Long-term changes in the chemistry of a soft-water lake under changing acid deposition rates and climate fluctuations

Limnology & Oceanography

et al. 2003

Chemical recovery of many acidified lakes in North America has been delayed or reversed as a result of interactions between climatic variability (alterations between drought and nondrought periods) and previously deposited acids stored in wetlands, but effects of this wetland-mediated reacidification phenomenon on aquatic biota remain unknown. We compare changes in diatom assemblages in 200-yr-long sediment cores from two lakes with similar basin characteristics but different wetland area (4.4% of catchment at Chub Lake, 0% at Blue Chalk Lake) to evaluate the role of wetland-mediated interactions among acid deposition and climatic variability on algal communities in acid-sensitive lakes. Diatom assemblages were significantly more variable in Chub Lake than in Blue Chalk Lake. Variance partitioning analysis of approximately annually resolved sedimentary diatom analyses identified that unique effects of water chemistry, independent of acid deposition and climatic factors, accounted for the greatest amount of variation (25%) in diatom assemblages at Chub Lake. Acid deposition (24%) and climatic factors (22%) accounted for similar, significant amounts of variation in diatom communities. Complex interactions among all three factors, which are attributable to wetland-mediated drought-induced reacidification, explained an additional 10% of the variation in diatoms at Chub Lake but only 1% at Blue Chalk Lake. Droughtrelated reacidification effects on water chemistry might thus cause important effects on algal communities in acidsensitive lakes with modest wetland coverage, but not in lakes without wetlands.Despite the implementation of sulfur emission control programs in North America and a 60% decrease in bulk sulfate deposition in eastern Ontario since the late 1970s (Clair et al. 1995;Schindler 1998), recent evidence has shown that chemical recovery of acidified lakes has been delayed or reversed as a result of interactions between climatic variability and previously deposited acids stored in wetland(s) (Clair et al. 1995; Schindler et al. 1997;Eimers and Dillon 2002). This delay in recovery has been well documented in several acid-sensitive Precambrian Shield lakes in Ontario, where the anticipated recovery of pH, dissolved organic carbon concentrations ([DOC]), and [sulfate] has not occurred (Dillon et

mentioning

confidence: 94%

Effects of drought‐induced acidification on diatom communities in acid‐sensitive Ontario lakes

Faulkenham

Hall

Limnology & Oceanography

et al. 2003

“…Changes in SO 4 2 , NO 3 and NH 4 + deposition in the study area for parts of the present investigation period have been discussed in Dillon et al (1988), Dillon et al (1997), Dillon and Evans (2001), Eimers and Dillon (2002) and are summarised briefly here. Deposition from 1976 to 2000 is shown in Fig.…”

Section: Deposition Trendsmentioning

confidence: 99%

“…In North America, Dillon et al (1997) and Dillon and Evans (2001) reported a connection between S redox reactions and ENSO episodes. They found that elevated stream SO 4 2 concentrations and export rates in south-central Ontario occurred in the autumn of years with prolonged severe drought, and that these droughts occurred in the years following strong El Niño events, i.e.…”

Section: Introductionmentioning

confidence: 99%

“…However, the reductions in surface water SO 4 2 concentrations have often been much less than those anticipated, following the reduction in atmospheric S deposition (Driscoll et al, 1995;Dillon et al, 1997;Dillon and Evans, 2001;Löfgren et al, 2001). Furthermore, other important measures of chemical recovery, namely increases in lake pH and acid neutralising capacity, ANC, have provided conflicting evidence.…”

Section: Introductionmentioning

confidence: 99%

“…In a few cases (Kahl et al, 1993;Webster and Brezonik, 1995;Stoddard et al, 1998), they have provided limited evidence of chemical recovery but in many others (Clair et al, 1995;Houle et al, 1997;Dillon et al, 1997), there has been little or no change in these parameters despite declining S deposition. The apparent lack of proportional response in lake SO 4 2 concentrations in certain areas has been attributed to several mechanisms, including 1) re-oxidation of reduced S in the lakes catchments followed by increasing flux to the lakes (Dillon and LaZerte, 1992;Schindler et al, 1996;Dillon et al, 1997;Dillon and Evans, 2001), 2) desorption of previously adsorbed SO 4 2 in the soil (Driscoll et al, 1995;Löfgren et al, 2001;Alewell, 2001;Wilander, 2001;Hill et al, 2002) and/or 3) mineralisation and oxidation of organically bound S (Löfgren et al, 2001;Mitchell et al, 2001) from the catchments.…”

Section: Introductionmentioning

confidence: 99%

See 2 more Smart Citations

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

Hydrol. Earth Syst. Sci.

Somers

Findeis

et al. 2003

Self Cite

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 (18‐year) changes in sulphate concentrations in two Ontario headwater lakes and their inflows in response to decreasing deposition and climate variations

Eimers

Watmough

2004

Hydrological Processes

Self Cite

Abstract:Sulphate concentrations in two headwater lakes and their major inflows were evaluated over an 18 year period (1980-81 to 1997-98) during which time sulphate bulk deposition declined by approximately 40%. The two lake catchments represent either end of the spectrum of acid sensitivity in the Muskoka-Haliburton region of Ontario. Between 1980 and 1998, sulphate concentrations in Harp and Plastic Lakes decreased, but the decrease was much less than expected (28% and 21% respectively) given the magnitude of change in deposition. Sulphate export in streams draining into the lakes greatly exceeded sulphate input to catchments in most years, which quantitatively explains the response of lake-sulphate concentration. Furthermore, temporal patterns in mean annual sulphate concentrations in streams were similar, and appeared to be related to climate factors. Specifically, catchment export of sulphate was greater and stream-sulphate concentrations were higher in years that had warm, dry summers, i.e. when streamflow in many catchments ceased for up to several weeks. Increased sulphate export from catchments resulted in higher sulphate concentrations in lakes, but the response of lake sulphate was not as immediate or dramatic as the response of stream sulphate to changes in catchment dryness. Factors that affect sulphate retention or export in catchments exert a strong influence on sulphate concentrations in lakes and streams and need to be considered when evaluating the response of surface water chemistry to changes in sulphate deposition.