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1.
The penetration of sunlight into the water column plays a critical role in the aquatic ecosystem. The irradiance available for primary production in a water body depends on the incident light at the water surface, light extinction in the water column, and depth. In this study, the light attenuation through the water column of the Danshuei River–Keelung River estuary was estimated. The measurement of photosynthetically active radiation (PAR) indicates that the conventional exponential attenuation of light with depth is a very good model. A light attenuation coefficient may be derived from the PAR measurements at each location. The regression with salinity yields a good correlation, indicating that the fraction of seawater should be a good parameter for estimating the water column light attenuation coefficient (K d ). A laterally averaged two-dimensional finite difference model for hydrodynamic and water quality model was performed and applied to simulate the phytoplankton population at the lower reach of the Danshuei River estuary. In the process of phytoplankton population simulation, the regression model of K d and salinity was incorporated in the water quality model. The simulated results show that the modeled concentration of chlorophyll a matched the measured values at the lower reach of the Danshuei River estuary.  相似文献   

2.
In the shallow microtidal Patos Lagoon estuary, southern Brazil (32° 07′ S–52° 06′ W), chlorophyll a (Chl a) variability was studied at different time scales during the last 25 years (hourly–daily sampling in 1984/1985; weekly sampling in 1986 and from 1988 to 1990; monthly sampling from 1993 to 2008). Phytoplankton biomass variation seems to be most influenced by hydrology, which is primarily driven by meteorological factors like wind, rainfall, and evaporation. However, it was observed that the hydrological driving forces play different roles at different time scales. For instance, short-term Chl a variability is mainly controlled by winds, while long-term changes are related to the freshwater input by rainfall. Significant correlation was found between the total amount of rain in the year and the mean annual value of Chl a, though this relationship was linear until 1,500 mm of rain per year. After this threshold, mean annual Chl a values dropped significantly, probably due to a washout of the produced biomass from the estuary. Similarly, low rainfall levels and drought years lead to small phytoplankton biomass due to scarcity of nutrient, mainly silicate, or a possible inhibitory effect generated by high ammonium concentration. In this sense, large-scale Chl a variability would be related to the El Ni?o-Southern Oscillation climatic anomaly, which influences the rainfall levels in Southern Brazil, though sampling periodicity has also great influence on this relationship. No Chl a or nutrient enrichment was observed in the estuarine region along the last years, indicating that this estuary is not subject to an eutrophication process. In contrast, signals of an ongoing oligotrophication are observed, possibly a remote effect of the eutrophication in the Northern area of the lagoon where the phytoplankton nutrients uptake may act as a biological filter mechanism.  相似文献   

3.
We investigated spatial and temporal changes in spectral irradiance, phytoplankton community composition, and primary productivity in North Inlet Estuary, South Carolina, USA. High concentrations of colored dissolved organic matter (CDOM) were responsible for up to 84 % of the attenuation of photosynthetically available radiation (PAR). Green-yellow wavelengths were the predominant colors of light available at the two sampling sites: Clam Bank Creek and Oyster Landing. Vertical attenuation coefficients of PAR were 0.7–2.1 m?1 with corresponding euphotic zone depths of 1.5–6.7 m. Phytoplankton biomass (as chlorophyll a [chl a]) varied seasonally with a summer maximum of 16 μg chl a l?1 and a winter minimum of 1.4 μg chl a l?1. The phytoplankton community consisted mainly of diatoms, prasinophytes, cryptophytes and haptophytes, with diatoms and prasinophytes accounting for up to 67 % of total chl a. Changes in phytoplankton community composition showed strongest correlations with temperature. Light-saturated chl a-specific rates of photosynthesis and daily primary productivity varied with season and ranged from 1.6 to 14 mg C (mg chl a) ?1?h?1 (32–803 mg C m?3?day?1). Calculated daily rates added up to an annual carbon fixation rate of 84 g C m?3?year?1. Overall, changes in phytoplankton community composition and primary productivity in North Inlet showed a strong dependence on temperature, with PAR and spectral irradiance playing a relatively minor role due to short residence times, strong tidal forcing and vertical mixing.  相似文献   

