result fromsoil degradation in drained fens, which leadsto decreased infiltration of rainwater in thepeat body and increased surface run-off 197 .Mires also influence the hydrology of theirsurroundings because of theirevapotranspiration characteristics. In fens(which are also fed by mineral soil water)evapotranspiration often exceedsprecipitation, leading to a decrease in runoff198 .Groundwater charge from peatlands, i.e. thequantity of water flowing downwards throughthe peat into the groundwater of theunderlying bedrock, is generally small 199 . Inthe long run the accumulation of peat in thelower parts of the catchment may lead to arise in the regional groundwater level 200 . Thereverse may happen in the cases of peatlanddrainage and peat extraction.(p) Regulation of catchmenthydrochemistry 201Ecosystems are linked with their neighbouringsystems and continuously exchange matter,energy and information. Ecosystems regulatethe flow of an in-flowing substance throughtransformation, buffering or storage(accumulation) resulting in a change inchemical concentrations in the outflow 202 .Mires accumulate carbon, nitrogen,phosphorus and other nutrients when annualproduction exceeds annual aerobic andanaerobic microbial decay. First, thevegetation transforms inorganic substances,e.g. CO 2, NO 3or NH 4,via biochemicalprocesses into organic components (C org;N org). Then the dead plant material undergoesseveral deformation processes collectivelycalled decomposition, decay or humificationresulting in the formation of peat.The decay of organic matter in mires isdetermined by many factors including oxygenconcentrations in the acrotelm and catotelm,the temperature regime, the chemicalcomposition of the plant material, and pH.An important factor for the rate of peataccumulation is how long litter stays in theacrotelm before the anoxic conditions (lackof oxygen) in the catotelm peat layer reach it.The relation between aerobic conditions inthe acrotelm and anaerobic conditions in thecatotelm is highly sensitive to changes in thehydrological conditions caused by climaticor human factors. Lowering of the water levelincreases the oxygen in the soil and fosters