Browsing by Author "Haig, Heather A."

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Open Access
Abrupt changes in the physical and biological structure of endorheic upland lakes due to 8-m lake-level variation during the 20 th century
(Wiley, 2022-03-07) Bjorndahl, Judith A.; Gushulak, Cale A.C.; Mezzini, Stefano; Simpson, Gavin L.; Haig, Heather A.; Leavitt, Peter R; Finlay, Kerri
Climate-induced variation in lake level can affect physicochemical properties of endorheic lakes, but its consequences for phototrophic production and regime shifts are not well understood. Here, we quantified changes in the abundance and community composition of phototrophs in Kenosee and White Bear lakes, two endorheic basins in the parkland Moose Mountain uplands of southeastern Saskatchewan, Canada, which have experienced > 8 m declines in water level since ~ 1900. We hypothesized that lower water levels and warmer temperatures should manifest as increased abundance of phytoplankton, particularly cyanobacteria, and possibly trigger a regime shift to turbid conditions due to evaporative concentration of nutrients and solutes. High-resolution analysis of sedimentary pigments revealed an increase in total phototrophic abundance (as β-carotene) concurrent with lake-level decline beginning ~ 1930, but demonstrated little directional change in cyanobacteria. Instead, significant increases in obligately anaerobic purple sulfur bacteria (as okenone) occurred in both lakes during ~ 1930–1950, coeval with alterations to light environments and declines in lake level. The presence of okenone suggests that climate-induced increases in solute concentrations may have favored the formation of novel bacterial habitats where photic and anoxic zones overlapped. Generalized additive models showed that establishment of this unique habitat was likely preceded by increased temporal variance of sulfur bacteria, but not phytoplankton or cyanobacteria, suggesting that this abrupt change to physical lake structure was unique to deep-water environments. Such climate-induced shifts may become more frequent in the region due to hydrological stress on lake levels due to warming temperatures across the Northern Great Plains.
Open Access
Comparison of isotopic mass balance and instrumental techniques as estimates of basin hydrology in seven connected lakes over 12 years
(Elsevier, 2019-11-22) Haig, Heather A.; Hayes, Nicole M.; Simpson, Gavin L.; Yi, Y.; Wissel, Bjoern; Hodder, Kyle; Leavitt, Peter R
Mass-balance models using stable isotopes of hydrogen and oxygen provide useful estimates of the water balance of lakes, particularly in the absence of instrumental data. However, isotopic mass balances are rarely compared directly to measured water fluxes. Here we compared instrumental and isotope-based determinations of water fluxes in seven connected lakes over 12 years to quantify how agreement between the two approaches is affected by lake type and its position in the landscape. Overall, lake-specific ratios of evaporation to inflow (E/I) from instrumental measurements (median, x̃ = 0.06, median absolute deviation, MAD = 0.06) agreed well with isotopic estimates using headwater models (x̃ = 0.14, MAD = 0.08), with the exception of one lake with limited channelized inflow of surface waters (x̃ instrumental = 0.51 vs. x̃ headwater = 0.24). Isotope-instrument agreement improved (x̃ = 0.09 vs. x̃ = 0.03) when basin-specific (‘best-fit’) isotope models also considered local con- nectivity to upstream water bodies. Comparison among years revealed that mean isotopic E/I values were lowest in 2011 (mean, μ = 0.06, standard deviation, σ = 0.09) during a 1-in-140 year spring flood, and highest during a relatively arid year, 2003 (μ = 0.22, σ = 0.19), while interannual variability in E/I generally increased with distance downstream along the mainstem of the watershed. Similar patterns of agreement between methods were recorded for water-residence time. Isotope models also documented the expected low water yield from lake catchments (μ = 36.2 mm yr−1 , σ = 62.3) suggesting that isotope models based on late-summer samples integrate annual inputs from various sources that are difficult to measure with conventional methods. Overall, the strong positive agreement between methods confirms that water isotopes can provide substantial insights into landscape patterns of lake hydrology, even in ungauged systems.
Open Access
Effects of lake warming on the seasonal risk of toxic cyanobacteria exposure
(Wiley, 2020-06-18) Hayes, Nicole M.; Haig, Heather A.; Simpson, Gavin L.; Leavitt, Peter R
Incidence of elevated harmful algal blooms and concentrations of microcystin are increasing globally as a result of human-mediated changes in land use and climate. However, few studies document changes in the seasonal and interannual concentrations of microcystin in lakes. Here, we modeled 11 yr of biweekly microcystin data from six lakes to characterize the seasonal patterns in microcystin concentration and to ascertain if there were pronounced changes in the patterns of potential human exposure to microcystin in lakes of central North America. Bayesian time series analysis with generalized additive models found evidence for a regional increase in microcystin maxima and duration but recorded high variation among lakes. During the past decade, warmer temperatures, but not nutrient levels, led to a marked increase in the number of days when concentrations exceeded drinking and recreational water thresholds set by the World Health Organization and United States Environmental Protection Agency.
