Planktonic and whole system metabolism in a nutrient-rich estuary (the Scheldt estuary)     

Frédéric Gazeau  Jean-Pierre Gattuso  Jack J. Middelburg  Natacha Brion  Laure-Sophie Schiettecatte  Michel Frankignoulle  Alberto Vieira Borges 《Estuaries and Coasts》2005,28(6):868-883

Planktonic gross primary production (GPP), community respiration (CR), and nitrification (NIT) were measured monthly in the Scheldt estuary by the oxygen incubation method in 2003. No significant evolution of planktonic GPP was observed since the 1990s with high rates in the freshwater area (salinity 0; 97±65 mmol C m⁻² d⁻¹) decreasing seaward (22–37 mmol C m⁻² d⁻¹). A significant decrease of NIT was observed with regard to previous investigations although this process still represents up to 20% of total organic matter production in the inner estuary. Planktonic CR was highest in the inner estuary and seemed to be mainly controlled by external organic matter inputs. Planktonic net community production was negative most of the time in the estuary with values ranging from −300 to 165 mmol C m⁻² d⁻¹. Whole estuary net ecosystem production (NEP) was investigated on an annual scale using the results mentioned above and published benthic metabolic rates. A NEP of −39±8 mmol C m⁻² d⁻¹ was estimated, which confirms the strong heterotrophic status of this highly nutrified estuary. NEP rates were computed from June to December 2003 to compare with results derived from the Land-Ocean Interaction in the Coastal Zone budgeting procedure applied to dissolved inorganic phosphorus and carbon (DIP and DIC). DIP budgets failed to provide realistic estimates in the inner estuary where abiotic processes account for more than 50% of the nonconservative DIP flux. DIC budgets predicted a much lower NEP than in situ incubations (−109±31 versus −42±9 mmol C m⁻² d⁻¹) although, as each approach is associated with several critical assumptions, the source of this discrepancy remains unclear.  相似文献   

Benthic biogeochemistry beneath the Mississippi River plume     

John W. Morse  Gilbert T. Rowe 《Estuaries and Coasts》1999,22(2):206-214

Biogeochemical processes occurring near the sediment-water interface of shallow (≈20 m) water sediments lying beneath the Mississippi River plume on the Louisiana shelf were studied using benthic chambers and sediment cores. Three sites were chosen with distinctly different characteristics. One was overlain by oxic water where aerobic respiration dominated organic matter remineralization. The second site was overlain by oxic water but organic matter remineralization was dominated by sulfate reduction. The third site was overlain by hypoxic water and aerobic remineralization was of minor significance. Major differences were observed in the fluxes of CO₂(17–56 mmol m⁻² d⁻¹), O₂(2–56 mmol m⁻² d⁻¹) and nutrients (e.g., NH₄ ⁺, 2.6–4.2 mmol m⁻² d⁻¹) across the sediment-water interface, and the relative importance of different electron acceptors, even though the sites were in close proximity and at nearly the same water depth. Large variations in the efficiency of organic-C burial (3%–51%) were also calculated based on a simplified model of the relationships between the fraction of organic matter remineralized by sulfate reduction and the fraction of sulfide produced that is buried as pyrite. These observations demonstrate the high degree of spatial heterogeneity of benthic biogeochemistry in this important near-deltaic environment.  相似文献   

Sediment and Lower Water Column Oxygen Consumption in the Seasonally Hypoxic Region of the Louisiana Continental Shelf   总被引：1，自引：0，他引：1  

Michael C. Murrell  John C. Lehrter 《Estuaries and Coasts》2011,34(5):912-924

We report integrated measurements of sediment oxygen consumption (SOC) and bottom water plankton community respiration rates (WR) during eight cruises from 2003 to 2007 on the Louisiana continental shelf (LCS) where hypoxia develops annually. Averaged by cruise, SOC ranged from 3.9 to 25.8 mmol O₂ m⁻² day⁻¹, whereas WR ranged from 4.1 to 10.8 mmol O₂ m⁻³ day⁻¹. Total below-pycnocline respiration rates ranged from 46.4 to 104.5 mmol O₂ m⁻² day⁻¹. In general, below-pycnocline respiration showed low variability over a large geographic and temporal range, and exhibited no clear spatial or inter-annual patterns. SOC was strongly limited by dissolved oxygen (DO) in the overlying water; whereas, WR was insensitive to low DO, a relationship that may be useful for parameterizing future models. The component measures, WR and SOC, were similar to most prior measurements, both from the LCS and from other shallow estuarine and coastal environments. The contribution of SOC to total below-pycnocline respiration averaged 20 ± 4%, a finding that differs from several prior LCS studies, but one that was well supported from the broader estuarine and oceanic literature. The data reported here add substantially to those available for the LCS, thus helping to better understand oxygen dynamics on the LCS.  相似文献   

Nitrogen dynamics in nontidal littoral sediments: Role of microphytobenthos and denitrification     

