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Identifying the mechanisms that contribute to the variability of suspended particulate matter concentrations in coastal areas is important but difficult, especially due to the complexity of physical and biogeochemical interactions involved. Our study addresses this complexity and investigates changes in the horizontal spread and composition of particles, focusing on cross-coastal gradients in the southern North Sea and the English Channel. A semi-empirical model is applied on in situ data of SPM and its organic fraction to resolve the relationship between organic and inorganic suspended particles. The derived equations are applied onto remote sensing products of SPM concentration, which provide monthly synoptic maps of particulate organic matter concentrations (here, particulate organic nitrogen) at the surface together with their labile and less reactive fractions. Comparing these fractions of particulate organic matter reveals their characteristic features along the coastal-offshore gradient, with an area of increased settling rate for particles generally observed between 5 and 30 km from the coast. We identify this area as the transition zone between coastal and offshore waters with respect to particle dynamics. Presumably, in that area, the turbulence range and particle composition favor particle settling, while hydrodynamic processes tend to transport particles of the seabed back towards the coast. Bathymetry plays an important role in controlling the range of turbulent dissipation energy values in the water column, and we observe that the transition zone in the southern North Sea is generally confined to water depths below 20 m. Seasonal variations in suspended particle dynamics are linked to biological processes enhancing particle flocculation, which do not affect the location of the transition zone. We identify the criteria that allow a transition zone and discuss the cases where it is not observed in the domain. The impact of these particle dynamics on coastal carbon storage and export is discussed.

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This study investigated the effect of the landscape pattern of permeable/impermeable patches on NO3--N and particulate organic nitrogen (PON) concentrations during stormwater runoff transport and their source contributions. Six landscape pattern indices, namely, mean proximity index (MPI), largest patch index (LPI), mean shape index (MSI), landscape shape index (LSI), connect index (CONNECT), and splitting index (SPLIT), were selected to reflect the fragmentation, complexity, and connectivity of permeable patches in urban catchments. The results show that lower fragmentation, higher complexity, and greater connectivity can reduce NO3--N concentrations in road runoff and drainage flow (i.e., the flow in the stormwater drainage network), as well as PON concentrations in road runoff. Further, the above landscape pattern is effective for mitigating the contributions of NO3--N and PON from road runoff. Low impact development (LID) can be incorporated with the landscape pattern of permeable/impermeable patches to mitigate nitrogen pollution in urban stormwater at the catchment scale by optimizing the spatial arrangement.

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Nitrogen pollution in urban stormwater has led to serious quality issues in urban water. Nitrogen pollution mitigation requires fully understanding the transport process and major nitrogen sources in urban stormwater. In this study, the concentrations and flux of various nitrogen forms during urban stormwater transport were analyzed. It was found that the concentration and flux of NO3--N and NH3-N decreased in the order of roof runoff, road runoff, and drainage runoff, while the concentration and flux of dissolved organic nitrogen (DON) and particulate nitrogen (PN) were found to be the highest in road runoff. Source quantification found that roof runoff (34%) and rainwater (34%) were the main contributors to nitrate pollution during light and moderate rains (<25 mm), while road runoff was identified as the major source (49%) of nitrate pollution during heavy rains (>25 mm) due to the large road runoff volume. Regarding particulate organic nitrogen (PON), the road runoff in commercial areas contributed most (23%) to PON pollution during light and moderate rains, while the runoff generated from pervious surfaces and drainage sediments were the primary two sources (22%) of PON during heavy rains. Moreover, the influence of rainfall characteristics on nitrate and PON source contributions was identified. The results show that antecedent dry periods were an important factor influencing nitrogen source contributions during light and moderate rains, while rainfall amount and intensity were critical factors impacting the nitrogen source contributions during heavy rains. Taking various transport processes, source contributions, and rainfall characteristics into consideration, several recommendations were given for the mitigation of nitrogen pollution in urban stormwater. This study can provide a useful perspective to understand the transport and sources of nitrogen, thus developing constructive strategies to control urban nonpoint source pollution management.

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Information on the sources and transformations of particulate organic N (PN) and dissolved organic N (DON) at the coastal interface remains insufficient due to technological difficulties and complicated features of intensive physical mixing and rapid biological activities. Here, we investigated the spatial distribution of concentrations and isotopic compositions of PN and DON in the Changjiang plume during the summer flood period. In average, DON and PN accounted for 25.6 ± 12.1% and 8.1 ± 9.1% (n = 55), respectively, of the total N pool, with the remaining N primarily in the form of nitrate (NO3-). Mean δ15N values were the lowest for DON (-0.1 ± 2.7‰, n = 58) and slightly higher for PN (2.0 ± 1.6‰, n = 101), and the highest for NO3- (6.5 ± 2.2‰, n = 67), suggesting multiple transformations had occurred to differentiate isotopic characteristics among the three N pools. By applying a conservative mixing model, we found DON deficits (-3.5 ± 3.7 µmol L-1, n = 43) and negative shift in δ15NDON (-3.6 ± 2.2‰, n = 43) in the Changjiang plume, revealing nonconservative DON behaviors. In the offshore surface plume where Chlorophyll a was high, the most likely cause is the DON uptake by phytoplankton with a strong inverse isotope effect (around -40‰). This DON assimilation by phytoplankton contributed to ~16 ± 12% of the PN production, with the remaining supported by NO3- assimilation, producing an overall isotope effect of 4-9‰. However, in waters near the river mouth and at the bottom of the offshore plume where total suspended matter concentrations were high (>5 mg L-1), the DON deficit was most likely induced by the selective adsorption of 15N enriched moieties of DON onto particulate surfaces (with an isotope effect of -20‰ to -5‰). Unlike dissolved organic carbon to behave conservatively in most estuaries, our results show that active transformations had occurred between the DON and PN pools in the Changjiang plume.

