Search

Climate‐driven decreases in ice‐cover duration have the potential to impact lake ecosystems, yet we have only partial understanding of the effects of winter conditions on physical, chemical, and biological properties of lakes. We used 39 years of monitoring data to examine under‐ice changes in nutrients, oxygen, and phytoplankton in a shallow drinking‐water reservoir. Two phases of winter were identified. Early winter was characterized by declining oxygen. In this phase, there were increases in specific conductance and concentrations of ammonium (NH4+‐N) and soluble reactive phosphorus (SRP). In the month prior to ice off these trends reversed themselves and phytoplankton began to increase. Specific conductance declined as meltwater entered the lake. Nutrients (SRP and NH4+‐N) declined, concurrent with increases in chlorophyll a and oxygen during late winter. This work demonstrates that chemical and biotic changes through winter are highly time dependent and differ between early and late winter phases. The late winter phase is often unstudied because of unsafe ice conditions, but here, the "spring" bloom commonly occurs in late winter under ice. The phases of winter, which are likely driven by changes in light, must be considered as we work to understand how diverse lakes will respond to declining periods of ice cover, and what drives differences in the spring ecology of diverse ice‐covered lakes. [ABSTRACT FROM AUTHOR]

With changes in ice cover duration, nutrient loading, and anoxia risk, it is important to understand the mechanisms that control nitrogen cycling and oxygen depletion in lakes through winter. Current understanding is largely limited to description of changes in chemistry, with few measurements of the processes driving winter changes, how they differ across lakes, and how they are impacted by under-ice conditions. Nitrification is a process which consumes oxygen and ammonium (NH4+), and supplies nitrate (NO3–). To date, nitrification has been measured under ice cover in only two lakes globally. Here, we used 15NH4+ enrichment to measure rates of pelagic nitrification in thirteen water bodies in two ecozones. Our work demonstrates ecologically important rates of nitrification can occur despite low water temperatures, impacting NH4+, NO3– and, most importantly, oxygen concentrations. However, high rates are not the norm. When, where and why is nitrification important in winter? We found that nitrification rates were highest in a eutrophic lake chain downstream of a wastewater treatment effluent (mean: 226.5 μg N L-1 d-1), and in a semi-saline prairie lake (110.0 μg N L-1 d-1). In the boreal shield, a eutrophic lake had nitrification rates exceeding those of an oligotrophic lake by 6-fold. Supplementing our results with literature data we found NH4+ concentrations were the strongest predictor of nitrification rates across lentic ecosystems in winter. Higher nitrification rates were associated with higher concentrations of NH4+, NO3– and nitrous oxide (N2O). While more work is required to understand the switch between high and low nitrification rates and strengthen our understanding of winter nitrogen cycling, this work demonstrates that high nitrification rates can occur in winter. [ABSTRACT FROM AUTHOR]

The Northern Great Plains is a key region to global food production. It is also a region of water stress that includes poor water quality associated with high concentrations of nutrients. Agricultural nitrogen and phosphorus loads to surface waters need to be reduced, yet the unique characteristics of this environment create challenges. The biophysical reality of the Northern Great Plains is one where snowmelt is the major period of nutrient transport, and where nutrients are exported predominantly in dissolved form. This limits the efficacy of many beneficial management practices (BMPs) commonly used in other regions and necessitates place-based solutions. We discuss soil and water management BMPs through a regional lens—first understanding key aspects of hydrology and hydrochemistry affecting BMP efficacy, then discussing the merits of different BMPs for nutrient control. We recommend continued efforts to "keep water on the land" via wetlands and reservoirs. Adoption and expansion of reduced tillage and perennial forage may have contributed to current nutrient problems, but both practices have other environmental and agronomic benefits. The expansion of tile and surface drainage in the Northern Great Plains raises urgent questions about effects on nutrient export and options to mitigate drainage effects. Riparian vegetation is unlikely to significantly aid in nutrient retention, but when viewed against an alternative of extending cultivation and fertilization to the waters' edge, the continued support of buffer strip management and refinement of best practices (e.g., harvesting vegetation) is merited. While the hydrology of the Northern Great Plains creates many challenges for mitigating nutrient losses, it also creates unique opportunities. For example, relocating winter bale-grazing to areas with low hydrologic connectivity should reduce loadings. Managing nutrient applications must be at the center of efforts to mitigate eutrophication. In this region, ensuring nutrients are not applied during hydrologically sensitive periods such as late autumn, on snow, or when soils are frozen will yield benefits. Working to ensure nutrient inputs are balanced with crop demands is crucial in all landscapes. Ultimately, a targeted approach to BMP implementation is required, and this must consider the agronomic and economic context but also the biophysical reality. [ABSTRACT FROM AUTHOR]

