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Zooplankton community composition of northern lakes is changing due to the interactive effects of climate change and recovery from acidification, yet limited data are available to assess these changes combined. Here, we built a database using archives of temperature, water chemistry and zooplankton data from 60 Scandinavian lakes that represent broad spatial and temporal gradients in key parameters: temperature, calcium (Ca), total phosphorus (TP), total organic carbon (TOC), and pH. Using machine learning techniques, we found that Ca was the most important determinant of the relative abundance of all zooplankton groups studied, while pH was second, and TOC third in importance. Further, we found that Ca is declining in almost all lakes, and we detected a critical Ca threshold in lake water of 1.3 mg L−1, below which the relative abundance of zooplankton shifts toward dominance of Holopedium gibberum and small cladocerans at the expense of Daphnia and copepods. Our findings suggest that low Ca concentrations may shape zooplankton communities, and that current trajectories of Ca decline could promote widespread changes in pelagic food webs as zooplankton are important trophic links from phytoplankton to fish and different zooplankton species play different roles in this context. [ABSTRACT FROM AUTHOR]

Cyanobacterial blooms pose a significant threat to water security, with anthropogenic forcing being implicated as a key driver behind the recent upsurge and global expansion of cyanobacteria in modern times. The potential effects of land‐use alterations and climate change can lead to complicated, less‐predictable scenarios in cyanobacterial management, especially when forecasting cyanobacterial toxin risks. There is a growing need for further investigations into the specific stressors that stimulate cyanobacterial toxins, as well as resolving the uncertainty surrounding the historical or contemporary nature of cyanobacterial‐associated risks. To address this gap, we employed a paleolimnological approach to reconstruct cyanobacterial abundance and microcystin‐producing potential in temperate lakes situated along a human impact gradient. We identified breakpoints (i.e., points of abrupt change) in these time series and examined the impact of landscape and climatic properties on their occurrence. Our findings indicate that lakes subject to greater human influence exhibited an earlier onset of cyanobacterial biomass by 40 years compared to less‐impacted lakes, with land‐use change emerging as the dominant predictor. Moreover, microcystin‐producing potential increased in both high‐ and low‐impact lakes around the 1980s, with climate warming being the primary driver. Our findings chronicle the importance of climate change in increasing the risk of toxigenic cyanobacteria in freshwater resources. [ABSTRACT FROM AUTHOR]

In recent years, unexplained declines in lake total phosphorus (TP) concentrations have been observed at northern latitudes (> 42°N latitude) where most of the world's lakes are found. We compiled data from 389 lakes in Fennoscandia and eastern North America to investigate the effects of climate on lake TP concentrations. Synchrony in year‐to‐year variability is an indicator of climatic influences on lake TP, because other major influences on nutrients (e.g., land use change) are not likely to affect all lakes in the same year. We identified significant synchrony in lake TP both within and among different geographic regions. Using a bootstrapped random forest analysis, we identified winter temperature as the most important factor controlling annual TP, followed by summer precipitation. In Fennoscandia, TP was negatively correlated with the winter East Atlantic Pattern, which is associated with regionally warmer winters. Our results suggest that, in the absence of other overriding factors, lake TP and productivity may decline with continued winter warming in northern lakes. [ABSTRACT FROM AUTHOR]

In October 2011, the Halloween Nor'easter produced unusually early and heavy snowfall while leaves were still on the trees, causing extensive damage throughout the northeastern United States. This storm is an example of winter weather whiplash, in which an abrupt, back-and-forth swing in winter weather affects coupled human and natural systems. Research on the social-ecological drivers and impacts of winter weather whiplash is scarce because most studies only consider meteorological causes and consequences of extreme events. In this study, we used publicly available data of snowfall accumulation, vegetation phenology, road density, and per capita income to predict storm impacts, which we estimated with textual analysis of Halloween Nor'easter newspaper coverage. We demonstrated that a combination of meteorological, natural, and human system drivers was better able to predict the impact of the storm than meteorological drivers alone. Although we focused on the Halloween Nor'easter, our work highlights the necessity of understanding how multiple drivers and hazards can intersect to create rare and possibly novel conditions that may become more common as the climate warms and becomes more variable. [ABSTRACT FROM AUTHOR]

Watershed resilience is the ability of a watershed to maintain its characteristic system state while concurrently resisting, adapting to, and reorganizing after hydrological (for example, drought, flooding) or biogeochemical (for example, excessive nutrient) disturbances. Vulnerable waters include non-floodplain wetlands and headwater streams, abundant watershed components representing the most distal extent of the freshwater aquatic network. Vulnerable waters are hydrologically dynamic and biogeochemically reactive aquatic systems, storing, processing, and releasing water and entrained (that is, dissolved and particulate) materials along expanding and contracting aquatic networks. The hydrological and biogeochemical functions emerging from these processes affect the magnitude, frequency, timing, duration, storage, and rate of change of material and energy fluxes among watershed components and to downstream waters, thereby maintaining watershed states and imparting watershed resilience. We present here a conceptual framework for understanding how vulnerable waters confer watershed resilience. We demonstrate how individual and cumulative vulnerable-water modifications (for example, reduced extent, altered connectivity) affect watershed-scale hydrological and biogeochemical disturbance response and recovery, which decreases watershed resilience and can trigger transitions across thresholds to alternative watershed states (for example, states conducive to increased flood frequency or nutrient concentrations). We subsequently describe how resilient watersheds require spatial heterogeneity and temporal variability in hydrological and biogeochemical interactions between terrestrial systems and down-gradient waters, which necessitates attention to the conservation and restoration of vulnerable waters and their downstream connectivity gradients. To conclude, we provide actionable principles for resilient watersheds and articulate research needs to further watershed resilience science and vulnerable-water management. [ABSTRACT FROM AUTHOR]

Ecologists collectively predict that climate change will enhance phytoplankton biomass in northern lakes. Yet there are unique variations in the structures and regulating functions of lakes to make this prediction challengeable and, perhaps, inaccurate. We used archived Landsat TM/ETM+ satellite products to estimate epilimnetic chlorophyll‐a (Chl‐a) concentration as a proxy for phytoplankton biomass in 281 northern temperate lakes over 28 years. We explored the influence of climate (air temperature, precipitation) and landscape proxies for nutrient sources (proportion of wetlands in a contributing catchment, size of the littoral zone, potential for wind‐driven sediment resuspension as estimated by the dynamic ratio) or nutrient sinks (lake volume) in a random forest model to explain heterogeneity in peak Chl‐a. Lakes with higher Chl‐a (median Chl‐a = 2.4 μg L−1, n = 40) had smaller volumes (<44 × 104 m3) and were more sensitive to increases in temperature. In contrast, lakes with lower Chl‐a (median Chl‐a = 0.6 μg L−1, n = 241) had larger volumes (≥44 × 104 m3), contributing catchments with smaller proportions of wetlands (<4.5% of catchment area, n = 70), smaller littoral zones (<16.4 ha, n = 137), minimal wind‐driven sediment resuspension (as defined by the dynamic ratio; <0.45, n = 232), and were more sensitive to increases in precipitation. Lakes with larger volumes were generally less responsive to climate factors; however, larger volume lakes with a significant proportion of wetlands and larger littoral zones behaved similarly to lakes with smaller volumes. Our finding that lakes with different landscape properties respond differently to climate factors may help predict the susceptibility of lakes to eutrophication under changing climatic conditions. [ABSTRACT FROM AUTHOR]

Meromictic lakes provide a physically stable environment in which proxies for potentially harmful cyanobacteria are exceptionally well-preserved in the sediments. In Sunfish Lake, a meromictic lake that has recently become the focus of citizen concern due to the apparent rise in cyanobacteria blooms, we used a multi-proxy paleolimnological approach pairing novel spectral (i.e., VNIRS) and molecular (i.e., qPCR) assessment tools to explore long-term cyanobacteria trends. We hypothesized that climate change over the past 50 years altered the Sunfish Lake environment to favour cyanobacteria dominance, resulting in an increased incidence of bloom events. Spectral and genetic results aligned to reveal an unprecedented abundance of cyanobacteria in modern times and coincided with warmer and wetter climatic conditions in the region. Our findings offer evidence for climate-driven shifts in cyanobacteria abundance and suggest that a shift towards warmer and wetter conditions supports the rise of cyanobacteria in lakes. [ABSTRACT FROM AUTHOR]

