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1.
This study was designed to examine effects of low dissolved oxygen on finfish, lobster, and squid under field conditions in western Long Island Sound. The relationship between bottom dissolved oxygen (DO) and catch was examined for effects on abundance, numbers of species, and mean length, for trawl sites throughout the sound. Examination of mean catch per tow, and species number per tow, showed that both abundance and diversity decreased markedly with bottom DO, with dramatic declines at sites with DO<2 mg l?1. Of 18 species examined, 15 were found to occur with greater frequency at sites with DO>3 mg l?1 compared to sites with <2 mg l?1, and three of these species occurred significantly less frequency at a DO of 2–3 mg l?1. Trawl samples taken in the Narrows west of Greenwich, an area which chronically experiences summer hypoxia (DO<3 mg l?1) consistently yielded below average species number during hypoxic events. However, when DO was>3 mg l?1, 13 of 14 tows had above average species number. Abundance of five common species at sites>3 mg l?1 DO were significantly higher than at sites <3 mg l?1 DO in this area. Lobster was the only species not showing this DO threshold. Patterns in abundance vs DO for squid, bluefish, and butterfish suggest that these species are among the most sensitive to hypoxia. Only one of the four examined species, winter flounder, showed a decrease in mean length with DO. Scup, bluefish, and lobster lengths did not vary significantly with respect to dissolved oxygen. 相似文献
2.
To fill in the large existing data gap, this study presents results of a comprehensive data set from Kuwait Bay (KB), showing the horizontal and vertical distribution of its prominent hydrodynamic variables (i.e., water temperature, seawater salinity, seawater density) and water quality variables (i.e., chlorophyll-a concentration, turbidity, dissolved oxygen (DO) concentration, DO saturation, apparent oxygen utilization, photosynthetic active radiation). Field measurements were carried out between 11 September 2014 and 17 August 2015 covering number of monitoring stations in the entire bay. The results revealed significant seasonal variations and apparent three-dimensional features of the measured variables exemplifying the necessity of not considering the bay as a well-mixed water body in the future oceanographic studies anytime of the year. However, well-mixed conditions (with the Brunt-Vaisala frequency of about 0.0002 s?1) were existent only in the winter. Bay’s water column began stratifying in late spring, and these were significantly intensified (with the Brunt-Vaisala frequency of about 0.0008 s?1) during the summer and early autumn. The stratification, together with the increase oxygen demand for decomposition processes and decrease in DO solubility in summer, led to the formation of a lower DO water mass (daytime DO concentration <4.2 mg l?1) at the lower layers. Results also suggested that the water of the KB is more transparent (indicated by lower turbidity) compared to the adjacent sea water. Measurement of light intensity along the water column indicated that the light extincts rapidly (i.e., the light reduced to approximately 10 % of the surface values at water depth of 2–6 m) in KB and many times absent at the water near the seabed. This study also suggested that the KB can be classified at a year-round negative, hypersaline, inverse, and hyperpycnal estuary. 相似文献
3.
Hypoxia occurs during summer in the southeastern region of Corpus Christi Bay, Texas. The objectives of this study were to identify potential causes of recurrent hypoxic events, to determine hypoxic effects on benthic macroinfauna, and to develop models of benthic response. Long-term and short-term hydrographic surveys were performed, and macroinfaunal samples were collected from normoxic and hypoxic regions of the bay. Hypoxia occurred in seven of the nine summers sampled (1988 to 1996). In 1994, the hypoxic event persisted for approximately 3 wk. Hypoxic events were associated with water column stratification where the difference between bottom and surface salinity was as high as 7.2‰ and averaged 4.1‰ The salinity difference is surprising because water column stratification is not expected in shallow (< 4 m), windy (average 18.5 km h−1) bays. Stratification did occur—hypersaline bottom water in a relatively stagnant portion of the bay—in spite of mixing forces (i.e., high winds), giving rise to hypoxia. Benthic biomass decreased 12-fold, and abundance and diversity decreased 5-fold under hypoxic conditions. In addition, dominance patterns shifted as oxygen levels declined from 5 mg O2 1−1 to <1 mg O2 1−1. The polychaete Streblospio benedicti and oligochaetes tolerated low oxygen better than other infauna. Community response to hypoxic disturbance was fit to a nonparametric categorical model and a parametric logistic model. Biomass, abundance, and diversity exhibited a lag response at <3 mg l−1, and increased exponentially from 3 mg 1−1 to 6 mg 1−1. Based on both models, 3 mg 1−1 appears to define the breakpoint between normoxic and hypoxic benthic communities in Corpus Christi Bay. This value is higher than traditional definitions of hypoxia, <2 mg 1−1 or <2 ml 1−1 (ca. 2.8 mg 1−1). *** DIRECT SUPPORT *** A01BY085 00002 相似文献
4.
