Search for: All records

Blood Falls is a unique feature that appears at the snout of the Taylor Glacier in the upper Taylor Valley, East Antarctica. It is an iron-rich brine that occasionally gets expulsed from a subglacial source due to the weight and movement of the overlying glacier. The brine that emanates stains the glacier as it oxidizes at the surface and flows towards the West Lobe of Lake Bonney (WLB). Recent work (Spigelet al.2018, Lawrenceet al.2020) has shown that, besides the Blood Falls contribution, the brine enters the WLB all along the front of Taylor Glacier, creating cold water anomalies at the depth where this subglacial brine’s density is matched by the surrounding lake water. Mikuckiet al.(2015) detected substantial brine at the base of Taylor Glacier using an airborne transient electromagnetic sensor. Badgeleyet al.(2017) used radio echo sounding to delineate the brine further and to show that there are subglacial flow pathways that direct the brine to the centre and south side of Taylor Glacier’s snout, in addition to what flows from Blood Falls. 

Abstract Many ecosystems can abruptly shift between states, and shallow lakes are a classic example. Biomanipulation via the removal of benthivores can shift a shallow lake from a turbid to a clear-water macrophyte-dominated state, but the limited number of long-term studies indicates that persistence in this state rarely lasts beyond 5–10 years. We analyzed 12 years of pre-removal (1996–2007) and 17 years of post-removal (2008–2024) data to assess the ecological impacts of a common carp (Cyprinus carpio) removal from Lake Wingra, a shallow eutrophic lake in Madison, Wisconsin, USA. Summer water clarity abruptly increased following the winter 2008 carp removal, resulting in a 64% increase in mean Secchi depth in post-removal summers and a major expansion of the littoral zone. Fast growing submerged macrophytes (for example,Ceratophyllum demersumand invasiveMyriophyllum spicatum) rapidly expanded into deeper zones, reaching the maximum colonization depth of 3.96 m within four summers. Post-removal nutrient concentrations declined by 24–34% and became more correlated with precipitation, suggesting a shift from internal to external regulation of nutrient loading. Three likely interacting mechanisms for maintaining water clarity include predation by centrarchids maintaining low carp populations, the high and stable coverage of submerged macrophytes, and abundant filamentous algae that provide an additional nutrient sink. However, high biomass of invasive species and filamentous algae can degrade ecosystem services and function, and increased variability of precipitation-driven nutrient inputs may destabilize the macrophyte-dominated state in the future. We demonstrate with long-term data the sustained shift of a shallow eutrophic lake out of the turbid state with a single biomanipulation. 

Abstract Freshwater salinization disrupts aquatic ecosystem processes such as organismal development, replenishment of dissolved oxygen, and geochemical cycling. A well‐documented but poorly understood signature of salinization to streams and rivers is “episodic salinization,” or short‐term pulses of salinity from extreme events. Across a 1/3 of the United States, or a 22‐state region covering 1.9 million km², runoff from winter road salt can spike river conductivity 1,000 s of μS cm⁻¹. Salinity pulses threaten river health due to the abrupt changes in environmental conditions and the sensitivity of many aquatic organisms to such swings. Using 436 sites from the U.S. Geological Survey national river gage network, we investigated the circumstances under which rivers experience episodic salinization. Using a random forest model we found a strong link to road salt application, urban development, groundwater hydrology, and no relationship to stream discharge. Applying this model to the entire 22‐state area of study, we find that 6.3% of rivers are prone to episodic salinization, with smaller streams more at risk. The results of this advance our understanding of the spatiotemporal extent and severity of freshwater salinization due to winter road salting, and gives us a tool to identify at‐risk rivers in order to improve management of roadways during winter months and better balance human safety with ecosystem health. 

Abstract Stormwater ponds are common features in urbanized landscapes because they enhance flood reduction and nutrient retention. With shallow depths and high inputs of organic matter, these systems can be highly productive with rapid oxygen depletion when thermally stratified or ice‐covered. However, most of our understanding of the biogeochemistry of stormwater ponds comes from the open water period. We explored under‐ice oxygen dynamics in 20 stormwater ponds in Madison, WI (USA) that were ice covered from late December to early March to investigate the drivers of bottom water oxygen saturation and the impact on the accumulation of carbon dioxide (CO₂) and methane (CH₄). Winter anoxia was driven by ice transmissivity, winter nutrient concentrations, and precedent summer productivity. Oxygen depletion led to overall higher concentrations of greenhouse gases in pond surface waters. This research enhances our understanding of winter pond biogeochemistry and its links to summer productivity. 