Kristina Sundbäck  Alison Miles  Frank Linares 《Estuaries and Coasts》2006,29(6):1196-1211

Previous measurements from cool microtidal temperate areas suggest that microphytobenthic incorporation of nitrogen (N) exceeds N removal by denitrification in illuminated shallow-water sediments. The present study investigates if this is true also for fully nontidal sediments in the Baltic Sea., Sediment-water fluxes of inorganic (DIN) and, organic nitrogen (DON) and oxygen, as well as denitrification, were measured in early autumn and spring, in light and dark, at four sites representing different sediment types. All sediments were autotrophic during the daytime both in the autumn and spring. On a 24-h time scale, they were autotrophic in the spring and heterotrophic in early autumn. Sediments funcitoned as sources of DIN and DON during the autumn and sinks during the spring, with DON fluxes dominating or being as important as DIN fluxes. Microphytobenthos (MPB) activity controlled fluxes of both DIN and DON. Significant differences between sites were found, although sediment type (sand or silt) had no consistent effect on the magnitude of MPB production or nutrient fluxes. The clearest effect related to sediment type was found for denitrification, although only in the autumn, with higher rates in silty sediments. Estimated N assimilation by MPB, based on both net primary production (0.7–6.5 mmol N m⁻² d⁻¹) and on 80% of gross primary production (1.9–9.4 mmol N m⁻² d⁻¹) far exceeded measured rates of denitrification (0.01–0.16 mmol N m⁻² d⁻¹). A theoretical calculation showed that MPB may incorporate between 40% and 100% of the remineralized N, while denitrification removes, <5%. MPB assimilation of N appears to be a far more important N consuming process than denitrification in these nontidal, shallow-water sediments.  相似文献   

Primary production in Long Island sound     

Nicole L. Goebel  James N. Kremer  Christopher A. Edwards 《Estuaries and Coasts》2006,29(2):232-245

Daily and annual integrated rates of primary productivity and community respiration were calculated using physiological parameters measured in oxygen-based photosynthesis-irradiance (P-I) incubations at 8 stations throughout central and western Long Island Sound (cwLIS) during the summer and autumn of 2002 and 2003 and the late spring of 2003. Each calculation takes into account actual variations in incident irradiance over the day and underwater irradiance and standing stock with depth. Annual peak rates, ±95% confidence interval of propagated uncertainty in each measurement, of gross primary production (GPP, 1,730±610 mmol O₂ m⁻² d⁻¹), community respiration (R_c, 1,660±270 mmol O₂ m⁻² d⁻¹), and net community production (NCP, 1,160±1,100 mmol O₂ m⁻² d⁻¹) occurred during summer at the western end of the Sound. Lowest rates of GPP (4±11 mmol O₂ m⁻² d⁻¹), R_c (−50±300 mmol O₂ m⁻² d⁻¹), and NCP (−1,250±270 mmol O₂ m⁻² d⁻¹) occurred during late autumn-early winter at the outer sampled stations. These large ranges in rates of GPP, R_c, and NCP throughout the photic zone of cwLIS are attributed to seasonal and spatial variability. Algal respiration (R_a) was estimated to consume an average of 5% to 52% of GPP, using a literature-based ratio of R_a:R_c. From this range, we established that the estimated R_a accounts for approximately half of GPP, and was used to estimate daily net primary production (NPP), which ranged from 2 to 870 mmol O₂ m⁻² d⁻¹ throughout cwLIS during the study. Annual NPP averaged 40±8 mol O₂ m⁻² yr⁻¹ for all sampled stations, which more than doubled along the main axis of the Sound, from 32±14 mol O₂ m⁻² yr⁻¹ at an eastern station to 82±25 mol O₂ m⁻² yr⁻¹ at the western-most station. These spatial gradients in productivity parallel nitrogen loads along the main axis of the Sound. Daily integrals of productivity were used to test and formulate a simple, robust biomass-light model for the prediction of phytoplankton production in Long Island Sound, and the slope of the relationship was consistent with reports for other systems.  相似文献   

Sulfate reduction and porewater chemistry in a gulf coast<Emphasis Type="Italic">Juncus roemerianus</Emphasis> (Needlerush) marsh     

Glen?A.?Miley  Ronald?P.?KieneEmail author 《Estuaries and Coasts》2004,27(3):472-481

