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1.
Experimental chambers were used in a Virginia salt marsh to partition the tidal flux of dissolved nutrients occurring at the marsh surface and in the water column. On five dates from June to October 1989, six replicate chambers in the short Spartina alterniflora zone were monitored over complete tidal cycles. When reservoir water, used to simulate tidal flooding in the chambers, was initially low in dissolved nutrients, the marsh surface was a source of both ammonium and phosphate to the water column. Calculations of the physical processes of diffusion and advection could not account for total nutrient release from the marsh surface. We hypothesize the primary source of nutrients was organic matter mineralization in surface sediments, which released nutrients into the flooding water column. Assimilation (uptake) of phosphate measured in water-column incubation experiments was nearly equal to phosphate released from the marsh surface. Surface release of ammonium, however, was somewhat greater than water-column uptake. In this salt marsh, benthic production and release of ammonium and phosphate is comparable in magnitude to pelagic consumption, thereby yielding only a small “net” transfer of these nutrients to the estuary.  相似文献   

2.
Salt marshes are an important transition zone between terrestrial and marine ecosystems, and in their natural state, they often function to cycle or trap terrestrially derived nutrients and organic matter. Many US salt marshes were ditched during the twentieth century, potentially altering their functionality. The goal of this 4-year study was to assess the impact of water from ditches within seven salt marshes on estuarine water quality and plankton communities within four estuaries on Long Island, NY, USA. We found that concentrations of inorganic nutrients (ammonium, phosphate), dissolved and particulate organic nitrogen and carbon (POC, PON, DOC, DON), and total coliform bacteria were significantly enriched in salt marsh ditches compared to the estuaries they discharged into. In addition, concentrations of ammonium and DON became more enriched in ditches as tidal levels decreased, suggesting these constituents were generated in situ. Quantification of nitrogen sources in Flanders Bay, NY, suggested salt marsh ditches could represent a substantial source of N to this estuary during summer months. Experimental incubations demonstrated that water from salt marsh ditches was capable of significantly enhancing the growth of multiple classes of phytoplankton, with large diatoms and dinoflagellates displaying the most dramatic increases in growth. Experiments further demonstrated that salt marsh ditchwater was capable of significantly enhancing pelagic respiration rates, suggesting discharge from ditches could influence estuarine oxygen consumption. In summary, this study demonstrates that tidal draining of salt marsh ditches is capable of degrading multiple aspects of estuarine water quality.  相似文献   

3.
This contribution presents a new perspective on water chemistry and its relation to tidal hydrology in marsh-dominated estuaries. Results are derived from both field and modeling experiments. A heuristic model based on a tidally-averaged advection-dispersion equation is used in conjunction with source-sink terms (for benthic, marsh surface, and open-water exchanges) to make predictions of nutrient concentrations in the water column. Spring-neap tidal contrasts are associated with significant changes in water-column chemistry for a variety of nutrients sampled during the growing season in the Parker River estuary (Massachusetts). For ammonium, phosphate, nitrate plus nitrite, total dissolved N, and total dissolved P, concentrations are significantly lower during spring tides (marshes flooded) than during neap tides (marshes unflooded). Model results indicate that physical changes and open-water processing are insufficient to produce the observed effect, and that explicit biogeochemical processing on marsh surfaces is required. Field observations of changes in nutrient to nutrient ratios with the onset of marsh inundation also support this conclusion. As tides progress from the neap to spring condition, a “spectrum” of trajectories emerges in salinity-nutrient plots developed from both observational datasets and model output. Care must therefore be exercised in designing sampling programs for water chemistry in marsh-dominated ecosystems and in interpreting the resulting mixing diagrams.  相似文献   