This paper addresses temporal variability in bottom hypoxia in broad shallow areas of Mobile Bay, Alabama. Time-series data
collected in the summer of 2004 from one station (mean depth of 4 m) exhibit bottom dissolved oxygen (DO) variations associated
with various time scales of hours to days. Despite a large velocity shear, stratification was strong enough to suppress vertical
mixing most of the time. Bottom DO was closely related to the vertical salinity gradient (ΔS). Hypoxia seldom occurred when
ΔS (over 2.5 m) was <2 psu and occurred almost all the time when ΔS was >8 psu in the absence of extreme events like hurricanes.
Oxygen balance between vertical mixing and total oxygen demand was considered for bottom water from which oxygen demand and
diffusive oxygen flux were estimated. The estimated decay rates at 20°C ranging between 0.175–0.322 d−1 and the corresponding oxygen consumption as large as 7.4 g O2 m−2 d−1 fall at the upper limit of previously reported ranges. The diffusive oxygen flux and the corresponding vertical diffusivity
estimated for well mixed conditions range between 8.6–9.5 g O2 m−2 d−1 and 2.6–2.9 m2 d−1, respectively. Mobile Bay hypoxia is likely to be associated with a large oxygen demand, supported by both water column and
sediment oxygen demands, so that oxygen supply from surface water during destratification events would be quickly exhausted
to return to hypoxic conditions within a few hours to days after destratification events are terminated. 相似文献
5.
M. R. Roman J. J. Pierson D. G. Kimmel W. C. Boicourt X. Zhang 《Estuaries and Coasts》2012,35(5):1261-1269
The northern Gulf of Mexico (NGOMEX) was surveyed to examine the broad-scale spatial patterns and inter-relationships between hypoxia (<2?mg?L?1 dissolved oxygen) and zooplankton biovolume. We used an undulating towed body equipped with sensors for conductivity, temperature, depth, oxygen, fluorescence, and an optical plankton counter to sample water column structure, oxygen, and zooplankton at high spatial resolution (1?m??vertical; 0.25?C1?km??horizontal). We contrast the distribution of zooplankton during summer surveys with different freshwater input, stratification, and horizontal and vertical extent of bottom-water hypoxia. Bottom-water hypoxia did not appear to influence the total amount of zooplankton biomass present in the water column or the areal integration of zooplankton standing stock in the NGOMEX region surveyed. However, where there were hypoxic bottom waters, zooplankton shifted their vertical distribution to the upper water column during the day where they normally would reside in deeper and darker waters. When bottom waters were normoxic (>2?mg?L?1 dissolved oxygen), the daytime median depth of the water column zooplankton was on average 7?m deeper than the median depth of zooplankton in water columns with hypoxic bottom waters. A reduction in larger zooplankton when there were hypoxic bottom waters suggests that if zooplankton cannot migrate to deeper, darker water under hypoxic conditions, they may be more susceptible to size-selective predation by visual predators. Thus, habitat compression in the northern Gulf of Mexico due to hypoxic bottom water may have implications for trophic transfer by increasing the contact between predators and prey. 相似文献
6.
Bottom water hypoxic events were observed in Narragansett Bay, Rhode Island during the summer of 2001 using a towed sensor, vertical casts at fixed stations, and continuous monitoring buoys. This combination of approaches allowed for both extensive spatial and temporal sampling. Oxygen concentrations below the U.S. Environmental Protection Agency (EPA) acute hypoxia criterion of 2.3 mg l?1 were observed in the northern parts of Narragansett Bay, including the Providence River. We estimate 39% of the area of the Providence River was affected by acute hypoxia between July and September 2001. All other regions experienced only small areas of acute hypoxia (<5%), and no acute hypoxia was observed from Quonset Point south. The area encompassing oxygen concentrations below the EPA chronic hypoxia criterion of 4.8 mg l?1 was much more extensive in the upper half of Narragansett Bay, sometimes covering the majority of the region, though it is unclear whether exposure to concentrations below this criterion persisted long enough to significantly affect marine species in these areas. Vertical profiles of dissolved oxygen typically exhibited a mid water oxygen minimum near the pycnocline, followed by a slight increase in oxygen with depth. The surface waters above the pycnocline were typically supersaturated with oxygen. The northern portions of the Bay where the most extensive hypoxia was observed corresponded to the regions with both the greatest thermohaline stratification, the highest nutrient inputs, and the highest primary productivity. 相似文献
7.