4.
Seasonal and interannual patterns in the spatial distribution of bluefish (Pomatomus saltatrix) within a Middle Atlantic Bight estuary were examined using multipanel gillnets fished biweekly at 14 fixeds stations in the Sandy Hook Bay-N avesink River estuary during May–November of 1998 and 1999. To characterize habitats along the estuarine gradient, we measured several abiotic and biotic variables concurrently with gillnet sampling. Juvenile (age-0 and age-1+) bluefish were captured regularly during both years along with large numbers of Atlantic menhaden (Brevoortia tyrannus), which were confirmed by diet analyses to be bluefish’s primary forage species. The date of initial appearance of age-0 bluefish and menhaden in the estuary varied between years and may have been related to interannual differences in seawater temperatures on the continental shelf during spring. Delayed estuarine arrival of prey fishes may have contributed to variability in bluefish diets between years. Within the estuary, bluefish spatial distribution were consistent across seasons and years: bluefish were most common in areas associated with high concentrations of suspended materials and the presence of menhaden. Community analyses also indicated habitat overlap between bluefish and menhaden. Spatial distribution patterns revealed the consistent occurrence of piscivorous bluefish in shallow estuarine habitats that retained suspended materials and aggregated prey fishes. Foraging success of bluefish and other estuarine piscivores may be closely linked with the availability of these productive habitat, highlighting the need for future study of biological interactions and the governing physical processes.  相似文献   

5.
In shallow estuaries with strong river influence, the short residence time and pronounced gradients generate an environment for plankton that differs substantially in its dynamics from that of the open ocean, and the question arises “How is phytoplankton biomass affected?” This study assesses the small-scale spatial and temporal distribution of phytoplankton in Apalachicola Bay, a shallow bar-built estuary in the Florida Panhandle. Phytoplankton peaks were characterized to gain insights into the processes affecting spatial heterogeneity in biomass. Chlorophyll a (Chl a) distribution at 50-m spatial resolution was mapped using a flow-through sensor array, Dataflow©, operated from a boat that sampled four transects across the bay every 2 weeks for 16 months. Chl a peaks exceeding background concentrations had an average width of 1.3?±?0.7 km delineated by an average gradient of 3.0?±?6.0 μg Chl a L?1 km?1. Magnitude of E-W wind, velocity of N-S wind, tidal stage, and temperature affected peak characteristics. Phytoplankton contained in the peaks contributed 7.7?±?2.7% of the total integrated biomass observed along the transects during the study period. The river plume front was frequently a location of elevated Chl a, which shifted in response to river discharge. The results demonstrate that despite the shallow water column, river flushing, and strong wind and tidal mixing, distinct patchiness develops that should be taken into consideration in ecological studies and when assessing productivity of such ecosystems.  相似文献   

6.
English sole (Pleuronectes vetulus) is one of a few commercially important marine fishes on the Pacific coast of North America that use estuarine areas as nurseries for juvenile stages. Trawl surveys of four United States Pacific Northwest estuaries were conducted to determine spatial patterns of juvenile English sole residence in estuaries during 1998–2000. Additional data from 1983–1988 were also analyzed. Two size classes of juvenile English sole were identified during surveys, with densities of small (Total length [TL] <50 mm) sole ranging from 0 to 11,300 fish ha?1 across all sites, and densities of large (TL 50–150 mm) sole ranging from 0 to 33,000 fish ha?1 across all sites. Principal components analysis of static habitat data collected at each trawl survey site was used to define habitat types within each estuary, and discriminant function analysis was used to test the resulting classification scheme. Both small and large cohort English sole used lower side channel locations at significantly higher densities than other estuarine areas. Small English sole also showed significant relationships with both bottom temperature and depth. These patterns in habitat use were consistent across all estuaries and indicate that English sole used shallow depth areas surrounded by extensive tidal flats, where temperatures were optimal for growth. The analysis also suggested a carrying capacity may exist for large English sole in nursery estuaries.  相似文献   