4.
The Columbia River estuary is characterized by relatively large tidal currents and water residence times of a few days or less. These and other environmental conditions tend to suppress water column productivity and favor the export of riverborne nutrients to the coastal ocean. However, hotspots of biological activity may allow for significant nutrient transformation and removal within the estuary, but these processes have previously been difficult to quantify due to the challenges of obtaining measurements at appropriate frequency and duration. In this study, nutrient biogeochemical dynamics within the salt-influenced region of the estuary were quantified using high-resolution in situ observations of nutrients and physical water properties. During 2010, three autonomous nutrient sensors (Satlantic SUNA, SubChem Systems Inc. APNA, WET Labs Cycle-PO4) that together measured nitrate?+?nitrite, orthophosphate, ammonium, silicic acid, and nitrite were deployed on fixed observatory platforms. Hourly measurements captured tidal fluctuations and permitted an analysis of river and ocean end-member mixing. The results suggested that during summer, the lower estuary released high concentrations of ammonium and phosphate despite low concentrations in the river and coastal ocean. This was likely a result of organic matter accumulation and remineralization in the estuarine turbidity maximum and the lateral bays adjacent to the main channel.  相似文献   

5.
Tidal freshwater sections of the Cooper River Estuary (South Carolina) include extensive wetlands, which were formerly impounded for rice culture during the 1,700s and 1,800s. Most of these former rice fields are now open to tidal exchange and have developed into productive wetlands that vary in bottom topography, tidal hydrography and vegetation dominants. The purpose of this project was to quantify nitrogen (N) transport via tidal exchange between the main estuarine channel and representative wetland types and to relate exchange patterns to the succession of vegetation dominants. We examined N concentration and mass exchange at the main tidal inlets for the three representative wetland types (submerged aquatic vegetation [SAV], floating leaf vegetation, and intertidal emergent marsh) over 18-21 tidal cycles (July 1998–August 2000). Nitrate + nitrite concentrations were significantly lower during ebb flow at all study sites, suggesting potential patterns of uptake by all wetland types. The magnitude of nitrate decline during ebb flow was negatively correlated with oxygen concentration, reflecting the potential importance of denitrification and nitrate reduction within hypoxic wetland waters and sediments. The net tidal exchange of nitrate + nitrite was particularly consistent for the intertidal emergent marsh, where flow-weighted ebb concentrations were usually 18–40% lower than during flood tides. Seasonal patterns for the emergent marsh indicated higher rates of nitrate + nitrite uptake during the spring and summer (> 400 μmol N m-2 tide-1) with an annual mean uptake of 248 ± 162 μmol m–2 tide–1. The emergent marsh also removed ammonium through most of the year (207 ± 109 μmol m–2 tide–1), and exported dissolved organic nitrogen (DON) in the fall (1,690 ± 793 μmol m–2 tide–1), suggesting an approximate annual balance between the dissolved inorganic N uptake and DON export. The other wetland types (SAV and floating leaf vegetation) were less consistent in magnitude and direction of N exchange. Since the emergent marsh site had the highest bottom elevation and the highest relative cover of intertidal habitat, these results suggest that the nature of N exchange between the estuarine waters and bordering wetlands is affected by wetland morphometry, tidal hydrography, and corresponding vegetation dominants. With the recent diversion of river discharge, water levels in the upper Cooper estuary have dropped more than 10 cm, leading to a succession of wetland communities from subtidal habitats toward more intertidal habitats. Results of this study suggest that current trends of wetland succession in the upper Cooper River may result in higher rates of system-wide inorganic N removal and DON inputs by the growing distributions of intertidal emergent marshes.  相似文献   

6.
Tidal marsh functions are driven by interactions between tides, landscape morphology, and emergent vegetation. Less often considered are the diurnal pattern of tide extremes and seasonal variation of solar insolation in the mix of tidal marsh driver interactions. This work demonstrates how high-frequency hydroperiod and water temperature variability emerges from disparate timescale interactions between tidal marsh morphology, tidal harmonics, and meteorology in the San Francisco Estuary. We compare the tidal and residual flow and temperature response of neighboring tidal sloughs, one possessing natural tidal marsh morphology, and one that is modified for water control. We show that the natural tidal marsh is tuned to lunar phase and produces tidal and fortnight water temperature variability through interacting tide, meteorology, and geomorphic linkages. In contrast, temperature variability is dampened in the modified slough where overbank marsh plain connection is severed by levees. Despite geomorphic differences, a key finding is that both sloughs are heat sinks in summer by latent heat flux-driven residual upstream water advection and sensible and long-wave heat transfer. The precession of a 335-year tidal harmonic assures that these dynamics will shift in the future. Water temperature regulation appears to be a key function of natural tidal sloughs that depends critically on geomorphic mediation. We investigate approaches to untangling the relative influence of sun versus tide on residual water and temperature transport as a function of system morphology. The findings of this study likely have ecological consequences and suggest physical process metrics for tidal marsh restoration performance.  相似文献   