Increased reports of phytoplankton blooms in remote pristine lakes provide the perception that climate-driven fundamental changes may be occurring in lake ecosystems. There is a crucial need for detailed surveys of lakes covering large spatial and temporal scales to determine whether phytoplankton biomass is on the rise in northern forested landscapes. To characterize spatial and temporal variation in chlorophyll-a (Chl-a) as a proxy of phytoplankton biomass in lakes located in the relatively intact northern temperate forest in the Great Lakes-St. Lawrence forest region, we developed a regression model that relates Landsat 4–5 TM and 7 ETM + optical reflectance in blue, green, and red bands to Chl-a from 45 lake water samples. Reflectance from the Landsat three-band algorithm ((B1-B3)/B2) showed the strongest correlation with in situ data explaining 78% of the variance in Chl-a. We applied this model to produce a 28-year time series of Chl-a in 12,644 lakes within the northern temperate forest. By applying a two-way analysis of variance, we were able to quantify the different components of variation in Chl-a. We found that space and time components combined explained 55.9% of the total variation in Chl-a (35.6% for space and 20.3% for time), while the space × time interaction component explained 44.1% of the variation. The spatial pattern revealed relatively low Chl-a in headwater lakes to higher Chl-a in lower reaches of watersheds. Only a minority of lakes were found to have a temporal trend in Chl-a; some lakes displayed positive trends while others displayed negative trends. The trends were substantial enough to indicate changes in trophic states (that is, oligotrophic lakes becoming eutrophic, or vice versa). These spatial and temporal patterns indicate the complex interactions of local and regional catchment characteristics and lake-specific properties that filter the response of northern lakes to climate change. The large proportion of the space × time interaction component shows the importance of processes occurring within lakes that affect water mixing and nutrient concentrations and therefore availability of the nutrients to phytoplankton. [ABSTRACT FROM AUTHOR]

Northern lakes are experiencing widespread increases in dissolved organic carbon (DOC) that are likely to lead to changes in pelagic phytoplankton biomass. Pelagic phytoplankton biomass responds to trade-offs between light and nutrient availability. However, the influence of DOC light absorbing properties and carbon–nutrient stoichiometry on phytoplankton biomass across seasonal or spatial gradients has not been assessed. Here, we analyzed data from almost 5000 lakes to examine how the carbon–phytoplankton biomass relationship is influenced by seasonal changes in light availability, DOC light absorbing properties (carbon-specific visual absorbance, SVA420), and DOC–nutrient [total nitrogen (TN) and total phosphorus (TP)] stoichiometry, using TOC as a proxy for DOC. We found evidence for trade-offs between light and nutrient availability in the relationship between DOC and phytoplankton biomass [chlorophyll (chl)-a], with the shape of the relationship varying with season. A clear unimodal relationship was found only in the fall, particularly in the subsets of lakes with the highest TOC:TP. Observed trends of increasing TOC:TP and decreasing TOC:TN suggest that the effects of future browning will be contingent on future changes in carbon–nutrient stoichiometry. If browning continues, phytoplankton biomass will likely increase in most northern lakes, with increases of up to 76% for a 1.7 mg L−1 increase in DOC expected in subarctic regions, where DOC, SVA420, DOC:TN, and DOC:TP are all low. In boreal regions with higher DOC and higher SVA420, and thus lower light availability, lakes may experience only moderate increases or even decreases in phytoplankton biomass with future browning. [ABSTRACT FROM AUTHOR]

Increasing inputs of dissolved organic matter (DOM) to northern lakes is resulting in ‘lake browning.’ Lake browning profoundly affects phytoplankton community composition by modifying two important environmental drivers—light and nutrients. The impact of increased DOM on native isolates of red and green-pigmented cyanobacteria identified as Pseudanabaena, which emerged from a Dolichospermum bloom (Dickson Lake, Algonquin Provincial Park, Ontario, Canada) in 2015, were examined under controlled laboratory conditions. The genomes were sequenced to identify phylogenetic relatedness and physiological similarities, and the physical and chemical effects of increased DOM on cellular performance and competitiveness were assessed. Our study findings were that the isolated red and green phenotypes are two distinct species belonging to the genus Pseudanabaena; that both isolates remained physiologically unaffected when grown independently under defined DOM regimes; and that neither red nor green phenotype achieved a competitive advantage when grown together under defined DOM regimes. While photosynthetic pigment diversity among phytoplankton offers niche-differentiation opportunities, the results of this study illustrate the coexistence of two distinct photosynthetic pigment phenotypes under increasing DOM conditions. [ABSTRACT FROM AUTHOR]

Lake browning—the increase in catchment-derived (allochthonous) dissolved organic matter (DOM) to lakes—is altering lake physicochemical environments, with consequences for phytoplankton biomass and community composition. We hypothesized that as lakes brown, there will be an increase in phytoplankton biomass and a shift to cyanobacteria-dominated phytoplankton communities as a result of the reduced light availability and increased DOM-bound nutrients (e.g., nitrogen, phosphorus, iron). We tested this hypothesis by sampling temperate lakes in central Ontario (Canada) spanning DOM quantity and quality gradients. We found that lake browning results in larger concentrations of more refractory (i.e., aromatic, high molecular weight) DOM and greater concentrations of nutrients; however, internal nutrient loading was also an important nutrient source in these lakes. We also found that these changes were related to the predominant species in the phytoplankton community. Diatoms dominated in clear oligotrophic lakes. Low levels of lake browning, with concentrations of dissolved organic carbon (DOC) between 4 and 8 mg L− 1, resulted in a shift from diatoms to cyanobacteria. Higher levels of lake browning, with concentrations of DOC between 8 and 12 mg L− 1, resulted in a replacement of cyanobacteria with mixotrophic species. Lake browning appears to fuel phytoplankton chlorophyll-a concentrations while triggering shifts to phytoplankton able to survive if not thrive in progressively browner waters. Lake browning may therefore have consequences on energy transfer through the lower food web. [ABSTRACT FROM AUTHOR]

The article focuses on harmful algal blooms at Great Lakes St. Lawrence River Basin. It mentions key elements for establishing such a framework, including possible legal and coordinating mechanisms, guiding legal principles, scientifically-based management measures, and the necessity of process, accountability, and enforcement for maintaining public health.

The article informs on the 2020 Canada-U.S. Law Institute Symposium on a state-provincial approach to harmful algal blooms in the Great Lakes Basin. It mentions greater coordination between two countries in terms of being able to monitor where these blooms, and sub-federal, binational approach to harmful algal blooms, and to get their responses, at least preliminarily through the use of data.

The article informs on the 2020 Canada-U.S. Law Institute Symposium on a state-provincial approach to harmful algal blooms in the Great Lakes Basin. It mentions that rich diversity of algal species in a harmful algal bloom event, including both native species and invasive ones, and greater coordination between our two countries in terms of being able to monitor where these blooms, and where toxic blooms occur.

