Nutrient exchange across the sediment-water interface in the Potomac River estuary     

Edward Callender  Douglas E. Hammond 《Estuarine, Coastal and Shelf Science》1982,15(4):395-413

The flux of ammonia, phosphate, silica and radon-222 from Potomac tidal river and estuary sediments is controlled by processes occurring at the sediment-water interface and within surficial sediment. Calculated diffusive fluxes range between 0·6 and 6·5 mmol m^?2 day^?1 for ammonia, 0·020 and 0·30 mmol m^?2 day^?1 for phosphate, and 1·3 and 3·8 mmol m^?2 day^?1 for silica. Measured in situ fluxes range between 1 and 21 mmol m^?2 day^?1 for ammonia, 0·1 and 2·0 mmol m^?2 day^?1 for phosphate, and 2 and 19 mmol m^?2 day^?1 for silica. The ratio of in situ fluxes to diffusive fluxes (flux enhancement) varied between 1·6 and 5·2 in the tidal river, between 2·0 and 20 in the transition zone, and from 1·3 to 5·1 in the lower estuary. The large flux enhancements from transition zone sediments are attributed to macrofaunal irrigation. Nutrient flux enhancements are correlated with radon flux enhancements, suggesting that fluxes may originate from a common region and that nutrients are regenerated within the upper 10–20 cm of the sediment column.The low fluxes of phosphate from tidal viver sediments reflect the control benthic sediment exerts on phosphorus through sorption by sedimentary iron oxyhydroxides. In the tidal river, benthic fluxes of ammonia and phosphate equal one-half and one-third of the nutrient input of the Blue Plains sewage treatment plant. In the tidal Potomac River, benthic sediment regeneration supplies a significant fraction of the nutrients utilized by primary producers in the water column during the summer months.  相似文献   

Benthic denitrification and nitrogen cycling at the slope and rise of the N.W. European Continental Margin (Goban Spur)     

W. Balzer  W. Helder  E. Epping  L. Lohse  S. Otto 《Progress in Oceanography》1998,42(1-4)

The rate of benthic denitrification in slope and rise sediments of a transect across the N.W. European Continental Margin (Goban Spur) was evaluated from 31 pore water nitrate profiles obtained during six cruises between May and October. All profiles had well separated zones of nitrification and denitrification. High near-surface nitrate concentrations prevented the influx of nitrate from the bottom water. The denitrification rates obtained from steady-state-modelling ranged from 0.13 to 2.56 μmol N cm⁻² y⁻¹ and showed an exponential increase both with decreasing water depth and with increasing rate of organic carbon degradation. Denitrification rates in a nearby canyon, which did not follow these relationships, were estimated to be much higher as a result of erosion and redistribution of organic matter. Denitrification at the Goban Spur slope and rise is much lower than previously reported for similar environments in the Pacific resulting predominantly from the different oxygen and nitrate concentrations in the bottom water. A weighted average for the whole slope and rise sediment system shows that 17% of the particulate organic nitrogen input (8.93 μmol N cm⁻² y⁻¹) is denitrified and only 1% is buried, the rest being released as nitrate. Although being ten times higher compared with basin sediments, denitrification on the slope and rise is several times lower than on the adjacent shelf.  相似文献   

Potential rates and environmental controls of denitrification and nitrous oxide production in a temperate urbanized estuary     

《Marine environmental research》2011,71(5):336-342

Denitrification may play a major role in inorganic nitrogen removal from estuarine ecosystems, particularly in those subjected to increased nitrate and organic matter loads. The Douro estuary (NW Portugal) suffers from both problems: freshwater input of nitrate and organic load from untreated wastewater discharges. To assess how these factors might control sediment denitrification, a 12-month survey was designed. Denitrification potential and nitrous oxide (N₂O) production were measured at different locations using the slurry acetylene blockage technique. Denitrification rate ranged from 0.4 to 38 nmol N g⁻¹ h⁻¹, increasing towards the river mouth following an urban pollution gradient. N₂O production, a powerful greenhouse gas implicated on the destruction of the ozone layer, was significantly related with sediment organic matter and accounted for 0.5–47% of the N gases produced. Additional enrichment experiments were consistent with the results found in the environment, showing that sediments from the upper less urban stretch of the estuary, mostly sandy, respond positively to carbon and, inversely, in organic rich sediments from the lower estuary, the denitrification potential was limited by nitrate availability. The obtained results confirmed denitrification as an important process for the removal of nitrate in estuaries. The presence of wastewater discharges appears to stimulate nitrogen removal but also the production of N₂O, a powerful greenhouse gas, exacerbating the N₂O:N₂ ratio and thus should be controlled.  相似文献   

