Ecology of Red Maple Swamps in the Glaciated Northeast: A ...

tern, swamps may augment domestic and municipal
water supplies. Hydrogeologic studies have
shown that heavy pumping of wells located in
stratified drift; aquifers may induce recharge of
water from the surface, or from the soils, of overlying
wetlands (Motts and O'Brien 1981; OzbiXgin
1982). While this gain of groundwater may be
beneficial from an engineering standpoint, the
loss of water from the wetland may be detrimental
to fish and wildlife, recreation, and other wetland
functions and values.
Except for surface-water depression wetlands
that are perched above the regional groundwater
table, natural recharge in most red maple swamps
is likely to be a relatively brief seasonal phenomenon
(OBrien 1977). It occurs mainly during the late
summer or early fall when, due to cumulative evapotranspiration
losses, groundwater levels have
dropped below the wetland surface, and groundwater
discharge has ceased. OBrien calculated that
one red maple swamp in eastern Massachusetts
recharged the regional groundwater body with
7 million gallons of water during a 6-week period in
the fall; he noted that recharge could be significant
during dry periods. In most cases, however, the
volume of groundwater recharge in red maple
swamps probably is far less than in the surrounding
uplands--depending on the slope and soil permeability
of the uplands-particularly 011 an annual
basis.
RRd maple swamps lying on slopes or in basins
that intersect the regional groundwater table are
predominantly areas of groundwater discharge.
These swamps exist precisely because groundwater
is emerging at the surface in the form of springs or
seeps. The discharge of groundwater is important
in itself because this water supplements public
surface-water supplies, maintains fish and wildlife
habitats, and improves the water quality of lakes
wrd strew degraded by excess nutrient loads,
toxic chemicals, or thermal discharges (Adamus
1984;). Groundwater discharge maintab base flow
of streams and keeps stream and lake temperatures
low during the late summer, when both of
these conditions are critical to aquatic invertebrates
and cold-water fishes. Note, however, that
evaptranspiration losses from swamps may lower
base flow of streams during dry periods @%Her
1965).
Aside from recharge and discharge considerations,
the spatial association of wetlands and
groundwater aquifers is of great significance.
Motts and O'Brien (1981) determined that, on an
area basis, about two-thirds of Massachusetts
wetlands overlie potential high-yield aquifers,
and that at least 60 communities in that state
obtain water from wells located in or near wetlands.
Ekcause the best location for municipal
wells, from a purely hydrologic standpoint, is
often near wetlands, and because wetlands are
often hydrologically linked to underlying aquifers,
Motts and O'Brien concluded that the protection
of wetlands and their surroundings from pollution
should be a integral part of any groundwater
management program.
Water Quality lmprouement
Since the mid-1970's there has been a great
deal of research on the pollution-abatement potential
of wetlands (e.g., Tilton et al. 1976; Kadlec
and Kadlec 1979; Godfrey et al. 1985; Nixon and
Lee 1986). This research has shown that many
types of wetlands retain, remove, or transform
pollutants and thus improve the quality of surface
water. This pollution-abatement function is accomplished
through physical settling, plant uptake,
adsorption by soil particles, complexing with
other chemicals in the soil, and microbial transformation
(Burton 1981; Nixon and Lee 1986).
Most of the research on the water quality improvement
function of forested wetlands has occurred
outside of the glaciated Northeast. Hardwood
swamps in various parts of the United
States have been shown to significantly reduce
concentrations of nitrogen and phosphorus in surface
water during periods of inundation (Kitchens
et al. 1975; Mitsch et al. 1979; Brinson et al.
1981b), and the potential capacity of forested wetlands
for removing pesticides and heavy metals is
believed to be high (Winger 1986). Only two papers
have reported on the water quality improvement
capacity of northeastern red maple swamps.
In a comparison of grass- and forest-vegetated
filter strips in Rhode Island, Groffman et al.
(1991) demonstrated that denitrification rates
were significantly greater (P < 0.05) in poorly
drained soils of red maple swamps than in well
drained soils of adjacent upland forests. In a second
Rhode Island study, Gold and Simmons (1990)
found that removal of nitrate from groundwater
generally exceeded 80% in both poorly drained
and very poorly drained soils of red maple swamps
throughout the year. In almost all cases, nitrate
attenuation was significantly higher (P < 0.05) in
the swamps than in the moist (somewhat poorly
drained and moderately well drained) forest soils