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1.
Xi Bin Ji Wen Zhi Zhao Er Si Kang Zhi Hui Zhang Bo Wen Jin 《Environmental Earth Sciences》2011,64(3):619-629
Fluxes of carbon dioxide, water vapor, and heat were measured above crop canopy using the eddy covariance method during the
2008 maize growing season, over an agricultural field within an oasis located in the middle reaches of Heihe River basin,
northwest China. The values for friction velocity, the Monin–Obukhov stability parameter, and energy balance closure indicated
that the eddy covariance system at this study site provided reliable flux estimates. Results from measurements showed that
the mean sensible heat flux was 70 W m−2 with a maximum value of 164 W m−2 (May) and a minimum value of 45 W m−2 (July) during the maize growing season. In contrast, the mean latent heat was 278 W m−2 with a maximum value of 383 W m−2 (July) and minimum of 101 W m−2 (May). The mean downward soil heat flux was 55 W m−2 with a maximum value of 127 W m−2 (May) and minimum of 49 W m−2 (July). The magnitude of mean daytime net CO2 uptake was −11.50 μmol m−2 s−1 with a maximum value of −28.32 μmol m−2 s−1 (18 and 19 July) and a minimum values of −0.32 μmol m−2 s−1 (18 and 19 May). Correlation was observed between daytime half-hourly carbon dioxide flux and canopy conductance. In addition,
the relationship between carbon dioxide flux and photosynthetically active radiation for selected days during different stages
of maize growing season indicated the carbon dioxide flux uptake by the canopy was controlled by actual photosynthetic activity
related to the variation of green leaf area index for the different growing stages. 相似文献
2.
Among several salt lakes in the Thar Desert of western India, the Sambhar is the largest lake producing about 2 × 105 tons of salt (NaCl) annually. The “lake system” (lake waters, inflowing river waters, and sub-surface brines) provides a
unique setting to study the geo-chemical behavior of uranium isotopes (238U, 234U) in conjunction with the evolution of brines over the annual wetting and evaporation cycles. The concentration of 238U and the total dissolved solids (TDS) in lake water increase from ~8 μg L−1 and ~8 g L−1 in monsoon to ~1,400 μg L−1 and 370 g L−1, respectively, during summer time. The U/TDS ratio (~1 μg g−1 salt) and the 234U/238U activity ratio (1.65 ± 0.05), however, remain almost unchanged throughout the year, except when U/TDS ratio approaches to
3.8 at/or beyond halite crystallization. These observations suggest that uranium behaves conservatively in the lake waters
during the annual cycle of evaporation. Also, uranium and salt content (TDS) are intimately coupled, which has been used to
infer the origin and source of salt in the lake basin. Furthermore, near uniform ratios in evaporating lake waters, when compared
to the ratio in seawater (~0.1 μg g−1 salt and 1.14 ± 0.02, respectively), imply that aeolian transport of marine salts is unlikely to be significant source of
salt to the lake in the present-day hydrologic conditions. This inference is further consistent with the chemical composition
of wet-precipitation occurring in and around the Sambhar lake. The seasonal streams feeding the lake and groundwaters (within
the lake’s periphery) have distinctly different ratios of U/TDS (2–69 μg g−1 salt) and 234U/238U (1.15–2.26) compared to those in the lake. The average U/TDS ratio of ~1 μg g−1 salt in lake waters and ~19 μg g−1 salt in river waters suggest dilution of the uranium content by the recycled salt and/or removal processes presently operating
in the lake during the extraction of salt for commercial use. Based on mass-balance calculations, a conservative estimate
of "uranium sink" (in the form of bittern crust) accounts for ~5 tons year−1 from the lake basin, an estimate similar to its input flux from rivers, i.e., 4.4 tons year−1. 相似文献
3.
