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AbstractLaird KR, Li S, Gushulak CAC, Moir KE, Wang Y, Leavitt PR, Cumming BF. 2023. Influence of cultural eutrophication, climate, and landscape connectivity on 3 Kawartha lakes (Ontario, Canada) since the early 1800s . Lake Reserv Manage. 39:120–140.Paleolimnological analyses of 3 lakes within the Trent-Severn Waterway (TSW) were examined to evaluate the role of regional land-use practices (forestry and agriculture), climate change, and landscape position on cultural eutrophication and lake response over the past ∼200 yr. The lakes were selected to represent lake position along the chain of lakes of the TSW; these 3 lakes vary in lake-water conditions from a lower nutrient headwater lake (Cameron Lake) to more nutrient-rich sites (Pigeon and Stony lakes) downstream. Diatom-inferred total phosphorus (TP) concentrations estimate that all lakes had TP levels of ∼15 µg/L in the 1700s, which increased to ∼20–30 µg/L in the 1800s and 1900s. Significant changes in diatom and Cladocera assemblages circa the 1830s are consistent with increased water levels and elevated phosphorus conditions associated with the intensification of forest harvest, agriculture, and development of the TSW. Diatom-inferred TP levels varied among lakes since the early 1900s, declining in Cameron Lake, increasing in Pigeon Lake, and stabilizing in Stony Lake, reflective of landscape position, degree of water inflow from the northern forested regions, and responsiveness of basins to point-source nutrient reductions and climate change. Timing of changes in TP, and changes in planktonic community composition varied among lakes. Lake production (as pigments) increased coherently in 2 lakes over the past ∼20 yr, and modern algal composition (diatoms and pigments) are lake specific and unique in comparison to the last ∼200 yr, likely reflecting combined effects of climate change and changes in nutrient loading.

An annually laminated succession in Crawford Lake, Ontario, Canada is proposed for the Global boundary Stratotype Section and Point (GSSP) to define the Anthropocene as a series/epoch with a base dated at 1950 CE. Varve couplets of organic matter capped by calcite precipitated each summer in alkaline surface waters reflect environmental change at global to local scales. Spheroidal carbonaceous particles and nitrogen isotopes record an increase in fossil fuel combustion in the early 1950s, coinciding with early fallout from nuclear and thermonuclear testing – 239+240Pu and 14C:12C, the latter more than compensating for the effects of old carbon in this dolomitic basin. Rapid industrial expansion in the North American Great Lakes region led to enhanced leaching of terrigenous elements by acid precipitation during the Great Acceleration, and calcite precipitation was reduced, producing thin calcite laminae around the GSSP that is marked by a sharp decline in elm pollen (Dutch Elm disease). The lack of bioturbation in well-oxygenated bottom waters, supported by the absence of fossil pigments from obligately anaerobic purple sulfur bacteria, is attributed to elevated salinities and high alkalinity below the chemocline. This aerobic depositional environment, highly unusual in a meromictic lake, inhibits the mobilization of Pu, the proposed primary stratigraphic guide for the Anthropocene.

AbstractStager JC, Wiltse B, Cumming BF, Holsen TM, Stetler J, Laxson C, Marcillo CE, Charles DF. 2019. A novel ecological state at Bear Pond (Adirondack Mountains, NY, USA) following acidification and partial recovery. Lake Reserv Manage. 35:208–223.The pH of precipitation in the northeastern United States has risen as industrial sulfur and nitrogen oxide emissions have declined following amendment of the Clean Air Act in 1990, but the effects of this change on the region's lakes are not yet fully documented. Here we use the siliceous remains of diatoms and chrysophyte algae in a sediment core from Bear Pond (Adirondack State Park, NY), which acidified during the 20thcentury, to reconstruct pH variability during the last 2 centuries, evaluate the extent to which the lake has recovered from acidification, and determine the timing of that reversal to help identify its causes. Inferred pH declined erratically from a high of 6.4 during the 1860s to 5.7–5.9 during the 1930s, then decreased to the 4.9–5.4 range by 1995–2010. After 2010, inferred pH rose and remained within the 5.4–5.6 range following an abrupt rise in the pH of regional precipitation. Although the acidification trend at Bear Pond has now reversed, the lake ecosystem has not returned to its pre-impact condition. Distinctive members of the pre-acidification diatom community are still absent, chrysophytes have become unusually abundant, and water clarity (Secchi depth) has decreased by about half. Furthermore, the original fish community was lost due to stocking and piscicide treatment in 1958, and high concentrations of toxaphene residues from the piscicide are present in the sediments. Full ecological restoration of formerly acidic lakes such as Bear Pond may be unlikely due to complicating factors such as climate change and fisheries management practices.