The global rise of cyanobacterial blooms emphasizes the need to develop tools to manage water bodies prone to cyanobacterial dominance. Reconstructing cyanobacterial baselines and identifying environmental drivers that favour cyanobacterial dominance are important to guide management decisions. Conventional techniques for estimating cyanobacteria in lake sediments require considerable resources, creating a barrier to routine reconstructions of cyanobacterial time-series. Here, we compare a relatively simple technique based on spectral inferences of cyanobacteria using visible near-infrared reflectance spectroscopy (VNIRS) with a molecular technique based on real-time PCR quantification (qPCR) of the 16S rRNA gene conserved in cyanobacteria in 30 lakes across a broad geographic gradient. We examined the sedimentary record from two perspectives: 1) relationships throughout the entire core (without radiometric dating); 2) relationships post-1900s with the aid of radiometric dating (i.e., 210Pb). Our findings suggest that the VNIRS-based cyanobacteria technique is best suited for reconstructing cyanobacterial abundance in recent decades (i.e., circa 1990 onwards). The VNIRS-based cyanobacteria technique showed agreement with those generated using qPCR, with 23 (76%) lakes showing a strong or very strong positive relationship between the results of the two techniques. However, five (17%) lakes showed negligible relationships, suggesting cyanobacteria VNIRS requires further refinement to understand where VNIRS is unsuitable. This knowledge will help scientists and lake managers select alternative cyanobacterial diagnostics where appropriate. These findings demonstrate the utility of VNIRS, in most instances, as a valuable tool for reconstructing past cyanobacterial prevalence. • Paleolimnology expands monitoring windows, helping establish cyanobacteria baselines. • Limited access to cyano-paleolimnological tools represents a management challenge. • Cyanobacteria VNIRS represents an inexpensive and rapid cyanobacteria diagnostic tool. • Cyanobacteria VNIRS yields similar results to traditional paleolimnological proxies. [ABSTRACT FROM AUTHOR]

The interacting effects of global changes—including increased temperature, altered precipitation, reduced acidification and increased dissolved organic matter loads to lakes—are anticipated to create favourable environmental conditions for cyanobacteria in northern lakes. However, responses of cyanobacteria to these global changes are complex, if not contradictory. We hypothesized that absolute and relative biovolumes of cyanobacteria (both total and specific genera) are increasing in Swedish nutrient‐poor lakes and that these increases are associated with global changes. We tested these hypotheses using data from 28 nutrient‐poor Swedish lakes over 16 years (1998–2013). Increases in cyanobacteria relative biovolume were identified in 21% of the study sites, primarily in the southeastern region of Sweden, and were composed mostly of increases from three specific genera: Merismopedia, Chroococcus and Dolichospermum. Taxon‐specific changes were related to different environmental stressors; that is, increased surface water temperature favoured higher Merismopedia relative biovolume in low pH lakes with high nitrogen to phosphorus ratios, whereas acidification recovery was statistically related to increased relative biovolumes of Chroococcus and Dolichospermum. In addition, enhanced dissolved organic matter loads were identified as potential determinants of Chroococcus suppression and Dolichospermum promotion. Our findings highlight that specific genera of cyanobacteria benefit from different environmental changes. Our ability to predict the risk of cyanobacteria prevalence requires consideration of the environmental condition of a lake and the sensitivities of the cyanobacteria genera within the lake. Regional patterns may emerge due to spatial autocorrelations within and among lake history, rates and direction of environmental change and the niche space occupied by specific cyanobacteria. [ABSTRACT FROM AUTHOR]

The chemical form of nitrogen (N) is deemed to be decisive in shaping the composition of the primary producer community. Recently, there has been a shift in the dominant form of N delivered to agricultural landscapes. Urea‐based fertilizers are a mainstay in modern agriculture, and their ubiquitous use has increased the likelihood of urea export to nearby freshwaters. The shift to urea fertilizers has coincided with the recent expansion of cyanobacteria harmful algal blooms (cyanoHABs). This study investigated N drawdown patterns between two major freshwater phytoplankton groups—chlorophytes and cyanobacteria. Experiments were designed to understand if different patterns of N drawdown occurred among taxa and the potential synergistic effects of multiple N substrates. Nitrate (NO3−), ammonium (NH4+), and urea were supplied in a series of paired combinations, and N concentrations were monitored to track N drawdowns. We did not find significant differences between phytoplankton classes when supplied with a single N substrate. However, we found that when N substrates were supplied in combination, significant differences in N drawdown patterns were observed. Urea was consumed more rapidly among cyanobacteria, being drawn down at significantly higher rates relative to inorganic N substrates. In contrast, inorganic N substrates were drawn down more rapidly among chlorophytes relative to urea. Our findings support the emerging urea–cyanoHAB link and the potential importance of urea in freshwater eutrophication. As society becomes increasingly dependent on urea for agricultural crops, the need to understand how urea influences phytoplankton community composition may be instrumental in predicting bloom dynamics. [ABSTRACT FROM AUTHOR]

Atmospheric changes are leading to the browning of northern lakes (i.e. increases in catchment‐derived dissolved organic matter [DOM]), consequently altering phytoplankton biomass and community composition.We hypothesised that lake browning and the concurrent increase in nutrients drive a shift towards greater cyanobacteria biomass. We further hypothesised that, as a consequence of this shift in phytoplankton, the content of ω‐3 (n‐3) essential fatty acids (EFA) in seston would decline, affecting the subsequent transfer of EFA to consumers across the plant–animal interface in pelagic regions of lakes.We tested these hypotheses in the epilimnion of 30 temperate lakes in Ontario (Canada), representing a gradient of lake browning, with dissolved organic carbon (DOC) ranging from 2 to 10 mg/L and total phosphorus ranging from 6.0 to 48.5 μg/L. In each of these lakes, the concentration and composition of DOM, the biomass of phytoplankton and cyanobacteria, and the EFA content of seston, cladocerans, and copepods were measured.An increase in aromatic DOM was associated with increased phytoplankton and cyanobacteria biomass. Due to the lower content of the EFA eicosapentaenoic acid (EPA; 20:5n‐3) and docosahexaenoic acid (DHA; 22:6n‐3) in cyanobacteria, this increase in phytoplankton biomass was associated with a decline in EPA and DHA content in lake seston. However, there was no significant change in EFA content of cladocerans and copepods. This homeostatic (diet‐independent) EFA composition in zooplankton suggested that, as the phytoplankton community shifted towards more cyanobacteria with lower EFA content, the cladocerans and copepods may have met their nutritional requirements by relying on alternative food sources (e.g. heterotrophic ciliates and flagellates) capable of either trophically upgrading phytoplankton‐produced EPA and DHA, or synthesising EPA and DHA de novo.Results from this study indicate that increasing DOC from low (2 mg DOC/L) to moderate levels (15 mg DOC/L) may increase the importance of the microbial pathway in the trophic transfer of EPA and DHA from basal resources to zooplankton. However, this supplementary transfer of EFA through the microbial food web may not sustain high EPA and DHA levels in zooplankton when lake browning starts to limit primary production (>15 mg DOC/L). [ABSTRACT FROM AUTHOR]

Iron (Fe) is an important regulator of phosphorus and nitrogen use efficiency by phytoplankton. We tested the prediction that pelagic cyanobacteria biomass in surface waters of shallow eutrophic lakes with low ferric ion concentration is linked to the presence, and potential utilization, of low molecular weight Fe-binding ligands. We sampled 30 lakes in Alberta, Canada, in 2012 for nutrients, cyanobacteria biomass, Fe-binding ligands (hydroxamates and catecholates), and toxins. Bioavailable ferric ion concentration (estimated as pFe) was significantly correlated to cyanobacteria biomass (curvilinear relationship, r2 = 0.45, P < 0.05). Nonmetric multidimensional models indicated that high cyanobacteria biomass corresponded to lakes with low ferric ion concentration (pFe ∼ 19), and regression tree analyses identified a threshold in ferric ion concentration (pFe = 22.1) that separated lakes with relatively low versus high cyanobacteria biomass. Where ferric ion concentration was low, hydroxamate-reactive compound concentration was positively correlated to cyanobacteria biomass. As the environment goes from higher to lower ferric ion concentration, the presence of cyanobacteria increases, and with further reduction of Fe, the environmental need for Fe-binding ligands becomes manifest. [ABSTRACT FROM AUTHOR]

