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1.
The spatio-temporal variations in stable isotope signatures (??13C and ??15N) and C/N ratios of particulate organic matter (POM), and physicochemical parameters in a creek water column were examined in an estuarine mangrove ecosystem of Xuan Thuy National Park, Vietnam. The objective was to examine the factors influencing creek water properties, and the sources and exchange of POM in this important mangrove ecosystem. The diel and seasonal variations in water temperature, flow velocity, pH, dissolved oxygen, and salinity demonstrated that tidal level, season, and biological factors affected the creek water properties. Mangroves had relatively low ??15N and very low ??13C values, with respective average values of 1.5?±?0.9?? and ?28.1?±?1.4??. The low mangrove leaf ??15N indicated minor anthropogenic nitrogen loading to the mangrove forests. A significant positive correlation between POM?C??13C and salinity along the axis of Ba Lat Estuary, Red River, indicated that marine phytoplankton (??13C value, ?21.4?±?0.5??) was the predominant source of POM at the estuary mouth. Based on the co-variation of ??13C and C/N ratios, marine phytoplankton and mangrove detritus were predominant in POM of major creeks and small creeks, respectively. During the diurnal tidal cycle, the dynamics of POM were affected by sources of organic matter, tidal energy, and seasonal factors. The contribution of mangrove detritus to POM reached a maximum at the low tide and was enhanced during the rainy season, whereas marine phytoplankton contribution was highest at high tide.  相似文献   

2.
Statistical aspects of estimating net fluxes of nutrients between a salt marsh and a tidal creek on a tidal cycle basis and an annual basis are explored. For individual tidal cycles, the instantaneous flux of a nutrient is written in a constrained linear model as a function of time. The model is rewritten as an unconstrained model, and net flux is shown to be a linear combination of the parameters of the model. Standard linear models techniques can be used to make inferences about net fluxes on a tidal cycle basis. Considering a year as a finite population of tidal cycles, annual net flux can be estimated using a regression estimator. In the case of the flux of dissolved nitrite plus nitrate, the marsh was found to be a statistically significant sink for nitrogen (in this form) from adjacent tidal creeks.  相似文献   

3.
Multi-year nitrogen (N) and phosphorus (P) budgets were developed for the Patuxent River estuary, a seasonally stratified and moderately eutrophic tributary of Chesapeake Bay. Major inputs (point, diffuse, septic, and direct atmospheric) were measured for 13 years during which, large reductions in P and then lesser reductions in N-loading occurred due to wastewater treatment plant improvements. Internal nutrient losses (denitrification and long-term burial of particulate N and P) were measured in tidal marshes and sub-tidal sediments throughout the estuary as were nutrient storage in the water column, sediments, and biota. Nutrient transport between the oligohaline and mesohaline zones and between the Patuxent and Chesapeake Bay was estimated using a salt and water balance model. Several major nutrient recycling terms were directly and indirectly evaluated and compared to new N and P inputs on seasonal and annual time-scales. Major findings included: (1) average terrestrial and atmospheric inputs of N and P were very close to the sum of internal losses plus export, suggesting that dominant processes are captured in these budgets; (2) both N and P export were a small fraction (13% and 28%, respectively) of inputs, about half of that expected for N based on water residence times, and almost all exported N and P were in organic forms; (3) the tidal marsh-oligohaline estuary, which by area comprised ~27% of the full estuarine system, removed about 46% and 74% of total annual upland N and P inputs, respectively; (4) recycled N and P were much larger sources of inorganic nutrients than new inputs during warm seasons and were similar in magnitude even during cold seasons; (5) there was clear evidence that major estuarine processes responded rapidly to inter-annual nutrient input variations; (6) historical nutrient input data and nutrient budget data from drought periods indicated that diffuse nutrient sources were dominant and that N loads need to be reduced by about 50% to restore water quality conditions to pre-eutrophic levels.  相似文献   

