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1.
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
2.
This study examined freshwater discharge of dissolved organic matter (DOM) to the shallow Lavaca–Matagorda (LM) Bay estuarine
system along the central Texas coast and investigated whether chromophoric DOM (CDOM) photochemical reactions have the potential
to stimulate microbial activity within LM estuarine waters. Dissolved organic carbon (DOC) concentrations ranged from 3 to
10 mg C l−1 and CDOM levels (reported as a
305) ranged from 8 to 77 m−1 during April and July, 2007, when the LM system was experiencing very high freshwater inputs. DOC and CDOM levels were well-correlated
with salinities > 3, but exhibited considerable variability at salinities < 3. CDOM photobleaching rates (i.e., decrease in
a
305 resulting from exposure to solar radiation) for estuarine samples ranged from 0.014 to 0.021 h−1, corresponding to photobleaching half-lives of 33–50 h. Our data indicate when Matagorda Bay waters photobleach; dissolved
organic carbon utilization is enhanced perhaps due to enhanced microbial respiration of biologically labile photoproducts
(BLPs). Net ecosystem metabolism calculations indicate that most of the LM system was net heterotrophic during our study.
We estimate that BLP formation could support up to 20% of the daily microbial respiratory C demand in LM surface waters and
combined with direct photochemical oxygen consumption could have an important influence on O2 cycles in the LM system. 相似文献
3.
Nitrate pollution of groundwater in Toyserkan,western Iran 总被引:5,自引:2,他引:3
Mohsen Jalali 《Environmental Earth Sciences》2011,62(5):907-913
A total of 95 groundwater samples were collected from Toyserkan, western Iran to assess the chemical composition and nitrate
(NO3
−) status of groundwater. The most prevalent water type is Ca–HCO3 followed by water types Ca–Mg–HCO3. In comparison with the World Health Organization (WHO) drinking water guideline of 50 mg l−1 for NO3
−, a total of nine wells (9.5%) showed higher concentrations. In 36% of samples (34) NO3
− concentration was low (<20 mg l−1), and in 53.7% of samples (51), in the range of 20–50 mg l−1. The samples were classified into four groups based on NO3
− and chloride (Cl−) concentrations. Of the samples, 40% were classified as group 4 and were relatively high in Cl− and NO3
− (Cl− > 47 mg l−1, NO3
− > 27 mg l−1). The high correlation between NO3
− and Cl− (r = 0.86, p < 0.01) is consistent with a manure source, resulting from the practice of adding salt to animal feed. Pollution of groundwaters
appeared to be affected by the application of inorganic fertilizer at greater than agronomic rates, Cl-salt inputs, and irrigation
practice. 相似文献
4.
Long-Term and Seasonal Changes in Nutrients,Phytoplankton Biomass,and Dissolved Oxygen in Deep Bay,Hong Kong 总被引:1,自引:0,他引:1
Jie Xu Kedong Yin Joseph H. W. Lee Hongbin Liu Alvin Y. T. Ho Xiangcheng Yuan Paul J. Harrison 《Estuaries and Coasts》2010,33(2):399-416
Deep Bay is a semienclosed bay that receives sewage from Shenzhen, a fast-growing city in China. NH4 is the main N component of the sewage (>50% of total N) in the inner bay, and a twofold increase in NH4 and PO4 concentrations is attributed to increased sewage loading over the 21-year period (1986–2006). During this time series, the
maximum annual average NH4 and PO4 concentrations exceeded 500 and 39 μM, respectively. The inner bay (Stns DM1 and DM2) has a long residence time and very
high nutrient loads and yet much lower phytoplankton biomass (chlorophyll (Chl) <10 μg L−1 except for Jan, July, and Aug) and few severe long-term hypoxic events (dissolved oxygen (DO) generally >2 mg L−1) than expected. Because it is shallow (~2 m), phytoplankton growth is likely limited by light due to mixing and suspended
sediments, as well as by ammonium toxicity, and biomass accumulation is reduced by grazing, which may reduce the occurrence
