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1.
A 22-month study was conducted to determine the exchange of nitrogen and phosphorus between a mesohaline vegetated marsh in the Carter's Creek area of Virginia and the surrounding estuary, focusing on the role of the vegetated marsh surface in the processing of these constituents. On an annual basis there was a removal of NH4+, PO43?, NO3?, dissolved organic nitrogen, dissolved organic phosphorus, particulate nitrogen and particulate phosphorus from the tidal water as it resided on the vegetated marsh. Only nitrite was transported from the marsh to the estuary. Most of the nitrogen and phosphorus species showed distinct seasonal trends with respect to the direction of transport except nitrate and orthophosphate. The ammonium flux data indicates that this nutrient was removed from the inundating water during late spring and fall, with a slight release of this constituent into the tidal water during the late summer. The transport of nitrite was from the estuary to the marsh for most of the year except during the fall. The large release of this nutrient into the tidal water at this time is associated with the senescence of the marsh vegetation. There was a large removal of DON from the tidal water during the fall, while the flux of DOP was from the estuary to the marsh for most of the year except during the summer. The largest removal of particulate nitrogen and phosphorus from the tidal water occurred during the summer months when the turbidity of the tidal water was highest, especially when wave scouring of the mudflats brings material into the water column. A loss of particulate nitrogen from the marsh to the estuary was evident during the fall and winter.  相似文献   

2.
Tidal exchanges of nitrogen, phosphorus, and organic carbon by a high and a low elevation marsh in the Rhode River estuary were measured throughout the year. Both marshes tended to import particulate matter and export dissolved matter, although they differed in the fluxes of certain nutrients. Compared with tidal exchanges, bulk precipitation was a major source of ammonia and nitrate and a minor source of other nutrients. There was a net retention of nutrients by the portion of the Rhode River that included both marshes and a mudflat. However, the marshes accounted for only 10% of the phosphorus retention and 1% of the nitrogen retention while they released organic carbon amounting to 20% of the retention. This suggests that the mudflat acted as a sink for nutrients. The primary role of the marshes seems to be transformation of particulate to dissolved nutrients rather than nutrient retention or release.  相似文献   

3.
This study addresses the impact marshes have on the dissolved oxygen content of tidal waters, particularly during summer when respiratory demand for oxygen in adjacent coastal waters is at a maximum and the solubility of oxygen is lowest. The net transports of dissolved oxygen, salt and heat have been measured for 65 tidal cycles during late spring and summer for a small (0·14 km2) salt marsh basin near North Inlet, S.C. The results indicate that export of dissolved oxygen occurs only on tidal cycles that begin between 2:00 am and 10:00 am such that high tide occurs within 4 h of noon. The largest exports of oxygen and heat are produced by spring tides beginning near sunrise. Although the time window for oxygen export is only about 8 h in duration, there is a more or less overall long-term balance between export and import because the magnitude of oxygen export is about 25% greater than import. The magnitude of heat export similarly exceeds heat import but because the time windows for heat export and import are equal, there is an overall export of heat. This study thus suggests that in summer salt marshes of the Atlantic coast export heat and are in balance with respect to the export and import of dissolved oxygen. However, because of the interaction of the diurnal tide with the daily cycle of solar radiation, transient dissolved oxygen concentrations in tidal waters can range from 1.5 to 10.0 ppm. Thus loading of additional oxygen consuming materials to these waters possibly could lead to significant periods of anoxia.  相似文献   

