Organic matter in ria sediments: Relevance of terrestial sources and temporal variations in rates of accumulation     

Graham EvansRicardo Prego  John E. Marshall 《Estuarine, Coastal and Shelf Science》2011,94(3):246-254

The Ria of Vigo, one of the classical rias of SW Europe, is an environment of high production of organic matter naturally induced by the Galician upwelling. The organic matter is partly supplied by small rivers but mainly by sewage plants along the ria shoreline; jointly they contribute 725 t y⁻¹ of POC, of which 72% is of anthropogenic origin. The freshwater flux is equivalent to a supply of 5 g m⁻² yr⁻¹ of allochtonous POC to the ria floor. However the rate of accumulation of POC is dominated by the order of magnitude higher supply of autochthonous material from the net primary production. The present accumulation rate of organic matter (49-58 g_POC m⁻² yr⁻¹) is lower than the average supply, estimated from the sedimentary record, to the ria since the middle of the nineteen Century (>60 g_POC m⁻² yr⁻¹). This difference may be due to anthropogenic activity or changes in the upwelling pattern. The composition of the organic matter in the sediment reflects the relative importance of the various sources (terrestrial-marine). While terrestrial woody materials dominate the inner ria, phytoplankton remains dominate the remainder of the ria. Rock-Evaluation analysis indicates the inner ria is the site of deposition of gas-prone material and it is inferred that the outer ria of oil-prone organic matter. The controls on the accumulation of POC in the rias show many differences to those found in estuaries affected by anthropogenic activities e.g. agriculture and increasing human population.  相似文献   

Fish farming enhances biomass and nutrient loss in Posidonia oceanica (L.) Delile     

Eugenia T. Apostolaki  Núria Marbà  Marianne Holmer  Ioannis Karakassis 《Estuarine, Coastal and Shelf Science》2009,81(3):390-400

Fish farming impact on the seasonal biomass, carbon and nutrient (nitrogen and phosphorus) balance of the endemic Mediterranean seagrass Posidonia oceanica was assessed in the Aegean Sea (Greece) in order to detect changes in magnitude and fate of seagrass production and nutrient incorporation with organic loading of the meadows. Phosphorus concentration in the leaves, rhizomes and roots was enhanced under the cages throughout the study. Standing biomass was diminished by 64% and carbon, nitrogen and phosphorus standing stock by 64%, 61% and 48%, respectively, under the cages in relation to those at the control. Seagrass production decreased by 68% and element (C, N, P) incorporation by 67%, 58% and 58%, respectively, under the cages. Leaf shedding was reduced by 81% and loss of elements (C, N, and P) through shedding by 82%, 74% and 72%, respectively, under the cages. Leaf and element (C, N, P) residual loss rate, accounting for grazing and mechanical breakage of leaves, was decreased by 79%, 85%, 100% and 96%, respectively, at the control station. At the control station, 13.98 g C m^?2 yr^?1, 1.91 g N m^?2 yr^?1 and 0.05 g P m^?2 yr^?1 were produced in excess of export and loss. In contrast, under the cages 12.69 g C m^?2 yr^?1, 0.31 g N m^?2 yr^?1 and 0.04 g P m^?2 yr^?1 were released from the meadow. Organic loading due to fish farm discharges transformed the seagrass meadow under the cages from a typical sink to a source of organic carbon and nutrients.  相似文献   

Inputs of iron,manganese and aluminium to surface waters of the Northeast Atlantic Ocean and the European continental shelf     

Jeroen T.M. de Jong  Marie Boyé  Maria D. Gelado-Caballero  Klaas R. Timmermans  Marcel J.W. Veldhuis  Rob F. Nolting  Constant M.G. van den Berg  Hein J.W. de Baar 《Marine Chemistry》2007

Dissolved Fe, Mn and Al concentrations (dFe, dMn and dAl hereafter) in surface waters and the water column of the Northeast Atlantic and the European continental shelf are reported. Following an episode of enhanced Saharan dust inputs over the Northeast Atlantic Ocean prior and during the cruise in March 1998, surface concentrations were enhanced up to 4 nmol L^− 1 dFe, 3 nmol L^− 1 dMn and 40 nmol L^− 1 dAl and returned to 0.6 nmol L^− 1 dFe, 0.5 nmol L^− 1 dMn and 10 nmol L^− 1 dAl towards the end of the cruise three weeks later. A simple steady state model (MADCOW, [Measures, C.I., Brown, E.T., 1996. Estimating dust input to the Atlantic Ocean using surface water aluminium concentrations. In: Guerzoni. S. and Chester. R. (Eds.), The impact of desert dust across the Mediterranean, Kluwer Academic Publishers, The Netherlands, pp. 301–311.]) was used which relies on surface ocean dAl as a proxy for atmospheric deposition of mineral dust. We estimated dust input at 1.8 g m^− 2 yr^− 1 (range 1.0–2.9 g m^− 2 yr^− 1) and fluxes of dFe, dMn and dAl were inferred. Mixed layer steady state residence times for dissolved metals were estimated at 1.3 yr for dFe (range 0.3–2.9 yr) and 1.9 yr for dMn (range 1.0–3.8 yr). The dFe residence time may have been overestimated and it is shown that 0.2–0.4 yr is probably more realistic. Using vertical dFe versus Apparent Oxygen Utilization (AOU) relationships as well as a biogeochemical two end member mixing model, regenerative Fe:C ratios were estimated respectively to be 20 ± 6 and 22 ± 5 μmol Fe:mol C. Combining the atmospheric flux of dFe to the upper water column with the latter Fe:C ratio, a ‘new iron’ supported primary productivity of only 15% (range 7%–56%) was deduced. This would imply that 85% (range 44–93%) of primary productivity could be supported by regenerated dFe. The open ocean surface data suggest that the continental shelf is probably not a major source of dissolved metals to the surface of the adjacent open ocean. Continental shelf concentrations of dMn, dFe, and to a lesser extent dAl, were well correlated with salinity and express mixing of a fresher continental end member with Atlantic Ocean water flowing onto the shelf. This means probably that diffusive benthic fluxes did not play a major role at the time of the cruise.  相似文献   