of hypoxia. Since nutrients were not limiting in the inner bay, the significant long-term increase in Chl a (0.52–0.57 μg L−1 year−1) was attributed to climatic effects in which the significant increase in rainfall (11 mm year−1) decreased salinity, increased stratification, and improved water stability. The outer bay (DM3 to DM5) has a high flushing
rate (0.2 day−1), is deeper (3 to 5 m), and has summer stratification, yet there are few large algal blooms and hypoxic events since dilution
by the Pearl River discharge in summer, and the invasion of coastal water in winter is likely greater than the phytoplankton
growth rate. A significant long-term increase in NO3 (0.45–0.94 μM year−1) occurred in the outer bay, but no increasing trend was observed for SiO4 or PO4, and these long-term trends in NO3, PO4, and SiO4 in the outer bay agreed with those long-term trends in the Pearl River discharge. Dissolved inorganic nitrogen (DIN) has
approximately doubled from 35–62 to 68–107 μM in the outer bay during the last two decades, and consequently DIN to PO4 molar ratios have also increased over twofold since there was no change in PO4. The rapid increase in salinity and DO and the decrease in nutrients and suspended solids from the inner to the outer bay
suggest that the sewage effluent from the inner bay is rapidly diluted and appears to have a limited effect on the phytoplankton
of the adjacent waters beyond Deep Bay. Therefore, physical processes play a key role in reducing the risk of algal blooms
and hypoxic events in Deep Bay. 相似文献
5.
Behzad Mortazavi Ashley A. Riggs Jane M. Caffrey Hélène Genet Scott W. Phipps 《Estuaries and Coasts》2012,35(3):862-877
Benthic oxygen, dinitrogen, and nutrient fluxes (NH4+, NO3−, and PO43−) were measured monthly during a 1-year period at two locations in Weeks Bay, a shallow (1.4 m) and eutrophic estuary in Alabama.
Gross primary productivity (GPP), ecosystem respiration (R), and net ecosystem metabolism were determined from high-frequency
dissolved oxygen measurements. Peak water column NO3− (55 μM) and chlorophyll a (138 μg/l) concentrations were measured during spring and fall, respectively. Sediments were a net source of NH4+ (102 μmol m−2 h−1) and PO43− (0.9 μmol m−2 h−1) but a sink for NO3− (−30 μmol m−2 h−1). Benthic N2 fluxes indicated net N fixation (12 μmol N m−2 h−1). Sediment oxygen demand (0.55 g O2 m−2 day−1) accounted for <10% of R (7.3 g O2 m−2 day−1). Despite high GPP rates (4.7 g O2 m−2 day−1), the estuary was net heterotrophic. Benthic regeneration supplied, on average, 7.5% and 4% of primary productivity N and
P demands, respectively. These results contrast with the conventional view that benthic regeneration accounts for a large
fraction of phytoplankton nutrient demand in shallow estuaries. 相似文献
6.
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
7.
Source and distribution of trace metals and nutrients in Narmada and Tapti river basins,India 总被引:2,自引:1,他引:1
The study was designed to establish the distributions of trace metals, dissolved organic carbon, and inorganic nutrients as
well as to assess the extent of anthropogenic inputs into the Narmada and Tapti rivers. Water and sediment qualities are variable
in the rivers, and there are major pollution problems at certain locations, mainly associated with urban and industrial centers.
The metal concentrations of samples of the aquatic compartments investigated were close to the maximum permissible concentration
for the survival of aquatic life, except for higher values of Cu (5–763 μg l−1), Pb (24–376 μg l−1), Zn (24–730 μg l−1), and Cr (70–740 μg l−1) and for drinking water except for elevated concentrations of metals such as Pb, Fe (850–2,060 μg l−1), Cr, and Ni (20–120 μg l−1). In general, the concentrations of trace metals in the rivers vary down stream which may affect the “health” of the aquatic
ecosystem and may also affect the health of the rural community that depends on the untreated river water directly for domestic
use. The assessment of EF, I
geo, and PLI in the sediments reveals overall moderate pollution in the river basins. 相似文献
8.
