Lake Ontario water quality during the 2003 and 2008 intensive field years and comparison with long-term trends

Abstract

Phosphorus loading declined between the 1970s and the 1990s, leading to oligotrophication of the offshore waters of Lake Ontario during that time period. Using lake-wide data from the intensive field years of 2003 and 2008 and from available long-term data sets on several trophic state indicators (total phosphorus [TP], soluble reactive silica [SRSi], chlorophyll a and Secchi disc transparency [SDT]), we tested the hypothesis that oligotrophication of the offshore waters of Lake Ontario has continued in the 2000s. Significant differences between 2003 and 2008 include higher spring (April) TP, SRSi, and SDT in 2008, lower summer (July–August) SDT in 2008, higher summer chlorophyll a in 2008, and lower fall (September) TP, SRSi, and chlorophyll a in 2008. The decline in SRSi from spring to summer was greater in 2008 than in 2003. Change point and regression analyses on the long-term data revealed no trend in spring TP since 1996, in summer chlorophyll a since 1994, in spring SDT since 1998, in spring SRSi or SRSi decline from spring to summer since 1999, or in summer SDT since 2001. Neither the comparison of the 2003 and 2008 surveys nor the analysis of the long-term data supported our hypothesis of continued oligotrophication of the offshore of Lake Ontario in the 2000s.

A regional analysis of trace element water chemistry with applications for reconstructing environmental life history of fishes

“…Long-term fish monitoring programs exist and have been used to evaluate impacts from physical habitat change, invasive species introductions, climate change, and the influence of harvest (McClelland et al 2012;Counihan et al 2018;Nieman et al 2021). Similarly, long-term monitoring of water quality has helped to quantify ecological impacts from land-use change, agricultural practices, and other disturbances (Holeck et al 2015;Bock et al 2023). Though long-term water quality monitoring is prevalent throughout North America, few monitoring programs document elemental concentrations.…”

Spatial extent and dissipation of the deep chlorophyll layer in Lake Ontario during the Lake Ontario lower foodweb assessment, 2003 and 2008

“…However, nutriclines are often difficult to identify in the Great Lakes because phosphorus is at such low concentrations. In the summer cruises of 2003 and 2008 for Lake Ontario, soluble reactive phosphorus (SRP) was below detection limits within the offshore SML (Gouvêa et al, 2006;Holeck et al, 2015). In 2003, dissolved phosphorus increased with depth >100 m while total phosphorus (TP) decreased with depth at Site 64 (Gouvêa et al, 2006).…”

“…The Lake Ontario Lower foodweb Assessment (LOLA) program was a joint USA/Canada effort to monitor the status of the lower foodweb in Lake Ontario in 2003 and 2008 (Holeck et al, 2008;Holeck et al, 2015;Rudstam et al, 2015). Several components including nutrients, phytoplankton, zooplankton, and the microbial foodweb were sampled.…”