High mortality of Zostera marina under high temperature regimes but minor effects of the invasive macroalgae Gracilaria vermiculophylla     

H. Höffle  M.S. Thomsen  M. Holmer 《Estuarine, Coastal and Shelf Science》2011

The present study tested for density-dependent effects of the invasive drift macroalgae Gracilaria vermiculophylla (Ohmi) Papenfuss on growth and survival of the native eelgrass, Zostera marina L., under different temperature levels. Three weeks laboratory experiments were conducted in Odense, Denmark, combining three algae densities (control, low 1.9 kg WW m⁻², high 4.5 kg WW m⁻²) with typical Danish summer temperatures (18 °C) and elevated temperatures (21 °C and 27 °C). There was a significant effect of temperature on shoot survival with on average 68% mortality in the high temperature treatment but almost no mortality at the two lower temperatures. The higher mortality was probably caused by high sulphide levels in the sediment pore water (0.6 mmol l⁻¹ at 18 °C compared to 3.7 mmol l⁻¹ at 27 °C). Above-ground growth of the surviving shoots was also significantly affected by temperature, with leaf elongation rates being negatively affected, while the leaf plastochrone interval increased. Relative growth rate was significantly higher at 21 °C than at 18 °C or 27 °C, whereas rhizome elongation was significantly lowest at 27 °C. Elemental sulphur content in the plant tissues increased significantly with temperature and was up to 34 times higher (S⁰ in rhizomes) at 27 °C compared to the lower temperatures. In contrast to the temperature effects, cover by G. vermiculophylla did not cause significant effects on any seagrass responses. However, there was a (non-significant) negative effect of algal cover at the highest temperature, where the seagrass is already stressed. The latter results suggest that more studies should test for interaction effects between temperature and other anthropogenic stressors given that temperature is predicted to increase in the near future.  相似文献   

Rates and regulation of nitrogen cycling in seasonally hypoxic sediments during winter (Boknis Eck,SW Baltic Sea): Sensitivity to environmental variables     

A.W. Dale  S. SommerL. Bohlen  T. TreudeV.J. Bertics  H.W. BangeO. Pfannkuche  T. SchorpM. Mattsdotter  K. Wallmann 《Estuarine, Coastal and Shelf Science》2011

This study investigates the biogeochemical processes that control the benthic fluxes of dissolved nitrogen (N) species in Boknis Eck – a 28 m deep site in the Eckernförde Bay (southwestern Baltic Sea). Bottom water oxygen concentrations (O_2−BW) fluctuate greatly over the year at Boknis Eck, being well-oxygenated in winter and experiencing severe bottom water hypoxia and even anoxia in late summer. The present communication addresses the winter situation (February 2010). Fluxes of ammonium (NH₄⁺), nitrate (NO₃⁻) and nitrite (NO₂⁻) were simulated using a benthic model that accounted for transport and biogeochemical reactions and constrained with ex situ flux measurements and sediment geochemical analysis. The sediments were a net sink for NO₃⁻ (−0.35 mmol m⁻² d⁻¹ of NO₃⁻), of which 75% was ascribed to dissimilatory reduction of nitrate to ammonium (DNRA) by sulfide oxidizing bacteria, and 25% to NO₃⁻ reduction to NO₂⁻ by denitrifying microorganisms. NH₄⁺ fluxes were high (1.74 mmol m⁻² d⁻¹ of NH₄⁺), mainly due to the degradation of organic nitrogen, and directed out of the sediment. NO₂⁻ fluxes were negligible. The sediments in Boknis Eck are, therefore, a net source of dissolved inorganic nitrogen (DIN = NO₃⁻ + NO₂⁻ + NH₄⁺) during winter. This is in large part due to bioirrigation, which accounts for 76% of the benthic efflux of NH₄⁺, thus reducing the capacity for nitrification of NH₄⁺. The combined rate of fixed N loss by denitrification and anammox was estimated at 0.08 mmol m⁻² d⁻¹ of N₂, which is at the lower end of previously reported values. A systematic sensitivity analysis revealed that denitrification and anammox respond strongly and positively to the concentration of NO₃⁻ in the bottom water (NO₃⁻_BW). Higher O_2−BW decreases DNRA and denitrification but stimulates both anammox and the contribution of anammox to total N₂ production (%R_amx). A complete mechanistic explanation of these findings is provided. Our analysis indicates that nitrification is the geochemical driving force behind the observed correlation between %R_amx and water depth in the seminal study of Dalsgaard et al. (2005). Despite remaining uncertainties, the results provide a general mechanistic framework for interpreting the existing knowledge of N-turnover processes and fluxes in continental margin sediments, as well as predicting the types of environment where these reactions are expected to occur prominently.  相似文献   

