Blood Transcriptomics Analysis of Fish Exposed to Perfluoro Alkyls Substances: Assessment of a Non-Lethal Sampling Technique for Advancing Aquatic Toxicology Research.

In contrast to mammals, the blood from other vertebrates such as fish contains nucleated red cells. Using a fathead minnow ( Pimephales promelas) oligonucleotide microarray, we compared altered transcripts in the liver and whole blood after exposure to environmentally relevant concentrations of perfluorooctanesulfonic acid (PFOS) and a mixture of seven types of perfluoro alkyl substances (PFAS), including perfluorooctanoic acid (PFOA). We used quantitative polymerase chain reactions and cell-based assays to confirm the main effects and found that blood responded with a greater number of altered genes than the liver. The exposure to PFAS altered similar genes with central roles in a cellular pathway in both tissues, including estrogen receptor α and peroxisome proliferator activator ß and γ, indicating that the genes previously associated with PFAS exposure are differentially expressed in blood and liver. The altered transcripts are involved with cholesterol metabolism and mitochondrial function. Our data confirmed that PFAS are weak xenoestrogens and exert effects on DNA integrity. Gene expression profiling from blood samples not related with the immune system, including very-low-density lipoprotein, vitellogenin, estrogen receptor, and thyroid hormone receptor, demonstrated that blood is a useful tissue for assessing endocrine disruption in non-mammalian vertebrates. We conclude that the use of blood for non-lethal sampling in genomics studies is informative and particularly useful for assessing the effects of pollution in endangered species. Further, using blood will reduce animal use and widen the experimental design options for studying the effects of contaminant exposure on wildlife.

δ(15)N and δ(18)O Reveal the Sources of Nitrate-Nitrogen in Urban Residential Stormwater Runoff.

Nitrogen (N) sources are widely distributed in the complex urban environment. High-resolution data elucidating N sources in the residential catchments are not available. We used stable isotopes of N and oxygen (O) of nitrate (δ(18)O-NO3(-) and δ(15)N-NO3(-)) along with δ(18)O and hydrogen (δD) of water (H2O) to understand the sources and transformations of N in residential stormwater runoff. Stormwater runoff samples were collected over 25 stormwater events at 5 min intervals using an autosampler installed at the residential catchment outlet pipe that drained 31 low-density homes with a total drainage area of 0.11 km(2). Bayesian mixing model results indicated that atmospheric deposition (range 43-71%) and chemical N fertilizers (range <1-49%) were the dominant NO3-N sources in the stormwater runoff and that there was a continuum of source changes during the stormwater events. Further, the NO3-N transport in the stormwater runoff from the residential catchment was driven by mixing of multiple sources and biotic (i.e., nitrification) processes. This work suggests that a better understanding of N transport and sources is needed to reduce N export and improve water quality in urban water systems.

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.

Phosphorus Leaching in Soils Amended with Animal Manures Generated from Modified Diets.

New dietary modifications for dairy (reducing P content in feed) and poultry (addition of feed additives such as phytase) aim to reduce P excretion in manures. Our objective was to investigate if dietary changes were effective at reducing P leaching loss on land application of manures. We used 54 undisturbed lysimeters (30 cm diameter, 50 cm deep) collected from three typical mid-Atlantic soils. Lysimeters received 85 kg total P ha from fertilizer (superphosphate), dairy manures generated from low- or high-P diets, or broiler litters generated from normal diet or reduced P- and phytase-amended diets. Lysimeters were irrigated with 50 mm of water each week for 9 wk. The major forms of P in the leachate were dissolved (dissolved unreactive > dissolved reactive P [DRP]) rather than particulate (total particulate P). The higher P solubility (100%) in superphosphate resulted in greater leaching of DRP, whereas the lower P solubility (<30%) in dairy manures or broiler litters resulted in lower DRP leaching from soils. Preferential flow in two soils caused greater DRP leaching; this effect was more pronounced in the superphosphate-amended than in the manure/litter-amended lysimeters. The dairy and poultry dietary modification was effective at reducing the amount of P in manures and litters. However, the application of treatments at similar P rate (85 kg ha) resulted in the addition of a higher amount of manure (54-66%) in lysimeters that received low-P dairy manure-amended and phytase-amended broiler litter, which then controlled P leaching from soils.

