Molecular characterization of dissolved organic matter in urban stormwater pond and municipal wastewater discharges transformed by the Florida red tide dinoflagellate Karenia brevis.

Karenia brevis blooms occur almost annually in southwest Florida, imposing significant ecological and human health impacts. Currently, 13 nutrient sources have been identified supporting blooms, including nearshore anthropogenic inputs such as stormwater and wastewater outflows. A 21-day bioassay was performed, where K. brevis cultures were inoculated with water sourced from three stormwater ponds along an age gradient (14, 18, and 34 yrs.) and one municipal wastewater effluent sample, with the aim of identifying biomolecular classes and transformations of dissolved organic matter (DOM) compounds used by K. brevis. All sample types supported K. brevis growth and showed compositional changes in their respective DOM pools. Fourier-transform ion cyclotron resonance mass spectrometry (FT-ICR MS) catalogued the molecular composition of DOM and identified specific compound classes that were biodegraded. Results showed that K. brevis utilized species across a wide range of compositions that correspond to amino sugars, humic, and lignin-like biomolecular classes. The municipal wastewater and the youngest stormwater pond (SWP 14) effluent contained the largest pools of labile DOM compounds which were bioavailable to K. brevis, which indicates younger stormwater pond effluents may be as ecologically important as wastewater effluents to blooms. Conversely, generation of DOM compounds of greater complexity and a wide range of aromaticity was observed with the older (SWP 18 and SWP 34) stormwater pond treatments. These data confirm the potential for stormwater ponds and/or wastewater to contribute nutrients which can potentially support K. brevis blooms, revealing the need for improved nutrient retention strategies to protect coastal waters from the potential ill effects of urban effluent.

Nitrogen forms and dissolved organic matter optical properties in bulk rainfall, canopy throughfall, and stormwater in a subtropical urban catchment.

The study of nitrogen (N) transformation in urban ecosystems is crucial in the protection of coastal water bodies because excess N may fuel harmful algae blooms (HABs). The purpose of this investigation was to study and identify the forms and concentrations of N in rainfall, throughfall, and stormwater runoff for 4 storm events in a subtropical urban ecosystem and to use fluorescence spectroscopy to evaluate the optical properties and expected lability of dissolved organic matter (DOM) in the same samples. The rainfall contained both inorganic and organic N pools, and organic N as nearly 50 % of total dissolved N in the rainfall. As water moved through the urban water cycle, from rainfall to stormwater and from rainfall to throughfall, it was enriched in total dissolved N, with most of the enrichment coming from dissolved organic N. Throughfall fluxes of total dissolved N were as high as 0.67 kg ha-1, compared to 0.44 kg ha-1 from rainfall, suggesting that the urban tree canopy can facilitate anthropogenic subsidies of N to the urban water cycle. Through analysis of sample optical properties, we saw that the throughfall presented the highest humification index and the lowest biological index when compared to rainfall, suggesting throughfall likely consists of higher molecular weight compounds of greater recalcitrance. This study highlights the importance of the dissolved organic N fraction of urban rainfall, stormwater, and throughfall and shows how the chemical composition of dissolved organic nutrients can change as rainfall is transformed into throughfall in the urban tree canopy.

Sources and concentrations of nutrients in surface runoff from waterfront homes with different landscape practices.

Development along Florida's coastal waterways has led to significant degradation in water quality over time. Numerous sources have contributed to increased nutrient loads in surface waters. Nitrogen (N) and phosphorus (P) pollution from urban fertilizer use has been addressed at the state, county, and municipality level yet the success of these efforts is rarely evaluated. This study aimed to validate these efforts by assessing the source and concentration of nutrients from surface water associated with waterfront homes with or without Florida Friendly Landscaping™, a nonstructural best management practice. The objectives were: to compare nutrient concentrations in runoff from differing landscape designs; compare the NO3- isotopic signature to that of known N sources; and evaluate the impact of a fertilizer ordinance blackout that is in effect during the wet season. Results from the study indicate no statistical reduction in the nutrient concentration of lawn runoff from either landscape design or the implementation of a fertilizer blackout ordinance. Results show that the sources of N in home landscapes are highly variable and cannot be solely attributed to fertilizer sources and highlight the influence of atmospheric depositions and soil nutrient pools which contribute 53-65% of the nitrate in lawn runoff. Nutrient management strategies need to address multiple sources of urban nutrients and mitigation efforts will not be immediate.

Copper concentration data for water, sediments, and vegetation of urban stormwater ponds treated with copper sulfate algaecide.

