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1.
Salinity and sodicity of groundwater are the principal water quality concerns in irrigated areas of arid and semi-arid regions.
The hydrochemical characteristics and sodicity of groundwater in the Shirin Sou area, western Iran were investigated in this
study by chemical analyses of groundwater samples from 49 wells. Chemical analysis of the groundwater showed that the mean
concentration of the cations was in the order: Na + > Ca 2+ > Mg 2+ > K +, while that for anions was SO 3
2− > Cl − > HCO 3
− > NO 3
−. The most prevalent water type is Na–SO 4 followed by water types Na–Cl and Ca–SO 4. The chemical evolution of groundwater is primarily controlled by water–rock interactions: mainly weathering of aluminosilicates,
dissolution of sulfate minerals, and cation exchange reactions. Sulfate dissolution and pyrite weathering may both contribute
to the SO 4
2− load of the groundwater. High Na + concentrations in groundwater participate in ion-exchange processes, resulting in the displacement of base cations into solution
and raised concentrations in groundwater. The principal component analysis (PCA) performed on groundwater identified three
principal components controlling variability of groundwater chemistry. Electrical conductivity, Ca 2+, Mg 2+, Na +, SO 4
2−, and Cl − content were associated in the same component (PC1) (salinity), most likely linked to anthropogenic activities. 相似文献
2.
The apparent isotope enrichment factor ε macrophyte of submerged plants (ε macrophyte–DIC = δ 13C macrophyte − δ 13C DIC) is indicative of dissolved inorganic carbon (DIC) supply in neutral to alkaline waters and is related to variations in aquatic
productivity (Papadimitriou et al. in Limnol Oceanogr 50:1084–1095, 2005). This paper aims to evaluate the usage of ε macrophyte inferred from isotopic analyses of submerged plant fossils in addition to analyses of lake carbonate as a palaeolimnological
proxy for former HCO 3
− concentrations. Stable carbon isotopic analysis of modern Potamogeton pectinatus leaves and its host water DIC from the Tibetan Plateau and Central Yakutia (Russia) yielded values between −23.3 and +0.4‰
and between +14.0 and +6.5‰, respectively. Values of ε
Potamogeton–DIC (range −15.4 to +1.1‰) from these lakes are significantly correlated with host water HCO 3
− concentration (range 78–2,200 mg/l) ( r = −0.86; P < 0.001), thus allowing for the development of a transfer function. Palaeo-ε
Potamogeton–ostracods values from Luanhaizi Lake on the NE Tibetan Plateau, as inferred from the stable carbon isotope measurement of fossil Potamogeton pectinatus seeds (range −24 to +2.8‰) and ostracods (range −7.8 to +7.5%) range between −14.8 and 1.6‰. Phases of assumed disequilibrium
between δ 13C DIC and δ 13C ostracods known to occur in charophyte swards (as indicated by the deposition of charophyte fossils) were excluded from the analysis
of palaeo-ε. The application of the ε
Potamogeton–DIC-HCO 3
− transfer function yielded a median palaeo-HCO 3
− -concentration of 290 mg/l. Variations in the dissolved organic carbon supply compare well with aquatic plant productivity
changes and lake level variability as inferred from a multiproxy study of the same record including analyses of plant macrofossils,
ostracods, carbonate and organic content. 相似文献
3.
The lead pollution history, based on the accumulation rate of total Pb and ratio of stable isotopes ( 206Pb/ 207Pb), was studied in the annually laminated sediment of a small lake in Finland (62°20′ N; 25°41′ E). The sediment chronology
based on varve counting provided a unique opportunity to explore and date signals of Pb emissions, including the ancient metallurgical
activities of the Roman Empire at the beginning of the Current Era. Changes in the ratio of stable isotopes gave a pronounced
signal of the atmospheric Pb fallout in AD 32–392, although this was not distinguishable in the accumulation rate of total
Pb, as it was observed in previous work. Calculated accumulations of the ancient pollution Pb were low, the highest values
being 0.2–0.3 mg m 2 a −1 in AD 144–392, corresponding 14–21% of the accumulation of total Pb. The accumulation of pollution Pb collapsed in the fifth
century and remained at or close to the background level up to the eleventh century. After this, the accumulation rate of
pollution Pb began to increase and reached 1.2 mg m 2 a −1 in AD 1420–1439, corresponding to 44% of the total Pb accumulation. During five centuries, from AD 1420–1895, the average
accumulation of pollution Pb was 2.6 mg m 2 a −1, the variation being from 0.8 to 4.8 mg m 2 a −1. The accumulation of Pb started to increase exponentially in the early twentieth century, and the highest accumulations of
pollution Pb (11–22 mg m 2 a −1, corresponding 50–76% of the annual accumulation of total Pb) were dated to AD 1926–1985. The banning of the use of leaded
fuel has led to a pronounced decrease in the accumulation of pollution Pb since the 1980s, and the present accumulation rate
represents the level that prevailed 80–120 years ago. 相似文献
4.
