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1.
The Haji-Gak iron deposit of eastern Bamyan Province, eastern Afghanistan, was studied extensively and resource calculations
were made in the 1960s by Afghan and Russian geologists. Recalculation of the resource estimates verifies the original estimates
for categories A (in-place resources known in detail), B (in-place resources known in moderate detail), and C 1 (in-place resources estimated on sparse data), totaling 110.8 Mt, or about 6% of the resources as being supportable for the
methods used in the 1960s. C 2 (based on a loose exploration grid with little data) resources are based on one ore grade from one drill hole, and P 2 (prognosis) resources are based on field observations, field measurements, and an ore grade derived from averaging grades
from three better sampled ore bodies. C 2 and P 2 resources are 1,659.1 Mt or about 94% of the total resources in the deposit. The vast P 2 resources have not been drilled or sampled to confirm their extent or quality. The purpose of this article is to independently
evaluate the resources of the Haji-Gak iron deposit by using the available geologic and mineral resource information including
geologic maps and cross sections, sampling data, and the analog-estimating techniques of the 1960s to determine the size and
tenor of the deposit. 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.
Spatial uncertainty analysis is a complex and difficult task for orebody estimation in the mining industry. Conventional models (kriging and its variants) with variogram-based statistics fail to capture the spatial complexity of an orebody. Due to this, the grade and tonnage are incorrectly estimated resulting in inaccurate mine plans, which lead to costly financial decision. Multiple-point geostatistical simulation model can overcome the limitations of the conventional two-point spatial models. In this study, a multiple-point geostatistical method, namely SNESIM, was applied to generate multiple equiprobable orebody models for a copper deposit in Africa, and it helped to analyze the uncertainty of ore tonnage of the deposit. The grade uncertainty was evaluated by sequential Gaussian simulation within each equiprobable orebody models. The results were validated by reproducing the marginal distribution and two- and three-point statistics. The results show that deviations of volume of the simulated orebody models vary from ? 3 to 5% compared to the training image. The grade simulation results demonstrated that the average grades from the different simulation are varied from 3.77 to 4.92% and average grade 4.33%. The results also show that the volume and grade uncertainty model overestimates the orebody volume as compared to the conventional orebody. This study demonstrates that incorporating grade and volume uncertainty leads to significant changes in resource estimates. 相似文献
4.
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
5.
Stable isotopes (δ 18O and δD) are useful tracers for investigating hydrologic and climatic variability on a variety of temporal and spatial scales.
Since the early isotopic studies on mountainous glaciers in the late 1960s, a great deal of information has been generated
on the isotopic composition of rainfall, snow, ice, surface waters, and lake carbonate sediments across the Tibetan Plateau.
However, measurements of δ 18O and δD values of lake water are scarce. Here we present a new dataset of δ 18O and δD values of lake waters collected from 27 lakes across the plateau during a reconnaissance survey in summer 2009. δ 18O and δD values of lake water range from −19.9 to 6.6‰ and from −153 to −16‰, respectively. The average values of δ 18O and δD are −6.4 and −72‰, considerably greater than those of precipitation observed in this region. The derived Tibetan
lake water line, δD = 5.2δ 18O − 38.9, is significantly different from the global meteoric water line. Most of the lakes, including some freshwater lakes,
contain water with negative values of d-excess ( d). There is a negative correlation between d and total dissolved solids (TDS). Each of these findings indicates that evaporation-induced isotopic enrichment prevails
in Tibetan lakes. Moreover, we develop an isotope modeling scheme to calculate E/P ratios for Tibetan lakes, using a combination
of existing isotopic fractionation equations and the Rayleigh distillation model. We use the intersection of the local evaporation
line and GMWL as a first approximation of δ 18O and δD values of lake water inputs to infer an E/P ratio for each lake. Our modeling calculations reveal that although variable
from lake to lake, the water budget across the plateau is positive, with an average E/P of 0.52. This is in good agreement
with other observational and model data that show varying degrees of increases in lake size from satellite imagery and significant
decreases in lake salinity in many lakes on the plateau over the last several decades. Together with the new isotopic dataset,
the proposed modeling framework can be used to examine and quantify past changes in a lake’s hydrologic balance from the isotopic
record of downcore carbonate sediments in the region. 相似文献
6.
