Nitrogen In Coastal Waters Research Articles

Sources of polyamines in coastal waters and their links to phytoplankton

Polyamines are key components of labile dissolved organic nitrogen in coastal waters. They are found in all living organisms, which are the sources of dissolved organic matter in marine environments. The concentrations of dissolved polyamines are generally low and are controlled as much by production as by consumption. Understanding the dynamics of intracellular pools of polyamines could provide insight to their dynamics in the environment and their potential contribution to ecosystem processes. We measured the concentrations of 6 common polyamines (putrescine, cadaverine, norspermidine, spermidine, norspermine and spermine) extracted from particles in water samples collected on the continental shelf of the South Atlantic Bight (SAB). The total concentrations of extractable polyamines (EPs) decreased from inshore to the shelf-break of the SAB, following a pattern similar to chlorophyll a and opposite to salinity. The composition of EPs was highly correlated with the distribution of phytoplankton species assessed as the abundance of diatom 18S rRNA genes, and with densities of picoeukaryote, Synechococcus and Prochlorococcus cells, suggesting that phytoplankton are the primary source of EPs, followed by a freshwater or nearshore source. Our data suggest that putrescine, norspermidine and spermidine are released primarily from diatoms and picoeukaryotes, while Synechococcus and dinoflagellates are the likely sources of norspermine and spermine.

Assessing the Resiliency of Salt Marshes Under Increasing Nitrogen Loading

Understanding the threat to ecosystems from excess nitrogen in coastal waters is a priority issue in scientific research and natural resource management. Previous field studies have demonstrated that high nitrogen loading can decrease the health and resiliency of salt marshes through shifting biomass allocation, increasing decomposition, and causing creek bank instability, all of which can lead to increased marsh loss with sea-level rise. However, other studies have shown relatively little impact of increasing nitrogen on the structure and function of these systems. Due to the long history of eutrophication in Long Island Sound, aggressive nitrogen reduction strategies have been enacted in this region, but detrimental nutrient inputs persist at variable levels throughout the watershed. Here, the extent of nitrogen-linked salt marsh change under varying levels of nutrient stress was measured, testing the hypothesis that salt marsh resilience (as measured by Spartina alterniflora belowground biomass and marsh edge stability) decreases with increasing nitrogen loading. S. alterniflora growth (stem height, stem density, and biomass) and within-marsh creek area were quantified in 10 salt marshes along a nitrogen-loading gradient. Increasing nitrogen loading showed a significant negative relationship with dead belowground biomass in S. alterniflora; the loss of this belowground biomass in higher nitrogen systems may decrease salt marshes’ ability to keep pace with sea-level rise. Neither shifts in live biomass allocation nor a positive relationship between aboveground biomass or stem height and increasing nitrogen was observed that might promote additional sediment capture, but higher stem density could play a role in promoting sedimentation on the marsh surface in more sediment-rich systems. Aerial photography analysis revealed marsh creek expansion since 1934 at 90% of the marshes studied, but unlike findings from prior experimental enrichment studies, the rate of marsh loss did not increase with increasing nitrogen loading. Given the importance of these ecosystems and the potential of nitrogen to decrease their resiliency, understanding the impacts of eutrophication on salt marshes is critical. However, these results show that the relative importance of nitrogen in driving salt marsh loss in Long Island Sound may be less than studies from other regions have suggested.

Composition and sources of aerosol organic matter in a highly anthropogenic influenced semi-enclosed bay: Insights from excitation-emission matrix spectroscopy and isotopic evidence

Organic matter in aerosols is an important allochthonous source of organic carbon and nitrogen in coastal waters. In this study, we investigated the constituents, sources, and formation process of organic matter in aerosols using excitation−emission matrix (EEM) spectroscopy and stable isotopes. The concentration of aerosol organic matter (AOM), including particle organic matter (POM) and water-soluble organic matter (WSOM), were higher in the northeast monsoon (NEM) season than in the southwest monsoon and typhoon (SWM) season due to the considerable contribution of organic aerosols from the Pearl River Delta (PRD), eastern mainland China and local emissions. The results of stable isotope (δ13C and δ15N) combined with a MixSIAR model showed that fossil fuel combustion (vehicle exhausts and coal combustion) was the most important source of aerosol organic matter, which contributed more than 60% of the total AOM input, throughout the year. The EEM spectroscopy results indicated that protein-like and non-N-containing species were the primary components of aerosol organic matter, while highly-oxygenated species, mostly humic-like substances (HULIS), were identified only in the NEM season. The highly-oxygenated species in the NEM season may be attributed to the formation of secondary organic aerosols induced by higher ozone levels and increased organic radical through the severe pollution in this season.

