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1.
The effect of a 7-mo drought (La Niña 1988) was evaluated on pelagic properties in the large Patos Lagoon (30°12′–32°12′S, 50°40′–52°15′W). From December 1987 to December 1988, surface water was sampled along the longitudinal axis of the lagoon for temperature (10–29°C), salinity (0–31.4), dissolved inorganic phosphate (0.02–4.73 μM), nitrate (0.05–66.25 μM), nitrite (0.01–3.54 μM), ammonium (0.09–33.19 μM), silicate (1.11–359.20 μM), phytoplankton chlorophylla (chl; 0.4–41.2 mg m?3), primary production (gross PP 1.72–161.82 mg C m3 h?1; net PP 0.04–126.19 mg C m3 h?1), and species composition and abundance (42–4,961 ind ml?1). In the wet season the whole system acted as a river and light availability limited phytoplankton growth. During the drought from February to August monthly freshwater runoff was low and the inflow of marine water to the southern sector generated spatial variability of the analyzed properties and five functional areas were recognized. The northernmost Guaíba River (1) presented low light availability and phytoplankton chl concentration compared to the northern limnetic area (2) (chl mean 13.3 μg I?1; max 41.2 μg I?1; gross PP mean 52.6 mg C m3 h?1), which acted as a biological filter removing dissolved inorganic nutrients. Silicate concentration was strongly diminished in this area due to diatom uptake (Aulacoseira granulata, 9,330 cells ml?1). In the northern limnetic and central oligohaline (3) areas, phytoplankton biomass was controlled by light but nitrogen also played a limiting role. In the southern area (4) that is under marine influence, low chl concentration (mean 4.5 μg I?1) and gross PP (mean 28.1 mg C m3 h?1) coincided with co-limitation of nitrogen and light while the channel to the ocean (5) was strongly light limited. This study demonstrated that low light and high silicate input had a buffer effect at Patos Lagoon, hampering negative expression of cultural eutrophication. The main effect during the drought period occurred in the northern limnetic region, where low silicate values due to diatom uptake led to higher cyanobacteria abundance, and enhanced mineralization occurred in the central oligohaline lagoon. Increased rainfall resulted in light limitation and decreasing primary production in the entire freshwater lagoon, and the adjacent coastal region benefited from nutrient enrichment.  相似文献   

2.
Seasonal patterns of aboveground and belowground biomass, leaf chlorophyll (chl) content, and in situ differences in photosynthetic parameters were examined in the shoal grass Halodule wrightii along an estuarine gradient in the western Gulf of Mexico. Continuous measurements of biomass were collected over a 5-yr period (1989–1994) with respect to several abiotic factors in three estuarine systems that were characterized by significant differences in salinity and ambient dissolved inorganic nitrogen (DIN; NO2 ?+NO3 ?) regimes that ranged from 5–25‰ (0–80 μM DIN) in the Guadalupe estuary to 35–55‰ (0–9 μM DIN) in the upper Laguna Madre, Photosynthesis versus irradiance (P vs. I) parameters, measured from December 1989 to April 1991, showed no significant differences among the three sites, and there were no significant differences in leaf chlorophyll content and chl a:b ratios among sites over the entire 5-yr period. Saturation irradiance in Halodule wrightii is estimated at 319 μmoles photons m?2 s?1 based on measurements collected at the three sites over a 2-yr period. No strong seasonal variations were observed in total plant biomass, but root:shoot ratios (RSR) showed a clear pattern of maximum RSR values in winter and minimum values in summer. There were no significant differences in RSR among sites, and no consistent correlations could be established between plant parameters and sediment porewater NH4 +, salinity, or temperature. Sediment porewater NH4 + values generally ranged from 50 μM to 400 μM (average 130–150 μM) but could not be correlated with significant differences in sediment composition between the sites. The high productivity of Halodule wrightii under a variety of light, nutrient, and salinity conditions explains its ubiquitous distribution and opportunistic strategy as a colonizing species. However, the persistence of a dense algal bloom in Laguna Madre coincident with low DIN levels (<5 μM) contradicts previously accepted relationships on nutrient stimulation of algal growth, and provides strong evidence that water quality parameters for estuarine seagrasses are decidedly estuarine-specific. Consequently, a knowledge of the long-term history of estuarine systems is critical to habitat managers, who are required to establish minimum water quality criteria for the protection of submerged aquatic vegetation in estuarine systems. *** DIRECT SUPPORT *** A01BY074 00028  相似文献   