Nitrate contamination of groundwater in an agroecosystem in Zhangye Oasis,Northwest China 总被引:5,自引:2,他引:3
In order to assess the extent of groundwater contamination by nitrate (NO3
−–N) and to provide information about the deterioration of the groundwater quality in Zhangye Oasis, Northwest China, a study
was conducted in this area. The mean value of NO3
−–N concentrations in groundwater samples was 10.66 ± 0.19 mg l−1. NO3
−–N concentrations exceeding 10 mg l−1 (the threshold for drinking water set by the World Health Organization) were found in 32.4% of 71 wells, and were 13, 33.3,
52.4 and 50.0% in the groundwater samples from drinking wells, irrigation wells, hand-pumping wells and groundwater table
observation wells, respectively. The result showed that the groundwater samples that had NO3
−–N concentrations exceeding the threshold for drinking water were mostly collected from a depth of less than 20 m. Groundwater
NO3
−–N concentrations in areas used for the cultivation of vegetables, seed maize and intercropped maize were significantly higher
than those in urban or paddy areas. NO3
−–N contamination of groundwater in areas with sandy soil was more severe than in those with loam soil. 相似文献
9.
Groundwater nitrate contamination and risk assessment in an agricultural area,South Korea 总被引:2,自引:1,他引:1
Jae-Yeol Cheong Se-Yeong Hamm Jeong-Hwan Lee Kwang-Sik Lee Nam-Chil Woo 《Environmental Earth Sciences》2012,66(4):1127-1136
The nitrate of groundwater in the Gimpo agricultural area, South Korea, was characterized by means of nitrate concentration,
nitrogen-isotope analysis, and the risk assessment of nitrogen. The groundwaters belonging to Ca–(Cl + NO3) and Na–(Cl + NO3) types displayed a higher average NO3
− concentration (79.4 mg/L), exceeding the Korean drinking water standard (<44.3 mg/L NO3
−). The relationship between δ18O–NO3
− values and δ15N–NO3
− values revealed that nearly all groundwater samples with δ15N–NO3
− of +7.57 to +13.5‰ were affected by nitrate from manure/sewage as well as microbial nitrification and negligible denitrification.
The risk assessment of nitrate for groundwater in the study area was carried out using the risk-based corrective action model
since it was recognized that there is a necessity of a quantitative assessment of health hazard, as well as a simple estimation
of nitrate concentration. All the groundwaters of higher nitrate concentration than the Korean drinking water standard (<44.3 mg/L NO3
−) belonged to the domain of the hazard index <1, indicating no health hazard by nitrate in groundwater in the study area.
Further, the human exposure to the nitrate-contaminated soil was below the critical limit of non-carcinogenic risk. 相似文献
10.
Sulfide Inhibition of Nitrate Removal in Coastal Sediments 总被引:1,自引:0,他引:1
Microbial nitrate (NO3−) removal via denitrification (DNF) at high sulfide (H2S) concentrations was compared in sediment from a coastal freshwater pond in a developed area that receives salt-water influx
during storm events, and a saline pond proximal to an undeveloped estuary. Sediments were incubated with added SO42− (1,000 μg per gram dry weight basis (gdw)) to determine whether acid volatile sulfides (AVS) were formed. DNF in the sediments
was measured with NO3–N (300 μg gdw−1) alone, and with NO3–N and H2S (1,000 μg S2− gdw−1). SO42− addition to the freshwater sediments resulted in AVS formation (970 ± 307 μg S gdw−1) similar to the wetland with no added SO42− (986 ± 156 μg S gdw−1). DNF rates measured with no added H2S were greater in the freshwater than the wetland site (10.6 ± 0.6 vs. 6.4 ± 0.1 μg N2O–N gdw−1 h−1, respectively). High H2S concentrations retained NH4–N in the undeveloped wetland and retained NO3–N in the developed freshwater site, suggesting that potential salt-water influx may reduce the ability of the freshwater
sediments to remove NO3–N. 相似文献
11.
