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1.
Comprehensive bimonthly field surveys were carried out from September 2000 to June 2002 to study the seasonal dynamics and the inter-annual variability of dissolved inorganic nitrogen (DIN; nitrate, nitrite and ammonium) and dissolved inorganic phosphorus (DIP) in a subtropical mountain river system, the Danshuei tributary, the largest urbanized estuarine system in Taiwan. The headwaters were found to be well aerated, saturated with oxygen, with low ambient DIN (<9 μM) and DIP (<0.2 μM) concentration. As the river flows through the city of Taipei, the river becomes hypoxic because re-aeration rates cannot keep up with elevated oxygen consumption, and the concentrations of DIP (7.53 μM) and DIN (390 μM) increase drastically. Conservative mixing was mostly observed for silicate while DIP and DIN mostly showed non-conservative removal characteristics. Silicate originates from weathering and erosion of bedrocks in the watershed, whereas nitrogen- and phosphorus-bearing nutrients come mainly from urban discharges. Ammonium is the predominant dissolved nitrogenous species, ranging from 10 to 1000 μM. The nutrient chemistry is complex and dynamic due to anthropogenic perturbations and reactions in the tidally mixed zone of strong redox gradients. On average, the annual loading rates of dissolved phosphate and dissolved inorganic nitrogen from the Danshuei River to the ocean are 0.1 and 3.2 Gmol/year, respectively, which represent 0.1% and 0.2% of the world's total river discharge of dissolved inorganic nitrogen and phosphate.  相似文献   

2.
The spatial distributions of dissolved manganese and nutrients were examined in the Columbia River plume off Oregon and Washington during the summer of 2004 and 2005 as part of the River Influence on Shelf Ecosystems (RISE) program. Factors influencing the hydrochemical characteristics of the freshly formed and aged Columbia River plume were investigated. Hydrographic data and nutrient concentrations were used to delineate three distinct water sources for the Columbia River Plume: California Current surface water, coastal upwelled water, and Columbia River water. The warm, intermediate salinity, nutrient poor California Current water contains low levels of dissolved manganese (< 5 nM) and silicic acid (< 5 μM), and is depleted in nitrate. The cold, high salinity, nutrient rich, freshly upwelled water is highly variable (2–20 nM) in dissolved manganese and can be as high as  45 μM in silicic acid and  30 μM nitrate. The variable Columbia River has summer temperatures ranging from  13 to 24 °C, high silicic acid concentrations (ranging from  120 to 200 μM), and lower nitrate concentrations (ranging from  2 to 20 μM). During the summer, the concentrations of silicic acid and dissolved manganese can exceed 100 μM and 200 nM, respectively, in near-field Columbia River plumes. These values are markedly greater than those of surface coastal waters (even during upwelling conditions). As the plume advects and mixes, the concentrations of these two constituents remain relatively high within plume waters. The concentrations of dissolved manganese in the near-field plume vary with tidal amplitude, exhibiting much higher concentrations for a given salinity during spring tides than during neap tides. For example, the Columbia River plume at a salinity of 20 has a concentration of dissolved manganese of  240 nM during spring tides, as compared to only  60 nM during low amplitude tides. Silicic acid concentrations in the near-field plume remain relatively constant throughout the tidal month. Calculations indicate there is roughly an equivalent yearly delivery of dissolved manganese and silicic acid to the coastal waters off Oregon and Washington by upwelled waters and by the Columbia River plume.  相似文献   

3.
This work investigates the alkaline phosphatase activity in a littoral marine ecosystem (Toulon Bay and Le Niel Bay, France) in order to study its biochemical characteristics with respect to pH, sea water composition and phosphate sensitivity. We also characterise the active forms in sea water and determine the extent to which zooplankton generate phosphatase activity with respect to other plankton classes. In Toulon Bay, phosphatase was produced mostly by the microplankton fraction (>90 μm), accounting for more than 90% of total activity. In contrast, most of the phosphatase activity in Le Niel Bay was generated by the nanoplankton fraction (5–90 μm) and the picoplankton fraction (0.25–5 μm). The microplankton enzymes had non Michaelis-Menten kinetics suggesting the involvement of multiple enzyme processes with distinct kinetic constants. This activity is in major part secreted into the sea water and is stimulated by the ionic strength and the pH of the sea water. Cypris larvae of the genus Balanus played a special role in this release. For the nanoplankton and picoplankton, part of this activity was due to non-secreted enzymes, probably bound to membranes or occurring intracellularly. Moreover, nano and picoplankton phosphatase required higher pH than microplankton enzyme. For all plankton size classes, there was no activity at low pH, suggesting that acid phosphatases were not involved in reactions with substrates dissolved in water.  相似文献   