We characterized copper (Cu) concentrations in the water, sediments, and shoreline plants of stormwater ponds in the urban Tampa, Florida area. We selected 6 urban residential stormwater ponds that receive summer wet season (May to September) Cu sulfate applications at least twice a month. We collected triplicate water and sediment samples from each pond and analyzed for Cu, as well as nutrient pools (inorganic N and P) and a suite of other physicochemical properties (e.g., water temperature, pH, conductivity, alkalinity, etc.). We analyzed shoreline plant tissue samples for Cu. The raw dataset provides values for Cu concentrations in water, sediments and plant tissue, and other measured parameters in water and sediments. This dataset is important for characterizing the fate and potential mobility of Cu in freshwater ponds treated with Cu sulfate algaecides. This applied research data will provide baseline understanding of Cu concentrations in water, sediments, and select plant tissue samples, providing insights on potential toxicity of Cu and any threats that Cu sulfate algaecides may pose to aquatic organisms and downstream waters. This dataset can also inform future research designs aimed at elucidating the effects of Cu on denitrifying bacteria and N removal in stormwater pond ecosystems. Finally, the plant tissue data shows variable Cu concentrations among plant species, and this data can inform future phytoremediation experiments.

Wet season nitrogen export from a residential stormwater pond.

Stormwater runoff is recognized as a cause of water quality degradation because it may carry nitrogen (N) and other pollutants to aquatic ecosystems. Stormwater ponds are a stormwater control measure often used to manage stormwater runoff by holding a permanent pool of water, which reduces the peak flow, magnitude of runoff volume, and concentrations of nutrients and pollutants. We instrumented the outlet of a stormwater pond in an urban residential neighbourhood in Florida, United States to (1) investigate the concentration and composition of N forms during the summer rainy season (May to September 2016), and (2) determine the bioavailability of organic N in the stormwater pond with a bioassay experiment. A total of 144 outflow water samples over 13 storm events were collected at the outlet of the stormwater pond that collects runoff from the residential catchment. Samples were analysed for various inorganic N [ammonium (NH4-N), nitrate (NO3-N)], and organic N forms [dissolved organic nitrogen (DON), and particulate organic nitrogen (PON)]. Flow-weighted mean concentration of total N (TN) in pond outflow for all collected storm events was 1.3±1.42 mg L-1, with DON as the dominant form (78%), followed by PON and NO3-N (each at 8%), and NH4-N (6%). In the bioassay experiment, organic N (DON+PON) was significantly decreased by 25-28% after 5 days of incubation, suggesting that a portion of the DON carried from the pond outflow to receiving water bodies may be bioavailable. These results suggest that efforts to mitigate stormwater N outflows from urban ponds should incorporate both inorganic and organic N in management plans.

Composition of nitrogen in urban residential stormwater runoff: Concentrations, loads, and source characterization of nitrate and organic nitrogen.

Stormwater runoff is a leading cause of nitrogen (N) transport to water bodies and hence one means of water quality deterioration. Stormwater runoff was monitored in an urban residential catchment (drainage area: 3.89 hectares) in Florida, United States to investigate the concentrations, forms, and sources of N. Runoff samples were collected over 22 storm events (May to September 2016) at the end of a stormwater pipe that delivers runoff from the catchment to the stormwater pond. Various N forms such as ammonium (NH4-N), nitrate (NOx-N), dissolved organic nitrogen (DON), and particulate organic nitrogen (PON) were determined and isotopic characterization tools were used to infer sources of NO3-N and PON in collected runoff samples. The DON was the dominant N form in runoff (47%) followed by PON (22%), NOx-N (17%), and NH4-N (14%). Three N forms (NOx-N, NH4-N, and PON) were positively correlated with total rainfall and antecedent dry period, suggesting longer dry periods and higher rainfall amounts are significant drivers for transport of these N forms. Whereas DON was positively correlated to only rainfall intensity indicating that higher intensity rain may flush out DON from soils and cause leaching of DON from particulates present in the residential catchment. We discovered, using stable isotopes of NO3-, a shifting pattern of NO3- sources from atmospheric deposition to inorganic N fertilizers in events with higher and longer duration of rainfall. The stable isotopes of PON confirmed that plant material (oak detritus, grass clippings) were the primary sources of PON in stormwater runoff. Our results demonstrate that practices targeting both inorganic and organic N are needed to control N transport from residential catchments to receiving waters.

Organic nitrogen in residential stormwater runoff: Implications for stormwater management in urban watersheds.