A decade of widespread increases in surface water concentrations of total organic carbon (TOC) in some regions has raised
questions about longer term patterns in this important constituent of water chemistry. This study uses near-infrared spectroscopy
(NIRS) to infer lake water TOC far beyond the decade or two of observational data generally available. An expanded calibration
dataset of 140 lakes across Sweden covering a TOC gradient from 0.7 to 24.7 mg L −1 was used to establish a relationship between the NIRS signal from surface sediments (0–0.5 cm) and the TOC concentration
of the water mass. Internal cross-validation of the model resulted in an R
2 of 0.72 with a root mean squared error of calibration (RMSECV) of 2.6 mg L −1. The TOC concentrations reconstructed from surface sediments in four Swedish lakes were typically within the range of concentrations
observed in the monitoring data during the period represented by each sediment layer. TOC reconstructions from the full sediment
cores of four lakes indicated that TOC concentrations were approximately twice as high a century ago. 相似文献
5.
We developed an inference model to infer dissolved organic carbon (DOC) in lakewater from lake sediments using visible-near-infrared
spectroscopy (VNIRS). The inference model used surface sediment samples collected from 160 Arctic Canada lakes, covering broad
latitudinal (60–83°N), longitudinal (71–138°W) and environmental gradients, with a DOC range of 0.6–39.6 mg L −1. The model was applied to Holocene lake sediment cores from Sweden and Canada and our inferences are compared to results
from previous multiproxy paleolimnological investigations at these two sites. The inferred Swedish and Canadian DOC profiles
are compared, respectively, to inferences from a Swedish-based VNIRS-total organic carbon (TOC) model and a Canadian-based
diatom-inferred (Di-DOC) model from the same sediment records. The 5-component Partial Least Squares (PLS) model yields a
cross-validated ( CV) RCV2 R_{CV}^{2} = 0.61 and a root mean squared error of prediction ( RMSEP
CV
) = 4.4 mg L −1 (11% of DOC gradient). The trends inferred for the two lakes were remarkably similar to the VNIRS-TOC and the Di-DOC inferred
profiles and consistent with the other paleolimnological proxies, although absolute values differed. Differences in the calibration
set gradients and lack of analogous VNIRS signatures in the modern datasets may explain this discrepancy. Our results corroborate
previous geographically independent studies on the potential of using VNIRS to reconstruct past trends in lakewater DOC concentrations
rapidly. 相似文献
6.
Zooplankton collections were made during 1985, 1986, 1988 and 1989 from 17 lakes in Saskatchewan and 3 in Alberta. Salinity
ranged from 2.8 to 269 g L −1 (total filtrable residue). A total of 35 species was present in four taxa: Anostraca (3 species), Cladocera (11), Copepoda
(7) and Rotifera (14). Species richness was greatest at salinities <7 g L −1 (15–16 species). Lakes with salinities between 7 and 100 g L −1 generally had 6–8 zooplankton species, while the most saline lakes (>100 g L −1) had 2–5 species. The largest concentrations of zooplankton occurred at <30 g L −1, but some species ( Brachionus plicatilis, Hexarthra polyodonta, Artemia franciscana, Diaptomus connexus) were abundant at salinities >50 g L −1. Eurysaline species included the rotifers Asplanchna girodi (3–111 g L −1), Brachionus plicatilis (13–146) and Keratella quadrata (2.8–103). Artemia franciscana (33–269—but absent from Big Quill Lake, 49–82), Daphnia similis (3–104). D. connexus (9–82), Diacyclops thomasi (3–72), and Cletocamptus albuquerquensis (17 to 126—but never abundant in the plankton). About half the species were restricted to hyposaline waters (3–20 g L −1), but some ( Hexarthra fennica, Moina hutchinsoni, Hexarthra polyodonta) occurred only at intermediate salinities. The latter two species were also only present at high pH values (>9.2). There
was a trend of decreasing species richness with increasing salinity.