4.
Dissolved organic carbon (DOC), dissolved organic nitrogen (DON) and dissolved organic phosphorus (DOP) measured in deep profiles in the N-E Atlantic and in the N-W Mediterranean in the period 1984–2002 are described. After accurate validation, they show close agreement with those previously published.Classic profiles were obtained, with concentrations decreasing in deep waters. In the Mediterranean and in the Atlantic comparable concentrations were found in the 1500–2000 m waters, 44–46 μmol l−1 DOC, 2.6–2.8 μmol l−1 DON and 0.02–0.03 μmol l−1 DOP. In the surface layers, DOC concentrations were higher, but DON and DOP concentrations lower, in the Mediterranean than in the Atlantic, leading to higher element ratios in the Mediterranean. In autumn, values were, respectively, DOC:DON 17 vs. 14, DOC:DOP 950 vs. 500 and DON:DOP 55 vs. 35. The data suggest an increase in DOC and DON in the North Atlantic Central Water over 15 years, which may be linked to the North Atlantic climatic oscillations.Refractory DOM found in the 1500–2000 m layer exhibited C:N:P ratios of 1570:100:1. The labile+semi-labile (=non-refractory) DOM (nrDOM) pool was computed as DOM in excess of the refractory pool. Its contribution to total DOM above the thermocline in the open sea amounted to 25–35% of DOC, 30–35% of DON, and 60–80% of DOP. Element ratios of the nrDOM varied among stations and were lower than those of refractory DOM, except for C:N in the Mediterranean: nrDOC:nrDON 10–19, nrDOC:nrDOP 160–530 and nrDON:nrDOP 15–38. The specific stoichiometry of DOM in the Mediterranean led us to postulate that overconsumption of carbon is probably a main process in that oligotrophic sea.By coupling non-refractory DOM stoichiometry and relationships between the main DOM elements in the water column, the relative mineralization of C, N and P from DOM was studied. Below the thermocline, the preferential removal of phosphorus with regard to carbon from the semi-labile DOM can be confirmed, but not the preferential removal of nitrogen. In the ocean surface layers, processes depend on the oceanic area and can differ from deep waters, so preferential carbon removal seems more frequent. Bacterial growth efficiency data indicate that bacteria are directly responsible for mineralization of a high proportion of DON and DOP in the deep water.  相似文献   

5.
Alkaline phosphatase activity (APA) was determined in bulk particulate material and in a single-cell (ELF) assay at station L4 in the western English Channel during the summer of 2007. Throughout this period, the UK experienced its heaviest summertime rainfall since records began in 1914; with the result that riverine run-off into coastal waters was also elevated relative to long-term averages. Between May and August 2007, three distinct periods of elevated river run-off were observed which resulted in salinity minima at L4 on days 141, 190 and 232. An extended period of high river run-off between days 170 and 210 was responsible for decreases in near-surface salinity at L4 from 35.2068 to a minimum on day 190 of 34.7422. This contributed to the development of haline stratification which supported the development of an intense bloom of the centric diatom Chaetoceros debelis, with maximum observed chlorophyll a concentration of 8.69 μg l−1. Minima in salinity, and maxima in chlorophyll concentration on day 190 were coincident with a peak in river-derived dissolved inorganic nitrogen (DIN) of 1.9 μmol l−1 which was >5 times greater than the summertime mean and 24 times the concentrations experienced at L4 on weeks immediately before and after. There was no accompanying increase in dissolved inorganic phosphorus (DIP), and the DIN:DIP ratio increased to 49. With the inherent phosphorus stress that this caused, rates of APA increased from <4 to 42.4 nmolP l−1 h−1. ELF analysis on day 197 identified two taxa actively expressing alkaline phosphatase: the dinoflagellate Prorocentrum micans and ciliate Tiarana sp.  相似文献   