Population dynamics and secondary production of the cockle Cerastoderma edule: A comparison between Merja Zerga (Moroccan Atlantic Coast) and Arcachon Bay (French Atlantic Coast)     

Mériame Gam  Xavier de Montaudouin  Hocein Bazairi 《Journal of Sea Research》2010,63(3-4):191-201

Cockle (Cerastoderma edule) population dynamics were studied at the southern limit of the distribution of this marine bivalve in Merja Zerga, Morocco. Parameters such as growth, mortality, and production were compared with those of a population at Arcachon Bay (France) a site in the center of the cockle's range. At each sampling period between two and three cohorts were simultaneously observed at each site and the average total abundance was usually higher at Merja Zerga. Recruitment occurred at both sites in spring when temperature rose above 19 °C, independently of the month. In Merja Zerga, winter recruitment was also observed at one occasion, following high sediment disturbance. The first year (2005–06) at Merja Zerga, the mortality rate was close to nil for juveniles and was Z = 1.5 yr^? 1 for adults, providing a high production (64 g dry weight m^? 2 yr^? 1). At Arcachon during the same period, the juvenile mortality rate was Z = 10.9 yr^? 1, the adult mortality rate was 3.4 yr^? 1 and production was 26 gDW m^?2 yr^? 1. The second year (2006–07), mortality after recruitment was much higher (Z = 8.6 yr^? 1, for juveniles) and similar to what was observed at Arcachon (Z = 8.4 yr^? 1). Mortality rate of adults was higher at Merja Zerga (Z = 3.0 yr^? 1) than at Arcachon (Z = 1.5 yr^? 1). Production was lower at Arcachon than at Merja Zerga although growth performances were higher at Arcachon. The higher growth performance at Arcachon (Φ′ = 3.3) was mainly due to high asymptotic length (L_∞ = 38 mm) and was related to low intraspecific competition compared to Merja Zerga where cockle abundance was higher (Φ′ = 3.1, L_∞ = 31 mm). P/B was low in both sites and slightly higher at Arcachon (1.1–1.5 against 1.0–1.1 yr^? 1). At Arcachon, recruitment was correlated with temperature, a peak occurring when temperature rose above 19 °C (June–July). At Merja Zerga, recruitment was already 2–3 months earlier but was not significantly correlated to temperature.This study showed that population dynamics of cockles at the southern limit of this distribution fell in the range of what was observed elsewhere in the North-Eastern Atlantic coast. Most factors that were involved in population regulation (intraspecific competition, predation and sediment dynamics) were not strictly dependent on latitude. The direct role of temperature (latitude dependent factor) was not obvious. Variation in temperature could explain the recruitment delay between Arcachon and Merja Zerga and the low maximum shell length at Merja Zerga.  相似文献   

Benthic nutrient fluxes along the Laurentian Channel: Impacts on the N budget of the St. Lawrence marine system     

Benoît Thibodeau  Moritz F. Lehmann  Jacqueline Kowarzyk  Alfonso Mucci  Yves Gélinas  Denis Gilbert  Roxane Maranger  Mohammad Alkhatib 《Estuarine, Coastal and Shelf Science》2010

Water column concentrations and benthic fluxes of dissolved inorganic nitrogen (DIN) and oxygen (DO) were measured in the Gulf of St. Lawrence and the Upper and Lower St. Lawrence Estuary (USLE and LSLE, respectively) to assess the nitrogen (N) budget in the St. Lawrence (SL) system, as well as to elucidate the impact of bottom water hypoxia on fixed-N removal in the LSLE. A severe nitrate deficit, with respect to ambient phosphate concentrations (N*∼−10 μmol L⁻¹), was observed within and in the vicinity of the hypoxic bottom water of the LSLE. Given that DO concentrations in the water column have remained above 50 μmol L⁻¹, nitrate reduction in suboxic sediments, rather than in the water column, is most likely responsible for the removal of fixed N from the SL system. Net nitrate fluxes into the sediments, derived from pore water nitrate concentration gradients, ranged from 190 μmol m⁻² d⁻¹ in the hypoxic western LSLE to 100 μmol m⁻² d⁻¹ in the Gulf. The average total benthic nitrate reduction rate for the Laurentian Channel (LC) is on the order of 690 μmol m⁻² d⁻¹, with coupled nitrification-nitrate reduction accounting for more than 70%. Using average nitrate reduction rates derived from the observed water column nitrate deficit, the annual fixed-N elimination within the three main channels of the Gulf of St. Lawrence and LSLE was estimated at 411 × 10⁶ t N, yielding an almost balanced N budget for the SL marine system.  相似文献   