TWINSPAN classification of 94 lake samples (six parameters) based on zooplankton species abundances yielded a dendrogram with
14 ‘indicator’ species characteristic of seven lake groups related partly to a salinity gradient, but with other environmental
factors such as water column depth, pH, Secchi disk transparency, water temperature and month sampled also influenced lake
separation. *** DIRECT SUPPORT *** A02GG004 00002 相似文献
7.
The northern Great Plains of Canada stretch from the Precambrian Shield near Winnipeg, Manitoba, westward for ∼1,700 km to
the Rocky Mountains foothills. This vast region of flat to gently rolling terrain contains a very large number of salt lakes.
Major ion chemical data on ∼500 of them are available. Although the average brine (salinity, 37 ppt) is a Na +−SO 4
2− type of water, the lakes exhibit a wide range of salinities and ionic compositions. This diversity is confirmed by Q-mode
cluster analysis; it identified thirteen major water chemistry types. Most ions display distinct trends, both spatially and
with increasing salinity. All dissolved components increase with increasing salinity, but at different rates. The relative
proportions of Ca 2+ and HCO 3
−+CO 3
2− ions show a strong decrease with increasing brine salinity, whereas SO 4
2− ions increase with increasing salinity. The ionic proportions of Na +, Mg 2+, K + and Cl − exhibit no significant relationship with salinity. R-mode factor analysis of the lake water chemistry, combined with selected
environmental parameters, identifies groundwater composition, climate, and the elevation of the lake within the drainage system
as most important in controlling brine chemistry and salinity on a regional basis. Variability in source of ions, reaction
processes and products are undoubtedly key factors in helping to explain brine chemistry of an individual basin or variation
from a local perspective, but these factors are generally poorly understood and not quantified on a regional basis.
Palliser Triangle Global Change Project Contribution Number 3. 相似文献
8.
A thorough study on understanding of groundwater recharge sources and mechanisms was attempted by integrating the hydrogeological, geochemical and isotopic information along with groundwater dating and end-member mixing analysis (EMMA). This study was necessitated due to prolonged dryness and unavailability of freshwater in semi arid Deccan trap regions of Central India. In addition, groundwater resources are not characterized well in terms of their geochemical nature and recharge sources. The hydrogeochemical inferences suggest that aquifer I consists of recently recharged water dominated by Ca–Mg–HCO3 facies, while groundwater in aquifer II shows water–rock interaction and ion exchange processes. Presence of agricultural contaminant, nitrate, in both aquifers infers limited hydraulic interconnection, which is supported by unconfined to semi-confined nature of aquifers. Groundwater in both aquifers is unsaturated with respect to carbonate and sulfate minerals indicating lesser water–rock interaction and shorter residence time. This inference is corroborated by tritium age of groundwater (aquifer I: 0.7–2 years old and aquifer II: 2–4.2 years old). Stable water isotopes (δ2H, δ18O) suggest that groundwater is a mixture of rainwater and evaporated water (surface water and irrigation return flow). EMMA analysis indicates three groundwater recharge sources with irrigation return flow being the dominant source compared to others (rainwater and surface waters). A conceptual model depicting groundwater chemistry, recharge and dynamics is prepared based on the inferences. 相似文献
9.
We inferred late Pleistocene and early Holocene (24–10 ka BP) environmental conditions in and around Lago Petén Itzá, Guatemala
from ostracode remains in the lake sediments. Multivariate statistics were run on autecological information for 29 extant
ostracode species collected in 63 aquatic ecosystems on the Yucatán Peninsula along a steep, increasing NW–S precipitation
gradient and across a large altitudinal range. Conductivity and water depth are the most important factors that shape ostracode
communities. Transfer functions were developed and applied to fossil ostracode assemblages in a ~76-m sediment core (PI-6,
~85 ka) taken in 71 m of water from Lago Petén Itzá, to infer past shifts in conductivity and water level. Results suggest
climate was cold and wet during the Last Glacial Maximum (LGM). Alternating dry and wet conditions characterized the deglacial.