The policy landscape is changing as Canada considers its energy future. The Canadian boreal zone has a large amount of natural resources, giving Canada options in terms of its energy future. However, the sustainability of the boreal zone has been deemed at risk because of the cumulative effects of intensifying natural resource activities (forestry, mining, oil and gas, and renewable energy) on ecosystems in the face of the uncertainty associated with climate change. As Canada considers the future of the boreal zone, there will be additional challenges to ensure that we do not further disadvantage marginalized human populations living in the boreal zone who are at high risk of the consequences of climate change. In response to these challenges, the Boreal 2050 project was initiated to understand the risk of failing to achieve the future sustainability of the boreal zone using the ISO 31000 risk management framework. First, we identified the major drivers of the risks to the sustainability of the boreal zone, which include atmospheric change, the demand for provisioning and nonprovisioning ecosystem services, demographics and societal values, industrial innovation and infrastructure, and governance. Second, we analyzed the risk of failing to achieve a sustainable boreal zone using scenario analysis, where we framed four plausible future scenarios around two axes of change: the global economy's energy and society's capacity to adapt. Third, we evaluated the risk and determined that present governance systems are driving Canada towards failing to achieve a sustainable boreal zone. To ensure the future sustainability of the boreal, we need to shift from an oil/gas/coal-producing country to a renewable energy leader and shift from using a top-down strategy where Canadians have a low capacity to adapt towards a mixture of top-down and bottom-up participatory strategies where Canadians—particularly Indigenous peoples living in the boreal zone—have a higher capacity to adapt. To facilitate this shift in governance, substantive changes will be required in institutional arrangements designed to protect boreal ecosystems. [ABSTRACT FROM AUTHOR]

Canada will be unable to meet its greenhouse gas pledges—of reducing greenhouse gas emissions by 30% over 2005 levels by 2030—without transitioning away from the current high-carbon economy. This transition will bring new challenges, especially to the Canadian boreal zone. The boreal zone continues to experience intensive natural resource activities including the extraction of forest, mining, oil and gas, and renewable energy products, which in combination with climate change, is placing the future sustainability of the boreal zone at risk. We explored policy options to reduce the risk to the future sustainability of the boreal zone in light of the inevitable energy transition to either a higher or a lower dependence on carbon and the uncertainty of society's capacity to adapt to change. Current policies are putting us on a path towards failure to achieve sustainability of the boreal zone. While current policies may be moving us towards a low-carbon future, they lack a shared vision of what the energy transition will be and engagement by those members of society most impacted; they are top-down, prescriptive, and fragmented, and they lack capacity, accountability, and enforcement. Together these limitations create barriers to society's capacity to adapt to the low-carbon future. Sustainability of the boreal zone will not only require a transition to a low-carbon economy but will require policies that overcome these barriers and create a higher capacity for society to adapt. [ABSTRACT FROM AUTHOR]

Ecosystems experiencing pressures are at risk of rapidly transitioning ("tipping") from one state to another. Identifying and managing these so-called tipping points continue to be a challenge in marine, freshwater, and terrestrial ecosystems, particularly when multiple potentially interacting drivers are present. Knowledge of tipping points, the mechanisms that cause them, and their implications for management practices are evolving, but often in isolation within specific ecological realms. Here, we summarize current knowledge of tipping points in marine, freshwater, and terrestrial realms and provide a multi-realm perspective of the challenges and opportunities for applying this knowledge to ecosystem management. We brought together conservation practitioners and global experts in marine, freshwater, and terrestrial tipping points and identified seven challenges that environmental policymakers and managers contend with including (1) predictability, (2) spatiotemporal scales, (3) interactions, (4) reversibility, (5) socio-ecological context, (6) complexity and heterogeneity, and (7) selecting appropriate action. We highlight opportunities for cross-scalar and cross-realm knowledge production and provide recommendations for enabling the management of tipping points. Although knowledge of tipping points is imperfect, we stress the need to continue working toward incorporating tipping points perspectives in environmental management across all realms. [ABSTRACT FROM AUTHOR]

Wetland protection and restoration strategies that are designed to promote hydrologic resilience do not incorporate the location of wetlands relative to the main stream network. This is primarily attributed to the lack of knowledge on the effects of wetland location on wetland hydrologic function (e.g., flood and drought mitigation). Here, we combined a watershed‐scale, surface–subsurface, fully distributed, physically based hydrologic model with historical, existing, and lost (drained) wetland maps in the Nose Creek watershed in the Prairie Pothole Region of North America to (1) estimate the hydrologic functions of lost wetlands and (2) estimate the hydrologic functions of wetlands located at different distances from the main stream network. Modeling results showed wetland loss altered streamflow, decreasing baseflow and increasing stream peakflow during the period of the precipitation events that led to major flooding in the watershed and downstream cities. In addition, we found that wetlands closer to the main stream network played a disproportionately important role in attenuating peakflow, while wetland location was not important for regulating baseflow. The findings of this study provide information for watershed managers that can help to prioritize wetland restoration efforts for flood or drought risk mitigation. Research Impact Statement: Wetlands close to the main stream network play a disproportionately important role in attenuating peakflow, while wetland location may not be important for regulating baseflow. [ABSTRACT FROM AUTHOR]

Wetland loss alters the hydrology of wetlandscapes in poorly understood ways. To quantify the effects of wetland loss on subsurface hydrology, a physically based hydrologic model that simulates the timing and pathways of subsurface hydrologic connections was coupled with wetland inventories over a 50‐year period during which substantial wetland loss occurred. The model revealed, based on vertical variations in saturated hydraulic conductivities, wetland loss of different degrees led to a contraction of catchment contributing areas to local surface waters but an expansion of contributing areas to the regional surface water body. This shift in groundwater contributing areas reflected (1) a decrease in baseflow contribution to the local surface water bodies, and (2) an increase in the transit time and length of subsurface hydrologic connections with an associated increase in the magnitude and age of baseflow discharging to the regional surface water body. The model also showed regions with thick permeable aquifers were particularly sensitive to the loss of wetlands. Our ability to predict these changes in hydrology of the watershed provides important support for designing science‐based policies to promote sustainable water resource management. Research Impact Statement: Wetland loss alters the source, pathway, and timing of subsurface water discharged into local and regional surface water bodies, and decreases baseflow supply to local surface water bodies. [ABSTRACT FROM AUTHOR]

Abstract: Northern ecosystems are experiencing some of the most dramatic impacts of global change on Earth. Rising temperatures, hydrological intensification, changes in atmospheric acid deposition and associated acidification recovery, and changes in vegetative cover are resulting in fundamental changes in terrestrial–aquatic biogeochemical linkages. The effects of global change are readily observed in alterations in the supply of dissolved organic matter (DOM)—the messenger between terrestrial and lake ecosystems—with potentially profound effects on the structure and function of lakes. Northern terrestrial ecosystems contain substantial stores of organic matter and filter or funnel DOM, affecting the timing and magnitude of DOM delivery to surface waters. This terrestrial DOM is processed in streams, rivers, and lakes, ultimately shifting its composition, stoichiometry, and bioavailability. Here, we explore the potential consequences of these global change‐driven effects for lake food webs at northern latitudes. Notably, we provide evidence that increased allochthonous DOM supply to lakes is overwhelming increased autochthonous DOM supply that potentially results from earlier ice‐out and a longer growing season. Furthermore, we assess the potential implications of this shift for the nutritional quality of autotrophs in terms of their stoichiometry, fatty acid composition, toxin production, and methylmercury concentration, and therefore, contaminant transfer through the food web. We conclude that global change in northern regions leads not only to reduced primary productivity but also to nutritionally poorer lake food webs, with discernible consequences for the trophic web to fish and humans. [ABSTRACT FROM AUTHOR]