Accurate measurements to assess the influence of soil moisture on CO2 flux requires the absolute estimates of soil CO2 flux. Thus, it was constructed a calibration system where CO2 with fixed concentration flowed through the different porous material. Previous to measurement, in order to verify the performance
and reliability of a closed dynamic chamber, different discontinuous air-mixing rates and times were tested. The CO2 flux was estimated through sequential lectures and the best fit for flux measurements was obtained taking short readings
every 3 min, during a total time of 12 min (R
2 = 0.99). The best mixing rate was attained for 250 mL min−1, allowing 25 s of mixing previous to CO2 extraction for an infrared gas analyzer. The deviation of the measured values for dry sand from the reference CO2 flux (0.097 and 0.071 g m−2 min−1) was 5 and 7%. On dry sandy loam soil (SLS) the deviation was 2%. The measured fluxes decreased 73 and 22% with content moisture
of 20 and 10% (sand), and 78% with content moisture of 31% (SLS). This work allowed to estimate how much the measured emission
rates deviate from the true ones for the specified chamber and sampling conditions. 相似文献
4.
Humberto Marotta Luiz Bento Francisco de A. Esteves Alex Enrich-Prast 《Estuaries and Coasts》2009,32(4):654-660
The purpose of this research was to assess the effects of dredging performed in a marginal wetland colonized by aquatic macrophytes
on eutrophication of the adjacent shallow tropical lake (Imboassica Lake, Brazil). The river mouth of the Imboassica River
that drains into Imboassica Lake had been densely colonized by aquatic vegetation dominated by Typha domingensis (Pers.) when it was dredged. Total and dissolved nitrogen and phosphorus concentrations were measured monthly over 13 years
at four stations in the Imboassica river-lake system. Dredging activities reduced phosphorus and nitrogen retention at the
river mouth and subsequently increased these nutrient stocks in the lake waters. Nutrient retention by non-dredged wetland
was estimated to be ca. 1,200 kg year−1 (87.3 g m−2 year−1) for nitrogen and 60 kg year−1 (4.5 g m−2 year−1) for phosphorus. Our whole-lake approach suggested that dredging might intensify rather than mitigate eutrophication in shallow
tropical lakes when the removal of aquatic macrophytes is coupled to the persistence of anthropogenic nutrient inputs from
the watershed. 相似文献
5.
A study of Halodule wrightii in a shallow subtropical Texas lagoon was performed to obtain seasonal data on its physiological ecology. Leaf production
and biomass dynamics of H. wrightii were intensively monitored along with the underwater light environment at a 1.2-m depth study site over a 21-month period
from June 1995 to February 1997. The annual photosynthetically active radiation (PAR) flux of 6,764 mol m−2 year−1 was more than twice as high as 2,400 mol m−2 year−1, the minimum annual PAR required for maintenance of growth. As light intensity declined, blade chlorophyll a/b ratios increased suggesting that the plants were photo-adapting. Seasonal trends were evident in shoot growth and biomass.
Compared to other Halodule populations in Texas, H. wrightii in LLM displayed slow growth and low biomass, high leaf tissue N content, and low C/N ratio but high N/P ratio of 38 suggesting
that the plants were phosphorus-limited. 相似文献
6.
Measurements taken between July 2006 to May 2007 at the Maqu station in the Upper Yellow River area were used to study the
surface radiation budget and soil water and heat content in this area. These data revealed distinct seasonal variations in
downward shortwave radiation, downward longwave radiation, upward longwave radiation and net radiation, with larger values
in the summer than in winter because of solar altitudinal angle. The upward shortwave radiation factor is not obvious because
of albedo (or snow). Surface albedo in the summer was lower than in the winter and was directly associated with soil moisture
and solar altitudinal angle. The annual averaged albedo was 0.26. Soil heat flux, soil temperature and soil water content
changed substantially with time and depth. The soil temperature gradient was positive from August to February and was related
to the surface net radiation and the heat condition of the soil itself. There was a negative correlation between soil temperature
gradient and net radiation, and the correlation coefficient achieved a significance level of 0.01. Because of frozen state
of the soil, the maximum soil thermal conductivity value was 1.21 W m−1°C−1 in January 2007. In May 2007, soil thermal conductivity was 0.23 W m−1°C−1, which is the lowest value measured in the study, likely due to the fact that the soil was drier then than in other months.
The soil thermal conductivity values for the four seasons were 0.27, 0.38, 0.55 and 0.83 W m−1°C−1, respectively. 相似文献
7.
