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Residential lawn management often includes fertilizer application to encourage healthy plant growth and support the aesthetic preferences of homeowners and communities. These inputs may negatively impact the environment by increasing nutrient export to aquatic ecosystems via surface runoff or leaching through soil into groundwater. Fertilizer management and nutrient export are of particular concern in karst areas like North‐Central Florida, where the underlying karst geology leads to rapid, direct connections between surface and groundwater ecosystems. We quantified nitrogen (N) and phosphorus (P) leaching from residential landscapes in North‐Central Florida. We investigated nutrient leaching from landscapes spanning a real estate gradient and across different fertility treatments (no N fertilizer, synthetic mineral fertilizer, biosolids‐based organic mineral fertilizer, compost topdressing, natural areas). We measured leachate from these landscapes weekly for 1 year. All residential landscapes, including control yards that received no N fertilizer, leached >10x more nitrate than natural areas, and landscapes treated with synthetic fertilizer exhibited an >80x increase in nitrate leaching. Fertilizer treatments also appeared to alter the N leaching composition, with a greater proportion of total dissolved N leaching coming from nitrate in fertilized treatments (synthetic and organic) compared to natural, control, or compost‐treated landscapes. These results show that landscape management and human actions are important drivers of nutrient leaching in residential landscapes. While all residential lawns leached more N than natural areas, less leaching was associated with certain management approaches. When implemented at larger scales, these approaches may reduce the likelihood of negative impacts of residential landscapes on regional water quality. Fertilizer application onto residential lawns is a source of nitrogen and phosphorus in urban watersheds.Restrictions on fertilizer applications are intended to improve water quality, but their efficacy is debated.Nitrate leaching in residential landscapes, including unfertilized control lawns, was higher than in natural areas.Application of synthetic fertilizer increased annual nitrate leaching by 83 times compared to natural areas.Leaching volume and nutrient loads were correlated with soil characteristics but not property values. Applying fertilizer to lawns is a common source of nutrient pollution in residential landscapes. Understanding how fertilizer moves through the soil can improve our ability to reduce nutrient export in urban areas. We measured nutrient leaching from residential landscapes receiving different fertilizer management practices over an entire year. We installed leaching samplers underneath the soil in residential lawns to capture nutrients moving through the soil into groundwater. We also measured leaching in natural areas as a baseline for comparison. We found that all lawns leached more than 10 times as much nitrogen as natural landscapes, even if they did not receive any fertilizer throughout the study. The traditional fertilizer practice leached more than 80 times as much nitrogen as the natural landscapes. These results demonstrate the impacts of different residential lawn management practices and strategies for reducing the impacts of lawn management on urban water quality.

Lakes process both terrestrial and aquatic organic matter, and the relative contribution from each source is often measured via ecosystem metabolism and terrestrial resource use in the food web (i.e., consumer allochthony). Yet, ecosystem metabolism and consumer allochthony are rarely considered together, despite possible interactions and potential for them to respond to the same lake characteristics. In this study, we compiled global datasets of lake gross primary production (GPP), ecosystem respiration (ER), and zooplankton allochthony to compare the strength and shape of relationships with physicochemical characteristics across a broad set of lakes. GPP was positively related to total phosphorus (TP) in lakes with intermediate TP concentrations (11–75 μg L−1) and was highest in lakes with intermediate dissolved organic carbon (DOC) concentrations. While ER and GPP were strongly positively correlated, decoupling occurred at high DOC concentrations. Lastly, allochthony had a unimodal relationship with TP and related variably to DOC. By integrating metabolism and allochthony, we identified similar change points in GPP and zooplankton allochthony at intermediate DOC (4.5–10 mg L−1) and TP (8–20 μg L−1) concentrations, indicating that allochthony and GPP may be coupled and inversely related. The ratio of DOC:nutrients also helped to identify conditions where lake organic matter processing responded more to autochthonous or allochthonous organic matter sources. As lakes globally face eutrophication and browning, predicting how lake organic matter processing will respond requires an updated paradigm that incorporates nonlinear dynamics and interactions.

The steadily rising global urban population has placed substantial strain on urban water quality, and this strain is projected to increase for the foreseeable future. Considerable attention has been given to the hydrological and physico‐chemical effects of urbanization on stream ecosystems. However, due to the relative infancy of the field of urban ecology, long‐term water quality analyses in urban streams are sparse. Using a 15‐yr stream chemistry monitoring record from Baltimore, Maryland, we quantified long‐term trends in nitrate, phosphate, total nitrogen, total phosphorus, chloride, and sulfate export at several sites along a rural–urban gradient. We found no significant change in solute export at most sites, although we did find specific patterns of interest for certain solutes. For example, nitrogen export declined at the most headwater urban site, while phosphorus export declined at the most downstream urban site. Coupling long‐term monitoring with data on gray and green infrastructure management throughout the landscape, we established relationships between solute export at the most downstream urban monitoring site and sanitary sewer overflows (SSOs), best management practice (BMP) implementation, and road salt application rates. Phosphorus export was correlated with BMP implementation in the watershed, whereas nitrogen export was related to SSOs. Despite highly urbanized watersheds, water quality does not appear to be declining at most of these sites, suggesting that current management may have limited further impairment. Results of our study suggest that both gray and green infrastructure are key for maintaining and improving water quality in this highly urbanized watershed.