The distribution and intensity of hypoxia (low dissolved oxygen) in estuaries is increasing worldwide due to cultural eutrophication.
This study quantifies the strength of associations between the duration of diel-cycling severe hypoxia (≤2 mg O2 l−1) in bottom water (∼15 cm above bottom) of a shallow (<2 m) coastal lagoon estuary (Delaware, USA) and abiotic environmental
variables (water temperature, insolation, tide, streamflow, and wind) and predicts the duration of severe hypoxia given different
combinations of these variables. The intensity and spatial extent and dynamics of diel-cycling severe hypoxia events were
defined. Vertical variability in dissolved oxygen (DO) concentration during the daytime was also determined. During the summers
of 2001–2005, bottom DO data were collected for periods of weeks to months at multiple sites using automated sondes. Multiple
linear regression (MLR) and regression tree analysis (RTA) were used to determine the relative importance of the environmental
variables in predicting the number of hours of severe hypoxia per day. Key findings of the study were that severe hypoxia
events of minutes to hours in duration occurred frequently in all four tributaries sampled, primarily between 0200 and 1000
hours. Severe hypoxia duration and diel-cycling amplitudes of DO concentration increased in the up-tributary direction. Hierarchically,
the duration of severe hypoxia was influenced mostly by the mean daily water temperature, then by preceding days’ total insolation,
percentage of morning hours (02:00 to 10:00 a.m.) ebb tide, and daily streamflow. Collectively, the variables examined by the MLR and the RTA approaches accounted for 62%
and 65% of the variability in the duration of severe hypoxia, respectively. RTA demonstrated that daily mean water temperature
above 26.3°C and previous day’s total insolation below 13.6 kW m−2 were associated with the longest lasting severe hypoxic events (9.56 h). The environmental variables and combinations of
conditions that modulate or augment diel-cycling hypoxia presented in this paper enhance understanding of this widespread
and growing phenomenon and provide additional insight regarding the extent to which it can impact food webs in very shallow
estuarine waters that often serve as nursery habitat. 相似文献
8.
Late summer hypoxia (<3 ppm oxygen) in western Long Island Sound (WLIS) is a persistent environmental and management issue whose controlling processes are poorly understood. Measured rates of sediment and water-column oxygen consumption in the bottom water suggest that a condition of no oxygen should be attained on the time scale of 13–30 d. Observations, however, indicate the onset of hypoxia is of the order 150 d. Therefore, horizontal and/or vertical transport of oxygen into the area of hypoxia must play an important role. Hypoxia decreases benthic activity and the sediment flux of222Rn. The resulting horizontal gradient in bottom water222Rn was measured and used to estimate the effective horizontal transport rate (>5–50 m2 s?1), which is considerably slower than previous estimates. Scale analysis of the hypoxia process indicates that horizontal transport rates alone can explain the slow progression of hypoxia in XLIS but that vertical processes may also be capable of delaying the onset of hypoxia especially under conditions of weak stratification or weak intermediate layer oxygen consumption. This scale analysis indicates a delicately balanced process that is sensitive to both climatologically-driven variability in the rates of horizontal and vertical transport as well as the biologically-driven rates of oxygen consumption. An improved ability to predict and/or control hypoxia must be based on a better understanding of temporal and spacial variations in circulation, mixing, and stratification as well as the biological processes in the water column and the sediments. 相似文献
9.
The Sungai Merbok estuary, in wet tropical Peninsular Malaysia, borders the Straits of Malacca. Tide, current, and salinity data are used to describe the salient hydrographic features of the mangrove-fringed system. The Sungai Merbok estuary is characterized by a 1.7 m semidiurnal tide with a 0.16 form number, peak currents of 1.3 m s?1, and mean freshwater discharge of 20 m3 s?1. The system is classified as 2a/2b estuary (Hansen and Rattray 1966) or 1a/1b during periods of low runoff. Gravitational circulation is highly variable (but coincides with the neap stratification) and vertical stratification varies from 10?2 to 1. The estuary displays a pronounced fortnightly neap-spring stratification-destratification cycle. The effective longitudinal dispersion coefficient is approximately 100 m2 s?1. 相似文献
10.
