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

li&r (Fig. 6.3) is relatively high in value for all of
these features.
In the seasonally fiooded Gwat Dismd SWmlp,
red maple leaf litter decayed about 37% after 1 year
and 46% after 2 yem (Day 1982). Maple wood
decomposed only l6O.0 the first year and 27Oio in
2 years. hn~position raks of md maple litter
placed in litter bags in maple -gun1 stmlds were not
significantly different from decomposition rates for
red maple litter placed in Atlantic white cedw
swamps, mixed hardwood (Qu~nus spp.) forests, or
baldcypress (Tlzxdurn distkhunr) swmlps, suggesting
that litter composition was the primary
fador controlling decay rate (Day 1982).
Temperature, water regime, and pH ~1.e other
impsrtant factors influencing deconipositioxl rates.
Brimon et d. (1981a) suggested that temperature
is probably the single most imlwrta~x.t variable
when moisture and oxygen availability are not limiting.
Although a clear relation betweexl decomposition
rates and hydrologic regime is difficult to
demonstrate, the usunl assumption is that rates
are lowest under conti~luously anaerobic conditions.
hay rates tend to ir~crease when aerobic
and anaerobic conditions alhrr~ate, md they are
probably greatest when, dong with some degree of
wetting and drying, aerobic conditions prevail
(Brown et al. 1979; Brinson et al. 1981a; Gomez
and Day 1982). Gomez nnd Day (1982) suggested
that alternating periods of exposure md inundation
promote pulses of decay and nutrient release.
In contrast ta the above, Day (1982) found the
decomposition rate of red maple litter to increase
with the duration of flooding. IIe noted that soil pH
and nutrient concentrations were higher at flooded
sites than at dewatered sites and hypothesized that
the higher decay rates stemmed from the more
favorable substrate conditions for microbial deconlposers.
These contradictory furdings underscore
the need for additional research on the complex
relationships among the various factors influencing
decomposition rates of red maple litter (i.e., litter
composition, water regime, temperature, and other
physicochemical conditions).
Oxygen levels in northeastern swamp soils vary
seasonally. Decomposition rates in most swamps
are probably greatest durixg mid Lo late summer,
when temperatures are highest and both soils arrd
litter are most likely to be aerobic. The rak of
decomposition may dso vary among years, along
with variatiom in swamp water levels.
Nu tricnt Cycling
Biovhenlical cycles in wetlmds RIP. conlplex,
at least partly of the varied influence of
groundwakr and surface-water hydrology, continuous
changes irr soil and water oxygen levels, seasorld
metabolic changes, arid mthropogenic influences.
Obtaining even a simplified \u>derstanding
of cyclixlg for key nutrients (e.g., N, 1: Ca, K) requires
infornlatioxz on nutrient soilrces mid trwmport,
into the ecosystem, potential sinks within the
wetland, m~d transfer rates of nutrients between
the major compartments (soil, plant^, water) of the
system. An understsulding of the controIling factors
for each of these processes also is required
@ichwirdson et a1. 1978). Constructing a nutrient
budget that accurately prt;rays the cycling in any
wetlmd system is difficult; no such research has
been conducted for northeastern red maple
swamps. General discussion of nutrient cycling in
natural wetlands can be? foilnd in Richardsox~ et al.
(1978)) van der Valk et d. (1979), Nixon and IAX.
(1986), and Bowden (19871, among others. We reconunend
these publications for an overview of key
pathways.
Many of the processes observed in nonfowsled
wetlands or in forested wetlmds outside the Northeast
clearly occur in northeastern red maple
sw~nlps as well (see Fig. 5.4), but tile relative magnitude
of the various cloxnponents in these cycles is
u*kxlown. Important sources of both N and P include
surface-water and grot~ndwater inflow and
atmospheric deposition. Nitrogen fixation also may
contribute significant loadings of N in some wet-
lands (surxun~arized in Nixon and Lee I%), but the
significance of this process in red maple swamps is
urhowrr. Potential nutrient removal processes
(i.e., sinks) within swamps include sedimentation
(burial of particulate nnd adsorbed fractions), denitrification
(the biochemical reduction of nitrate to
nitrogen gas), and chemical complexing of phosphorus
with ions such as iron Lo form insoluble compounds
(vm der Valk et al. 1979; Nixon and b~
1986). The seasoxmal uptake of nutrients by higher
plants and microbes temporarily detains these elements,
md may result in trmfomations from
inorganic to organic forms.
Nutrients taken up by vegetation may be returned
to the water or soil through leaching, litter
fall, or root excretions. Many studies in wetlands
have demonstrated significant losses of certain
soluble minerals from plant tissues within a few
days or weeks after senescence (Willoughby 1974,
cited in Day 1983; Boyd 1970; Mason and Bryant