7.
Transport of ammonium (NH4 +), nitrate + nitrite (NO3 ?), total Kjeldahl nitrogen (TKN), soluble reactive phosphate (SRP), and total suspended solids (TSS) was measured in a freshwater tidal bayou located in a marsh system near the mouth of the Atchafalaya River in Louisiana. Sampling was conducted six times over one year and was timed to assess effects of seasonal variation in river flow and mean sea level of the Gulf of Mexico on material fluxes. Net fluxes of all materials were large and ebb directed in all seasons except fall, when net transport was 2 to 3 orders-of-magnitude smaller than in any other season. These results demonstrate that riverine forcing was the primary influence on materials transport in all seasons except fall when tidal forcing was most important. The range of net fluxes (g s?1) for each nutrient was as follows (a negative sign indicates a net export toward the Gulf): NO3 ?, ?0.006 to ?6.69; TKN, 0.09 to ?10.41; NH4 +, ?0.02 to ?1.36; SRP, ?0.001 to ?0.53; TSS, ?2 to ?81. Analysis of nutrient concentrations indicated the marsh/aquatic system removed NO3 ?, SRP, and TSS from the water column from late spring through early fall and released NH4 + and TKN in summer. The results of this study show that net materials export per unit cross section channel area increased as riverine influence increased.  相似文献   

8.
Field experiments were completed to determine patterns of evapotranspirative water loss from salt and tidal freshwater marshes in Virginia. Water losses from “Mariotte systems” attached to open-water lysimeters and lysimeters vegetated by dominant marsh macrophytes were used to calculate hourly rates of open-water evaporation (Eo) and evapotranspiration (ET), respectively, during low tide. In the tidal freshwater marsh, ET was significantly greater than Eo (p=0.002, n=6); in the salt marsh, there were no differences between mean rates of ET and Eo (p=0.200, n=3). The ratio ET:Eo was highly correlated with leaf area index (LAI) (r2=0.82). In the tidal freshwater marsh, the amount of water loss due to plant transpiration was partitioned from total evapotranspiration by covering the water surface of the lysimeters with styrofoam beads. Measured transpiration rates in the tidal freshwater marsh were strongly correlated with leaf area index according to the following linear regression equation: T=0.355(LAI)?0.084 (r2=0.797, n=10). Because LAI was shown to be a good predictor of the relative increase in ET over Eo, it is likely that in vegetated tidal freshwater marshes with high leaf densities most atmospheric water loss comes from plants, not from the surface of the marsh. In salt marshes, low plant densities do not contribute substantially to atmospheric water loss, suggesting that paths of water transport and patterns of solute concentration in the subsurface environment are different compard to the tidal freshwater marsh.  相似文献   

9.
Surface films on marsh creeks form water-air interfaces of high biological activity. The development, movement, deposition, and breakup of the tidal creek surface film in a naturalSpartima alterniflora-dominated salt marsh in Delaware were followed seasonally over tidal cycles. The metabolic activity, i.e., photosynthesis and respiration, of the surface film and underlying water were determined in the field at the time of peak film formation, just prior to high tide, and the particulate material and chlorophylla were quantified over the tidal cycles. The quantities of organic and inorganic components of the particulate material were all significantly higher in the surface film than in the underlying water (on a volume basis). Numbers of algal cells and quantities of chlorophyll were orders of magnitude greater in the surface film than in the water column. Photosynthesis and respiration were significantly higher in the surface film than in the underlying water. The spectrum of fatty acids was more diverse and their total content was significantly greater in the surface film than in the water column, indicating a concentrated food source contributed by the film as well as a biological richness of the film. When water in the creek flooded the marsh plain at high tide, film deposition was greatest on simulated creek bankS. alterniflora stems, compared to stems along rivulets in the marsh and those in the marsh plain. Using surface film dry weight measurements on an areal basis and film velocity in the creek, both measured throughout a tidal cycle during the summer, it was determined that approximately 12 kg (dry weight) of particulate material moved on the creek surface (2 m wide) past a given point on the flood tide, and 14 kg moved in the opposite direction on the ebb tide. The biological and physical data collected in this study illuminate the contribution of the surface film to the biological (food web) and physical (sediment transport and deposition) functions of a salt marsh.  相似文献   