Seasonal and interannual variability in particle fluxes of carbon,nitrogen and silicon from time series of sediment traps at Ocean Station P, 1982–1993: relationship to changes in subarctic primary productivity     

《Deep Sea Research Part II: Topical Studies in Oceanography》1999,46(11-12):2735-2760

An extended time series of particle fluxes at 3800 m was recorded using automated sediment traps moored at Ocean Station Papa (OSP, 50°N, 145°W) in the northeast Pacific Ocean for more than a decade (1982–1993). Time-series observations at 200 and 1000 m, and short-term measurements using surface-tethered free-drifting sediment traps also were made intermittently. We present data for fluxes of total mass (dry weight), particulate organic carbon (POC), particulate organic nitrogen (PON), biogenic Si (BSi), and particulate inorganic carbon (PIC) in calcium carbonate. Mean monthly fluxes at 3800 m showed distinct seasonality with an annual minimum during winter months (December–March), and maximum during summer and fall (April–November). Fluxes of total mass, POC, PIC and BSi showed 4-, 10-, 7- and 5-fold increases between extreme months, respectively. Mean monthly fluxes of PIC often showed two plateaus, one in May–August dominated by <63 μm particles and one in October–November, which was mainly >63 μm particles. Dominant components of the mass flux throughout the year were CaCO₃ and opal in equal amounts. The mean annual fluxes at 3800 m were 32±9 g dry weight g m⁻² yr⁻¹, 1.1±0.5 g POC m⁻² yr⁻¹, 0.15±0.07 g PON m⁻² yr⁻¹, 5.9±2.0 g BSi m⁻² yr⁻¹ and 1.7±0.6 g PIC m⁻² yr⁻¹. These biogenic fluxes clearly decreased with depth, and increased during “warm” years (1983 and 1987) of the El Niño, Southern Oscillation cycle (ENSO). Enhancement of annual mass flux rates to 3800 m was 49% in 1983 and 36% in 1987 above the decadal average, and was especially rich in biogenic Si. Biological events allowed estimates of sinking rates of detritus that range from 175 to 300 m d⁻¹, and demonstrate that, during periods of high productivity, particles sink quickly to deep ocean with less loss of organic components. Average POC flux into the deep ocean approximated the “canonical” 1% of the surface primary production.  相似文献   

Mangrove litter fall: Extrapolation from traps to a large tropical macrotidal harbour     

Kristin N. Metcalfe  Donald C. Franklin  Keith A. McGuinness 《Estuarine, Coastal and Shelf Science》2011

Mangrove litter is a major source of organic matter for detrital food chains in many tropical coastal ecosystems, but scant attention has been paid to the substantial challenges in sampling and extrapolation of rates of litter fall. The challenges arise due to within-stand heterogeneity including incomplete canopy cover, and canopy that is below the high tide mark. We sampled litter monthly for three years at 35 sites across eight mapped communities in the macrotidal Darwin Harbour, northern Australia. Totals were adjusted for mean community canopy cover and the occurrence of canopy below the high tide mark. The mangroves of Darwin Harbour generate an estimated average of 5.0 t ha⁻¹ yr⁻¹ of litter. This amount would have been overestimated by 32% had we not corrected for limited canopy cover and underestimated by 11% had we not corrected for foliage that is below the high tide mark. Had we made neither correction, we would have overestimated litter fall by 17%. Among communities, rates varied 2.6-fold per unit area of canopy, and 3.9-fold among unit area of community. Seaward fringe mangroves were the most productive per unit of canopy area but the canopy was relatively open; Tidal creek forest was the most productive per unit area of community. Litter fall varied 1.1-fold among years and 2.0-fold among months though communities exhibited a range of seasonalities. Our study may be the most extensively stratified and sampled evaluation of mangrove litter fall in a tropical estuary. We believe our study is also the first such assessment to explicitly deal with canopy discontinuities and demonstrates that failure to do so can result in considerable overestimation of mangrove productivity.  相似文献   

Tiller dynamic and production on a SW Atlantic Spartina alterniflora marsh     

G. González Trilla  P. Kandus  V. Negrin  R. Vicari  J. Marcovecchio 《Estuarine, Coastal and Shelf Science》2009

We used non-destructive methods to study the bi-monthly changes in standing stock, turnover, and net aerial primary productivity (NAPP) of Spartina alterniflora in the Bahía Blanca Estuary, Argentina, from 2005 to 2007. Tillers were tagged and counted bimonthly and a weight:height relationship developed for the live and dead stems in a regularly flooded zone (low marsh, LM) and an irregularly flooded one (high marsh, HM). The annual tiller natality in year one compared to year two decreased from 440 ± 68 to 220 ± 58 new individuals m^–2 yr^–1 in the HM and from 500 ± 103 to 280 ± 97 new individuals m⁻² yr⁻¹ in the LM (μ ± 1 SE). Tiller mortality averaged 670 ± 70 individuals m⁻² yr⁻¹.  相似文献   

