Madeline Schreiber

Microbial communities play an important role in aquifer systems as both hazards (e.g., pathogens and carriers of antibiotic resistance genes) and contributors to contaminant remediation. However, monitoring native microbial communities in situ remains challenging. To address this challenge, we developed a passive sampler that employs removable cartridges containing solid media designed to recreate the aquifer environment in a controlled fashion and support consistent, repeatable, time‐series sampling. With a bench‐scale, continuous‐loop setup circulating advanced‐treated wastewater, we compared microbial community dynamics across three candidate porous media: native aquifer sediment, zirconia beads, and laboratory‐grade silica sand. 16S rRNA gene amplicon sequencing revealed that native aquifer sediment best reflected influent microbial composition and temporal shifts. Native aquifer sediment also exhibited more spatial consistency in microbial diversity along the sampler. These findings suggest that native aquifer sediment is an optimal porous medium for long‐term, in situ monitoring of microbial communities for managed aquifer recharge and other applications in groundwater systems.

Microbial communities play an important role in aquifer systems, as both hazards (e.g., pathogens, carriers of antibiotic resistance genes) and contributors to contaminant remediation. However, monitoring native microbial communities in situ remains challenging. To address this challenge, we developed a passive sampler with that employs removable cartridges containing solid media designed to re-create the aquifer environment in a controlled fashion and support consistent, repeatable, time-series sampling. With a bench-scale, continuous-loop setup circulating advanced-treated wastewater, we compared microbial community dynamics across three candidate porous media: native aquifer sediment, zirconia beads, and laboratory-grade silica sand. 16S rRNA gene amplicon sequencing revealed that native aquifer sediment best reflected influent microbial composition and temporal shifts. Native aquifer sediment also exhibited more spatial consistency in microbial diversity along the sampler. These findings suggest that native aquifer sediment is an optimal porous medium for long-term, in situ monitoring of microbial communities for managed aquifer recharge and other applications in groundwater systems.

Phytoplankton blooms create harmful toxins, scums, and taste and odor compounds and thus pose a major risk to drinking water safety. Climate and land use change are increasing the frequency and severity of blooms, motivating the development of new approaches for preemptive, rather than reactive, water management. While several real-time phytoplankton forecasts have been developed to date, none are both automated and quantify uncertainty in their predictions, which is critical for manager use. In response to this need, we outline a framework for developing the first automated, real-time lake phytoplankton forecasting system that quantifies uncertainty, thereby enabling managers to adapt operations and mitigate blooms. Implementation of this system calls for new, integrated ecosystem and statistical models; automated cyberinfrastructure; effective decision support tools; and training for forecasters and decision makers. We provide a research agenda for the creation of this system, as well as recommendations for developing real-time phytoplankton forecasts to support management.

Water level drawdowns are increasingly common in lakes and reservoirs worldwide as a result of both climate change and water management. Drawdowns can have direct effects on physical properties of a waterbody (e.g., by altering stratification and light dynamics), which can interact to modify the waterbody's biology and chemistry. However, the ecosystem‐level effects of drawdown remain poorly characterized in small, thermally stratified reservoirs, which are common in many regions of the world. Here, we intensively monitored a small eutrophic reservoir for 2 years, including before, during, and after a month‐long drawdown that reduced total reservoir volume by 36%. During drawdown, stratification strength (maximum buoyancy frequency) and surface phosphate concentrations both increased, contributing to a substantial surface phytoplankton bloom. The peak in phytoplankton biomass was followed by cascading changes in surface water chemistry associated with bloom degradation, with sequential peaks in dissolved organic carbon, dissolved carbon dioxide, and ammonium concentrations that were up to an order of magnitude higher than the previous year. Dissolved oxygen concentrations substantially decreased in surface waters during drawdown (to 41% saturation), which was associated with increased total iron and manganese concentrations. Combined, our results illustrate how changes in water level can have cascading effects on coupled physical, chemical, and biological processes. As climate change and water management continue to increase the frequency of drawdowns in lakes worldwide, our results highlight the importance of characterizing how water level variability can alter complex in‐lake ecosystem processes, thereby affecting water quality.

Water level drawdowns are increasingly common in lakes and reservoirs worldwide as a result of both climate change and water management. Drawdowns can have direct effects on physical properties of a waterbody (e.g., by altering stratification and light dynamics), which can interact to modify the waterbody’s biology and chemistry. However, the ecosystem-level effects of drawdown remain poorly characterized in small, thermally-stratified reservoirs, which are common in many regions of the world. Here, we intensively monitored a small eutrophic reservoir for two years, including before, during, and after a month-long drawdown that reduced total reservoir volume by 36%. During drawdown, stratification strength (maximum buoyancy frequency) and surface phosphate concentrations both increased, contributing to a substantial surface phytoplankton bloom. The peak in phytoplankton biomass was followed by cascading changes in surface water chemistry associated with bloom degradation, with sequential peaks in dissolved organic carbon, dissolved carbon dioxide, and ammonium concentrations that were up to an order of magnitude higher than the previous year. Dissolved oxygen concentrations substantially decreased in the surface waters during drawdown (to 41% saturation), which was associated with increased total iron and manganese concentrations. Combined, our results illustrate how changes in water level can have cascading effects on coupled physical, chemical, and biological processes. As climate change and water management continue to increase the frequency of drawdowns in lakes worldwide, our results highlight the importance of characterizing how water level variability can alter complex in-lake ecosystem processes, thereby affecting water quality.