Phosphorus (P) in lake sediments is stored within diverse forms, often associated with metals, minerals, and organic matter. Sediment P can be remobilized to the water column, but the environmental conditions influencing the P retention-release balance depend upon the sediment chemistry and forms of P present. Sequential fractionation approaches can be used to help understand forms of P present in the sediments, and their vulnerability to release. We assessed P composition in surficial sediments (as an assemblage of six P-fractions) and its relationship with watershed, and lake-specific explanatory variables from 236 lakes across Canada. Sediment P composition varied widely across the 12 sampled Canadian ecozones. The dominant P-fractions were the residual-P and the labile organic P, while the loosely bound P corresponded to the smallest proportion of sediment TP. Notable contrasts in sediment P composition were apparent across select regions – with the most significant differences between sediment P in lakes from the mid-West Canada region (Prairies and Boreal Plains ecozones) and both Eastern coastal (Atlantic Maritime and Atlantic Highlands) and Western coastal (Pacific Maritime) ecozones. The ecozone attributes most critical to sediment P speciation across Canadian lakes were related to soil types in the watershed (e.g., podzols, chernozems, and Luvisols) and the chemical composition of lake water and sediments, such as dissolved Ca in lake water, bulk sedimentary Ca, Al, and Fe, dissolved SO 4 in lake water, lake pH, and salinity. Understanding predictors of the forms of P stored in surficial sediments helps advance our knowledge of in-lake P retention and remobilization processes across the millions of unstudied lakes and can help our understanding of controls on internal P loading. [Display omitted] • Lake sediment phosphorus (P) composition varied widely across 12 Canadian ecozones. • Three soil orders were the strongest watershed predictors of sediment P composition. • Water chemistry and sediment composition were also critical in-lake predictors. • Lake sediment P composition differed most among Mid-western and maritime ecozones. • Sediment P differed across classes of lake pH, depth, and trophic state. [ABSTRACT FROM AUTHOR]

The ice‐covered period on lakes in the northern hemisphere has often been neglected or assumed to have less importance relative to the open water season. However, recent studies challenge this convention, suggesting that the winter period is more dynamic than previously thought. In this review, we synthesize the current understanding of under‐ice carbon dioxide (CO2) and methane (CH4) dynamics, highlighting the annual importance of CO2 and CH4 emissions from lakes at ice‐melt. We compiled data from 25 studies that showed that the ice‐melt period represents 17% and 27% of the annual CO2 and CH4 emissions, respectively. We also found evidence that the magnitude and type of emission (i.e., CO2 and CH4) varies with characteristics of lakes including geographic location, lake morphometry, and physicochemical conditions. The scarcity of winter and spring carbon data from northern lakes represents a major gap in our understanding of annual budgets in these lakes and calls for future research during this key period. [ABSTRACT FROM AUTHOR]

Many physical, chemical, and biological processes in freshwater ecosystems mobilize the nutrient phosphorus (P) from sediments, which in turn may contribute to the formation of harmful algal blooms. Here, we critically reviewed internal P loading in Canadian fresh waters to understand the geographic patterns and environmental drivers of this important process. From 43 publications, we consolidated 618 estimates of internal P loading from Canadian freshwater ponds, lakes, reservoirs, and coastal wetlands ( n = 70). Expressed in terms of total P, short-term gross rates in sediment samples ( Lgross) ranged from −27 to 54 mg·m−2·day−1 ( n = 461), while long-term net rates in whole ecosystems ( Lnet) ranged from −1694 to 10 640 mg·m−2·year−1 ( n = 157). The main environmental drivers of this variation were oxygen, pH, geology, and trophic state. Internal P loading tended to be higher during the open-water season and most prominent in small prairie lakes. Priorities for future research on internal P loading should include resolving methodological problems, assessing the relative importance of different mechanisms, examining the influence of anthropogenic activities, and quantifying rates in understudied ecosystems. [ABSTRACT FROM AUTHOR]