Atmospheric nitrogen deposition to the Mullica River-Great Bay Estuary     

《Marine environmental research》2008,65(5):590-600

Measurements of nitrate and ammonium in precipitation and associated with aerosols were conducted at Rutgers University Marine Field Station in Tuckerton, New Jersey from March 2004 to March 2005 to characterize atmospheric nitrogen deposition to the Mullica River-Great Bay Estuary. The arithmetic means of nitrate and ammonium concentrations for precipitation samples were 2.3 mg L⁻¹ and 0.42 mg L⁻¹, respectively. Nitrate and ammonium concentrations in aerosol samples averaged 3.7 μg m⁻³ and 1.6 μg m⁻³, respectively. Wet deposition rates appeared to vary with season; the highest rate of inorganic nitrogen deposition (nitrate + ammonium) occurred in the spring with an average value of 1.33 kg-N ha⁻² month⁻¹. On an annual basis, the total (wet and dry) direct atmospheric deposition fluxes into the Mullica River-Great Bay Estuary were 7.08 kg-N ha⁻² year⁻¹ for nitrate and 4.44 kg-N ha⁻² year⁻¹ for ammonium. The total atmospheric inorganic nitrogen directly deposited to the Mullica River-Great Bay Estuary was estimated to be 4.79 × 10⁴ kg-N year⁻¹, and the total atmospheric inorganic nitrogen deposited to the Mullica River watershed was estimated to be 1.69 × 10⁶ kg-N year⁻¹. Only a fraction of the nitrogen deposited on the watershed will actually reach the estuary; most of the nitrogen will be retained in the watershed due to utilization and denitrification during transport. The amount of N reaching the Mullica River-Great Bay Estuary indirectly is estimated to be 5.07 × 10⁴ kg-N year⁻¹, approximately 97% is retained within the watershed. This atmospheric nitrogen deposition may stimulate phytoplankton productivity in the Mullica River-Great Bay ecosystem.  相似文献   

Assessment of excess nitrate development in the subtropical North Atlantic     

D.A. Hansell  D.B. Olson  F. Dentener  L.M. Zamora   《Marine Chemistry》2007,106(3-4):562-579

Geochemical estimates of N₂ fixation in the North Atlantic often serve as a foundation for estimating global marine diazotrophy. Yet despite being well-studied, estimations of nitrogen fixation rates in this basin vary widely. Here we investigate the variability in published estimates of excess nitrogen accumulation rates in the main thermocline of the subtropical North Atlantic, testing the assumptions and choices made in the analyses. Employing one of these previously described methods, modified here with improved estimates of excess N spatial gradients and ventilation rates of the main thermocline, we determine a total excess N accumulation rate of 7.8 ± 1.7 × 10¹¹ mol N yr^− 1. Contributions to excess N development include atmospheric deposition of high N:P nutrients (adding excess N at a rate of 3.0 ± 0.9 × 10¹¹ mol N yr^− 1 for  38% of the total), high N:P dissolved organic matter advected into and mineralized in the main thermocline (adding excess N at 2.2 ± 1.1 × 10¹¹ mol N yr^− 1 for  28% of the total), and, calculated by mass balance of the excess N field, N₂ fixation (adding excess N at 2.6 ± 2.2 × 10¹¹ mol N yr^− 1 for  33% of the total). Assuming an N:P of 40 and this rate of excess N accumulation due to the process, N₂ fixation in the North Atlantic subtropical gyre is estimated at  4 × 10¹¹ mol N yr^− 1. This relatively low rate of N₂ fixation suggests that i) the rate of N₂ fixation in the North Atlantic is greatly overestimated in some previous analyses, ii) the main thermocline is not the primary repository of N fixed by diazotrophs, and/or iii) the N:P ratio of exported diazotrophic organic matter is much lower than generally assumed. It is this last possibility, and our uncertainty in the N:P ratios of exported material supporting excess N development, that greatly lessens our confidence in geochemical measures of N₂ fixation.  相似文献   

Secondary production in a Laminaria hyperborea kelp forest and variation according to wave exposure     

Kjell M. Norderhaug  Hartvig Christie 《Estuarine, Coastal and Shelf Science》2011

The secondary production of mobile invertebrate fauna in the Laminaria hyperborea (Gunn.) Foslie kelp forest increases with wave exposure level. This faunal group has a key function in transferring kelp carbon to higher levels in the food web. By using a size-frequency method the calculated production was 68 (±18) g D.W. m⁻² yr⁻¹ (±S.E.) at low, 250 (±57) at medium and 308 (±64) at high exposure levels. The calculations included 30 macrofauna species, which accounted for 96% of the specimens registered, with Gastropods, amphipods and bivalves being the most abundant taxa. The calculated secondary production is high, but comparable to that previously reported from other macrophyte systems and was 3%, 8% and 8% of the total primary production at low, medium and high exposure levels, respectively. Our results indicate that large quantities of Laminaria kelp are exported from the system, although the production of sessile animals was not taken into account. The most important factor in determining faunal densities and secondary production was probably habitat size but at low exposure levels the percentage of egg-carrying crustacean females and juveniles were lower than at medium and high exposure levels, thereby indicating lower fitness for animals at low exposure stations.  相似文献   