Interaction of acid mine drainage with waters and sediments at the Corona stream, Lousal mine (Iberian Pyrite Belt, Southern Portugal) 总被引:1,自引:0,他引:1
E. Ferreira da Silva C. Patinha P. Reis E. Cardoso Fonseca J. X. Matos J. Barrosinho J. M. Santos Oliveira 《Environmental Geology》2006,50(7):1001-1013
This study investigates the geochemical characteristics of the acid mine drainage discharged from the abandoned mine adits and tailing piles in the vicinity of the Lousal mine and evaluates the extent of pollution on water and on the stream sediments of the Corona stream. Atmospheric precipitation interacting with sulphide minerals in exposed tailings produces runoff water with pH values as low as 1.9–2.9 and high concentrations of
(9,249–20,700 mg l−1), Fe (959–4,830 mg l−1) and Al (136–624 mg l−1). The acidic effluents and mixed stream water carry elevated Cu, Pb, Zn, Cd and As concentrations that exceed the water quality standards. However, the severity of contamination generally decreases 4 km downstream of the source due to mixing with fresh waters, which causes the dilution of dissolved toxic metals and neutralization of acidity. Some natural attenuation of the contaminants also occurs due to the general reduced solubility of most trace metals, which may be removed from solution, by either co-precipitation or adsorption to the iron and aluminium precipitates. 相似文献
12.
Fluoride,nitrate and water hardness in groundwater supplied to the rural communities of Ensenada County,Baja California,Mexico 总被引:1,自引:0,他引:1
L. W. Daesslé L. Ruiz-Montoya H. J. Tobschall R. Chandrajith V. F. Camacho-Ibar L. G. Mendoza-Espinosa A. L. Quintanilla-Montoya K. C. Lugo-Ibarra 《Environmental Geology》2009,58(2):419-429
The hydrogeochemistry of 26 wells belonging to ten different aquifers in the county of Ensenada, Baja California, is studied.
These wells are all used to supply the rural communities in the region, which comprise ~37,000 inhabitants, excluding the
city of Ensenada. High total dissolved solids (TDS) concentrations (maximum 7.35 g l−1) indicate that salt is a ubiquitous contaminant in the aquifers due to seawater intrusion. The aquifers that support extensive
agriculture activities (Maneadero, San Quintín, San Simón and El Rosario) are characterized by higher N–NO3 concentrations (maximum 20 mg l−1) derived from fertilizers. Fluoride concentrations exceed the 1.5 mg l−1 Mexican official limit in only four wells. The enrichments of F− in the southern aquifers are thought to be associated to water–rock interactions controlled mainly by Na–Ca equilibrium reactions
with fluorite, as suggested from high dissolved Na concentrations in these waters. In the northern aquifer of Maneadero, no
enrichment of Na is found and a geothermal source for F− is likely. Water is hard to moderately hard, with Ca/Mg ratios >1. Although drinking water directly from the tap is not a
common practice in these localities, most sources have concentrations of major ions and TDS that exceed the Mexican official
limits. 相似文献
13.
Yongsik Sin Bonggil Hyun Quang-Dung Bach Sungryull Yang Chul Park 《Estuaries and Coasts》2012,35(3):839-852
Temporal and spatial variations in phytoplankton in Asan Bay, a temperate estuary under the influence of monsoon, were investigated
over an annual cycle (2004). Phytoplankton blooms started in February (>20 μg chl l−1) and continued until April (>13 μg chl l−1) during the dry season, especially in upstream regions. The percentage contribution of large phytoplankton (micro-sized)
was high (78–95%) during the blooms, and diatoms such as Skeletonema costatum and Thalassiosira spp. were dominant. The precipitation and freshwater discharge from embankments peaked and supplied nutrients into the bay
during the monsoon event, especially in July. Species that favor freshwater, such as Oscillatoria spp. (cyanobacteria), dominated during the monsoon period. The phytoplankton biomass was minimal in this season despite nutrient
concentrations that were relatively sufficient (enriched), and this pattern differed from that in tropical estuaries affected
by monsoon and in temperate estuaries where phytoplankton respond to nutrient inputs during wet seasons. The flushing time
estimated from the salinity was shorter than the doubling time in Asan Bay, which suggests that exports of phytoplankton maximized
by high discharge directly from embankments differentiate this bay from other estuaries in temperate and tropical regions.