4.
Water flows, concentrations of total (TOC), dissolved (DOC), and particulate (POC) organic carbon and seston were monitored for 52 diel periods in the single creek draining a 270-ha Spartina patens-Distichlis spicata marsh on the upper Texas coast. Rainfall, creek water flows, and water levels in the creek and on the marsh were measured by recording instruments.Rainfall accounted for most marsh flooding, and water outflow was significantly correlated with both rainfall and marsh water level. Creek flows were predominantly outward because microtopographic features and dense vegetation restricted overmarsh water flows and thereby reduced tidal flooding while extending the time of precipitation runoff. Concentrations of organic carbon in water leaving the marsh were highest in spring and summer and averaged 25·62, 21·41 and 3·35 mg l?1 of TOC, DOC and POC, respectively. These were 9·34, 9·93 and 0·04 mg l?1, respectively, higher than bay water. Most POC was 0·3–28 μm in diameter. Seston > 28μ leaving the marsh was 95% amorphous material; the rest was plankton, grass particles and fecal pellets. Loss of organic carbon was directly correlated with net water flux, and thus rainfall accounted for most carbon loss. Net carbon loss averaged 196 kg TOC, 150 kg DOC and 32 kg POC per day. Net annual loss was 2·4–5·5% of net aerial primary productivity (NAPP), or 21·55-30·09 g TOC m?2 year?1.Export from this marsh falls within the range found for other marshes and the data collectively indicate that coastal marshes are not losing as much organic carbon as has been suggested by indirect measurements. The discrepancy between potential and realized export is explained by the fact that export is not a simple removal of excess detritus by tidal action but is a more complicated process mediated by the interaction of additional factors such as rainfall, vegetation structure, microtopographic variation and decomposition, which can serve to reduce the amount and quality of NAPP exported.  相似文献   

5.
Water column concentrations of total suspended solids (TSS), particulate organic carbon (POC) and particulate nitrogen (PN) were measured at three different depths in four different locations bracketing the estuarine turbidity maximum (ETM) along the main channel of a temperate riverine estuary (Winyah Bay, South Carolina, USA). Measurements were carried out over full tidal cycle (over 24 h). Salinity, temperature, current magnitude and direction were also monitored at the same time throughout the water column. Tidally averaged net fluxes of salt, TSS, POC and PN were calculated by combining the current measurements with the concentration data. Under the extreme low river discharge conditions that characterized the study period, net landward fluxes of salt were measured in the lower part of the study area, suggesting that the landward transport through the main channel of the estuary was probably balanced by export out through the sides. In contrast, the net fluxes of salt in the upper reaches of the study area were near zero, indicating a closed salt balance in this part of the estuary. In contrast to salt, the net fluxes of TSS, POC and PN in the deeper parts of the water column were consistently landward at all four sites in Winyah Bay indicating the non-conservative behavior of particulate components and their active transport up the estuary in the region around the ETM.The carbon contents (%POC), carbon:nitrogen ratios (org[C:N]a) and stable carbon isotopic compositions (δ13CPOC) of the suspended particles varied significantly with depth, location and tidal stage. Tidally averaged compositions showed a significant increase up the estuary in the %POC and org[C:N]a values of suspended particles consistent with the preferential landward transport of carbon-rich particles with higher vascular plant debris content. The combination of tidal resuspension and flood-dominated flow appeared to be responsible for the hydrodynamic sorting of particles along the estuary that resulted in denser, organic-poor particles being transported landward less efficiently. The elemental and isotopic compositions indicated that vascular C3 plants and estuarine algae were the major sources of the particulate organic matter of all the samples, without any significant contributions from salt marsh C4 vegetation (Spartina alterniflora) and/or marine phytoplankton.  相似文献   