7.
Submersed aquatic vegetation (SAV) is an important component of shallow water estuarine systems that has declined drastically in recent decades. SAV has particularly high light requirements, and losses of SAV have, in many cases, been attributed to increased light attenuation in the water column, frequently due to coastal eutrophication. The desire to restore these valuable habitats to their historical levels has created the need for a simple but accurate management tool for translating light requirements into water quality targets capable of supporting SAV communities. A procedure for calculating water quality targets for concentrations of chlorophyll and total suspended solids (TSS) is derived, based on representing the diffuse attenuation coefficient for photosynthetically active radiation, Kd(PAR), as a linear function of contributions due to water plus colored dissolved organic matter (CDOM), chlorophyll, and TSS. It is assumed that Kd(PAR) conforms to the Lambert-Beer law. Target concentrations are determined as the intersection of a line representing intended reduction of TSS and chlorophyll by management actions, with another line describing the dependence of TSS on chlorophyll at a constant value of Kd(PAR). The validity of applying the Lambert-Beer law to Kd(PAR) in estuarine waters was tested by comparing the performance of a linear model of Kd(PAR) with data simulated using a more realistic model of light attenuation. The linear regression model tended to underestimate Kd(PAR) at high light attenuation, resulting in erroneous predictions of target concentrations at shallow restoration depths. The errors result more from the wide spectral bandwidth of PAR, than from irrecoverable nonlinearities in the diffuse attenuation coefficient per se. In spite of the failure of the Lambert-Beer law applied to Kd(PAR), the variation of TSS with chlorophyll at constant Kd(PAR) determined by the more mechanistic attenuation model was, nevertheless, highly linear. Use of the management tool based on intersecting lines is still possible, but coefficients in the line describing the dependence of TSS on chlorophyll at constant Kd(PAR) must be determined empirically by application of an optical model suitably calibrated for the region of interest. An example application of the procedure to data from the Rhode River, Maryland, indicates that approximately 15% reduction in both TSS and chlorophyll concentrations, or 50% reduction in chlorophyll alone, will be needed to restore conditions for growth of SAV to levels that existed in the late 1960s.  相似文献   

8.
The coastal bays and lagoons of Maryland extend the full length of the state's Atlantic coast and compose a substantial ecosystem at the land-sea margin that is characterized by shallow depth, a well-mixed water column, slow exchange with the coastal ocean, and minimal freshwater input from the land. For at least 25 years, various types of measurements have been made intermittently in these systems, but almost no effort has been made to determine if water quality or habitat conditions have changed over the years or if distinctive spatial gradients in these features have developed in response to changing land uses. The purpose of this work was to examine this fragmented database and determine if such patterns have emerged and how they may be related to land uses. Turbidity, dissolved inorganic phosphate, algal biomass, and primary production rates in most areas of the coastal bays followed a regular seasonal pattern, which was well correlated with water temperature. Nitrate concentrations were low (<5 μM), and only modestly higher in tributary creeks (<20 μM). Additionally, there was little indication of the spring bloom typical of river-dominated systems. There does appear to be a strong spatial gradient in water quality conditions (more eutrophic in the upper bays, especially in tributary creeks). Comparisons of water quality data collected between 1970 and 1991 indicate little temporal change in most areas and some small improvements in a few areas, probably related to decreases in point-source discharges. Seagrass communities were once extensive in these systems but at present are restricted to the eastern portion of the lower bays where water clarity is sufficient to support plant survival. Even in these areas, seagrass densities have recently decreased. Examination of diel dissolved oxygen data collected in the summer indicates progressively larger diel excursions from lower to upper bays and from open bays to tributary subsystems; however, hypoxic conditions (<2 mg 1?1) were rarely observed in any location. Nitrogen input data (point, surface runoff, groundwater and atmospheric deposition to surface waters) were assembled for seven regions of the coastal bay system; annual loading rates ranged from 2.4 g N m?2 yr?1 to 39.7 g N m?2 yr?1. Compared with a sampling of loading rates to other coastal systems, those to the upper and lower bays were low while those to tributaries were moderate to high. Regression analysis indicated significant relationships between annual nitrogen loading rates and average annual total nitrogen and chlorophyll a concentrations in the water column. Similar analyses also indicated significant relationships between chlorophyll a and the magnitude of diel dissolved oxygen changes in the water column. It is concluded that these simple models, which could be improved with a well-designed monitoring program, could be used as quantitative management tools to relate habitat conditions to nutrient loading rates.  相似文献   