Early Holocene climate was warmer and wetter. The LGM was characterized by low ostracode species richness (4 spp.) and abundance
(<940 valves g −1), dominance of benthic over nektobenthic taxa, abundant Physocypria globula, conductivity as low as 190 μS cm −1, and clay-rich sediments with relatively high total organic carbon and low C/N ratios (<14), suggesting relatively deeper
water at the core site associated with abundant precipitation. Greatest water depth at the core site during the LGM occurred
late in the period and was ~50 m. The deglacial was characterized by drier conditions, higher ostracode species richness (6
spp.) and abundances up to 18,115 valves g −1, dominance of nektobenthic species, and presence of shallow-water and littoral-zone indicators such as Heterocypris punctata and Strandesia intrepida, conductivity up to 550 μS cm −1, C/N ratios as high as 37, and gypsum deposition. Lowest inferred lake depth at the core site during the deglacial was ~20 m.
The early Holocene was characterized by high numbers of ostracode remains, up to 25,500 valves g −1, and the presence of L. opesta and P. globula. Cytheridella ilosvayi was absent from late Pleistocene sediments, suggesting it colonized northern Central America during the Holocene. 相似文献
10.
We present a sedimentary geochemical record of human perturbation in the watershed and related changes in trace metals (Cr,
Ni, Zn and Pb), phosphorus and abundant rock-forming elements (Al, Fe, K, Mg, etc.) in Chaohu Lake over the past 500 years,
a period spanning historical agricultural expansion and modern economic development. The record exhibited a stable terrestrial
detrital input to Chaohu Lake before ca. 1540 AD, a period with less human perturbation of the watershed, which resulted in
low and constant values of trace metals and phosphorus (TP) concentrations as well as Al, Fe, K, Mg, fine silt (<16 μm), the
chemical index of alteration (CIA) and K/Na ratio. Two periods of successive marked increases in Al, Fe, K, Mg, fine silt,
chemical index of alteration (CIA) and K/Na ratio occurred after ca. 1540 AD and 1950 AD. The former period apparently resulted
from enhanced well-weathered topsoil erosion in the watershed related to the expansion of arable land, and the latter resulted
from further enhancement of human perturbation in the watershed during the modern period. Concentrations of trace metals and
TP were positively correlated with that of the rock-forming elements and fine silt. Trace metal pollution was limited during
1540–1950 AD, according to the low enrichment factors (EFs = 0.8–1.1), when an increase in trace metal concentrations was
also linked to changes in detrital input. In addition to detrital regulation, pollution also contributed to an increase in
TP concentrations (average EF 1.4) during 1540–1950 AD and the average accumulation rate of anthropogenic phosphorus was 87.3 mg m −2 a −1. Anthropogenic phosphorus increased further and Pb and Zn pollution also occurred after 1950 AD, reaching maximum values
after 1980 AD, when the average accumulation rates of anthropogenic Zn, Pb and phosphorus (mainly in the form of NaOH-P) were
242.2, 43.3 and 811.8 mg m −2 a −1, respectively. The increase in phosphorus pollution in recent decades is probably from the domestic sewage sources of Hefei
City and non-point sources related to agricultural utilization of commercial fertilizer, whereas Zn and Pb pollution is probably
derived mainly from industrial sources of Hefei City, as deduced from their spatial variations in the sediments of the river
mouths. 相似文献
11.
A knowledge of pre-disturbance conditions is important for setting realistic restoration targets for lakes. For European waters
this is now a requirement of the European Council Water Framework Directive where ecological status must be assessed based
on the degree to which present day conditions deviate from reference conditions. Here, we employ palaeolimnological techniques,
principally inferences of total phosphorus from diatom assemblages (DI-TP) and classification of diatom composition data from
the time slice in sediment cores dated to ~1850 AD, to define chemical and ecological reference conditions, respectively,
for a range of UK lake types. The DI-TP results from 169 sites indicate that reference TP values for low alkalinity lakes
are typically <10 μg L −1 and in many cases <5 μg L −1, whilst those for medium and high alkalinity lakes are in the range 10–30 and 20–40 μg L −1, respectively. Within the latter two alkalinity types, the deeper waters (>3 m mean depth) generally had lower reference
TP concentrations than the shallow sites. A small group of shallow marl lakes had concentrations of ~30 μg L −1. Cluster analysis of diatom composition data from 106 lakes where the key pressure of interest was eutrophication identified
three clusters, each associated with particular lake types, suggesting that the typology has ecological relevance, although
poor cross matching of the diatom groups and the lake typology at type boundaries highlights the value of a site-specific
approach to defining reference conditions. Finally the floristic difference between the reference and present day (surface
sample) diatom assemblages of each site was estimated using the squared chord distance dissimilarity coefficient. Only 25
of the 106 lakes experienced insignificant change and the findings indicate that eutrophication has impacted all lake types
with >50% of sites exhibiting significant floristic change. The study illustrates the role of the sediment record in determining
both chemical and ecological reference conditions, and assessing deviation from the latter. Whilst restoration targets may
require modification in the future to account for climate induced alterations, the long temporal perspective offered by palaeolimnology
ensures that such changes are assessed against a sound baseline. 相似文献
12.