6.
Distribution of yttrium and rare earths in Florida Bay sediments   总被引：2，自引：1，他引：2  
The distribution of yttrium and rare earth elements (YREEs) in surface sediments was measured on samples collected from 40 stations in Florida Bay (June 2000 and February 2001). Florida Bay is the largest shallow carbonate estuary in South Florida with nearly pristine conditions. It receives fresh waters from some rivers and several canals from the Everglades which contribute rare earth elements and metals to the Bay. This paper is the first extensive study of YREEs in Florida Bay. Concentrations of YREEs (Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu) were determined by ICP-MS. The YREEs show a similar distribution pattern for the two months studied. The maximum concentrations were found in the western and north-central zones (near the Everglades) and the minimum concentrations were found in the south-central zone near the Florida Keys. The pattern of YREEs in Florida Bay sediments correlated strongly with those in the North American Shale Composite, indicating a dominant crustal source for these elements. However, the REE concentrations in Florida Bay sediments are depleted with respect to NASC. All REEs exhibited a strong correlation with Fe and Al from continental input and river runoff from the Everglades. The heavy REEs and Y showed a strong correlation with Al (R2 > 0.84). The light and medium REEs showed a strong correlation with Fe (R2 > 0.9). Correlations of all the YREEs with Mn were slightly lower (R2  0.7–0.75). The concentration of all the YREEs, Al and Fe are dependent on the bottom types and zones in the Bay, except Mn which decreases as it moves from the land to the sea.  相似文献   

7.
A series of experiments was conducted to evaluate the appropriateness of cross-flow ultrafiltration (CFUF) techniques for the determination of the phase speciation of monomethyl mercury (MeHg) in natural waters. Spiral-wound cartridge (Amicon S1Y1) and Miniplate (Amicon) were evaluated for their nominal molecular weight cut-offs of 1 and 10 kDa, respectively. The ultrafiltration behavior of standard macromolecules showed that the permeation of high molecular weight (HMW) organic macromolecules was not significant when a concentration factor (CF)>15 was used. The retention of low molecular weight (LMW) molecules was significant, especially at a low CF<5, suggesting that the use of a high CF (15) will minimize the retention of LMW molecules. Sorptive losses of MeHg in the solution phase to the 1 kDa membrane were negligible, but MeHg bound to HMW macromolecules was still retained (20%), even with a preconditioned membrane. The mass balance recovery of MeHg during ultrafiltration averaged 101±15% (n=7) and 105±14% (n=5) for the 1 and 10 kDa membranes, respectively. Sample storage over 24 h caused significant coagulation (47%) of the <10 kDa MeHg into the 10 kDa–0.45 μm colloidal or the particulate MeHg pool. The 1 kDa–0.45 μm colloidal MeHg in Galveston Bay and the Trinity River water samples accounted for 40–48% of the filter-passing MeHg, although the most abundant fraction (52–60%) of MeHg was the truly dissolved fraction (<1 kDa). The partition coefficient between the colloidal (1 kDa–0.45 μm) and truly dissolved MeHg (average log KC=5.2) was higher than the partition coefficient based on particle/filter-passing (average log KD=4.6) or particle/truly dissolved MeHg (average log KP=4.8), suggesting that MeHg has stronger affinity for natural colloids than macroparticulate materials (>0.45 μm).  相似文献   

8.
Based on lab-culture experiments analyzing limitation and combination of iron and phosphorus on the growth of Cryptomonas sp. (Cryptophyceae), and the study of accumulation and release of Fe-bound P in sediment cores collected from the marine region of the Pearl River Estuary, China, reasons for the high frequency of phytoplankton bloom therein are discussed. Results show that the combined effect of Fe and P can obviously accelerate algal development, and the optimum culture conditions maintaining maximum growth rate are 0.05 μM Fe and 50 μM P. Cellular contents of Fe and P is consistent and the P:Fe molar ratio is 159:1. The optimum range of the P:Fe molar ratio in culture experiments for cell incubation is 500–1400. The vertical trends of total Fe and total P variations in sediments are parallel. Fe-bound P is the main species of inorganic sedimentary P. Through continuous leaching with agitation, 34–80% of exchangeable P and 4–23% of exchangeable Fe are concurrently released from the surficial sediments. This is a possible way by which nutrients are made available to phytoplankton. These factors might be responsible for a high frequency of harmful algal blooms in the Pearl River Estuary.  相似文献   

