Biological integrity has been defined as "the health and stability of a biological system as well as the capacity for self-repair" (Karr and Dudley, 1981). Wetland assessment of both natural and replacement wetlands is important in order to keep these systems in good health. Health "defines a condition favorable for the functioning of the whole organism that is actively defended by homeostatic processes" (Calow 1992). It is important to measure the effects of disturbances on natural wetlands, while in replacement wetlands it is critical to evaluate the success of the project.
There are several methods used to assess wetlands. The most common way to evaluate wetland health is to conduct a comparison study between the wetland in question and a natural, minimally impacted wetland. These comparison studies are known as biological monitoring and they "measure the condition of biological systems in the broadest sense" (Karr and Chu 1997). The method behind biological monitoring allows one to gain a better understanding of the biological consequences of human activity (Karr and Chu 1997). It is important to understand the baseline, or reference, conditions of an ecosystem and the processes behind these conditions; therefore, the least disturbed ecosystem is studied (Karr and Chu 1997). After sampling a degraded system, it is possible to determine why a system has become degraded by comparing processes to a pristine system (Keddy et al. 1993). The effect of humans on an ecosystem can ultimately be determined, and steps to decrease impact can be taken (Keddy et al. 1993).
Another common way to measure ecological integrity is the use of biological indicators. Studies have shown that the presence of a rare or sensitive species in an ecological system is an indicator of integrity (Keddy et al. 1993). In order to conduct an indicator species assessment there are four major steps: 1) define integrity, 2) select environmental variables that represent integrity, 3) create a scale of integrity (high to low) for each variable, and 4) develop a system to monitor integrity (Keddy et al. 1993). Ecological indicators should be closely tied to system processes, present at every individual system, have several species that can be measured at a community level, sensitive to disturbances, and easy to measure (Keddy et al. 1993). Due to the sensitive nature of ecological indicators, their presence in an ecosystem indicates the quality of that system is high (Keddy et al. 1993). Determining the number of exotic species in accordance with indicator species in an ecosystem is typical. Exotic flora and fauna are often a sign of disturbance or degradation and threaten the existence of indigenous plants and animals (Keddy et al. 1993). When exotic species are found in a system, it generally indicates that conditions that native species thrive in are worsening, thus exotic species are able to infiltrate and compete against these native species. The presence of an exotic species may act as a warning that the ecosystem is under stress. Two major systems have been recently established using indicator species and exotics to measure ecological integrity, the Amphibian Quantitative Assessment Index (AQAI) and the Flora Quantitative Assessment Index (FQAI) (Andreas and Lichvar 1995, Micacchion et al. 2000).
A site in Ohio affectionately named "Bluebird". Wetland function was far from being reached at this mitigation site.