Open Access
Effects of seasonal and interannual variability in water isotopes (δ2H, δ18O) on estimates of water balance in a chain of seven prairie lakes
(Elsevier, 2020-12-10) Haig, Heather A.; Hayes, Nicole M.; Simpson, Gavin L.; Yi, Y.; Wissel, Bjoern; Hodder, Kyle; Leavitt, Peter R
Stable isotopes of hydrogen (δ2H) and oxygen (δ18O) provide important quantitative measures of lake hydrology and water balance, particularly in lakes where monitoring of fluxes is incomplete. However, little is known of the relative effects of seasonal variation in water isotopes on estimates of lake hydrology, particularly over decadal scales. To address this gap, we measured water isotopes bi-weekly May-September during 2003–2016 in seven riverine lakes within the 52,000 km2 Qu’Appelle River drainage basin of the Canadian Prairies. Analyses revealed that within-year variation in δ18O values routinely exceeded that among years, reflecting rapid changes in water source, particularly in lakes with water residence times <1 year. Isotopic variation was greatest during spring following snowmelt, except in large deep lakes which exhibited limited differences among seasons or years. In contrast, large hydrological events (e.g., 1-in-140-year flood in 2011) homogenized isotopic values, even among riverine lakes separated by over 150 km, and exerted particularly strong legacy effects on large lakes. Overall, study lakes exhibited a strongly positive moisture balance (evaporation < inflow), despite regional precipitation deficits of 30 cm yr−1, with greater reliance on rainfall (vs. snow) and possibly evaporation in downstream lakes within more humid regions. We conclude that seasonal samples of water isotopes are required to characterize the hydrology of shallow lakes, or those with unknown reliance on snowmelt waters, as well as to better quantify lake susceptibility to climate variability.
Open Access
Effects of spatial variation in benthic phototrophs along a depth gradient on assessments of whole-lake processes
(Wiley, 2021-09-16) Gushulak, Cale A.C.; Haig, Heather A.; Kingsbury, Melanie V.; Wissel, Bjoern; Cumming, Brian F.; Leavitt, Peter R
1. Phytobenthos are often underrepresented in both limnological and paleolimnological studies but may play key roles in whole-lake production and ecosystem processes including eutrophication, food-web dynamics, and ecosystem state changes. 2. Photosynthetic pigments, stables isotopes, and diatoms were quantified from surface sediments (0-1 cm) collected across a depth transect of a small, DOC-rich, mesotrophic lake in boreal northwestern Ontario to assess spatial variation in phytobenthos abundance and production. 3. Maximal concentrations of siliceous algae and cyanobacteria pigments occurred at ~2–6 m depth, with abundant tychoplanktonic diatoms, depleted sedimentary δ13C C values, and elevated 33 ratios of precursor chlorophyll a to product pheophytin a, all aligning well with the depths of the thermocline, epilimnetic mixing, and maximum light penetration. 4. These patterns demonstrated the presence of three discrete community assemblages, with greatest mass accumulation occurring at intermediate depths where warm illuminated sediments provide habitat for tychoplanktonic diatoms and cyanobacteria between turbulent shallows and cold and dark depths. 5. If widespread among boreal lakes, this tychoplanktonic zone may exert important effects on whole-lake production, carbon sequestration, benthic-pelagic food-web coupling, eutrophication, and ecosystem state change.
Open Access
Marked blue discoloration of late winter ice and water due to autumn blooms of cyanobacteria
(Taylor and Francis Group, 2021-11-17) Haig, Heather A.; Chegoonian, Amir M.; Davies, John-Mark; Bateson, Deirdre; Leavitt, Peter R
Continued eutrophication of inland waters by nutrient pollution can combine with unprecedented atmospheric and lake warming to create emergent environmental surprises. Here we report the first known occurrence of marked blue discoloration of ice and water in highly eutrophic prairie lakes during late winter 2021. Intense blue staining was reported first to governmental agencies by ice fishers in early March 2021, then communicated widely through social media, resulting in First Nations and public concern over potential septic field release, toxic spills, urban pollution, and agricultural mismanagement. Analysis of water from stained and reference sites using ultraviolet (UV)–visible spectrophotometry and high-performance liquid chromatography demonstrated that the blue color arose from high concentrations (∼14 mg/L) of the cyanobacterial pigment C-phycocyanin that was released after an unexpected bloom of Aphanizomenon flos-aquae in late October 2020 was frozen into littoral ice. Remote sensing using the Sentinel 3 A/B OLCI and Sentinel 2 A/B MSI satellite platforms suggested that blue staining encompassed 0.68 ± 0.24 km2 (4.25 ± 1.5% of lake surface area), persisted over 4 weeks, and was located within 50 m of the lakeshore in regions where fall blooms of cyanobacteria had been particularly dense. Although toxin levels were low (∼0.2 μg microcystin/L), high concentrations of C-phycocyanin raised public concern over eutrophication, pollution, and climate change, and resulted in rapid governmental and academic response. Given that climate change and nutrient pollution are increasing the magnitude and duration of cyanobacterial blooms, blue staining of lake ice may become widespread in eutrophic lakes subject to ice cover.