Stormwater runoff containing organic nitrogen (N) is a source of potentially bioavailable N in water bodies. Characterization and concentrations of dissolved organic N (DON) and particulate organic N (PON) in urban stormwater runoff are rarely reported and considered in stormwater management. Our objectives were to (1) characterize the organic (DON, PON) and inorganic (NO3- and NH4+) N pools in residential stormwater runoff and (2) determine the rainfall driven landscape sources of runoff PON using an isotopic mixing model with 13C and 15N during a wet season (June-September). We instrumented a 13 ha (0.13 km2) residential catchment located in Florida, United States with an ISCO autosampler and collected stormwater runoff samples (n = 52) over 11 individual stormwater runoff events. Mean concentration of total N in runoff during the wet season was 1.61 mg L-1, of which 37% was DON and 25% was PON. A strong seasonal first flush of PON, giving rise to a large PON:TN ratio, was observed as the wet season progressed from June (PON:TN = 0.39;) to September (PON:TN = 0.12), whereas DON did not display any seasonal variability (mean: 0.66 mg L-1). The isotope mixing model estimated that 76% of PON in the runoff originated from oak detritus (leaves: 50%, acorns: 26%) and the remaining 24% from lawn grass clippings. The dominance of organic N fractions in the urban stormwater runoff suggests that landscape controls on PON and DON are needed to reduce N loading in the urban stormwater runoff. The seasonal first flush of PON indicates that monitoring strategies should focus on how nutrient concentrations in runoff may respond to seasonal drivers such as leaf litterfall and that there may be optimal times for N management, such as after a prolonged dry season in which materials accumulate and pose the risk for later mobilization.

Characterization of dissolved organic nitrogen in leachate from a newly established and fertilized turfgrass.

Understanding the mechanisms of nitrogen (N) retention and loss from fertilized urban turfgrass is critical to develop practices that mitigate N transport and protect water quality in urban ecosystems. We investigated the fate of N in lysimeters sodded with St. Augustine turfgrass and amended with labeled 15N from either ammonium sulfate or urea. Fourier transform ion cyclotron resonance mass spectroscopy (FTICR-MS) was employed to identify various biomolecular classes in the leached dissolved organic N (DON) from one lysimeter for each treatment and the control. Mean DON concentrations, over 92 days, were 88, 94, and 94% of total N in the leachate from the control, urea, and ammonium sulfate treatments, respectively. Isotopic analysis showed that <3% of N in the leachate originated from newly applied N fertilizer, suggesting that the remainder of the N in the leachate was derived from the lysimeter soil or sod biomass pools. The 15N fertilizer recovery was greatest in soil (44-48%), followed by sod+thatch (18-33%), grass clippings (10-13%), and leachate (<3%). Despite isotopic evidence of little contribution of N from fertilizers in the leachate, a fraction of ammonium sulfate fertilizer was recovered as DON in the leachate, likely after uptake and conversion of inorganic fertilizer to organic plant exudates and/or microbial byproducts. FTICR-MS identified N-bearing organic molecular formulas in the leachate from urea and ammonium sulfate treatments, providing evidence of N leaching from newly established turfgrass of DON compounds in a range of biomolecular compositions such as lipid-, protein-, carbohydrate-, and lignin-like molecules.

Dissolved organic nitrogen in urban streams: Biodegradability and molecular composition studies.

A portion of the dissolved organic nitrogen (DON) is biodegradable in water bodies, yet our knowledge of the molecular composition and controls on biological reactivity of DON is limited. Our objective was to investigate the biodegradability and molecular composition of DON in streams that drain a gradient of 19-83% urban land use. Weekly sampling over 21 weeks suggested no significant relationship between urban land use and DON concentration. We then selected two streams that drain 28% and 83% urban land use to determine the biodegradability and molecular composition of the DON by coupling 5-day bioassay experiments with high resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS). Both urban streams contained a wide range of N-bearing biomolecular formulas and had >80% DON in lignin-like compounds, with only 5-7% labile DON. The labile DON consisted mostly of lipid-and protein-like structures with high H/C and low O/C values. Comparison of reactive formulas and formed counterparts during the bioassay experiments indicated a shift toward more oxygenated and less saturated N-bearing DON formulas due to the microbial degradation. Although there was a little net removal (5-7%) of organic-bound N over the 5-day bioassay, there was some change to the carbon skeleton of DON compounds. These results suggest that DON in urban streams contains a complex mixture of compounds such as lipids, proteins, and lignins of variable chemical structures and biodegradability.

Biodegradability and Molecular Composition of Dissolved Organic Nitrogen in Urban Stormwater Runoff and Outflow Water from a Stormwater Retention Pond.

Dissolved organic nitrogen (DON) can be a significant part of the reactive N in aquatic ecosystems and can accelerate eutrophication and harmful algal blooms. A bioassay method was coupled with Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) to determine the biodegradability and molecular composition of DON in the urban stormwater runoff and outflow water from an urban stormwater retention pond. The biodegradability of DON increased from 10% in the stormwater runoff to 40% in the pond outflow water and DON was less aromatic and had lower overall molecular weight in the pond outflow water than in the stormwater runoff. More than 1227 N-bearing organic formulas were identified with FT-ICR-MS in the stormwater runoff and pond outflow water, which were only 13% different in runoff and outflow water. These molecular formulas represented a wide range of biomolecules such as lipids, proteins, amino sugars, lignins, and tannins in DON from runoff and pond outflow water. This work implies that the urban infrastructure (i.e., stormwater retention ponds) has the potential to influence biogeochemical processes in downstream water bodies because retention ponds are often a junction between the natural and the built environment.