Summary 1. Diel variation in metabolism contributes to variation in oxygen (O2) concentrations in streams. This variation in O2 and other parameters (e.g. pH) can in turn affect the rates of microbial nitrogen (N) processing, concentrations of nitrogenous solutes and production of the greenhouse gas nitrous oxide (N2O). We investigated diel variability in emissions of N2O and the magnitude of short-term variability in N solutes across 10 streams. 2. Nitrous oxide fluxes varied on average 2.3-fold over diel cycles. Concentrations would be underestimated by sampling around noon, but N2O fluxes would not show a consistent bias. Time-weighted mean daily N2O flux was strongly related to nitrate concentration ( r2 = 0.58). Diel patterns in N2O and dissolved N species were often complex (rather than simple sinusoidal curves), probably reflecting complex underlying processes. 3. Reliance on samples obtained around noon would overestimate daily mean nitrate concentrations by 5% and underestimate ammonium by 32% (average bias across all streams and dates). 4. Dissolved organic N did not show consistent day-night variation. However, the magnitude of diel variability was similar to that observed for dissolved inorganic N. Organic and inorganic N concentrations were often similar. Both appear to be dynamic components of stream N budgets. 5. The Intergovernmental Panel on Climate Change (IPCC) relies upon an emission factor to estimate indirect agricultural N2O emissions from streams and ground water. The measured emission factor (defined as the ratio of concentrations of N2O-N to -N) was typically below the recently revised IPCC default figure. Measured values varied on average 1.8-fold over approximately 24-h periods and were slightly higher at night than by day. The emission factor was actually highest in streams that were net sinks for N2O, highlighting a conceptual problem in the current IPCC method. 6. Typical sampling programmes rely on daytime-only sampling, which might cause bias in results. In our study streams, the bias was generally small. Diel variation in nitrate concentrations was related to mean temperature; variation in ammonium and N2O concentrations was greatest at low concentrations of nitrite and ammonium. [ABSTRACT FROM AUTHOR]

The current Intergovernmental Panel on Climate Change (IPCC) method for tabulating agricultural nitrous oxide (N2O) emissions suggests that aquatic ecosystems may be important N2O sources. However, estimates are highly uncertain, and the method to estimate emissions is rarely tested. The default IPCC emission factor for groundwater and surface drainage (EF5-g; defined as N2O-N:nitrate-N) has been lowered recently. Our data support further reduction. Notably, we present the first EF5-g data under ice, which reflects groundwater inputs not confounded by gas exchange. These under-ice data suggest an EF5-g of 0.13%, approximately half the current IPCC default value. Our data from the open-water season also suggest a reduction to 0.11% (based on annual means). The data highlight major problems with the IPCC method. EF5-g was extremely variable, with the highest values observed in a stream that was a net sink of N2O. Testing the overall method for freshwater emissions is more problematic because of the multidecade transit time from headwaters in our study region to the Atlantic Ocean and limited information on emissions from lakes. [ABSTRACT FROM AUTHOR]

Global models have indicated agriculturally impacted rivers and streams may be important sources of the greenhouse gas nitrous oxide (N2O). However, there is significant uncertainty in N2O budgets. Isotopic characterization can be used to help constrain N2O budgets. We present the first published measurements of the isotopic character of N2O emitted from low (2-4) order streams. Isotopic character of N2O varied seasonally, among streams, and over diel periods. On an annual basis, δ 18O of emitted N2O (+47.4 to +51.4‰; relative to VSMOW) was higher than previously reported for larger rivers, but δ 15N of emitted N2O (-16.2 to +2.4‰ among streams; relative to atmospheric N2) was similar to that of past studies. On an annual basis, all streams emitted N2O with lower δ 15N than tropospheric N2O. Given these streams have elevated nitrate concentrations which are associated with enhanced N2O fluxes, this supports the hypothesis that streams are contributing to the accumulation of 15N-depleted N2O in the troposphere. [ABSTRACT FROM AUTHOR]

While benthic algal biomass is one of the most commonly measured variables within littoral communities, it is also one of the most poorly characterized. The use of chlorophyll a as an estimate of biomass, while easy and inexpensive, can be affected by changes in environmental conditions and algal community composition. Biovolume-based measurements often have high variability and are affected by changes in cell volume due to preservation. Using 12 years of data from the Experimental Lakes Area (northwestern Ontario, Canada) as well as short-term surveys and experimental studies from the Experimental Lakes Area and the Canadian Rocky Mountains, we demonstrate that biovolume and chlorophyll a are often decoupled in the littoral zone of temperate oligotrophic lakes. We recommend that researchers revisit the limitations of both metrics and specifically caution against the use of chlorophyll a as a biomass indicator when light, temperature, or species composition vary significantly. [ABSTRACT FROM AUTHOR]