6.
We construct a one-dimensional ecosystem model (nitrate, ammonium, phytoplankton, zooplnakton and detritus) with simple physics and biology in order to focus on the structural relations and intrinsic properties of the food web that characterizes the biological regime in the central equatorial Pacific at 140°W. When possible, data collected during the EgPac and other cruises were used to calibrate model parameters for two simulations that differ in the limiting nutrient, i.e. nitrogen or iron. Both simulations show annual results in good agreement with the data, but phytoplankton biomass and primary production show a more pronounced annual variability when iron is used as the limiting nutrient. This more realistically reproduces the variability of biological production and illustrates the greater coupling between vertical physical processes and biological production when the limiting nutrient is iron rather than nitrogen. The iron simulation also illustrates how iron supply controls primary production variability, how grazingbalances primary production and controls phytoplankton biomass, and how both iron supply and grazingcontrol primary production. These results suggest that it is not possible to capture primary production variability in the central equatorial Pacific with biological models using nitrogen as the limiting nutrient. Other indirect results of this modeling study were: (1) partitioning of export production between dissolved and particulate matter is almost equal, suggesting that the importance of DOC export may have been previously overestimated; (2) lateral export of live biomass has to be taken into account in order to balance the nitrogen budget on the equator at 140°W; and (3) preferential uptake of ammonium (i.e. nitrate uptake inhibition by ammonium) associated with high regeneration of nitrogen (low f ratio as a consequence of the food web structure imposed by iron limitation) largely accounts for the surface build-up of upwelled nitrate.  相似文献   

7.
Water samples were collected at 15 min intervals over 11 tidal cycles from a tidal creek draining the mangrove-covered basin of Tuff Crater, Auckland, New Zealand. The samples were filtered and total suspended sediment (TSS), inorganic suspended sediment (ISS) and organic suspended sediment (OSS) were determined. Variation in TSS was high, the concentration varied over a tidal cycle and during over-bank flows concentrations were lowest at or near slack high water. Covariance between TSS concentrations and velocity and discharge meant that the calculation of particulate matter flux over tidal hemicycles was particularly dependent on the method of estimating tidal flux. The hypsometrically-based volumetric method was found to be inappropriate, predicting a positive budget (import) more often than observed. Instead particulate matter budgets were calculated by means of the velocity-area method and indicate a net export of TSS, ISS and OSS. Floating macrodetritus was observed on both the flood and ebb tides, but a net export was found on the two tides monitored. It is considered that on an annual basis floating macrodetritus export accounts for less than 2% of the detrital production in the basin, and organic suspended sediment export from the basin is less than 3 kg C ha?1 day?1 and is below the rate of detrital production. It is implied that a proportion of the organic detritus produced in this basin is degraded and recycled in situ.  相似文献   

8.
Studies of the concentrations of particulate and dissolved organic carbon in the Duplin River, of the tidal exchange of POC and DOC in the marsh, of the standing stock and movement of Spartina alterniflora wrack in the Duplin, and of the removal of carbon from the surface of the marsh by rain were conducted at Sapelo Island, Georgia in order to test three hypotheses about export of carbon from the Duplin River watershed. We found that the gradients in POC and DOC concentrations are such that carbon is being transported down the Duplin River throughout the year, although in smaller quantities than previously believed. In contrast, almost all tidal exchanges within the marsh result in deposition of carbon. Most of this deposited carbon is subsequently eroded as a result of rain falling on the exposed marsh surface, and is washed back into the tidal creeks. This cycle of deposition and erosion is a possible mechanism keeping POC in the thin aerobic surface layer of the marsh, thus increasing its availability to detritivores and aerobic microbes. The standing stock of wrack is only a fraction of the S. alterniflora produced each year, and its export is a negligible term in the carbon balance equation.  相似文献   

9.
Nutrient concentrations in interstitial water were measured throughout the year in two brackish tidal marshes differing in elevation and vegetation. At all sites, sulfate to chloride ratios were lowest during the fall. In contrast, dissolved ammonia, phosphate, organic nitrogen, and organic phosphorus concentrations did not vary seasonally but differed among sample sites. These nutrients were generally enriched in interstitial water relative to tidal water and those that were most enriched declined in concentration with increasing proximity to creeks. In the low elevation marsh, flow of interstitial water towards creek banks was traced with Rhodamine WT dye. Consequent seepage of interstitial water into the creek of the low marsh was estimated from continuous monitoring of water table heights and from measurements of hydraulic conductivity. The estimated seepage could account for a portion, probably less than half, of the tidal export of dissolved nutrients from the low marsh.  相似文献   