3.
Sediment-water exchanges of ammonium (NH4 +), nitrate + nitrite (NOx ?), filterable reactive phosphorus (FRP, primarily ortho-phosphate), and oxygen (O2) under aphotic (heterotrophic) conditions were determined at 2–5 stations in the Neuse River Estuary, from 1987 to 1989. Shallow (1 m), sandy stations were sampled along the salinity gradient. Fluxes from deep (>2 m) sites were compared to the shallow sites in two salinity zones. Grain size became finer and organic content increased with depth in the oligohaline zone but not in the mesohaline zone. Net release of NH4 + and FRP occurred at all sites. Fluxes varied from slight uptake to releases of 200–500 μmol m?2 h?1 (NH4 +) and 150–900 μmol m?2 h?1 (FRP). Net NOx ? exchange was near zero, but were ±100 μmol m?2 h?1 over the year. Release of NH4 + and FRP from the shallow sandy stations decreased with distance down the estuary, but O2 uptake did not change. The deeper oligohaline site had twofold higher rates of NH4 + and FRP release and O2 uptake than the shallow site, but no differences occurred between depths in the mesohaline zone. Temperature and organic content were important controls for all fluxes, but water column NOx ? concentration was also important in regulating NOx ? exchanges. Ratios of oxygen consumption to NH4 + release were near the predicted ratio (Redfield model) at oligohaline sites but increased down estuary at mesohaline sites. This may be due to greater nitrification rates promoted by autotrophy in the sediments.  相似文献   

4.
Sediment-water oxygen and nutrient (NH4 +, NO3 ?+NO2 ?, DON, PO4 3?, and DSi) fluxes were measured in three distinct regions of Chesapeake Bay at monthly intervals during 1 yr and for portions of several additional years. Examination of these data revealed strong spatial and temporal patterns. Most fluxes were greatest in the central bay (station MB), moderate in the high salinity lower bay (station SB) and reduced in the oligohaline upper bay (station NB). Sediment oxygen consumption (SOC) rates generally increased with increasing temperature until bottom water concentrations of dissolved oxygen (DO) fell below 2.5 mg l?1, apparently limiting SOC rates. Fluxes of NH4 + were elevated at temperatures >15°C and, when coupled with low bottom water DO concentrations (<5 mg l?1), very large releases (>500 μmol N m?2 h?1) were observed. Nitrate + nitrite (NO3 ?+NO2 ?) exchanges were directed into sediments in areas where bottom water NO3 ?+NO2 ? concentrations were high (>18 μM N); sediment efflux of NO3 ?+NO2 ? occurred only in areas where bottom water NO3 ?+NO2 ? concentrations were relatively low (<11 μM N) and bottom waters well oxygenated. Phosphate fluxes were small except in areas of hypoxic and anoxic bottom waters; in those cases releases were high (50–150 μmol P m?2 h?1) but of short duration (2 mo). Dissolved silicate (DSi) fluxes were directed out of the sediments at all stations and appeared to be proportional to primary production in overlying waters. Dissolved organic nitrogen (DON) was released from the sediments at stations NB and SB and taken up by the sediments at station MB in summer months; DON fluxes were either small or noninterpretable during cooler months of the year. It appears that the amount and quality of organic matter reaching the sediments is of primary importance in determining the spatial variability and interannual differences in sediment nutrient fluxes along the axis of the bay. Surficial sediment chlorophyll-a, used as an indicator of labile sediment organic matter, was highly correlated with NH4 ?, PO4 3?, and DSi fluxes but only after a temporal lag of about 1 mo was added between deposition events and sediment nutrient releases. Sediment O:N flux ratios indicated that substantial sediment nitrification-denitrification probably occurred at all sites during winter-spring but not summer-fall; N:P flux ratios were high in spring but much less than expected during summer, particularly at hypoxic and anoxic sites. Finally, a comparison of seasonal N and P demand by phytoplankton with sediment nutrient releases indicated that the sediments provide a substantial fraction of nutrients required by phytoplankton in summer, but not winter, especially in the mid bay region.  相似文献   