This implies that the change in physical properties, especially in the freshwater discharge rates, has mainly been a regulator
of phytoplankton dynamics since the construction of embankments in Asan Bay. 相似文献
14.
A 52-yr record of dissolved oxygen in Chesapeake Bay (1950–2001) and a record of nitrate (NO3
−) loading by the Susquehanna River spanning a longer period (1903, 1945–2001) were assembled to describe the long-term pattern
of hypoxia and anoxia in Chesapeake Bay and its relationship to NO3
− loading. The effect of freshwater inflow on NO3
− loading and hypoxia was also examined to characterize its effect at internannual and longer time scales. Year to year variability
in river flow accounted for some of the observed changes in hypoxic volume, but the long-term increase was not due to increased
river flow. From 1950–2001, the volume of hypoxic water in mid summer increased substantially and at an accelerating rate.
Predicted anoxic volume (DO<0.2 mg I−1) at average river flow increased from zero in 1950 to 3.6×109 m3 in 2001. Severe hypoxia (DO<1.0 mg I−1) increased from 1.6×109 to 6.5×109 m3 over the same period, while mild hypoxia (DO<2.0 mg I−1) increased from 3.4×109 to 9.2×109 m3. NO3
− concentrations in the Susquehanna River at Harrisburg, Pennsylvania, increased up to 3-fold from 1945 to a 1989 maximum and
declined through 2001. On a decadal average basis, the superposition of changes in river flow on the long-term increase in
NO3
− resulted in a 2-fold increase in NO3
− loading from the Susquehanna River during the 1960s to 1970s. Decadal average loads were subsequently stable through the
1990s. Hypoxia was positively correlated with NO3
− loading, but more extensive hypoxia was observed in recent years than would be expected from the observed relationship. The
results suggested that the Bay may have become more susceptible to NO3
− loading. To eliminate or greatly reduce anoxia will require reducing average annual total nitrogen loading to the Maryland
mainstem Bay to 50×106 kg yr−1, a reduction of 40% from recent levels. 相似文献
15.
Drinking water quality in villages of southwestern Haryana,India: assessing human health risks associated with hydrochemistry 总被引:1,自引:0,他引:1
Vinod K. Garg Surindra Suthar Sushma Singh Aleenjeet Sheoran Garima Meenakshi Sandeep Jain 《Environmental Geology》2009,58(6):1329-1340
The chemical quality of groundwater of western Haryana, India was assessed for its suitability for drinking purposes. A total
of 275 water samples were collected from deep aquifer based hand-pumps situated in 37 different villages/towns of Bhiwani
region. The water samples were analyzed for different physico-chemical properties, e.g., pH, total dissolved solids (TDS),
total harness (TH), total alkalinity (TA), calcium, magnesium, carbonate, bicarbonate, sulphate, chloride and fluoride concentrations.
In this study, the average TDS content was greater ranging 1,692 (Bhiwani block) to 2,560 mg l−1 (Siwani block), and other important parameters of water, e.g., TA (442–1,232 mg l−1), TH (437–864 mg l−1) and bicarbonate (554–672 mg l−1), were also higher than maximum permissible limit by WHO or BIS. The fluoride appeared as a major problem of safe drinking
water in this region. We recorded greater fluoride concentration, i.e., 86.0 mg l−1 from Motipura village that is highest fluoride level ever recorded for Haryana state. The average fluoride concentration ranged between
7.1 and 0.8 mg l−1 in different blocks of western Haryana. On the basis of fluoride concentration, Siwani block showed the maximum number of water samples (84% of total collected samples) unsuitable for drinking purposes (containing
fluoride >1.5 mg l−1) followed by Charki Dadri block (58%), Bhiwani block (52%), Bawani Khera block (33%) and Loharu block (14%). This study clearly suggest that some health deteriorating chemicals in drinking water were at dangerous level and;
therefore, water quality could be a major health threat for local residents of western Haryana. The high fluoride level in
drinking water has posed some serious dental health risks in local residents. 相似文献
16.