Scleractinian coral population size structures and growth rates indicate coral resilience on the fringing reefs of North Jamaica   总被引：1，自引：1，他引：0  

M.J.C. Crabbe   《Marine environmental research》2009,67(4-5):189-198

Coral reefs throughout the world are under severe challenges from many environmental factors. This paper quantifies the size structure of populations and the growth rates of corals from 2000 to 2008 to test whether the Discovery Bay coral colonies showed resilience in the face of multiple acute stressors of hurricanes and bleaching. There was a reduction in numbers of colonies in the smallest size class for all the species at all the sites in 2006, after the mass bleaching of 2005, with subsequent increases for all species at all sites in 2007 and 2008. Radial growth rates (mm yr⁻¹) of non-branching corals and linear extension rates (mm yr⁻¹) of branching corals calculated on an annual basis from 2000–2008 showed few significant differences either spatially or temporally. At Dairy Bull reef, live coral cover increased from 13 ± 5% in 2006 to 20 ± 9% in 2007 and 31 ± 7% in 2008, while live Acropora species increased from 2 ± 2% in 2006 to 10 ± 4% in 2007 and 22 ± 7% in 2008. These studies indicate good levels of coral resilience on the fringing reefs around Discovery Bay in Jamaica.  相似文献   

Biogenic fluxes in the Cariaco Basin: a combined study of sinking particulates and underlying sediments     

《Deep Sea Research Part I: Oceanographic Research Papers》2003,50(6):781-807

The fluxes of total mass, organic carbon (OC), biogenic opal, calcite (CaCO₃) and long-chain C₃₇ alkenones (ΣAlk₃₇) were measured at three water depths (275, 455 and 930 m) in the Cariaco Basin (Venezuela) over three separate annual upwelling cycles (1996–1999) as part of the CARIACO sediment trap time-series. The strength and timing of both the primary and secondary upwelling events in the Cariaco Basin varied significantly during the study period, directly affecting the rates of primary productivity (PP) and the vertical transport of biogenic materials. OC fluxes showed a weak positive correlation (r²=0.3) with PP rates throughout the 3 years of the study. The fluxes of opal, CaCO₃ and ΣAlk₃₇ were strongly correlated (0.6<r²<0.8) with those of OC. The major exception was the lower than expected ΣAlk₃₇ fluxes measured during periods of strong upwelling. All sediment trap fluxes were significantly attenuated with depth, consistent with marked losses during vertical transport. Annually, strong upwelling conditions, such as those observed during 1996–1997, led to elevated opal fluxes (e.g., 35 g m⁻² yr⁻¹ at 275 m) and diminished ΣAlk₃₇ fluxes (e.g., 5 mg m⁻² yr⁻¹ at 275 m). The opposite trends were evident during the year of weakest upwelling (1998–1999), indicating that diatom and haptophyte productivity in the Cariaco Basin are inversely correlated depending on upwelling conditions.The analyses of the Cariaco Basin sediments collected via a gravity core showed that the rates of OC and opal burial (10–12 g m⁻² yr⁻¹) over the past 5500 years were generally similar to the average annual water column fluxes measured in the deeper traps (10–14 g m⁻² yr⁻¹) over the 1996–1999 study period. CaCO₃ burial fluxes (30–40 g m⁻² yr⁻¹), on the other hand, were considerably higher than the fluxes measured in the deep traps (∼10 g m⁻² yr⁻¹) but comparable to those obtained from the shallowest trap (i.e. 38 g m⁻² yr⁻¹ at 275 m). In contrast, the burial rates of ΣAlk₃₇ (0.4–1 mg m⁻² yr⁻¹) in Cariaco sediments were significantly lower than the water column fluxes measured at all depths (4–6 mg m⁻² yr⁻¹), indicating the large attenuation in the flux of these compounds at the sediment–water interface. The major trend throughout the core was the general decrease in all biogenic fluxes with depth, most likely due to post-depositional in situ degradation. The major exception was the relatively low opal fluxes (∼5 g m⁻² yr⁻¹) and elevated ΣAlk₃₇ fluxes (∼2 mg m⁻² yr⁻¹) measured in the sedimentary interval corresponding to 1600–2000 yr BP. Such compositions are consistent with a period of low diatom and high haptophyte productivity, which based on the trends observed from the sediment traps, is indicative of low upwelling conditions relative to the modern day.  相似文献   

Morphodynamics of a high discharge tropical delta, San Juan River, Pacific coast of Colombia     