Sulfate reduction rates were measured over the course of a year in the sediments of aJuncus roemerianus marsh located in coastal Alabama. Sulfate reduction rates were typically highest in the surface 0–2 cm and at depths corresponding to peak belowground biomass of the plants. The highest volume-based sulfate reduction rate measured was 1,350 μmol liter-sediment⁻¹ d⁻¹ in September 1995. Areal sulfate reduction rates (integrated to 20 cm depth) were strongly correlated to sediment temperature and varied seasonally from 15.2 mmol SO ₄ ²⁻ m⁻² d⁻¹ in January 1995 to 117 mmol SO ₄ ²⁻ m⁻² d⁻¹ in late August 1995. Despite high sulfate reduction rates porewater dissolved sulfide concentrations were low (<73 μM), indicating rapid sulfide oxidation or precipitation. Sulfate depletion data indicated that net oxidation of sediment sulfides occurred in March through May, following a period of infrequent tidal flooding and during a period of high plant production. Porewater Fe(II) reached very high levels (maximum of 969 μM; mean for all dates was 160 μM), particularly during periods of high sulfate reduction. The annual sulfate reduction rate integrated over the upper 20 cm of sediment was 22.0 mol SO ₄ ²⁻ m⁻² yr⁻¹, which is among the highest rates measured in a wetland ecosystem. Based on literature values of net primary production inJ. roemerianus marshes, we estimate that an amount equivalent to 16% to 90% of the annual belowground production may be remineralized through sulfate reduction.  相似文献   

Benthic metabolism and nutrient cycling along an estuarine salinity gradient     

Charles S. Hopkinson  Anne E. Giblin  Jane Tucker  Robert H. Garritt 《Estuaries and Coasts》1999,22(4):863-881

Benthic metabolism and nutrient exchange across the sediment-water interface were examined over an annual cycle at four sites along a freshwater to marine transect in the Parker River-Plum Island Sound estuary in northeastern Massachusetts, U.S. Sediment organic carbon content was highest at the freshwater site (10.3%) and decreased along the salinity gradient to 0.2% in the sandy sediments at the marine end of the estuary. C:N ratios were highest in the mid estuary (23:1) and lowest near the sea (11:1). Chlorophyll a in the surface sediments was high along the entire length of the estuary (39–57 mg chlorophyll a m⁻²) but especially so in the sandy marine sediments (172 mg chlorophyll a m⁻²). Chlorophyll a to phaeophytin ratios suggested most chlorophyll is detrital, except at the sandy marine site. Porewater sulfide values varied seasonally and between sites, reflecting both changes in sulfate availability as overlying water salinity changed and sediment metabolism. Patterns of sediment redox potential followed those of sulfide. Porewater profiles of inorganic N and P reflected strong seasonal patterns in remineralization, accumulation, and release. Highest porewater NH₄ ⁺ values were found in upper and mid estuarine sediments, occasionally exceeding 1 mM N. Porewater nitrate was frequently absent, except in the sandy marine sediments where concentrations of 8 μM were often observed. Annual average respiration was lowest at the marine site (13 mmol O₂ m⁻² d⁻¹ and 21 mmol TCO₂ m⁻² d⁻¹) and highest in the mid estuary (130 mmol O₂ m⁻² d⁻¹ and 170 mmol TCO₂ m⁻² d⁻¹) where clam densities were also high. N₂O and CH₄ fluxes were low at all stations throughout the year: Over the course, of a year, sediments varied from being sources to sinks of dissolved organic C and N, with the overall spatial pattern related closely to sediment organic content. There was little correlation between PO₄ ³⁻ flux and metabolism, which we attribute to geochemical processes. At the two sites having the lowest salinities, PO₄ ³⁻ flux was directed into the sediments. On average, between 22% and 32% of total system metabolism was attributable to the benthos. The mid estuary site was an exception, as benthic metabolism accounted for 95% of the total, which is attributable to high densities of filter-feeding clams. Benthic remineralization supplied from less than 1% to over 190% of the N requirements and 0% to 21% of the P requirements of primary producers in this system. Estimates of denitrification calculated from stoichiometry of C and N fluxes ranged from 0% for the upper and mid estuary site to 35% for the freshwater site to 100% of sediment organic N remineralization at the marine site. We hypothesize that low values in the upper and mid estuary are attributable to enhanced NH₄ ⁺ fluxes during summer due to desorption of exchangeable ammonium from rising porewater salinity. NH₄ ⁺ desorption during summer may be a mechanism that maintains high rates of pelagic primary production at a time of low inorganic N inputs from the watershed.  相似文献   

Microelectrode Study of Oxygen Uptake and Organic Matter Decomposition in The Sediments of Xiamen Western Bay   总被引：2，自引：0，他引：2  