9.
Particulate matter in aquatic systems is an important vehicle for the transport of particulate organic carbon (POC). Its accurate measurement is of central importance for the understanding of marine carbon cycling. Previous work has shown that GF/F-filter-based bottle-sample-derived concentration estimates of POC are generally close to or higher than large-volume in-situ-pump-derived values (and in some rare cases in subzero waters are up to two orders of magnitude higher). To further investigate this phenomenon, water samples from the surface and mid-water Northeast Atlantic and the Baltic Sea were analyzed. Our data support a bias of POC concentration estimates caused by adsorption of nitrogen-rich dissolved organic material onto GF/F filters. For surface-ocean samples the mass per unit area of exposed filter and composition of adsorbed material depended on the filtered volume. Amounts of adsorbed OC were enhanced in the surface ocean (typically 0.5 μmol cm− 2 of exposed filter) as compared to the deep ocean (typically 0.2 μmol cm− 2 of exposed filter). These dependencies should be taken into account for future POC methodologies. Bottle/pump differences of samples that were not corrected for adsorption were higher in the deep ocean than in the surface ocean. This discrepancy increased in summer. It is shown that POC concentration estimates that were not corrected for adsorption depend not only on the filtered volume, true POC concentration and mass of adsorbed OC, but also on the filter area. However, in all cases we studied, correction for adsorption was important, but not sufficient, to explain bottle/pump differences. Artificial formation of filterable particles and/or processes leading to filterable material being lost from and/or missed by sample-processing procedures must be considered. It can be deduced that the maximum amounts of POC and particulate organic nitrogen (PON) that can be artificially formed per liter of filtered ocean water are  3–4 μM OC (5–10% of dissolved OC) and  0.2–0.5 μM ON (2–10% of dissolved ON), respectively. The relative sensitivities of bottle and pump procedures, and of surface- and deep-ocean material, to artificial particle formation and the missing/losing of material are evaluated. As present procedures do not exist to correct for all possible biasing effects due to artificial particle formation and/or miss/loss of filterable material, uncertainties of filtration-based estimates of POC concentrations need further testing. The challenge now is to further constrain the magnitude of the biasing effects that add to the adsorption effect to reduce the uncertainties of estimates of POC concentrations, inventories and fluxes in the ocean.  相似文献   

10.
We report measurements of dissolved iron (dFe, <0.4 μm) in seawater collected from the upper 300 m of the water column along the CLIVAR SR3 section south of Tasmania in March 1998 (between 42°S and 54°S) and November–December 2001 (between 47°S and 66°S). Results from both cruises indicate a general north-to-south decrease in mixed-layer dFe concentrations, from values as high as 0.76 nM in the Subtropical Front to uniformly low concentrations (<0.1 nM) between the Polar Front and the Antarctic continental shelf. Samples collected from the seasonal sea-ice zone in November–December 2001 provide no evidence of significant dFe inputs from the melting pack ice, which may explain the absence of pronounced ice-edge algal blooms in this sector of the Southern Ocean, as implied by satellite ocean-color images. Our data also allow us to infer changes in the dFe concentration of surface waters during the growing season. South of the Polar Front, a comparison of near-surface with subsurface (150 m depth) dFe concentrations in November–December 2001 suggests a net seasonal biological uptake of at least 0.14–0.18 nM dFe, of which 0.05–0.12 nM is depleted early in the growing season (before mid December). A comparison of our spring 2001 and fall 1998 data indicates a barely discernible seasonal depletion of dFe (0.03 nM) within the Polar Frontal Zone. Further north, most of our iron profiles do not exhibit near-surface depletions, and mixed-layer dFe concentrations are sometimes higher in samples from fall 1998 compared to spring 2001; here, the near-surface dFe distributions appear to be dominated by time-varying inputs of aerosol iron or advection of iron-rich subtropical waters from the north.  相似文献   

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