Mass Balance of Water and Nitrogen in the Mounded Drainfield of a Drip-Dispersal Septic System.

Quantitative assessment of nitrogen (N) loading from septic systems is needed to protect groundwater contamination. We determined the mass balance of water and N in the mounded drainfield of a drip-dispersal septic system. Three lysimeters (152.4 cm long, 91.4 cm wide, 91.4 cm high, with 1:1 side slope) were constructed using pressure-treated wood to mimic mounded drainfields. Of total water inputs, septic tank effluent (STE) added 57% water and natural rainfall added 43% water from January 2013 to January 2014. Outputs included leached water (46%) from the lysimeters over 67 sampling events ( = 15 daily and = 52 weekly flow-weighted), potential evapotranspiration (28%), and water stored in the drainfields (26%). Over 13 mo, each drainfield received 227 g of total N (STE, 99%; rainfall, 1%), of which 33% leached, 23% accumulated in the drainfield, and 6% was taken up by grass, with the remainder (38%) estimated to be gaseous N loss. Using these data, the leaching of water from 2.5 million drip-dispersal drainfields in the state of Florida was estimated to be 2.29 × 10 L yr, which would transport 2.4 × 10 kg of total N yr from the drainfields to shallow groundwater. Further reduction of N below drainfields in the soil profile could be expected before STE reaches groundwater. Our results provide quantitative information on the water and N loading and can be used to optimize drainfield conditions to attenuate N and protect groundwater quality.

High Removal of Effluent-borne Nitrogen with Multiple External Electron Donors in the Engineered Drainfield of an Advanced Septic System.

Septic systems can be a major source of nitrogen (N) in shallow groundwater. We designed an in situ engineered drainfield with aerobic-anaerobic (sand-woodchips) and anaerobic (elemental sulfur-oyster shell) media to remove N in the vadose zone and reduce N transport to groundwater. Effluent was dispersed on top of the engineered drainfield (3.72 m infiltrative surface) and then infiltrated through the aerobic-anaerobic and anaerobic media before reaching natural soil. Water samples were collected over 64 sampling events (May 2012-December 2013) from three parts of the drainfield: (i) a suction cup lysimeter installed at the sand-woodchips interface, (ii) a pipe after effluent passed through the aerobic-anaerobic media, and (iii) a tank containing anaerobic media. In the effluent, most of the total N (66 mg L) was present as NH-N (88.8%), whereas at the sand-woodchips interface the dominant N form was NO-N (31 mg L; 85% of total N). As the effluent passed through the aerobic-anaerobic media in the drainfield, heterotrophic denitrification reduced NO-N to 5.4 mg L. In the tank containing anaerobic media, autotrophic denitrification, facilitated by elemental sulfur, further reduced NO-N to 1 mg L. Overall, 90% of total added N was removed as the effluent passed through the aerobic-anaerobic and anaerobic media within the engineered drainfield. We conclude that the use of multiple electron donors from external media (sand-woodchips and elemental sulfur-oyster shell) was effective at removing N in the engineered drainfield and will reduce the risk of groundwater N contamination from septic systems in areas with shallow groundwater.

Tolerance and antioxidant response of a dark septate endophyte (DSE), Exophiala pisciphila, to cadmium stress.

The growth, oxidative damage and antioxidant response of Exophiala pisciphila ACCC32496, a dark septate endophyte isolated from an abandoned lead-zinc mining area, were measured at cadmium (Cd) concentrations of 0, 25, 50, 100, 200 and 400 mg L(-1). The EC50 values of E. pisciphila ACCC32496 to Cd were 332.2 mg L(-1) after 30 days on solid medium and 111.2 mg L(-1) after 7 days in liquid medium. Cd stress markedly stimulated the production of superoxide anion, H2O2 and malondialdehyde in the fungal mycelia. The activities of superoxide dismutase and catalase reached their maxima at 100 mg L(-1) Cd. The glutathione and non-protein thiol contents, along with the total antioxidant capability, reached their maxima at 50 mg L(-1) Cd. Low Cd concentrations induced a noticeable increase in antioxidant defense, while high Cd concentrations decreased the antioxidant defense.