Enteromorpha and the cycling of nitrogen in a small estuary     

N.J.P. Owens  W.D.P. Stewart 《Estuarine, Coastal and Shelf Science》1983,17(3):287-296

The nitrogen relations of Enteromorpha spp. growing on intertidal mud flats have been examined over a twelve-month period. Nitrogen assimilation rates using ¹⁵N have been used to calculate the production of the alga and were between 0·046 and 0·217 mg $\text{NH}{}_4{}^{\mathrm{+}}\text{N}$ (g dry wt alga)^?1 h^?1 A considerable quantity of the alga was buried beneath the sediment over the growth season and was calculated to be equivalent to an input of up to 9·52 g N m^?2 per month and 32 g N m^?2 over one complete growth season. Based on carbon, this latter value represented an input of approximately 320 g C m^?2 annually. Low rates of nitrogenase activity (acetylene reduction) were found to be associated with the Enteromorpha. The organisms responsible for the nitrogenase activity were probably heterotrophic bacteria but they did not contribute significant quantities of nitrogen to the alga.  相似文献   

Dynamic patterns of dissolved nitrogen in the Southern Bight of the North Sea     

Willy Baeyens  Jean-Paul Mommaerts  Leo Goeyens  Frank Dehairs  Hugues Dedeurwaerder  Ghislain Decadt 《Estuarine, Coastal and Shelf Science》1984,18(5):499-510

Spatial and temporal variations of dissolved inorganic nitrogen (DIN) have been assessed in onshore and offshore areas of the Southern Bight on the basis of several years' measurements. They indicate that both the residual flow lines and DIN isoconcentration lines run parallel with the coast except in the vicinity of important freshwater discharge points such as the Scheldt estuary. Evidence was found that the seasonal DIN oscillations are not created through fluctuations in input conditions at the lateral boundaries, despite considerable fluctuations in these inputs which include the English Channel (from 500 tons(t) N day^?1 in June up to approximately 2000 t N day^?1 in February) and also rivers such as the Scheldt estuary (up to 50 t N day^?1 in January but less than 5 t N day^?1 in June–July). In both the onshore and offshore areas the sum of daylight phytoplanktonic nitrogen intake and sediment release of nitrogen corresponds to the observed DIN variations during most of the year. Pelagic N-mineralization from natural or grazing mortality of phytoplankton (220 mg N m^?2 day^?1 onshore at its maximum) can account for the differences (200 mg N m^?2 day^?1 onshore at its maximum), especially at the end of the phytoplankton spring bloom. Although the causes of DIN oscillations onshore and offshore are the same, the results differ because offshore (1) the vegetative season lasts longer, and (2) DIN is exhausted at the end of the phytoplankton spring bloom.  相似文献   

Benthic Denitrification in the Gulf of Bothnia   总被引：1，自引：0，他引：1  

A. Stockenberg  R.W. Johnstone 《Estuarine, Coastal and Shelf Science》1997,45(6):835-843

Denitrification was measured over an 8-month period in the Bothnian Bay and the Bothnian Sea, the two northernmost basins of the Baltic Sea. The recorded rates varied between 0 and 0·94 mmol N m⁻²day⁻¹. In the Bothnian Sea, a seasonal pattern could be discerned with high rates in spring, no rate in summer and a moderate rate in winter. In the Bothnian Bay, no such seasonality was observed. It is suggested that denitrification in the Gulf of Bothnia is regulated by sediment nitrification. Calculation of annual mean rates of denitrification gave that the amount of nitrogen consumed by denitrification corresponded to 1·45×10⁴tons N year⁻¹for the Bothnian Bay and 3·45×10⁴tons N year⁻¹for the Bothnian Sea. A comparison with total N input (river runoff, point sources and atmospheric deposition) to the two basins showed that the proportion of N removed through denitrification amounted to 23% for the Bothnian Bay and 31% for the Bothnian Sea.  相似文献   