5.
Benthic macroinvertebrate biomass and ammonium excretion rates were measured at four stations in the Gulf of Mexico near the Mississippi River mouth. Calculated areal excretion rates were then compared to sediment-water nitrogen fluxes measured in benthic bottom lander chambers at similar stations to estimate the potential importance of macroinvertebrate excretion to sediment nitrogen mineralization. Excretion rates for individual crustaceans (amphipods and decapods) was 2–21 nmoles NH4 + (mg dry weight)?1 h?1. The mean excretion rates for the polychaetes, Paraprionaspio pinnata [6–12 nmoles NH4 + (mg dry weight)?1h?1] and Magelona sp. [27–53 nmoles NH4 + (mg dry weight)?1h?1], were comparable or higher than previous measurements for similar size benthic or pelagic invertebrates incubated at the same temperature (22±1°C). Although the relatively high rates of excretion by these selective feeders may have been partially caused by experimental handling effects (e.g., removal from sediment substrates), they probably reflected the availability of nitrogen-rich food supplies in the Mississippi River plume. When the measured weight-specific rates were extrapolated to total areal biomass, areal macroinvertebrate excretion estimates ranged from 7 μmole NH4 + m?2h?1 at a 40-m deep station near the river mouth to 18 μmole NH4 + m?2h?1 at a shallower (28-m deep) station further from the river mouth. The net flux of ammonium and nitrate from the sediments to the water measured in bottom lander chambers in the same region were 15–53 μmole NH4 + m?2h?1 and ?25–21 μmole NO3 ? m?2h?1. These results suggest that excretion of NH4 + by macroinvertebrates could be a potentially important component of benthic nitrogen regeneration in the Mississippi River plume-Gulf shelf region.  相似文献   

6.
A study of nutrient limitation of phytoplankton biomass production with emphasis on nitrate-nitrogen (NO3 ?) and ortho-phosphate-phosphorus (PO4 3?) was conducted in Perdido Bay, Alabama-Florida. The experimental design employed 18-1 outdoor microcosms operated in a static renewal mode. Phytoplankton growth responses (i.e., growth stimulation) measured as chlorophyll a (chl a) fell into three principal categories: primary P stimulation occurred mostly during the cooler months at the upper bay (tidal brackish) and mid bay (lower mesohaline) stations; a total of 12 out of 36 experiments; primary N stimulation occurred mostly during the warmer months primarily at the mid-bay station and infrequently at the upper and lower bay stations (upper mesohaline); a total of 7 out of 36 experiments; and N+P costimulation occurred primarily during the warmer months in the upper bay and mid bay and during both warmer and cooler months of the lower bay; a total of 17 out of 36 experiments. Primary P stimulation was generally associated with high ratios of dissolved inorganic nitrogen (DIN) to dissolved inorganic phosphate (DIP) (ratio range: 18 to 288). Conversely, primary N stimulation was associated with decreasing DIN:DIP ratios (range 8–46). Redfield ratios of particulate organic N (PON) to particulate organic P (POP) often indicated N limitation (i.e., values often less than 10). PON:chl a ratios often indicated N sufficiency, but three occasions were noted where PON:POP and PON:chl a ratios were not congruent. It is difficult to reconcile the inorganic and organic N and P ratios with the relatively low DIP and DIN concentrations. The phytoplankton assemblage appeared not to be strongly nutrient-limited but, given a nutrient increase, responded differentially to N and P, both seasonally and along the longitudinal salinity gradient. Grazing pressure in concert with nutrient limitation was advanced as an hypothesis to explain N+P co-limitation.  相似文献   