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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.

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Nitrogen (N) is one of the key nutrients for algal growth and is an integral part of many cellular components, for example in proteins. Being able to determine the inorganic and organic pools of N is consequently critical for algal cultivation. In this chapter we present the methods we use for determining dissolved inorganic nitrogen (DIN), dissolved organic nitrogen (DON), and particulate organic nitrogen (PON). The methods presented here for DIN rely on colorimetric methods and those of DON and PON on filtration and high temperature catalytic oxidation.

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Nitrogen deposition is one of the most important factors affecting carbon (C) and nitrogen (N) cycling in terrestrial ecosystem. A six-year N addition experiment was carried out to explore how N deposition affected C and N fractions in soil aggregates in the secondary aspen forest (YHL) and primary Korean pine broad-leaved forest (HSL). We investigagted the effects of N addition on dissolved organic carbon and nitrogen (DOC and DON), microbial biomass carbon and nitrogen (MBC and MBN), particulate organic carbon and nitrogen (POC and PON) in soil aggregates with different particle sizes. The results showed that the contents of carbon and nitrogen fractions generally increased with the decrease of particle sizes of soil aggregates except for POC and PON. In soil aggregates of HSL, POC and PON significantly decreased by 20.7% and 22.6% in N treatment, respectively, but DOC increased by 11.6%. In YHL, N addition treatment had no signi-ficant effect on C and N fractions in soil aggregates. Total carbon or nitrogen correlated well with the active C and N fractions in soil aggregates, with a great significant negative correlation between POC and DOC in HSL (r=-0.503) and a significant positive correlation between DOC and MBC (r=0.462). In HSL, the negative effect of N treatment on POC and PON and the positive effect on DOC was mainly attributed to the accelerated decomposition of POM by stimulating microbial activity. Soil C and N pools in HSL were more vulnerable to N deposition than that in YHL.

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Wastewater-derived organic nitrogen (org-N) can act as both nutrients and carcinogenic nitrogenous disinfection byproduct precursors. In this study, the concentration, composition, bioavailability, and N-nitrosodimethylamine (NDMA) formation potential of particulate organic nitrogen (PON) from three different municipal wastewater treatment plants were characterized and compared with that of effluent dissolved organic nitrogen (DON). The average effluent PON and DON concentrations ranged from 0.09 to 0.55mgN/L and from 0.91 to 1.88mgN/L, respectively. According to principal component analysis, org-N composition and characterization differed in PON and DON samples (n=20). Compared with DON, PON tended to be enriched in protein and nucleic acids, and showed a more proteinaceous character. Composition of org-N functional groups estimated from the X-ray photoelectron spectroscopy N 1s spectra indicate no significant differences in the molecular weight distribution of the protein-like materials between PON and DON. Moreover, PON exhibited a significantly higher bioavailability (61.0±13.3%) compared to DON (38.5±12.4%, p˂0.05, t-test) and a significantly higher NDMA yields (791.4±404.0ng/mg-N) compared to DON (374.8±62.5ng/mg-N, p˂0.05, t-test). Accordingly, PON contributed to approximately 12.3-41.7% of the total bioavailable org-N and 22.0-38.4% of the total NDMA precursors in wastewater effluents. Thus, the potential adverse effects of PON on wastewater discharge and reuse applications should not be overlooked, even though it only accounted for 7.4-26.8% of the total effluent org-N.

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Macronutrient elements (C, N and P) and micronutrient elements (Fe, Co, Cu, Zn and Mn) are widely measured in their various physico-chemical forms in open ocean, shelf sea, coastal and estuarine waters. These measurements help to elucidate the biogeochemical cycling of these elements in marine waters and highlight the ecological and socio-economic importance of the oceans. Due to the dynamic nature of marine waters in terms of chemical, biological and physical processes, it is advantageous to make these measurements in situ and in this regard flow injection analysis (FIA) provides a suitable shipboard platform. This review, therefore, discusses the role of FIA in the determination of macro- and micro-nutrient elements, with an emphasis on manifold design and detection strategies for the reliable shipboard determination of specific nutrient species. The application of various FIA manifolds to oceanographic nutrient determinations is discussed, with an emphasis on sensitivity, selectivity, high throughput analysis and suitability for underway analysis and depth profiles. Strategies for enhancing sensitivity and minimizing matrix effects, e.g. refractive index (schlieren) effects and the important role of uncertainty budgets in underpinning method validation and data quality are discussed in some detail.

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