AbstractSimmatis B, Jeziorski A, Zemanek A, Selbie DT, Hyatt K, Fryer JK, Cumming BF, Smol JP. 2018. Long-term reconstruction of deep-water oxygen conditions in Osoyoos Lake: implications for Okanagan River sockeye salmon. Lake Reserve Manage. 34:392–400.Osoyoos Lake is the primary nursery lake supporting sockeye salmon (Onchorhynchus nerka) originating from the Okanagan River system in south-central British Columbia, Canada. By the early 1960s, Osoyoos Lake had experienced significant cultural eutrophication related to rapid human development of the watershed, increasing total phosphorus concentrations, and frequent algal blooms. Concern exists regarding recent (post-1990s) declines in hypolimnetic oxygen concentrations and the potential degradation of salmon habitat in this multi-basin lake. However, reliable observations are largely unavailable for oxygen conditions prior to the mid-1990s. We reconstructed late-summer volume-weighted hypolimnetic oxygen (VWHO) concentrations in Osoyoos Lake from the late 1800s to 2009 by examining past chironomid (Diptera: Chironomidae) subfossil assemblages from 210Pb-dated lake sediment cores. Chironomid-inferred VWHO revealed only slight variations since the late 1800s (mean values for the north and south basins are 4.4 and 2.9 mg/L, respectively), with seemingly little response to the cultural eutrophication of the mid-20th century. The chironomid-inferred VWHO trends suggest that the current management target of 5.8 mg/L dissolved oxygen for both basins of Osoyoos Lake may require revision to better reflect reference conditions and natural seasonal anoxia.

Sediment cores comprised of sediments deposited during the last 40–100 years were retrieved from two reservoirs in the recently populated Dry Zone of Sri Lanka. Both cores are initially dominated by littoral cladoceran taxa and undergo a pronounced change to the pelagic Bosminopsis dietersi, in the mid 1950s in Nuwarawewa reservoir, and in the early 1980s in Kalawewa reservoir. The correlations between human population and the accumulation rates of cladoceran remains in the sediments are strong and significant. An increase in Cladocera production is consistent with agricultural development and human settlement. Government documents reveal that after the 1950s, the human population around Nuwarawewa increased exponentially, forest cover decreased exponentially and crop production increased as a result of a large-scale human resettlement program. This resettlement was facilitated by canal renovations that resulted in enhanced water flow to the reservoirs. Similar changes occurred around Kalawewa, but increases in the human population did not occur until 1965, and large changes in forest cover and agricultural production did not occur until 1975. Observed increases in pelagic Cladocera in both reservoirs suggest increases in both water level and nutrients which are consistent with the timing of watershed modifications that would promote higher water levels and nutrients.

AbstractTo determine pre-disturbance limnological conditions, evaluate the impact of environmental stressors (surface water acidification, nutrient inputs, climate change, and winter deicing salt), and set realistic recovery targets for lake management strategies, a rapid assessment paleolimnological approach was used to determine the amount (and likely causes) of environmental changes over the past ∼100–150 years in 51 urban lakes from Halifax, Nova Scotia (Canada). Diatom assemblages from lake sediment cores were used with “top” (recently deposited, surface) samples being matched to measured limnological conditions, and “bottom” (generally from >15 cm deep) samples used to infer pre-disturbance limnological conditions such as pH, total phosphorus (TP), specific conductance, and shifts due to changing climatic conditions. Environmental change was assessed by calculating the metric of change in species composition between present-day and pre-disturbance diatom assemblages, and inferences from quantitative estimates of diatom-inferred pH, specific conductance, and TP. All 51 study lakes have experienced floristic changes in diatom species composition since pre-disturbance times, but different environmental stressors were implicated: 8 of the 51 lakes underwent significant (i.e., >2 times the root mean-squared error [2X RMSE] of the inference model) decreases in diatom-inferred pH; 8 lakes had significant increases in diatom-inferred TP; and 19 otherwise relatively pristine lakes had increases in planktonic taxa consistent with observations linked to changes in lake seasonality and limnological changes most closely linked to climate warming in Nova Scotia and other regions. The remaining 16 lakes did not have large and consistent changes in diatom flora or changes in diatom-inferred TP or pH >2X RMSE of the prediction of the models. Lake-specific factors were related to these inferences, and the lakes that acidified were mainly the currently most acidic sites, whereas those that experienced issues related to eutrophication were generally among the most alkaline sites. Of our 51 lakes, 22 (including some experiencing pH, TP, or showing floristic changes linked to climate changes) had increases in measured conductivity (1980–2002) and, correspondingly, increased relative abundances of halophilic diatom taxa. These lakes, often with catchments containing high surface areas of impervious surfaces, are examples of a trend of increasing salinity in northeastern North American lakes likely related to winter application of deicing (road) salt. The application of this paleolimnological approach enabled us to identify which lakes have undergone significant changes in diatom assemblages, as well as which environmental stressor(s) were most probable. This information can help lake managers develop more targeted and effective management strategies.