Amino acid composition of suspended particles,sediment-trap material,and benthic sediment in the Potomac Estuary 总被引：1，自引：0，他引：1
Sediment trap deployments in estuaries provide a method for estimating the amount of organic material transported to the sediments from the euphotic zone. The amino acid composition of suspended particles, benthic sediment, and sediment-trap material collected at 2.4 m, 5.8 m, and 7.9 m depths in the Potomac Estuary was determined in stratified summer waters, and in well-mixed oxygenated waters (DO) in late fall. The total vertical flow, or flux, of material into the top traps ranged from 3 g m?2 d?1 in August to 4.9 g m?2 d?1 in October. The carbon and nitrogen fluxes increased in the deepest traps relative to the surface traps during both sampling periods, along with that of the total material flux (up to 47.3 g m?2 d?1 in the deepest trap), although the actual weight percent of organic carbon and organic nitrogen decreased with depth. Amino acid concentrations ranged from 129 mg g?1 in surface water particulate material to 22 mg g?1 in particulate material in 9-m-deep waters and in the benthic sediment. Amino acid concentrations from 2.4-mg-depth sediment traps averaged 104±29 mg g?1 in stratified waters and 164±81 mg g?1 in well-mixed waters. The deep trap samples averaed, 77.3±4.8 mg g?1 amino acids in summer waters and 37±16 mg g?1 in oxygenated fall waters. Amino acids comprised 13% to 39% of the organic carbon and 12% to 89% of the orgnaic nitrogen in these samples. Analysis of the flux results suggest that resuspension combined with lateral advection from adjacent slopes can account for up to 27% of the material in the deep traps when the estuary was well-mixed and unstratified. When the estuary was stratified in late summer, the amino acid carbon produced by primary productivity in the euphotic zone decreased by 85% (86% for total organic carbon) at the pycnocline at 6 m depth, leaving up to 15% of the vertical organic flux available for benthic sediment deposition. 相似文献
11.
Data are presented on dissolved oxygen (DO) concentrations and their relationship to salinity, suspended particulate matter (SPM), concentrations, and the turbidity maximum in the Humber-Ouse Estuary, United Kingdom, during summer 1995. Measurements in the upper Humber during March 1995 showed DO in the range 82% to 87% of saturation. Suspended particulate matter concentrations were <5000 mg l?1 and salinity was in the range 0.5 to 12. In contrast, a pronounced DO sag occurred in the upper reaches of the Ouse during medium and spring tide, summer conditions. The DO minimum was essentially an anoxic level and was associated with the location of the turbidity maximum, at salinities between about 0.4 and 1.5. SPM concentrations at 1 m beneath the surface reached 25,000 mg l?1 in the turbidity maximum, between about 20 km and 40 km from the tidal limit. Suspended particulate matter concentrations were much lower at neap tides, although dense suspensions of SPM (>60,000 mg l?1) occurred within 1 m of the bed in the turbidity maximum region. A spring-neap record showed a dramatic and tidally controlled decrease in DO at very low salinities as the tides progressed from neaps to springs. An anchor station located down-channel of the turbidity maximum showed that about 95% of the variance in DO, which varied from 28% at low-water slack to 67% at high-water slack, could be explained in terms of salinity variation. At the up-channel margins of the turbidity maximum, DO increased from zero (anoxia) near high water to 60% near low water slack, in contrast to the behavior down-channel of the turbidity maximum. About 82% of the variance in DO could be explained in terms of salinity variations alone. Only 43% of the DO variance could be explained in terms of SPM alone. Up-channel of the turbidity maximum, SPM concentrations were relatively low (<3000 mg l?1) and DO levels varied from 48% of saturation near high water to 83% near low water slack. About 76% of the variance in DO could be explained in terms of salinity variations alone. Within the turbidity maximum region, DO varied from <2% saturation on the early flood and late ebb and maximized around 7% at high water slack. About 63% of the variance in DO could be explained in terms of salinity variation alone. This increased to 70% when suspended particulate matter was taken into account. Only 29% of the DO variance could be explained in terms of suspended particulate matter alone. Because bacteria were likely to have been the cause of the observed reduction in DO, the numbers of bacteria, both free-living and attached to particles, were measured in the turbidity maximum region. Numbers of free-living bacteria were low and most of the bacteria were attached to sediment particles. There was a linear correlation between total bacterial number and suspended particulate matter concentration, suggesting that the strong DO demand was exerted locally as a result of bacterial activity associated with increased suspended particulate matter concentrations. An order of magnitude analysis of DO consumption within the Ouse’s turbidity maximum, based on the premise that DO depletion was directly related to suspended particulate matter concentrations and that DO addition was due to reaeration, indicates that complete deoxygenation could have occurred with an oxygen depletion rate of ～0.01 mg DO h?1/g suspended particulate matter during the residence time of waters within the turbidity maximum (～7 d). This rate was sufficiently fast that anoxic to aerobic conditions were able to develop a spring-neap periodicity within the turbidity maximum, but too slow to generate substantial intratidal fluctuations in DO. This is in accordance with the observations, which show that relatively little of the intratidal variance in DO could be explained in terms of suspended particulate matter fluctuations, whereas most of the variance could be explained in terms of salinity, which behaved as a surrogate measure for the proximity of the turbidity maximum. 相似文献
12.