Compositions and transport of lipid biomarkers through the water column and surficial sediments of the equatorial Pacific Ocean   总被引：2，自引：0，他引：2  

Stuart G. Wakeham  John I. Hedges  Cindy Lee  Michael L. Peterson  Peter J. Hernes 《Deep Sea Research Part II: Topical Studies in Oceanography》1997,44(9-10)

A systematic investigation of fluxes and compositions of lipids through the water column and into sediments was conducted along the U.S. JGOFS EgPac transect from l2°N to l5°S at 140°W. Fluxes of lipids out of the euphotic zone varied spatially and temporally, ranging from ≈0.20 – 0.6 mmol lipid-C m⁻² day⁻¹. Lipid fluxes were greatly attenuated with increasing water column depth, dropping to 0.002-0.06 mmol lipid-C m⁻² day⁻¹ in deep-water sediment traps. Sediment accumulation rates for lipids were ≈ 0.0002 – 0.00003 mmol lipid-C m⁻² day⁻¹. Lipids comprised ≈ 11–23% of C_org in net-plankton, 10–30% in particles exiting the euphotic zone, 2–4% particles in the deep EgPac, and 0.1-1 % in sediments. Lipids were, in general, selectively lost due to their greater reactivity relative to bulk organic matter toward biogeochemical degradation in the water column and sediment. Qualitative changes in lipid compositions through the water column and into sediments are consistent with the reactive nature of lipids. Fatty acids were the most labile compounds, with polyunsaturated fatty acids (PUFAs) being quickly lost from particles. Branchedchain C₁₅ and C₁₇ fatty acids increased in relative abundance as particulate matter sank and was incorporated into the sediment, indicating inputs of organic matter from bacteria. Long-chain C₃₉ alkenones of marine origin and long-chain C₂₀-C₃₀ fatty acids, alcohols and hydrocarbons derived from land plants were selectively preserved in sediments. Compositional changes over time and space demonstrate the dynamic range of reactivities among individual biomarker compounds, and hence of organic matter as a whole. A thorough understanding of biogeochemical reprocessing of organic matter in the oceanic water column and sediments is, thus, essential for using the sediment record for reconstructing past oceanic environments.  相似文献   

Particulate organic matter in the coastal and estuarine waters of Goa and its relationship with phytoplankton production     

X.N. Verlencar  S.Z. Qasim 《Estuarine, Coastal and Shelf Science》1985,21(2):235-243

In the coastal and estuarine waters of Goa, particulate organic carbon (POC) varied from 0.52 to 2.51 mg l^?1 and from 0.28 to 5.24 mg l^?1 and particulate phosphorus (PP) varied from 0.71 to 5.18 μg l^?1 and from 0.78 to 20.34 μg l^?1, respectively. The mean values of chlorophyll and primary productivity were 1.94 mg m^?3 and 938.1 mg C m^?2 day^?1 in the coastal waters and 4.3 mg m^?3 and 636.5 mg C m^?1 day^?1 in the estuarine waters, respectively.$\text{POC}\text{chl}$ ratios were low in June and October even when POC values were quite high. The POC in surface waters was linearly correlated with the chlorophyll content. Also PP increased when chlorophyll and primary productivity remained high. The results suggest that the phytoplankton was sharply increasing and contributed to POC and PP content. The percentage of detritus calculated from the intercept values of chlorophyll on POC varied from 46 to 76% depending on season. Results indicate that the major portion of POC and PP during postmonsoon (October–January) is derived from phytoplankton production while the allochthonous matter predominate during monsoon (June–September).  相似文献   

Role of Zooplankton in the Vertical Mass Flux in the Kara and Laptev Seas in Fall     

A. V. Drits  M. D. Kravchishina  A. F. Pasternak  A. N. Novigatsky  O. M. Dara  M. V. Flint 《Oceanology》2017,57(6):841-854