10.
Oceanic upwelling results in the intermittent intrusion of cold ocean water enriched in nitrate, and to a lesser extent soluble reactive phosphorus (SRP), into the Kariega Estuary (South Africa). Laboratory measocosm experiments were conducted to determine the effects of such changes on fluxes of dissolved nutrients across the surface of a salt marsh within the estuary. When replicate mesocosms of the tidal creek and salt marsh were inundated with nonupwelled water (at 25°C and nitrate concentrations of 4.5 μmoll?1), nitrate fluxes in both regions were small, and the tidal creek exhibited net uptake (negative value) of nitrate from the water column (?85 μmol m?2 tide?1), and the marsh, net release (positive values; 113 μmol m?2 tide?1). When the mesocosms were inundated with upwelled water, at 16°C and with nitrate concentrations of 24.2 μmol l?1, both regions exhibited large net uptakes of nitrate (?514 μmol m?2 tide?1 and ?226 μmol m?2 tide?1 for the tidal creek and salt marsh, respectively). In contrast to nitrate, the fluxes of nitrite, ammonium, and SRP were not significantly different under upwelling and nonupwelling conditions, probably because initial concentrations in the two water types were similar. To determine the extent to which the nitrate uptakes were caused by decreased water temperatures or increased concentrations of nitrate, experiments were conducted in which mesocosms were inundated with water with a range of nitrate concentrations (1.8–25 μmol l?1), at two temperatures representative of summer upwelling (16°C) and nonupwelling conditions (25°C). In both regions, the net fluxes of nitrate were positively correlated with initial concentrations of nitrate in the water column. For any given concentration, the fluxes at 16°C fell within the range of values at 25°C, indicating that the shifts in fluxes caused by upwelling occurred in response to increased concentrations in the water column and not reduced temperatures.  相似文献   

11.
A vertical two-dimensional, laterally averaged hydrodynamic and water quality model CE-QUAL-W2 was used to simulate water temperature, dissolved oxygen, electrical conductivity, chlorophyll a, total suspended solids, alkalinity, ammonium, phosphate, and total iron in the Sejnane Dam (North Tunisia) in response to external forcings that characterize main features of climate in the southern side of the Mediterranean Sea. The hydrodynamic modelling results show that the model is able to reproduce accurately the measured water surface elevation, spatio-temporal patterns of temperature, dissolved oxygen and other state of variables and to capture most of the seasonal changes in the reservoir. Three scenarios involving the impacts of severe drought season, summer rainfall and total suspended solids load on hydrodynamics and water quality are analyzed. Severe drought reduces the thickness of hypoxic waters from 10 to 2–4 m and shifts the temperature of the entire water column up to 5 °C during summer and about 1.2 °C in winter. The thermocline takes place 1 month before that of the reference and sinks to the bottom faster by 1–2 m per month. Summer rainfall dilutes the first waves of the autumn rains and disrupts the thermal gradient in the water column, which may show complex thermal structures. TSS load has the most negative effects on water quality in that it shifts the phosphorus concentration by 1–3 mg/l and promotes an early warming of surface water in spring and an early cooling since late summer by up to 1 °C. During summer stratification, it contributes to the cooling of the metalimnion by 2 °C on average, which may alter its structure and dynamics as an aquatic biotope.  相似文献   