Evidence suggests that low cobalt (Co) may limit heterocyst frequency (HF) in filamentous diazotrophic cyanobacteria. Therefore, the effect of three Co concentrations on HF in four species in the genera Aphanizomenon and Dolichospermum was examined in N‐depleted (N was not added) culture. Long‐term HF data were also analysed in experimentally fertilised N‐limited Lake 227.HF ranges and means at 0.17, 17, and 170 nmol Co/L were 4.1%–5.7% (4.6%), 5.4%–7.4% (6.4%), and 5.9%–9.3% (7.4%), respectively, after 11 days of growth in batch cultures suggesting that Co plays a role in regulating HF. HF at 0.17 nmol/L was significantly different from HF at the two higher concentrations in all species implicating Co in heterocyst differentiation. However, growth rates and final biovolume yields were not significantly affected by Co in any of the species.Applying the ratio of total phosphorus (TP)/Co in culture media (106) at 0.17 nmol Co/L to an N‐limited system implies that dissolved Co would have to be less than 1 pmol/L to severely limit HF at 1 μmol TP/L. This Co concentration is much lower than dissolved Co in Lake 227 during an Aphanizomenon skujae bloom with 1 μmol TP/L in 2017. Furthermore, Co increased from 0.7 to 2.0 nmol/L simultaneously increasing with HF and cyanobacteria biomass suggesting that Co probably did not limit HF and bloom biomass in Lake 227.Mean summer HFs in Lake 227 during 2000–2020 were 3.4% (epilimnion) and 4.0% (metalimnion), similar to HF at the lowest Co in the cultures. However, HF was significantly higher after 2015 following a shift in dominant bloom species from A. schindlerii to the smaller A. skujae. Calculations suggest that the decrease in cell size may have prompted a higher HF in A. skujae in order to fix an amount of N per unit biomass similar to that fixed by the larger A. schindlerii. Thus, two previously unidentified factors, Co and cell size, can be added to the list of factors that affect HF. [ABSTRACT FROM AUTHOR]

Hydrologic management of shallow lakes is often undertaken to prevent fluctuations in lake level, and to ensure sufficient water volume for economic, domestic, and recreational uses, but there is inconsistent evidence of whether lake‐level stabilisation through hydrological management promotes or hinders eutrophication.Here we used multi‐proxy paleolimnological assessments of water quality (sedimentary carbon, nitrogen, total phosphorus, fossil pigments), and zooplankton community ecology (fossil Cladocera assemblages), combined with Landsat‐derived estimates of lake surface area in two shallow eutrophic lakes, in the Prairies of southern Saskatchewan, Canada, to quantify how 8 decades of contrasting hydrological management strategies (continuous or intermittent) affect primary production and phytoplankton composition.Analysis revealed that irregular hydrological management of Pelican Lake led to sharp increases in primary production concomitant with lake‐level decline. In contrast, continuously managed Buffalo Pound Lake, a drinking water reservoir for regional cities, exhibited slow, persistent eutrophication over decades despite active regulation of water levels. In both lakes, strong correlations of δ 15N values with pigments from diazotrophic cyanobacteria (canthaxanthin) showed that N2‐fixation increased during eutrophication irrespective of the timing of change. Finally, variation in fossil cladoceran density and composition reflected changes in pelagic and littoral habitats (e.g., reduced macrophyte cover) due to changes in both lake level and water quality.Basin comparison shows that while hydrologic management can moderate water quality degradation due to lake‐level change, it does not prevent eutrophication when nutrient influx remains high.Given that regional water availability is forecast to decline in coming decades, we anticipate that continued hydrological management will be unavoidable and will be unable to improve water quality unless nutrient influx is also controlled. [ABSTRACT FROM AUTHOR]

Decades ago, Dr Noel Hynes eloquently summarized the inherent interconnectedness of a stream and its valley and made the case that human alteration of the valley would have direct negative consequences for freshwater systems. Currently, the freshwater biodiversity crisis extends across all continents and demands urgent attention from environmental planners, practitioners, and policymakers to protect streams and their valleys. As we work to slow losses of freshwater biodiversity and restore freshwater ecosystems, it is time to revisit the important messages from Hynes. One of the most obvious and immediate actions that could be undertaken is to "back off"—that is, to limit human activity and new development in floodplain and riparian areas immediately adjacent to freshwater systems, including streams, rivers, lakes, and wetlands, while minimizing impacts and risks in areas with existing development. From reducing erosion and flood damage to maintaining cool water temperatures, filtering pollutants, protecting critical habitats, and enabling lateral connectivity, intact riparian zones mitigate many of the threats that degrade freshwater ecosystems. There has been much research to identify optimal setbacks and buffer-strip widths to protect against harm. As such, in many areas, our ability to protect the stream and its valley is not limited by natural science but rather our failure to consistently apply floodplain and riparian regulations and the absence of political will. We are too quick to trade off the environment for short-term economic development. In areas that are already developed, solutions are more complicated but, in many cases, represent a key priority for healing damaged ecosystems and for addressing economic and social risks of vulnerable development. We need to redefine our relationship with freshwater ecosystems, and the first step is to back off and give freshwater ecosystems the opportunity to heal while ensuring that as-of-yet intact riparian areas continue to support freshwater resiliency. In doing so, we will also gain climate adaptive benefits, given that maintaining intact riparian areas is an effective nature-based solution. [ABSTRACT FROM AUTHOR]

In this article the author discusses eutrophication, which is a process leading to increased algal productivity in lakes through time, and why nutrient control in aquatic ecosystems requires asking the right questions. Topics include the impact of eutrophication on key ecosystem services, the importance of preventing a state shift into an undesirable state via nutrient control, and the role of nitrogen (N), and N control, in eutrophication.

