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1.
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   

2.
The physicochemical qualities of a typical rural-based river were assessed over a 12-month period from August 2010 to July 2011 spanning the spring, summer, autumn and winter seasons. Water samples were collected from six sampling sites along Tyume River and analysed for total nitrogen, orthophosphate, biochemical oxygen demand (BOD), temperature, pH, dissolved oxygen (DO), electrical conductivity (EC), total dissolved solids (TDS) and turbidity. BOD regimes did not differ significantly between seasons and between sampling points and ranged from 0.78 to 2.76 mg/L across seasons and sampling points, while temperature ranged significantly (P < 0.05) between 6 and 28 °C. Turbidity varied significantly (P < 0.05) from 6 to 281 nephelometric turbidity units while TDS (range 24–209 ppm) and conductivity (range 47.6–408 mg/L) also varied significantly (P < 0.05) across sampling points with a remarkable similarity in their trends. Orthophosphate concentrations varied from 0.06 to 2.72 mg/L across seasons and sampling points. Negative correlations were noted between temperature and the nutrients, DO and temperature (r = ?0.56), and TDS and DO (r = ?0.33). Positive correlations were noted between TDS and temperature (r = 0.41), EC and temperature (r = 0.15), and DO and pH (r = 0.55). All nutrients were positively correlated to each other. Most measured parameters were within prescribed safety guidelines. However, the general trend was that water quality tended to deteriorate as the river flows through settlements, moreso in rainy seasons.  相似文献   

3.
Neomysis americana, a common prey item in the diet of estuarine fish, is seasonally abundant in saltmarsh tidal creeks of North Inlet, South Carolina. Visual examination of mysids collected in winter revealed only diatom tests in their guts, with nearly all of the ingesta unidentifiable. Immunological diet analysis provided strong evidence that proteins fromSpartina alterniflora detritus were present in the guts of field-collected mysids. Laboratory determinations of weight-specific ingestion rates for male and female mysids fed particulateS. alterniflora were best described by a curvilinear quadratic function. Ingestion rates ranged from zero to 0.116 mg C ingested per mg C body weight per hr, or greater than 200% of body carbon per day if continuous feeding is assumed. These high ingestion rates may indicate low assimilation efficiency, but ifN. americana’s assimilation efficiency is similar to that of other mysid species, then this mysid may represent an efficient trophic link between saltmarsh macrophyte production and higher trophic levels. The occurrence ofSpartina detritus in the guts of winter mysids suggests that detritivory may be important during periods of scarce food.  相似文献   

4.
Feeding habits ofMenidia peninsulae were analyzed monthly over a one year period and compared to planktonic prey available at the capture site. Three feeding stages were found: (1) In early spring, young-of-the-year fed on tychoplankton and detritus. (2) From late spring through winter,M. peninsulae preyed selectively on calanoid copepods and cypris larvae. (3) GravidM. peninsulae fed primarily on amphipods and larval silversides. In the Crystal River area,M. peninsulae reproduce in early spring. Silversides apparently migrate from the higher salinity bays to the lower salinity marshes in the summer, and then move back into the bays in fall.  相似文献   

5.
Flax Pond is a small (0.5 km2) salt marsh on the north shore of Long Island, New York. Two 1 m2 plots within each of the following environments were covered with a marker layer of either brick dust or aluminum glitter: 1) bare mud flats; 2) areas newly colonized by Spartina alterniflora; and 3) high intertidal. S. alterniflora peat surfaces. Monthly cores revealed the amount of sediment that accumulated since placement of the marker. Accretion rates from October, 1974 to February, 1976 were as follows: bare mud flats ?20.5 to 45.5 mm/yr; recently vegetated mud flats ?9.5 to 37.0 mm/yr; and high intertidal peat surfaces ?2.0 to 4.25 mm/yr. Sedimentation rates decrease with increasing elevation because of the reduced tidal submergence time and decreased height of the overlying water column. In areas of low elevation, ice and storms cause either erosion or a reduced rate of accretion during the winter months. The average mud accretion rate over the past 173 years is 3.4 mm/yr. Differences between the short-term rate and the long-term rate indicate substantial annual variation in the accumulation of mud in salt marshes. Short-term rates of peat accretion are similar to long-term estimates, indicating that rates of peat accretion are relatively constant over long intervals.  相似文献   