Juan D Restrepo  Björn Kjerfve  Iván D CorreaJuan González 《Marine Geology》2002,192(4):355-381

The San Juan River has one of the most extensive and best developed deltas on the Pacific coast of South America, measuring 800 km². The river drainage basin measures 16?465 km² and is located in one of the areas with the highest precipitation in the western hemisphere. The annual rainfall varies from 7000 to 11?000 mm, and as a result the San Juan River has the highest water discharge (2550 m³ s⁻¹), sediment load (16×10⁶ t yr⁻¹), and basin-wide sediment yield (1150 t km⁻² yr⁻¹) on the west coast of South America. The San Juan delta growth began approximately 5000 years BP. The structure of the delta is determined by the interactions between fluvial deposition and the effect of 1.7-m significant swells, mostly from the SW, and strong tidal currents. Analysis of delta progradation indicates that during 1848-1992 the morphology of the delta was characterized by beach ridge accretion, spit growth, narrowing of inlets, and a general advance of the delta shoreline. During the past decade processes such as rapid erosion of the delta shore, narrowing of barrier islands, and breaching of a new inlet, are the result of a long-term relative sea-level rise of 2.6 mm yr⁻¹ due to tectonically induced subsidence coupled with a eustatic rise of sea-level. The delta also experiences strong oceanographic manifestations associated with the El Niño-La Niña cycle, causing regional sea-level elevation of 20-30 cm during El Niño years. Recent coastal subsidence in the delta is evidenced by: (1) increased occurrence of non-storm washover events; (2) increased erosion of barrier islands with average loss of 11 m yr⁻¹ during 1993-1997; and (3) a relative sea-level rise of 3.4 mm yr⁻¹ during 1991-1999. The morphology and recent evolution of the San Juan delta are unique when compared to other deltas of South America because of the singular combination of extreme climatic, geologic, and oceanographic conditions under which the delta has formed and the absence of human-induced impact in the drainage basin.  相似文献   

Interannual variability of Si and N cycles at the time-series station KERFIX between 1990 and 1995 – a 1-D modelling study     

《Deep Sea Research Part I: Oceanographic Research Papers》2000,47(2):223-257

Interannual variability of nutrients and plankton cycles were studied at the time-series station KERFIX (50°40′S, 68°25′E) using a 1-D coupled physical-biogeochemical model that is descended from that of Pondaven et al. (1998). At KERFIX, a high half saturation constant for silicic acid uptake (K_Si) and a high Si/N uptake ratio are required to reproduce the Si and N cycles. Although very high in comparison with most data from temperate systems, these values are consistent with K_Si and Si/N uptake ratios measured in the Indian sector of the Southern Ocean. Past and recent finding on the role of light and iron limitation on nutrient consumption ratios might explain these “unusual” silicon uptake kinetic parameters. Comparison of model results with observations show that the model correctly reproduces the observed interannual variability of nutrients and plankton cycles at KERFIX between 1992 and 1995. Characteristic features of this region are a spring phytoplankton bloom of 1.0–1.5 mg Chlorophyll a m⁻³ and a net excess of silicic acid utilisation over that of nitrate. This high silicic acid utilisation leads to low Si concentrations in late summer and subsequent Si limitation of diatom growth. The interannual variability of production of silicon and nitrogen predicted by the model is 1.93±0.04 mol Si m⁻² yr⁻¹ and 1.35±0.07 mol N m⁻² yr⁻¹ (±SD). In parallel, the predicted export is 1.12±0.04 mol Si m⁻² yr⁻¹ and 0.06±0.01 mol N m⁻² yr⁻¹. It is shown that diatoms may contribute significantly to export if diatom sinking is taken into account. An interannual variability of the predicted Si and N cycles is detected. This variability is associated with changes in the mixed layer properties, which have been documented to be linked to the Pacific El Niño Southern Oscillation or displacement of the Polar Front.  相似文献   

Factors controlling silicon and nitrogen biogeochemical cycles in high nutrient,low chlorophyll systems (the Southern Ocean and the North Pacific): Comparison with a mesotrophic system (the North Atlantic)     