The link between under ice processes and open water eutrophication dynamics has been proven in the field. Water quality models still lack the capability to capture the connection between both environments. The hydrodynamic-ecological model CE-QUAL-W2 is being applied to a eutrophic drinking water reservoir on the Canadian Prairies as part of larger collaborative research project. CE-QUAL-W2 is one of the few water quality models that includes an ice algorithm, yet is restricted by a fixed albedo coefficient. Field studies have shown albedo to change through the ice cover season – varying the solar radiation that reaches the ice-water interface as a result. In order to better represent the light and heat environment during the under ice periods we modify the ice algorithm to incorporate a variable albedo rate. While assessing the modified version of CE-QUAL-W2 on the reservoir we encounter a number of challenges during the calibration process. These challenges pertain to difficulties with modelling the under ice environment, and with modelling shallow lakes and reservoirs. We recommend a targeted monitoring program to supplement available data that will reduce the uncertainty associated with the results of the reservoir model. [ABSTRACT FROM AUTHOR]

Remote retrieval of near-surface chlorophyll-a (Chla) concentration in small inland waters is challenging due to substantial optical interferences of various water constituents and uncertainties in the atmospheric correction (AC) process. Although various algorithms have been developed to estimate Chla from moderate-resolution terrestrial missions (∼10–60 m), the production of both accurate distribution maps and time series of Chla has proven challenging, limiting the use of remote analyses for lake monitoring. Here, we develop a support vector regression (SVR) model, which uses satellite-derived remote-sensing reflectance spectra ( R r s δ ) from Sentinel-2 and Landsat-8 images as input for Chla retrieval in a representative eutrophic prairie lake, Buffalo Pound Lake (BPL), Saskatchewan, Canada. Validated against in situ Chla from seven ice-free seasons (N ∼ 200; 2014–2020), the SVR model outperformed both locally tuned, R r s δ -fed empirical models (Normalized Difference Chlorophyll Index, 2- and 3-band, and OC3) and Mixture Density Networks (MDNs) by 15–65%, while exhibiting comparable performance to a locally trained MDN, with an error of ∼35%. Comparison of Chla retrieval models, AC processors (iCOR, ACOLITE), and radiometric products (Rayleigh-corrected, surface, and top-of-atmosphere reflectance) showed that the best Chla maps and optimal time series (up to 100 mg m−3) were produced using a coupled SVR-iCOR system. [ABSTRACT FROM AUTHOR]

Globally, hydrological connectivity between rivers and their floodplains has been reduced by river flow management and land transformation. The Saskatchewan River Delta is North America's largest inland delta and a hub for fish and fur production. To determine the influence of connectivity on limnology within this northern floodplain, water chemistry and stable isotopes (δ18O and δ2H) were analyzed during the winter of 2014 in 26 shallow lakes along a hydrological gradient. A total of five lake connectivity categories were determined by optical remote sensing imagary of surface water coverage area from years of varying flood intensities. Accuracy of categories was verified by degree of 18O and 2H enrichment within lakes. Both isotopes showed marked successional enrichment between connectivity categories, with more isolated lakes exhibiting greater enrichment. Water chemistry in lakes with greater connectivity to the main channel were characterized by higher pH, dissolved oxygen, nitrates, and sulfates and lower total nitrogen, total phosphorus, and ammonium compared with more isolated lakes. These findings illustrate how connectivity influences water chemistry in northern floodplain lakes and how it might determine the suitability of these lakes as winter refuge for fishes. Additionally, our study provides supporting evidence for the effective use of optical remote sensing imagery, an inexpensive and accessible source of data for researchers, when determining connectivity characteristics of large northern floodplain systems. Additionally, this study provides further evidence that the inundation of floodplain lakes by river water during peak discharge has an impact on the conditions within the lakes long into the winter ice-cover season. Understanding the year-round influence of river-floodplain connection is imperative for assessing potential impacts of climate change and future water regulation on such ecosystems. [ABSTRACT FROM AUTHOR]

Taste and odor problems can impede public trust in drinking water and impose major costs on water utilities. The ability to forecast taste and odor events in source waters, in advance, is shown for the first time in this paper. This could allow water utilities to adapt treatment, and where effective treatment is not available, consumers could be warned. A unique 24-year time series, from an important drinking water reservoir in Saskatchewan, Canada, is used to develop forecasting models of odor using chlorophyll a, turbidity, total phosphorus, temperature, and the following odor producing algae taxa: Anabaena spp., Aphanizemenon spp., Oscillatoria spp., Chlorophyta, Cyclotella spp., and Asterionella spp. We demonstrate, using linear regression and random forest models, that odor events can be forecast at 0-26 week time lags, and that the models are able to capture a significant increase in threshold odor number in the mid-1990s. Models with a fortnight time-lag show a high predictive capacity (R² = 0.71 for random forest; 0.52 for linear regression). Predictive skill declines for time lags from 0 to 15 weeks, then increases again, to R² values of 0.61 (random forest) and 0.48 (linear regression) at a 26-week lag. The random forest model is also able to provide accurate forecasting of TON levels requiring treatment 12 weeks in advance--93% true positive rate with a 0% false positive rate. Results of the random forest model demonstrate that phytoplankton taxonomic data outperform chlorophyll a in terms of predictive importance. [ABSTRACT FROM AUTHOR]