Algal bioassays detect modeled loading of wastewater-derived nitrogen in coastal waters of O'AHU, HAWAI'I.

Previous studies indicate coastlines are at risk of wastewater contamination from injection wells, cesspools, and septic systems. In this study, common marine algae were used to ground-truth modeled loading of wastewater-derived N to coastlines of O'ahu, Hawai'i. Macroalgae were collected and/or deployed at 118 sites and analyzed for tissue δ15N and N %. Wastewater source locations were used to estimate wastewater-derived N in groundwater with the modeling software MT3DMS/MODFLOW. Algal bioassays identified six coastal regions subjected to elevated wastewater-derived N loading. In a case study, submarine groundwater discharge (estimated by 222Rn mass balance) was related to wastewater loading from onsite sewage disposal systems (OSDS) and municipal wastewater injection wells in Waimānalo. The highest 222Rn-derived SGD rate and N flux were 21.4m3/m/d and 62.6g/m/d, respectively. The results of this study suggest that OSDS and injection wells discharge substantial volumes of wastewater and N across broad regions of coastal O'ahu.

Stable isotope analyses of manatee bones measure historical nitrogen pollution in Florida waters, 1975–2010

Nutrient pollution is a key driver of ecological change in coastal marine environments. Over the last 150 years, the dominant source of nitrogen in coastal waters has shifted from sewage to synthetic fertilizer in many regions including the Caribbean. Here, we use stable nitrogen isotope analyses of bones from manatees (Trichechus manatus latirostris) from along the coast of Florida, USA, to determine whether they record changes in coastal nitrogen pools over a 35-year period. Nitrogen isotopic composition (δ15N) of 172 manatee bones declined statewide at a rate of 0.07‰ year−1, from 9.8‰ in 1975 to 7.3‰ in 2010, suggesting a greater relative abundance of fertilizer, which has a lower δ15N value than that of sewage. Of the four coastal regions of Florida we examined, δ15N values declined significantly in two: the northeast and northwest coasts. The southeast coast, which includes some of the most densely populated counties and cities, had the highest mean δ15N values. In contrast, δ13C values did not vary over time or among coastal regions within the state, indicating that the source of the plant material in the manatee diets did not change substantively over the course of the study period. The general decline in δ15N values may be due to an increase in synthetic fertilizer nitrogen use by the agriculture industry in Florida, but that trend has now abated as overall fertilizer use has stabilized. It is also likely that the increased use of deep injection wells for treated wastewater disposal, which diverts sewage-derived nitrogen away from coastal waters, contributed to the long-term decline in δ15N values in spite of the state’s rising human population.

The effects of NO3(-) supply on Mazzaella laminarioides (Rhodophyta, Gigartinales) from southern Chile.

The effects of nitrate supply on growth, pigments, mycosporine-like amino acids (MAAs), C:N ratios and carrageenan yield were investigated in Mazzaella laminarioides cultivated under solar radiation. This species is economically important in southern Chile where an increase of nitrogen in coastal waters is expected as a consequence of salmon aquaculture activity. Apical segments were cultivated in enriched seawater with five different NO3(-) concentrations (0, 0.09, 0.18, 0.38 and 0.75 mm) during 18 days. Although phycoerythrin and phycocyanin content, as well as C:N ratios, were reduced in the control treatment (without NO3(-) supply), when compared to NO3(-) treatments, total MAA concentration, carrageenan yield and growth rates were similar in all tested conditions. Nevertheless, during the experiment, an important synthesis of mycosporine-glycine took place in a nitrate concentration-dependent manner, with accumulation being saturated around 0.18 mm of nitrate. These results indicate that exposure to high NO3(-) concentration of more than 100 times the values observed in the nature did not impair the photoprotection system, as determined by MAAs, nor did it have a deleterious effect on growth or carrageenan yield of M. laminarioides, a late successional species from Chile.