6.
The hypothesis thatTypha domingensis (cattail) can invade tidal marshes only after soil salinities are substantially reduced was tested experimentally by comparing the salt tolerance of seeds, seedlings, and plants reared from rhizomes. Germination rates for four southern California populations reached 100% in fresh water, decreasing to 2% at 20‰. The salt tolerance of seeds from three coastal populations was lower than that of the Salton Sea population. Salt tolerance of plants grown in the lab did not increase with age for seedlings up to 8 weeks old. Rhizome-bearing plants had greatly decreased growth at 10‰ and no growth at 25‰ However, rhizomes of about 5% of the plants survived 9 months at 45‰. The seeds and seedlings are salt sensitive, which explains why invasion into tidal marshes is restricted to prolonged periods of low soil salinity. The older, rhizome-bearing plants are salt tolerant, which explains how invading plants persist persist under hypersaline conditions.  相似文献   

7.
Juvenile spot,Leiostomus xanthurus (Pisces), were collected at 2-h intervals over two 48-h periods in a tidal creek in North Inlet, South Carolina, during July 1986. Gut fullness, dry gut contents weight as a percentage of fish wet weight, was measured to test the hypothesis that feeding intensity is randomly distributed through time. Spot were also collected and serially sacrificed from a holding tank to estimate their gut evacuation rate. Gut fullness was greatest during periods of ebb and high tides and was little affected by the amount of light available. Gut contents were evacuated at a rate of about 15% per hour in the laboratory, in close agreement with field emptying times of about 6 h from peak fullness to empty guts. A conservative estimate of daily ration for juvenile spot (19–42 mm standard length) was 4.5% of their live body weight per day. Studies of spot feeding ecology can be greatly affected by when fish are collected during the tidal cycle.  相似文献   

8.
Water samples have been taken daily at 1030 EST from three locations within North Inlet (South Carolina) since June of 1980 in order to evaluate the tidal, seasonal, and eventually annual variability in carbon concentrations within this system and generate hypotheses explaining the observed trends. Dissolved organic carbon (DOC) concentrations within North Inlet (South Carolina) vary inversely with salinity (r2=0.65), suggesting the main source of DOC in North Inlet is freshwater entering from the adjacent forested watershed. This assertion is supported by an observed decrease of tidal water salinity with the onset of streamflow. DOC variability is also associated with (1) groundwater advection and/or runoff and seepage from the marsh surface; (2) removal from tidal water via either physical sorption or biological uptake; (3) sampling location; and (4) origin of water mass. Particulate organic carbon (POC) concentrations vary seasonally, higher values found during the summer. POC variability is controlled by a series of physical and biological factors. Evidence suggests that in the smaller tidal creeks, POC concentrations are associated with (1) rain events scouring the marsh surface, (2) phytoplankton concentrations varying as a function of tidal stage, and (3) removal of particulate material from the marsh surface on the ebb tide. In the larger tidal creeks tidal water velocity appears to be the main factor influencing POC values.  相似文献   

9.
Assemblages of ichthyofauna of shallow inshore habitats along Californía’s central coast are described in terms of species composition, abundance, and life-style categories. A total of 22,334 fishes from 65 species and 27 families was collected with otter trawls at six sites in the main channel and tidal creeks of Elkhorn Slough, a tidal embayment and seasonal estuary, and two nearshore ocean stations in Monterey Bay during 44 months between August 1974 and June 1980. Greater than 90% of the catch comprised 10 species. The four dominant species,Cymatogaster aggregata, Leptocottus armatus, Phanerodon furcatus, andEmbiotoca jacksoni, occurred during most or all seasons and were classified as residents or partial residents. Several abundant species were marine immigrants that seasonally use the slough as spawning and nursery grounds; this resulted in higher abundance and species richness during summer. Species collected during winter largely were slough residents. Species compsosition and richness varied with distance from the slough entrance. The ocean assemblage was most different, and its similarity to other stations decreased progressively with distance inland and into the tidal creeks. During our study, 5,074 fishes were collected by beach seine in Bennett Slough, a remote shallow marsh basin adjacent to the entrance of Elkhorn Slough. Species richness was relatively low and three euryhaline species accounted for >80% of the total catch. The species assemblage was most similar to those at the tidal creek and most shallow stations of Elkhorn Slough. Resident species numerically dominated assemblages in Bennett Slough and the most inland areas of Elkhorn Slough. The high relative abundance of marine-related fishes (classified as marine, marine immigrant, and partial resident), entering Elkhorn Slough early in life or as spawning adults indicates the importance of this habitat to nearshore fish assemblages.  相似文献   