Along the river network, water, sediment, and nutrients are transported, cycled, and altered by coupled hydrological and biogeochemical processes. Our current understanding of the rates and processes controlling the cycling and removal of dissolved inorganic nutrients in river networks is limited due to a lack of empirical measurements in large, (nonwadeable), rivers. The goal of this paper was to develop a coupled hydrological and biogeochemical process model to simulate nutrient uptake at the network scale during summer base flow conditions. The model was parameterized with literature values from headwater streams, and empirical measurements made in 15 rivers with varying hydrological, biological, and topographic characteristics, to simulate nutrient uptake at the network scale. We applied the coupled model to 15 catchments describing patterns in uptake for three different solutes to determine the role of rivers in network‐scale nutrient cycling. Model simulation results, constrained by empirical data, suggested that rivers contributed proportionally more to nutrient removal than headwater streams given the fraction of their length represented in a network. In addition, variability of nutrient removal patterns among catchments was varied among solutes, and as expected, was influenced by nutrient concentration and discharge. Net ammonium uptake was not significantly correlated with any environmental descriptor. In contrast, net daily nitrate removal was linked to suspended chlorophyll a(an indicator of primary producers) and land use characteristics. Finally, suspended sediment characteristics and agricultural land use were correlated with net daily removal of soluble reactive phosphorus, likely reflecting abiotic sorption dynamics. Rivers are understudied relative to streams, and our model suggests that rivers can contribute more to network‐scale nutrient removal than would be expected based upon their representative fraction of network channel length. Developed models informed by field measurements to simulate nutrient spiraling at the network scaleRivers contribute more to nutrient removal than do streams relative to expectations generatedExplored the controls on nutrient removal and transport in river networks for each solute

Riverine biogeochemical processes are understudied relative to headwaters, and reach‐scale processes in rivers reflect both the water column and sediment. Denitrification in streams is difficult to measure, and is often assumed to occur only in sediment, but the water column is potentially important in rivers. Dissolved nitrogen (N) gas flux (as dinitrogen (N2)) and open‐channel N2exchange methods avoid many of the artificial conditions and expenses of common denitrification methods like acetylene block and 15N‐tracer techniques. We used membrane‐inlet mass spectrometry and microcosm incubations to quantify net N2and oxygen flux from the sediment and water column of five Midwestern rivers spanning a land use gradient. Sediment and water column denitrification ranged from below detection to 1.8 mg N m−2h−1and from below detection to 4.9 mg N m−2h−1, respectively. Water column activity was variable across rivers, accounting for 0–85% of combined microcosm denitrification and 39–85% of combined microcosm respiration. Finally, we estimated reach‐scale denitrification at one Midwestern river using a diel, open‐channel N2exchange approach based on reach‐scale metabolism methods, providing an integrative estimate of riverine denitrification. Reach‐scale denitrification was 8.8 mg N m−2h−1(95% credible interval: 7.8–9.7 mg N m−2h−1), higher than combined sediment and water column microcosm estimates from the same river (4.3 mg N m−2h−1) and other estimates of reach‐scale denitrification from streams. Our denitrification estimates, which span habitats and spatial scales, suggest that rivers can remove N via denitrification at equivalent or higher rates than headwater streams. We adapted dissolved N2methods and a novel modeling approach to estimate denitrification in riversThe water column accounted for 0–85% and 39–85% of combined denitrification and respirationRivers can remove nitrogen via denitrification at equivalent or higher rates than headwaters

Pharmaceuticals are commonly detected at low concentrations in surface waters, where they disrupt biological and ecological processes. Despite their ubiquity, the annual mass of pharmaceuticals exported from watersheds is rarely quantified. We used liquid chromatography–mass spectroscopy to screen for 92 pharmaceuticals in weekly samples from an urban stream network in Baltimore, MD, USA, that lacks wastewater treatment effluents. Across the network, we detected 37 unique compounds, with higher concentrations and more compounds in streams with higher population densities. We also used concentrations and stream discharge to calculate annual pharmaceutical loads at the watershed outlet, which range from less than 1 kg to ∼15 kg and are equivalent to tens of thousands of human doses. By calculating annual watershed mass balances for eight compounds, we show that ∼0.05 to ∼42% of the pharmaceuticals consumed by humans in this watershed are released to surface waters, with the importance of different pathways (leaking sewage vs treated wastewater effluent) differing among compounds. These results demonstrate the importance of developing, maintaining, and improving sewage infrastructure to protect water resources from pharmaceutical contamination.

In the face of mosquito-borne disease outbreaks, effective mosquito control is a primary goal for public health. Insect repellents, containing active compounds such as DEET and picaridin, are a first defence against biting insects. Owing to widespread use and incomplete sewage treatment, these compounds are frequently detected in surface waters, but their effects on aquatic taxa such as mosquito larvae or their naturally occurring aquatic predators are poorly understood. We investigated the effects of environmentally realistic concentrations of commercial products containing DEET and picaridin on survivorship of mosquito larvae, and their potential indirect effects on survival of larval salamanders, a major predator of mosquito larvae. Larval mosquitos were not affected by exposure to repellents containing DEET or picaridin. We found no larval salamander mortality in control and DEET treatments, but mortality rates in picaridin treatments ranged from 45 to 65% after 25 days of exposure. Salamander larvae exposed to repellents containing picaridin began to display tail deformities and impaired development four days after the experiment began. Our findings suggest the possibility that environmentally realistic concentrations of picaridin-containing repellents in surface waters may increase the abundance of adult mosquitos owing to decreased predation pressure.