The role of zooplankton in the vertical mass flux in the Kara and Laptev seas was studied during cruise 63 of the R/V Akademik Mstislav Keldysh in August–October 2015. Mass fluxes were estimated using sediment trap samples. The maximum values of the total vertical flux (19600 mg m^?2 day^?1) and particulate organic carbon (POC) flux (464 mg C m^?2 day^?1) were measured close to the Lena River Delta in the Laptev Sea. In the Kara Sea, the total flux (80–2700 mg m^?2 day^?1) and the POC flux (17–130 mg C m^?2 day^?1) were substantially higher than the estimates published earlier. The fecal pellet flux varied from 2 to 92 mg C m^?2 day^?1 and made up 4–190% of the total organic carbon flux. The mineral composition of fecal pellets largely mirrored that of suspended particulate matter. Clay minerals in the fecal pellets were more abundant than in particulate matter in the areas with noticeable freshwater impact. The flux of zooplankton carcasses varied from 0.1 to 66.4 mg C m^?2 day^?1 and made up 0.2–72% of total POC flux. The results are discussed in relation to the abundance and composition of zooplankton, the concentration and composition of suspended particulate matter, hydrophysical conditions, and methods of sample preparation for analysis.  相似文献   

Rapid sediment accumulation and microbial mineralization in forests of the mangrove Kandelia candel in the Jiulongjiang Estuary, China   总被引：2，自引：0，他引：2  

D.M. Alongi  J. Pfitzner  L.A. Trott  F. Tirendi  P. Dixon  D.W. Klumpp 《Estuarine, Coastal and Shelf Science》2005,63(4):605-618

Rates of sediment accumulation and microbial mineralization were examined at three Kandelia candel forests spanning the intertidal zone along the south coastline of the heavily urbanized Jiulongljiang Estuary, Fujian Province, China. Mass sediment accumulation rates were rapid (range: 10–62 kg m⁻² y⁻¹) but decreased from the low- to the high-intertidal zone. High levels of radionuclides suggest that these sediments originate from erosion of agricultural soils within the catchment. Mineralization of sediment carbon and nitrogen was correspondingly rapid, with total rate of mineralization ranging from 135 to 191 mol C m⁻² y⁻¹ and 9 to 11 mol N m⁻² y⁻¹; rates were faster in summer than in autumn/winter. Rates of mineralization efficiency (70–93% for C; 69–92% for N) increased, as burial efficiency (7–30% for C; 8–31% for N) decreased, from the low-to the high-intertidal mangroves. Sulphate reduction was the dominant metabolic pathway to a depth of 1 m, with rates (19–281 mmol S m⁻² d⁻¹) exceeding those measured in other intertidal deposits. There is some evidence that Fe and Mn reduction-oxidation cycles are coupled to the activities of live roots within the 0–40 cm depth horizon. Oxic respiration accounted for 5–12% of total carbon mineralization. Methane flux was slow and highly variable when detectable (range: 5–66 μmol CH₄ m⁻² d⁻¹). Nitrous oxide flux was also highly variable, but within the range (1.6–106.5 μmol N₂O m⁻² d⁻¹) measured in other intertidal sediments. Rates of denitrification were rapid, ranging from 1106 to 3780 μmol N₂ m⁻² d⁻¹, and equating to 11–20% of total sediment nitrogen inputs. Denitrification was supported by rapid NH₄ release within surface deposits (range: 3.6–6.1 mmol m⁻² d⁻¹). Our results support the notion that mangrove forests are net accumulation sites for sediment and associated elements within estuaries, especially Kandelia candel forests receiving significant inputs as a direct result of intense human activity along the south China coast.  相似文献   

Benthic fluxes of nitrogen in the tidal reaches of a turbid, high-nitrate sub-tropical river     

Perran L. M. Cook  Bradley D. Eyre  Rhys Leeming  Edward C. V. Butler   《Estuarine, Coastal and Shelf Science》2004,59(4):675-685

