Scientific poster as presented at IAGLR 2002

The State of the Lakes Ecosystem Conferences (SOLEC) are hosted by the U.S. Environmental Protection Agency and Environment Canada on behalf of the two countries. These conferences are held every two years in response to one reporting requirement of the binational Great Lakes Water Quality Agreement (GLWQA). The conferences are intended to report on the state of the Great Lakes ecosystem and the major factors impacting it, and to provide a forum for exchange of this information amongst Great Lakes decision-makers. These conferences are not intended to discuss the status of programs needed for protection and restoration of the Great Lakes basin, but do evaluate the effectiveness of these programs through analysis of the state of the ecosystem. Evaluation and redirection of programs are addressed through other means and conferences. Another goal of the conferences is to provide information to people in all levels of the government, corporate, and not-for-profit sectors who make decisions that affect the Lakes.

The conferences are the focal points of a process of gathering information from a wide variety of sources and engaging a variety of organizations. In the year following each conference the Governments prepare a report on the state of the Lakes based in large part upon the conference process.

These conferences have been instrumental in the development of ecological indicators, and SOLEC indicators will be used to report to the International Joint Commission and the public on progress made in restoring the chemical, physical, and biological integrity of the Great Lakes, as called for in the Great Lakes Water Quality Agreement

(From U.S EPA)

• It was historically abundant in Great Lakes mesotrophic (moderately nutrient enriched) waters.

• It is intolerant of polluted water, which caused their extirpation from those environments in the 1940-50's.

• It has recovered in one of those previously polluted environments after significant pollution reduction.

• It is ecologically important as a trophic indicator, linking detrital (bottom litter) energy resources directly to the many fish species that feed on Hexagenia and the highly visible mating swarms that tell the informed public that the water body is healthy.

The study was conducted in Lake St. Clair in Michigan and western Lake Erie and the purpose was to identify a reliable way to estimate the biomass (the weight of the Hexagenia in the lake, which is a good measure for how many there are) and the annual production (which accounts for growth, reproduction and mortality).

Sediment samples were collected and washed through a mesh screen which collected insects and large sediment components. The Hexagenia nymphs, which live in the sediment until they are ready to become adults and emerge from the water, were taken back to the lab for weighing, measuring and counting.

Two methods were used for analyzing the data and they were compared for effectiveness.

Method 1: Use of Size Frequency to Estimate B and P Analysis of the data led to mean annual biomass (B) and annual production (P). These were used to estimate annual turnover of the populations (for further explanation, please see Scientific Poster). A fine mesh screen was used to separate the insects from the sediment.

Method 2: Cohort-based (age group) approach. A simplified method for estimating biomass and production. Sediment samples are washed down through a much coarser mesh screen, which yields fewer nymphs, thus reducing processing time, and eliminating nymphs from the younger age groups.

The first method was found to be a reliable way to determine biomass and production, but was very labor and cost intensive. The second method is reliable and quick if the age groups can be reliably separated (more on methods, see Scientific Poster).