Assessing shifts in diatom communities in eastern Ontario recreational lakes in relation to land-use and climatic changes over the past ~ 150 years using a top–bottom paleolimnological approach
摘要
Eastern Ontario, Canada, is a lake-rich, rural region, located over the Precambrian Shield or Paleozoic dolomite and limestone bedrock. These lakes are typically nutrient-limited with total phosphorus (TP) less than 20 µg L−1, and serve as the primary tourist attraction, contributing substantially to the local economy of this region. However, in recent years, residents have become concerned about the perceived increase in nuisance algal blooms. A spatial analysis was conducted to determine if present-day TP concentrations were influenced by modern land-use patterns and this analysis showed that percentage of croplands and wetlands in nearshore riparian buffer zones (300 m) was positively correlated with present-day TP concentrations of the lakes. Due to the lack of long-term water quality monitoring data little information exists on pre-impact conditions and water quality trends in these lakes. To address this gap, a top–bottom paleolimnological approach was used to examine diatom community shifts in thirty-five oligo-mesotrophic lakes (TP 5 –19 µg L−1) located within the Mississippi River and Rideau River watersheds in eastern Ontario. Generally, the relative abundance of benthic taxa (e.g. Staurosirella pinnata, Pseudostaurosira brevistriata, Staurosira construens, Gogorevia exilis) has decreased, while planktonic taxa (e.g. Pantocsekiella comensis, Asterionella formosa, Fragilaria crotonensis) has increased. Tychoplanktonic Aulacoseira ambigua has decreased in relative abundance at oligotrophic lakes (TP 5 – 10 µg L−1) while it has increased in mesotrophic lakes (TP 11 – 19 µg L−1). The diatom-inferred TP (DI-TP) has decreased across most study lakes. The diatom assemblage changes across the 35 lakes suggest that climate-mediated changes to lake-thermal properties (e.g. long ice-free season, longer and stronger thermal stratification) are influencing the recent assemblage composition. At the landscape level, climate-mediated changes are structuring assemblage composition in most study lakes where nutrient levels have been decreasing. However, in some mesotrophic lakes, local land-use changes and an increase in TP concentrations may be influencing recent algal assemblages.