Benthic fluxes of dissolved inorganic nitrogen (NO₃⁻ and NH₄⁺), dissolved organic nitrogen (DON), N₂ (denitrification), O₂ and TCO₂ were measured in the tidal reaches of the Bremer River, south east Queensland, Australia. Measurements were made at three sites during summer and winter. Fluxes of NO₃⁻ were generally directed into the sediments at rates of up to −225 μmol N m⁻² h⁻¹. NH₄⁺ was mostly taken up by the sediments at rates of up to −52 μmol N m⁻² h⁻¹, its ultimate fate probably being denitrification. DON fluxes were not significant during winter. During summer, fluxes of DON were observed both into (−105 μmol m⁻² h⁻¹) and out of (39 μmol m⁻² h⁻¹) the sediments. Average N₂ fluxes at all sampling sites were similar during summer (162 μmol N m⁻² h⁻¹) and winter (153 μmol N m⁻² h⁻¹). Denitrification was fed both by nitrification within the sediment and NO₃⁻ from the water column. Sediment respiration rates played an important role in the dynamics of nitrification and denitrification. NO₃⁻ fluxes were significantly related to TCO₂ fluxes (p<0.01), with a release of NO₃⁻ from the sediment only occurring at respiration rates below 1000 μmol C m⁻² h⁻¹. Rates of denitrification increased with respiration up to TCO₂ fluxes of 1000 μmol C m⁻² h⁻¹. At sediment respiration rates above 1000 μmol C m⁻² h⁻¹, denitrification rates increased less rapidly with respiration in winter and declined during summer. On a monthly basis denitrification removed about 9% of the total nitrogen and 16% of NO₃⁻ entering the Bremer River system from known point sources. This is a similar magnitude to that estimated in other tidal river systems and estuaries receiving similar nitrogen loads. During flood events the amount of NO₃⁻ denitrified dropped to about 6% of the total river NO₃⁻ load.  相似文献   

Denitrification in coastal Louisiana: A spatial assessment and research needs     

Victor H. Rivera-Monroy  Peter Lenaker  Robert R. Twilley  Ronald D. Delaune  Charles W. Lindau  William Nuttle  Emad Habib  Robinson W. Fulweiler  Edward Castañeda-Moya 《Journal of Sea Research》2010,63(3-4):157-172

By transforming fixed nitrogen (N) into nitrogen gas, the biochemical processes that support denitrification provide a function critical to maintaining the integrity of ecosystems subjected to increased loading of N from anthropogenic sources. The Louisiana coastal region receives high nitrate (NO₃^?) concentrations (> 100 µM) from the Mississippi–Ohio–Missouri River Basin and is also an area undergoing high rates of wetland loss. Ongoing and anticipated changes in the Louisiana coastal region promise to alter biogeochemical cycles including the net rate of denitrification by ecosystems. Projecting what these changes could mean for coastal water quality and natural resources requires an understanding of the magnitude and patterns of variation in denitrification rates and their connection to estuarine water quality at large temporal and spatial scales under current conditions. We compile and review denitrification rates reported in 32 studies conducted in a variety of habitats across coastal Louisiana during the period 1981– 2008. The acetylene inhibition and ¹⁵N flux were the preferred techniques (95%); most of the studies used sediment slurries rather than intact sediment cores. There are no estimates of denitrification rates using the N₂/Ar ratio and isotope pairing techniques, which address some of the problems and limitations of the acetylene inhibition and ¹⁵N flux techniques. These studies have shown that sediments from estuaries, lakes, marshes, forested wetlands, and the coastal shelf region are capable of high potential denitrification rates when exposed to high NO₃^? concentrations (> 100 µM). Maximum potential denitrification rates in experimental and natural settings can reach values > 2500 µmol m² h^? 1. The lack of contemporary studies to understand the interactions among critical nitrogen transformations (e.g., organic matter mineralization, immobilization, aquatic plant assimilation, nitrification, nitrogen fixation, dissimilatory nitrate reduction to ammonium (DNRA) and anaerobic ammonium oxidation (annamox) limits our understanding of nitrogen cycling in coastal Louisiana, particularly the role of respiratory and chemolithoautotrophic denitrification in areas undergoing wetland restoration.  相似文献   

Natural abundances of 15N as a source indicator for near-shore marine sedimentary and dissolved nitrogen   总被引：1，自引：0，他引：1  