Abstract: Urea‐based fertilisers have grown in popularity over the past half‐century and are now the dominant nitrogen (N) form applied to agricultural landscapes. The widespread use of urea fertilisers has favoured its export to local waterways, and urea pollution may be contributing to the propagation and maintenance of cyanobacteria harmful algal blooms in fresh waters. The relative success of cyanobacteria in response to urea and inorganic N additions was studied to understand whether the recent changes in the magnitude and composition of N loading have created a scenario that now favours the dominance of cyanobacteria in fresh waters. Growth and photosynthetic efficiency of three bloom‐forming freshwater cyanobacteria (Microcystis, Dolichospermum and Synechococcus) grown on nitrate ( NO 3 −), ammonium ( NH 4 +) and urea (CO(NH2)2) as the sole N form were monitored. We hypothesised that N substrates that require the lowest energetic investment or offer the highest energetic return would favour optimal growth and photosynthetic performance. We predicted that urea would result in higher cellular growth and pigment production relative to NH 4 + or NO 3 −, as urea provides twice the amount N and an additional carbon (C) source making it more energetically efficient. Cyanobacteria biomass was not significantly enhanced on urea relative to inorganic N forms. Growth on urea was matched by NO 3 − for all species, whereas growth on NH 4 + was halved compared urea or NO 3 −. However, cyanobacteria cells had higher pigment concentrations when grown on urea relative to inorganic N sources. These findings suggest that the additional nutrient building blocks supplied from the hydrolysis of urea were not directed towards active growth, but rather accumulated in secondary pools to increase production of N‐rich compounds, such as pigments. Although urea did not influence cyanobacteria quantity “(i.e. biomass)” compared to inorganic N sources, it produced higher “quality” cells by enhancing pigment synthesis and potentially giving cyanobacteria a competitive advantage in light‐limiting conditions. Furthermore, when supplied in excess, cyanobacteria rapidly consumed urea in excess of their biosynthetic requirements suggesting a form of urea “gluttony.” These results demonstrate the importance of N speciation on cyanobacteria physiological responses and reinforce the emerging links between urea and cyanobacteria harmful algal blooms in inland waters. [ABSTRACT FROM AUTHOR]

Abstract: Mitigation and offset programs designed to compensate for ecosystem function losses due to development must balance losses from affected ecosystems with gains in restored ecosystems. Aggregation rules applied to ecosystem functions to assess site equivalence are based on implicit assumptions about the substitutability of functions among sites and can profoundly influence the distribution of restored ecosystem functions on the landscape. We investigated the consequences of rules applied to the aggregation of ecosystem functions for wetland offsets in the Beaverhill watershed in Alberta, Canada. We considered the fate of 3 ecosystem functions: hydrology, water purification, and biodiversity. We set up an affect‐and‐offset algorithm to simulate the effect of aggregation rules on ecosystem function for wetland offsets. Cobenefits and trade‐offs among functions and the constraints posed by the quantity and quality of restorable sites resulted in a redistribution of functions between affected and offset wetlands. Hydrology and water purification functions were positively correlated with one another and negatively correlated with biodiversity function. Weighted‐average rules did not replace functions in proportion to their weights. Rules prioritizing biodiversity function led to more monofunctional wetlands and landscapes. The minimum rule, for which the wetland score was equal to the worst performing function, promoted multifunctional wetlands and landscapes. The maximum rule, for which the wetland score was equal to the best performing function, promoted monofunctional wetlands and multifunctional landscapes. Because of implicit trade‐offs among ecosystem functions, no‐net‐loss objectives for multiple functions should be constructed within a landscape context. Based on our results, we suggest criteria for the design of aggregation rules for no net loss of ecosystem functions within a landscape context include the concepts of substitutability, cobenefits and trade‐offs, landscape constraints, heterogeneity, and the precautionary principle. [ABSTRACT FROM AUTHOR]

Improved models are needed to predict the fate of carbon in forest soils under changing environmental conditions. Within a temperate sugar maple forest, soil CO efflux averaged 3.58 µmol m s but ranged from 0.02 to 25.35 µmol m s. Soil CO efflux models based on temperature and moisture explained approximately the same amount of variance on gentle and steep hillslopes (r = 0.506, p < 0.05 and r = 0.470, p < 0.05 respectively). When soil carbon content and sorption capacity were added to the models, the amount of explanation increased slightly on a gentle hillslope (r = 0.567, p < 0.05) and substantially on a steep hillslope (r = 0.803, p < 0.05). Within the organic-rich surface of the mineral soil, carbon content was positively related and sorption capacity was negatively related to soil CO efflux rates. There were general patterns of smaller carbon pools and lower sorption capacity in the upland positions than in the lowland and wetland positions, likely a result of hydrological transport of particulate and dissolved substances downslope, leading to higher soil CO efflux in the upland positions. However, the magnitude of the soil CO efflux was mitigated by the higher sorption capacity of the organic-rich surface layer of the mineral soils, which was negatively correlated to soil CO efflux. More accurate estimates of forest soil CO efflux must take into account topographic influences on the carbon pool, the environmental factors that affect rates of carbon transformation, as well as the physicochemical factors that determine the fraction of the carbon pool that can be transformed. [ABSTRACT FROM AUTHOR]

• In an era of unprecedent global change, cyanobacteria management decisions have become increasingly complex • Significant advances are available to prevent causes or mitigate the consequences of blooms. • Climate-driven changes on cyanobacteria blooms are projected to be multifaceted and site-specific, requiring site-specific preventive or mitigation decision making. Management of cyanobacteria has become an increasingly complex venture. Cyanobacteria risks have amplified as society moves forward in an era of accelerated global changes. The cyanobacteria management "pendulum" has progressively shifted from prevention to mitigation, with management considerations often put forth after bloom formation. A universal system (i.e., one-size-fits-all management) fails to provide a management path forward due to the inherent complexities of each lake. A tailored management plan is needed: the right species at the right time in the right place (i.e., the three Rs). The three Rs represent a customizable management strategy that is flexible and informed by advances in scientific understanding to lower cyanobacteria-associated risks. Identifying thresholds in risk tolerance, where thresholds are defined by community collectives, is essential to frame cyanobacteria management targets and to decide on what management interventions are warranted. [Display omitted] [ABSTRACT FROM AUTHOR]

For over a century, governments on both sides of the Canada–US border have employed diverse policy instruments and management tools to protect the Great Lakes. This crucial freshwater resource continues to show signs of degradation. We explore how the International Organization for Standardization Risk Management Standard (ISO 31000) can be used by governments to reduce the risk of failing to achieve the policy objectives of the Great Lakes. ISO 31000 facilitates the analysis of human activities that drive the causal pathways of ecosystem pressures–effects–impacts and analyzes the links between these causal pathways and the performance of management measures operating within the Great Lakes. ISO 31000 allows governments to shed light on why, despite best intentions, management measures are not working and enables governments to continually improve the management system until the risks of policy failures are reduced to acceptable levels, bringing new hope to the future of the Great Lakes. [ABSTRACT FROM AUTHOR]

Geographically isolated wetlands (GIWs), those surrounded by uplands, exchange materials, energy, and organisms with other elements in hydrological and habitat networks, contributing to landscape functions, such as flow generation, nutrient and sediment retention, and biodiversity support. GIWs constitute most of the wetlands in many North American landscapes, provide a disproportionately large fraction of wetland edges where many functions are enhanced, and form complexes with other water bodies to create spatial and temporal heterogeneity in the timing, flow paths, and magnitude of network connectivity. These attributes signal a critical role for GIWs in sustaining a portfolio of landscape functions, but legal protections remain weak despite preferential loss from many landscapes. GIWs lack persistent surface water connections, but this condition does not imply the absence of hydrological, biogeochemical, and biological exchanges with nearby and downstream waters. Although hydrological and biogeochemical connectivity is often episodic or slow (e.g., via groundwater), hydrologic continuity and limited evaporative solute enrichment suggest both flow generation and solute and sediment retention. Similarly, whereas biological connectivity usually requires overland dispersal, numerous organisms, including many rare or threatened species, use both GIWs and downstream waters at different times or life stages, suggesting that GIWs are critical elements of landscape habitat mosaics. Indeed, weaker hydrologic connectivity with downstream waters and constrained biological connectivity with other landscape elements are precisely what enhances some GIW functions and enables others. Based on analysis of wetland geography and synthesis of wetland functions, we argue that sustaining landscape functions requires conserving the entire continuum of wetland connectivity, including GIWs. [ABSTRACT FROM AUTHOR]