Water quality assessment of groundwater in some rock types in parts of the eastern region of Ghana 总被引:2,自引:2,他引:0
Samuel Y. Ganyaglo Bruce Banoeng-Yakubo Shiloh Osae Samuel B. Dampare Joseph R. Fianko 《Environmental Earth Sciences》2011,62(5):1055-1069
A baseline study involving analyses of subsurface water samples from the Cape Coast granitoid complex, Lower Birimian, Togo
Formation and the Voltaian Group, was carried out to assess their suitability for drinking, domestic and agricultural purposes.
Study results show that pH within the range (3.0 ≤ pH ≤ 6.5) constitutes 74% of the boreholes analysed, and 51% have hardness
values ranging from 7.89 to 73.24 mg/l as CaCO3 and are described as soft. Total dissolved solids are less than 1,000 mg/l and generally characterized by low conductivity
values, of which 95% are within the range (55 ≤ EC ≤ 1,500 μS/cm). The mean values of the major cations (Ca2+, Mg2+, Na+, K+) and anions (SO42−, Cl−, HCO3−) are all within the World Health Organisation (WHO) standards. Five (5) of the boreholes sampled have nitrate (NO3−) contamination. Even though NO3− contamination and acidic waters exist in some of the boreholes, the majority of the boreholes are excellent for drinking
and domestic purposes. Assessment of the groundwaters for agricultural irrigation revealed three main categories. These are
low salinity–low sodicity (C1–S1), medium salinity–low sodicity (C2–S1) and high salinity–low sodicity (C3–S1), using the
US Salinity Laboratory (USSL) classification scheme. As much as 95% of the samples plotted in the ‘excellent to good’ and
‘good to permissible’ categories on the Wilcox diagram. The groundwater in the study area may therefore be regarded as good
for irrigation activities. The major identifiable geochemical processes responsible for the evolution of the various ions
are mineral weathering and chemical reactions. 相似文献
17.
There is increasing concern about soil enrichment with K+ and subsequent potential losses following long-term application of poor quality water to agricultural land. Different models
are increasingly being used for predicting or analyzing water flow and chemical transport in soils and groundwater. The convective–dispersive
equation (CDE) and the convective log-normal transfer function (CLT) models were fitted to the potassium (K+) leaching data. The CDE and CLT models produced equivalent goodness of fit. Simulated breakthrough curves for a range of
CaCl2 concentration based on parameters of 15 mmol l−1 CaCl2 were characterised by an early peak position associated with higher K+ concentration as the CaCl2 concentration used in leaching experiments decreased. In another method, the parameters estimated from 15 mmol l−1 CaCl2 solution were used for all other CaCl2 concentrations, and the best value of retardation factor (R) was optimised for each data set. A better prediction was found. With decreasing CaCl2 concentration the value of R is required to be more than that measured (except for 10 mmol l−1 CaCl2), if the estimated parameters of 15 mmol l−1 CaCl2 are used. The two models suffer from the fact that they need to be calibrated against a data set, and some of their parameters
are not measurable and cannot be determined independently. 相似文献
18.
M. A. Halim R. K. Majumder S. A. Nessa K. Oda Y. Hiroshiro B. B. Saha S. M. Hassain Sk. A. Latif M. A. Islam K. Jinno 《Environmental Geology》2009,58(1):73-84
An integrated study has been carried out to elucidate the distribution and occurrence of arsenic in selected groundwater samples
in the area of Sherajdikhan, Bangladesh. Arsenic and other parameters (T, pH, EC, Na+, K+, Ca2+, Mg2+, Cl−, NO3
−, SO4
2−, HCO3
−, PO4
3−, Fe, Mn and DOC) have been measured in groundwater samples collected from shallow/deep tube wells at different depths. Hydrogeochemical
data suggest that the groundwaters are generally Ca–Mg–HCO3 and Mg–Ca–HCO3 types with bicarbonate (HCO3
−) as the dominant anion, though the other type of water has also been observed. Dissolved arsenic in groundwater ranged from
0.006 to 0.461 mg/l, with 69% groundwater samples exceeded the Bangladesh limit for safe drinking water (0.05 mg/l). Correlation
and principal component analysis have been performed to find out possible relationships among the examined parameters in groundwater.