Groundwater is the major source of drinking water in Nahavand city. However, the groundwater quality at the agricultural areas
has been deteriorating in recent years. Ground water quality monitoring is a tool which provides important information for
water management and sustainable development of the water resources in Nahavand. Hydrochemical investigations were carried
out in an agricultural area in Nahavand, western Iran, to assess chemical composition of groundwater. In this study, 64 representative
groundwater samples were collected from different irrigation wells and analyzed for pH, electrical conductivity, major ions,
and nitrate. The results of the chemical analysis of the groundwater showed that concentrations of ions vary widely and the
most prevalent water type is Ca–Mg–HCO 3, followed by other water types: Ca–HCO 3, Ca–Na–HCO 3, and Na–Cl, which is in relation with their interactions with the geological formations of the basin, dissolution of feldspars
and chloride and bicarbonate minerals, and anthropogenic activities. Thirty-seven percent of the water samples showed nitrate
(NO 3
−) concentrations above the human affected value (13 mg L −1). The phosphorous (P) concentration in groundwater was between 0.11 and 0.90 mg L −1, with an average value of 0.30 mg L −1, with all of the samples over 0.05 mg L −1. The most dominant class C2-S1 (76.5%) was found in the studied area, indicating that sodicity is very low and salinity is
medium, and that these waters are suitable for irrigation in almost all soils. Agronomic practices, such as cultivation, cropping,
and irrigation water management may decrease the average NO 3
− concentration in water draining from the soil zone. 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.
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
9.
For researching the spatio-temporal variation of the stable isotopic composition of the riverine dissolved inorganic carbon(DIC),we had carried out a survey throughout the hydrologic year during which theδ^13CDIC of the surface water and its physicochemical parameter were examined along the Xijiang River Inner Estuarine waterway from September 2006 to June 2007.There was a striking seasonal variation on the averageδ^13CDIC,as the averageδ^13CDIC in summer(-13.91‰)or autumn(-13.09‰)was much less than those in spring(-11.71‰)or winter(-12.26‰).The riverineδ13C DIC was controlled by decomposed condition of the riverine organic matter linking the seasonal variation of the physicochemical parameter in the surface water according to the correlation analysis which indicated notable relations betweenδ^13CDIC and water temperature(p=0.000;r=-0.569)or betweenδ^13CDIC and oxide-reduction potential(p=0.000;r=0.646).The striking positive correlation between δ^13CDIC and the sampling distance happened in the summer rainy season,while striking negative correlation happened in the spring dry season,indicating that river-sea interaction influenced water physicochemical parameters and controlled the riverine DIC property in the survey waterway.In view of the riverineδ^13CDIC decreasing for the decomposition of the terrestrial organic matter in the rainy season in summer and increasing for the briny invaded zone extending in the spring dry season along the waterway from the Makou gauging station to the Modaomen outlet,theδ^13CDIC spatio-temporal variation was closely related to the geographical environment of the Xijiang drainage basin. 相似文献
10.
A plutonic porphyry gold deposit model is proposed that is imilar to the plutonic porphyry copper deposit model. However, unlike the plutonic porphyry copper deposit model, the proposed model is deficient in copper and contains less than 1 percent total sulfides. In the proposed model, gold is accompanied by scheelite, molybdenite, arsenopyrite, a variety of bismuth sulfides, tellurides, and native bismuth. The host rock varies from granite to granodiorite stock. Most of the ore is in the pluton. Deposits cited as examples of the proposed model are the Mokrsko deposit in Czechoslovakia, the Fort Knox deposit in the United States, and the Dublin Gulch deposit in Canada. In each of these deposits, pervasive potassic or phyllic alteration zones accompany the gold ore, which is disseminated in quartz-rich stockworks, veinlet swarms, and veins. Tonnages of gold-bearing material are large, but grades are low in the cited deposits. The proposed model is distinct from other gold deposit models because of the low Cu to Au ratio and the association of Au, Bi, W, and Mo. 相似文献
11.
Palaeovariations of the atmospheric 210Pb flux in Northeast China (Long Gang area, Jilin province), quantified by high resolution 210Pb measurements on seasonally laminated sediments of Lake Sihailongwan are presented on decadal scale. The mean flux of unsupported
210Pb between 1790 and 1970 for the centre of the lake basin is 517 Bq m −2 yr −1 with maximum deviations between −23% and +27% of this value. Flux rates above this average were found between 1783 and 1813,
around 1836, and between 1860 and 1901. The mean 210Pb exc flux rates derived were clearly lower around 1821, 1908, 1930, and 1953. The 210Pb exc flux reached its minimum of 344 Bq m −2 yr −1 during the period 1977–1982. The atmospheric flux of unsupported 210Pb is correlated with the precipitation frequency during the summer monsoon and shows coinciding variability with geochemical
proxies that document the groundwater inflow into the lake. Al 2O 3-rich dust of remote provenance scavenged by wet-deposition in the rainy season is the major carrier of the atmospheric 210Pb exc flux. 相似文献
12.