4.
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   

5.
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   

6.
We conducted monthly bioassay experiments to characterize light and nutrient use efficiency of phytoplankton communities from the chlorophyll-a maximum located in the tidal freshwater region of the James River Estuary. Bioassay results were interpreted in the context of seasonal and inter-annual variation in nutrient delivery and biomass yield using recent and long-term data. Bioassay experiments suggest that nutrient limitation of phytoplankton production has increased over the past 20 years coinciding with reductions in point source inputs and estuarine dissolved nutrient concentrations. Despite increasing nutrient stress, chlorophyll concentrations have not declined due to more efficient nutrient usage. Greater CHLa yield (per unit of N and P) may be due to feedback mechanisms by which the presence of toxin-producing cyanobacteria inhibits grazing by benthic and pelagic filter-feeders. Seasonal patterns in nutrient limitation indicate that phytoplankton in the James respond to variations in inflow concentrations of dissolved nutrients. This association gives rise to an atypical pattern whereby the severity of nutrient limitation diminishes with low discharge in late summer due to minimal dilution of local point sources inputs by riverine discharge. We suggest that this may be a common feature of estuaries located in proximity to urbanized areas.  相似文献   

7.
An annual budget for dissolved silica (DSi) and biogenic silica (BSi) was constructed for the Scheldt estuary and for the entire riverine and estuarine Scheldt tidal system (Belgium/The Netherlands) using previously published silica concentrations and fluxes for the period 2003–2005. The annual estuarine DSi mass-balance was established, based on seasonal fluxes estimated using measured DSi concentrations and (fully transient) model simulations of conservative transport. The annual BSi mass-balance was deduced from measured BSi contents in the suspended particulate matter and annual mud fluxes taken from the literature. The Scheldt estuary acted as a net sink not only for the BSi carried by the tidal river as well as that produced by diatoms in the estuary, but also for large amounts of BSi imported from the coastal zone. This results in the retention of dissolved and biogenic silica higher than that of DSi alone, which is in contrast with the classical consideration that rivers act as a source of BSi for the coastal zone. DSi and silica (DSi + BSi) retentions amounted to, respectively, 28 and 64 % in the estuary, and 33 and 66 % in the entire tidal system. This study highlights thus the predominant role of the estuary in the entire Scheldt tidal system when dealing with silica dynamics, as well as the importance of including BSi when investigating estuarine silica retention.  相似文献   

8.
A 16-month study of estuarine habitats in poly-, meso-, and oligohaline salinity regimes near Charleston Harbor assessed the distribution and abundance of megalopae and early crab stages of the blue crab,Callinectes sapidus. Blue crab were sampled with a plankton net and a cylindrical drop sampler. Blue crab were most abundant in plankton collections at night, accounting for 68% of the megalopae and over 88% of the juveniles collected in day and night tows combined. At night, densities of megalopae were greatest in surface samples, whereas densities in daylight collections were greater on the bottom. Juvenile densities were greatest on the bottom in both day and night collections, although catch rates at night were more variable than those of the megalopae. This suggests that megalopae, and possibly juvenile stages, experience a diel vertical migration. Results indicate that ingress to estuarine nursery areas occurs at the megalopal stage. Megalopal densities were highest at the polyhaline site, while juvenile blue crab were most abundant in the oligohaline area. Habitat utilization by juvenile blue crab was estimated using a cylindrical drop sampler and Venturi suction pump on three bottom types in the intertidal zone. Densities were greatest over the sandy-mud substrate, although catch rates were much lower than those reported for other geographical areas. These results suggest that juvenile blue crab do not occur in abundance on the marsh surface but remain on the creek bottom, possibly because creek physiography and large tidal amplitudes may restrict accessibility to the marsh surface.  相似文献   