9.
Particulate organic carbon (POC), dissolved organic carbon (DOC), and plant pigments (chlorophylls and carotenoids) were measured approximately bimonthly from March 1992 to October 1993 in the Sabine-Neches estuary (Sabine Lake region), located on the Texas-Louisiana border. High freshwater inflow into this shallow turbid estuary results in the shortest hydraulic residence time (ca. 7 d) of all Texas estuaries (Baskaran et al. in press). Annual averages of chlorophyll-a (3.0 μg l?1) and particulate organic carbon (1.1 mg l?1) in the water column were extremely low in comparison to other shallow estuaries. The highest chlorophyll-a concentrations were observed in October 1993, in the mid and lower regions of the estuary, during the lowest river discharge. Zeaxanthin and fucoxanthin concentrations suggested that much of the chlorophyll-a during this low flow period was represented by cyanobacteria and diatoms that entered from the Gulf of Mexico. The range of DOC concentrations was generally high (4.4–20.9 mg l?1) and were significantly correlated with POC, but not with chlorophyll-a concentrations. When total suspended particulate (TSP) concentrations were below 20 to 30 mg l?1, there were significant increases in %POC and %PON of the TSP. The unusually high POC: chlorophyll-a ratios (highest value of 1423) suggested that much of the POC contained low concentrations of chlorophyll-a that had degraded during transport from wetlands in the Sabine and Neches rivers. Based on these data, this estuary can be characterized as a predominantly heterotrophic system, with low light penetrance, short particle-residence times, high DOC, and low inputs from autochthonous carbon sources.  相似文献   

10.
Material transfer between estuaries and the nearshore zone has long been of interest, but information on the processes affecting Pacific Northwest estuaries has lagged behind other areas. The west coast of the U.S. is a region of seasonally variable upwelling that results in enhanced phytoplankton production in the nearshore zone. We examined estuarine-nearshore links over time by measuring physical oceanographic variables and chlorophylla concentration from an anchor station in South Slough, Oregon. Data was collected during 24-h cruises conducted at approximately weekly intervals during summer 1996 and spring 1997. The results demonstrate that the physical oceanography of this estuarine site was strongly influenced by the coastal ocean. Marine water reached the estuarine site on every sampled tide, and chlorophylla was clearly advected into the estuary with this ocean water. In contrast, phytoplankton concentrations were comparatively reduced in the estuarine water. There were, however, large fluctuations in the import of chlorophyll over the course of the summer. These variations likely reflect upwelling-generated phytoplankton production in the coastal ocean and subsequent cross-shelf transport to the estuary. Suspension feeding organisms in South Slough likely depend on the advection of this coastally-derived phytoplankton. The large allochthonous chlorophyll input measured for this system appears dissimilar from most estuaries studied to date. Previous investigations have focused on the outwelling and inwelling of materials in estuaries. We must now consider the influence of coastal upwelling and downwelling processes on estuarine material exchange.  相似文献   