The neurotoxic alkaloid β-N-methyl-amino-l-alanine (BMAA) and related isomers, including N-(2-aminoethyl glycine) (AEG), β-amino-N-methyl alanine (BAMA), and 2,4-diaminobutyric acid (DAB), have been reported previously in cyanobacterial samples. However, there are conflicting reports regarding their occurrence in surface waters. In this study, we evaluated the impact of amending lake water samples with trichloroacetic acid (0.1 M TCA) on the detection of BMAA isomers, compared with pre-existing protocols. A sensitive instrumental method was enlisted for the survey, with limits of detection in the range of 5–10 ng L−1. Higher detection rates and significantly greater levels (paired Wilcoxon's signed-rank tests, p < 0.001) of BMAA isomers were observed in TCA-amended samples (method B) compared to samples without TCA (method A). The overall range of B/A ratios was 0.67–8.25 for AEG (up to +725%) and 0.69–15.5 for DAB (up to +1450%), with absolute concentration increases in TCA-amended samples of up to +15,000 ng L−1 for AEG and +650 ng L−1 for DAB. We also documented the trends in the occurrence of BMAA isomers for a large breadth of field-collected lakes from Brazil, Canada, France, Mexico, and the United Kingdom. Data gathered during this overarching campaign (overall, n = 390 within 45 lake sampling sites) indicated frequent detections of AEG and DAB isomers, with detection rates of 30% and 43% and maximum levels of 19,000 ng L−1 and 1100 ng L−1, respectively. In contrast, BAMA was found in less than 8% of the water samples, and BMAA was not found in any sample. These results support the analyses of free-living cyanobacteria, wherein BMAA was often reported at concentrations of 2–4 orders of magnitude lower than AEG and DAB. Seasonal measurements conducted at two bloom-impacted lakes indicated limited correlations of BMAA isomers with total microcystins or chlorophyll-a, which deserves further investigation. [ABSTRACT FROM AUTHOR]

Here, we explore how people entangled in natural resource conflicts employ and discuss data. We draw on ethnographic research with two cases of conflict: salmon fisheries in Alaska, USA, and agricultural water management in Saskatchewan, Canada. Both cases illustrate how data, through the scientization of environmental governance, can become a means of empowerment and disempowerment: empowering those with access and influence over data and disempowering those without such access. In both locales, people find it necessary to perform their expertise, justify the veracity of their data, and discount the data held by others if they wish to achieve or maintain standing. We call this "datamentality" and draw lessons from these cases for how we can structure environmental governance such that it benefits from robust data and science while meeting the needs of individuals, avoiding or managing power struggles, and protecting the rights of all involved. [ABSTRACT FROM AUTHOR]

Abstract: Freshwater lakes are known to release carbon dioxide (CO2) and methane (CH4) to the atmosphere; however, the importance of lakes in global nitrous oxide (N2O) budgets is not yet known. Further, despite the abundance of small lakes on the landscape, neither emissions of these gases nor their drivers are well described. Dissolved concentrations of CO2, CH4 and N2O greenhouse gases were related to water chemistry, hydrology and catchment characteristics in order to identify factors controlling gas concentrations for 121 small Irish headwater lakes (median area: 2.0ha) in relatively undisturbed catchments; lake–atmosphere gas fluxes were also calculated. The majority of lakes were supersaturated (relative to the atmosphere) with CO2 and N2O while CH4 was above saturation in all lakes. Dissolved gas concentrations were correlated with land cover (rock, forest and grassland), deuterium excess (an indicator of hydrologic character) and lake organic carbon concentrations, although dissolved CO2 exhibited few significant relationships. Principal components analysis indicated that higher levels of CH4 and N2O supersaturation were exhibited under different conditions. Methane supersaturation was highest in low elevation catchments with an evaporative hydrologic character and high organic carbon concentrations. In contrast, lakes characteristic of N2O supersaturation were low in carbon and located in more rapidly flushed higher elevation catchments. Estimated fluxes of CO2, CH4 and N2O to the atmosphere averaged 14, 0.36 and 1.3×10−3 mmolm−2 d−1, respectively. [Copyright &y& Elsevier]