9.
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   

10.
Mangrove water biogeochemistry has been frequently studied under tropical climates, but less is known regarding mangroves in semi-arid climates. In this study, we examine the carbon and nutrient biogeochemistry in a mangrove tidal creek and in the main branch of a semi-arid estuary in New Caledonia. Porewater seepage represents a source of nutrients (DON, NH4 +, and DIP), carbon (DOC and CO2), and alkalinity for the water column, but seawater dilution of the mangrove inputs is observed. Spatial and tidal variations in CO2 fluxes along the tidal creek suggest that porewater seepage is a driver of CO2 emission into the atmosphere. Large seasonal and spatial differences in the biogeochemical functioning of the main channel are observed and are mainly related to the seasonal rainfall pattern. During the rainy season, the watershed influences the entire estuary, which exhibits a typical positive circulation. During the dry season, the estuary turns into a salt-plug region with positive and negative circulations in the upper and lower reaches, respectively. In this case, the upper and lower reaches seem to function independently, and the biogeochemical functioning of their water column is not controlled by the same processes. Surprisingly, pCO2@27 °C values tend to be higher during the dry season, as do the total alkalinity (TAlk) values, while the pH values exhibit an opposite trend. Moreover, the TAlk values are higher in the lower reaches during the wet season and in the upper reaches during the dry season. These results indicate high in situ biogeochemical reactions and high porewater influence during the dry season, likely because of a low flushing rate and high water residence time after salt plug establishment. Although our results suggest that salt plugs may significantly affect the water column’s biogeochemistry and may promote CO2 emissions of mangrove-derived carbon, further investigations, especially mass balance studies, are required to quantify their role in the biogeochemical functioning of such estuarine systems.  相似文献   

11.
Tillamook Bay, Oregon, is a drowned river estuary that receives freshwater input from 5 rivers and exchanges ocean water through a single channel. Similar to other western United States estuaries, the bay exhibits a strong seasonal change in river discharge in which there is a pronounced winter maximum and summer minimum in precipitation and runoff. The behavior of major inorganic nutrients (phosphorus, nitrogen, and silica) within the watershed is examined over seasonal cycles and under a range of river discharge conditions for October 1997–December 1999. Monthly and seasonal sampling stations include transects extending from the mouth of each river to the mouth of the estuary as well as 6–10 sites upstream along each of the 5 major rivers. Few studies have examined nutrient cycling in Pacific Northwest estuaries. This study evaluates the distributions of inorganic nutrients to understand the net processes occurring within this estuary. Based upon this approach, we hypothesize that nutrient behavior in the Tillamook Bay estuary can be explained by two dominant factors: freshwater flushing time and biological uptake and regeneration. Superimposed on these two processes is seasonal variability in nutrient concentrations of coastal waters via upwelling. Freshwater flushing time determines the amount of time for the uptake of nutrients by phytoplankton, for exchange with suspended particles, and for interaction with the sediments. Seasonal coastal upwelling controls the timing and extent of oceanic delivery of nutrients to the estuary. We suggest that benthic regeneration of nutrients is also an important process within the estuary occurring seasonally according to the flushing characteristics of the estuary. Silicic acid, nitrate, and NH4 + supply to the bay appears to be dominated by riverine input. PO4 −3 supply is dominated by river input during periods of high river flow (winter months) with oceanic input via upwelling and tidal exchange important during other times (spring, summer, and fall months). Departures from conservative mixing indicate that internal estuarine sources of dissolved inorganic phosphorus and nitrogen are also significant over an annual cycle.  相似文献   

12.
A study of the isotopic composition of plankton from Woods Hole Harbor was conducted to investigate seasonal variation in carbon and nitrogen stable isotopes in a shallow coastal environment. Stable isotopic ratios of carbon and nitrogen both showed temporal variation on the scale of weeks to months, with heaviest (most positive) values in summer to fall for both isotopes. Particulate organic matter (POM) δ13C values were highest (?19‰ to ?21‰) in August to November and lower (?21‰ to ?25‰) at other times of the year, while δ13N-POM values were highest (9.5‰ to 12‰) in March to September and lower (7.5‰ to 9.5‰) at other times of the year. Stable isotopic values were significantly correlated with temperature, DI13C, and C∶N ratios, but not with [DIC], [POC], [PN], [chlorophyll], or the taxonomic composition of the phytoplankton. There was no direct evidence of allochthonous inputs of carbon and nitrogen to the system. Woods Hole δ13C values were virtually identical to Georges Bank plankton values; similar POC: Chlorophyll and C∶N ratios in the two systems further suggest that Woods Hole Harbor is principally a marine system. The high δ13C values of net plankton (>20 μm) during summer and early fall are consistent with a smaller degree of photosynthetic isotopic fractionation at that time, related to temperature and/or [CO2(aq)]. This pattern was not seen, however, in total POM. Plankton δ13N values were higher in Woods Hole Harbor than on Georges Bank, especially during warmer periods, possibly due to high rates of nitrification and organic matter recycling in Woods Hole waters. Relatively wide ranges of stable isotopic values from both Woods Hole Harbor and Georges Bank suggest that seasonality should be considered when attempting to establish endmember C and N isotopic values for temperate marine plankton. Preliminary results from size-fractionated samples suggest that cyanobacteria may fractionate carbon isotopes to a greater degree than net phytoplankton.  相似文献   