1. The frequency and intensity of cyanobacterial blooms (cyanoblooms) is increasing globally. While cyanoblooms in eutrophic (nutrient-rich) freshwater lakes are expected to persist and worsen with climate change projections, many of the 'new' cyanobloom reports pertain to oligotrophic (nutrient-poor) freshwater lakes with no prior history of cyanobloom occurrence. 2. Iron (Fe) is required in nearly all pathways of cyanobacterial macronutrient use, although its precise role in regulating cyanobacterial biomass across a lake trophic gradient is not fully understood. 3. In all lakes sampled representing a gradient in trophic status from oligotrophic to hypereutrophic (2.2-561.2 ºgL-1 total phosphorus), the relative cyanobacterial biomass was highest at low predicted Fe bioavailability in eutrophic Alberta lakes (<1.0 9 10-22 mol L-1 ) and low Fe concentration in oligotrophic Ontario Lakes (<3.2 ºgL-1). 4. Fe-binding organic ligands were measured within this range of low bioavailable Fe. Concentrations of ligands with reactive hydroxamate moieties were positively correlated to cyanobacterial biomass in lakes with low Fe bioavailability and supply, suggesting a possible cellular origin (i.e. siderophores) mediated by low Fe. 5. These findings suggest that Fe serves as a possible cofactor that maintains cyanobacterial biomass across a lake trophic gradient and that cyanobacteria invoke a similar Fe-scavenging system to overcome Fe limitation in lakes of all trophic states. [ABSTRACT FROM AUTHOR]

A better understanding is needed of how hydrological and biogeochemical processes control dissolved organic carbon (DOC) concentrations and dissolved organic matter (DOM) composition from headwaters downstream to large rivers. We examined a large DOM dataset from the National Water Information System of the US Geological Survey, which represents approximately 100 000 measurements of DOC concentration and DOM composition at many sites along rivers across the United States. Application of quantile regression revealed a tendency towards downstream spatial and temporal homogenization of DOC concentrations and a shift from dominance of aromatic DOM in headwaters to more aliphatic DOM downstream. The DOC concentration-discharge (C-Q) relationships at each site revealed a downstream tendency towards a slope of zero. We propose that despite complexities in river networks that have driven many revisions to the River Continuum Concept, rivers show a tendency towards chemostasis (C-Q slope of zero) because of a downstream shift from a dominance of hydrologic drivers that connect terrestrial DOM sources to streams in the headwaters towards a dominance of instream and near-stream biogeochemical processes that result in preferential losses of aromatic DOM and preferential gains of aliphatic DOM. [ABSTRACT FROM AUTHOR]

Wetlands provide many ecosystem services, including sediment and carbon retention, nutrient transformation, and water quality improvement. Although all wetlands are biogeochemical hotspots, geographically isolated wetlands (GIWs) receive fewer legal protections compared with other types of wetlands because of their apparent isolation from jurisdictional waters. Here, we consider controls on biogeochemical functions that influence water quality, and estimate changes in ecosystem service delivery that would occur if these landscape features were lost following recent US Supreme Court decisions (i.e., Rapanos, SWANCC). We conclude that, despite their lack of persistent surfacewater connectivity or adjacency to jurisdictional waters, GIWs are integral to biogeochemical processing on the landscape and therefore maintaining the integrity of US waters. Given the likelihood that any GIW contributes to downstream water quality, we suggest that the burden of proof could be shifted to assuming that all GIWs are critical for protecting aquatic systems until proven otherwise. [ABSTRACT FROM AUTHOR]

Climate warming is projected to affect forest water yields but the effects are expected to vary. We investigated how forest type and age affect water yield resilience to climate warming. To answer this question, we examined the variability in historical water yields at long-term experimental catchments across Canada and the United States over 5-year cool and warm periods. Using the theoretical framework of the Budyko curve, we calculated the effects of climate warming on the annual partitioning of precipitation (P) into evapotranspiration (ET) and water yield. Deviation (d) was defined as a catchment's change in actual ET divided by P [AET/P; evaporative index (EI)] coincident with a shift from a cool to a warm period - a positive d indicates an upward shift in EI and smaller than expected water yields, and a negative d indicates a downward shift in EI and larger than expected water yields. Elasticity was defined as the ratio of interannual variation in potential ET divided by P (PET/P; dryness index) to interannual variation in the EI - high elasticity indicates low d despite large range in drying index (i.e., resilient water yields), low elasticity indicates high d despite small range in drying index (i.e., nonresilient water yields). Although the data needed to fully evaluate ecosystems based on these metrics are limited, we were able to identify some characteristics of response among forest types. Alpine sites showed the greatest sensitivity to climate warming with any warming leading to increased water yields. Conifer forests included catchments with lowest elasticity and stable to larger water yields. Deciduous forests included catchments with intermediate elasticity and stable to smaller water yields. Mixed coniferous/deciduous forests included catchments with highest elasticity and stable water yields. Forest type appeared to influence the resilience of catchment water yields to climate warming, with conifer and deciduous catchments more susceptible to climate warming than the more diverse mixed forest catchments. [ABSTRACT FROM AUTHOR]

Our conceptual understanding of factors that promote cyanobacterial growth is inadequate in the face of rising public concern about cyanobacterial blooms in oligotrophic freshwater lakes., We hypothesised that cyanobacterial density would be highest in lakes with low levels of phosphorus ( P), nitrogen ( N), total dissolved iron ( TDFe) and dissolved organic matter ( DOM) with labile properties, where cyanobacteria use siderophores to scavenge Fe and overcome Fe limitation. We tested this hypothesis by measuring cyanobacterial density during peak biomass in 25 oligotrophic lakes representing gradients in total P ( TP), nitrate, TDFe and DOM concentrations., Total phytoplankton biomass, using chlorophyll- a (chl- a) as a proxy, was a function of TP ( r2 = 0.83, P < 0.001). Cyanobacterial density was highest in lakes with low chl- a, low TP, variable (low and high) nitrate and low TDFe. Regression tree analysis confirmed that TDFe, specifically low concentrations (<3.2 μg L−1), gave rise to the highest cyanobacterial densities in lakes., All lakes had detectable concentrations of hydroxamate and/or catecholate siderophores. In lakes with relatively low TDFe (<3.2 μg L−1), cyanobacterial density was positively correlated with hydroxamate siderophore concentration ( r2 = 0.77, P = 0.01). In lakes with higher TDFe (≥3.2 μg L−1), cyanobacterial density was positively correlated with nitrate ( r2 = 0.84, P < 0.001) and ammonium ( r2 = 0.75, P < 0.001) concentrations., Dissolved organic matter may have an overriding control on cyanobacterial density, with cyanobacterial densities typically highest where DOM concentrations were low (<5 mg L−1) and with a humification index <5. These findings suggest that DOM with labile properties may allow cyanobacteria to gain access to Fe complexed with DOM and thus to overcome Fe limitation, while DOM with refractory properties may bind Fe tightly so that Fe is not readily bioavailable to cyanobacteria., A new conceptual model is presented that emphasises the potential influence of DOM quantity and quality on the functioning of siderophores and the provision of a supply of Fe to cyanobacteria in lakes with low macronutrient supply. [ABSTRACT FROM AUTHOR]

The effects of lake browning on trophic functioning of planktonic food webs are not fully understood. We studied the effects of browning on the response patterns of polyunsaturated fatty acids and n−3/n−6 ratio in seston and compared them between boreal and temperate lakes. We also compared the regional differences and the effects of lake browning on the reliance of zooplankton on heterotrophic microbial pathways and the mass fractions of eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA) in zooplankton. Lake browning was associated with increasing phytoplankton biomass and concentrations of EPA and DHA in both temperate and boreal lakes, but the seston n−3/n−6 ratio was lower in temperate than boreal lakes, most likely due the differences in phytoplankton community composition. The browning-induced increase in phytoplankton biomass was associated with increased reliance of zooplankton on a heterotrophic microbial pathway for both cladocerans and copepods in boreal and temperate lakes. This increased reliance on the heterotrophic microbial diet was correlated with a decrease in the EPA and DHA mass fractions in temperate copepods and a decrease in the n−3/n−6 ratio in boreal cladocerans and copepods. Our results indicate that although phytoplankton responses to lake browning were similar across regions, this did not directly cascade to the next trophic level, where zooplankton responses were highly taxa- and region-specific. These results indicate that lake browning should be considered as an overarching moderator that is linked to, e.g., nutrient increases, which have more immediate consequences on trophic interactions at the phytoplankton–zooplankton interface. [ABSTRACT FROM AUTHOR]

