Biomonitoring using diatoms and paleolimnology in the western Great Lakes national parks

Edlund, Mark; Ramstack, Joy; Engstrom, Dan; Elias, Joan; Lafrancois, Brenda

A biomonitoring approach was developed for the Great Lakes Network (GLKN) parks to analyze diatom communities in lake, river, and lagoon sediments in an inventory and monitoring framework. We used combined analysis of sediment cores in the GLKN park lakes with repeated sampling of modern sedimented diatom communities and water quality monitoring to determine historical biological and water quality change, modern biological change, and the potential drivers of change. Thirteen sediment cores from GLKN lakes were analyzed for changes in geochemistry and diatom communities from ca. 1800 A.D. through the 2000s A.D. Surface sediments were collected from more than 60 lakes in the GLKN parks in conjunction with water quality monitoring to document the modern diatom assemblages and determine the abiotic gradients that independently control diatom abundance and distribution in the GLKN parks. Weighted averaging models were developed that use sediment diatom assemblages to quantitatively estimate pH, total phosphorus, and conductivity. Biological change was estimated over two time periods in the sediment cores using the squared chord distance between pre-Euro-American settlement and modern diatom communities and between diatom communities deposited at the time of each park's formation and modern diatom communities. Last, surface sediment diatom communities in two parks were resampled in 2008 and 2009 to determine the amount of diatom community change since 2005.Results show that most of the GLKN park lakes that had long sediment cores analyzed did not show significant change in diatom-inferred water quality parameters during the last 200 years. In contrast, most lakes showed periods of biological change based on diatom microfossil analysis. Lakes that showed significant changes in diatom-inferred water quality were primarily located in SLBE and included changes in conductivity, and pH. The timing of the water quality shifts at SLBE was consistent with the development of farming in the region and may be related to hydrological changes associated with land clearance. The first biological shifts recorded in cores from GLKN lakes took place from the 1870s through the 1930s coincident with Euro-American settlement in the region and in most lakes the shifts represented the largest diatom community change in the last 200 years. Concomitant with biological shifts in the GLKN lakes were geochemical shifts, notably increased sedimentation rates and inorganic content of many cores. These changes were likely a result of enhanced erosion due to land clearance, changes in runoff, and potentially changes in lake levels.In most lakes we also resolved a secondary biological shift in the sediment cores that took place as early as the 1950s and as late at the 2000s, with many lakes showing change from the 1970s to 1980s. The biological changes cannot be easily ascribed to known land use changes, although some lakes exhibited their secondary shifts concurrent with park formation. Regardless, in no case did the GLKN lakes return to a reference (pre-Euro-American) biological community while under NPS management and protection. Alternatively, the secondary shifts in diatom communities may be related to climate change. Because these lakes are spread across a wide geographic region, and are in relatively pristine and protected areas, climate may be driving observed ecological changes in the lakes. Floristic change was calculated between repeat surface samples from PIRO (2008) and SLBE (2009) lakes by comparing to surface samples collected in 2005 from the same lakes. Many of the lakes showed very large and unexpected floristic changes between 2005 and 2008/2009. Although these changes may represent unprecedented recent change in the GLKN lakes, we also suggest that lake-specific sampling approaches should be implemented to ensure that 3-5 years of sedimented diatom communities are collected during future repeat surface sediment sampling.

Biomonitoring using diatoms and paleolimnology in the western Great Lakes national parks

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