10.
Patterns in seasonal abundance (no. per m2 surface area), growth and biomass (g per m2 surface area) of an annual fish, the Atlantic silverside, Menidia menidia (L.) were investigated in a marsh and more seaward bay region of Essex Bay, Massachusetts from August 1976 to May 1978 using a quantitative beach seining technique. Silverside abundance varied greatly by season and year class during the study period. Abundance was high in 1976 but winter mortality (99%) left an adult density of only .01 per m2 surface area in the marsh during spring 1977. Resultant 1977 year class density in the marsh was 1.88 per m2 by late fall 1977 but winter mortality again produced an adult density of .01 per m2 in spring 1978. Abundance was generally higher in the marsh than in the bay region especially during spring and late fall when catches in the bay were negligible. Based on catch rate comparisons, the summer and fall juvenile abundance of the 1976 year class was much higher than the juvenile abundance of the 1977 year class. Coincidentally, mean lengths and condition of the abundant 1976 year class in the late fall were significantly lower than those of the 1977 year class, suggesting density dependent population regulation. In both years, juveniles grew rapidly and reached full adult size by November when an offshore movement to deeper waters outside Essex Bay occurred. Biomass peaked in the marsh region in late fall 1977 at 7.8 g per m2 wet weight. Winter mortality was size selective, favoring larger individuals. The annual life history design of M. menidia including an offshore winter movement and high winter mortality suggests that silversides represent an important pathway of energy flow from marsh to offshore trophic systems.  相似文献   

11.
During 1973 and 1974 seasonal abundance and mean total length of Atlantic croaker,Micropogonias undulatus, were investigated by otter trawl at 33 stations in South Carolina estuaries in relation to bottom salinity and temperature. Relative abundance of Atlantic croaker was measured by catch per unit effort at 3°C temperature intervals and 3‰ salinity intervals. Croaker occurred over a bottom temperature range of 9.0–31.4°C while occurring most abundantly in waters above 24.0°C. No significant correlation between size and temperature was found. Croaker were collected in salinities from 0.4 to 34.4‰. High correlations of size and salinity were evident in 1973 during winter (r=0.79), summer (r=0.82), and fall (r=0.94). In 1974, correlations were significant only during fall (r=0.76).  相似文献   

12.
Solar cycle and equatorial stratopause temperature   总被引：1，自引：0，他引：1  
Variations in a solar activity and their effect if any on the temperature of the stratopause are studied. Monthly mean stratopause temperatures during 1969–1976 and departures from the monthly mean value of eight-year period, determined for four equatorial rocket launching stations,viz. Ascension Island, Kwajalem, Fort Sherman and Thumba, are statistically compared with sunspot number departures. To study the effects of seasonal variation on stratopause temperature, the data have been divided into winter, summer and equinoctial periods. Seasonwise study indicates that the correlation between the stratopause temperature and sunspot number is positive and just below the significant level for Thumba and positive and highly significant over all the other stations with a better relationship in equinoctial periods than in both winter and summer. The estimated regression coefficients are positive and significant.  相似文献   

13.
Tidal wetlands are affected by sea level rise. In the tidal freshwater stretches of estuaries in the temperate zone, willows (Salix spp.) form tidal freshwater forests above the mean high water level. Willows tolerance to prolonged periodic flooding in riverine systems is well documented, whereas effects of tidal flooding on willows are largely unknown. Flooding stress may play a major role in regeneration failure of willows in tidal forest stands along estuarine shores, and juvenile willows might be specifically affected by partial or total submergence. To assess the tolerance of juvenile willows to tidal flooding, we conducted a mesocosm experiment with cuttings from Salix alba and Salix viminalis, which are both characteristic species for tidal freshwater forests in Europe. Cuttings originating from either fresh or brackish tidal forest stands were grown under four tidal treatments with up to a tidal flooding of 60 cm. A general tolerance to a tidal flooding of 60 cm was observed in chlorophyll fluorescence, growth rates, and biomass production in both willow species. Overall, S. alba showed higher leaf and shoot growth, whereas S. viminalis produced more biomass. S. alba with brackish origin performed worst with increasing tidal flooding, suggesting a possible pre-weakening due to stressful site conditions in tidal wetlands at the estuarine brackish stretch. This study demonstrates that juvenile willows of S. alba and S. viminalis tolerate tidal flooding of up to 60 cm. It is concluded that tidal inundation acts as a stress by causing submergence and soil anaerobiosis, but may also act as a subsidy by reestablishing aerobic conditions and thus maintaining willows performance. Therefore, we suggest investigations on Salix tidal flooding tolerance and possible effects of willows on tidal wetland accretion under estuarine field conditions.  相似文献   