Zongqiang Chang Qi Feng Jianhua Si Yonghong Su Haiyang Xi Jianlin Li 《Environmental Geology》2009,58(3):483-490
Field experiments on the CO2 flux of alpine meadow soil in the Qilian Mountain were conducted along the elevation gradient during the growing season of
2004 and 2005. The soil CO2 flux was measured using the Li-6400-09 soil respiration chamber attached to the Li-6400 portable photosynthesis system. The
effects of water and heat and roots on the soil CO2 flux were statistically analyzed. The results show that soil CO2 flux along the elevation gradient gradually decreases. The soil CO2 flux was low at night, with lowest value occurring between 0200 and 0600 hours, started to rise rapidly during 0700–0830
hours, and then descend during 1600–1830 hours. The peak CO2 efflux appears during 1100–1600 hours. The diurnal average of soil CO2 efflux was between 0.56 ± 0.32 and 2.53 ± 0.76 μmol m−2 s−1. Seasonally, soil CO2 fluxes are relatively high in summer and autumn and low in spring and winter. The soil CO2 efflux, from the highest to the lowest in the ranking order, occurred in July and August (4.736 μmol m−2 s−1), June and September, and May and October, respectively. The soil CO2 efflux during the growing season is positively correlated with soil temperature, root biomass and soil water content. 相似文献
8.
Michael G. LaMontagne Valeria Astorga Anne E. Giblin Ivan Valiela 《Estuaries and Coasts》2002,25(2):272-281
To determine the removal of regenerated nitrogen by estuarine sediments, we compared sediment N2 fluxes to the stoichiometry of nutrient and O2 fluxes in cores collected in the Childs River, Cape Cod, Massachusetts. The difference between the annual PO4 3− (0.2 mol P m−2 yr−1) and NH4 + (1.6 mol N m−2 yr−1) flux and the Redfield N∶P ratio of 16 suggested an annual deficit of 1.5 mol N m−2 yr−1. Denitrification predicted from O2∶NH4 + flux ratios and measured as N2 flux suggested a nitrogen sink of roughly the same magnitude (1.4 mol N m−2 yr−1). Denitrification accounted for low N∶P ratios of benthic flux and removed 32–37% of nitrogen inputs entering the relatively highly nutrient loaded Childs River, despite a relatively brief residence time for freshwater in this system. Uptake of bottom water nitrate could only supply a fraction of the observed N2 flux. Removal of regenerated nitrogen by denitrification in this system appears to vary seasonally. Denitrification efficiency was inversely correlated with oxygen and ammonium flux and was lowest in summer. We investigated the effect of organic matter on denitrification by simulating phytoplankton deposition to cores incubated in the lab and by deploying chambers on bare and macroaglae covered sediments in the field. Organic matter addition to sediments increased N2 flux and did not alter denitrification efficiency. Increased N2 flux co-varied with O2 and NH4 + fluxes. N2 flux (261±60 μmol m−2 h−1) was lower in chambers deployed on macroalgal beds than deployed on bare sediments (458±70 μmol m−2 h−1), and O2 uptake rate was higher in chambers deployed on macroalgal beds (14.6±2.2 mmol m−2 h−1) than on bare sediments (9.6±1.5 mmol m−2 h−1). Macroalgal cover, which can retain nitrogen in the system, is a link between nutrient loading and denitrification. Decreased denitrification due to increasing macroalgal cover could create a positive feedback because decreasing denitrification would increase nitrogen availability and could increase macroalgae cover. 相似文献
9.
Benjamin S. Linhoff Philip C. Bennett Tamir Puntsag Ochir Gerel 《Environmental Earth Sciences》2011,62(1):171-183
Extremely high concentrations of uranium (U) were discovered in shallow, groundwater-fed hyperalkaline soda lakes in Eastern
Mongolia. A representative groundwater sample in this area is dilute and alkaline, pH = 7.9, with 10 mM TIC and 5 mM Cl−. In contrast, a representative lake water sample is pH ~ 10 with TIC and Cl− each more than 1,000 mM. Groundwater concentrations of U range from 0.03 to 0.43 μM L−1. Lake water U ranges from 0.24 to >62.5 μM, possibly the highest naturally occurring U concentrations ever reported in surface
water. Strontium isotopes 87Sr/86Sr varied in groundwaters from 0.706192 to 0.709776 and in lakes 87Sr/86Sr varied from 0.708702 to 0.709432. High concentrations of U, Na, Cl−, and K correlate to radiogenic Sr in lake waters suggesting that U is sourced from local Cretaceous alkaline rhyolites. Uranium-rich
groundwaters are concentrated by evaporation and U(VI) is chelated by CO3−2 to form the highly soluble UO2(CO3)3−4. Modeled evaporation of lakes suggests that a U-mineral phase is likely to precipitate during evaporation. 相似文献
10.