Evaluating total inorganic nitrogen in coastal waters through fusion of multi-temporal RADARSAT-2 and optical imagery using random forest algorithm

Satellites routinely provide frequent, large-scale, near-surface views of many oceanographic variables pertinent to plankton ecology. However, the nutrient fertility of water can be challenging to detect accurately using remote sensing technology. This research has explored an approach to estimate the nutrient fertility in coastal waters through the fusion of synthetic aperture radar (SAR) images and optical images using the random forest (RF) algorithm. The estimation of total inorganic nitrogen (TIN) in the Hong Kong Sea, China, was used as a case study. In March of 2009 and May and August of 2010, a sequence of multi-temporal in situ data and CCD images from China's HJ-1 satellite and RADARSAT-2 images were acquired. Four sensitive parameters were selected as input variables to evaluate TIN: single-band reflectance, a normalized difference spectral index (NDSI) and HV and VH polarizations. The RF algorithm was used to merge the different input variables from the SAR and optical imagery to generate a new dataset (i.e., the TIN outputs). The results showed the temporal-spatial distribution of TIN. The TIN values decreased from coastal waters to the open water areas, and TIN values in the northeast area were higher than those found in the southwest region of the study area. The maximum TIN values occurred in May. Additionally, the estimation accuracy for estimating TIN was significantly improved when the SAR and optical data were used in combination rather than a single data type alone. This study suggests that this method of estimating nutrient fertility in coastal waters by effectively fusing data from multiple sensors is very promising.

Distribution, sources and budgets of particulate phosphorus and nitrogen in the East China Sea

Suspended particles were collected from the northern East China Sea (ECS) in four spring and autumn cruises to study the sources and biogeochemical behavior of particulate inorganic and organic phosphorus and nitrogen (PIP, POP, PIN, and PON). PIP and PON were dominant forms of particulate P and N, accounting for 57.2% of TPP and 78.2% of TPN, respectively. PIP and POP concentrations decreased seaward from the estuary, and had high values near Zhoushan Islands and in the northern ECS. It was indicated that the Changjiang dilute water (CDW) and the Jiangsu coastal currents (JCC), which were rich in particulate phosphorus were the major sources of PIP and POP. PIN and PON concentrations exhibited decreasing trend from the middle shelf toward land and offshore, suggesting the dilution effect of N-depleted riverine particles on particulate nitrogen in coastal waters. The highest concentrations of PIN and PON were observed in the coast of Zhejiang and in the northern ECS, which were two productive areas in the ECS. PON and PIN were primarily of marine source and POP was also influenced by phytoplankton productivity. The concentrations, compositions and distribution of particulate nutrients varied between spring and autumn, in response to the seasonal variations of phytoplankton productivity and terrestrial input. Budget calculation demonstrated that the sediment flux of Changjiang accounted for 88% of total input flux in spring and summer, indicating that the Changjiang River was the major particle source in the ECS. Particulate P was mainly from phytoplankton and the input of the Changjiang River, while the major source of particulate N was phytoplankton. Phytoplankton production contributed 70% of TPP input flux and 95% of TPN input flux in spring and summer, while 64% of TPP input and 89% of TPN input in autumn and winter. It was shown that riverine particles were enriched in inorganic P, whereas marine particles had high organic P and N content, which suggested that the component characteristics of particles could be used to identify the particle sources.

The Whale Pump: Marine Mammals Enhance Primary Productivity in a Coastal Basin

It is well known that microbes, zooplankton, and fish are important sources of recycled nitrogen in coastal waters, yet marine mammals have largely been ignored or dismissed in this cycle. Using field measurements and population data, we find that marine mammals can enhance primary productivity in their feeding areas by concentrating nitrogen near the surface through the release of flocculent fecal plumes. Whales and seals may be responsible for replenishing 2.3×104 metric tons of N per year in the Gulf of Maine's euphotic zone, more than the input of all rivers combined. This upward “whale pump” played a much larger role before commercial harvest, when marine mammal recycling of nitrogen was likely more than three times atmospheric N input. Even with reduced populations, marine mammals provide an important ecosystem service by sustaining productivity in regions where they occur in high densities.

A submersible flow injection-based sensor for the determination of total oxidised nitrogen in coastal waters

The design and construction of a remotely deployed submersible sensor for the determination of total oxidised nitrogen (nitrate plus nitrite) in seawater is described. It was based on the flow injection principle with solid state spectrophotometric detection of the diazotisation product from the reaction of nitrite with N-(1-naphthyl)ethylenediamine dihydrochloride (N1NED) and sulphanilamide. Nitrate was pre-reduced in-line with a copperised cadmium powder column. The limit of detection (3 s) was 0.1 μM nitrate (1.4 μg l −1 N) and the linear range was 0.1–55 μM nitrate with a 20 mm path length flow cell and a 260 μl sample loop. The linear range was modified for different environmental conditions by changing the sample loop size and - or the flow cell path length. Results are presented for preliminary laboratory studies and field trials in the Tamar Estuary and for deployments in the North Sea. The sensor was successfully deployed on three separate occasions for complete tidal cycles (13 h) at a depth of 4 m from the bow of RRS Challenger. Field data are compared with results from a shipboard air segmented analyser and correlated with turbidity and salinity data.

