Page 318 - Hydrogeology Principles and Practice

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Groundwater resources and environmental management 301

of 1989–1992 when mean weekly flows in the river habitats (Groombridge & Jenkins 2000). The four
3 −1
fell to <0.8 m s , the predicted flow depletion is major wetland habitat types are bogs, fens, marshes
approximately 30% of this mean. By highlighting and swamps. Bogs are peat-producing wetlands in
spray irrigation, the catchment resource model moist climates where organic matter has accumu-
illustrates the future challenge of managing water lated over long periods. Water and nutrient input
resources in eastern England with the additional is entirely through precipitation. Bogs are typic-
factor of climate change (see Section 8.5). Unless ally acid and deficient in nutrients and are often dom-
farmers adapt, the expected warmer and drier sum- inated by Sphagnum moss. Fens are peat-producing
mers in this area are likely to lead to a greater demand wetlands that are influenced by soil nutrients flow-
for irrigation water in direct conflict with other water ing through the system and are typically supplied by
users and the need for water for environmental mineral-rich groundwater. Grasses and sedges, with
protection. mosses, are the dominant vegetation. Marshes are
inundated areas with emergent herbaceous vegeta-
tion, commonly dominated by grasses, sedges and
8.4 Wetland hydrogeology reeds, which are either permanent or seasonal and
are fed by groundwater or river water, or both.
The global extent of wetlands is estimated to be from Swamps are forested freshwater wetlands on water-
6
2
7 to 8 × 10 km and, compared to other ecosystems, logged or inundated soils where little or no peat
are an extremely productive part of the landscape with accumulation occurs. Like marshes, swamps may be
an estimated average annual production of 1.125 kg either permanent or seasonal.
−2 −1
Cm a (Mitsch et al. 1994). The relatively high Various attempts have been made to classify
productivity and biological diversity of wetlands wetlands and a variety of subdivisions have been re-
support an important landscape role in nutrient cognized based on broad features such as substratum
recycling, species conservation and plant and animal type, base status, nutrient status and water source,
harvest. Although very much smaller in extent water level and successional stage. The development
compared to marine habitats, inland water habitats of the main wetland habitat categories and terms, in
exhibit greater variety in their physical and chemical relation to the main ecological gradients, has been
characteristics. Wetlands, with their often abundant reviewed by Wheeler and Proctor (2000). Other
and highly conspicuous bird species, are protected approaches include hydrological and hydrogeolo-
by national and international agreements and legis- gical classifications based on the main inflows and
lation. Notable wetland protected areas include the outflows of water, flowpaths and water-level fluctu-
Moremi Game Reserve in the Okavango Delta, Bots- ations (Lloyd et al. 1993; Gilvear & McInnes 1994) and
wana, the Camargue National Reserve in France, a hydromorphological (or hydrotopographical) clas-
the Keoladeo (Bharatpur) National Park in India, sification based on the shape of the wetland and its
Doñana National Park in Spain and the Everglades situation with respect to apparent sources of water
National Park in the United States (Groombridge (Goode 1977). A simplification of the hydrogeological
& Jenkins 2000). Inland water ecosystems are un- classification is shown in Fig. 8.14 to illustrate the
usual in that an international convention, the 1975 influence of topography, geology and water source in
Convention of Wetlands of International Import- maintaining wetlands.
ance especially as Water-fowl Habitat (the Ramsar A change in the factors controlling the source of
Convention; Navid 1989), is dedicated specifically water to a wetland can have potentially devastating
to them. Inland water habitats can be divided into consequences for the fen community, particularly a
running or lotic systems (rivers) and standing or change in flow direction and volume. An example
lentic systems (lakes and ponds). Wetlands are typ- of the impact of groundwater abstraction on the
ically heterogeneous habitats of permanent or sea- freshwater habitat of a valley fen and the measures
sonal shallow water dominated by large aquatic taken to restore the fen is given in Box 8.5. When
plants and broken into diverse microhabitats occupy- land drainage and competing demands for water
ing transitional areas between terrestrial and aquatic for wetlands, agriculture and public supply conflict,