Chemical recovery is hypothesized to promote rapid recovery of benthic algal communities in formerly acidified lakes; this expectation needs modification. We evaluated the hypothesis in a small lake (L302S) in the boreal forest of northwestern Ontario, Canada, during a decade of pH recovery following a prior decade of experimental acidification from pH 6.7 to 4.5. To account for regional changes during the study, we also studied a nearby reference lake (L239). Taxonomic changes in the epilithon (biofilm on rock surfaces) included persistently lower cyanobacterial biomass following its acidification-related decline and increases in both diatoms and greens. Epilithic metabolic recovery was incomplete because the acidification-induced increase in respiration continued, although the prior decline in photosynthesis was reversed. Unexpectedly, blooms of metaphytic filamentous green algae occurred at higher pH during recovery than during acidification. Although several community attributes recovered fully, recovery of many aggregate functional and taxonomic properties lagged improvements in pH. Divergence was greater at the taxonomic than at the functional level. Despite pH recovery, potential causes of incomplete algal recovery include incomplete chemical recovery and the persistent absence of functionally important biota. Our findings counter the assumption that ecological recovery mirrors the pathway of damage caused by a human stressor. [ABSTRACT FROM AUTHOR]

Scientific Significance Statement: Metabolic stoichiometry predicts that dissolved oxygen (O2) and carbon dioxide (CO2) in aquatic ecosystems should covary inversely; however, field observations often diverge from theoretical expectations. Here, we propose a suite of metrics describing this O2 and CO2 decoupling and introduce a conceptual framework for interpreting these metrics within aquatic ecosystems. Within this framework, we interpret cross‐system patterns of high‐frequency O2 and CO2 measurements in 11 northern lakes and extract emergent insights into the metabolic behavior and the simultaneous roles of chemical and physical forcing in shaping ecosystem processes. This approach leverages the power of high‐frequency paired O2–CO2 measurements, and yields a novel, integrative aquatic system typology which can also be applicable more broadly to streams and rivers, wetlands and marine systems. [ABSTRACT FROM AUTHOR]

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 N2Omeasurements 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. [ABSTRACT FROM AUTHOR]

Abstract The heterogeneity of dissolved organic matter (DOM) in natural and human impacted waters and the variety of drinking water treatment processes employed has made a mechanistic understanding of disinfection byproduct (DBP) formation challenging. In this study, we examined the formation of the regulated DBPs (Trichloromethanes, THM, and Haloacetic acids, HAA) during full-scale water treatment operations both with prechlorination treatment (normal operations for the drinking water plant) and without (altered operations); followed by coagulation, flocculation, filtration, and chlorination. The source water DOM concentration ranged 6.4 to 7.3 mg-C/L. DOM composition was moderately humic and degraded with a mix of microbial- and terrestrial-like characteristics. Removal of raw water prechlorination caused an average reduction in total THM and HAA concentrations of 52.7% and 40.0%, respectively, with the greater reduction noted for chlorinated-DBPs rather than brominated-DBPs. Prechlorination treatment resulted in a higher relative production of Cl 3 CH and BrCl 2 CH associated with aromatic, humic, and terrestrial-like DOM. Without prechlorination, the DBP pool had higher proportions of brominated-DBPs (Br 3 CH, Br 2 ClCH, Br 2 CHCOOH, BrClCHCOOH, and BrCH 2 COOH) associated with microbial-like, processed humic-like, and protein-like DOM. These observed patterns could not be explained by chloride demand and DOM concentration, indicating that DOM composition played an important role in DBP formation. Graphical abstract Unlabelled Image Highlights • Changing surface water quality can alter disinfection byproduct (DBP) formation. • A plant-scale change was performed to measure effects of removing prechlorination. • Operational changes altered organic matter quality and DBP type and amount. • Removal of prechlorination was only effective in reducing a subset of DBPs. • Br-containing DBPs were less impacted by operationally change than Cl-DBPs. [ABSTRACT FROM AUTHOR]

Winter conditions are rapidly changing in temperate ecosystems, particularly for those that experience periods of snow and ice cover. Relatively little is known of winter ecology in these systems, due to a historical research focus on summer 'growing seasons'. We executed the first global quantitative synthesis on under-ice lake ecology, including 36 abiotic and biotic variables from 42 research groups and 101 lakes, examining seasonal differences and connections as well as how seasonal differences vary with geophysical factors. Plankton were more abundant under ice than expected; mean winter values were 43.2% of summer values for chlorophyll a, 15.8% of summer phytoplankton biovolume and 25.3% of summer zooplankton density. Dissolved nitrogen concentrations were typically higher during winter, and these differences were exaggerated in smaller lakes. Lake size also influenced winter-summer patterns for dissolved organic carbon ( DOC), with higher winter DOC in smaller lakes. At coarse levels of taxonomic aggregation, phytoplankton and zooplankton community composition showed few systematic differences between seasons, although literature suggests that seasonal differences are frequently lake-specific, species-specific, or occur at the level of functional group. Within the subset of lakes that had longer time series, winter influenced the subsequent summer for some nutrient variables and zooplankton biomass. [ABSTRACT FROM AUTHOR]