Climate warming is resulting in increases in the frequency and intensity of summer droughts in the Great Lakes-St. Lawrence forest region (Ontario, Canada), raising concerns for the fate of C stores. We hypothesized that deeper peat historically existing beneath the water table would produce significant CO2 efflux during summer droughts. To test this hypothesis, we collected saturated peat cores, partitioned them into depth intervals, incubated the peat under conditions that resulted in peat drying, and monitored daily CO2 production together with potential drivers of CO2 production, including peat quality, microbial biomass, and microbial extracellular enzyme activity. Peat CO2 production (pmol CO2 min-1 g-1 dry soil) was highest in the top 30 cm of the peat profile, with the highest production at intermediate volumetric water content (VWC). Peat substrates fuelling CO2 production had quotients of C to N of <20 and were characterized by more labile forms of C. Microbial biomass C (mg C g-1 dry soil) and most microbial extracellular enzymes (nmol g-1 h-1) were also highest in the top 30 cm of the peat profile. Activities of microbial extracellular enzymes shifted in their contribution to CO2 production as the peat dried, with hydrolases positively related to CO2 under dry conditions (5-35%) and negatively under wet conditions (65 and 85%), with phenol oxidase showing the opposite pattern. Currently, the relatively poor quality (i.e., high C/N) of peat in catotelm limits rapid release of CO2 with water table declines. However, this substantial C store may be vulnerable to decomposition if constraints on quality are alleviated. [ABSTRACT FROM AUTHOR]

Cyanobacterial harmful algal blooms (cyano HABs) are most often associated with large eutrophic lakes. In the past decade, an increase in the incidence of cyano HABs in small oligotrophic lakes within the Laurentian Great Lakes-St. Lawrence River Basin has been documented. We explored macro- and micronutrient conditions during peak phytoplankton biomass that result in high cyanobacterial densities., We hypothesised that the availability of biologically available iron (Fe) both limits the assimilation of phosphorus by competing taxa and selects for the predominance of cyanobacteria., We tested this hypothesis with a comparative study of 25 oligotrophic lakes in central Ontario, Canada. These lakes were sampled during peak phytoplankton biomass for 3 years (from 2009 to 2011) for concentrations of total phosphorus (TP), total nitrogen (TN), ammonium ( [ABSTRACT FROM AUTHOR]

The application of remote sensing data to empirical models of inland surface water chlorophyll-a concentrations (chl-a) has been in development since the launch of the Landsat 4 satellite series in 1982. However, establishing an empirical model using a chl-a retrieval algorithm is difficult due to the spatial heterogeneity of inland lake water properties. Classification of optical water types (OWTs; i.e., differentially observed water spectra due to differences in water properties) has grown in favour in recent years over traditional non-turbid vs. turbid classifications. This study examined whether top-of-atmosphere reflectance observations in visible to near-infrared bands from Landsat 4, 5, 7, and 8 sensors can be used to identify unique OWTs using a guided unsupervised classification approach in which OWTs are defined through both remotely sensed reflectance and surface water chemistry data taken from samples in North American and Swedish lakes. Linear regressions of algorithms (Landsat reflectance bands, band ratios, products, or combinations) to lake surface water chl-a were built for each OWT. The performances of chl-a retrieval algorithms within each OWT were compared to those of global chl-a algorithms to test the effectiveness of OWT classification. Seven unique OWTs were identified and then fit into four categories with varying degrees of brightness as follows: turbid lakes with a low chl-a:turbidity ratio; turbid lakes with a mixture of high chl-a and turbidity measurements; oligotrophic or mesotrophic lakes with a mixture of low chl-a and turbidity measurements; and eutrophic lakes with a high chl-a:turbidity ratio. With one exception (r2 = 0.26, p = 0.08), the best performing algorithm in each OWT showed improvement (r2 = 0.69–0.91, p < 0.05), compared with the best performing algorithm for all lakes combined (r2 = 0.52, p < 0.05). Landsat reflectance can be used to extract OWTs in inland lakes to provide improved prediction of chl-a over large extents and long time series, giving researchers an opportunity to study the trophic states of unmonitored lakes. [ABSTRACT FROM AUTHOR]

Analyses of long-term records at 35 headwater basins in the United States and Canada indicate that climate change effects on streamflow are not as clear as might be expected, perhaps because of ecosystem processes and human influences. Evapotranspiration was higher than was predicted by temperature in water-surplus ecosystems and lower than was predicted in water-deficit ecosystems. Streamflow was correlated with climate variability indices (e.g., the El Niño-Southern Oscillation, the Pacific Decadal Oscillation, the North Atlantic Oscillation), especially in seasons when vegetation influences are limited. Air temperature increased significantly at 17 of the 19 sites with 20- to 60-year records, but streamflow trends were directly related to climate trends (through changes in ice and snow) at only 7 sites. Past and present human and natural disturbance, vegetation succession, and human water use can mimic, exacerbate, counteract, or mask the effects of climate change on streamflow, even in reference basins. Long-term ecological research sites are ideal places to disentangle these processes. [ABSTRACT FROM AUTHOR]

Abstract: Notable physiological responses such as toxicity and sinking rates of the red tide forming raphidophyte Heterosigma akashiwo are correlated with high levels of macronutrient stress. Individual cells of this species are also capable of forming benthic vegetative cysts that overwinter in marine sediment and contribute to bloom propagation in subsequent seasons. It was hypothesized that there is variability in the rates of sinking within cell cultures and that sinking cells are more toxic than the neutrally buoyant or floating cells. Using laboratory-based settling columns, various isolates of H. akashiwo were allowed to separate, and the toxicities of sinking and floating populations were analyzed. Sinking and floating rates were significantly higher during the late stationary growth phase for all isolates. For two H. akashiwo isolates, sinking populations were significantly more toxic than those that were positively buoyant. A similar trend was observed in a third strain, however the relationship was not significant. Differences in adaptive ecophysiology among the different strain likely caused the variation. It is suggested that the most toxic cells within a bloom are those found at the lower depths, potentially interacting with the benthic community or ensuring that subsequent bloom propagation contains cells with the potential for toxicity. [Copyright &y& Elsevier]

Abstract: Topographic depressions in digital elevation models (DEMs) are frequently a combination of artefacts and actual features. It is common practice to remove all digital depressions, from DEMs that are used in hydrogeomorphic applications. This practice is inappropriate because actual depressions affect many of the environmental phenomena at study. Nonetheless, indiscriminate depression removal persists because of an inability to distinguish artefacts from actual depressions. Five potential approaches for distinguishing artefacts from actual depressions in DEMs are described in this paper: ground inspection, examining the source data, classification approaches, knowledge-based approaches, and modelling approaches. Of the five methods, ground inspection was the only approach that actually confirms the existence of digital depressions. The other four methods that were identified operate by establishing justification for why a digital depression is likely to be an artefact or actual depression. A comparison of the depression validation approaches for a small sub-catchment on the Canadian Shield showed that the modelling approach performed slightly better than the other methods. While being highly automated and applicable to all landscape types, this approach also explicitly handles DEM uncertainty. By applying the Monte Carlo method, this approach estimates the likelihood of a digital depression actually occurring in the landscape given the degree of uncertainty in local topography. After artefact and actual depressions are identified, it is then possible to remove the artefacts and to preserve the real features for incorporation into modelling. [Copyright &y& Elsevier]

The metabarcoding of prokaryotic and fungal (Ascomycota only) ribosomal DNA was used to describe the microbial communities in soils of a remnant equatorial rainforest, maize–bean intercrop, and sugarcane in western Kenya. Cropping systems influenced the microbial community composition and functional traits (energy source and nutrient cycling) of bulk soil in each crop. Microbial richness and diversity tended to increase with cultivation intensity. The soil of the maize–bean intercrop had lower percentages and sugarcane had higher percentages of unique amplicon sequence variants of both bacteria and fungi compared to the remnant forest. Functional traits were altered by cultivation intensity. Compared to remnant forest soils, maize–bean intercrop soil had lower percentages of aerobic chemoheterotrophic bacteria and higher percentages of N-cycling bacteria, while sugarcane had higher percentages of aerobic chemoheterotrophic bacteria and lower percentages of N-cycling bacteria. In the face of increasing forest loss and pressures for agricultural productivity, this landscape provides a rich site for studying the impacts of cropping systems on soil health. [ABSTRACT FROM AUTHOR]