Stable carbon and nitrogen isotope ratios have been determined on 41 strains of Artemia sp. from different geographic regions around the world. The δ 13C and δ 15N values ranged between −13.7 to−25.0 per mil and −0.7 to 21.2 per mil respectively. Artemia δ 13C values from coastal environments are consistent with a marine origin for the food source Artemia from inland salt lakes have a range of carbon isotope values suggesting C 3, C 4 and CAM based organic matter could form the base of the Artemia food chain. These data indicate that Artemia having a wide range of carbon and nitrogen isotope values are available for tropho-dynamic research studies that quantify
the effect of respired CO 2 on tissue and CaCO 3 shell 13C/ 12C ratios. Such stable isotope variation also suggests that stable isotope fingerprinting remains a viable technique for identifying
specific Artemia collection sites. 相似文献
13.
Carbon stable isotope ratios were determined in dominant biotic components of pelagic and littoral systems in Alchichica crater-lake.
Results showed that carbon signatures were significantly different between both systems. The pelagic environment was more
depleted (−26.15 to −15.14 per mille) than the littoral zone (−21.03 to −17.91 per mille). The potential source end-point
in the simplified pelagic community was established to be diatomaceous phytoplankton; its predicted value was −21.7 per mille.
There is a clear evidence that Nodularia does not sustain the pelagic food chain. In contrast, the highly diverse littoral community was sustained by epiphytes. No
allochthonous sources seemed to influence this food web. 13C enrichment was observed along the components of both systems with fractionations of 0.8 to 1.4 per mille. The contribution
of the seagrass Ruppia maritima is probably associated with the detritus pathway. Carbon source partitioning between both systems was not recorded. The δ 13C in Alchichica crater-lake was more enriched than in other saline lakes and could be attributed to different salinity and
CO 2 concentrations among lakes. 相似文献
14.
This paper describes the application of an unsupervised clustering method, fuzzy c-means (FCM), to generate mineral prospectivity models for Cu?±?Au?±?Fe mineralization in the Feizabad District of NE Iran. Various evidence layers relevant to indicators or potential controls on mineralization, including geochemical data, geological–structural maps and remote sensing data, were used. The FCM clustering approach was employed to reduce the dimensions of nine key attribute vectors derived from different exploration criteria. Multifractal inverse distance weighting interpolation coupled with factor analysis was used to generate enhanced multi-element geochemical signatures of areas with Cu?±?Au?±?Fe mineralization. The GIS-based fuzzy membership function MSLarge was used to transform values of the different evidence layers, including geological–structural controls as well as alteration, into a [0–1] range. Four FCM-based validation indices, including Bezdek’s partition coefficient (VPc) and partition entropy (VPe) indices, the Fukuyama and Sugeno (VFS) index and the Xie and Beni (VXB) index, were employed to derive the optimum number of clusters and subsequently generate prospectivity maps. Normalized density indices were applied for quantitative evaluation of the classes of the FCM prospectivity maps. The quantitative evaluation of the results demonstrates that the higher favorability classes derived from VFS and VXB (Nd?=?9.19) appear more reliable than those derived from VPc and VPe (Nd?=?6.12) in detecting existing mineral deposits and defining new zones of potential Cu?±?Au?±?Fe mineralization in the study area. 相似文献
15.
采用预处理—浸出工艺技术,解决了该矿床半氧化矿石中Au、Ag、Co、Ni、Cu、Mo、Bi的选矿技术,使Au、Ag、Co、Ni、Cu、Mo的浸出率达90%以上,Bi的浸出率85%以上。 相似文献
16.
