Search

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. Plain Language Summary: In urban areas, stormwater ponds are common to help manage flooding and filter out nutrients to improve water quality in downstream water bodies. In the summer, urban ponds can experience a loss of oxygen in the bottom water, but less is known about what happens in these ponds in the winter under ice cover. We measured oxygen profiles in 20 ponds during the winter to investigate the drivers of oxygen loss in the bottom waters. We also explored the consequence of oxygen loss by measuring greenhouse gas (carbon dioxide and methane) concentrations in the surface water. Winter oxygen loss was driven by snow and ice clarity, winter nutrients, and previous summer organic matter from either algae or floating plants. Ponds with less oxygen under ice had higher concentrations of greenhouse gases in the surface water. Warmer winters could increase freeze thaw cycles and decrease oxygen under ice or increase oxygen with more instances of open water. Key Points: Urban ponds exhibit a range of under‐ice oxygen regimesWinter anoxia is driven by ice transmissivity, nutrient concentrations, and preceding summer productivityA consequence of under‐ice oxygen depletion is the accumulation of methane and carbon dioxide [ABSTRACT FROM AUTHOR]

Microcystin poses a serious threat to aquatic ecosystems and human health. There is a pressing need to understand the production, movement, and storage of microcystin in lakes. We constructed a conceptual biogeochemical model for microcystin through a comprehensive literature synthesis, identifying four major pools and nine major fluxes in lakes that also connect to the terrestrial environment. This conceptual model can be used as the framework for developing ecosystem mass balances of microcystin. We propose that the concentration of microcystin in the water column is the balance between the import, sediment translocation, production and degradation, uptake, burial, and export. However, substantial unknowns remain pertaining to the magnitude and movement of microcystin. Future investigations should focus on sediment fluxes, drivers of biodegradation, and seasonal dynamics. Adopting the framework of a “microcystin cycle” improves our understanding of processes driving toxin prevalence and helps to prioritize strategies for minimizing exposure risks. [ABSTRACT FROM AUTHOR]

Algal blooms, the rapid proliferation of algal biomass often to nuisance or harmful levels, diminish aquatic ecosystem services. Freshwater blooms can cause substantial economic damage by interrupting water supply, limiting recreation, and reducing property values. The interaction between eutrophication and climate change has been hypothesized to drive widespread intensification of blooms in inland waters, although there is little empirical evidence that this trend is pervasive. Here, we show that bloom intensification in inland waterbodies – defined as trends in chlorophyll‐a of increasing bloom magnitude, severity, or duration – has not been widespread for hundreds of lakes in the US. Only 10.8% of the 323 waterbodies analyzed had significant bloom intensification. Conversely, 16.4% of the waterbodies had significant decreasing trends during the same period. While it is encouraging that bloom intensification is not currently widespread, continued efforts toward aquatic ecosystem protection and restoration are imperative for maintaining ecosystem services into the future. [ABSTRACT FROM AUTHOR]

Microevolution can have consequences at higher levels of ecological organization. Although divergence among populations can be rapid and driven by anthropogenic changes to the environment, the ecological relevance of evolution induced by human activities remains poorly understood.A frequent way in which human activities drive microevolution is the increase in supply of nutrients such as phosphorus (P) that are required for fitness‐relevant traits such as growth and reproduction. Because higher P concentrations decrease P‐use efficiency and feeding rate in heterotrophic consumers such as Daphnia, we hypothesized that such adjustments should alter consumer–resource dynamics.We examined how cultural eutrophication in temperate lakes causes trait variation in the grazer Daphnia pulicaria. We tested for variation in Daphnia traits and genetic variation in the metabolic enzyme phosphoglucose isomerase (Pgi) which are each known to respond to eutrophication. We then examined the impact of this variation on consumer–resource dynamics using a combination of experiments and a multi‐lake survey.We found that Daphnia from hypereutrophic lakes responded to experimental hypereutrophic conditions with increased growth rates and fecundity when raised on P‐fertilized seston, but had reduced performance on P‐poor seston relative to eutrophic source Daphnia. These results suggest that Daphnia may face a trade‐off in performance at low versus excess P that may be mediated in part by genetic variation at the Pgi locus.The variation observed in laboratory growth experiments scaled up to Daphnia populations in both mesocosm experiments and among lakes. In both the mesocosm experiment and in the lake survey, Daphnia from hypereutrophic source lakes reached high biomass while phytoplankton biomass also remained high.Given the prevalence and rapid eutrophication of freshwater ecosystems worldwide, these results indicate that considering the potential effects of evolutionary change in ecosystem models could be useful in forecasting the effects of anthropogenic environmental change on pivotal ecosystem services. [ABSTRACT FROM AUTHOR]