Environmental Engineering Reference
In-Depth Information
and Brush ( 1998 ) recommend the following sampling intervals: tidal freshwater
wetland, 2-4 weeks; salt marsh, 4-8 weeks; floodplain, varies with flood regime.
These should be taken as initial guidelines and adjusted as needed with experience.
Erosion monitoring requires that the height of each side of the tile above the
marsh surface be determined at installation. Also during installation attempts
should be made to keep the tile level with the bottom of the tile just touching
the marsh surface. If not, any deviations should be recorded. If the tile was flat on
the ground upon installation, erosion depth is determined by measuring the height
of each tile side above the marsh surface and averaging the measurements. If the tile
was not flat, measurements need to be adjusted for the known deviations. A mass
estimate of erosion can be determined by multiplying erosion depth by sediment
bulk density (see Bulk Density above).
7.11 Biogeochemical Indicators for Evaluating
Wetland Condition
Many of the biogeochemical assays are expensive, require a high level of technical
expertise, and require multiple site visits. Therefore, a number of wetland scientists
have evaluated a surrogate approach in which readily measureable indicators of a
biogeochemical process or pool are identified and used in lieu of the more complex
assay. The surrogate approach may address an individual wetland service, the
impact of a specific type of anthropogenic disturbance, or overall wetland condi-
tion. A major benefit of this approach is that since the required information can be
collected in one visit, a greater number of wetlands can be assessed.
As an example of the surrogate approach to individual wetland services,
researchers at the University of Delaware developed an assessment of denitrifica-
tion capacity for slope wetlands based on soil morphology. In this procedure,
wetlands are classified as having high, medium, or low denitrification capacity on
the presence of specific hydric soil indicators. Field Indicators of Hydric Soils
( USDA, NRCS 2010 ) are a series of individual soil morphology characteristics that
were developed to identify hydric soils in the field. The majority of the indicators
are visual and require only a ruler, a shovel, and a Munsell Color Chart. Differences
between indicators reflect in part differences in hydroperiods which impact denitri-
fication potential.
There is presently a national wetland monitoring effort based on the use of
indicators to assess the impact of a specific type of anthropogenic disturbance or
overall wetland condition. Natural and anthropogenic disturbances that negatively
impact the functional capacity of a wetland are called “stressors”. Widespread
anthropogenic disturbances include artificial drainage (e.g., ditches), timber
harvesting, and nutrient loading. Commonly, wetland condition is assessed as the
degree of deviation from the undisturbed condition. This requires the collection of
Search WWH ::




Custom Search