7.
The Casamance estuary, on the coast of Senegal, is an inverse hypersaline estuary: salinity increases landward, and dry season salinity values are up to 172 psu due to the evaporation of seawater. Dissolved inorganic carbon (DIC) concentrations decreased landward as a negative linear function of salinity. Thermodynamic modelling and the absence of CaCO3 in the sediments indicate that this loss of DIC was not due to calcite precipitation in the main water body. The innermost, almost landlocked, waters contained high phytoplankton biomass (50–300 μg chl I?1) and high concentrations of allochthonous dissolved organic carbon. Photosynthetic uptake of DIC and subsequent particulate organic carbon sedimentation is proposed as hypothetical explanation of the relationship between DIC and salinity; localized overheating in shallow waters might also be involved.  相似文献   

8.
This paper aims to reveal the reciprocal influence of Kürtün Dam and wastewaters from the settlements on the water quality in the stream Har?it, NE Turkey. Several key water-quality indicators were measured: water temperature (T), pH, dissolved oxygen (DO), electrical conductivity, water hardness, chemical oxygen demand (COD), ammonium nitrogen (NH4 +–N), nitrite nitrogen (NO2 ?–N), nitrate nitrogen (NO3 ?–N), total Kjeldahl nitrogen (TKN), total nitrogen (TN), orthophosphate phosphorus (PO4 3?–P), and methylene blue active substances (MBAS). The monitoring and sampling studies were conducted every 15 days from March 2009 to February 2010 at two stations selected in the upstream and downstream of the Kürtün Dam. It was concluded that the Kürtün Dam Lake had a high-quality water in terms of T, pH, DO, COD, NH4 +–N, NO2 ?–N and NO3 ?–N values, but slightly polluted water with respect to TKN, PO4 3?–P, and MBAS according to the Turkish Water Pollution Control Regulation. The dam improved the stream water quality by increasing the DO concentration, and decreasing the NO2 ?–N and PO4 3?–P concentrations thanks to its hydraulic residence time despite the wastewater discharge by the nearby settlements. However, the wastewater discharge deteriorated the stream water quality increasing the COD, NH4 +–N, NO3 ––N, and TN concentrations.  相似文献   

9.
Widespread use of septic tanks in the Florida Keys increase the nutrient concentrations of limestone groundwaters that discharge into shallow nearshore waters, resulting in coastal eutrophication. This study characterizes watershed nutrient inputs, transformations, and effects along a land-sea gradient stratified into four ecosystems that occur with increasing distance from land: manmade canal systems (receiving waters of nutrient inputs), seagrass meadows, patch reefs, and offshore bank reefs. Soluble reactive phosphorus (SRP), the primary limiting nutrient, was significantly elevated in canal systems compared to the other ecosystems, while dissolved inorganic nitrogen (DIN; NH4 + and NO3 ?) a secondary limiting nutrient, was elevated both in canal systems and seagrass meadows. SRP and NH4 + concentrations decreased to low concentrations within approximately 1 km and 3 km from land, respectively. DIN and SRP accounted for their greatest contribution (up to 30%) of total N and P pools in canals, compared to dissolved organic nitrogen (DON) and dissolved organic phosphorus (DOP) that dominated (up to 68%) the total N and P pools at the offshore bank reefs. Particulate N and P fractions were also elevated (up to 48%) in canals and nearshore seagrass meadows, indicating rapid biological uptake of DIN and SRP into organic particles. Chlorophylla and turbidity were also elevated in canal systems and seagrass meadows; chlorophylla was maximal during summer when maximum watershed nutrient input occurs, whereas turbidity was maximal during winter due to seasonally maximum wind conditions and sediment resuspension. DO was negatively correlated with NH4 + and SRP; hypoxia (DO<2.5 mg l?1) frequently occurred in nutrient-enriched canal systems and seagrass meadows, especially during the warm summer months. These findings correlate with recent (<5 years) observations of increasing algal blooms, seagrass epiphytization and die-off, and loss of coral cover on patch and bank reef ecosystems, suggesting that nearshore waters of the Florida Keys have entered a stage of critical eutrophication.  相似文献   

