Re-browning of Sudbury (Ontario, Canada) lakes now approaches pre-acid deposition lake-water dissolved organic carbon levels

Carsten Meyer-Jacob; Andrew L Labaj; Andrew M Paterson; Brie A Edwards; Wendel Bill Keller; Brian F Cumming; John P Smol

doi:10.1016/j.scitotenv.2020.138347

Re-browning of Sudbury (Ontario, Canada) lakes now approaches pre-acid deposition lake-water dissolved organic carbon levels

Sci Total Environ. 2020 Jul 10:725:138347. doi: 10.1016/j.scitotenv.2020.138347. Epub 2020 Apr 1.

Authors

Carsten Meyer-Jacob¹, Andrew L Labaj², Andrew M Paterson³, Brie A Edwards⁴, Wendel Bill Keller⁵, Brian F Cumming², John P Smol²

Affiliations

¹ Paleoecological Environmental Assessment and Research Lab, Department of Biology, Queen's University, Kingston, ON K7L 3N6, Canada; Department of Ecology and Environmental Science, Umeå University, 90187 Umeå, Sweden. Electronic address: carsten.meyerjacob@gmail.com.
² Paleoecological Environmental Assessment and Research Lab, Department of Biology, Queen's University, Kingston, ON K7L 3N6, Canada.
³ Dorset Environmental Science Centre, Ontario Ministry of the Environment, Conservation and Parks, Dorset, ON P0A 1E0, Canada.
⁴ Ontario Ministry of the Environment, Conservation and Parks, Cooperative Freshwater Ecology Unit, Vale Living with Lakes Centre, Laurentian University, Sudbury, ON P3E 2C6, Canada.
⁵ Cooperative Freshwater Ecology Unit, Vale Living with Lakes Centre, Laurentian University, Sudbury, ON P3E 2C6, Canada.

PMID: 32304963
DOI: 10.1016/j.scitotenv.2020.138347

Abstract

Since the implementation of large-scale lake monitoring in the ~1980s, water color and dissolved organic carbon (DOC) concentrations have increased in many northern lakes (i.e., lake browning), impacting the functioning of aquatic ecosystems. In regions that formerly experienced high levels of acid deposition, this browning trend has been largely attributed to the recovery from the impacts of past acid deposition. However, the extent to which DOC levels have now returned to naturally higher, pre-industrial conditions is still poorly understood. In this study, we assessed whether DOC levels are still influenced by acid deposition in lakes near Sudbury, Ontario, a region that has been heavily affected by sulfur dioxide emissions from local metal smelting during the 20th century. We analyzed water chemistry monitoring data (1981-2018), together with comparisons between modern and pre-industrial DOC levels inferred from sediment spectroscopy, for 51 acid-sensitive and 24 buffered reference lakes across the Sudbury landscape. Since 1981, DOC concentrations doubled in acid-sensitive lakes, with a mean increase of +1.6 mg/L, whereas in more buffered reference lakes, mean DOC levels increased by only 0.8 mg/L. Similarly, sediment-inferred DOC trends indicate that current DOC levels are, on average, ~22% below pre-industrial levels in acid sensitive systems compared to only ~10% in buffered lakes. Weakening correlations between DOC and acidification-related water chemistry variables (e.g., pH, alkalinity, metals) further indicate a diminishing influence of acid deposition on DOC in Sudbury lakes. These results highlight the strong impact that acid deposition has historically had on lake-water DOC dynamics in this region, but also suggest that DOC levels are approaching natural baseline levels in less acid-sensitive lakes, and that other drivers, such as changes in climate or vegetation cover, are now becoming the dominant controls on changes in DOC concentrations.

Keywords: Atmospheric acid deposition; Carbon cycling; Climate change; Dissolved organic carbon (DOC); Paleolimnology; Water quality.