Phosphorus speciation in manure and fertilizer impacted Mid-Atlantic coastal plain soils.

Historical applications of manures and fertilizers at rates exceeding crop P removal in the Mid-Atlantic region (United States) have resulted in decades of increased water quality degradation from P losses in agricultural runoff. As such, many growers in this region face restrictions on future P applications. An improved understanding of the fate, transformations, and availability of P is needed to manage P-enriched soils. We paired chemical extractions (i.e., Mehlich-3, water extractable P, and chemical fractionation) with nondestructive methods (i.e., x-ray absorption near edge structure [XANES] spectroscopy and x-ray fluorescence [XRF]) to investigate P dynamics in eight P-enriched Mid-Atlantic soils with various management histories. Chemical fractionation and XRF data were used to support XANES linear combination fits, allowing for identification of various Al, Ca, and Fe phosphates and P sorbed phases in soils amended with fertilizer, poultry litter, or dairy manure. Management history and P speciation were used to make qualitative comparisons between the eight legacy P soils; we also speculate about how P speciation may affect future management of these soils with and without additional P applications. With continued P applications, we expect an increase in semicrystalline Al and Fe-P, P sorbed to Al (hydro)oxides, and insoluble Ca-P species in these soils for all P sources. Under drawdown scenarios, we expect plant P uptake first from semicrystalline Al and Fe phosphates followed by P sorbed phases. Our results can help guide management decisions on coastal plain soils with a history of P application.

Temporal variability in water quality parameters--a case study of drinking water reservoir in Florida, USA.

Our objective was to evaluate changes in water quality parameters during 1983-2007 in a subtropical drinking water reservoir (area: 7 km(2)) located in Lake Manatee Watershed (area: 338 km(2)) in Florida, USA. Most water quality parameters (color, turbidity, Secchi depth, pH, EC, dissolved oxygen, total alkalinity, cations, anions, and lead) were below the Florida potable water standards. Concentrations of copper exceeded the potable water standard of <30 µg l(-1) in about half of the samples. About 75 % of total N in lake was organic N (0.93 mg l(-1)) with the remainder (25 %) as inorganic N (NH3-N: 0.19, NO3-N: 0.17 mg l(-1)), while 86 % of total P was orthophosphate. Mean total N/P was <6:1 indicating N limitation in the lake. Mean monthly concentration of chlorophyll-a was much lower than the EPA water quality threshold of 20 µg l(-1). Concentrations of total N showed significant increase from 1983 to 1994 and a decrease from 1997 to 2007. Total P showed significant increase during 1983-2007. Mean concentrations of total N (n = 215; 1.24 mg l(-1)) were lower, and total P (n = 286; 0.26 mg l(-1)) was much higher than the EPA numeric criteria of 1.27 mg total N l(-1) and 0.05 mg total P l(-1) for Florida's colored lakes, respectively. Seasonal trends were observed for many water quality parameters where concentrations were typically elevated during wet months (June-September). Results suggest that reducing transport of organic N may be one potential option to protect water quality in this drinking water reservoir.

Changes in heavy metal contents in animal feeds and manures in an intensive animal production region of China.

The 360 feed and manure samples were collected from 150 animal farms in Jiangsu Province, China and analyzed for heavy metals. Concentrations of Zn and Cu in animal feeds were 15.9-2041.8 and undetected-392.1 mg/kg respectively, while Hg, As, Pb, Cd, and Cr in all feeds were below 10 mg/kg. Concentrations of Cu, Zn, and Cr in animal manures were 8.4-1726, 39.5-11379, and 1.0-1602 mg/kg respectively, while As, Cd, Hg, and Pb were < 10 mg/kg. The concentration of Cu, Zn, As and Cr in animal feed and manure were positively correlated (p < 0.001), but the Cd, Hg, and Pb were not statistically correlated between the feed and the manure. Concentrations of Cu and Zn were highest in pig feed and manure, followed by poultry and dairy feeds and manures. During 1990-2008, Cu, Zn, As, Cr, Cd contents increased by 771%, 410%, 420%, 220%, and 63% in pig manure, 212%, 95%, 200%, 791%, and -63% in dairy manure, and 181%, 197%, 1500%, 261, and 196% in poultry manure. Most of the increases occurred from 2002 to 2008, which reflects the extensive use of feed additives after 2002. In contrast, Pb and Hg in manures continuously decreased from 1990 to 2008. The results suggest that the heavy metal contents in animal manure have been greatly increased over 18 years and the contribution of manures to soil should be considered.