13.
We compared the distribution and nutrient status of native haplotype F ofPhragmites australis along the freshwater to mesohaline tidal marsh gradient of the Rappahannock River, Virginia, for comparison with the nonnative, invasive haploty M. Using GIS analysis of aerial photography and GPS-based ground truthing, we identified 55 separate clones of native haplotype F comprising a total of 3.68 ha (range 0.002–0.734 ha), all found in tidal wetlands where surface water salinity was 0 psu. We identified 219 separate clones of the invasive haplotype M covering 68.3 ha along the same stretch of river (range 0.004–11.86 ha), found in wetlands where salinity ranged from 0 to 11 psu. From 15 separate clones for each haplotype, average carbon content in leaves of the native was significantly higher than the invasive (43.90±0.08% versus 42.82±0.15%, F1,28=20.938, p<0.01), and nitrogen content was significantly lower (2.22±0.03% versus 2.58±0.07%, F1,28=11.972, p<0.01). The average C:N:P ratio for leaf tissue was 1100∶48∶1 for haplotype F and 1084∶56∶1 for haplotype M. Relative to the native, the invasive haplotype forms larger stands distributed throughout a broader estuarine reach and incorporates more nitrogen in leaf tissue. From a management standpoint, nativePhragmites protection should focus on deterring nonnative haplotype invasion through the minimization of both adjacent upland disturbance and nutrient enrichment in tidal freshwater marshes.  相似文献   

14.
辛沛  金光球  李凌 《水科学进展》2009,20(3):379-384
滨海盐沼是重要的陆地-海洋交界带生态系统。目前国际上存在关于盐沼的两大假设:盐沼系统输出养分和盐沼植物带状分布。为验证这两大假设,增强对盐沼湿地的了解,盐沼孔隙水流动及溶质运移研究至关重要。为模拟复杂盐沼系统孔隙水流动及溶质运移,改进了美国地质勘测局编制的SUTRA程序。基于假定的潮沟横断面物理条件,对孔隙水流动及溶质运移过程进行了模拟分析。结果表明潮沟附近孔隙水及溶质交换较快,潮水浸淹会减缓潮沟附近出现物质集结。落潮时潮沟附近有明显垂向流和水平流,远潮沟地带主要为水平流。潮沟附近土壤通气条件较好。这些模拟结果较好的吻合了潮沟附近较盐沼内部盐沼植物长势较好的现象。  相似文献   