Uptake and regeneration of inorganic nitrogen in coastal waters influenced by the Mississippi River spatial and seasonal variations

The Mississippi and Atchafalaya Rivers introduce large amounts of nutrients to surface waters of the northern Gulf of Mexico. This paper reports the most complete data to date on inorganic nitrogen uptake and regeneration in a broad range of coastal environments influenced by the river water, along with information on nutrient concentrations and including pico-, nano-, and microplankton species composition. Nitrate in surface waters is greatly reduced near the river plume, at salinities between 5 and 25 PSU, where the largest variance in uptake rates was observed, and was coincident with peaks in surface chlorophyll. Despite the depletion of nitrate, nitrogen limitation was a rare event during the study, because of relatively high ammonium concentrations (>1 μmol NH4+ I−1 and regeneration rates. Two contrasting situations characterize the seasonal nitrogen dynamics in surface shelf waters. High nitrate input during the spring caused a large bloom in which the cells were well adapted to use nitrate.The dominant phytoplankton species were chain forming diatoms, also reported in sediment-trap studies in the area. Ammonium regeneration only accounted for a small fraction of the nitrogen requirements during the bloom. In contrast, the low flow of river water during summer resulted in low nitrate concentrations in surface water. In this case phytoplankton productivity was highly reduced and may depend greatly on ‘in sita’ ammonium regeneration.

Isotopic tracers of nitrogen from atmospheric deposition to coastal waters

Nitrogen deposition to global oceans from the atmosphere can be about two times that of natural riverine input [see Duce et al. (1991) for recent comprehensive review]. Even accounting for the increased loading of riverine nitrogen by anthropogenic inputs, total atmospheric deposition (AD) is essentially equal to that of riverine sources. Among growth-limiting nutrients, nitrogen plays a key role in regulating primary and secondary productivity both on regional and global scales (e.g., Ryther and Dunstan, 1971; Nixon et al., 1986). As such, proper identification and characterization of nitrogen sources and their impacts on nutrient flux and trophic utilization is of prime concern in understanding biogeochemical responses in coastal ecosystems (Eppley and Peterson, 1979; Paerl, 1985; Legendre and Gosselin, 1989). AD represents a quantitatively-important, but poorly assessed, nitrogen source in these ecosystems (Paerl, 1985; Fisher et al., 1988; Prado-Fiedler, 1990; Loye-Pilot et al., 1990). Current estimates indicate that from 20% to as much as 50% of annual nitrogen loading is attributable to AD alone in geographically-diverse coastal regions, including those along the U.S. Eastern Seaboard (Fisher et al., 1988 ). Even among large bodies of water such as the Baltic and Mediterranean Seas, AD constitutes a highly-significant N source (PradoFiedler, 1990; Loye-Pilot et al., 1990). In North Carolina's adjacent coastal Atlantic waters, AD is a major source (35-80%) of new nitrogen. Assumptions for this type of calculation include the following: ( 1 ) advective input of N from Gulf Stream is very low; ( 2 ) no upwelling is occurring; and (3) N2 fixation accounts for no more than 10% of new N inputs. Here, AD has been shown to significantly stimulate primary production by as much as 50-200% at natural input levels (Paerl, 1985; Paerl et al., 1990). The need to have a more detailed understanding of the impacts of AD of nitrogen in coastal waters is pressing, because previouslypristine segments of the coastal oceans are now exhibiting both incipient and advanced stages of eutrophication. Nitrogen from AD may be a unique nutrient source in the coastal zone for two reasons. Firstly, direct surface water deposition, as wet and dryfall, frequently occurs downstream of oligoand mesohaline estuarine nutrient stripping regions that assimilate a majority ofterrigenous N inputs (Boynton et al., 1982; Sharp et al., 1984). In shallow coastal areas, such as those present along the mid-Atlantic states, dilution of AD is minimized, which amplifies its importance as a new nitrogen source. Secondly, AD is highly dynamic in terms of the magnitudes of dissolved inorganic nitrogen (DIN) and dissolved organic nitro-