The heat capacity at constant pressure, C
p, of chlorapatite [Ca5(PO4)3Cl – ClAp], and fluorapatite [Ca5(PO4)3F – FAp], as well as of 12 compositions along the chlorapatite–fluorapatite join have been measured using relaxation calorimetry
[heat capacity option of the physical properties measurement system (PPMS)] and differential scanning calorimetry (DSC) in
the temperature range 5–764 K. The chlor-fluorapatites were synthesized at 1,375–1,220°C from Ca3(PO4)2 using the CaF2–CaCl2 flux method. Most of the chlor-fluorapatite compositions could be measured directly as single crystals using the PPMS such
that they were attached to the sample platform of the calorimeter by a crystal face. However, the crystals were too small
for the crystal face to be polished. In such cases, where the sample coupling was not optimal, an empirical procedure was
developed to smoothly connect the PPMS to the DSC heat capacities around ambient T. The heat capacity of the end-members above 298 K can be represented by the polynomials: C
pClAp = 613.21 − 2,313.90T
−0.5 − 1.87964 × 107
T
−2 + 2.79925 × 109
T
−3 and C
pFAp = 681.24 − 4,621.73 × T
−0.5 − 6.38134 × 106
T
−2 + 7.38088 × 108
T
−3 (units, J mol−1 K−1). Their standard third-law entropy, derived from the low-temperature heat capacity measurements, is S° = 400.6 ± 1.6 J mol−1 K−1 for chlorapatite and S° = 383.2 ± 1.5 J mol−1 K−1 for fluorapatite. Positive excess heat capacities of mixing, ΔC
pex, occur in the chlorapatite–fluorapatite solid solution around 80 K (and to a lesser degree at 200 K) and are asymmetrically
distributed over the join reaching a maximum of 1.3 ± 0.3 J mol−1 K−1 for F-rich compositions. They are significant at these conditions exceeding the 2σ-uncertainty of the data. The excess entropy of mixing, ΔS
ex, at 298 K reaches positive values of 3–4 J mol−1 K−1 in the F-rich portion of the binary, is, however, not significantly different from zero across the join within its 2σ-uncertainty. 相似文献
11.
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
12.
Morgane Lejart Jacques Clavier Laurent Chauvaud Christian Hily 《Estuaries and Coasts》2012,35(2):622-632
Respiration and calcification rates of the Pacific oyster Crassostrea gigas were measured in a laboratory experiment in the air and underwater, accounting for seasonal variations and individual size,
to estimate the effects of this exotic species on annual carbon budgets in the Bay of Brest, France. Respiration and calcification
rates changed significantly with season and size. Mean underwater respiration rates, deducted from changes in dissolved inorganic
carbon (DIC), were 11.4 μmol DIC g−1 ash-free dry weight (AFDW) h−1 (standard deviation (SD), 4.6) and 32.3 μmol DIC g−1 AFDW h−1 (SD 4.1) for adults (80–110 mm shell length) and juveniles (30–60 mm), respectively. The mean daily contribution of C. gigas underwater respiration (with 14 h per day of immersion on average) to DIC averaged over the Bay of Brest population was 7.0 mmol DIC m−2 day−1 (SD 8.1). Mean aerial CO2 respiration rate, estimated using an infrared gas analyzer, was 0.7 μmol CO2 g−1 AFDW h−1 (SD 0.1) for adults and 1.1 μmol CO2 g−1 AFDW h−1 (SD 0.2) for juveniles, corresponding to a mean daily contribution of 0.4 mmol CO2 m−2 day−1 (SD 0.50) averaged over the Bay of Brest population (with 10 h per day of emersion on average). Mean CaCO3 uptake rates for adults and juveniles were 4.5 μmol CaCO3 g−1 AFDW h−1 (SD 1.7) and 46.9 μmol CaCO3 g−1 AFDW h−1 (SD 29.2), respectively. The mean daily contribution of net calcification in the Bay of Brest C. gigas population to CO2 fluxes during immersion was estimated to be 2.5 mmol CO2 m−2 day−1 (SD 2.9). Total carbon release by this C. gigas population was 39 g C m−2 year−1 and reached 334 g C m−2 year−1 for densely colonized areas with relative contributions by underwater respiration, net calcification, and aerial respiration
of 71%, 25%, and 4%, respectively. These observations emphasize the substantial influence of this invasive species on the
carbon cycle, including biogenic carbonate production, in coastal ecosystems. 相似文献
13.
