Estuarine Health

Chemical monitoring

Physical and chemical monitoring of estuarine ecosystems is comparatively inexpensive, but only provides information on environmental conditions at the time of sampling. Such a program may not detect a short period between two sets of samples where environmental conditions were such that all the animals in the estuary were killed. Another problem with chemical monitoring is that the variables naturally fluctuate over time making it difficult to detect small changes. Changes to the plant and animal communities frequently occur below the detectable levels of a physical and chemical monitoring program. Consequently, physical and chemical monitoring is best at detecting whether an estuary has become grossly polluted but this type of monitoring has poor ability to detect if the environment has been slightly modified and there has been a change in the plants and animals present.

Biomonitoring

Biomonitoring is labour intensive and thus expensive. Advantages over chemical monitoring are that organisms integrate environmental conditions over a long period of time. Thus conclusions about environmental conditions between sampling periods can be made. Also, conditions of intermittent or mild pollution, which are hard to detect by chemical means, may be readily detected by changes in the fauna. Biomonitoring measures the actual effects on biota, whereas physical and chemical methods must eventually be interpreted on a biological basis.

Biomonitoring can be carried out on individual species or different community types. Where there are strong commercial interests biomonitoring is frequently based on a single species (oysters, crabs or fish). For estuarine health monitoring at a community level is more appropriate. Communities that are frequently used in monitoring programs are macrobenthos, plankton, fish, birds and single celled diatom plants. Financial constraints usually limit monitoring programs to one or two of these assemblages.

What is an AusRivAS-type approach to environmental health?

The AusRivAS (Australian River Assessment System) method for assessing environmental health of our rivers was described by Richard Norris in his article "Bugs and Computers" in the Summer 1999 edition of Rivers for the Future. The method provides a technique that allows managers to compare the environmental health of a river or specific site with reference sites.

Using a database of species and abiotic variables at reference sites, an AusRivAS computer model predicts the probability of collecting each species from a test site based on the site's abiotic variables. This information can then be used to assess the environmental health of the test site by dividing the number of species observed in the sample by the number of species expected to occur, the O/E ratio. Assuming the model is reliable, an O/E ratio of one is anticipated and any divergence indicates an environmental perturbation.