The Sierra de Los Tuxtlas is a recently active volcanic field, with eruptions in 1664 and 1792. It holds one of the reserves
of tropical evergreen forest in Mexico, as well as several maar lakes. One of them, Lago Verde, was chosen for a three-fold
study (1) on its present limnological conditions, (2) on the algal community living in the water column and preserved in the
surface sediments; and (3) on its recent history (ca. 340 yr). The palaeolimnological study was based on multiproxy analyses
on core material dated by 210Pb, 137Cs and 14C. Lago Verde is a small, shallow lake with dilute, slightly alkaline water (CO 32− + HCO 3− > Cl − > SO 42−, Na + + K + > Ca 2+ > Mg 2+). It is turbid, eutrophic, with high phosphorus levels. It is a warm polymictic lake, with thermal and oxygen stratification
establishing by midday during the warm months. The lake does not stratify in winter. Diatoms dominate the phytoplankton community
in the cold ‘nortes’ season, Cyanobacteria in summer, and Chlorophyta in autumn. Cyanobacteria (Chroococcales) are not well
preserved in the surface sediments while Chlorophyta are better preserved. Sedimentary diatoms are well preserved, dominated
by the three most abundant species in the water column: Achnanthidium minutissimum, Fragilaria capucina and Aulacoseira granulata. The base of the studied sequences is constrained by the historic eruption of 1664. The period from 1664 to 1963 is characterised
by a meso-eutrophic lake. Tropical Forest vegetation reaches maximum values between ca. 1800 and 1963. Between ca. 1785 and
1885 the lake was slightly shallower than in the rest of the 1664–1963 period, probably recording climatic variability. An
early pulse of anthropogenic disturbance was recorded by ca. 1921 and after ca. 1963 intense forest clearance and high erosion
rates led to a more turbid, more productive, nutrient-rich lake. The highest anthropogenic impact was reached by ca. 1988;
afterwards the lake and its basin reached a new balance, with the establishment of the present modern conditions. 相似文献
13.
This study presents detailed lithostratigraphy and stable carbon and nitrogen isotopic variations in a 520-cm-long sediment
core from a cirque basin in the Labsky důl Valley, Krkonoše Mountains, Czech Republic. Detailed study of the core reveals
five major periods of sedimentation during the last 7600 years: silt and sand deposition during ~7.6–5.1 ka cal BP, Sphagnum peat accumulation during ~5.1–4.0 ka cal BP, sandy silt and sand during ~4.0–2.8 ka cal BP, raised peat bog during ~2.8–2.0 ka cal
BP ( Sphagnum peat), and sedimentation of sandy silt since ~2.0 ka cal BP. The δ 13C values of the organic matter in the core vary in the range typical for C3 plants, from −24.35 to −27.68‰, whereas the δ 15N values vary from −2.65 to +4.35‰. Core sections having ash contents ≥70% have δ 15N > 1‰ and δ 13C < −26‰, whereas those having ≤70% ash content have δ 15N < 1‰ and δ 13C > −26‰. Strong linear correlations are observed between δ 13C and δ 15N values as well as between C:N ratios and δ 15N values in the horizons with ash content >10%, primarily for sand and silt horizons. On the other hand, poor correlations
between δ 13C and C:N ratio, as well as δ 15N and C:N ratio, were observed in Sphagnum peat layers (45–125 and 185–265 cm). We conclude that the primary stable isotope variations are not preserved in the layers
where significant correlation between δ 15N and C:N ratio is observed. The relatively small δ 13C variation in the uppermost Sphagnum peat layer suggests stable temperature during ~2.8–2.0 ka cal BP. 相似文献
14.