《Deep Sea Research Part I: Oceanographic Research Papers》1999,46(11):1923-1968

A 1-D coupled physical-biogeochemical model is used to study the seasonal cycles of silicon and nitrogen in two High Nutrient Low Chlorophyll (HNLC) systems, the Antarctic Circumpolar Current (ACC) and the North Pacific Ocean, and a mesotrophic system, the North Atlantic Ocean. The biological model consists of nine compartments (diatoms, nano-flagellates, microzooplankton, mesozooplankton, two types of detritus, nitrate, ammonium and silicic acid) forced by irradiance, temperature, mixing and deep nitrate and silicic acid concentrations. At all sites, nanophytoplankton standing crop variations are low, in spite of variations in primary production, because of a “top–down” control by microzooplankton. Although nanophytoplankton sustain more than 60% of the annual primary production in these areas, their contribution to the export production does not exceed 1% of the total. The differences in the seasonal plankton cycle among these regions come mainly from differences in the dynamics of large phytoplankton (here diatoms). In the ACC, the chlorophyll maximum remains <1.5 mg m⁻³, as an unfavourable light/mixing regime and a likely trace-metal limitation keep diatoms from blooming. In the northeast Pacific, trace-metal limitation seems to keep diatoms from blooming throughout the year. In both these systems, light or iron limitations induce high Si/N uptake ratios. Incidentally these high Si/N uptake ratios lead to a net excess of silicic acid utilization over nitrate, and to a subsequent silicic acid limitation during the summertime. In the North Atlantic, under favourable light/mixing regime and nutrient-replete conditions at the onset of the growing period, diatoms outburst and sustain a bloom >3.5 mg Chl-a m⁻³. Thereafter, mesozooplankton grazing pressure and silicic acid limitation induce the collapse of the chlorophyll maximum and the persistence of lower chlorophyll concentrations in summer. Although the ACC and the North Pacific show HNLC features, they support a high biogenic silica production (1.9 and 1.07 mol Si m⁻² yr⁻¹) and export flux (0.79 and 0.61 mol Si m⁻² yr⁻¹), compared to the North Atlantic (production: 0.23 mol Si m⁻² yr⁻¹, export: 0.12 mol Si m⁻² yr⁻¹). The differences in Si production and export between the HNLC systems and the mesotrophic North Atlantic come from both higher Si concentrations and Si/N uptake ratios in the HNLC areas compared to the North Atlantic. Also, the low dissolution rate of biogenic silica compared to nitrogen degradation rate, and the inhibition of nitrate uptake by ammonium, reinforce the net excess of silicic acid utilization over nitrate. As a result, the model also illustrates the efficiency of the silica pump for the three sites: about 50% of the biogenic silica synthesized in the euphotic layer is exported out of the first 100 m, while only 4–11% of the particulate organic nitrogen escapes recycling in the surface layer.  相似文献   

Anthropogenic increases of catchment nitrogen and phosphorus loads in New Zealand     

Ton H. Snelder  Scott T. Larned  Rich W. McDowell 《新西兰海洋与淡水研究杂志》2018,52(3):336-361

Spatial regression models were used to predict yields (kg?ha^?1?yr^?1) of nitrogen (N) and phosphorus (P) discharged from catchments throughout New Zealand under natural and current conditions. The models were derived using loads (kg?yr^?1) of TN, NO₃-N, TP and DRP calculated for 592 river water quality monitoring sites. Anthropogenic increases in yields above natural levels were associated with the proportions of catchments occupied by the intensive agricultural land cover and were unevenly distributed across regions. Anthropogenic increases in national loads of TN, NO₃-N, TP and DRP exported to the ocean were 74%, 159%, 48% and 18%, respectively. Increases in loads exported to the ocean varied considerably at smaller scales, with catchments having significant load increases between 4- and 26-fold for N and 6- to 9-fold for P. Predictions of yields and loads reported here have utility in the development of strategies to manage nutrients.  相似文献   

Ambient iron concentration regulates the sulfate reducing activity in the mangrove swamps of Diwar,Goa, India     

Kuldeep Attri  Savita Kerkar  P.A. LokaBharathi 《Estuarine, Coastal and Shelf Science》2011

In order to test the hypothesis that the ambient iron concentrations could regulate sulfate reducing activity (SRA) in mangrove areas, 10 cm cores were examined from test and reference sites. The test site at Diwar mangrove ecosystem is highly influenced by iron released by the movement of barges carrying iron ore during the non-monsoon seasons and the reference site at Tuvem is relatively pristine. The average iron concentrations were 17.9% (±8.06) at Diwar and 6.3% (±1.5) at Tuvem. Sulfate reducing rates (SRR) ranged from 50.21 to 698.66 nM cm⁻³ d⁻¹ at Tuvem, and from 23.32 to 294.49 nM cm⁻³d⁻¹ in Diwar. Pearson’s correlation coefficients between SRR and environmental parameters showed that at Tuvem, the SRR was controlled by SO₄⁻² (r = 0.498, p < 0.001, n = 60) more than organic carbon (r = 0.316 p < 0.05, n = 60). At Diwar, the SRR was governed by the iron concentrations at an r-value of −0.761 (p < 0.001, n = 60), suggesting that ca.58% of the variation in SRR was influenced negatively by variations in ambient iron concentrations. This influence was more than the positive influence of TOC (r = 0.615, p < 0.001, n = 60). Laboratory experiments to check the influence of iron on SRR also supported our field observations. At an experimental manipulation of 50 ppm Fe³⁺ there was an increase in SRR but at 100 ppm an inhibitory effect was observed. At 1000 ppm Fe³⁺ there was a decrease in the SRR up to 93% of the control. Thus, our study showed that ambient iron concentrations influence SRR negatively at Diwar and counters the positive influence of organic carbon. Consequently, the influence could cascade to other biogeochemical processes in these mangrove swamps, especially the mineralization of organic matter to carbon dioxide by sulfate respiration.  相似文献