A multi agency project funded by US EPA's STAR Program
 

Results: Fish-based Indicators

Scientists with the Great Lakes Environmental Indicator (GLEI) project and their collaborators have tested and confirmed the validity of two indices that indicate the condition of Great Lakes coastal wetlands. Wetland ecological condition has been especially difficult to assess because changing water levels have such a dramatic impact on the extent and local conditions. Wetlands are often characterized by their vegetation. But each species tends to have specific requirements of water depth and clarity. Wetland fauna often depend on particular plant species when picking places to build nests or lay eggs.

Ecological Indicator: Scientists with the Great Lakes Coastal Wetlands Consortium had previously proposed that because submergent plant communities adapt quickly to changing water levels, perhaps the fish communities associated with plant types could be used as indices of wetland condition. They proposed a fish index of biotic integrity (IBI) for wetlands dominated by cattails (Typha) and another IBI for those in which bulrushes (Scirpus) were the most common species.

Text Box: Text Box:
Scirpus (bullrush)-dominated wetland
Typha (cattail)-dominated wetland.

 

Measuring Fish Index Scores Across the Human Stress Gradient of Coastal Zones

GLEI researchers have developed a unique way to divide the coastal regions of the Great Lakes in the U.S. into 762 watersheds that encompassed the tributary streams and coastal wetlands. For each of these watersheds, 6 different measures of human influence were calculated, based on the way the land is used and the materials carried from the land into the Great Lakes2. To assess the relationship between fish community condition and the human-related stressors, GLEI researchers used live-trap nets to catch and identify the fishes in 82 Great Lakes coastal wetlands, 33 of which were dominated by either cattails or bulrushes (Bagat et al in review).

The fish IBI scores calculated for these wetlands did indeed vary, but only according to specific classes of human-related stress. Fish communities in cattail-dominated wetlands became degraded as a disturbance variable that combined population density, road density and urban development in the watershed surrounding the wetland increased.

In contrast, the fish communities of bulrush-dominated wetlands reflected the impacts of nutrient and chemical inputs associated with the intensity of agricultural activity in the surrounding landscape. These effects were observed in data collected over several years, during which time Great Lakes water levels varied by up to 100 cm, thus confirming the effectiveness of the Indices under changing water conditions. The fish IBI scores in bulrush wetlands were very much lower once a threshold level of agricultural-input stress had been exceeded. In contrast, the IBI scores in cattail wetlands gradually declined with increasing population disturbance. Thus, The proposed indices appear to effectively indicate the effects of some but not all classes of anthropogenic disturbance on fish communities at Great Lakes coastal margins.

Text Box: Environmental Application

The cattail and bulrush IBI Indices are useful tools for helping environmental managers to assess the condition of wetland fish communities and possible causes of their degradation. The fish species in bulrush-dominant wetlands are apparently sensitive to nitrogen and phosphorus loadings and direct pollutant discharges. Strong changes in fish IBI were observed to correspond to specific nitrogen and phosphorus input values. These values can provide managers with potentially important guidelines for planning allowable concentrations of nutrients and chemicals in agricultural runoff. Similar guidelines can be derived for allowable inputs of total nitrogen and total phosphorus from non-agricultural sources that would protect the fish communities of receiving wetlands. In addition, these data provide information that is of value to managers seeking to understand the causes of impairment at sites that do not meet designated use criteria.

The results of this study verify that the Uzarski et al. (2006) IBI scores reflect specific classes anthropogenic stress in coastal wetlands dominated by cattails and bulrushes. However, the Indices reflect only certain types of human disturbance. They are most suitable for assessing wetland condition in response to agriculture or population density rather than generalized disturbance. Diagnosing causes of water quality impairment is an important component of the Great Lakes Water Quality Agreement of the governments of Canada and the U.S., and the U.S. federal Clean Water Act. These results address one of the weaknesses of the IBI approach, in that a single value representing ecological condition does not address the cause of impairment.
           

References

Uzarski, D.G., T. M. Burton, M.J. Cooper, J.W. Ingram, and S. Timmermans. 2006. Fish habitat use within and across wetland classes in coastal wetlands of the five Great Lakes: development of a fish-based index of biotic integrity. Journal of Great Lakes Research 32: In Press.

Danz, N.P., R.R. Regal, G.J. Niemi, V.J. Brady, T. Hollenhorst, L.B. Johnson, G.E. Host, J.M. Hanowski, C.A. Johnston, T. Brown, J. Kingston, and J.R. Kelly. 2005. Environmentally stratified sampling design for the development of Great Lakes environmental indicators. Environmental Monitoring and Assessment 102:41-65.

Bhagat, Y., J.J.H. Ciborowski, L.B. Johnson, T.M. Burton, D.G. Uzarski, and J.W. Ingram.In review. Testing a fish index of biotic integrity for Great Lakes coastal wetlands: stratification by plant zones. Submitted to Wetlands, April /06.