11.
The composition and metabolic capability of bacterioplankton communities were examined over seasonal and spatial gradients and related to the source, composition, and quantity of dissolved organic matter (DOM) in the blackwater estuary Winyah Bay, Georgetown County, SC, USA and its tributary rivers. Bacterial community composition (BCC) was measured by terminal restriction fragment length polymorphism, and bacterial metabolic capability (BMC) was measured by defined substrate utilization patterns (Biolog GN2 plates). Spatial patterns were not important, despite the anticipated watershed effects and the well-documented influence of salinity gradients on estuarine bacterioplankton, but DOM, BCC, and BMC all showed varying degrees of temporal patterns; DOM-based groupings differentiated BCC samples better than spatiotemporal categories, but not BMC. BCC was closely related to properties describing DOM composition, particularly those related to DOM source (i.e., cypress swamps vs. in situ phytoplankton production, indicated by chlorophyll a, colored DOM spectral slope, α355/dissolved organic carbon (DOC), and DOC concentration), and to associated physicochemical variables, such as temperature, pH, and salinity. BMC was more strongly related to abiotic factors, such as temperature and dissolved nutrients, as well as to chlorophyll a and percent bioavailable DOC. In contrast with previous studies, BCC and BMC were significantly correlated in this highly heterotrophic estuary, suggesting that DOM source variability may select for specialist phylotypes above a background of generalists. This study, therefore, supports a causative pathway from DOM to BMC to BCC while suggesting that BCC and BMC may be simultaneously influenced by different suites of DOM characteristics and physicochemical parameters.  相似文献   

12.
Freshwater inputs often play a more direct role in estuarine phytoplankton biomass (chlorophyll a) accumulation than nitrogen (N) inputs, since discharge simultaneously controls both phytoplankton residence time and N loading. Understanding this link is critical, given potential changes in climate and human activities that may affect discharge and watershed N supply. Chlorophyll a (chla) relationships with hydrologic variability were examined in 3-year time series from two neighboring, shallow (<5?m), microtidal estuaries (New and Neuse River estuaries, NC, USA) influenced by the same climatic conditions and events. Under conditions ranging from drought to floods, N concentration and salinity showed direct positive and negative responses, respectively, to discharge for both estuaries. The response of chla to discharge was more complex, but was elucidated through conversion of discharge to freshwater flushing time, an estimate of transport time scale. Non-linear fits of chla to flushing time revealed non-monotonic, unimodal relationships that reflected the changing balance between intrinsic growth and losses through time and along the axis of each estuary. Maximum biomass occurred at approximately 10-day flushing times for both systems. Residual analysis of the fitted data revealed positive relationships between chla and temperature, suggesting enhanced growth rates at higher temperatures. N loading and system-wide, volume-weighted chla were positively correlated, and biomass yields per N load were greater than other marine systems. When combined with information on loss processes, these results on the hydrologic control of phytoplankton biomass will help formulate mechanistic models necessary to predict ecosystem responses to future climate and anthropogenic changes.  相似文献   

13.
Nutrient inputs have degraded estuaries worldwide. We investigated the sources and effects of nutrient inputs by comparing water quality at shallow (< 2m deep) nearshore (within 200 m) locations in a total of 49 Chesapeake subestuaries and Mid-Atlantic coastal bays with differing local watershed land use. During July–October, concentrations of total nitrogen (TN), dissolved ammonium, dissolved inorganic N (DIN), and chlorophyll a were positively correlated with the percentages of cropland and developed land in the local watersheds. TN, DIN, and nitrate were positively correlated with the ratio of watershed area to subestuary area. Total phosphorus (TP) and dissolved phosphate increased with cropland but were not affected by developed land. The relationships among N, P, chlorophyll a, and land use suggest N limitation of chlorophyll a production from July–October. We compared our measurements inside the subestuaries to measurements by the Chesapeake Bay Program in adjacent estuarine waters outside the subestuaries. TP and dissolved inorganic P concentrations inside the subestuaries correlated with concentrations outside the subestuaries. However, water quality inside the subestuaries generally differed from that in adjacent estuarine waters. The concentration of nitrate was lower inside the subestuaries, while the concentrations of other forms of N, TP, and chlorophyll a were higher. This suggests that shallow nearshore waters inside the subestuaries import nitrate while exporting other forms of N as well as TP and chlorophyll a. The importance of local land use and the distinct biogeochemistry of shallow waters should be considered in managing coastal systems.  相似文献   