12.
We investigated the historical ecology of Elkhorn Slough, a 1,200 ha tidal wetland system in central California. The goal of this study was to identify patterns of change in the extent and distribution of wetland habitats during a 150-yr period and to investigate the causes of these changes. Using a geographic information system (GIS), we interpreted historic maps, charts, and aerial photographs. We created a series of summary maps to illustrate and quantify changes in tidal flow and habitat types at six representative historical periods. With the aid of custom software tools, we performed semi-automated spatial analysis of historic aerial photographs to quantify changes in marsh cover at fixed quadrats and tidal creek width at fixed cross sections. Our multiscale analysis documents dramatic shifts in the distribution of habitat types resulting from anthropogenic modifications to the hydrology of the slough. More than half of the marshlands were diked, and more than two thirds have either degraded or been converted to other habitat types. The construction of an artificial mouth abruptly transformed the wetland system from depositional to highly erosional, enlarging channels, widening creeks, and converting marsh to intertidal mudflat or open water. Increased tidal amplitude and velocity are the likely causes. In recent decades, levee failure and intentional breaching have restored the acreage under tidal influence to nearly historic levels, but recolonization of former wetlands by salt marsh vegetation has been minimal. Degraded former marshland and unvegetated mudflat are now the dominant habitat types at Elkhorn Slough. The rate of habitat change remains high, suggesting that a new equilibrium may not be reached for many decades. This study can help tidal wetland managers identify patterns and mechanisms of habitat change and set appropriate conservation and restoration goals.  相似文献   

13.
This study provides new insights in the relative role of tidal creeks and the marsh edge in supplying water and sediments to and from tidal marshes for a wide range of tidal inundation cycles with different high water levels and for marsh zones of different developmental stage. Net import or export of water and its constituents (sediments, nutrients, pollutants) to or from tidal marshes has been traditionally estimated based on discharge measurements through a tidal creek. Complementary to this traditional calculation of water and sediment balances based on creek fluxes, we present novel methods to calculate water balances based on digital elevation modeling and sediment balances based on spatial modeling of surface sedimentation measurements. In contrast with spatial interpolation, the presented approach of spatial modeling accounts for the spatial scales at which sedimentation rates vary within tidal marshes. This study shows that for an old, high marsh platform, dissected by a well-developed creek network with adjoining levees and basins, flow paths are different for tidal inundation cycles with different high water levels: during shallow inundation cycles (high water level <0.2 m above the creek banks) almost all water is supplied via the creek system, while during higher inundation cycles (high water level >0.2 m) the percentage of water directly supplied via the marsh edge increases with increasing high water level. This flow pattern is in accordance with the observed decrease in sedimentation rates with increasing distance from creeks and from the marsh edge. On a young, low marsh, characterized by a gently seaward sloping topography, material exchange does not take place predominantly via creeks but the marsh is progressively flooded starting from the marsh edge. As a consequence, the spatial sedimentation pattern is most related to elevation differences and distance from the marsh edge. Our results imply that the traditional measurement of tidal creek fluxes may lead in many cases to incorrect estimations of net sediment or nutrient budgets.  相似文献   

14.
Ten years (1985–1994) of data were analyzed to investigate general patterns of phytoplankton and nutrient dynamics, and to identify major factors controlling those dynamics in the York River Estuary, Virginia. Algal blooms were observed during winter-spring followed by smaller summer blooms. Peak phytoplankton biomass during the winter-spring blooms occurred in the mid reach of the mesohaline zone whereas peak phytoplankton biomass during the summer bloom occurred in the tidal fresh-mesohaline transition zone. River discharge appears to be the major factor controlling the location and timing of the winter-spring blooms and the relative degree of potential N and P limitation. Phytoplankton biomass in tidal fresh water regions was limited by high flushing rates. Water residence time was less than cell doubling time during high flow seasons. Positive correlations between PAR at 1 m depth and chlorophylla suggested light limitation of phytoplankton in the tidal fresh-mesohaline transition zone. Relationships of salinity difference between surface and bottom water with chlorophylla distribution suggested the importance of tidal mixing for phytoplankton dynamics in the mesohaline zone. Accumulation of phytoplankton biomass in the mesohaline zone was generally controlled by N with the nutrient supply provided by benthic or bottom water remineralization.  相似文献   