10.
Transport processes were studied in a gully between a salt marsh and an estuary. After storm tides, ebb currents in the gully reached high values. It is concluded that particulate matter (both organic and inorganic) are imported into the marsh. Coarse organic debris is exported during storm tides, but this amount is low when compared with the primary production on the marsh. Exports are shown for dissolved organic carbon, ammonia, phosphate and silica, while nitrate and possibly nitrite are imported. Organic matter derived from in situ production and net import is buried and partly mineralized in the marsh.  相似文献   

11.
In coastal ecosystems, denitrification is a key process in removing excess dissolved nitrogen oxides and participating in the control of eutrophication process. Little is known about the role of salt marshes on nitrogen budgets in cold weather coastal areas. Although coastal salt marshes are important sites for organic matter degradation and nutrient regeneration, bacterial-mediated nitrogen cycling processes, such as denitrification, remain unknown in northern and sub-arctic regions, especially under winter conditions. Using labelled nitrogen (15N), denitrification rates were measured in an eastern Canadian salt marsh in August, October and December 2005. Freshly sampled undisturbed sediment cores were incubated over 8h and maintained at their sampling temperatures to evaluate the influence of low temperatures on the denitrification rate. From 2 to 12 degrees C, average denitrification rate and dissolved oxygen consumption increased from 9.6 to 25.5 micromol N2 m-2 h-1 and from 1.3 to 1.8 mmol O2 m-2 h-1, respectively, with no statistical dependence of temperature (p>0.05). Nitrification has been identified as the major nitrate source for denitrification, supplying more than 80% of the nitrate demand. Because no more than 31% of the nitrate removed by sediment is estimated to be denitrified, the presence of a major nitrate sink in sediment is suspected. Among possible nitrate consumption mechanisms, dissimilatory reduction of nitrate to ammonium, metal and organic matter oxidation processes are discussed. Providing the first measurements of denitrification rate in a St. Lawrence Estuary salt marsh, this study evidences the necessity of preserving and restoring marshes. They constitute an efficient geochemical filter against an excess of nitrate dispersion to coastal waters even under cold northern conditions.  相似文献   

12.
The aim of the present study was to investigate seasonal and spatial patterns of soil oxygen consumption, nitrification, denitrification and fluxes of dissolved inorganic nitrogen (DIN) in a tidal salt marsh of the Lagoon of Venice, Italy. In the salt marsh, intact soil cores including overlying water were collected monthly at high tide from April to October in salt marsh creeks and in areas covered by the dominant vegetation, Limonium serotinum. In May, cores were also collected in areas with vegetation dominated by Juncus maritimus and Halimione portulacoides. In laboratory incubations at in situ temperature in the dark, flux rates of oxygen and DIN were monitored in the overlying water of the intact cores. 15N-nitrate was added to the overlying water and nitrification and denitrification were measured using isotope-dilution and -pairing techniques. The results show that highest soil oxygen consumption coincided with the highest water temperature in June and July. The highest denitrification rates were recorded in spring and autumn coinciding with the highest nitrate concentrations. Soil oxygen consumption and nitrification rates differed between sampling sites, but denitrification rates were similar among the different vegetation types. The highest rates were recorded in areas covered with L. serotinum. Burrowing soil macrofauna enhanced oxygen consumption, nitrification and denitrification in April and May. The data presented in this study indicate high temporal as well as spatial variations in the flux of oxygen and DIN, and nitrogen transformations in the tidal salt marshes of the Venice lagoon during the growth season. The results identify the salt marshes of the Venice lagoon as being metabolically very active ecosystems with a high capacity to process nitrogen.  相似文献   

