Effects of climate and atmospheric deposition on a boreal lake chemistry: A synthesis of 36 years of monitoring data

Charles Marty; Louis Duchesne; Suzanne Couture; Christian Gagnon; Daniel Houle

doi:10.1016/j.scitotenv.2020.143639

Effects of climate and atmospheric deposition on a boreal lake chemistry: A synthesis of 36 years of monitoring data

Sci Total Environ. 2021 Mar 1:758:143639. doi: 10.1016/j.scitotenv.2020.143639. Epub 2020 Nov 20.

Authors

Charles Marty¹, Louis Duchesne², Suzanne Couture³, Christian Gagnon³, Daniel Houle⁴

Affiliations

¹ Carbone boréal, Département des sciences fondamentales, 555 boulevard de l'Université, Université du Québec à Chicoutimi, Chicoutimi, QC G7H 2B1, Canada.
² Direction de la Recherche Forestière, Ministère de la Forêt, de la Faune et des Parcs, 2700 rue Einstein, Sainte-Foy, Québec G1P 3W8, Canada.
³ Science and Technology Branch, Environment Canada and Climate Change, 105 McGill St., QC, H2Y 2E7 Montreal, Canada.
⁴ Science and Technology Branch, Environment Canada and Climate Change, 105 McGill St., QC, H2Y 2E7 Montreal, Canada; Ouranos, Consortium sur la Climatologie Régionale et l'Adaptation aux Changements Climatiques, 550 Sherbrooke W, Montréal, Québec H3A 1B9, Canada. Electronic address: daniel.houle2@canada.ca.

PMID: 33248783
DOI: 10.1016/j.scitotenv.2020.143639

Abstract

Reduction in SO₄^2- and NO₃^- atmospheric deposition in the past decades has improved surface water quality in several catchments but recent studies suggest an increasing influence of climate and dissolved organic carbon (DOC). Here, we report on long-term trends in climate variables, strong acid anions and base cations concentrations in precipitation and at the lake outlet (stream) of a boreal catchment in Québec, Canada, and assess the combined effects of these trends on stream chemistry. Annual SO₄^2- and NO₃^- depositions respectively decreased by ~85% (from 23 to ~3 kg ha^-1) and ~70% (from 18 to ~5 kg ha^-1 yr^-1) from 1981 to 2016. As a response, stream SO₄^2- and Ca²⁺ concentrations decreased by 50% (from 3.9 to 1.9 mg L^-1) and ~35% (from 2.4 to 1.5 mg L^-1), respectively. Stream NO₃^- concentration decreased by ~89% (from 0.6 to 0.07 mg L^-1) mainly due to the decline in NO₃^- deposition and possibly to increased vegetation N uptake. Unexpectedly, stream alkalinity decreased, likely due to the decline in Ca²⁺ concentration and to an increase in DOC concentration. Variations in stream pH and Na⁺ concentrations were best explained by climatic changes than by changes in acid deposition, likely reflecting the effect of climate change on chemical weathering in the region. In addition, the average daily temperature between May and September had a strong influence on stream Ca²⁺ concentration in the last two decades (negative relationship), suggesting an increasing vegetation nutrient uptake caused by improved growth conditions. Overall, decreased acidic deposition resulted in a general recovery of surface water although the parallel increase in DOC concentration prevented from an increase in water alkalinity. Our data also indicate an increasing influence of climate on water chemistry at the study site, probably mediated by increasing weathering rate and vegetation nutrient uptake.

Keywords: Acid deposition; Alkalinity; Boreal watersheds; Climate; DOC; Nitrate; Sulfate.