Microbial communities change along the 300 km length of the Grand River for extreme high- and low-flow regimes.

The Grand River watershed is the largest catchment in southern Ontario. The river's northern and southern sections are influenced by agriculture, whereas central regions receive wastewater effluent and urban runoff. To characterize in-river microbial communities, as they relate to spatial and environmental factors, we conducted two same-day sampling events along the entire 300 km length of the river, representing contrasting flow seasons (high flow spring melt and low flow end of summer).

Enigmatic persistence of aerobic methanotrophs in oxygen-limiting freshwater habitats.

Methanotrophic bacteria mitigate emissions of the potent greenhouse gas methane (CH4) from a variety of anthropogenic and natural sources, including freshwater lakes, which are large sources of CH4 on a global scale. Despite a dependence on dioxygen (O2) for CH4 oxidation, abundant populations of putatively aerobic methanotrophs have been detected within microoxic and anoxic waters and sediments of lakes. Experimental work has demonstrated active aerobic methanotrophs under those conditions, but how they are able to persist and oxidize CH4 under O2 deficiency remains enigmatic.

High Voltage: The Molecular Properties of Redox-Active Dissolved Organic Matter in Northern High-Latitude Lakes.

Redox-active functional groups in dissolved organic matter (DOM) are crucial for microbial electron transfer and methane emissions. However, the extent of aquatic DOM redox properties across northern high-latitude lakes and their relationships with DOM composition have not been thoroughly described. We quantified electron donating capacity (EDC) and electron accepting capacity (EAC) in lake DOM from Canada to Alaska and assessed their relationships with parameters from absorbance, fluorescence, and ultrahigh resolution mass spectrometry (FT-ICR MS) analyses.

Nitrogen and Phosphorus Treatment Can Be Sustainable During on-Site Wastewater Disposal.

Monitoring of a seasonal-use, on-site wastewater disposal system (septic system) in Canada, over a 33-year period from 1988 to 2021, showed that during recent sampling the groundwater plume had TIN (total inorganic nitrogen) averaging 12.2 mg/L that was not significantly different than early values, representing 80% removal, whereas SRP (soluble reactive phosphate), although higher than early values averaging 0.08 mg/L, was still 99% lower than the effluent concentration.

Large Fractionation in Iron Isotopes Implicates Metabolic Pathways for Iron Cycling in Boreal Shield Lakes.

Stable Fe isotopes have only recently been measured in freshwater systems, mainly in meromictic lakes. Here we report the δFe of dissolved, particulate, and sediment Fe in two small dimictic boreal shield headwater lakes: manipulated eutrophic Lake 227, with annual cyanobacterial blooms, and unmanipulated oligotrophic Lake 442. Within the lakes, the range in δFe is large (ca.

Composition Wheels: Visualizing dissolved organic matter using common composition metrics across a variety of Canadian ecozones.

Dissolved organic matter (DOM) is a ubiquitous component of aquatic systems, impacting aquatic health and drinking water quality. These impacts depend on the mixture of organic molecules that comprise DOM. Changing climates are altering both the amount and character of DOM being transported from the terrestrial system into adjacent surface waters, yet DOM composition is not monitored as often as overall concentration.

Isotopic Characterization of Sulfate in a Shallow Aquifer Impacted by Agricultural Fertilizer.

The stable isotope ratios of groundwater sulfate ( S/ S, O/ O) are often used as tracers to help determine the origin of groundwater or groundwater contaminants. In agricultural watersheds, little is known about how the increased use of sulfur as a soil amendment to optimize crop production is affecting the isotopic composition of groundwater sulfate, especially in shallow aquifers. We investigated the isotopic composition of synthetic agricultural fertilizers and groundwater sulfate in an area of intensive agricultural activity, in Ontario, Canada.

Nitrogen Attenuation in Septic System Plumes.