A retrospective analysis of available data was conducted to characterize the spatial distribution and temporal trends in dissolved oxygen (DO) concentrations in Long Island Sound (LIS) over the past four decades. A general east-to-west gradient of decreasing bottom DO was evident in all historical data examined. In our review of data from the 1950s, collected by Gordon Riley and colleagues, and from contemporary surveys, we found no evidence of hypoxia (DO≤0.3, mg 1?1) in the Eastern Basin; however, in the deeper waters of the Central Basin, there is some evidence for a recent (1986) emergence of moderate hypoxia. The Western Basin experienced episodes of hypoxia during the 1970s which became more recurrent and possibly more severe in the late 1980s. The most severe, persistent and chronically recurrent hypoxia occurred throughout the water column of the East River and in bottom waters of the Western Narrows. An unprecedented episode of anoxia was observed in both the Western and Eastern Narrows regions of LIS in 1987. Previously, anoxia occurred rarely, was short-lived, and was confined to the East River. Statistical trend analyses revealed a significant increase in the summer minimum bottom DO in the lower and middle reaches of the East River over the past 20 years. Beginning in 1981, however, DO declined markedly in the adjacent Narrows bordering the Nassau County nearshore. The improvements in East River water quality over the previous 15–20 years appear to have been gained at the, expense of poorer water quality in the western sound. Mechanisms potentially responsible for the recent decline in bottom DO in western LIS are suggested. 相似文献
13.
Hypoxia/anoxia in bottom waters of the Rappahannock River, a tributary estuary of Chesapeake Bay, was observed to persist throughout the summer in the deep basin near the river mouth; periodic reoxygenation of bottom water occurred on the shallower sill at the river mouth. The reoxygenation events were closely related to spring tide mixing. The dissolved oxygen (DO) in surface waters was always near or at the saturation level, while that of bottom waters exhibited a characteristic spatial pattern. The bottom DO decreased upriver from river mouth, reaching a minimum upriver of the deepest point of the river and increasing as the water becaume shallower further upriver. A model was formulated to describe the longitudinal distribution of DO in bottom waters. The model is based on Lagrangian concept—following a water parcel as it travels upriver along the estuarine bottom. The model successfully describes the characteristic distribution of DO and also explains the shifting of the minimum DO location in response to spring-neap cycling. A diagnostic study with the model provided insight into relationships between the bottom DO and the competing factors that contribute to the DO budget of bottom waters. The study reveals that both oxygen demand, either benthic or water column demand, and vertical mixing have a promounced effect on the severity of hypoxia in bottom waters of an estary. However, it is the vertical mixing which controls the longitudinal location of the minimum DO. The strength of gravitational circulation is also shown to affect the occurrence of hypoxia. An estuary with stronger circulation tends to have less chance for hypoxia to occur. The initial DO deficit of bottom water entering an estuary has a strong effect on DO concentration near the river mouth, but its effect diminishes in the upriver direction. 相似文献
14.
