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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]

Molot LA, Schiff SL, Venkiteswaran JJ, Baulch HM, Higgins SN, Zastepa A, Verschoor MJ, Walters D. 2021. Low sediment redox promotes cyanobacteria blooms across a trophic range: implications for management. Lake Reserv Manage. 37:120–142. Field observations and experimental manipulations with different oxidizing agents including nitrate demonstrate that high sediment redox prevents cyanobacteria blooms in eutrophic freshwaters. Conversely, low sediment redox caused by depletion of dissolved oxygen and nitrate allows blooms to form. This explains why bloom risk increases with phosphorus levels: Higher productivity increases the spatial and temporal extent of low sediment redox. The intermediate link between low redox and cyanobacteria blooms appears to be internal loading of ferrous iron (Fe2+) from reduced sediments with diffusion to depths accessible to migrating cyanobacteria, providing a source for their high iron demand. Regardless of whether Fe2+ release is the intermediate link, the concept of "low sediment redox as promoter" has major potential to improve bloom management if managers consider the impact of their nutrient management choices, nutrient targets, and in-lake methods on sediment redox. Phosphorus input targets can be adjusted as climate change alters the extent of anoxia, and short-term bloom prediction models that incorporate the sediment redox concept could predict onset of blooms earlier than current models that depend on detection of photosynthetic pigments associated with blooms. [ABSTRACT FROM AUTHOR]

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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]

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]

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]