15.
Transports of nitrate and suspended solids were measured six times from January 1984 until January 1985 in a small freshwater tidal bayou in south-central Louisiana. The bayou and adjacent marshes are influenced by Atchafalaya River discharges, tides, and coastal weather patterns. Large net ebb-directed water transports occurred in winter, spring, and summer, coincident with high river discharges, indicating riverine dominance. A very small net flood-directed water transport occurred in fall, indicating tidally dominated hydrology. Nitrate and suspended solids transports were net ebb-directed in all seasons, but were two orders of magnitude higher during high river flow. Exports changed as hydrology switched from river dominated to tidally dominated, and as concentrations of materials changed. Comparison of suspended solids and nitrate concentrations in the river and bayou shows that these materials were usually lower in the bayou, indicating retention by the marsh/aquatic system.  相似文献   

16.
Macronutrients and micronutrients were measured during the phytoplankton bloom period and then seasonally monitored after the bloom in the polluted Izmir Bay. Iron and the macronutrients (phosphate, ammonium, nitrate, nitrite, and silicate) were abundant in the waters of the inner and middle sections of Izmir Bay. The iron concentration decreased exponentially from the eutrophic inner bay to the oligotrophic outer bay. Suboxic–anoxic processes and the resuspension dynamics in the sediment were the most important factor in the control of iron, ammonium, and phosphate enrichment in the bay beside the anthropogenic activities. The biological removal of Fe in the inner and middle bay and nonbiological removal in the outer bay were effective in controlling iron concentration in Izmir Bay. The nitrate, nitrite, and ammonium nitrogen (N) and Si decreased to critical levels in the middle and outer bay at the end of the summer as long as the concentration of phosphate was high. The N/P ratios in the bay suggested that N might be the controlling nutrient for phytoplankton growth particularly in the middle and outer bay throughout summer. Furthermore, Si was also able to have controlling impact probably on diatom growth during autumn and winter in the inner and middle bay and in the early spring in the outer bay. The N/Si/Chelex labile Fe ratios implied that the iron could be a critical controlling nutrient for phytoplankton growth during early April in the outer bay unless the other macronutrients were low.  相似文献   

17.
In October of 2004, a 3-d observational program to measure flow and sediment resuspension within a coastal intertidal salt marsh was conducted in the North Inlet/Winyah Bay National Estuarine Research Reserve located near Georgetown, South Carolina. Current and acoustic backscatter profiles were obtained from a moored acoustic Doppler current profiler (ADCP) deployed in a shallow tidal channel during the spring phase of the tidal cycle under high discharge conditions. The channel serves as a conduit between Winyah Bay, a large brackish estuary, and North Inlet, a saline intertidal coastal salt marsh with little freshwater input. Salinity measurements indicate that the water column is vertically well mixed during flood, but becomes vertically stratified during early ebb. The stratification results from brackish (15 psu) Winyah Bay water entering North Inlet via the tidal channel, suggesting an exchange mechanism that permits North Inlet to receive a fraction of the poor water quality and high discharge flow from upland rivers. Although maximum flood currents exceed maximum ebb currents by 0.2 m s−1, suspended sediment concentrations are highest during the latter ebb phase and persist for a longer fraction of the ebb cycle. Even though the channel is flood-dominated, the higher concentrations occurring over a longer fraction of the ebb phase indicate net particulate transport from Winyah Bay to North Inlet during spring tide accompanied by high discharge. Our evidence suggests that the higher concentrations during ebb result from increased bed friction caused by flow asymmetries and variations in water depth in which the highest stresses occur near the end of ebb near low water despite stronger maximum currents during flood.  相似文献   