Robert E. Sweeney  I.R. Kaplan 《Marine Chemistry》1980,9(2):81-94

Because organic matter originating in the euphotic zone of the ocean may have a distinctive nitrogen isotope composition (¹⁵N/¹⁴N), as compared to organic matter originating in terrestrial soils, it may be used to evaluate the relative nitrogen contribution to marine and estuarine sediment. The nitrogen isotope ratios of 42 sediment samples of total nitrogen and 38 dissolved pore-water ammonium samples from Santa Barbara Basin sediment cores were measured. The range of δ¹⁵N values for total nitrogen was $\text{+2.89 – +9.4‰}$ with a mean of $\text{+6.8‰}$ and for pore water ammonium, $\text{+8.2 – +12.4‰}$ with a mean of 10.2‰.The results suggest that the dissolved ammonium in the pore water is produced from bacterial degradation of marine organic matter. The range of δ¹⁵N values for total nitrogen in the sediment is interpreted as resulting from an admixture of nitrogen derived from marine ($\text{+10‰}$) and terrestrial (+2‰ marines. The marine component of this mixture, composed principally of calcium carbonate with smaller amounts of opal and organic matter, contains ～ 1.0% nitrogen. The terrestrial component, which comprises over 80% of the sediment, contains ～ 0.1% organically bound nitrogen and accounts for > 25% of the total nitrogen in Santa Barbara Basin sediment.  相似文献   

Methane fluxes in the southeastern Baltic Sea   总被引：2，自引：2，他引：0  

Marina Ulyanova  Vadim Sivkov  Timur Kanapatskij  Pavel Sigalevich  Nikolay Pimenov 《Geo-Marine Letters》2012,32(5-6):535-544

New data from surveys of gas-bearing mud areas in the Gdansk Deep (southeastern Baltic Sea) were collected during four research cruises in 2009–2011. These revealed the presence of seven large pockmarks apart from the three already known, and enabled significant improvement of the existing digital map of gassy mud distribution. Based on geochemical sediment analyses, calculated diffusive methane fluxes from the upper (0–5?cm) seabed layer into near-bottom waters were highest—3.3?mmol/(m²?day)—in pockmark mud, contrasting strongly with the minimum value of 0.004?mmol/(m²?day) observed in typical, background mud. However, fluxes of less than 0.1?mmol/(m²?day) were observed in all sediment types, including pockmarks. In a newer attempt to roughly estimate budgets at a more regional scale, diffusive methane venting amounts to 280?×?10⁶?mmol/day for southeastern Baltic Sea muddy sediments. Elongated pockforms in the southern Gotland Deep, known since the end of the 1980s as pockmarks, had methane concentrations that were similar to those of gassy mud from the Gdansk Basin, and there was no geo-acoustic evidence of considerably increased gas levels.  相似文献   

Manganese and Iron Oxidation During Benthic Oxygenic Photosynthesis     

E.H.G. Epping  V. Schoemann  H. de Heij 《Estuarine, Coastal and Shelf Science》1998,47(6):753-767

The effect of benthic oxygenic photosynthesis on sediment-water fluxes of manganese and iron was studied for an intertidal sediment. Undisturbed sediments were incubated at an incident surface irradiance of 250 μE m⁻² s⁻¹at 26 °C. Oxygenic photosynthesis was selectively inhibited by adding [3-(3,4-dichloro)-1,1-dimethyl-urea] (DCMU). Benthic fluxes were determined experimentally from the change in manganese and iron concentrations in the overlying water, and were predicted from the pore water concentration gradients at the sediment-water interface assuming molecular diffusion as the transport mechanism. The experimental fluxes of manganese and iron in DCMU-treated cores amounted to −0·84 and −0·59 mmol m⁻²day⁻¹, respectively, and were directed from the sediment towards the overlying water. In the control cores, showing high rates of benthic oxygenic photosynthesis, the fluxes of manganese and iron were directed towards the sediment, 0·06 and 0·01 mmol m⁻²day⁻¹, respectively. Mass balances for the 0·1–0·14 cm thick oxic zone, calculated from the experimental fluxes and the predicted fluxes, suggest a minimum areal reoxidation of 0·6 mmol m⁻²day⁻¹for manganese and of 0·48 mmol m⁻²day⁻¹for iron in cores showing benthic photosynthesis. The estimated turnover times for dissolved Mn²⁺and dissolved Fe²⁺in the oxic surface layer during benthic photosynthesis were 0·8 and 0·25 h, respectively. Sediment oxygen microprofiles and the sediment pH profiles suggest that chemical precipitation and reoxidation dominates the retention of manganese and iron during benthic oxygenic photosynthesis in shallow intertidal sediments.  相似文献   