AbstractAssessment of flux rates and concentrations of potentially toxic elements in sediment cores from 5 lakes adjacent to the McClean Lake uranium mines in northern Saskatchewan (impact lakes) compared to results from a set of 5 upwind and distant lakes (reference lakes) clearly indicated enrichment of several elements in lakes close to the mining operations. The flux of uranium to the sediments of the 5 impact lakes was significantly higher post-1960 from the mean pre-1960 background conditions by 1.5 to 23 times. Flux rates of arsenic, molybdenum, and selenium also indicated significant enrichment from background conditions in the majority of the impact lakes. In contrast, large and significant increases in flux only occurred in 1 of the 5 reference lakes for arsenic. The highest levels of enrichment were found in the 3 lakes either in closest proximity to the tailings management facility, waste-rock piles, or downstream from the treated effluent management system. High flux rates and concentrations of elements such as arsenic and vanadium in both the reference lakes and in pre-mining samples of the impact lakes indicated that potentially toxic elements can occur naturally in this region. Sediment core analyses of elemental flux and concentration in both reference lakes and pre-1960 conditions in the impact lakes provided an estimate of natural background conditions. Our data suggest that the McClean Lake mine may be a source for the enrichments of toxic elements in the lakes in close proximity to the mining operations.

Postglacial climatic conditions were inferred from cores taken from Big Lake in southern British Columbia. Low concentrations of nonarboreal pollen and pigments near the base of the core suggest that initial conditions were cool. Increases in both aquatic and terrestrial production suggest warmer and moister conditions until ∼8500 cal yr B.P. Hyposaline diatom assemblages, increases in nonarboreal pollen, and increased concentrations of pigments suggest the onset of arid conditions from ∼8500 to ∼7500 cal yr B.P. Slightly less arid conditions are inferred from ∼7500 until ∼6660 cal yr B.P. based on the diatoms, small increases and greater variability in biogenic silica and pigments, and higher percentages of arboreal pollen. At ∼6600 cal yr B.P., changes in diatoms, pigments, biogenic silica, and organic matter suggest that Big Lake became fresh, deep, and eutrophic until ∼3600 cal yr B.P., when water levels and nutrients decreased slightly. Our paleoclimatic inferences are similar to pollen-based studies until ∼6600 cal yr B.P. However, unlike these studies, our multiple lines of evidence from Big Lake imply large changes in effective moisture since 6000 cal yr B.P.

We measured variability in the composition of diatom and chrysophyte assemblages, and the pH inferred from these assemblages, in sediment samples from Big Moose Lake, in the Adirondack Mountains of New York. Replicate samples were analyzed from (1) a single sediment core interval, (2) 12 different intervals from each of 3 separate cores, and (3) 10 widely spaced surface sediment samples (0–1 cm). The variability associated with sample preparation (subsampling, processing, and counting) was relatively small compared to between-core and within-lake variability. The relative abundances of the dominant diatom taxa varied to a greater extent than those of the chrysophyte scale assemblages. Standard deviations of pH inferences for multiple counts from the same sediment interval from diatom, chrysophyte, and diatom plus chrysophyte inference equations were 0.04 (n=8), 0.06 (n=32), and 0.06 (n=8) of a pH unit, respectively. Stratigraphic analysis of diatoms and chrysophytes from three widely spaced pelagic sediment cores provided a similar record of lake acidification trends, although with slight differences in temporal rates of change. Average standard deviations of pH inferences from diatom, chrysophyte and diatom plus chrysophyte inference equations for eight sediment intervals representing similar time periods but in different cores were 0.10, 0.20, and 0.09 pH unit, respectively. Our data support the assumption that a single sediment core can provide an accurate representation of historical change in a lake. The major sources of diatom variability in the surface sediments (i.e., top 1.0 cm) were (1) differences in diatom assemblage contributions from benthic and littoral sources, and (2) the rapid change in assemblage composition with sediment depth, which is characteristic of recently acidified lakes. Because scaled chrysophytes are exclusively planktonic, their spatial distribution in lake sediments is less variable than the diatom assemblages. Standard deviations of pH inferences for 10 widely spaced surface sediment samples from diatom, chrysophyte and diatom plus chrysophyte inference equations were 0.21, 0.09, and 0.16 of a pH unit, respectively.

Diatom and chrysophyte assemblages from varved sediments of meromictic Crawford Lake, Ontario record major environmental changes resulting from spatially broadening anthropogenic environmental stressors related to the “Great Acceleration” in the mid-20th century. Biannual assessment of diatom and chrysophyte assemblages over the last ~200 years allowed for rate of change analysis between adjacent samples that increased substantially during the mid-20th century, concurrent with significant generalized additive model trends. Changes in diatom and chrysophyte assemblages were likely driven by multiple anthropogenic stressors including local forestry harvesting, agriculture, and milling activities, acidic deposition from regional industrial processes, and anthropogenic climate warming. Novel siliceous algal assemblages now exist in Crawford Lake, likely related to the complexities of the above mentioned local and regional stressors. The major assemblage changes at the proposed base of the Anthropocene Epoch detected in this study support the laminated sequence from Crawford Lake as a strong potential candidate for the Anthropocene GSSP.

P. SAM LAKE. 2011. Drought and Aquatic Ecosystems. Wiley‐Blackwell. ISBN‐13: 978‐1‐405‐18560‐8. 400pp $89.95 400 pp.