Fate and transformations of dissolved phosphorus forms in runoff: Effect of poultry litter and products extracted with variable water extraction ratios.

In many intensive animal production areas, the over-application of manure has resulted in a build-up of soil phosphorus (P) and the creation of legacy P soils that threaten water quality. We investigated dissolved P forms losses in runoff using simulated rainfall in packed soil boxes amended with three poultry litter and products, including raw (unprocessed) litter, granulated litter with the addition of urea, and heated raw litter. These were applied at 3 kg water-extractable P (WEP) ha-1 as determined with three litter-to-water extraction ratios (1:10, 1:100, and 1:200). Over three simulated rainfall events, the amount of dissolved reactive P (DRP) lost was significantly greater in runoff from soils amended with granulated litter (1.09 ± 0.02 kg ha-1) than raw (0.81 kg ha-1) and heated (0.58 kg ha-1) litters. No significant differences in the amount of dissolved unreactive P (DUP) in runoff (0.38 ± 0.07 kg ha-1) were observed among three litter amended soils. The soil test P (i.e., Mehlich 3-P) increased from 6.9 mg kg-1 in control to 10.4-11.6 mg kg-1 in litter amended soils, whereas the total WEP (0.26 ± 0.03 mg kg-1) in soils was similar after three rainfall simulation events. We conclude that (1) an accurate litter-to-water extraction ratio (>1:200) is critical to determine the amount of WEP in manure as it will ensure similar amounts of soluble P application and will result in identical runoff losses of dissolved P, and (2) the granulation and heating of litter created a product that could enhance the use of poultry litter, especially in non-agricultural markets, resulting in sustainably using manure and reducing the risk of P loss to water bodies.

Molecular characterization of dissolved organic nitrogen and phosphorus in agricultural runoff and surface waters.

Agricultural runoff is a significant contributor to nitrogen (N) and phosphorus (P) pollution in water bodies. Limited information is available about the molecular characteristics of the dissolved organic N (DON) and P (DOP) species in the agricultural runoff and surface waters. We employed Fourier Transform-Ion Cyclotron Resonance-Mass Spectrometry (FT-ICR-MS) to investigate the changes in the molecular characteristics of DON and DOP at three watershed positions (upstream water, runoff from agricultural fields, and downstream waters). Across three watershed locations, more-bioavailable compounds (such as amino sugars, carbohydrates, lipids, and proteins) accounted for <5% of DON and 4-31% of DOP molecules, whereas less-bioavailable compounds (such as lignin, tannins, condensed hydrocarbons, and unsaturated hydrocarbons) were >95% of DON and 69-96% of DOP. Of the dissolved organic matter, runoff waters from agricultural fields contained the greatest proportion of DON formulas (20-25%) than upstream (18%) and downstream (13-14%) waters, indicating the presence of a greater diversity of DON species in the runoff. Various nutrient sources present in agricultural fields such as crop residues, soil organic matter, and transformed fertilizers likely contributed to the diverse composition of DON and DOP in the runoff, which were likely altered as the surface water traversed along the flow pathways in the watershed. The presence of more-bioavailable molecules detected in upstream compared to agricultural runoff and downstream waters suggests that photochemical and/or microbial processes likely altered the characteristics of DON and DOP compounds. The findings of this study increase our understanding of DON and DOP compounds lability and transformations in runoff and surface waters , which may be useful in quantifying the contribution of organic N and P sources to water quality impairment in aquatic ecosystems.

X-ray absorption near edge structure spectroscopy reveals phosphate minerals at surface and agronomic sampling depths in agricultural Ultisols saturated with legacy phosphorus.