Kunming Xu  Liping Zhang  Wenbin Zou 《Estuaries and Coasts》2009,32(3):425-435

Sediment cores were sampled from Xiamen Western Bay at five sites during the summer and winter of 2006 and Hg–Au microelectrodes were used to make on board measurements of the concentration gradients of dissolved oxygen, Mn²⁺, and Fe²⁺ within the sediments. The O₂ concentrations decreased sharply from about 200 μmol L⁻¹ in the bottom seawater to zero within a depth of a few millimeters into the sediment. Dissolved Mn²⁺ was detected below the oxic zones with peak concentrations up to 600 μmol L⁻¹, whereas dissolved Fe²⁺ had peak concentrations up to 1,000 μmol L⁻¹ in deeper layers. The elemental contents of organic carbon and nitrogen within the sediments were analyzed and their C/N ratios were in the range of 9.0 to 10.1, indicative of heavy terrestrial origin. Sediments from two sites near municipal wastewater discharge outlets had higher organic contents than those from the other sites. These high organic contents corresponded to shallow O₂ penetration depths, high dissolved Mn²⁺ and Fe²⁺ concentrations, and negative redox potentials within the sediments. This indicated that the high organic matter content had promoted microbial respiration within the sediments. Overall, the organic content did not show any appreciable decrease with increasing sediment depths, so a quadratic polynomial function was used to fit the curve of O₂ profiles within the sediments. Based on the O₂ profiles, O₂ fluxes across the seawater and sediment interface were estimated to be in the range 6.07 to 14.9 mmol m⁻² day⁻¹, and organic carbon consumption rates within the surface sediments were estimated to be in the range 3.3 to 20.8 mgC cm⁻³ a⁻¹. The case demonstrated that biogeochemistry within the sediments of the bay was very sensitive to human activities such as sewage discharge.  相似文献   

Denitrification and the stoichiometry of nutrient regeneration in Waquoit Bay, Massachusetts     

Michael G. LaMontagne  Valeria Astorga  Anne E. Giblin  Ivan Valiela 《Estuaries and Coasts》2002,25(2):272-281

To determine the removal of regenerated nitrogen by estuarine sediments, we compared sediment N₂ fluxes to the stoichiometry of nutrient and O₂ fluxes in cores collected in the Childs River, Cape Cod, Massachusetts. The difference between the annual PO₄ ³⁻ (0.2 mol P m⁻² yr⁻¹) and NH₄ ⁺ (1.6 mol N m⁻² yr⁻¹) flux and the Redfield N∶P ratio of 16 suggested an annual deficit of 1.5 mol N m⁻² yr⁻¹. Denitrification predicted from O₂∶NH₄ ⁺ flux ratios and measured as N₂ flux suggested a nitrogen sink of roughly the same magnitude (1.4 mol N m⁻² yr⁻¹). Denitrification accounted for low N∶P ratios of benthic flux and removed 32–37% of nitrogen inputs entering the relatively highly nutrient loaded Childs River, despite a relatively brief residence time for freshwater in this system. Uptake of bottom water nitrate could only supply a fraction of the observed N₂ flux. Removal of regenerated nitrogen by denitrification in this system appears to vary seasonally. Denitrification efficiency was inversely correlated with oxygen and ammonium flux and was lowest in summer. We investigated the effect of organic matter on denitrification by simulating phytoplankton deposition to cores incubated in the lab and by deploying chambers on bare and macroaglae covered sediments in the field. Organic matter addition to sediments increased N₂ flux and did not alter denitrification efficiency. Increased N₂ flux co-varied with O₂ and NH₄ ⁺ fluxes. N₂ flux (261±60 μmol m⁻² h⁻¹) was lower in chambers deployed on macroalgal beds than deployed on bare sediments (458±70 μmol m⁻² h⁻¹), and O₂ uptake rate was higher in chambers deployed on macroalgal beds (14.6±2.2 mmol m⁻² h⁻¹) than on bare sediments (9.6±1.5 mmol m⁻² h⁻¹). Macroalgal cover, which can retain nitrogen in the system, is a link between nutrient loading and denitrification. Decreased denitrification due to increasing macroalgal cover could create a positive feedback because decreasing denitrification would increase nitrogen availability and could increase macroalgae cover.  相似文献   

Dissolution of Carbonate Sediments Under Rising <Emphasis Type="Italic">p</Emphasis>CO<Subscript>2</Subscript> and Ocean Acidification: Observations from Devil’s Hole,Bermuda     

Andreas J. Andersson  Nicholas R. Bates  Fred T. Mackenzie 《Aquatic Geochemistry》2007,13(3):237-264

Rising atmospheric pCO₂ and ocean acidification originating from human activities could result in increased dissolution of metastable carbonate minerals in shallow-water marine sediments. In the present study, in situ dissolution of carbonate sedimentary particles in Devil’s Hole, Bermuda, was observed during summer when thermally driven density stratification restricted mixing between the bottom water and the surface mixed layer and microbial decomposition of organic matter in the subthermocline layer produced pCO₂ levels similar to or higher than those levels anticipated by the end of the 21st century. Trends in both seawater chemistry and the composition of sediments in Devil’s Hole indicate that Mg-calcite minerals are subject to selective dissolution under conditions of elevated pCO₂. The derived rates of dissolution based on observed changes in excess alkalinity and estimates of vertical eddy diffusion ranged from 0.2 mmol to 0.8 mmol CaCO₃ m⁻² h⁻¹. On a yearly basis, this range corresponds to 175–701 g CaCO₃ m⁻² year⁻¹; the latter rate is close to 50% of the estimate of the current average global coral reef calcification rate of about 1,500 g CaCO₃ m⁻² year⁻¹. Considering a reduction in marine calcification of 40% by the year 2100, or 90% by 2300, as a result of surface ocean acidification, the combination of high rates of carbonate dissolution and reduced rates of calcification implies that coral reefs and other carbonate sediment environments within the 21st and following centuries could be subject to a net loss in carbonate material as a result of increasing pCO₂ arising from burning of fossil fuels.  相似文献   

