Andrew M. Paterson

Trends in Surface Water Chemistry in Acidified Areas in Europe and North America from 1990 to 2008

Acidification of lakes and rivers is still an environmental concern despite reduced emissions of acidifying compounds. We analysed trends in surface water chemistry of 173 acid-sensitive sites from 12 regions in Europe and North America. In 11 of 12 regions, non-marine sulphate (SO4*) declined significantly between 1990 and 2008 (−15 to −59xa0%). In contrast, regional and temporal trends in nitrate were smaller and less uniform. In 11 of 12 regions, chemical recovery was demonstrated in the form of positive trends in pH and/or alkalinity and/or acid neutralising capacity (ANC). The positive trends in these indicators of chemical recovery were regionally and temporally less distinct than the decline in SO4* and tended to flatten after 1999. From an ecological perspective, the chemical quality of surface waters in acid-sensitive areas in these regions has clearly improved as a consequence of emission abatement strategies, paving the way for some biological recovery.

Global warming triggers the loss of a key Arctic refugium

We document the rapid transformation of one of the Earths last remaining Arctic refugia, a change that is being driven by global warming. In stark contrast to the amplified warming observed throughout much of the Arctic, the Hudson Bay Lowlands (HBL) of subarctic Canada has maintained cool temperatures, largely due to the counteracting effects of persistent sea ice. However, since the mid-1990s, climate of the HBL has passed a tipping point, the pace and magnitude of which is exceptional even by Arctic standards, exceeding the range of regional long-term variability. Using high-resolution, palaeolimnological records of algal remains in dated lake sediment cores, we report that, within this short period of intense warming, striking biological changes have occurred in the regions freshwater ecosystems. The delayed and intense warming in this remote region provides a natural observatory for testing ecosystem resilience under a rapidly changing climate, in the absence of direct anthropogenic influences. The environmental repercussions of this climate change are of global significance, influencing the huge store of carbon in the regions extensive peatlands, the worlds southern-most polar bear population that depends upon Hudson Bay sea ice and permafrost for survival, and native communities who rely on this landscape for sustenance.

Marked recent increases of colonial scaled chrysophytes in boreal lakes: implications for the management of taste and odour events

SUMMARY 1. Lake managers suspect that taste and odour-causing algal blooms are increasing in frequency and intensity, although long-term monitoring records are scarce, and a number of critical scientific and management questions remain unanswered. 2. In nutrient-poor lakes and reservoirs, these events are caused primarily by sporadic outbreaks of some chrysophyte algae, which leave identifiable markers in lake sediments. We examine the siliceous remains of these organisms in more than fifty boreal lakes at broad temporal and spatial scales. 3. Colonial scaled chrysophytes, including the taste and odour-causing Synura petersenii, have increased markedly in more that 90% of the lakes examined since pre-industrial times. 4. Detailed stratigraphic analyses of two lakes show a rise in the abundance of colonial taxa in the 1930s to 1950s, with a sharp increase over the past two decades. 5. An examination of biogenic silica and biological ratios in Crosson Lake, Ontario, Canada, indicate that these changes represent true increases in the absolute abundance of colonial chrysophytes. 6. Rapid increases over the past two decades indicate that these trends are the result of one or more anthropogenic stressors that are operating at a broad, regional scale.

Diatom and chrysophyte algal response to long-term PCB contamination from a point-source in Northern Labrador, Canada

The long-term response of diatom and chrysophyte communities to local PCB contamination was examined in an impacted and referencelake in northern Labrador. Beginning in the late 1950s, lake Saglek-2 (SK-2) received direct inputs of the contaminant in runoff, leaving a record of rising PCB concentrations in lake sediments. An examination of sediment samples spanning the past∼ 150 yr revealed chrysophyte and diatom assemblages characteristic of clear, slightly acidic, oligotrophic lakes, butsurprisingly little change in either community was observed through time. The lack of response may be explained by severalfactors. For example, elevated PCB concentrations in lake sediments may not reflect bioavailable concentrations in lakewater. Therefore, realized concentrations may be too low to exhibit detrimental effects in phytoplankton communities. Our findings do, however, have important implications for studies ofclimate change in circumpolar regions. First, we provide additional evidence that climatic change has been minimal in northern Labrador, in contrast to changes observed in other Arctic and sub-Arctic regions. Second, our findings support thenotion that recent, marked changes in species composition observed in other Arctic lakes are the result of recent climatechange and not caused by the contamination of lakes from the long-range transport of pollutants.

Comparing different methods of calculating volume-weighted hypolimnetic oxygen (VWHO) in lakes

Abstract.In the limnological literature there is no standard method for calculating hypolimnetic volumes using temperature profile data. Consequently, calculations of hypolimnetic dissolved oxygen concentrations differ based on the method chosen. This study examined the differences in calculations of volume-weighted hypolimnetic oxygen (VWHO) concentrations based on different methodologies and profile sampling resolution. Comparisons of VWHO values indicated that differences among methods were greatest in smaller lakes with less hypolimnetic volume. VWHO calculation methodology based on 1 m resolution for profile sampling, where the hypolimnion is defined as the strata below the lower limit of the thermocline (temperature change < 1°C m−1), produced lower VWHO values compared to other methodologies using coarser (2m) sample resolution and hypolimnetic volume determination based on visually inspecting inflection points of a temperature profile. Differences in calculated VWHO were surprisingly large, highlighting the need for researchers to standardize methodology and sampling resolution used in VWHO calculations. VWHO calculation using a 1 m sampling resolution that defines the hypolimnion as the lower limit of the thermocline is the preferred methodology when VWHO is used as a water quality parameter in assessing the habitat of lake biota sensitive to low VWHO.

