Response of a Lake Michigan coastal lake to anthropogenic catchment disturbance

A paleolimnological investigation of post-European sediments in a Lake Michigan coastal lake was used to examine the response of Lower Herring Lake to anthropogenic impacts and its role as a processor of watershed inputs. We also compare the timing of this response with that of Lake Michigan to examine the role of marginal lakes as ‘early warning’ indicators of potential changes in the larger connected system and their role in buffering Lake Michigan against anthropogenic changes through biotic interactions and material trapping. Sediment geochemistry, siliceous microfossils and nutrient-related morphological changes in diatoms, identified three major trophic periods in the recent history of the lake. During deforestation and early settlement (pre-1845–1920), lake response to catchment disturbances results in localized increases in diatom abundances with minor changes in existing communities. In this early phase of disturbance, Lower Herring Lake acts as a sediment sink and a biological processor of nutrient inputs. During low-lake levels of the 1930s, the lake goes through a transitional period characterized by increased primary productivity and a major shift in diatom communities. Post-World War II (late 1940s–1989) anthropogenic disturbances push Lower Herring Lake to a new state and a permanent change in diatom community structure dominated by Cyclotella comensis . The dominance of planktonic summer diatom species associated with the deep chlorophyll maximum (DCM) is attributed to epilimnetic nutrient depletion. Declining Si:P ratios are inferred from increased sediment storage of biogenic silica and morphological changes in the silica content of Aulacoseira ambigua and Stephanodiscus niagarae . Beginning in the late 1940s, Lower Herring Lake functions as a biogeochemical processor of catchment inputs and a carbon, nutrient and silica sink. Microfossil response to increased nutrients and increased storage of biogenic silica in Lower Herring Lake and other regional embayments occur approximately 20–25 years earlier than in a nearby Lake Michigan site. Results from this study provide evidence for the role of marginal lakes and bays as nutrient buffering systems, delaying the impact of anthropogenic activities on the larger Lake Michigan system.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/43091/1/10933_2004_Article_1688.pd

A Retrospective Analysis and Comparative Study of Stony Coral Assemblages in Biscayne National Park, FL (1977-2000)

The hardbottom, patch, and bank reefs of Biscayne National Park (BNP) are among the most northern reef communities in the Florida Keys reef tract. The close proximity of BNP reefs to highly developed areas (i.e., the greater Miami metropolitan area) make them both heavily used and susceptible to a multitude of anthropogenic stresses. This study analyzes a unique 1977-1981 data set on stony-coral abundances and percent cover, collected from eight reefs in BNP, and compares this more than 25-year old data set with published data from surveys conducted from 1994-1996 and 1998-2000. In 1977-81, stony-coral cover on the eight reefs ranged between 8% and 28%, whereas coral cover reported from surveys in 1998-2000 ranged between 0.4% and 10%. Significant declines in cover of all coral species were seen at BNP reefs in the -20 years between data sets, although few changes were observed in species richness and taxonomic distinctness values. Spatial differences were observed between lagoonal patch reefs and outer bank reefs, consistent with previous reports of greater loss of coral cover on offshore reefs. Previous reports have suggested that high juvenile coral mortality due to fish predation, physical stresses, and thermal stresses have contributed to reduced cover at offshore BNP reefs