The persistence of inorganic nitrogen is assessed in a set of 21 septic system plumes located in Ontario, Canada, that were studied over a 31-year period from 1988 to 2019. In the plume zones underlying the drainfields, site mean NO values averaged 34 ± 27 mg N/L and exceeded the nitrate drinking water limit (DWL) of 10 mg N/L at 16 of 21 sites. In plume zones extending up to 30 m downgradient from the drainfields, site mean NO values averaged 24 ± 20 mg N/L and exceeded the DWL at 9 of 13 sites.

Freshwater microbial community diversity in a rapidly changing High Arctic watershed.

Current models predict increases in High Arctic temperatures and precipitation that will have profound impacts on the Arctic hydrological cycle, including enhanced glacial melt and thawing of active layer soils. However, it remains uncertain how these changes will impact the structure of downstream resident freshwater microbial communities and ensuing microbially driven freshwater ecosystem services. Using the Lake Hazen watershed (Nunavut, Canada; 82°N, 71°W) as a sentinel system, we related microbial community composition (16S rRNA gene sequencing) to physicochemical parameters (e.

Review of phosphorus attenuation in groundwater plumes from 24 septic systems.

This study reviews phosphorus (P) concentrations in groundwater plumes from 24 on-site wastewater treatment systems (septic systems) in Ontario, Canada. Site investigations were undertaken over a 30-year period from 1988 to 2018 at locations throughout the province that encompass a variety of domestic wastewater types and geologic terrain. The review focuses on P behaviour in the drainfield sediments and in the proximal plume zones, within 10 m of the drainfields, where plume conditions were generally at steady state.

Proglacial freshwaters are significant and previously unrecognized sinks of atmospheric CO.

Carbon dioxide (CO) emissions from freshwater ecosystems are almost universally predicted to increase with climate warming. Glacier-fed rivers and lakes, however, differ critically from those in nonglacierized catchments in that they receive little terrestrial input of organic matter for decomposition and CO production, and transport large quantities of easily mobilized comminuted sediments available for carbonate and silicate weathering reactions that can consume atmospheric CO We used a whole-watershed approach, integrating concepts from glaciology and limnology, to conclusively show that certain glacier-fed freshwater ecosystems are important and previously overlooked annual CO sinks due to the overwhelming influence of these weathering reactions. Using the glacierized Lake Hazen watershed (Nunavut, Canada, 82°N) as a model system, we found that weathering reactions in the glacial rivers actively consumed CO up to 42 km downstream of glaciers, and cumulatively transformed the High Arctic's most voluminous lake into an important CO sink.

Unprocessed Atmospheric Nitrate in Waters of the Northern Forest Region in the U.S. and Canada.

Little is known about the regional extent and variability of nitrate from atmospheric deposition that is transported to streams without biological processing in forests. We measured water chemistry and isotopic tracers (δO and δN) of nitrate sources across the Northern Forest Region of the U.S.

Nitrogen isotope fractionation factors (α) measured and estimated from the volatilisation of ammonia from water at pH 9.2 and pH 8.5.

This paper examines the nitrogen isotope fractionation factors (α) associated with the volatilisation of ammonia from water under controlled conditions at two pH values (8.5 and 9.2).

The world's largest High Arctic lake responds rapidly to climate warming.

Using a whole-watershed approach and a combination of historical, contemporary, modeled and paleolimnological datasets, we show that the High Arctic's largest lake by volume (Lake Hazen) has succumbed to climate warming with only a ~1 °C relative increase in summer air temperatures. This warming deepened the soil active layer and triggered large mass losses from the watershed's glaciers, resulting in a ~10 times increase in delivery of glacial meltwaters, sediment, organic carbon and legacy contaminants to Lake Hazen, a >70% decrease in lake water residence time, and near certainty of summer ice-free conditions. Concomitantly, the community assemblage of diatom primary producers in the lake shifted dramatically with declining ice cover, from shoreline benthic to open-water planktonic species, and the physiological condition of the only fish species in the lake, Arctic Char, declined significantly.

Artificial Sweeteners Reveal Septic System Effluent in Rural Groundwater.