10.
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   

11.
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   

12.
We apply an objective statistical analysis to a 6-yr, multiparameter dataset in an effort to describe the spatial dependence and inherent variation of water quality patterns in the Florida Bay-Whitewater Bay area. Principal component analysis of 16 water quality parameters collected monthly over a 6-yr period resulted in live principal components (PC) that explained 71.8% of the variance of the original variables. The “organic” component (PC1) was composed of TN, TON, APA, and TOC; the “inorganic N” component (PCII) contained NO2, NO3, and NH4 +, the “phytoplankton” component (PCIII) was made up of turbidity, TP, and Chl a; DO and temperature were inversely related (PCIV); and salinity was the only parameter included in PCV. A cluster analysis of mean and SD of PG scores resulted in the spatial aggregation of 50 fixed monitoring stations in Florida Bay and Whitewater Bay into six zones of similar influence (ZSI) defined as Eastern Florida Bay. Core Florida Bay, Western Florida Bay, Coot Bay, the Inner Mangrove Fringe, and the Outer Mangrove Fringe. Marked differences in physical, chemical, and biological characteristics among ZSI were illustrated by this technique. Comparison of medians and variability of parameter values among ZSI allowed large-scale generalizations as to underlying differences in water quality in these regions. For example. Fastern Florida Bay had lower salinity, TON, TOC, TP, and Chl a than the Core Bay as a function of differences in freshwater inputs and water residence time. Comparison of medians and variability within ZSI resulted in new hypotheses as to the processes generating these internal patterns. For example, the Core Bay had very high TON, TOC, and NH4 + concentrations but very low NO3 ?, leading us to postulate the inhibition of nitrification via CO production by TOC photolysis. We believe that this simple, objective approach to spatial analysis of fixed-station monitoring datasets will aid scientists and managers in the interpretation of factors underlying the observed parameter distribution patterns. We also expect that this approach will be useful in focussing attention on specific spatial areas of concern and in generating new ideas for hypothesis testing.  相似文献   

13.
The impact of erosion control geotextiles on the surface runoff from slopes is quite variable and depends strongly on site-specific conditions (soil characteristics, slope morphology, climate, etc.), as has been shown in several earlier studies. In addition, little is known about the proportion of runoff reduction that is caused by the geotextile and the proportion that is caused by soil characteristics. To shed more light on this issue, an experiment was carried out to test the impact of 500 g m?2 jute nets (J500) and 400 g m?2; 700 g m?2 coir nets (C400, C700) on the surface runoff from simulated rainfall of four different intensities (I 1 = 18.7; I 2 = 27.2; I 3 = 53.6; I 4 = 90.5 mm h?1). Data on runoff volume, peak discharge and time to peak discharge were collected from 40 simulated rainfall events. An impermeable “no-soil” subgrade was used to examine the impact of the geotextile on runoff without any influence of soil. All tested geotextiles significantly reduced runoff (volume, peak discharge) at all rainfall intensities, with the exception of C400 and C700 during simulated rainfall intensity I 4. J500 seemed to have the most effective runoff reduction performance at all rainfall intensities. In general, as the rainfall intensity increased, the effectiveness of the geotextiles decreased. Interesting behaviour was observed for J500 under simulated rainfall intensity I 4—the effectiveness of the geotextile increased with the duration of the rainfall.  相似文献   

14.
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   

15.
Rates of nitrification along an estuarine gradient in Narragansett Bay   总被引：1，自引：0，他引：1  
Rates of pelagic nitrification, measured using N-Serve-sensitive [14C]bicarbonate uptake, varied by as much as an order-of-magnitude among three sites along the salinity gradient of Narragansett Bay (Rhode Island, United States). Rates were always higher at the Providence River estuary site (0.04–11.2 μmol N I?1 d?1) than at either the lower Narragansett Bay site (0.02–0.98 μmol N I?1d?1) or the freshwater Blackstone River site (0.04–1.7 μmol N I?1d?1). Although temperature was the most important variable regulating the annual cycle of nitrification, ammonium concentrations were most likely responsible for the large differences in rates among the three sites in summer. At the levels found in this estuarine system, salinity and concentrations of oxygen or total suspended matter did not appear to have a direct measurable effect on nitrification and pH did only occasionally. Nitrification played an important role in the nitrogen cycle at all three sites. In Narragansett Bay, nitrification contributed 55% of the NO2 ? and NO3 ? entering annually, and was the major source during spring and summer. Water from offshore was the only other large source of NO2 ? and NO3 ?, contributing 34%. High summer rates of nitrification could support much of the phytoplankton uptake of NO2 ? and NO3 ?. In the Providence River estuary, the largest annual input of NO2 ? and NO3 ? was from rivers (54%), although nitrification (28%) and water from lower portions of the bay (11%) also made large contributions. Again, nitrification was most important in the summer. The high rates of nitrification in the Providence River estuary during summer were also likely to be important in terms of oxygen demand, and the production of nitric and nitrous oxides. In the Blackstone River, NO2 ? and NO3 ? concentrations increased as the river flowed through Rhode Island, and nitrification was a possible source.  相似文献   

