Coherent response of lakes in Ontario, Canada to reductions in sulphur deposition: the effects of climate on sulphate concentrations

Abstract

Sulphate deposition in south-central Ontario declined between 1976 and 2000 by more than 50%, whereas lake sulphate (SO 4 2 ) concentrations decreased by, on average, only half as much. To investigate the factors that controlled this slower than expected response, the temporal patterns in lake SO 4 2 concentrations were compared with patterns in both deposition and climate, since climate has a major influence on the hydrological cycle in this part of the continent. To do this, the temporal coherence in SO 4 2 concentrations between 9 lake basins was estimated using the intraclass correlation from a repeated-measures analysis of variance and two subsets of lakes were found (six in one group, four in the other), each with lakes having synchronous patterns. One subset (4 lakes) included the 3 with the longest water replenishment times (>3.4 yr) which are expected to respond to decreases in SO 4 2 deposition more slowly. However, the average pattern reflecting the temporal changes of each of the two subsets was very similar. The response of both subsets of lakes to the decreasing SO 4 2 deposition over two decades was independent of the degree of acidification or sensitivity to acidification of the lakes. In a determination of which factors best predicted each of those two subsets SO 4 2 time series, good predictive models were produced by regional/global-scale climate indices, specifically the Southern Oscillation Index (SOI) describing the El Niño Southern Oscillation (ENSO) and the North Atlantic Oscillation Index (NAOI), as well as by SO 4 2 deposition indices. When the predictor variables were combined, models which described the long-term changes in lake SO 4 2 concentration best included the SOI, the NAOI and SO 4 2 deposition. Thus, large-scale climate factors play a major role in determining the response of aquatic systems to changes in SO 4 2 deposition, perhaps through their influence on lake and/or catchment processes that effectively delay recovery.

Long-term patterns in dissolved organic carbon in boreal lakes: the role of incident radiation, precipitation, air temperature, southern oscillation and acid deposition

“…Schiff et al, 1998;Gennings et al, 2001;Dillon et al, 2003). Total precipitation, mean daily air temperature, and mean daily total PAR were measured at two nearby meteorological field stations (Locke and de Grosbois, 1986;Gennings et al, 2001).…”

“…Total precipitation, mean daily air temperature, and mean daily total PAR were measured at two nearby meteorological field stations (Locke and de Grosbois, 1986;Gennings et al, 2001). Measurements of SO 4 deposition, described in detail in Dillon et al (2003) were made on samples of bulk deposition collected in 48 continuously open, 0.25 m 2 , Teflon-coated collectors positioned in the catchments of the lakes studied and at the field laboratory. Deposition was estimated daily at each collector site and, because all deposition collectors (and lakes) lie within a 50 km radius, all data on any day were averaged to evaluate daily deposition.…”

“…Interestingly, the rate of recovery of the lakes from acid conditions is complex. Ultimately, SO 4 deposition rates affect lake acidity but global scale climate indices, the SOI and the North Atlantic Oscillation index influence, strongly, the timing and quantity of SO 4 entering the lakes (Dillon et al, 2003;Dillon et al, 1997). No relationship between the SOI and the multi-lake average ice-free DOC pattern was found.…”

Predicting recovery of acidified freshwaters in Europe and Canada: an introduction

“…The importance of such interactions is further supported by the analyses of Dillon et al (2003a;, who carried out coherence analysis on spatial and temporal sulphate concentrations in Norwegian and Canadian lakes. There was clear evidence that although lake chemistry in both regions responds to changes in deposition, this change was influenced by large-scale climate factors, such as the Artic and North Atlantic Oscillation Indices (AOI and NAOI), and the Southern and El Niño Southern Oscillation Indices (SOI and ENSOI).…”

Modelling acidification, recovery and target loads for headwater catchments in Nova Scotia, Canada

“…These programs were designed to reduce emissions of sulphuric acid precursors to the atmosphere; as a consequence, sulphate (SO 4 2− ) deposition in Canada has decreased over the last two decades (Dillon et al, 1988;Dillon et al, 2003;Jeffries et al, 2003). Surface waters in eastern Canada have responded to decreased SO 4 2− deposition through improvements in water quality, including substantial decreases in SO 4 2− concentrations and small improvements in acid neutralizing capacity (ANC) and pH Jeffries et al, 2003).…”