Stormwater ponds are common features in urbanized landscapes and can suffer from rapid oxygen depletion when thermally stratified or ice-covered. To investigate under-ice oxygen dynamics and drivers of bottom water oxygen saturation, we sampled 20 stormwater ponds in Madison, Wisconsin, USA during the summer of 2021 and winter 2022. The urban ponds ranged in age, shape, size, and depth. We repeatedly took YSI profiles of water temperature, oxygen, and specific conductance 7 times in the summer and 3 times in the winter. Water chemistry variables were collected in the surface waters, habitat surveys were conducted in the summer, and ice/snow thickness was recorded in the winter. We also measured the concentration of greenhouse gases in the surface waters as a consequence to oxygen depletion using the headspace equilibrium method. 

Abstract Widespread and increasing use of road deicing salt is a major driver of increasing lake chloride concentrations, which can negatively impact aquatic organisms and ecosystems. We used a simple model to explore the controls on road salt concentrations and predict equilibrium concentrations in lakes across the contiguous United States. The model suggests that equilibrium salt concentration depends on three quantities: salt application rate, road density, and runoff (precipitation minus evapotranspiration). High application combined with high road density leads to high equilibrium salt concentrations regardless of runoff. Yet if application can be held at current rates or reduced, concentrations in many lakes situated in lightly to moderately urbanized watersheds should equilibrate at levels below currently recommended thresholds. In particular, our model predicts that, given 2010–2015 road salt application rates, equilibrium chloride concentrations in the contiguous United States will exceed the current regulatory chronic exposure threshold of 230 mg L⁻¹in over 2000 lakes; will exceed 120 mg L⁻¹in over 9000 lakes; and will be below 120 mg L⁻¹in hundreds of thousands of lakes. Our analysis helps to contextualize current trends in road salt pollution of lakes, and suggests that stabilization of equilibrium chloride concentrations below thresholds designed to protect aquatic organisms should be an achievable goal. 

Abstract Species invasions can disrupt aquatic ecosystems by re‐wiring food webs. A trophic cascade triggered by the invasion of the predatory zooplankter spiny water flea (Bythotrephes cederströmii) resulted in increased phytoplankton due to decreased zooplankton grazing. Here, we show that increased phytoplankton biomass led to an increase in lake anoxia. The temporal and spatial extent of anoxia experienced a step change increase coincident with the invasion, and anoxic factor increased by 11 d. Post‐invasion, anoxia established more quickly following spring stratification, driven by an increase in phytoplankton biomass. A shift in spring phytoplankton phenology encompassed both abundance and community composition. Diatoms (Bacillaryophyta) drove the increase in spring phytoplankton biomass, but not all phytoplankton community members increased, shifting the community composition. We infer that increased phytoplankton biomass increased labile organic matter and drove hypolimnetic oxygen consumption. These results demonstrate how a species invasion can shift lake phenology and biogeochemistry. 

Abstract Record high temperatures were documented in the McMurdo Dry Valleys, Antarctica, on 18 March 2022, exceeding average temperatures for that day by nearly 30°C. Satellite imagery and stream gage measurements indicate that surface wetting coincided with this warming more than 2 months after peak summer thaw and likely exceeded thresholds for rehydration and activation of resident organisms that typically survive the cold and dry conditions of the polar fall in a freeze‐dried state. This weather event is notable in both the timing and magnitude of the warming and wetting when temperatures exceeded 0°C at a time when biological communities and streams have typically entered a persistent frozen state. Such events may be a harbinger of future climate conditions characterized by warmer temperatures and greater thaw in this region of Antarctica, which could influence the distribution, activity, and abundance of sentinel taxa. Here we describe the ecosystem responses to this weather anomaly reporting on meteorological and hydrological measurements across the region and on later biological observations from Canada Stream, one of the most diverse and productive ecosystems within the McMurdo Dry Valleys.