Hydrology and Wetland Restoration for Human Subsistence and Regional Biodiversity - Restorative Redevelopment of Devastated Ecocultural Landscapes - page 120

drainage (see chapter 6). The accumulation of high levels of salts or soil carbon-
ates can destroy wetland soil structure, fracture aquacludes, or damage wetland seed
banks. Where sodification or salinization is excessive, the soil structure will have
collapsed (see chapter 21). This will increase vulnerability to subsequent wind and
water erosion and may accelerate water losses to groundwater. Soil tensile strength is
typically weakened where clay lattice structure collapses, especially in the salinized
soda soils of arid places. All of these variables can affect the restoration of phreatic
zones, especially where an adequate temporal water supply is not available, or other
users or suppliers of river waters have caused changes in water quantity, quality, or
timing of availability.
Changes in hydrology, chemistry, and water tables often favor exotic species
that gravitate to stream courses and agricultural drains. Dried organic muck soils
are often seriously depleted in organic matter through oxidative decomposition in
heated climes. Nonwettable soil crusts often develop in former wetland soils that
have been altered by dewatering and these physicochemical changes, especially in
arid climates. Reflooded hydric soils often do not reestablish native species emerg-
ing from the seed bank as the dominants. Dense periphytic algal mats responding to
the availability of nutrients in the water column may choke out key native plant spe-
cies. Periphyton growth is often much faster in warm climates, especially in shallow
waters of arid areas. Seed bank depletion from prolonged dewatering and heat occurs
in substrates of arid regions. Some seeds may persist, but seed survival declines rap-
idly over time. Restoration success that depends on this seed bank is reduced.
In arid regions, rewetting dewatered wetlands can encourage rodent and water-
fowl depredation of germinating seed banks and planted stock (see chapter 5).
Rodent damage can also be severe through undermining water control structures
(e.g., earthen irrigation flumes, levees, dikes, etc.) because of the increased localized
water availability, moist soils, and more productive plant growth.
In many arid areas, montane snowloading far upstream provides hydrology for
riparian systems and associated wetlands. Seasonal precipitation and seepage may
control playa and other internally drained basins adjacent to riverine systems. Highly
dynamic hydrology cycles depend on rainfall patterns and snowloading and can
affect the extent, timing, and success of wetland restorations profoundly.
Ecotoxicological and biotoxic concerns are commonplace in the restoration of
arid-area wetlands. Midsummer to fall wetland dewatering that coincides with
waterfowl and shorebird migrations into wetlands also often coincides with avian
botulism or cholera outbreaks. Wetland systems in arid areas often become anoxic
(especially in highly altered systems), fish die-offs prevail, and subsistence uses
of the wetlands can be damaged. This is especially problematic the first few years
after restoration begins. Such outbreaks also occur where wetlands may be used for
water quality enhancements receiving organic material loading rates that contribute
to eutrophic and anaerobic conditions that support Clostridium botulinum types C
& E, the principle botulism disease-causing bacterium (Simmers, Apfelbaum, and
Bryniarski 1990; Ludwig and Bromley 1988). Exposure risks to wildlife from other
contaminants, including organochlorines (Ludwig, Apfelbaum, and Giesy 1997),
salts, selenium, boron, and other heavy metals, are common concerns in arid region
wetland restorations—especially on rivers that originate in mineralized montane