Legacy phosphorus (P) soils have received excessive P inputs from historic manure and fertilizer applications and present unique management challenges for protecting water quality as soil P saturation leads to increased soluble P to waterways. We used P K-edge X-ray absorption near edge structure (XANES) spectroscopy to identify and quantify the dominant P minerals in four representative legacy P soils under conventional till and no-till management in Maryland, USA. Various measures of extractable soil P, including water-extractable P (20.6-54.1 mg kg-1 at 1:10 soil-to-water ratio; 52.7-132.2 mg kg-1 at 1:100 soil-to-water ratio), plant available P extracted with Mehlich 3 (692-1139 mg kg-1), and Mehlich 3P saturation ratio (0.54-1.37), were above the environmental threshold values, suggesting the accumulation of legacy P in soils. The quantification of dominant P minerals may provide insights into the potential of legacy P soils to contribute to P release for crop use and soluble P losses. Linear combination fits of XANES spectra identified the presence of four phosphate mineral groups, consisting of (i) calcium-phosphate minerals (11-59%) in the form of fluorapatite, ß-tricalcium phosphate, and brushite, followed by (ii) iron-phosphate minerals (12-49%) in the form of ludlamite, heterosite, P sorbed to ferrihydrite, and amorphous iron phosphates, (iii) aluminum-phosphate minerals (15-33%) in the form of wavellite and P sorbed to aluminum hydroxide, and (iv) other phosphate minerals (5-35%) in the form of copper-phosphate (cornetite, 5-18%) and manganese-phosphate (hureaulite, 25-35%). Organic P consisting of phytic acid was found in most soils (13-24%) and was more pronounced in the surface layer of no-till (21-24%) than in tilled (16%) fields. Of the P forms identified with XANES, we conclude that P sorbed to Fe and Al, and Ca-P in the form of brushite and ß-tricalcium phosphate will likely readily contribute to the soil WEP pool as the soil solution P is depleted by crop uptake and lost via runoff and leaching.

Effect of tomato packinghouse wastewater properties on phosphorus and cation leaching in a spodosol.

Land application of wastewater is a common practice. However, coarse-textured soils and shallow groundwater in Florida present favorable conditions for leaching of wastewater-applied constituents. Our objective in this study was to determine phosphorus (P) and associated cations (Ca, Mg, K, Na) leaching in a Spodosol irrigated with tomato packinghouse wastewater. We packed 12 polyvinyl chloride soil columns (30 cm internal diameter × 50 cm length) with two soil horizons (Ap and A/E) and conducted 30 sequential leaching events by irrigating with wastewater at low (0.84 cm d), medium (1.68 cm d), and high (2.51 cm d) rates. The control treatment received deionized water at 1.68 cm d Leachate pH was lower (6.4-6.5) and electrical conductivity (EC) was higher in the wastewater-treated columns (0.85-1.78 dS m) than in the control treatment (pH 6.9; EC, 0.12 dS m) due to the low pH (6.2) and high EC (2.16 dS m) of applied wastewater. Mean leachate P concentrations were greatest in the control treatment (0.70 mg L), followed by the high (0.60 mg L) and low and medium wastewater-treated columns (0.28-0.33 mg L). Leachate concentrations of Na, Ca, Mg, and K were significantly ( < 0.05) greater in wastewater-treated columns than in the control. Concentrations of P, Na, and K in leachate remained lower than the concentrations in the applied wastewater, indicating their retention in the soil profile. In contrast, leachate Ca and Mg concentrations were greater than in applied wastewater during several leaching events, suggesting that additional Ca and Mg were leached from the soil. Our results suggest that tomato packinghouse wastewater can be beneficially land-applied at 1.68 cm d in Florida's Spodosols without significant P and cation leaching.

Enriched dissolved organic carbon export from a residential stormwater pond.