14.
This paper analyzes thermal energy transport in the narrow and tidally energetic Guadalquivir River Estuary (SW Spain). Measurements from a comprehensive monitoring campaign (2008–2011) reveal the forcing factors of the temperature field and its spatio-temporal variability. The along-channel thermal energy gradient reaches magnitudes of ～375 J/m4 near the mouth during the summer and winter. The water temperature is primarily controlled by shortwave radiation, latent heat transfer through the free surface, and tidal advection, whereas it depends less on freshwater discharge and longitudinal dispersion. The tidally averaged effective longitudinal thermal dispersion coefficient was evaluated at several stretches for each tidal cycle. The mean values of the coefficient tend to increase landward and are on the order of ～103, larger than (but of the same order of magnitude as) the salinity coefficient values. Based on these analyses, a deterministic operational model for thermal energy transport was developed. The model solves the tidally and cross-sectionally averaged advection–dispersion equation for the thermal energy balance and obtains accurate fits of the subtidal temperature field at any location within the estuary. The modeled water temperatures agreed well with the observations at all the stations (coefficients of determination, R 2 greater than 0.98), even after the seasonal oscillation in radiation was removed (R 2?>?0.77).  相似文献   

15.
The fish assemblages of two South Carolina estuarine tide pools located in the North Edisto River were sampled from June to October 1977, and during June and July 1978, by haul seine, lift net and channel net. The nekton was dominated numerically byFundulus heteroclitus, Leiostomus xanthurus, Menidia menidia andAnchoa mitchilli. Oyster reef areas were dominated numerically byGobiosoma bosci andF. heteroclitus. The relative abundance of tide pool fishes differs from deep water areas of the North Edisto River as described from otter trawls, but is similar to that described by others for South Carolina tidal creeks.  相似文献   

16.
Water volume discharge estimates were made at a sample cross-section of the Canary Creek salt marsh (Lewes, Delaware). To account for cross-sectional velocity variations, a dense spatial array of current meters was used. Simultaneous measurements were taken at hourly intervals over three complete tidal cycles. A practical method is presented whereby instantaneous average cross-sectional velocity, instantaneous cross-sectional discharge and tidal cycle discharge can be estimated from a dense current meter array, orideal data set. Based on theseideal estimates, it is shown that a simplified spatial array can be used to estimate water discharges within acceptable error limits. Instantaneous cross-sectional discharges and total tidal cycle discharges were estimated with uncertainties of ±11% and ±7%, respectively. To minimize errors when estimating material exchange between salt marshes and adjacent waters, it is suggested that a comprehensive assessment of cross-sectional lateral current velocity variations be conducted.  相似文献   

17.

Background

High salinity and arsenic (As) concentrations in groundwater are widespread problems in the tidal deltaplain of southwest Bangladesh. To identify the sources of dissolved salts and As, groundwater samples from the regional shallow Holocene aquifer were collected from tubewells during the dry (May) and wet (October) seasons in 2012–2013. Thirteen drill cores were logged and 27 radiocarbon ages measured on wood fragments to characterize subsurface stratigraphy.

Results

Drill cuttings, exposures in pits and regional studies reveal a >5 m thick surface mud cap overlying a ~30 m thick upper unit of interbedded mud and fine sand layers, and a coarser lower unit up to 60 m thick dominated by clean sands, all with significant horizontal variation in bed continuity and thickness. This thick lower unit accreted at rates of ~2 cm/year through the early Holocene, with local subsidence or compaction rates of 1–3 mm/year. Most tubewells are screened at depths of 15–52 m in sediments deposited 8000–9000 YBP. Compositions of groundwater samples from tubewells show high spatial variability, suggesting limited mixing and low and spatially variable recharge rates and flow velocities. Groundwaters are Na–Cl type and predominantly sulfate-reducing, with specific conductivity (SpC) from 3 to 29 mS/cm, high dissolved organic carbon (DOC) 11–57 mg/L and As 2–258 ug/L, and low sulfur (S) 2–33 mg/L.