14.
Phytoplankton chlorophyll a concentration, biovolume, cell diameter, and species composition differed across the narrow, low salinity zone between 0.6‰ to 4‰ and may influence copepod food availability in the northern San Francisco Bay Estuary. The highest chlorophyll a concentrations (range 3.2–12.3 μg 1?1), widest cell diameters (>5 μm diam), highest diatom densities and highest production rates of >10 μm diam cells occurred at the landward edge of the salinity zone in April during a strong spring tide and May during a strong neap tide. Near optimum predator/prey ratios, large prey estimated spherical diameters, and high chlorophyll a concentrations suggest these phytoplankton communities provided good food quantity and quality for the most abundant copepods, Eurytemora affinis, Sinocalanus doerrii, and Pseudodiaptomus forbesi. At the center of the zone, chlorophyll a concentrations, diatom densities, and production rates of >10 μm diam cells were lower and cell diameters were smaller than upstream. Downstream transport was accompanied by accumulation of phytoplankton with depth and tide; maximum biomass occurred on spring tide. The lowest chlorophyll a concentrations (1.4–3.6 μg 1?) and consistently high densities (3,000–4,000 cells ml?1) of <5 μm diam cells occurred at the seaward edge of the zone, where the green alga Nannochloris spp. and the bluegreen alga Synechococcus spp. were the most abundant phytoplankton. Low chlorophyll a concentrations and production rates of >10 μm diam cells, small prey estimated spherical diameters, and high predator/prey ratios suggested the seaward edge of the zone had poor phytoplankton food for copepodids and adult copepods. The seaward decrease in phytoplankton chlorophyll a concentration and cell diameter and shift in species composition in the low salinity zone were probably a function of an estuary-wide decrease in chlorophyll a concentration, cell diameter, and diatom density since the early 1980s that was enhanced in the low salinity zone by clam herbivory after 1987. *** DIRECT SUPPORT *** A01BY090 00008  相似文献   

15.
The composition, productivity, and standing crop of net (>20 μm) and nano-(<20 μm) phytoplankton of Peconic Bay, Long Island, New York was examined from June 1978 through May 1979. Nanoplankton, primarily small solitary flagellates, chlorophytes, and diatoms, dominated from May through September accounting for 88.5% of the productivity and 88.1% of the standing crop (measured as chlorophyll a). An apparent net plankton bloom began in December and continued through March. The dominant organism through most of the winter bloom was the chain-forming diatom Skeletonema costatum (Grev.) Cl. Net plankton at this time represented 66.4% of the standing crop. For both size fractions, productivity/chlorophyll a (g C per g chl a per d, integrated through the euphotic zone) was a function of light energy over the year with the exception of a few sampling dates during the post-winter bloom period. Assimilation numbers (g C per g chl a per h at saturating light intensities) were a function of temperature between 0 and 20°C. Nitrogen deficiency did not appear to be a factor in regulating phytoplankton growth rate through the euphotic zone, as ratios of 14C assimilation for dark bottles enriched with NH3 and with no enrichment exhibited no relationship to environmental dissolved inorganic nitrogen concentrations. Zooplankton grazing pressure appeared to have been an important factor in regulating the upper limit of phytoplankton biomass and in influencing size fraction dominance. Dominance of one phytoplankton size fraction over the other on any given date was not based on physiological differences between the two groups since both fractions were composed of the same species. Apparent net phytoplankton blooms (in terms of productivity and chlorophyll a) were artifacts of increased chain lengths of nanoplankton diatoms such as Skeletonema costatum, and to a lesser extent, Thalassiosira nordenskioldii Cl. and Detonula confervacea (Cl.) Gran, rather than to the dominance of large, solitary cells.  相似文献   