The present study reports on perturbations of the water column by large rainfall at Lake Alchichica, a saline lake in Central
Mexico. Alchichica is located in the “Llanos de San Juan,” a high-altitude plateau with a minimum elevation of 2,300 m above
sea level. The climate is arid with annual precipitation less than 400 mm and annual evaporation of 500–600 mm. A single day
large rainfall event delivered 1,810,000 m3 of water to the basin, raising the lake’s water level by about 1 m. Temperature and salinity profiles showed an atypical
temperature inversion up to 1°C in the upper layer accompanied by salinity decrease up to 0.5 g l−1. Transparency and pH were slightly altered, but dissolved oxygen, nutrients and chlorophyll a concentrations were not changed. In spite of the heavy rainfall and associated wind, the effects of the event were limited
to the upper half of the epilimnion. After 2 days, the lake water level returned to its original level. The rapid leakage
of the runoff minimized any long-term effects of the large rainfall. 相似文献
14.
Stephen G. Monismith James L. Hench Derek A. Fong Nicholas J. Nidzieko William E. Fleenor Laura P. Doyle S. Geoffrey Schladow 《Estuaries and Coasts》2009,32(1):100-110
In this paper, we discuss observations of temperature variability in the tidal portion of the San Joaquin River in California.
The San Joaquin River makes up the southern portion of the Sacramento San Joaquin Delta, the eastern end of San Francisco
Bay. Observations made in August 2004 and August 2005 show significant diurnal variations in temperature in response to surface
heat exchange. However, to account for observed changes in heat content a sizeable downstream heat flux (approximately 100 W
m−2) must be added to the surface heat flux. To account for this flux via Fickian dispersion, a flow-dependent dispersion coefficient
varying from 500 to 4,000 m2 s−1 is needed. These values are much larger than would be predicted for a river of this size, suggesting that the complex topology
of the Delta greatly enhances longitudinal dispersion. Building on these observations, we present a simple theory that explores
how the subtidal temperature field varies in response to changes in flow rate, dispersion, and heat exchange. 相似文献
15.
Daily and annual integrated rates of primary productivity and community respiration were calculated using physiological parameters
measured in oxygen-based photosynthesis-irradiance (P-I) incubations at 8 stations throughout central and western Long Island
Sound (cwLIS) during the summer and autumn of 2002 and 2003 and the late spring of 2003. Each calculation takes into account
actual variations in incident irradiance over the day and underwater irradiance and standing stock with depth. Annual peak
rates, ±95% confidence interval of propagated uncertainty in each measurement, of gross primary production (GPP, 1,730±610
mmol O2 m−2 d−1), community respiration (Rc, 1,660±270 mmol O2 m−2 d−1), and net community production (NCP, 1,160±1,100 mmol O2 m−2 d−1) occurred during summer at the western end of the Sound. Lowest rates of GPP (4±11 mmol O2 m−2 d−1), Rc (−50±300 mmol O2 m−2 d−1), and NCP (−1,250±270 mmol O2 m−2 d−1) occurred during late autumn-early winter at the outer sampled stations. These large ranges in rates of GPP, Rc, and NCP throughout the photic zone of cwLIS are attributed to seasonal and spatial variability. Algal respiration (Ra) was estimated to consume an average of 5% to 52% of GPP, using a literature-based ratio of Ra:Rc. From this range, we established that the estimated Ra accounts for approximately half of GPP, and was used to estimate daily net primary production (NPP), which ranged from 2
to 870 mmol O2 m−2 d−1 throughout cwLIS during the study. Annual NPP averaged 40±8 mol O2 m−2 yr−1 for all sampled stations, which more than doubled along the main axis of the Sound, from 32±14 mol O2 m−2 yr−1 at an eastern station to 82±25 mol O2 m−2 yr−1 at the western-most station. These spatial gradients in productivity parallel nitrogen loads along the main axis of the Sound.