Low concentrations of NO3
− and SO4
2−, and high concentrations of DOC, HCO3
− and PO4
3− indicate the reducing condition of subsurface aquifer where sediments are deposited with abundant organic matter. Distinct
relationship of As with Fe and Mn, and strong correlation with DOC suggests that the biodegradation of organic matter along
with reductive dissolution of Fe–Mn oxyhydroxides has being considered the dominant process to release As in the aquifers
studied herein. 相似文献
19.
This study assessed the levels of selected inorganic contaminants in streams and stream sediments in the effluent areas relating
to the pyrometallurgical and hydrometallurgical treatment of gold ores in the Obuasi gold mine, Ghana. Water and stream sediment
samples were taken from specific locations during the consecutive rainy and dry seasons, and concentrations of phosphate (PO4
3−), nitrate (NO3
−), chloride (Cl−), sulphate (SO4
2−), sodium (Na+), potassium (K+), calcium (Ca2+), magnesium (Mg2+), arsenic (As), copper (Cu), iron (Fe), zinc (Zn) and lead (Pb), were determined. Alkalinity, pH, temperature and specific
electrical conductivity were also measured. In the water samples, the average pH range for both the seasons is 6.9–7.4, most
anions and metals have relatively higher concentrations in the wet season than in the dry season at both the metallurgical
sites. Trace metals concentrations were comparatively low (<0.01–5.00 mg/l), higher in the dry season at the pyrometallurgical
sites. Irrespective of seasons, SO4
2− (0.80–949.50 mg/l) and PO4
3− (<0.01–6.30 mg/l) were pronounced at the pyrometallurgical sites, while NO3
− (0.01–98.45 mg/l) and Cl− (1.88-49.05 mg/l) were higher at the hydrometallurgical sites. In water samples, Ca2+ and SO4
2+ were the dominant cation and anion, respectively. In the stream sediments, except pH, NO3
−, Cl−, Na+ and Mg2+, all other parameter values were relatively higher at the hydrometallurgical areas. The average concentrations of Ca2+, Mg2+, As and Fe are remarkably high at both metallurgical sites (3,217–46,026 mg/kg). Overall, the level of parameters in the
water samples are pronounced at pyrometallurgical sites, whereas the levels in sediments are higher at the hydrometallurgical
sites. 相似文献
20.
Determination of denitrification in the Chesapeake Bay from measurements of N2 accumulation in bottom water 总被引:1,自引:0,他引:1
This study demonstrates the feasibility of using direct N2 measurements in an estuary for determination of denitrification. High precision measurements of dinitrogen: argon ratios
(N2∶Ar) were made by membrane inlet mass spectrometry on water samples taken along the length of the Chesapeake Bay in July and
October 2004. The N2∶Ar ratio in low salinity surface water was elevated relative to air saturation by 0.3–0.5% with no systematic change along
the length of the Bay. N2∶Ar in high salinity bottom water exhibited a linear increase in the landward direction along a 144-km longitudinal section.
In this section of the Bay covering 20% of the main stem, the bottom water salinity was statistically uniform and the increase
in N2∶Ar was in the direction of net residual current flow. The system was analyzed as a capped river with the assumption that
N2 entered the water from the underlying sediment where denitrification is known to take place. The rate of denitrification
needed to support the measured increase in N2 was calculated using an average residual current velocity and water column depth. The increase in N2 with distance (0.046μmol N l−1 km−1) equated to an average denitrification flux of 73 μmol N m−2 h−1. N2 fluxes determined on sediment cores taken from the source and terminus regions of the delineated water mass were 45±23 and
83±39 μmol N m−2 hr−1, respectively, which were not statistically different from the whole system estimate. The measured change in oxygen concentration
within the bottom water was used to estimate nitrogen remineralization and the efficiency of denitrification. Denitrification
efficiency (nitrogen denitrified/nitrogen remineralized) was estimated to be in the range of 22–28% for the bottom water sediment
system and 30–37% considering the sediment zone alone. 相似文献