Ecological Structures
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Threats to Biodiversity
in progress...

Threats to Biodiversity

V.1 Causes

Multiple Stresses


Habitat Loss


Ozone Depletion


Climate Change


Introduction of Exotic Species




V.2 Scale

Local Populations




Entire Ecosystems

Wetlands as an Example of Habitat Loss

Definition: A wetland is an area where water covers the soil, or is present at, or near the surface of the soil for part, or all of the year. Legally, a wetland has to have three characteristics present during part of the growing season: hydrophytic vegetation, hydrophytic soils, and appropriate hydrology. Hydrophytic vegetation typically includes cattails, bulrushes, willows, and sedges. Hydric soils are developed in areas where soil was oxygen limited for long periods. Soil surveys and other indicators such as the Munsell soil charts can be used to determine if hydric soil is present. Hydrology indicators can be determined with a field identification of standing/flowing water, water marks on trees, drift lines, or sediment layers. The Army Cops of Engineers (ACOE) maintains wetland delineation maps that show where many of the larger wetlands are located.

Uses: Wetlands are valued as an ecological resource, but are also valued for storage for floodwaters, natural water quality treatment (silt, nutrients, toxins), prevention of saltwater intrusion, shoreline stabilization, and recreation.

Why Losses? Wetlands now occupy less than 5% of land acreage in the United States. In the lower 48 states, 1/2 of wetland acreage has been lost. Historically, public policies served to destroy wetlands, e.g. government subsidies in the 1930s and 1940s for conversion to farmland (87%), use as landfills up until 1977 (5%), and use as building space for highways and housing developments (8%).

Permits/Regulations: Since 1972, to be able to fill, excavate, or mechanically clear in a wetland, lake, river, or stream, you need a Clean Water Act discharge permit. These are known as Section 404 permits and are granted if the applicant can show that the project will not have an unacceptable adverse impact on the ecosystem. The applicant typically applies to the ACOE for the section 404 permit. If a permit is needed, the applicant also needs a Section 401 water quality certification from the state environmental agency. The agency reviews the application to see if the activity complies with the water quality standard, and typically requires measures to minimize impacts. Often the applicant is required to compensate for the impacts. Permits can be denied.

Other Protection: The 1985 Farm Bill further protects wetlands from drainage, fill, or damage. The difficulty is often delineating the wetland and then determining if the project will have negative impacts. Several programs also exist to restore degraded wetlands and build new ones. These are administered by several not profit groups, the Fish and Wildlife Service, and the Department of Agriculture's Wetland Reserve program. Constructed wetlands are also being used for controlled stormwater and wastewater treatment.


V.3 Implications



  ©Copyright 2003 Carnegie Mellon University
This material is based upon work supported by the National Science Foundation under Grant Number 9653194. Any opinions, findings, and conclusions or recommendations expressed in this material are those of the authors and do not necessarily reflect the views of the National Science Foundation.