Daily integrals of productivity were used to test and formulate a simple, robust biomass-light model for the prediction of
phytoplankton production in Long Island Sound, and the slope of the relationship was consistent with reports for other systems. 相似文献
16.
We developed light requirements for eelgrass in the Pacific Northwest, USA, to evaluate the effects of short- and long-term
reductions in irradiance reaching eelgrass, especially related to turbidity and overwater structures. Photosynthesis-irradiance
experiments and depth distribution field studies indicated that eelgrass productivity was maximum at a photosynthetic photon
flux density (PPFD) of about 350–550 μmol quanta m−2 s−1. Winter plants had approximately threefold greater net apparent primary productivity rate at the same irradiance as summer
plants. Growth studies using artificial shading as well as field monitoring of light and eelgrass growth indicated that long-term
survival required at least 3 mol quanta m−2 day−1 on average during spring and summer (i.e., May-September), and that growth was saturated above about 7 mol quanta m−2 day−1. We conclude that non-light-limited growth of eelgrass in the Pacific Northwest requires an average of at least 7 mol quanta
m−2 day−1 during spring and summer and that long-term survival requires a minimum average of 3 mol quanta m−2 day−1. 相似文献
17.
Sulfate reduction rates were measured over the course of a year in the sediments of aJuncus roemerianus marsh located in coastal Alabama. Sulfate reduction rates were typically highest in the surface 0–2 cm and at depths corresponding
to peak belowground biomass of the plants. The highest volume-based sulfate reduction rate measured was 1,350 μmol liter-sediment−1 d−1 in September 1995. Areal sulfate reduction rates (integrated to 20 cm depth) were strongly correlated to sediment temperature
and varied seasonally from 15.2 mmol SO
4
2−
m−2 d−1 in January 1995 to 117 mmol SO
4
2−
m−2 d−1 in late August 1995. Despite high sulfate reduction rates porewater dissolved sulfide concentrations were low (<73 μM), indicating
rapid sulfide oxidation or precipitation. Sulfate depletion data indicated that net oxidation of sediment sulfides occurred
in March through May, following a period of infrequent tidal flooding and during a period of high plant production. Porewater
Fe(II) reached very high levels (maximum of 969 μM; mean for all dates was 160 μM), particularly during periods of high sulfate
reduction. The annual sulfate reduction rate integrated over the upper 20 cm of sediment was 22.0 mol SO
4
2−
m−2 yr−1, which is among the highest rates measured in a wetland ecosystem. Based on literature values of net primary production inJ. roemerianus marshes, we estimate that an amount equivalent to 16% to 90% of the annual belowground production may be remineralized through
sulfate reduction. 相似文献
18.
Hydrogeochemical processes in the groundwater environment of Heihe River Basin,northwest China 总被引：5，自引：0，他引：5
Zhu Gaofeng Su Yonghong Huang Chunlin Feng Qi Liu Zhiguang 《Environmental Earth Sciences》2010,60(1):139-153
The Heihe River Basin is a typical arid inland river basin for examining stress on groundwater resources in northwest China.
