Prior to implementation of a remedial action plan for an urbanized aquatic system, it is important for managers to clearly specify tangible ecosystem goals. This paper outlines a framework for defining tangible ecological goals for aquatic systems. In this paper I make the assumption that one objective of remediation would be to maintain or improve the condition of natural assemblages which include fish, benthos, macrophytes, etc. Since the focus of this workshop was the Laurel Creek watershed, I discuss such methods with respect to application of the framework to Laurel Creek.
Setting ecosystem goals requires that managers first specify the trophic group(s) that are hoped will be maintained or protected. Second, managers must obtain information that will allow them to determine acceptable conditions for the selected trophic group.
If we are interested in protecting fish, we should be setting limits based on fish. We should also be measuring an appropriate aspect of fish. For example, we could measure or monitor the abundances of a single game species (e.g., brook trout) in the system, or monitor variations in species composition. Kilgour (1997) demonstrated that monitoring species composition would more likely result in our ability to detect effects on fish, even if we were only interested in a single games species like brook trout. The improved ability to detect problems using whole community surveys is a result of whole community endpoints being less variable than abundances of single species.
Ecological criteria are the numeric values that denote acceptable and unacceptable conditions for our ecological endpoint. Ecological criteria can only be specified after we have accumulated data describing normal or background conditions. Figure 1 illustrates the usual distribution of observations of an ecological endpoint from a survey of unaltered locations. Regardless of what we are measuring, the normal range of variation usually follows a normal (bell) curve. We can use this normal curve to denote what are acceptable and unacceptable conditions in a fishery such as Laurel Creek. The normal range of variation is often denoted as the numeric values under the normal curve that include 95% of the observations from the reference locations (Kilgour, 1997). Observations outside of this range can be considered indicative of unacceptable ecological conditions because it would be unusual for a natural (unimpacted) community to have a larger or smaller value. Use of such an approach for setting ecological criteria has been common in the United States (Davis and Simon, 1995), and is now part of federal legislation in Canada (Environment Canada, 1997). The use of such criteria does, however, require novel statistical approaches as described by Kilgour (1997).
The use of benthos as a surrogate ecosystem endpoint also has potential. If rehabilitative measures are taken in Laurel Creek, benthos would be able to provide an earlier indication of success. Benthos would respond to true improvements within the first one to two years, whereas fish may not respond for up to 10 years. Consequently, the success of any rehabilitation is probably best monitored using benthic invertebrates.
Figure 1. The histogram represents the distribution of observations in unaltered reference locations. The 95th percentile denotes the numeric value for the limit of acceptable conditions. Values less than the 95th percentile would be considered acceptable. Values greater than the 95th percentile would be considered unacceptable.
Davis, W.S. and T.P. Simon (eds). 1995. Biological Assessment and Criteria, Tools for Water Resource Planning and Decision Making. Lewis Publishers, Boca Raton, Florida.
Fitzgerald, D.F. 1996. Evaluation of fish in anthropogenically modified streams within the Grand River watershed, Ontario. MSc thesis, University of Waterloo.
Kilgour, B.W. 1997. Fish-benthos correlations and effects on benthos that reflect significant effects on fish communities in southern Ontario streams. PhD thesis, University of Waterloo.