In urban watersheds, stormwater retention ponds are intermediate junctions that capture, store, and discharge stormwater, and provide an organic-rich environment that transforms and retains nutrients and other constituents. This study investigated the concentrations and loads of dissolved and particulate organic carbon (DOC and POC) in discharges from a stormwater retention pond that receives runoff from a residential catchment. We installed an autosampler, a flowmeter, and a rain gauge at the outlet (weir) of the stormwater retention pond and collected samples from 13 storm events during the 2016 wet season (May-September). Results showed the dominance of DOC (11.2 mg L-1) over POC (0.6 mg L-1) in the pond discharges. The elevated DOC levels in the pond were close to eutrophic lakes and ponds (~10.3 mg L-1), but not statistically different from urban runoff at a nearby site. High-frequency monitoring of pond discharge waters showed that DOC concentrations peaked at the beginning of storm events due to initial surface runoff following a rainstorm (first-flush effect). Rainfall samples analysis suggested that precipitation accounted for a small fraction of DOC pool, but carbon to nitrogen (C/N) ratios supported that in situ aquatic sources could dominate DOC inputs in some storms. Relative to DOC, the first-flush effect was even more apparent for POC, and POC inputs from in situ aquatic sources were more common based on C/N ratios. The calculated export of total organic C (TOC = DOC + POC) was 22.5 kg ha-1 over the observed events, and the estimated export was 33.8 kg ha-1 over the 2016 wet season. Our data suggest that reducing high DOC export from residential stormwater ponds warrant controls on both inputs from the watershed and in situ aquatic sources.

Residential catchments to coastal waters: Forms, fluxes, and mechanisms of phosphorus transport.

Controlling phosphorus (P) loss from land to water bodies is of immense scientific and societal interest and scrutiny. We investigated P forms in a longitudinal gradient in three typical urban junctions: stormwater from a residential catchment, pond discharges from a stormwater retention pond, and 13 coastal waters (rivers and estuary). Concentrations of total P (TP) were 122.7 ± 99.1 µg/L in the stormwater, 89.7 ± 35.8 µg/L in the pond discharges, and 212.1 ± 51.2 µg/L in 13 coastal water sites. Lower P concentrations in pond discharges reflect P attenuation in the stormwater pond, and higher P concentrations in surface waters are likely attributed to the additional contributing P sources in the watershed. Dissolved reactive P (DRP) was 38% of TP load in stormwater and 46% of TP concentrations in surface water sites, whereas particulate unreactive P (PUP) was 52% of TP load in pond discharges. The first-flush strength of P forms in the stormwater indicated the dominance of particulate P over dissolved P. More particulate P was transported in the early stages of storms due to the runoff of P associated with sediment, plant materials, and built up on impervious surfaces. Whereas more dissolved P was transported in the later stages of storms likely due to the flushing of P, as exacerbated by greater runoff amounts, from the landscape sources, i.e., grass clippings, tree leaves, and soil. In the pond discharges, DRP was a minor form suggesting its utilization by bacteria and algae in the pond. The high concentration and proportion of DRP in surface waters suggest an abundance of bioavailable P in urban waters. These results imply that treatment designs in urban areas should consider ways to remove P in urban landscapes focusing on attenuating P before the initiation of runoff and discharge to surface waters to protect downstream water quality.

Nitrate-nitrogen transport in streamwater and groundwater in a loess covered region: Sources, drivers, and spatiotemporal variation.

Water quality is an increasing concern in the dry regions of the world as it affects and reduces the quantity of available water. Our objective was to investigate the sources, drivers, spatiotemporal patterns of nitrate­nitrogen (NO3-N) transport in the streamwater and groundwater in a dry and a wet season in seven large rivers located in the Loess Plateau of China (640,000 km2, 100 million population), which is a region with marked influence of human activities on streamflow and groundwater. We collected 510 streamwater and groundwater samples and found that NO3-N was significantly lower in the dry season (< 5.0 mg L-1) than the wet season (> 5.0 mg L-1). In the wet season, NO3-N was lower in the streamwater than groundwater; however, the spatial variation in the NO3-N was greater in streamwater, with higher concentrations in two rivers (Wei and Fen). The source characterization using stable isotopes of NO3 from the Wei River showed that chemical N fertilizers and soil organic N contributed ~ 75% of NO3 to streamwater and that soil organic N was the greatest contributor of NO3 to groundwater (~ 60%) than streamwater (< 40%). The spatial pattern of NO3-N was dominated by fertilizer application and varied seasonally with rainfall-runoff and streamflow-groundwater connectivity. Our results showed the complicated patterns and sources of NO3 pollution in streamwater and groundwater and highlight that more emphasis should be placed to prevent and restore the degraded water quality in the dry regions.

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.

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.

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.