Organic arsenical herbicides, which include monosodium methylarsonate (MSMA), have been applied to golf courses and lawns
throughout Florida, USA, since the 1950s. These products convert rapidly to inorganic forms of arsenic (As) in soils and are
mobilized readily. Leachates have been known to contaminate groundwater and surface waters, although past studies have not
examined whether use of these products has led to significant As accumulation in lake sediments. We used paleolimnological
methods to document the depositional history and inventories of total As in sediments and porewaters of Little Lake Jackson
in Florida, which is adjacent to three golf courses. Six sediment cores, four of which were 210Pb dated, showed porewater total As concentrations as high as 435 μg l −1, and dry-sediment total As concentrations as high as 148 mg kg −1. Approximately 537 kg of total As is present in >19,000 metric tons of sediment (dry mass), and an additional 18 kg of As
is dissolved in 10.8 × 10 4 m 3 of porewaters. Total As content in surface sediments (mean = 47.3 mg kg −1) exceeds the consensus-based sedimentary concentration for probable toxicity effects in freshwater benthic fauna. Surface
and subsurface waters flow to the lake from topographically higher areas to the west, where golf courses and residential areas
are located. Total As concentrations were elevated highly in monitoring wells and in a stream that flows between the golf
courses and lake, but As was below detection limits in wells that were located at the distal perimeter of the golf courses.
Subsurface and surface waters exit the lake towards topographically lower areas to the east. Nearly all As in sediments remains
bound in the solid phase, indicating that As sedimentary profiles largely reflect depositional history. Sedimentary As concentrations
are correlated strongly with aluminum and iron, which suggests that As was scavenged from lake waters during the past. Sedimentary
As concentrations increased until the 1980s, then declined somewhat to the present time. Dissolved As was scavenged efficiently
from the water column when hypolimnetic waters were oxygenated persistently, but after eutrophication led to a seasonally
anoxic hypolimnion in the 1980s, apparently less As was co-precipitated, and more was lost to hydrological outflow. Arsenic
accumulation in sediments might be common in areas where As derived from organic arsenical herbicide applications is directed
by shallow water tables towards adjacent lakes. 相似文献
15.
We quantified differences in oxygen isotope fractionation among three biostratigraphically important subfossil ostracod species
( Metacypris cordata, Pseudocandona rostrata and Candonopsis kingsleii) from an early Holocene freshwater tufa layer in northern Estonia. Estimated mean δ 18O values are −10.05‰ for M. cordata, −9.34‰ for C. kingsleii and −8.75‰ for P. rostrata. All three species exhibit positive offset from the weighted mean annual δ 18O of contemporary precipitation (−10.7‰ in δ 18O V-PDB) and from the mean δ 18O value of authigenic tufa carbonate (−10.64‰) in the ostracod-bearing layer. Assuming that the known oxygen isotope fractionation
in P. rostrata (+2.5‰) and M. cordata (+1.5‰) has remained constant over time, the theoretical δ 18O V-SMOW of the early Holocene lake water was calculated to have been between −11.52 and −11.92‰, slightly less negative than the
local Ordovician groundwater (−11.7 to −12.2‰). δ 18O values of the tufa carbonate differ by +0.6 to +1.0‰ from the calculated theoretical isotope composition (δ 18O V-PDB) of lake water, indicating that the tufa also did not precipitate in isotopic equilibrium with ambient waters. Results show
that the greater the δ 18O offset from the calculated, theoretical isotope composition of lake water for an ostracod species, the lower is its preferred
mean July temperature. Both our data and earlier published results on δ 18O values in Holocene lacustrine carbonates and ostracods from north-eastern Europe, display pronounced decreases in δ 18O with an increase in latitude of the study site. This suggests that temperature-dependent, and therefore latitude-dependent
isotopic composition of meteoric waters controlled the δ 18O values in lacustrine tufa and ostracods throughout the Holocene. 相似文献
16.
The main limnological features of Lake Issyk-kul are described. The lake is a large (6,236 km 2), deep (z m, 668 m), closed lake in eastern Kirgizia. It lies at ∼1,607 m above sea level, but water-levels have been dropping since
the last century. It is slightly saline (salinity, ∼6g L −1), with Na +, Mg 2+, Cl − and SO
4
2−
the dominant ions. Nutrient levels are low and the lake is considered ultra-oligotrophic.
Characeae dominate the macrophytes. About 300 and 117 taxa of, respectively, phytoplankton and zooplankton have been identified,
with Arctodiaptomus salinus the most numerous in the zooplankton. Chironomids dominate the benthos. Several endemic taxa of fish occur, of which Leuciscus bergi was dominant until the 1970s. The fish fauna has been supplemented by many introduced species. Three mysids were introduced
in 1965–8 and are now a significant part of the ecosystem. The present annual fish catch permitted is 320 t.