Open Access
Regulation of carbon dioxide and methane in small agricultural reservoirs: optimizing potential for greenhouse gas uptake
(Copernicus Publications, 2019-11-08) Webb, Jackie; Leavitt, Peter R; Simpson, Gavin L.; Baulch, Helen M.; Haig, Heather A.; Hodder, Kyle; Finlay, Kerri
Small farm reservoirs are abundant in many agricultural regions across the globe and have the potential to be large contributing sources of carbon dioxide (CO2) and methane (CH4) to agricultural landscapes. Compared to natural ponds, these artificial waterbodies remain overlooked in both agricultural greenhouse gas (GHG) inventories and inland water global carbon (C) budgets. Improved understanding of the environmental controls of C emissions from farm reservoirs is required to address and manage their potential importance in agricultural GHG budgets. Here, we conducted a regional-scale survey (∼ 235 000 km2) to measure CO2 and CH4 surface concentrations and diffusive fluxes across 101 small farm reservoirs in Canada's largest agricultural area. A combination of abiotic, biotic, hydromorphologic, and landscape variables were modelled using generalized additive models (GAMs) to identify regulatory mechanisms. We found that CO2 concentration was estimated by a combination of internal metabolism and groundwater-derived alkalinity (66.5 % deviance explained), while multiple lines of evidence support a positive association between eutrophication and CH4 production (74.1 % deviance explained). Fluxes ranged from −21 to 466 and 0.14 to 92 mmol m−2 d−1 for CO2 and CH4, respectively, with CH4 contributing an average of 74 % of CO2-equivalent (CO2-e) emissions based on a 100-year radiative forcing. Approximately 8 % of farm reservoirs were found to be net CO2-e sinks. From our models, we show that the GHG impact of farm reservoirs can be greatly minimized with overall improvements in water quality and consideration to position and hydrology within the landscape.
Open Access
Spatial and temporal variation in nitrogen fixation and its importance to phytoplankton in phosphorus-rich lakes
(Wiley, 2018-11-27) Hayes, Nicole M.; Patoine, Alain; Haig, Heather A.; Simpson, Gavin L.; Swarbrick, Vanessa J.; Wiik, Emma; Leavitt, Peter R
1. Limnological theory posits that phosphorus (P) limits primary production in freshwater lakes, in part because fixation of atmospheric nitrogen (N2) can compensate for limitations in nitrogen (N) supply to phytoplankton. However, quantitative estimates of the degree to which N2 fixation satisfies planktonic N demand are rare. 2. Here we used biweekly sampling during summer in seven lakes over 2 decades to estimate both planktonic N2 fixation and phytoplankton N demand. We further assessed the ability of biologically fixed N to satisfy N needs of primary producers in productive hardwater lakes. 3. Phytoplankton N requirements, derived from estimates of phytoplankton productivity and N content, were moderately synchronous (S = 0.41) among lakes (ca. 0.1–9.2 mg N m–3 hr–1). In contrast, rates of N2 fixation determined using isotopic natural abundance method (NAM; 0.002–3.2 mg N m–3 hr–1), or heterocyte-based calculations (0.10–1.78 mg N m–3 hr–1), varied asynchronously (SNAM = –0.03 and SHeterocyte = –0.11) among basins, accounted for a median of 3.5% (mean 11.3% ± 21.6) of phytoplankton demand, and were correlated to the abundance of Nostocales cyanobacteria when analysed using generalised additive models. 4. Overall, the total mass of fixed N accounted for a median of only 3.0% of the spring standing stock of total dissolved N in study lakes (mean 7.5 ± 12.1%), with higher relative importance of fixed N in highly productive downstream lakes. Thus, while fixed N helps sustain primary productivity, particularly in years with high rates of N2-fixation, it does not appear to eliminate N limitation of phytoplankton growth in these P-rich hardwater lakes.