15.
Net ecosystem metabolism (NEM) was measured in the Piauí River estuary, NE Brazil. A mass balance of C, N, and P was used to infer its sources and sinks. Dissolved inorganic carbon (DIC) concentrations and fluxes were measured over a year along this mangrove dominated estuary. DIC concentrations were high in all estuarine sections, particularly at the fluvial end member at the beginning of the rainy season. Carbon dioxide concentrations in the entire estuary were supersaturated throughout the year and highest in the upper estuarine compartment and freshwater, particularly at the rainy season, due to washout effects of carbonaceous soils and different organic anthropogenic effluents. The estuary served as a source of DIC to the atmosphere with an estimated flux of 13 mol CO2 m?2 year?1. Input from the river was 46 mol CO2 m?2 year?1. The metabolism of the system was heterotrophic, but short periods of autotrophy occurred in the lower more marine portions of the estuary. The pelagic system was more or less balanced between auto- and heterotrophy, whereas the benthic and intertidal mangrove region was heterotrophic. Estimated annual NEM yielded a total DIC production in the order of 18 mol CO2 m?2 year?1. The anthropogenic inputs of particulate C, N, and P, dissolved inorganic P (DIP), and DIC were significant. The fluvial loading of particulate organic carbon and dissolved inorganic nitrogen (DIN) was largely retained in two flow regulation and hydroelectric reservoirs, promoting a reduction of C:N and C:P particulate ratios in the estuary. The net nonconservative fluxes obtained by a mass balance approach revealed that the estuary acts as a source of DIP, DIN, and DIC, the latter one being almost equivalent to the losses to the atmosphere. Mangrove forests and tidal mudflats were responsible for most of NEM rates and are the main sites of organic decomposition to sustain net heterotrophy. The main sources for this organic matter are the fluvial and anthropogenic inputs. The mangrove areas are the highest estuarine sources of DIP, DIC, and DIN.  相似文献   

16.
In situ measurements of the exchange of ammonia, nitrate plus nitrite, phosphate, and dissolved organic phosphorus between sediments and the overlying water column were made in a shallow coastal lagoon on the ocean coast of Rhode Island, U.S.A. The release of ammonia from mud sediments in the dark (20–440 μmol per m2 per h) averaged ten times higher than from a sandy tidal flat (0–60 μmol per m2 per h), and while mud sediments also released nitrate and phosphate, sandy sediments took up these nutrients. Fluxes of nutrients from mud sediments, but not from sandy areas, markedly increased with temperature. Ammonia release rates for mud sediments in the light (0–350 μmol per m2 per h) were lower than those in the dark and it is estimated that some 25% of the ammonia released to the water column on an annual basis may be intercepted by the benthic microfloral community. Estimates of the annual net exchange of nutrients across the sediment-water interface, weighted by sediment type for the lagoon as a whole, showed a release of 450 mmol per m2 of ammonia, 5 mmol per m2 of phosphate, 5 mmol per m2 of dissolved organic phosphorus, and an uptake of 80 mmol per m2 of nitrate. Although rates of ammonia and nitrate exchange were comparable to those described for the deeper heterotrophic bottom communities of nearby Narragansett Bay, rates of benthic phosphate release were significantly lower. On an annual basis the Bay benthos released approximately 20 times more inorganic phosphate per unit area than did the lagoon benthos. As a result., the N/P ratio for the flux from the sediments was 74∶1 in the lagoon, compared with 16∶1 in “average” marine plankton and 8∶1 for the benthic flux from Narragansett Bay. The lack of remineralized phosphate in the lagoon, is reflected in water, column phosphate concentrations (always <1 μm) and water column N/P ratios (annual N/P=27) and suggests that the lagoon may show phosphate limitation rather than the nitrogen limitation commonly associated with marine systems.  相似文献   

17.
In light of widespread coastal eutrophication, identifying which nutrients limit vegetation and the community consequences when limitation is relaxed is critical to maintaining the health of estuarine marshes. Studies in temperate salt marshes have generally identified nitrogen (N) as the primary limiting nutrient for marsh vegetation, but the limiting nutrient in low salinity tidal marshes is unknown. I use a 3-yr nutrient addition experiment in mid elevation,Spartina patens dominated marshes that vary in salinity along two estuaries in southern Maine to examine variation in nutrient effects. Nutrient limitation shifted across estuarine salinity gradients; salt and brackish marsh vegetation was N limited, while oligohaline marsh vegetation was co-limited by N and phosphorus (P). Plant tissue analysis ofS. patens showed plants in the highest salinity marshes had the greatest percent N, despite N limitation, suggesting that N limitation in salt marshes is partially driven by a high demand for N to aid in salinity tolerance. Fertilization had little effect on species composition in monospecificS. patents stands of salt and brackish marshes, but N+P treatments in species-rich oligohaline marshes significantly altered community composition, favoring dominance by high aboveground producing plants. Eutrophication by both N and P has the potential to greatly reduce the characteristic high diversity of oligohaline marshes. Inputs of both nutrients in coastal watersheds must be managed to protect the diversity and functioning of the full range of estuarine marshes.  相似文献   