16.
Seagrasses are typically light limited in many turbid estuarine systems. Light attenuation is due to water and three optically active constituents (OACs): nonalgal particulates, phytoplankton, and colored dissolved organic matter (CDOM). Using radiative transfer modeling, the inherent optical properties (IOPs) of these three OACs were linked to the light attenuation coefficient, K PAR, which was measured in North River, North Carolina, by profiles of photosynthetically active radiation (PAR). Seagrasses in the southern portion of Albemarle-Pamlico Estuarine System (APES), the second largest estuary in the USA, were found to be light limited at depths ranging from 0.87 to 2 m. This corresponds to a range of K PAR from 0.54 to 2.76 m?1 measured during a 24-month monitoring program. Turbidity ranged from 2.20 to 35.55 NTU, chlorophyll a from 1.56 to 15.35 mg m?3, and CDOM absorption at 440 nm from 0.319 to 3.554 m?1. The IOP and water quality data were used to calibrate an existing bio-optical model, which predicted a maximum depth for seagrasses of 1.7 m using annual mean water quality values and a minimum light requirement of 22% surface PAR. The utility of this modeling approach for the management of seagrasses in the APES lies in the identification of which water quality component is most important in driving light attenuation and limiting seagrass depth distribution. The calibrated bio-optical model now enables researchers and managers alike to set water quality targets to achieve desired water column light requirement goals that can be used to set criteria for seagrass habitat protection in North Carolina.  相似文献   

17.
Freshwater and sediment management in estuaries affects water quality, particularly in deltaic estuaries. Furthermore, climate change-induced sea-level rise (SLR) and land subsidence also affect estuarine water quality by changing salinity, circulation, stratification, sedimentation, erosion, residence time, and other physical and ecological processes. However, little is known about how the magnitudes and spatial and temporal patterns in estuarine water quality variables will change in response to freshwater and sediment management in the context of future SLR. In this study, we applied the Delft3D model that couples hydrodynamics and water quality processes to examine the spatial and temporal variations of salinity, total suspended solids, and chlorophyll-α concentration in response to small (142 m3 s?1) and large (7080 m3 s?1) Mississippi River (MR) diversions under low (0.38 m) and high (1.44 m) relative SLR (RSLR = eustatic SLR + subsidence) scenarios in the Breton Sound Estuary, Louisiana, USA. The hydrodynamics and water quality model were calibrated and validated via field observations at multiple stations across the estuary. Model results indicate that the large MR diversion would significantly affect the magnitude and spatial and temporal patterns of the studied water quality variables across the entire estuary, whereas the small diversion tends to influence water quality only in small areas near the diversion. RSLR would also play a significant role on the spatial heterogeneity in estuary water quality by acting as an opposite force to river diversions; however, RSLR plays a greater role than the small-scale diversion on the magnitude and spatial pattern of the water quality parameters in this deltaic estuary.  相似文献   

18.
The temporal and spatial distributions of salinity, dissolved oxygen, suspended particulate material (SPM), and dissolved nutrients were determined during 1983 in the Choptank River, an estuarine tributary of Chesapeake Bay. During winter and spring freshets, the middle estuary was strongly stratified with changes in salinity of up to 5‰ occurring over 1 m depth intervals. Periodically, the lower estuary was stratified due to the intrusion of higher salinity water from the main channel of Chesapeake Bay. During summer this intrusion caused minimum oxygen and maximum NH4 + concentrations at the mouth of the Choptank River estuary. Highest concentrations of SPM, particulate carbon (PC), particulate nitrogen (PN), total nitrogen (TN), total phosphorous (TP) and dissolved inorganic nitrogen (DIN) occurred in the upper estuary during the early spring freshet. In contrast, minimum soluble reactive phosphate (SRP) concentrations were highest in the upper estuary in summer when freshwater discharge was low. In spring, PC:PN ratios were >13, indicating a strong influence by allochthonous plant detritus on PC and PN concentrations. However, high concentrations of PC and PN in fall coincided with maximum chlorophyll a concentrations and PC:PN ratios were <8, indicating in situ productivity controlled PC and PN levels. During late spring and summer, DIN concentrations decreased from >100 to <10 μg-at l?1, resulting mainly from the nonconservative behavior of NO3 ?, which dominated the DIN pool. Atomic ratios of both the inorganic and total forms of N and P exceeded 100 in spring, but by summer, ratios decreased to <5 and <15, respectively. The seasonal and spatial changes in both absolute concentrations and ratios of N and P reflect the strong influence of allochthonous inputs on nutrient distributions in spring, followed by the effects of internal processes in summer and fall.  相似文献   