The importance of model choice on pH inferences from scaled chrysophyte assemblages in North America

The selection of a reliable inference model is a crucial step in developing ecologically sound reconstructions of environmental variables in the past. We compared intra- and inter-regional regression-based models, and an inter-regional Modern Analogue Technique (MAT) model in their ability to infer lakewater pH from scaled chrysophyte assemblages. The performance of each model was assessed by examining cross-validated coefficients of determination and prediction errors, and through reconstructing the pH of ≈50 modern and fossil samples in south-central Ontario, Canada. Using the intra- and inter-regional data sets, we found little difference in the ability of the regression-based models to infer present-day pH. Partial Least Squares (PLS) regression, Weighted Averaging (WA), and Weighted Averaging Partial Least Squares (WA-PLS) inference models showed similar values for jack-knifed coefficients of determination (r2jack), root mean squared errors of prediction (RMSEPjack), and mean and maximum biases. Based on an analogue matching approach, the inferred values from 48 fossil sediment samples suggested that the intra-regional model did not provide reliable reconstructions for approximately half of the fossil samples. However, inferences from the inter-regional MAT and regression-based models were found to have appropriate analogues and thus considered to be more reliable.

Assessment of benthic algal biomonitoring protocols to evaluate effects of shoreline development on the nearshore zone of Precambrian Shield lakes in Ontario

Abstract We assessed the ability of benthic algal biomonitoring protocols to detect effects of differences in shoreline development in the littoral zone of oligo- to mesotrophic Precambrian Shield lakes in south-central Ontario. The study sites (n = 28 in Aug 2006, n = 29 in Aug 2007) spanned a broad gradient of shoreline development (e.g., intact forest, cottages, marinas) but a modest gradient of nutrient concentration (3–22 μg/L total phosphorus). Each site was sampled for water chemistry (nutrients, ions, metals, pH) and 5 levels of benthic algal bioassessment, which differed in the amount of time, resources and expertise required. Level 1 involved visual descriptions of algal cover; Level 2 involved biomass measurements (chlorophyll a, ash-free dry mass); Level 3 involved enumeration of algae to a coarse taxonomic level (i.e., the major algal classes); Level 4 involved quantification of photosynthetic pigments by high-performance liquid chromatography; and Level 5 involved high taxonomic resolution enumeration of diatom communities. Multi- and univariate numerical analyses (e.g., PCA, ANOSIM, ANOVA) were used to assess relationships between measurements of shoreline development, water chemistry, and benthic algal metrics. Results identified that Level 5 was the most sensitive to track differences in the shoreline development among sites. For lakes on the Precambrian Shield, we suggest that benthic algal biomonitoring programs focus on Level 5, despite the higher requirements of time, technical skill, and training. We further recommend that the other levels of bioassessment be explored further in other regions where broader gradients of shoreline development and lake trophic status exist. [Supplemental materials are available for this article. Go to the publishers online edition of Lake and Reservoir Management to view the supplemental file.]

Long-term stability of cladoceran assemblages in small, shallow, Canadian Shield lakes experiencing marked calcium declines

A greater appreciation of biotic responses to environmental changes is warranted in small, shallow lakes because of the high number of these habitats, and their unique contributions to regional biodiversity. Furthermore, recent water chemistry monitoring data show that shallow lakes in Ontario are sensitive and have responded significantly to environmental stressors such as acid deposition and lake water calcium decline. Here, we use paleoecological techniques to examine cladoceran assemblages in modern and pre-industrial sediments of 30 shallow lakes to determine the key environmental gradients that influence present-day assemblages, and to assess how assemblage structure has changed since pre-industrial times (pre-1850s). Redundancy analysis of present-day cladoceran assemblages and key environmental variables identified lake surface area and Secchi depth as significant predictors of assemblage composition. In our data set, Secchi depth was not correlated to water clarity but rather to macrophyte cover, suggesting that cladoceran assemblages were highly influenced by habitat structure. In contrast to nearby, deeper lakes, where pelagic cladoceran taxa have changed significantly in relative abundance over time, cladoceran assemblages in present-day and pre-industrial sediments of shallow lakes did not differ significantly in composition. While the specific reasons for this muted response are unknown, we hypothesize that: (1) littoral taxa may be less sensitive to low Ca concentrations, or ecological thresholds have not yet been crossed or are lower for littoral taxa; (2) calcium availability may vary spatially within shallow lakes, and this is not captured in a single measure of water chemistry from the centre of the lake; and/or (3) habitat structure is more important than water chemistry as a predictor of assemblage composition in these study lakes, and this has not changed significantly over time.

A paleolimnological assessment of the effects of logging on two lakes in northwestern Ontario, Canada

Most of the recent srudies that have examined the effects of forest harvesting on aquatic ecosystems have focussed on stream environments. It has been shown that these disturbances may alter water quantiry through a disruption of hydrological regimes (HARTMAN & ScRJVENER 1990, MILLER et al. 1997), and water qualiry through elevated inputs of nutrients and suspended solids, and changes to mixing regimes (NICOLSON 1975, PATRIC 1980, KRAusE 1982, FELLER & KIMMINS 1984, LYNCH & CüRBETT 1990, KEENAN & K!MMINS 1993). Considerably fewer studies have examined the ecological effects of timber management on lakes (see reviews in KEENAN & KlMMINS 1993, MILLER et al. 1997).