Primary productivity in the German Bight (1994–1996)     

Hans J. Rick  Silke Rick  Urban Tillmann  Uwe Brockmann  Uwe Gärtner  Claus Dürselen  Jürgen Sündermann 《Estuaries and Coasts》2006,29(1):4-23

Within the KUSTOS program (Coastal Mass and Energy Fluxes-the Land-Sea Transition in the Southeastern North Sea) 28 to 36 German Bight stations were seasonally surveyed (summer 1994, spring 1995, winter 1995–1996) for light conditions, dissolved inorganic nutrient concentrations, chlorophylla (chla), and photosynthesis versus light intensity (P:E) parameters. Combining P:E curve characteristics with irradiance, attenuation, and chlorophyll data resulted in seasonal estimates of the spatial distribution of total primary production. These data were used for an annual estimate of the total primary production in the Bight. In winter 1996 the water throughout the German Bight was well mixed. Dissolved inorganic nutrient concentrations were relatively high (nitrogen [DIN], soluble reactive phosphorus [SRP], and silicate [Si]: 23, 1, and 10 μM, respectively). Chla levels generally were low (< 2 μg l⁻¹) with higher concentrations (4–16 μg l⁻¹) in North Frisian coastal waters. Phytoplankton was limited by light. Total primary production averaged 0.2 g C m⁻² d⁻¹. Two surveys in April and May 1995 captured the buildup of a strong seasonal thermo-cline accompained by the development of a typical spring diatom bloom. High nutrient levels in the mixed layer during the first survey (DIN, SRP, and Si: 46, 0.45, and 11 μM, respectively) decreased towards the second survey (DIN, SRP, and Si: 30.5, 0.12, and 1.5 μM, respectively) and average nutrient ratios shifted further towards highly imbalanced values (DIN:SRP: 136 in survey 1, 580 in survey 2; DIN:Si: 13.5 in survey 1, 96 in survey 2). Chla ranged from 2 to 16 μg l⁻¹ for the first survey and rose to 12–50 μg l⁻¹ in the second survey. Phytoplankton in nearshore areas continued to be light limited during the second survey, while data from the stratified regions in the open German Bight indicates SRP and Si limitation. Total primary production ranged from 4.0 to 6.3 g C m⁻² d⁻¹. During summer 1994 a strong thermal stratification was present in the German Bight proper and shallow coastal areas showed unusually warm (up to 22°C), mixed waters. Chla concentrations ranged from 2 to 18 μg l⁻¹. P:E characteristics were relatively high despite the low nutrient regime (DIN, SRP, and Si: 2, 0.2, and 1.5 μM, respectively), resulting in overall high total primary production values with an average of 7.7 g C m⁻² d⁻¹. Based on the seasonal primary production estimates of the described surveys a budget calculation yielded a total annual production of 430 g C m⁻² yr⁻¹ for the German Bight.  相似文献   

The Effects of Salinity on Nitrogen Losses from an Oligohaline Estuarine Sediment   总被引：4，自引：0，他引：4  

Anne E. Giblin  Nathaniel B. Weston  Gary T. Banta  Jane Tucker  Charles S. Hopkinson 《Estuaries and Coasts》2010,33(5):1054-1068

Benthic respiration, sediment–water nutrient fluxes, denitrification and dissimilatory nitrate reduction to ammonium (DNRA) were measured in the upper section of the Parker River Estuary from 1993 to 2006. This site experiences large changes in salinity over both short and long time scales. Sediment respiration ranged from 6 to 52 mmol m⁻² day⁻¹ and was largely controlled by temperature. Nutrient fluxes were dominated by ammonium fluxes, which ranged from a small uptake of −0.3 to an efflux of over 8.2 mmol N m⁻² day⁻¹. Ammonium fluxes were most highly correlated with salinity and laboratory experiments demonstrated that ammonium fluxes increased when salinity increased. The seasonal pattern of DNRA closely followed salinity. DNRA rates were extremely low in March, less than 0.1 mmol m⁻² day⁻¹, but increased to 2.0 mmol m⁻² day⁻¹ in August. In contrast, denitrification rates were inversely related to salinity, ranging from 1 mmol m⁻² day⁻¹ during the spring and fall to less than 0.2 mmol m⁻² day⁻¹ in late summer. Salinity appears to exert a major control on the nitrogen cycle at this site, and partially decouples sediment ammonium fluxes from organic matter decomposition.  相似文献   