Chemical determination of particulate nitrogen in San Francisco Bay. Nitrogen: chlorophyll a ratios in plankton     

S.W. Hager  D.D. Harmon  A.E. Alpine 《Estuarine, Coastal and Shelf Science》1984,19(2):193-204

Particulate nitrogen (PN) and chlorophyll a (Chla) were measured in the northern reach of San Francisco Bay throughout 1980. The PN values were calculated as the differences between unfiltered and filtered (0·4 μm) samples analyzed using the UV-catalyzed peroxide digestion method. The Chla values were measured spectrophotometrically, with corrections made for phaeopigments. The plot of all $\text{PN}\text{Chl}\text{a}$ data was found to be non-linear, and the concentration of suspended particulate matter (SPM) was found to be the best selector for linear subsets of the data. The best-fit slopes of $\text{PN}\text{Chl}\text{a}$ plots, as determined by linear regression (model II), were interpreted to be the N: Chla ratios of phytoplankton. The Y-intercepts of the regression lines were considered to represent easily-oxidizable detrital nitrogen (EDN). In clear water ( < 10 mg l^?1 SPM), the N: Chla ratio was 1·07 μg-at N per μg Chla. It decreased to 0·60 in the 10–18 mg l^?1 range and averaged 0·31 in the remaining four ranges (18–35, 35–65, 65–155, and 155–470 mg l^?1). The EDN values were less than 1 μg-at N l^?1 in the clear water and increased monotonically to almost 12 μg-at N l^?1 in the highest SPM range. The N: Chla ratios for the four highest SPM ranges agree well with data for phytoplankton in light-limited cultures. In these ranges, phytoplankton-N averaged only 20% of the PN, while EDN averaged 39% and refractory-N 41%.  相似文献   

Benthic fluxes in a tidal salt marsh creek affected by fish farm activities: Río San Pedro (Bay of Cádiz,SW Spain)     

S. Ferrón  T. Ortega  J.M. Forja 《Marine Chemistry》2009,113(1-2):50-62

Benthic fluxes of dissolved inorganic carbon, total alkalinity, oxygen, nutrients, nitrous oxide and methane were measured in situ at three sites of Río San Pedro salt marsh tidal creek (Bay of Cádiz, SW Spain) during three seasons. This system is affected by the discharges of organic carbon and nutrients from the surrounding aquaculture installations. Sediment oxygen uptake rates and inorganic carbon fluxes ranged respectively from 16 to 79 mmol O₂ m^? 2 d^? 1 and from 48 to 146 mmol C m^? 2 d^? 1. Benthic alkalinity fluxes were corrected for the influence of NH₄⁺ and NO₃^? + NO₂^? fluxes, and the upper and lower limits for carbon oxidation rates were inferred by considering two possible scenarios: maximum and minimum contribution of CaCO₃ dissolution to corrected alkalinity fluxes. Average C_ox rates were in all cases within ± 25% of the upper and lower limits and ranged from 40 to 122 mmol C m^? 2 d^? 1. Whereas carbon mineralization did not show significant differences among the sites, C_ox rates varied seasonally and were correlated with temperature (r² = 0.72). During winter and spring denitrification was estimated to account for an average loss of 46% and 75%, respectively, of the potentially recyclable N, whereas during the summer no net removal was observed. A possible shift from denitrification to dissimilatory nitrate reduction to ammonium (DNRA) during this period is argued. Dissolved CH₄ and N₂O fluxes ranged from 5.7 to 47 μmol CH₄ m^? 2 d^? 1 and 4.3 to 49 μmol N–N₂O m^? 2 d^? 1, respectively, and represented in all cases a small fraction of total inorganic C and N flux. Overall, about 60% of the total particulate organic matter that is discharged into the creek by the main fish farm facility is estimated to degrade in the sediments, resulting in a significant input of nutrients to the system.  相似文献   

Recovery of added ¹⁵N-labelled ammonium-N from Louisiana Gulf Coast estuarine sediment     

C.J. Smith  R.D. DeLaune 《Estuarine, Coastal and Shelf Science》1985,21(2):225-233