13.
The daily concentrations of NH4+, NO3?, and NO3? + NO2? within the North Inlet system are all negatively associated with tidal stage during the late summer, this association breaking down during the winter. The high concentrations of these constituents during low tide coupled with the lack of streamflow during the late summer suggests that there is an internal source for these species. Ammonium and orthophosphate most likely have their source in sediment diffusion from tidal creek sediments and/or seepage from the vegetated marsh surface during tidal exposure. It is hypothesized that high nitrate plus nitrite values at low tide are caused by nitrification within the tidal water or tidal creek sediments. During the summer there is evidence for a source of dissolved organic nitrogen and dissolved organic phosphorus within the North Inlet system, probably via diffusion from creek sediments. In general the main source of dissolved organic nitrogen is via stream-flow from the adjacent watershed. Particulate nitrogen and phosphorus concentrations are a function of: (1) wind and rain events which cause resuspension of particulate material from the tidal creek banks, (2) rain events which scour the marsh surface during tidal exposure, and (3) high tidal velocities which scour the creek bottoms.  相似文献   

14.
We use inverse analysis to model carbon and nitrogen flows in the upper ocean food web at Ocean Station Papa (OSP; 50°N, 145°W) for winter, spring, and late summer. The seasonal variability in basic physical, chemical, and biological characteristics is low, and the particulate carbon and nitrogen flux at 200 m is remarkably constant. Despite this apparent uniformity, the food web structure undergoes significant seasonal changes. The diversity of trophic pathways is higher during late summer than during the other two periods. The spring ecosystem is not in steady state and undergoes net phytoplankton growth and macronutrient consumption. The microbial loop is well developed only during late summer. Nevertheless, ammonium regeneration by the food web seems insufficient to meet demand by the primary producers. The difference may be due to recycling of dissolved organic nitrogen (urea+free amino acids), a process not represented in the model. The winter food web is the closest to steady state, with nitrate utilisation approximately in balance with export of particulate nitrogen. The inverse analysis suggests two main seasonally invariant features of the NE Pacific ecosystem. First, the major trophic pathway is always from picophytoplankton (0.2–5 μm) to microzooplankton (heterotrophic dinoflagellates and ciliates) to mesozooplankton. This supports the idea of a strong coupling between the microbial and metazoan food webs. Second, much of the primary production (and bacterial production in late summer) is not grazed and is recycled through the detrital pool. Both these features seem to arise from the requirement to conserve nitrogen as well as carbon in the food web. More complete measurements on the microzooplankton 20–200 μm in size, including the small metazoans like nauplii larvae, are required to improve the models presented here.  相似文献   

15.
Mercury fluxes between an impacted coastal lagoon and the Atlantic Ocean   总被引：1，自引：1，他引：0  
The objective was to estimate the seasonal and inter-tidal variability of dissolved and particulate mercury fluxes between the Ria de Aveiro (Portugal) and the Atlantic Ocean. The mercury fluxes were estimated by means of a two-dimensional vertically integrated hydrodynamic model. Results showed that the particulate fraction plays an important role in the transport of mercury while the contribution of the seston fraction to the transport of mercury was always <0.5%. During spring tides, in summer, about 2% of mercury transported in seston was present in an organic form. The mass balance for the mercury fractions revealed that the mercury export to the Atlantic Ocean varied with season and tidal regime, mainly in terms of the relative importance of the dissolved and particulate fractions. An approximate range of values for the annual mass balance between 42 and 77 kg shows that the export of dissolved and particulate mercury makes little impact on the near shore region of the Atlantic Ocean and that the recovery of the lagoon from mercury contamination is likely to remain a long-term issue.  相似文献   