The effects of multiple stressors on the balance between autotrophic and heterotrophic processes in an estuarine system     

Tracy?N.?WiegnerEmail author  Sybil?P.?Seitzinger  Denise?L.?Breitburg  James?G.?Sanders 《Estuaries and Coasts》2003,26(2):352-364

Responses of autotrophic and heterotrophic processes to nutrients and trace elements were examined in a series of experimental estuarine food webs of increasing trophic complexity using twenty 1-m³ mesocosms. Nutrients (nitrogen and phosphorus) and trace elements (a mix of arsenic, copper, cadmium) were added alone and in combination during four experimental runs spanning from spring 1997 to spring 1998. Diel changes in dissolved oxygen were used to examine whole system gross primary production (WS-GPP), respiration (WS-RESP), and net ecosystem metabolism (NEM). Nutrient and trace element additions had the greatest effect on WS-GPP, WS-RESP, and NEM; trophic complexity did not significantly affect any of these parameters (p>0.3). Effects of trophic complexity were detected in nutrient tanks where bivalves significantly (p=0.03) reduced WS-GPP. Nutrient additions significantly enhanced WS-GPP and to a lesser extent WS-RESP during most mesocosm runs. The system shifted from net heterotrophy (−17.2±1.8 mmol C m⁻³ d⁻¹) in the controls to net autotrophy (29.1±7.6 mmol C m⁻³ d⁻¹) in the nutrient tanks. The addition of trace elements alone did not affect WS-GPP and WS-RESP to the same extent as nutrients, and their effects were more variable. Additions of trace elements alone consistently made the system more net heterotrophic (−24.9±1.4 mmol C m⁻³ d⁻¹) than the controls. When trace elements were added in combination with nutrients, the nutrient-enriched system became less autotrophic (1.6±3.1 mmol C m⁻³ d⁻¹). The effects of trace elements on NEM occurred primarily through reductions in WS-GPP rather than increases in WS-RESP. Our results suggest that autotrophic and heterotrophic processes respond differently to these stressors.  相似文献   

Benthic Phosphorus Dynamics in the Gulf of Finland, Baltic Sea     

Lena Viktorsson  Elin Almroth-Rosell  Anders Tengberg  Roman Vankevich  Ivan Neelov  Alexey Isaev  Victor Kravtsov  Per O. J. Hall 《Aquatic Geochemistry》2012,18(6):543-564

Benthic fluxes of soluble reactive phosphorus (SRP) and dissolved inorganic carbon (DIC) were measured in situ using autonomous landers in the Gulf of Finland in the Baltic Sea, on four expeditions between 2002 and 2005. These measurements together with model estimates of bottom water oxygen conditions were used to compute the magnitude of the yearly integrated benthic SRP flux (also called internal phosphorus load). The yearly integrated benthic SRP flux was found to be almost 10 times larger than the external (river and land sources) phosphorus load. The average SRP flux was 1.25?±?0.56?mmol?m^?2?d^?1 on anoxic bottoms, and ?0.01?±?0.08?mmol?m^?2?d^?1 on oxic bottoms. The bottom water oxygen conditions determined whether the SRP flux was in a high or low regime, and degradation of organic matter (as estimated from benthic DIC fluxes) correlated positively with SRP fluxes on anoxic bottoms. From this correlation, we estimated a potential increase in phosphorus flux of 0.69?±?0.26?mmol?m^?2?d^?1 from presently oxic bottoms, if they would turn anoxic. An almost full annual data set of in situ bottom water oxygen measurements showed high variability of oxygen concentration. Because of this, an estimate of the time which the sediments were exposed to oxygenated overlying bottom water was computed using a coupled thermohydrodynamic ocean?Csea and ecosystem model. Total phosphorus burial rates were calculated from vertical profiles of total phosphorus in sediment and sediment accumulation rates. Recycling and burial efficiencies for phosphorus of 97 and 3%, respectively, were estimated for anoxic accumulation bottoms from a benthic mass balance, which was based on the measured effluxes and burial rates.  相似文献   

Origin of Ore-Forming Fluids of Mississippi Valley-Type （MVT） Pb-Zn Deposits in Kangdian Area, China   总被引：3，自引：1，他引：3  