The basin is composed of large volumes of unconsolidated Quaternary sediments of widely differing grain size, and during the
past half century, rapid socio-economic development has created an increased demand for groundwater resources. Understanding
the hydrogeochemical processes of groundwater and water quality is important for sustainable development and effective management
of groundwater resources in the Heihe River basin. To this end, a total of 30 representative groundwater samples were collected
from different wells to monitor the water chemistry of various ions and its quality for irrigation. Chemical analysis shows
that water presents a large spatial variability of chemical facies (SO4
2−–HCO3−, SO4
2−–Cl−, and Cl−–SO4
2−) as groundwater flow from recharge area to discharge area. The ionic ratio indicates positive correlation between the flowing
pairs of parameters: Cl− and Na+(r = 0.95), SO4
2− and Na+ (r = 0.84), HCO3
− and Mg2+(r = 0.86), and SO4
2− and Ca2+ (r = 0.91). Dissolution of minerals, such as halite, gypsum, dolomite, silicate, and Mirabilite (Na2SO4·10H2O) in the sediments results in the Cl−, SO4
2−, HCO3
−, Na+, Ca2+ and Mg2+ content in the groundwater. Other reactions, such as evaporation, ion exchange, and deposition also influence the water composition.
The suitability of the groundwater for irrigation was assessed based on the US Salinity Laboratory salinity classification
and the Wilcox diagram. The results show that most of the groundwater samples are suitable for irrigation uses barring a few
locations in the dessert region in the northern sub-basin. 相似文献
19.
René M. Price William K. Nuttle Bernard J. Cosby Peter K. Swart 《Estuaries and Coasts》2007,30(3):497-506
Variation and uncertainty in estimated evaporation was determined over time and between two locations in Florida Bay, a subtropical
estuary. Meteorological data were collected from September 2001 to August 2002 at Rabbit Key and Butternut Key within the
Bay. Evaporation was estimated using both vapor flux and energy budget methods. The results were placed into a long-term context
using 33 years of temperature and rainfall data collected in south Florida. Evaporation also was estimated from this long-term
data using an empirical formula relating evaporation to clear sky solar radiation and air temperature. Evaporation estimates
for the 12-mo period ranged from 144 to 175 cm yr−1, depending on location and method, with an average of 163 cm yr−1 (±9%). Monthly values ranged from 9.2 to 18.5 cm, with the highest value observed in May, corresponding with the maximum
in measured net radiation. Uncertainty estimates derived from measurement errors in the data were as much as 10%, and were
large enough to obscure differences in evaporation between the two sites. Differences among all estimates for any month indicate
the overall uncertainty in monthly evaporation, and ranged from 9% to 26%. Over a 33-yr period (1970–2002), estimated annual
evaporation from Florida Bay ranged from 148 to 181 cm yr−1, with an average of 166 cm yr−1. Rainfall was consistently lower in Florida Bay than evaporation, with a long-term average of 106 cm yr−1. Rainfall considered alone was uncorrelated with evaporation at both monthly and annual time scales; when the seasonal variation
in clear sky radiation was also taken into account both net radiation and evaporation were significantly suppressed in months
with high rainfall. 相似文献
20.
J.A.C. Barth H. Freitag H.J. Fowler A.P. Smith C. Ingle A. Karim 《Applied Geochemistry》2007,22(12):2684
The gradients between precipitation and runoff quantities as well as their water isotopes were used to establish a water balance in the Clyde River Basin (Scotland). This study serves as an example for a European extreme with poorly vegetated land cover and high annual rainfall and presents novel water stable isotope techniques to separate evaporation, interception and transpiration with annual averages of 0.029 km3 a−1, 0.220 km3 a−1 and 0.489 km3 a−1, respectively. Transpiration was further used to determine CO2 uptake of the entire basin and yielded an annual net primary production (NPP) of 352 × 109 g C (Giga gram) or 185.2 g C m−2. Compared to other temperate areas in the world, the Clyde Basin has only half the expected NPP. This lower value likely results from the type of vegetation cover, which consists mostly of grasslands. Subtracting the annual heterotrophic soil respiration flux (Rh) of 392 Gg (206.1 g C m−2 a−1) from the NPP yielded an annual Net Ecosystem Productivity (NEP) of −40 Gg C, thus showing the Clyde Watershed as a source of CO2 to the atmosphere. Despite the unusual character of the Clyde Watershed, the study shows that areas with predominant grass and scrub vegetation still have transpirational water losses that by far exceed those of pure evaporation and interception. This infers that vegetation can influence the continental water balances on time scales of years to decades. 相似文献