Browsing by Author "Hayes, Nicole M."

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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 nitrogen removal from wastewater on phytoplankton in eutrophic prairie streams
(Wiley, 2021-10-15) Bergbusch, Nathanael T.; Hayes, Nicole M.; Simpson, Gavin L.; Swarbrick, Vanessa J.; Quiñones-Rivera, Zoraida J.; Leavitt, Peter R
1. Biological nutrient removal (BNR) may be an effective strategy to reduce eutrophication; however, concerns remain about effects on receiving waters of removing both nitrogen (N) and phosphorus (P), rather than P alone. 2. Phytoplankton abundance (as µg chlorophyll a/L) and community composition (as nmol biomarker pigment/L) were quantified over 6 years in two connected eutrophic streams to determine how algae and cyanobacteria varied in response to a shift from tertiary (P removal) to BNR (N and P removal) wastewater treatment. 3. Phytoplankton were sampled biweekly at nine stations May to September and were analysed using generalised additive models (GAMs) to quantify landscape patterns of phototrophs and identify potential causal relationships both before (2010–2012) and after (2017–2019) BNR installation in 2016. 4. Analysis with GAMs showed that 69%–79% of deviance in phytoplankton abundance and composition could be explained by date- and site-specific variance in stream flow, temperature, and solute concentrations (mainly nutrients), whereas similar GAMs using only effluent N content (δ15Nwater) as a predictor explained c. 60% of phototroph deviance. Prior to BNR, phytoplankton levels (mainly chlorophytes) increased with urn:x-wiley:00465070:media:fwb13833:fwb13833-math-0001-rich effluent, whereas their abundance declined with δ15N after BNR (diatoms, chlorophytes). 5. Overall, declines in total effluent release of N (67%–97%) but not P (c. 0%) due to BNR resulted in a 52 ± 7% decline in phytoplankton abundance relative to upstream values, despite high inter-annual variation in discharge and baseline chlorophyll a concentration. 6. Nitrogen removal by BNR improved water quality in N-limited ecosystems.
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
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.
Open Access
Unexpected shift from phytoplankton to periphyton in eutrophic streams due to wastewater influx
(Wiley, 2021-05-08) Bergbusch, Nathanael T.; Hayes, Nicole M.; Simpson, Gavin L.; Leavitt, Peter R
Pollution with nitrogen (N) and phosphorous (P) impairs streams by favoring suspended algae and cyano- bacteria over diatom-rich periphyton. Recently, wastewater treatment plants have been upgraded to biological nutrient removal to eliminate both P and N (mainly NH4+), although little is known of the effects of this effluent on flowing waters. Here, we used high performance liquid chromatography to quantify how the abundance and composition of phytoplankton and periphyton varied in response to both influx of effluent produced by biologi- cal nutrient removal and physico-chemical conditions in small, turbid, P-rich streams of the northern Great Plains. At the catchment scale, analysis with generalized additive models (GAMs) explained 40.5–62.6% of devi- ance in total phototroph abundance (as Chl a) and 72.5–82.5% of deviance in community composition (as biomarker carotenoids) in both planktonic and benthic habitats when date- and site-specific physico-chemical parameters were used as predictors. In contrast, GAMs using wastewater input (as aqueous δ15 N) as a predictor explained up to 50% of deviance in Chl a, and ~60% of deviance in community composition, in both suspended (51.6% of Chl a, 67.1% of composition) and attached communities (21.5% of Chl a, 58.8% of composition). Phy- toplankton was replaced by periphyton within a 60-km wastewater-impacted reach due to dilution of streams by transparent effluent and addition of urban NO3 , although predominance of phytoplankton was re-established after confluence with higher-order streams. Overall, influx of effluent shifted turbid, phytoplankton-rich streams to clear ecosystems with abundant epilithon by improving water transparency and providing NO3 to favor benthic diatoms and chlorophytes.
Open Access
Widespread nitrous oxide undersaturation in farm waterbodies creates an unexpected greenhouse gas sink
(National Academy of Sciences, 2019-05-14) Webb, Jackie; Hayes, Nicole M.; Simpson, Gavin L.; Leavitt, Peter R; Baulch, Helen M.; Finlay, Kerri
Nitrogen pollution and global eutrophication are predicted to increase nitrous oxide (N2O) emissions from freshwater ecosystems. Surface waters within agricultural landscapes experience the full impact of these pressures and can contribute substantially to total landscape N2O emissions. However, N2O measurements to date have focused on flowing waters. Small artificial waterbodies remain greatly understudied in the context of agricultural N2O emissions. This study provides a regional analysis of N2O measurements in small (<0.01 km2) artificial reservoirs, of which an estimated 16 million exist globally. We show that 67% of reservoirs were N2O sinks (−12 to −2 μmol N2O⋅m−2⋅d−1) in Canada’s largest agricultural area, despite their highly eutrophic status [99 ± 289 µg⋅L−1 chlorophyll-a (Chl-a)]. Generalized additive models indicated that in situ N2O concentrations were strongly and nonlinearly related to stratification strength and dissolved inorganic nitrogen content, with the lowest N2O levels under conditions of strong water column stability and high algal biomass. Predicted fluxes from previously published models based on lakes, reservoirs, and agricultural waters overestimated measured fluxes on average by 7- to 33-fold, challenging the widely held view that eutrophic N-enriched waters are sources of N2O.