Environmental Engineering Reference
In-Depth Information
data from reference sites to identify baseline levels for comparison. Ideally, the
reference wetland would be pristine (i.e., un-impacted by anthropogenic activities).
However, in many regions such as the mid-Atlantic region of the U.S., it is difficult
to find undisturbed wetlands for each class so that minimally impacted sites are
used as reference sites. Reference sites should represent the same class of wetlands
as the wetlands in question. For example, a mineral soil flat would be compared to a
mineral soil flat reference site.
The U.S. EPA recognizes three levels of indicators for wetland monitoring -
Levels I, II, and III (U.S. EPA
2008
). Level I indicators are used for routine wetland
monitoring for condition or impacts. Level II and III indicators are often used to test
or support the validity of Level I indicators. The classes are based on the ease of
measurement and sensitivity to respond to change as follows:
1. Level I: easily measureable, low cost, less sensitive to stress, long response time,
low spatial variability
2. Level II: intermediate in complexity and sensitivity, intermediate response time,
moderate spatial variability
3. Level III: highly complex and sensitive, short response time, high spatial
variability
Because of the recognized importance of wetlands to water quality, one focus of
these monitoring efforts has been to develop methods to evaluate nutrient enrich-
ment of wetlands, which is one of the primary stressors to wetlands in many parts of
the country. Eutrophication is commonly considered to be the enrichment of bodies
of fresh water by inorganic plant nutrients (e.g., NO
3
,PO
4
2
). This may result in
increased primary productivity and a subsequent impact to water quality. Eutrophi-
cation of wetlands is usually attributed to nutrient loading, increased external inputs
of nutrients from point and non-point sources. However, eutrophication can also
result from an increase in nutrient cycling within the wetland itself without an
increase in external inputs. For example, artificial drainage or increased development
in the surrounding watershed will impact hydrologic characteristics of the wetland.
These changes will impact SOM decomposition rates, soil mineralization rates, and
denitrification rates. Destruction of vegetation in the wetland will diminish a primary
sink for N and P resulting in an increase in those nutrients in the water column.
Not all of the monitoring indicators have a biogeochemical basis. However,
because of the interdependence of biogeochemical cycles and the nutrient status of
soil and the water column, biogeochemical characteristics are well suited to serve as
indicators of wetland condition, especially with respect to nutrient enrichment.
Table
7.2
presents some examples of potential biogeochemical indicators to assess
nutrient impacts to wetlands. Additional information on using indicators to assess
wetland condition can be found in the following references:
Reddy and DeLaune (
2008
), U.S. EPA (
2008
),