王奖臻  李泽琴  倪师军 《中国地球化学学报》2003,22(4):369-376

Analyses of fluid-inclusion leachates from ore deposits show that Na/Br ratios are within the range of 75 - 358 and Cl/Br 67 - 394, respectively, and this variation trend coincides with the seawater evaporation trajectory on the basis of the Na/Br and Cl/Br ratios. The average Cl/Br and Na/Br ratios of mineralizing fluids are 185 and 173 respectively, which are very close to the ratios ( 120 and 233 ) of the residual evaporated seawater past the point of halite precipitation. It is suggested that the original mineralizing brine was derived from highly evapo-rated seawater with a high salinity. However, the inclusion fluids have absolute Na values of 69.9—2606.2 mmol kg^-1 and Cl values of 106.7 — 1995.5 mmol kg^-1. Most of the values are much less than those of seawater: Na, 485 mmol kg^-1 and Cl, 566 mmol kg^-1 , respectively; the salinity measured from fluid inclusions of the deposits ranges from 2.47 wt% to 15.78 wt% NaCl equiv. The mineralizing brine has been diluted. The δ ^18O and δD values of ore-forming fluids vary from -8.21‰ to 9.51‰ and from -40.3‰ to -94.3‰, respectively. The δD values of meteoric water in this region varied from - 80‰ to - 100‰ during the Jurassic. This evidenced that the ore-forming fluids are the mixture of seawater and meteoric water. Highly evaporated seawater was responsible for leaching and extracting Pb, Zn and Fe, and mixed with and diluted by descending meteoric water, which resulted in the formation of ores.  相似文献   

Temporal variability in summertime bottom hypoxia in shallow areas of Mobile Bay,Alabama     

Kyeong Park  Choong-Ki Kim  William W. Schroeder 《Estuaries and Coasts》2007,30(1):54-65

This paper addresses temporal variability in bottom hypoxia in broad shallow areas of Mobile Bay, Alabama. Time-series data collected in the summer of 2004 from one station (mean depth of 4 m) exhibit bottom dissolved oxygen (DO) variations associated with various time scales of hours to days. Despite a large velocity shear, stratification was strong enough to suppress vertical mixing most of the time. Bottom DO was closely related to the vertical salinity gradient (ΔS). Hypoxia seldom occurred when ΔS (over 2.5 m) was <2 psu and occurred almost all the time when ΔS was >8 psu in the absence of extreme events like hurricanes. Oxygen balance between vertical mixing and total oxygen demand was considered for bottom water from which oxygen demand and diffusive oxygen flux were estimated. The estimated decay rates at 20°C ranging between 0.175–0.322 d⁻¹ and the corresponding oxygen consumption as large as 7.4 g O₂ m⁻² d⁻¹ fall at the upper limit of previously reported ranges. The diffusive oxygen flux and the corresponding vertical diffusivity estimated for well mixed conditions range between 8.6–9.5 g O₂ m⁻² d⁻¹ and 2.6–2.9 m² d⁻¹, respectively. Mobile Bay hypoxia is likely to be associated with a large oxygen demand, supported by both water column and sediment oxygen demands, so that oxygen supply from surface water during destratification events would be quickly exhausted to return to hypoxic conditions within a few hours to days after destratification events are terminated.  相似文献   

Benthic nutrient fluxes in the intertidal flat within the Changjiang （Yangtze River） Estuary   总被引：1，自引：0，他引：1  

GAO Lei    LI Daoji  WANG Yanming  YU Lihua  KONG Dingjiang  LI Mei  LI Yun  and FANG Tao State Key Laboratory of Marine Geology  Tongji University  Shanghai  China State Key Laboratory of Estuarine  Coastal Research  East China Normal University  Shanghai  China 《中国地球化学学报》2008,27(1):58-71

In an annual cycle from March 2005 to February 2006, benthic nutrient fluxes were measured monthly in the Dongtan intertidal flat within the Changjiang （Yangtze River） Estuary. Except for NH4^＋, there always showed high fluxes from overlying water into sediment for other four nutrients. Sediments in the high and middle marshes, covered with halophyte and consisting of macrofauna, demonstrated more capabilities of assimilating nutrients from overlying water than the low marsh. Sampling seasons and nutrient concentrations in the overlying water could both exert significant effects on these fluxes. Additionally, according to the model provided by previous study, denitrification rates, that utilizing NO3- transported from overlying water （Dw） in Dongtan sediments, were estimated to be from -16 to 193 μmol·h^-1·m^-2 with an average value of 63 μmol·h^-1·m^-2 （n=18）. These estimated values are still underestimates of the in-situ rates owing to the lack of consideration of DN, i.e., denitrification supported by the local NO3^- production via nitrification.  相似文献   

The diel cycle of carbonyl sulfide in marine surface waters: Field study results and a simple model     