The effects of arsenate on the growth characteristics of five isolates of the freshwater alga, Chlorella vulgaris Beij., were examined. Two field isolates originated from arsenic-contaminated sites in Yukon, Canada and Kyushi, Japan; two reference isolates were obtained from the University of Texas Culture Collection. One isolate was selected for arsenic-tolerance in the laboratory. All five strains survived in culture solutions containing high arsenate concentrations. Arsenate (1-25 mM As) reduced photosynthesis and cell growth, as reflected by induced lag periods, slower growth rates and lower stationary cell yields. Fields isolates had shorter lag periods higher growth rates. and enhanced cell yields compared to lab isolateJ when exposed to the mine arsenic eontentrations. Growth of the phosphorus-limited field strains was stimulated by the addition of arsenic. The cell peld of phosphorus-limited C. vuigaris Yukon. when treated with arsenic, was two tones that of the phosphorus-limited control. This pattern was that evidece when photosynthesis was used as a measure of cell response. [ABSTRACT FROM AUTHOR]

The recent re-eutrophication of Lake Erie suggests an inadequate phosphorus management system that results in excessive loads to the lake. In response, governments in Canada and the U.S. have issued a new policy objective: 40% reductions in total phosphorus (TP) and dissolved reactive phosphorus (DRP) loads relative to 2008. The International Organization for Standardization (ISO) 31000 is a risk management standard. One of its analytical tools is the ISO 31010:2009 Bowtie Risk Analysis Tool, a tool that structures the cause-effect-impact pathway of risk but lacks the ability to capture the probability of reducing risk associated with different management systems. Here, we combined the Bowtie Risk Analysis Tool with a Bayesian belief network model to analyze the probability of different agricultural management systems of best management practices (BMPs) to achieve the 40% reductions in TP and DRP loads using different adoption rates. The commonly used soil conservation BMPs (e.g., reduced tillage) have a low probability of reducing TP and DRP to achieve the policy objective; while it can achieve the TP load reduction objective at increased adoptions rates >40%, it does not achieve the DRP load reduction objective, and in fact has the unintended consequence of increasing DRP loads. If decision makers continue to rely on soil conservation BMPs, the trade-offs between meeting objectives of different forms of phosphorus will require deciding whether the management priority is to achieve 40% load reduction objectives or to prevent further increases in DRP loads, the identified culprit causing the repeated algal blooms. In contrast, TP- and DRP-effective BMPS had higher probabilities of achieving the policy objective, especially at increased adoption rates >20%. The integration of Bayesian belief networks with the ISO risk management standard allows decision makers to determine the most probable outcomes of their management decisions, and to track and prepare for less probable outcomes, thereby decreasing the risk of failing to achieve policy objectives. Image 1 • Agriculture has led to phosphorus loads and re-eutrophication in Lake Erie. • U.S. and Canadian governments have targeted >40% reductions in phosphorus loads. • Management practices focused on soil conservation are not effective. • We need to shift management practices towards those that reduce phosphorus. • We also need to increase adoption rates to achieve >40% phosphorus reduction targets. [ABSTRACT FROM AUTHOR]

Wetland loss alters the hydrology of wetland-dominated watersheds in poorly understood ways. Knowledge on the effects of wetland loss on watershed-scale hydrologic responses is critically required to provide scientific support for the optimal design of wetland restoration/protection strategies in order to promote the hydrologic resilience of watersheds. To track the effects of wetland loss on watershed hydrologic responses, we (1) designed a subsurface-surface physically-based hydrologic model that simulates the timing and pathways of hydrologic connectivity of wetlands to local and regional surface water bodies, and (2) coupled this model with LiDaR-based wetland inventories over a 50-year period during which substantial wetland loss occurred, within two wetland-dominated watersheds in the prairie pothole region of North America. We found that wetland loss leads to a contraction of groundwater contributing areas to local surface waters, which increases the risk of drought of the local surface waters, but leads to an expansion of groundwater contributing areas to the regional surface water bodies with an increase in the age and amount of baseflow discharging into the regional surface water bodies. We also found that wetland loss increased stream peakflow during the period of the precipitation events that led to major flooding in the watersheds and downstream cities, with wetlands closer to the main stream network playing a disproportionately important role in reducing the risk of flood of regional surface water bodies. These findings provide important information for watershed managers that can help to prioritize wetland restoration efforts for flood or drought risk mitigation. [ABSTRACT FROM AUTHOR]

Concentrations of dissolved organic carbon (DOC) have increased recently in many lakes at high latitudes in North America and Europe, but it is unclear what effect this will have on the identity of the limiting nutrient for phytoplankton [nitrogen (N) vs. phosphorus (P)]. Identifying the effect of changing DOC on phytoplankton nutrient limitation is complicated by spatial covariation between atmospheric N deposition and increasing DOC in areas where lake browning occurs. We conducted nutrient-limitation assays in 27 lakes from three sites along gradients of climate and atmospheric N deposition in Sweden. Within each site, lakes were selected to represent the range of DOC concentrations. We also conducted statistical analyses of large-scale lake survey data (n = 4768 lakes divided into 47 regions) to investigate relationships between DOC and nutrient stoichiometry while controlling for differences in N deposition. Our findings confirmed that most lakes were dual-limited by both N and P in the south, whereas northern lakes were primarily N-limited. Throughout Sweden the ratio of dissolved inorganic nitrogen (DIN) to total phosphorus (TP) declined with increasing DOC in most regions, suggesting that browner lakes are more likely to be N limited. These results were not supported by our nutrient limitation assays, which identified no relationship between DOC and relative strength of limitation by N or P. Increased DOC also resulted in significant increases in both total and inorganic N and P fractions, suggesting that other factors such as light limitation or increased top-down control become more important as DOC increases. [ABSTRACT FROM AUTHOR]

Climate change is altering the hydrology of Canadian rivers to an unprecedented degree. Consequently, sustainable freshwater management practices need to adapt, which include the development of integrated water resource strategies and environmental flow recommendations. A particular challenge arises for these assessments due to the highly diverse nature of river ecosystems across Canada. This diversity can be addressed by using a classification system to create manageable spatial units. Building upon and adapting the results of a global river reach classification scheme, we present a multidisciplinary K-means clustering approach to categorize all river reaches of Canada into 23 types at fine spatial resolution. The typology is based on classifier variables related to hydrology, mostly derived from modelled long-term means of monthly discharges, physiography, climate, and fluvial geomorphology. Resulting maps provide baseline information for rivers of all size classes, from small headwater streams to very large rivers, across the entire country, including unmonitored regions such as the High Arctic. The classification system also points to some strategic expansion opportunities for the current Canadian monitoring network of river gauging stations. [ABSTRACT FROM AUTHOR]

Wetlands should not be considered as independent objects but as dynamically connected objects, collectively known as wetlandscapes. We developed a framework that analyzes the influences of wetland suitability and connectivity on amphibian distributions. We defined two indices: a Wetland Suitability Index describing wetland quality and a Movement Permeability Index characterizing wetland connectivity for amphibian population dynamics. These indices were calculated from raster datasets and time‐varying inundation estimates. The indices were used to define a wetlandscape and an amphibian model was used to simulate population dynamics within the wetlandscape. The framework was applied to the Nose Creek watershed, a highly modified wetlandscape in Alberta, Canada. Two amphibian species were selected with different habitat preferences: the Northern Leopard Frog that prefers wet habitats and has high mobility over land, and the Great Plains Toad that prefers terrestrial habitats and has low mobility over land. We found each amphibian species had a "preferred" wetlandscape, reflecting their life cycle traits and migration strategies which in turn were dependent on the hydrological and ecological connections within the wetlandscape. This study highlights the importance of investigating both individual wetlands and the wetlandscape and considering both wetland habitat quality and connectivity as non‐substitutable properties that act jointly, but differently, on population dynamics. Research Impact Statement: Both wetland habitat quality and connectivity act jointly but differently on amphibian population dynamics and should both be considered when managing wetlandscapes. [ABSTRACT FROM AUTHOR]