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

Abstract

Both lake-specific (e.g. pH) and regional (e.g. precipitation) factors affect DOC concentration and pattern. Using annual DOC concentration in nine boreal lakes in the ice-free season, the potential influences of five regional factors, air temperature, precipitation, SO 4 deposition, solar radiation (photosynthetically active radiation, or PAR) and the southern oscillation index (SOI) have been explored through multiple regression. Mean solar radiation, winter precipitation and summer precipitation explained 59% of the variation in the mean DOC concentration (F 3,17 = 8.29, p = 0.0013). Solar radiation and winter precipitation were correlated, negatively, while summer precipitation was correlated, positively, with DOC concentration. Because these relationships were based on only 21 years of data (1978 to 1998), the significance of the parameters in the regression model was evaluated with a randomisation test. This re-analysis indicated that summer precipitation did not contribute significantly to the regression model (p rand = 0.183). The final multiple regression explained 50% of the variation in DOC (F 2,18 = 9.33, p rand = 0.002) based on solar radiation and winter precipitation. These results suggest that solar radiation and winter precipitation have a significant role in determining long-term DOC concentration in boreal lakes.

Long-term Trends of Organic Carbon Concentrations in Freshwaters: Strengths and Weaknesses of Existing Evidence

“…In practice, monotonicity as such has rarely been statistically tested and data are generally assumed to be monotonic. However, cyclical patterns have been observed by some authors [34,35,46,56,65,77] either by looking at the graphical representation of the data or when applying smoothing methods such as the calculation of moving averages (also called running averages). Although not exempt from problems [105], calculation of moving averages provides a robust description of a data pattern and, although it has been seldom applied to OC data series, where it has been, cyclical patterns have appeared.…”

“…Another method, used only by Dillon and co-workers [35,[43][44][45]49,56] in Canadian lakes employs colorimetry with phenolphthalein as a detection method after UV oxidation of OC to CO 2 in acidic persulfate media. How this method compares with the usual infrared detection of CO 2 in WCO and HTC methods is unknown.…”

“…Data have sometimes been normalized using Z-scores [14,34,35,43,46]. Z-scores are calculated by subtracting from all values the mean over the period under study and dividing by the standard deviation.…”

Long-term trends of chemical and modelled photochemical parameters in four Alpine lakes

“…Variations in exposure of surface waters to sunlight may be due to changes in the duration of the ice-cover period that, however, do not apply to Garda which never freezes over. Moreover, a decrease of the ice-cover duration due to climate warming should increase sunlight exposure and might cause a DOC decrease through photomineralisation of organic matter (Hudson et al, 2003;Zhang et al, 2010). In contrast, the observed increase in DOC concentration in both lakes could be linked to higher runoff.…”

“…The DOC content of lake water is largely influenced by runoff, which in turn may be affected by climate change (Hudson et al, 2003;Zhang et al, 2010). Changes in DOC concentration are important because they affect the penetration of sunlight (and most notably of UV radiation) into the water column (Laurion et al, 2000), as well as several other processes including photochemical reactions (Schindler, 1997).…”