16.
Trends in the spatial distribution of chlorophylla (chla) and colloidal and total carbohydrates on the Molenplaat tidal flat in the Westerschelde estuary, Netherlands, reflected spatial differences in physical properties of the sediment. Results from a Spearman Rank Order Correlation indicated that many of the physical and biological measures covaried. Multiple regression analyses describing the relationship between colloidal carbohydrates and sediment properties resulted in several highly significant equations, although in all cases chla was able to predict colloidal carbohydrate content. Relationships between sediment surface chla and colloidal carbohydrate, and sediment erodibility (i.e., critical erosion threshold, Ucrit, and mass of sediment eroded at a velocity of 30 cm s?1) determined in annular flume experiments were examined. Overall sediment erodibility was lowest (i.e., high thresholds, low mass eroded) for the siltiest sediments in June 1996 when chla and colloidal carbohydrates were high (56.9 μg gDW?1 and 320.6 μg gluc.equ. gDW?1, respectively), and greatest (i.e., low thresholds, high mass eroded) at the sandier sediments in September 1996, when chla and colloidal carbohydrates were low (1.0 μg gDW?1 and 5.7 μg gluc.equ. gDW?1, respectively). When sediments were grouped according to relative silt content, the most significant relationships were found in muddy sand with a finegrained fraction (<63 μm) of 25–50%. Thresholds of erosion increased, while mass of sediment eroded decreased, with increasing chla and colloidal carbohydrate. A similar trend was observed for the sand-muddy sand (63 μm 10–25%). In the sand (63 μm 0–10%), there were no relationships for Ucrit, whereas mass eroded appeared to increase with increasing chla and colloidal carbohydrate. The increased carbohydrate may stick sand grains together, altering the nature of erosion from rolling grains to clumps of resuspension.  相似文献   

17.
The regulatory effect of salinity on nitrogen dynamics in estuarine sediments was investigated in the Randers Fjord estuary, Denmark, using sediment slurries and intact sediment cores and applying 15N-isotope techniques. Sediment was sampled at three representative stations varying in salinity, and all experiments were run at 0‰, 10‰, 20‰, and 30‰. The sediment NH4 + adsorption capacity decreased markedly at all stations when salinity was increased from 0‰ to 10‰; further increase showed little effect. In situ nitrification and denitrification also decreased with increasing salinities, with the most pronounced reduction of approximately 50% being observed when the salinity was raised from 0‰ to 10‰. The salinity-induced reduction in NH4 + adsorption capacity and stimulation of NH4 + efflux has previously been argued to cause a reduction in nitrification activity since the nitrifying bacteria become limited by NH4 + availability at higher salinities. However, using a potential nitrification assay where NH4 + was added in excess, it was demonstrated that potential nitrification activity also decreased with increasing salinity, indicating that the inhibitory salinity effect may also be a physiological effect on the microorganisms. This hypothesis was supported by the finding that denitrification based on NO3 − from the overlying water (Dw), which is independent of the nitrification process, and hence NH4 + availability, also decreased with increasing salinity. We conclude that changes in salinity have a significant effect on nitrogen dynamics in estuarine sediments, which must be considered when nitrogen transformations are measured and evaluated.  相似文献   