18.
Upland areas of southeastern United States tidal creek watersheds are popular locations for development, and they form part of the estuarine ecosystem characterized by high economic and ecological value. The primary objective of this work was to define the relationships between coastal development, with its concomitant land use changes and associated increases in nonpoint source pollution loading, and the ecological condition of tidal creek ecosystems including related consequences to human populations and coastal communities. Nineteen tidal creek systems, located along the southeastern US coast from southern North Carolina to southern Georgia, were sampled in the summer, 2005 and 2006. Within each system, creeks were divided into two primary segments based upon tidal zoning—intertidal (i.e., shallow, narrow headwater sections) and subtidal (i.e., deeper and wider sections)—and then watersheds were delineated for each segment. Relationships between coastal development, concomitant land use changes, nonpoint source pollution loading, the ecological condition of tidal creek ecosystems, and the potential impacts to human populations and coastal communities were evaluated. In particular, relationships were identified between the amount of impervious cover (indicator of coastal development) and a range of exposure and response measures including increased chemical contamination of the sediments, increased pathogens in the water, increased nitrate/nitrite levels, increased salinity range, decreased biological productivity of the macrobenthos, alterations to the food web, increased flooding potential, and increased human risk of exposure to pathogens and harmful chemicals. The integrity of tidal creeks, particularly the headwaters or intertidally dominated sections, was impaired by increases in nonpoint source pollution associated with sprawling urbanization (i.e., increases in impervious cover). This finding suggests that these habitats are valuable early warning sentinels of ensuing ecological impacts and potential public health and flooding risk from sprawling coastal development. The results also validate the use of a conceptual model with impervious cover thresholds for tidal creek systems in the southeast region.  相似文献   

19.
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   

20.
San Quintin Bay, Mexico, is a hypersaline coastal lagoon where the main external forcing of physical and biogeochemical processes is oceanic. Non-conservative fluxes of inorganic N (ΔDIN) and P (ΔDIP), and aspects of net ecosystem metabolism were studied in this lagoon during August 1995, August 1996, and February 1996, by following the LOICZ budgetary modeling approach. The whole-system water exchange time during summer (≈13 d) was shorter than in winter (≈26 d) as northwesterly winds enhancing mixing with the ocean are more intense during the spring-summer upwelling season. Whole-bay ΔDIP values of +0.2 to +0.3 mmol m?2 d?1 in August, and <+0.01 mmol m?2 d?1 in February indicate that the system is a net source of dissolved inorganic phosphorus (DIP). DIP fluxes from the Bay to the ocean during August are probably balanced by a net import of particulate organic matter between 1,000–1,300 × 103 mol C d?1, equivalent to a net ecosystem production (NEP) between ?24 and ?31 mmol C m?2 d?1. ΔDIN showed opposite trends in August 1995 and August 1996, with a net import of 13×103 mol N d?1 and a net export of 30× 103 mol N d?1, respectively. However, N fixation minus denitrification (“apparent denitrification”) estimates of ≈?4 mmol N m?2 d?1 in both periods indicate that San Quintin Bay is a net sink of nitrogen. Results from a 3-box model indicate that during summer Box C, adjacent to the ocean, contributed 70–80% of the excess DIP produced in the whole-system. This observation and high apparent denitrification values of ≈?7 mmol N m?2 d?1 at the entrance of the Bay, suggest that the net heterotrophic condition of San Quintin Bay in summer is largely determined by imports of labile phytoplanktonic carbon generated in the adjacent ocean during upwelling.A net flux of organic carbon of 30×106 mol C yr?1 was estimated from Box C, adjacent to the ocean, to Box B, locally known as Bahia Falsa, which is the area designated for oyster aquaculture in the lagoon. It is estimated that this net organic carbon supply is almost equivalent to the annual oyster food demand; our estimate is that oyster aquaculture in San Quintin Bay accounts for the vast majority of the net heterotrophy of Bahia Falsa.  相似文献   

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