Species of submerged aquatic vegetation (SAV) are frequently used in the management of estuarine systems to set restoration goals, nutrient load reduction goals, and water quality targets. As human need for water increases, the amount of freshwater required by estuaries has become an increasingly important issue. While the, science of establishing the freshwater needs of estuaries is not well developed, recent attempts have emphasized the freshwater requirements of fisheries. We evaluate the hypothesis that SAV can be used to establish freshwater inflow needs. Salinity tolerance data from laboratory and field studies of SAV in the Caloosahatchee estuary, Florida, are used to estimate a minimum flow required to maintain the salt-tolerant freshwater species,Vallisneria americana, at the head of the estuary and a maximum flow required to prevent mortality, of the marine speciesHalodule wrightii at its mouth. ForV. americana, laboratory experiments showed that little or no growth occurred between 10‰ and 15‰ In the field, lower shoot densities (<400 shoots m?2) were associated with salinities greater than 10‰. Results forH. wrightii were more variable than forV. americana. Laboratory experiments indicated that mortality could occur at salinities <6‰, with little growth occurring between 6‰ and 12‰. Field data indicated that higher blade densities (>600 blades m?2) tend to occur at salinities greater than 12‰ Relationships between salinity in the estuary and discharge from the Caloosahatchee River indicated that flows>8.5 m3 s?1 would produce tolerable salinity (<10‰) forV. americana and flows<89 m3 s?1 would avoid lethal salinities (<6‰) forH. wrightii. 相似文献
15.
Rafael Santana Guilherme C. Lessa John Haskins Kerstin Wasson 《Estuaries and Coasts》2018,41(1):99-113
Estuarine ecosystem diversity and function can be degraded by low oxygen concentrations. Understanding the spatial and temporal patterns of dissolved oxygen (DO) variation and the factors that predict decreases in DO is thus essential to inform estuarine management. We investigated DO variability and its drivers in Elkhorn Slough, a shallow, well-mixed estuary affected by high nutrient loading and with serious eutrophication problems. Long-term (2001–2012), high-resolution (15 min) time series of DO, water level, winds, and solar radiation from two fully tidal sites in the estuary showed that hypoxia events close to the bottom are common in the summer at the more upstream estuarine station. These events can occur in any lunar phase (spring to neap), at any time of the day, and both on sunny or cloudy days. They are, however, short-lived (lasting in average 40 min) and mainly driven by momentary low turbulent diffusion around slack tides (both at high and low water). Tidal advective transport explains up to 52.1% of the daily DO variability, and the water volume (or DO reservoir) contained in the estuary was not sufficient to avoid hypoxia in the estuary. Solar radiation was responsible for a positively correlated DO daily cycle but caused a decreased in the averaged DO in the summer at the inner station. Wind-driven upwelling reduced the average DO at the more oceanic station during spring. The approach we employed, using robust techniques to remove suspect data due to sensor drift combined with an array of statistical techniques, including spectral, harmonic, and coherence spectrum analysis, can serve as a model for analyses of long-term water quality datasets in other systems. Investigations such as ours can inform coastal management by identifying key drivers of hypoxia in estuaries. 相似文献
16.
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
17.
Peter A. Thompson 《Estuaries and Coasts》1998,21(4):801-817
During 1995 the phytoplankton in the Swan River were intensively sampled to assess biomass and species composition. Continuous measurements of fluorescence, salinity, and temperature were made weekly during 40 km sampling trips along the estuary and used to map the seasonal progression of the algal biomass. Weekly measurements of primary production were made and used to model net primary production from the vertical distribution of biomass, irradiance, and phytoplankton species composition. Potential nutrient limitation was assessed with “all but one” nutrient bioassays. The results indicate a complex mixture of potentially limiting factors, which vary in time and space. Although the data sequence is short, it suggests a annual succession pattern of diatoms, chlorophytes, diatoms, and finally dinoflagellates and cryptophytes in late summer-autumn. Peak seasonal biomass was observed during January to April. Mean annual chlorophylla biomass was greatest in upstream stations (5–9), where estimates of net primary production rates averaged 1.55 g C m?2 d?1 and gross primary production was 800–1000 g C m?2 yr?1. Potential nutrient limitation was most severe from November to May, although not during January 1995. Based on bioassay results, during the period of greatest potential for nutrient limitation, nitrogen was 15 to 30 times more limiting to biomass development than phosphate. Runoff due to consistent rainfall during winter eventually breaks down stratification and flushes the estuary with low-salinity, nutrient-rich water, producing, a light-limited, nutrient-rich aquatic ecosystem. Timing and magnitude of physical forcing events, mainly rainfall, appear critical in determining the susceptibility of this ecosystem to summer and autumn algal blooms. 相似文献
18.
