Geoscience Reference
In-Depth Information
• the draining and i lling of wetlands for agri-
culture or development
• habitat fragmentation
• aquaculture
• alteration of river regimes through diver-
sions, dams, impoundments, and l ood-
control mechanisms
• overharvesting of wetland products
• clearing of wetland vegetation
• contamination through agricultural and
industrial runoff
• eutrophication and algal blooms
• introduction of invasive species that crowd
out native plants and animals
• changes in land tenure and ownership
regimes
• changes in government policy
• encroachment by small-scale farmers and
ranchers
• political uncertainty
• absence of conservation management
• poverty and political conl ict
• variability in regional and global precipita-
tion and climate patterns
• sea-level rise or fall.
(Cutter and Renwick 2004). N is also leached
from the soil into ground and surface waters.
Human interference in the nitrogen cycle
has resulted in the overloading of N from
human waste, sewage and agricultural runoff
into wetland areas. Such overloads may cause
eutrophication, and the excessive growth of
algae in wetland pools and ponds may choke
out native wetland plants.
Like nitrogen, phosphorus is considered a
limiting nutrient in wetland ecosystems (Rich-
ardson and Vaithiyanathan 2009). Phosphorus is
found in terrestrial sinks and is made available
in the soil from rock weathering and erosion
processes. P makes its way through the food
chain via uptake by plants and onto consumers
until it is returned to the soil by decomposers.
Phosphorus is also made available through the
excessive use of fertilizers and runoff from
agricultural i elds, and through human waste,
leading to problems similar to those observed
with the overloading of N in wetlands.
Carbon enters the wetland ecosystem through
the photosynthesis process whereby plants take
in CO
2
in the presence of sunlight and water to
produce sugars. While carbon dioxide is returned
to the atmosphere through respiration and
decomposition, a signii cant amount of organic
matter made up of carbon is sequestered in
dead material within wetland soils (Dise 2009).
Due to slow decomposition processes in the
presence of water, wetlands play an important
role in the atmospheric carbon cycle serving as
an important repository or sink of carbon. As
Kusler (1999) pointed out, carbon sequestration
and storage in wetlands is dependent on their
size and type, the vegetation present, soil depth,
pH, temperature, precipitation, nutrients, and
ground-water levels. Hence, different wetland
types have different carbon accumulation and
storage capacities (Dise 2009). For instance,
peatlands may sequester carbon at a slow rate
for many thousands of years (Gorham et al.
2007).
The focus on carbon due to its critical role
in climate change has added urgency to under-
standing the role of wetlands in carbon storage.
Studies have suggested that signii cant amounts
of the world's soil carbon could be sequestered
Monitoring, education and conservation efforts
involving multiple stakeholders could be critical
to the sustainability of these habitats.
11.2.2 Wetlands and biogeochemical
cycles
Biogeochemical cycles play critical roles in
maintaining ecosystem functions and processes.
The cycling of nitrogen (N), phosphorus (P) and
carbon (C) through wetland ecosystems occurs
through a series of complex processes (see
chapter 10). Each of these is necessary for the
viability of wetlands and contributes to their
global cycles. Nitrogen is made available to wet-
lands through biological i xation, precipitation,
and through human point and non-point source
discharges (White and Reddy 2009). Wetlands
provide vast reservoirs of N in inorganic and
organic forms within soils. Plants assimilate
nitrogen into plant tissue and once incorpo-
rated, N moves through the food chain from
producers to consumers and then decomposers