19.
The objective of this study was to determine what effect, if any, large pile-supported platforms (piers) have on the habitat distribution and abundance of juvenile fishes. Trapping techniques were used in 1993 and 1994 under piers, in pile fields, and in open-water habitat types in shallow areas (<5 m) in the lower Hudson River estuary (40°44′N, 70°01′W). Nearly 1500 fishes, mostly juveniles, representing 24 species were collected in 1865 trap-days from May through October in the 2-yr study. The presence of relatively large numbers of young-of-the-year (YOY) fish during both years lends support to the idea that shallow areas in the lower Hudson River estuary currently function as nursery habitats for a variety of fishes. Two seasonal assemblages were apparent, but their composition varied somewhat between years.Microgadus tomcod andPseudopleuronectes americanus YOY dominated an early summer assemblage (May–July) while large numbers of YOYMorone saxatilis were collected as part of a late summer assemblage (August–September). The effects of habitat type on fish assemblage structure were significant during both years. Fish abundance and species richness were typically low under piers; YOY fishes were rare andAnguilla rostrata accounted for a large proportion of the total catch. In contrast, YOY fishes dominated collections at pile field and open-water stations, where abundance and species richness were high. These results indicate that habitat quality under the platforms of large piers (>20,000 m2) is probably poor for YOY fishes when compared with nearby pile field and open-water habitat types.  相似文献   

20.
Accurate measures of intertidal benthic microalgal standing stock (biomass) and productivity are needed to quantify their potential contribution to food webs. Oxygen microelectrode techniques, used in this study, provide realistic measures of intertidal benthic microalgal production. By dividing a salt-marsh estuary into habitat types, based on sediment and sunlight characteristics, we have developed a simple way of describing benthic microalgal communities. The purpose of this study was to measure and compare benthic microalgal biomass and production in five different estuarine habitats over an 18-mo period to document the relative contributions of benthic microalgal productivity in the different habitat types. Samples were collected bimonthly from April 1990 to October 1991. Over the 18-mo period, tall Spartina zone habitats had the highest (101.5 mg chlorophyll a (Chl a) m?2±6.9 SE) and shallow subtidal habitats the lowest (60.4±8.9 SE) microalgal biomass. There was a unimodal peak in biomass during the late winter-early spring period. The concentrations of photopigments (Chl a and total pheopigments) in the 0–5 mm of sediments were highly correlated (r2=0.73 and 0.88, respectively) with photopigment concentrations in the 5–10 mm depth interval. Biomass specific production (μmol O2 mg Chl a ?1 h?1) was highest in intertidal mudflat habitats (206.3±11.2 SE) and lowest in shallow subtidal habitats (104.3±11.1 SE). Regressions of maximum production (production at saturating irradiances) vs. biomass (Chl a) in the upper 2 mm of sediment by habitat type gave some of the highest correlations ever reported for benthic microalgal communities (r2 values ranged from 0.43 to 0.73). The habitat approach and oxygen microelectrode techniques provide a useful, realistic ranged from 0.43 to 0.73). The habitat approach and oxygen microelectrode techniques provide a useful, realistic method for understanding the biomass and production dynamics of estuarine benthic microalgal communities.  相似文献   

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