16.
The present study investigates the differences between nutrient fluxes and particulate organic matter within an artificial reef system (AR) deployed in August 2002 off Faro (Algarve, Southern Portugal) and in a non-reef area (NRA), and how fluxes and suspended material may be affected by the hydrodynamic regime. Surveys to collect sediment cores, suspended/settled particles and overlying water samples were carried out by divers, from March (2006) to October (2007) in AR and NRA. Sediment cores and settled particles were collected to determine grain size, organic and inorganic carbon, nitrogen and phosphorus content. Overlying water and pore water samples were analysed for ammonium, nitrite, nitrate, phosphate, silicate, dissolved organic nitrogen, dissolved organic phosphorus and chlorophyll a. Results from the period studied showed that: (1) the benthic export of dissolved N, P and Si was 2–3 times higher at AR; (2) the particulate organic carbon (POC), nitrogen (PON) and phosphorus (POP) in suspended/settled particles were about 1.5 times higher at AR; (3) at both AR and NRA, the benthic export of dissolved N, P and Si, during a calm weather period, was 2–4 times higher than during or immediately after a storm event; and (4) at both sites, particulate organic compounds (POC, PON and POP) increased about 20 times during a storm event. These findings suggest that both the nutrients transport from sediment to water column and the quantity/quality of suspended/settled particles were highly dependent on the existence of reef structures and on the hydrodynamic regime.  相似文献   

17.
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18.
The preferential inorganic nitrogen source for the seagrass Zostera noltii was investigated in plants from Ria Formosa, South Portugal. Rates of ammonium and nitrate uptake were determined at different concentrations of these nutrients (5, 25 and 50 μm ), supplied simultaneously (NH4NO3) or separately (KNO3 and NH4Cl). The activity of the enzymes nitrate reductase (NR) and glutamine synthetase (GS) was also assessed. The results showed that ammonium is the preferential inorganic nitrogen source for Z. noltii, but, in the absence of ammonium, the species also has a high nitrate uptake capacity. The simultaneous availability of both inorganic nitrogen forms enhanced the uptake rate of ammonium and decreased the uptake rate of nitrate compared to when only one of the nitrogen forms was supplied. The activity of both enzymes was much higher in the leaves than in the roots, highlighting the importance of the leaves as primary reducing sites in the nitrogen assimilation process.  相似文献   

19.
Tidal marsh exchange studies are relatively simple tools to investigate the interaction between tidal marshes and estuaries. They have mostly been confined to only a few elements and to saltwater or brackish systems. This study presents mass-balance results of an integrated one year campaign in a freshwater tidal marsh along the Scheldt estuary (Belgium), covering oxygen, nutrients (N, P and Si), carbon, chlorophyll, suspended matter, chloride and sulfate. The role of seepage from the marsh was also investigated. A ranking between the parameters revealed that oxygenation was the strongest effect of the marsh on the estuarine water. Particulate parameters showed overall import. Export of dissolved silica (DSi) was more important than exchange of any other nutrient form. Export of DSi and import of total dissolved nitrogen (DIN) nevertheless contributed about equally to the increase of the Si:N ratio in the seepage water. The marsh had a counteracting effect on the long term trend of nutrient ratios in the estuary.  相似文献   

20.
Nutrient flux and budget in the Ebro estuary   总被引：1，自引：0，他引：1  
The Ebro river flows to the Mediterranean coast of Spain. During its final stretch, the Ebro behaves in a similar way to a highly stratified estuary. This paper describes the transport of nutrients to the Ebro estuary, evaluates the general movement of nutrients in the estuarine region, using a mass balance approach, and estimates the amounts of nutrients discharged to the coastal environment. Given the strong saline stratification, this study only includes the surface layer that contains the continental freshwater. The annual nutrient budget for the Ebro estuary shows a net excess for nitrogen and phosphorus, while silicate almost attains equilibrium between addition and removal. There are several reasons for gains in nitrogen and phosphorous: a contribution of dissolved and particulate compounds in the freshwater (some of which are mineralized); a lower uptake of phytoplankton indicated by chlorophyll reduction in the estuary; an entrainment of the nutrient-rich upper part of the salt wedge; and, to a lesser extent, the impact of wastewater and agricultural water use. The biggest load discharged into the Mediterranean Sea by the Ebro is nitrogen, followed by silicate with over 10 000 tons of each deposited annually. Phosphorus is discharged at relatively low concentrations and with an annual load of about 200 t yr−1.  相似文献   

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