18.
The effect of tidal flooding on survival of juvenile muskrats (Ondatra zibethicus) was investigated in a brackish marsh in Louisiana by examining 50 muskrat lodges each month from July 1984 to June 1985 and tidal data over a 19-yr period. Tide levels increased at a rate of 1.58 cm yr?1 during the 19-yr period prior to the study, and during the study nest chambers in muskrat lodges were flooded on 43 d. Seventy-seven captured litters averaged 2.2±0.3 young per litter. older litters were less common than younger litters, but the number of young per litter did not differ among 5-d age classes, suggesting that mortality factors usually affected entire litters. The frequency of tidal flooding prior to opening of lodges each month was associated negatively with the number of litters and number of young per litter. If marsh subsidence and sea level rise continue, tidal flooding will become more prevalent and litter mortality will likely increase.  相似文献   

19.
The exchange of dissolved nutrients between marshes and the inundating water column was measured using throughflow marsh flumes built, in two microtidal Louisiana estuaries: the Barataria Basin estuary and Fourleague Bay. The flumes were sampled between September 1986 and April 1988, coincident with an extended period of low sea level on the Louisiana coast. The Barataria Basin estuary is in the later, deteriorating stage of the deltaic cycle, characterized by low freshwater inputs and subsiding marshes. Both brackish and saline marshes supplied dissolved organic nitrogen (DON), inorganic nitrogen (ammonium + nitrate + nitrite = DIN), dissolved organic carbon (DOC), and total nitrogen (as total Kjeldahl nitrogen = TKN) to the water column. The export of DIN is probably related to the N accumulated in earlier stages of deltaic development and released as these marshes deteriorate. Coastal brackish marshes of Fourleague, Bay, part of an accreting marsh system in an early, developmental stage of the deltaic cycle, exported TKN to the open water estuary in all samplings. This marsh apparently acted as a short-term buffer of DIN by taking up NH4 + in spring, when baywide concentrations were high, and supplying DIN to the estuary in summer and fall, when concentrations, in the bay were lower. Differences in phosphorus (P), DOC, and DON fluxes between these two estuaries were also observed. The Fourleague Bay site exported soluble reactive phosphorus (SRP) and total phosphorus (TP) and imported DOC. This P export may be related to remobilization of sediment-bound riverine P by the reducing, soils of the marshes. Fluxes of SRP at the Barataria Basin sites were variable and low while DOC was imported. Most imports of dissolved nutrients were correlated with higher upstream [source] concentrations, and flux rates were fairly consistent throughout the tide. Dissolved nutrient exports, did not correlate with upstream concentrations, though, and in many cases the flux was dominated by early, flood tide nutrient release. This pulsed behavior may be caused by rapid diffusion from the sediments early in the tidal cycle, when the sediment-water concentration gradient is largest. Interestuary differences were also seen in particulate organic matter fluxes, as the Fourleague Bay marsh exported POC and PON during all samplings while Barataria Basin imported these nutrients. In general, the magnitude and direction of nutrient exchanges in Louisiana marshes, seem to reflect the deltaic successional stage of the estuary.  相似文献   

20.
The amount of nitrogen present as ammonia, nitrate, nitrite, dissolved organic nitrogen, and particulate nitrogen was determined for nearshore Georgia shelf waters and for tidal water inundating a 0.5 hectare dikedSpartina alterniflora salt marsh in the adjacent estuary. Concentrations of ammonia, nitrate, and nitrite were comparatively low in offshore water (<2.2 μg-at N/1), and in high tide water in the marsh (<9.9 μg-at N/1). High concentrations of ammonia, up to 73.4 μg-at N/1, were measured in low tide water draining from marsh. The largest pools of nitrogen in offshore water and in high tide water in the marsh creek were dissolved organic nitrogen (DON) (2.5 to 20.4 μg-at N/1) and particulate nitrogen (PN) (0.1 to 30.0 μg-at N/1). Concentrations in marsh creek water at low tide were higher, ranging from 4.4 to 38.0 μg-at N/1 for DON and from 13.0 to 239.0 μg-at N/1 for PN. Comparisons of the average concentrations of dissolved and particulate forms of nitrogen in the marsh tidal creek during flood and during ebb tide suggested no net movement of the inorganic nitrogen nutrients, a net influx of PN to the marsh, and a net outflux of DON from the marsh.  相似文献   

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