A Comparison of Sampling Protocols to Estimate Species Composition, Percent Cover, and Biomass of Macrophytes in Chief Lake, Michigan

Abstract

Macrophytes are an important component of aquatic ecosystems and affect lake chemistry, water quality, and distributions and interactions of higher trophic levels. Three methods used for assessing macrophyte biomass or percent cover in Michigan lakes were compared in Chief Lake, Manistee County, Michigan. The first method assesses biomass from transects, the second method uses hydroacoustics to obtain results on percent cover, biomass, and plant height, and the third determines percent cover from visual estimations. The first two methods are used by the Michigan Department of Natural Resources (DNR) and the third is used by the Department of Environmental Quality (DEQ). Species abundances and the number of species each method found in total and at each sampling site were compared. Najas was the dominant species in the lake and represented 85.9% of the total plant biomass measured by the DNR and 53.7% of the plant cover estimated by the DEQ. The DNR Method found 28 species to the 20 species found by the DEQ Method. However, no significant difference was detected in the number of species found at each sampling site. Because the DNR Method measures biomass and the DEQ Method records percent cover, a correlation was sought between biomass and percent cover ranking. No significant correlation was found. A comparison of percent covers recorded for all three methods was made. This was possible due to an application of the DEQ visual estimation technique along DNR transects. The DEQ Method found 71.3% cover, the DNR Method found 74.0% cover, and the Hydroacoustic Method recorded 74.2% macrophyte cover in Chief Lake. The comparisons resulted in similar percent covers for all three methods, although a difference was found when comparing the percent cover from the Hydroacoustic Method in only the area covered by the DEQ to the DEQ results. Finally, the possibility of reducing sample sizes of each 2 method was considered. All methods could undergo substantial reductions in sample sizes and still obtain similar total percent cover or biomass results. While the data appears to show that the DEQ percent cover index can be applied to DNR transects and make the methods relatable in the future, other information suggests that these results are a fluke. Another method for surveying macrophytes, used by US Geological Survey’s Long Term Monitoring Program is suggested.