Algal blooms fueled by phosphorus (P) enrichment are threatening surface water quality around the world. Although P loss from arable land is a critical contributor to P loads in many agricultural watersheds, there has been a lack of understanding of P loss patterns and drivers across regions. Here, we synthesized edge-of-field P and sediment runoff data for 30 arable fields in the Canadian provinces of Saskatchewan, Manitoba and Ontario (a total of 216 site-years) to elucidate spatial and temporal differences in runoff and P mobilization in snowmelt and rainfall runoff, and discuss climatic, soil and management drivers for these patterns. Across all regions, precipitation inputs were positively correlated with runoff amounts and consequently P loads. Runoff and P losses were dominated by snowmelt across all sites, however, regional differences in runoff amounts, and P concentrations, loads and speciation were apparent. Proportions of total P in the dissolved form were greater in the prairie region (55–94% in Manitoba) than in the Great Lakes region (26–35% in Ontario). In Manitoba, dissolved P concentrations in both snowmelt and rainfall runoff were strongly positively correlated to soil Olsen P concentrations in the 0–5 cm soil depth; however, this relationship was not found for Ontario fields, where tile drainage dominated hydrologic losses. Although precipitation amounts and runoff volumes were greater in Ontario than Manitoba, some of the greatest P loads were observed from Manitoba fields, driven by management practices. This synthesis highlights the differences across the Canadian agricultural regions in P runoff patterns and drivers, and suggests the need of co-ordinated and standardized monitoring programs to better understand regional differences and inform management. Phosphorus runoff patterns vary with climatic regions across Canada. †The dissolved P was measured as total dissolved P in MB and dissolved reactive P in SK and ON. ‡Total P was not measured in SK. [Display omitted] • Phosphorus runoff patterns and drivers vary with climatic regions across Canada. • Co-ordinated and standardized monitoring programs are key to clarify regional differences. • Snowmelt dominates runoff volume and phosphorus loss across Canada. • The predominant form of P in runoff differs between the Prairie region and the Great Lakes region. • Reducing phosphorus sources is important for mitigating phosphorus runoff. [ABSTRACT FROM AUTHOR]

The distribution and quality of water resources vary dramatically across Canada, and human impacts such as land-use and climate changes are exacerbating uncertainties in water supply and security. At the national level, Canada has no enforceable standards for safe drinking water and no comprehensive water-monitoring program to provide detailed, timely reporting on the state of water resources. To provide Canada's first national assessment of lake health, the NSERC Canadian Lake Pulse Network was launched in 2016 as an academic-government research partnership. LakePulse uses traditional approaches for limnological monitoring as well as state-of-the-art methods in the fields of genomics, emerging contaminants, greenhouse gases, invasive pathogens, paleolimnology, spatial modelling, statistical analysis, and remote sensing. A coordinated sampling program of about 680 lakes together with historical archives and a geomatics analysis of over 80,000 lake watersheds are used to examine the extent to which lakes are being altered now and in the future, and how this impacts aquatic ecosystem services of societal importance. Herein we review the network context, objectives and methods. Unlabelled Image • About 90% of Canada's municipal drinking water supplies are from surface waters. • An academic-government group is providing the first national review of lake health. • Over 100 variables were sampled at about 680 lakes across Canada. • Topics range from greenhouse gases to emerging contaminants to invasive pathogens. • The impacts of land-use and climate changes on lake health are also studied. [ABSTRACT FROM AUTHOR]

Citizen science projects have a long history in ecological studies. The research usefulness of such projects is dependent on applying simple and standardized methods. Here, we conducted a citizen science project that involved more than 3500 Swedish high school students to examine the temperature difference between surface water and the overlying air (Tw-Ta) as a proxy for sensible heat flux (QH). If QH is directed upward, corresponding to positive Tw-Ta, it can enhance CO2 and CH4 emissions from inland waters, thereby contributing to increased greenhouse gas concentrations in the atmosphere. The students found mostly negative Tw-Ta across small ponds, lakes, streams/rivers and the sea shore (i.e. downward QH), with Tw-Ta becoming increasingly negative with increasing Ta. Further examination of Tw-Ta using high-frequency temperature data from inland waters across the globe confirmed that Tw-Ta is linearly related to Ta. Using the longest available high-frequency temperature time series from Lake Erken, Sweden, we found a rapid increase in the occasions of negative Tw-Ta with increasing annual mean Ta since 1989. From these results, we can expect that ongoing and projected global warming will result in increasingly negative Tw-Ta, thereby reducing CO2 and CH4 transfer velocities from inland waters into the atmosphere. [ABSTRACT FROM AUTHOR]