Conclusions

Groundwater compositions can be explained by burial of tidal channel water and subsequent reaction with dissolved organic matter, resulting in anoxia, hydrous ferric oxide (HFO) reduction, As mobilization, and sulfate (SO4) reduction and removal in the shallow aquifer. Introduction of labile organic carbon in the wet season as rice paddy fertilizer may also cause HFO reduction and As mobilization. Variable modern recharge occurred in areas where the clay cap pinches out or is breached by tidal channels, which would explain previously measured 14C groundwater ages being less than depositional ages. Of samples collected from the shallow aquifer, Bangladesh Government guidelines are exceeded in 46 % for As and 100 % for salinity.
  相似文献   

18.
Between September 1976 and August 1978, samples of four species of sponge,Microciona prolifera (Ellis and Solander),Haliclona loosanoffi Hartman,Lissodendoryx isodictyalis (Carter) andHalichondria bowerbanki Burton, were collected from subtidal shell debris in a North Edisto River, South Carolina saltmarsh creek and associated amphipods identified. Dominant spongicolous amphipods wereColomastix halichondriae Bousfield,Leucothoe spinicarpa (Abildgaard),Corophium simile Shoemaker,Corophium acherusicum Costa,Lembos cf.L. websteri Bate andMelita appendiculata (Say). Densities of amphipods inMicroclona prolifera andHalichondria bowerbanki usually exceeded those inLissodendoryx isodictyalis andHaliclona loosanoffi. Seasonal changes in amphipod dominance were however approximately the same in all sponge species. Winter dominance byCorophium spp., and on occasionLembos spp., is followed by spring dominance byMelita appendiculata and summer dominance byColomastix halichondriae. Harsher winter conditions in 1976–77 apparently resulted in more reduced populations of various sponge species as well asColomastix halichondriae andLeucothoe spinicarpa when compared with the following winter. With some exceptions during the winter, amphipod density inMicrociona prolifera generally decreased as sponge size increased. The range of gammarid amphipod densities inMicrociona prolifera was 128–724 individuals per 5 g (40.3 cm3) of sponge.  相似文献   

19.
Spatial and temporal distribution and characteristics of three eukaryotic biofilms were monitored for an 18-month period in an acid mine drainage environment at the Green Valley coalmine in Indiana, USA. Each biofilm is dominated (>90 %) by a single eukaryotic microorganism based on enumeration: Euglena mutabilis, the diatom species Nitzschia tubicola, and a filamentous alga belonging to the genus Klebsormidium sp. The E. mutabilis-dominated biofilm occurs year round, covering up to 100 % of the channel bottom in spring and fall. The N. tubicola-dominated biofilm is less abundant, exists as small patches in spring and fall, expands from these patches to cover up to 50 % of the channel bottom in June, and is absent in winter. The Klebsormidium-dominated biofilm is restricted to small patches covering <5 % of the channel bottom from spring through fall and is absent in winter. Also present are floating microbial scum layers. The eukaryotic biofilms and scum layers contribute to the attenuation of precipitates and to the formation of organosedimentary structures, or stromatolites, by trapping and binding chemical precipitates via aerotaxis and phototaxis and by serving as a medium for passive accumulation of precipitates. Each stromatolite layer represents the morphological characteristics of each eukaryotic biofilm that served as the architect of the layer and the time of year the biofilm populated the channel. Processes involved in stromatolite formation also attenuate chemical sediments by binding them to the channel bottom and prior stromatolite surface rather than allowing them to be carried to the adjacent drainage system where they may become bioavailable to other forms of life.  相似文献   

20.
The Asiatic clam,Corbicula fluminea (Müller), has extended its range to include the tidal fresh-water portion of the Potomac River, Maryland. Though patchily distributed, the clams have attained densities of 665 m?2. Size-class distributions indicate that the clams first appeared in 1975. About 90% of the population belong to year-class I and were less than 12 mm in length. Elsewhere, this species has created severe water quality problems; it should be closely watched in the Potomac.  相似文献   

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