An Idealized Model and Systematic Process Study of Oxygen Depletion in Highly Turbid Estuaries 总被引：1，自引：0，他引：1
The sensitivity of oxygen depletion in turbid estuaries to parameters like freshwater discharge, depth, and sediment availability
is investigated using an idealized model. The model describes tidally averaged circulation and suspended sediment concentration
(SSC), which are input into an advection–diffusion sink module of dissolved oxygen (DO). Based on the analysis of field data
collected in the Ems estuary, the modeled oxygen depletion rates are proportional to SSC. The model is calibrated to the observed
variation of DO with SSC and temperature. Modeled DO closely tracks changes to the estuarine turbidity zone (ETZ): increased
channel depth, decreased freshwater discharge, and decreased mixing move the ETZ upstream, amplify SSCs, and decrease DO.
Summertime temperatures produce lower DO than cooler periods. Model results are consistent with historical measurements in
the Ems, which indicate that hypoxic events (DO concentrations < 2 mg l−1) have occurred more frequently after deepening from 5 to 7 m. 相似文献
19.
Mindaugas Zilius Marco Bartoli Mariano Bresciani Marija Katarzyte Tomas Ruginis Jolita Petkuviene Irma Lubiene Claudia Giardino Paul A. Bukaveckas Rutger de Wit Arturas Razinkovas-Baziukas 《Estuaries and Coasts》2014,37(3):680-694
We investigated the dissolved oxygen metabolism of the Curonian Lagoon (Baltic Sea) to assess the relative contributions of pelagic and benthic processes to the development of transient hypoxic conditions in shallow water habitats. Metabolism measurements along with the remote sensing-derived estimates of spatial variability in chlorophyll a were used to evaluate the risk of hypoxia at the whole lagoon level. Our data demonstrate that cyanobacterial blooms strongly inhibit light penetration, resulting in net heterotrophic conditions in which pelagic oxygen demand exceeds benthic oxygen demand by an order of magnitude. The combination of bloom conditions and reduced vertical mixing during calm periods resulted in oxygen depletion of bottom waters and greater sediment nutrient release. The peak of reactive P regeneration (nearly 30 μmol m?2 h?1) coincided with oxygen depletion in the water column, and resulted in a marked drop of the inorganic N:P ratio (from >40 to <5, as molar). Our results suggest a strong link between cyanobacterial blooms, pelagic respiration, hypoxia, and P regeneration, which acts as a feedback in sustaining algal blooms through internal nutrient cycling. Meteorological data and satellite-derived maps of chlorophyll a were used to show that nearly 70 % of the lagoon surface (approximately 1,000 km2) is prone to transient hypoxia development when blooms coincide with low wind speed conditions. 相似文献
20.
Michael A. Mallin Matthew R. McIver Heather A. Wells Douglas C. Parsons Virginia L. Johnson 《Estuaries and Coasts》2005,28(5):750-760
The New River Estuary consists of a series of broad shallow lagoons draining a catchment area of 1,436 km2, located in Onslow County, North Carolina. During the 1980s and 1990s it was considered one of the most eutrophic estuaries
in the southeastern United States and sustained dense phytoplankton blooms, bottom water anoxia and hypoxia, toxic outbreaks
of the dinoflagellatePfiesteria, and fish kills. High nutrient loading, especially of phosphorus (P), from municipal and military sewage treatment plants
was the principal cause leading to the eutrophic conditions. Nutrient addition bioassay experiments showed that additions
of nitrogen (N) but not P consistently yielded significant increases in phytoplankton production relative to controls. During
1998 the City of Jacksonville and the U.S. Marine Corps Base at Camp Lejeune completely upgraded their sewage treatment systems
and achieved large improvements in nutrient removal, reducing point source inputs of N and P to the estuary by approximately
57% and 71%, respectively. The sewage treatment plant upgrades led to significant estuarine decreases in ammonium, orthophosphate,
chlorophylla, and turbidity concentrations, and subsequent increases in bottom water dissolved oxygen (DO) and light penetration. The
large reduction in phytoplankton biomass led to a large reduction in labile phytoplankton carbon, likely an important source
of biochemical oxygen demand in this estuary. The upper estuary stations experienced increases in average bottom water DO
of 0.9 to 1.4 mg l−1, representing an improvement in benthic habitat for shellfish and other organisms. The reductions in light attenuation and
turbidity should also improve the habitat conditions for growth of submersed aquatic vegetation, an important habitat for
fish and shellfish. 相似文献