18.
Measurements of primary production in surf-zone habitats are relatively rare and often utilize simulation approaches, owing to the physical challenges of working in surf. The study reported here examined primary production in situ at two open ocean sandy beaches in southeastern North Carolina during relatively calm summer conditions. In situ bottle incubations using 14C uptake methods were complemented by simultaneous measures of phytoplankton photo-physiology assessed by Fast Repetition Rate Fluorometry (FRRF) in flow-through mode at the two sites across a spring-neap tidal cycle in July, 2010. The surf-zone phytoplankton was dominated by small centric and pennate diatoms as well as cyanobacteria and chlorophytes with biomass concentrations of 3.63?C9.23?mg chl a m?3. Primary productivity was relatively high, ranging from 31.5?C88.0?mg?C?m?3?h?1 by 14C. Biomass-specific productivity averaged ??9.4?mg C (mg chl a)?1?h?1 by 14C, indicating healthy phytoplankton populations. Measurements of the functional absorption cross section of photosystem II, ??PSII, via FRRF were 327?C380, comparable to values reported by other investigators of open ocean phytoplankton. Averaged values of the maximum effective quantum yield, F v/F m, corresponded to proportions of photochemically competent PSII reaction centers of 62.6?% to 72?%, indicating that the phytoplankton were nutrient-replete. These data suggest that the surf zone, although a spatially confined habitat, is a productive one that plays a significant role in coastal ocean ecology. Further investigation is needed to better understand primary productivity of phytoplankton in the surf zone and the effect of the dynamic environment on their physiological responses.  相似文献   

19.
In an attempt to more fully understand the dissolved inorganic nitrogen dynamics of the Neuse River estuary, 15NH4 + and 15NO3 ? uptake rates were measured and daily depth-integrated rates calculated for seven stations distributed along the salinity gradient. Measurements were made at 2–3-wk intervals from March 1985 to February 1989. Significant dark NH4 + uptake occurred and varied both spatially and seasonally, accounting for as much as 95% of light uptake with the median being 33%. Apparent NH4 + uptake ranged from 0.001 μmol N 1?1 h?1 to 4.2 μmol N 1?1 h?1, with highest rates occurring during late summer-fall in the oligohaline estuary. Apparent NH4 + uptake was significantly related to NH4 + concentration (p<0.01); however, the regression explained <3% of the variation. Daily-integrated NH4 + uptake ranged from 0.1 mmol N m?2 d?1 to 133 mmol N m?2 d?1 and followed the trend of apparent uptake. Annual NH4 + uptake of the estuary was significantly lower in 1988 than for any other year. Dark uptake of NO3 ? was only 14% of maximum light uptake. Apparent NO3 ? uptake rates ranged from 0.001 μmol N 1?1 h?1 to 1.84 μmol N 1?1 h?1 with highest rates occurring in the oligohaline estuary. Apparent NO3 ? uptake was significantly related to NO3 ? concentration (p<0.01); however, the regression explained <5% of the variation. In general, NO3 ? uptake was only 20% of total dissolved inorganic nitrogen (DIN) uptake. Daily-integrated NO3 ? uptake ranged from 0.1 mmol N m?2 d?1 to 53 mmol N m?2 d?1 and followed similar patterns of apparent uptake. Annual NH4 + uptake was 11.39 mol N m?2 yr?1, 10.28 mol N m?2 Yr?1, 10.93 mol N m?2 yr?1, and 7.38 mol N m?2 yr?1, and 1.84 mol N m?2 yr?1, with the 4-yr mean being 10.0. Annual NO3 ? uptake was 3.12 mol N m?2 yr?1, 3.40 mol N m?2 yr?1, 1.96 mol N m?2 yr?1, and 1.84 mol N m?2 yr?1, with the 4-yr mean being 2.6. The total annual DIN uptake was more than twice published estimates of phytoplankton DIN demand, indicating that there is an important heterotrophic component of DIN uptake occurring in the water column. The extrapolation of nitrogen demand from primary productivity results in serious underestimates of estuarine nitrogen demand for the Neuse River estuary and may be true for other estuaries as well.  相似文献   

20.
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   

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