It has been widely documented that municipal wastewater treatment plant effluents are a major source of artificial sweeteners to surface waters. However, in rural areas, the extent to which septic systems contribute these same compounds to groundwater aquifers is largely unknown. We examined the occurrence of four commonly used artificial sweeteners in an unconfined sand aquifer that serves as a water supply for rural residents, as a receptor of domestic wastewater from septic systems, and as a source of baseflow to the Nottawasaga River, ON, Canada.

Multiple sources and sinks of dissolved inorganic carbon across Swedish streams, refocusing the lens of stable C isotopes.

It is well established that stream dissolved inorganic carbon (DIC) fluxes play a central role in the global C cycle, yet the sources of stream DIC remain to a large extent unresolved. Here, we explore large-scale patterns in δC-DIC from streams across Sweden to separate and further quantify the sources and sinks of stream DIC. We found that stream DIC is governed by a variety of sources and sinks including biogenic and geogenic sources, CO evasion, as well as in-stream processes.

From the ground up: global nitrous oxide sources are constrained by stable isotope values.

Rising concentrations of nitrous oxide (N2O) in the atmosphere are causing widespread concern because this trace gas plays a key role in the destruction of stratospheric ozone and it is a strong greenhouse gas. The successful mitigation of N2O emissions requires a solid understanding of the relative importance of all N2O sources and sinks. Stable isotope ratio measurements (δ15N-N2O and δ18O-N2O), including the intramolecular distribution of 15N (site preference), are one way to track different sources if they are isotopically distinct.

Potential for long-term transfer of dissolved organic carbon from riparian zones to streams in boreal catchments.

Boreal regions store most of the global terrestrial carbon, which can be transferred as dissolved organic carbon (DOC) to inland waters with implications for both aquatic ecology and carbon budgets. Headwater riparian zones (RZ) are important sources of DOC, and often just a narrow 'dominant source layer' (DSL) within the riparian profile is responsible for most of the DOC export. Two important questions arise: how long boreal RZ could sustain lateral DOC fluxes as the sole source of exported carbon and how its hydromorphological variability influences this role.

Large carbon dioxide fluxes from headwater boreal and sub-boreal streams.

Half of the world's forest is in boreal and sub-boreal ecozones, containing large carbon stores and fluxes. Carbon lost from headwater streams in these forests is underestimated. We apply a simple stable carbon isotope idea for quantifying the CO2 loss from these small streams; it is based only on in-stream samples and integrates over a significant distance upstream.

Proper interpretation of dissolved nitrous oxide isotopes, production pathways, and emissions requires a modelling approach.

Stable isotopes ([Formula: see text]15N and [Formula: see text]18O) of the greenhouse gas N2O provide information about the sources and processes leading to N2O production and emission from aquatic ecosystems to the atmosphere. In turn, this describes the fate of nitrogen in the aquatic environment since N2O is an obligate intermediate of denitrification and can be a by-product of nitrification. However, due to exchange with the atmosphere, the [Formula: see text] values at typical concentrations in aquatic ecosystems differ significantly from both the source of N2O and the N2O emitted to the atmosphere.

Nonlinear response of riverine N2O fluxes to oxygen and temperature.

One-quarter of anthropogenically produced nitrous oxide (N2O) comes from rivers and estuaries. Countries reporting N2O fluxes from aquatic surfaces under the United Nations Framework Convention on Climate Change typically estimate anthropogenic inorganic nitrogen loading and assume a fraction becomes N2O. However, several studies have not confirmed a linear relationship between dissolved nitrate (NO3-) and river N2O fluxes.

Artificial sweeteners in a large Canadian river reflect human consumption in the watershed.

Artificial sweeteners have been widely incorporated in human food products for aid in weight loss regimes, dental health protection and dietary control of diabetes. Some of these widely used compounds can pass non-degraded through wastewater treatment systems and are subsequently discharged to groundwater and surface waters. Measurements of artificial sweeteners in rivers used for drinking water production are scarce.

Wastewater effluent impacts ammonia-oxidizing prokaryotes of the Grand River, Canada.

The Grand River (Ontario, Canada) is impacted by wastewater treatment plants (WWTPs) that release ammonia (NH3 and NH4+) into the river. In-river microbial communities help transform this ammonia into more oxidized compounds (e.g.