The most important value of the lake is as a recreational resource. To promote and sustain this value requires careful, ongoing
management. The most significant threats to the lake are local pollution, visitor pressure, and declining water-levels. 相似文献
17.
Rapid urbanization and increased tourism around Nainital Lake in the Kumaun Himalayan region in north India has raised concerns
about sediment and water pollution. Lead-210 dated sediment cores from the lake represent ~95 years of accumulation and yield
a mean sedimentation rate of ~4.7 mm year −1. Total organic carbon (TOC), percent N and S and their atomic C/N and C/S ratios, stable isotopes (δ 13C, δ 15N, and δ 34S), and specific biomarkers ( n-alkanes and pigments) were measured in the core. Organic matter is primarily derived from in-lake algal production and TOC
flux varies from 1.0 to 3.5 g m −2 year −1. Sediments are anoxic (Eh −328 to −187 mV) and have low (0.10–0.30 g m −2 year −1) N, but high (0.37–1.0 g m −2 year −1) S flux. Shifts in δ 13C, δ 15N, and δ 34S suggest in-lake microbial processes dominated by denitrification and sulfate reduction. The sediments are dominated by short-chain
hydrocarbons with low Carbon Preference Index values. The pigments indicate a gradual shift to cyanobacterial domination of
the phytoplankton community in recent years. Despite an increase in external input of nutrients, the trophic state of the
lake has remained largely unchanged, and the perceived human-induced impacts are limited. 相似文献
19.
A 72-lake diatom training set was developed for the Irish Ecoregion to examine the response of surface sediment diatom assemblages
to measured environmental variables. A variety of multivariate data analyses was used to investigate environmental and biological
data structure and their inter-relationships. Of the variables used in determining a typology for lakes in the Irish Ecoregion,
alkalinity was the only one found to have a significant effect on diatom assemblages. A total of 602 diatom taxa were identified,
with 233 recorded at three or more sites with abundances ≥1%. Generally diatom data displayed a high degree of heterogeneity
at the species level and non-linear ecological responses. Both pH and total phosphorus (TP) (in the ranges of 5.1–8.5 and
4.0–142.3 μg l −1 respectively) were shown to be the most significant variables in determining the surface sediment diatom assemblages. The
calibration models for pH and TP were developed using the weighted averaging (WA) method; data manipulation showed strong
influences on model performances. The optima WA models based on 70 lakes produced a jack-knifed coefficient of determination
( r
2
jack) of 0.89 with a root mean squared error (RMSEP) of 0.32 for pH and r
2
jack of 0.74 and RMSEP of 0.21 (log 10 μg l −1) for TP. Both models showed strong performances in comparison with existing models for Ireland and elsewhere. Application
of the pH and TP transfer functions developed here will enable the generation of quantitative water quality data from the
expanding number of palaeolimnological records available for the Irish Ecoregion, and thus facilitate the use of palaeolimnological
approaches in the reconstruction of past lake water quality, ecological assessment and restoration. 相似文献
20.
A rapid increase in the number of tourists has placed a heavy demand for freshwater on Manukan Island, a small island located
offcoast of Kota Kinabalu, Sabah. Hydrochemical and numerical approaches have been applied in this study to evaluate the groundwater
quality of unconfined aquifer lying in Manukan Island, Sabah, East Malaysia. This is vital to enhance better understanding
about groundwater management. Hydrochemical analysis output indicated NaCl water type in sampling locations. Seawater intrusion
is marked by its relatively high Na +, Mg 2+, Cl − and SO 4
2− concentrations. Hydrochemical analysis output clearly showed the influence of seawater in groundwater of Manukan Island.
The numerical model output proved the influence of seawater in groundwater of Manukan Island by indicating the upconing process
at the beneath of the pumping well. Current status of seawater intrusion in Manukan Island is about 14.6% of freshwater and
seawater mixing ratio in low lying area of Manukan Island as simulated by SEAWAT-2000 model output. Numerical model SEAWAT-2000
output showed clearly that the upconing process is the possible route of seawater to influence the fresh groundwater aquifer
chemistry in Manukan Island. The results have enhanced the current understanding of seawater intrusion in the study area.
Future studies will focus on using numerical models to simulate and suggest suitable groundwater management plans in Manukan
Island. 相似文献
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