The loss of added ¹⁵N-labelled NH₄⁺ from bottom sediment was studied in situ in a shallow saline Louisiana Gulf Coast lake. ¹⁵N-labelled NH₄⁺ was uniformly mixed with sediment at the level of 35 μg N g^?1 dry sediment for 24 h before being weighed into polyethylene containers. The ¹⁵N-enriched sediment was incubated on the lake bottom for periods up to 337 days. At intervals, triplicate samples were taken and analyzed for inorganic NH₄⁺, organic N, and denitrification rates. Concentrations of NH₄⁺ in the ¹⁵NH₄⁺ enriched sediment samples were at levels similar to those measured in vertical intact cores removed from the lake at each sampling date. The initial and final isotopic compositions of NH₄⁺ in the incubated sediments were 44.26 and 0.521 atom % ¹⁵N excess, respectively. ¹⁵N enrichment in the organic N fraction increased rapidly during the first 15 days of incubation and then increased slowly from 15 to 123 days. Denitrification, estimated by the acetylene blockage technique, ranged from 0.994 to 0.079 ng N g^?1 dry sediment per hour. The mean denitrification rate for the 337-day period was 0.28 ng N g^?1 h^?1. There was no statistical difference in the recovery of ¹⁵N between 15 and 337 days of incubation. When the added ¹⁵N became incorporated into the organic N pool, little or no further ¹⁵N was lost.  相似文献   

Accumulation of total CO₂ during stagnation in the Baltic Sea deep water and its relationship to nutrient and oxygen concentrations     

B. Schneider  G. Nausch  H. Kubsch  I. Petersohn 《Marine Chemistry》2002,77(4)

Accumulation of total CO₂ (C_T) was investigated in the sub-halocline deep water of the Gotland Sea (Baltic Sea) during a period of stagnation from 1995 to 1999. Depth profiles for C_T, nitrate, phosphate, and oxygen were measured during seven cruises in a grid consisting of 26 stations. The mean C_T increased by more than 60 μmol/kg from October 1995 to July 1999 corresponding to a mean accumulation rate of 1.1 mol/m² year. Taking into account vertical mixing, the vertical distribution of the C_T accumulation was used to determine mineralization rates at different depths. High rates immediately below the halocline indicated the existence of a fraction of organic matter, which is rapidly mineralized during sinking through the water column. A second fraction is more refractive and accumulates at the sediment surface in the deep center of the basin where it is slowly mineralized and partly buried. Phosphate release rates in anoxic waters and especially at the redoxcline were substantially higher than those estimated on the basis of the carbon mineralization and the Redfield C/P ratio. This is attributed to non-Redfield mineralization ratios and the dissolution of iron oxide/phosphate associates. The formation of nitrate by mineralization under oxic conditions was almost completely compensated by denitrification. Using the carbon mineralization rates and a C/N ratio of 8.4, a denitrification rate of 280 mmol/m² year was obtained, which approximately balances the input of nitrate/ammonia into the surface water. Relating the apparent oxygen utilization (AOU) to the C_T fraction that was generated by mineralization yielded a carbon mineralization/O₂ consumption ratio of 0.83.  相似文献   

Water filtration through reflective microtidal beaches and shallow sublittoral sands and its implications for an inshore ecosystem in Western Australia     

Anton McLachlan  Ian G. Eliot  Des J. Clarke 《Estuarine, Coastal and Shelf Science》1985,21(1):91-104

Volumes of seawater filtered through the intertidal zone were measured on three modally reflective microtidal beaches in Western Australia. The filtered volumes were large, 19 m³ m^?1 day^?1 and 73 m³ m^?1 day^?1 on two ‘clean’ beaches but only 0·4 m³ m^?1 per tidal cycle on a beach covered in kelp and seagrass wrack. The mean residence times of this water in the interstitial system and its percolation paths were both short, 1–7 h and 2–5 m respectively. Water input was greater across a beach cusp horn than across a cusp embayment. Most input occurred in the upper swash zone where the water table was less than 20 cm deep. Tidal variations in input volumes were evident even with tide ranges of only 20 cm. The inshore zone off these beaches filters on average 0·07 m³ m^?2 day^?1 at an average depth of 5·5 m under 0·4 m waves of 6·5 s duration. The importance of these procedures in the mineralization of organic materials and the regeneration of nutrients for an inshore ‘lagoon ecosystem’ is estimated and discused.  相似文献