5.8.2. Pressures on Wetland Services
Pressures on wetlands are likely to be mediated through changes in hydrology,
direct and indirect effects of changes in temperature, and land-use change.
There would be interactions among these pressures and subsequent impacts on
services and good from these ecosystems.
188.8.131.52. Changes in Hydrology
Climate change will affect the hydrology of individual wetland ecosystems mostly
through changes in precipitation and temperature regimes. Because the hydrology
of the surface layer of bogs is dependent on atmospheric inputs (Ingram, 1983),
changes in the ratio of precipitation to evapotranspiration may be expected
to be the main factor in ecosystem change. However, work on the large peatland
complexes of the former Glacial Lake Aggazzi region indicate that the hydrology
of bogs cannot be considered in isolation or independent of local and regional
groundwater flow systems (Siegel and Glaser, 1987; Branfireun and Roulet, 1998)
and that groundwater flow reversals, even in ombrotrophic peatlands, can have
an impact on their water storage and biogeochemistry (Siegel et al., 1995; Devito
et al., 1996). From the perspective of assessment of climate variability and
change of peatlands, these systems need to be viewed in the broader context
of their hydrogeological setting.
Fen, marsh, and floodplain wetlands receive additional water influx from the
surrounding basin, including underground sourcessometimes from a considerable
distance. This means that climate change impacts are partially mediated through
changes in the whole basin area or even further afield where groundwater reserves
do not correspond with surface basins. These changes also may affect the geochemistry
of wetlands. Recharge of local and regional groundwater systems, the position
of the wetland relative to the local topography, and the gradient of larger
regional groundwater systems are critical factors in determining the variability
and stability of moisture storage in wetlands in climatic zones where precipitation
does not greatly exceed evaporation (Winter and Woo, 1990). Changes in recharge
external to the wetland may be as important to the fate of the wetland under
changing climatic conditions as the change in direct precipitation or evaporation
on the wetland itself (Woo et al., 1993).