Günther Uher  Meinrat O. Andreae 《Aquatic Geochemistry》1996,2(4):313-344

The concentrations of atmospheric and dissolved carbonyl sulfide (COS) were measured during a Lagrangian study aboard the R/V Meteor in the northeast Atlantic Ocean, April/May 1992, and during a campaign on the research platform Nordsee in the German Bight (southeastern North Sea), September 1992. The arithmetic means and standard deviations of the COS saturation ratios were 1.27 ± 0.58 (northeast Atlantic) and 3.23 ± 0.73 (German Bight). Sea surface COS showed a pronounced diel cycle with highest concentrations in the late afternoon and a mean concentration amplitude of about 2. To account for this diel cycle, we analyze our results using a simple empirical model, which includes a zeroth order photoproduction constant, sea surface UV light intensity, and terms for hydrolysis removal and air-sea exchange. Fitted and observed COS concentrations agreed to within11 % (northeast Atlantic) and 14% (German Bight). The in situ COS photoproduction constants were (0.030 ± 0.008) fmol L^–1 s^–1 W^–1 m² in the northeast Atlantic (n = 8) and (0.17 ± 0.07) fmol L^–1 s^–1 W^–1 m² in the German Bight (n = 10). After normalization to the cloud cover corrected UV irradiance at 40 latitude, we obtained sea surface COS production rates of (0.034 ± 0.017) nmol L^–1 d^–1 in the northeast Atlantic and (1.62 ± 0.62) nmol L^–1 d^–1 in the German Bight. Currently available in situ photoproduction rates show a high degree of correlation with the UV absorbance (r ² = 0.98, n = 4) and fluorescence (r ² = 0.85, n = 4) of chromophoric dissolved organic matter (CDOM). The regional differences between the COS productivity in the northeast Atlantic Ocean and the German Bight is attributed to the distribution pattern of CDOM optical properties.  相似文献   

The application of δ¹³C and C/N ratios as indicators of organic carbon sources and paleoenvironmental change of the mangrove ecosystem from Ba Lat Estuary, Red River, Vietnam     

Nguyen Tai Tue  Hideki Hamaoka  Atsushi Sogabe  Tran Dang Quy  Mai Trong Nhuan  Koji Omori 《Environmental Earth Sciences》2011,64(5):1475-1486

In this study, two sediment cores (~70 cm) were collected from separate mangrove forests straddling the Ba Lat Estuary, Red River of northern Vietnam, to examine the origins of sedimentary organic carbon (SOC) and reconstruct the paleoenvironment. In addition, mangrove leaves and particulate organic matter were collected and measured for δ¹³C to trace the origins of SOC. The cores were analyzed by high-resolution sections for δ¹³C, TOC, C/N ratios, sediment grain size, water content, and porosity, with values of δ¹³C, TOC, and C/N ratios ranging from −28.19 to −22.5‰, 2.14–30.94 mg/g, and 10.29–18.32, respectively. The δ¹³C and TOC relationship indicated that there were some small residual effects of diagenetic processes on TOC and δ¹³C values in mangrove sediments. However, the shifts of δ¹³C and C/N ratios from the bottom to the surface sediment of the cores explained the change in organic matter sources, with values of C/N > 12 and δ¹³C < −25‰, and C/N < 12 and δ¹³C > −25‰ indicated terrestrial (e.g., mangrove litter) and marine phytoplankton sources, respectively. The covarying δ¹³C, C/N ratios, and sediment grain sizes during the past 100 years in sediment cores showed that the paleoenvironment may be reconstructed into three environments (subtidal, tidal flat, and intertidal mangrove). General trends in δ¹³C and C/N followed a gradual increase in the C/N ratio and a concomitant decrease in δ¹³C from the subtidal, through to tidal flat, and to the intertidal mangrove. δ¹³C and C/N ratios are therefore effective in measuring the continuum of environmental change in mangrove ecosystem.  相似文献   

Water quality analysis of a freshwater diversion at Caernarvon, Louisiana     

Robert R. Lane  John W. Day  Burnell Thibodeaux 《Estuaries and Coasts》1999,22(2):327-336

Since 1991, Mississippi River water has been diverted at Caernarvon, Louisiana, into Breton Sound estuary. Breton Sound estuary encompasses 1100 km² of fresh and brackish, rapidly subsiding wetlands. Nitrite + nitrate, total Kjeldahl nitrogen, ammonium, total phosphorus, total suspended sediments, and salinity concentrations were monitored at seven locations in Breton Sound from 1988 to 1994. Statistical analysis of the data indicated decreased total Kjeldahl nitrogen with associated decrease in total nitrogen, and decreased salinity concentrations in the estuary due to the diversion. Spring and summer water quality transects indicated rapid reduction of nitrite + nitrate and total suspended sediment concentration as diverted Mississippi River water entered the estuary, suggesting near complete assimilation of these constituents by the ecosystem. Loading rates of nitrite + nitrate (5.6–13.4 g m⁻² yr⁻¹), total nitrogen (8.9–23.4 g m⁻² yr⁻¹), and total phosphorus (0.9–2.0 g m⁻² yr⁻¹) were calculated along with removal efficiencies for these constituents (nitrite + nitrate 88–97%; total nitrogen 32–57%; total phosphorus 0–46%). The low impact of the diversion on water quality in the Breton Sound estuary, along with assimilation of TSS over a very short distance, suggests that more water may be introduced into the estuary without detrimental affects. This would be necessary if freshwater diversions are to be used to distribute nitrients and sediments into the lower reaches of the estuary, in an effort to compensate for relative sea-level rise, and reverse the current trend of rapid loss of wetlands in coastal Louisiana.  相似文献