A sediment core from Lake Koucha (eastern Tibetan Plateau) was investigated using organic biomarkers and their stable carbon
isotope signatures. The correlation between TOC content, total amount of aquatic macrophyte-derived n-alkanes (e.g. nC 23) and δ 13C values of TOC and nC 23 indicates that Lake Koucha was macrophyte-dominated before 8 cal ka BP. Shortly after the lake turned from a saline to a
freshwater system at 7.2 cal ka BP, a variety of algal and bacterial markers such as hopanoids and isoprenoids emerged, of
which phytane, pentamethylicosene (PMI), moretene and diploptene are particularly abundant. Phytane and PMI show different
isotopic signals (≈−18 and ≈−28‰, respectively), which indicates that they originated from different sources. Phytane may
have been derived from cyanobacteria, while methanogenic archaea may be the source of PMI. The isotopic depletion of diploptene
and moretene (≈−60‰) indicates the presence of methanotrophs. After 6.1 cal ka BP, the saturated C 20 highly branched isoprenoid (HBI) became the dominant constituent of the aliphatic hydrocarbon fraction. Such dominance has
rarely been reported in lacustrine environments, and indicates a strong presence of algae (most likely diatoms) or cyanobacteria.
At 4.7 cal ka BP, the appearance of an unsaturated C 25 HBI, which is a specific biomarker for diatoms, was noted. Furthermore, the level of nC 17-alkane was observed to increase in abundance in the uppermost two samples. These results suggest that the lake was phytoplankton-dominated
during the last 6.1 ka. Relatively low biomarker concentrations and δ 13C values at 6.0, 3.1 and 1.8 cal ka BP indicate the occurrence of cool periods, which is in agreement with inferences from
other locations on the Tibetan Plateau. The δ 13C values of nC 23 range from −23.5 to −12.6‰, with high values at the peak of macrophyte abundance at ca. 11 cal ka BP and at the phytoplankton
maximum between ca 6.1 and 2.8 cal ka BP. Thus, aquatic macrophyte-derived mid-chain n-alkanes have been found to be excellent indicators of carbon-limiting conditions, which lead to the assimilation of isotopically-enriched
carbon species. The limitation of carbon sources could be a localized phenomenon occurring in dense plant stands (as in the
older section of the core), or it may be induced by high primary productivity (as in the younger section). Since the δ 13C value of the inorganic carbon source may vary, the offset between the δ 13C values of nC 23 and TIC could serve as a more precise proxy for carbon-limiting conditions in lacustrine environments, which could in turn
be interpreted with respect to lacustrine paleo-productivity. 相似文献
17.
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
18.
A 7.6-m lake sediment core from a marl lake, Lough Inchiquin, records variation in landscape evolution from 16,800 cal yrs
B.P. to 5,540 cal yrs B.P. We observe significant variations (up to 12‰) in δ
13C org and δ
13C calcite values that are interpreted to reflect secular changes in lake water δ
13C DIC values that result from a regional landscape transition from barren limestone bedrock to a forested ecosystem. Lake water
δ
13C DIC values are therefore influenced by two isotopically distinct sources of carbon: terrestrial organic material (−27.1 to −31.2‰VPDB)
via oxidized soil organic matter and weathered limestone bedrock (+3.4‰VPDB). Isotope excursions in lacustrine sediment records
are forced not only by changes in productivity but also by changes in the terrestrial environment. This has profound implications
for the interpretation of paleoclimate records derived from lacustrine sediment and suggests that selection of appropriate
lakes can provide records of terrestrial change where other related records are not available. 相似文献
19.
A geologic anomaly is a geologic feature or structure that departs markedly from its surrounding environment with respect
to composition, texture, or genesis. The analysis of geologic anomalies related to mineralization is based upon specific geologic
factors and a combination of features, such as structural, temporal, and spatial, and draws upon special effects that are
due to ore-forming processes. An analysis of the geologic anomalies in the, middle-lower Yangtze area in southeastern China
has led to an interpretation of the relation between anomaly subtypes and the occurrence and spatial distribution of ore deposits.
Consequently, the following conclusions have been reached: the type of anomaly reflects the controlling factors that led to
the formation of iron, copper, and gold deposits in the area; sedimentary geologic anomalies are most closely associated with
stratiform deposits; structral complexity anomalies are most closely associated with Cu−Fe−Au deposits; magmatic anomalies
reflect geologic processes in which Fe and Cu elements were separated from magma and enriched into ores; and the geologic
combination entropy anomaly is proposed as a comprehensive variable that is related to favorable ore-forming environments
and that can serve as a quantitative index that can be used in mineral exploration. 相似文献
20.
We used elemental carbon, nitrogen, phosphorus and hydrogen ratios (C/N, N/P and H/C) with total organic carbon (TOC) and
total phosphorus (TP) as well as stable carbon and nitrogen isotopes (δ 13C and δ 15N) to investigate the source and depositional conditions of organic matter in sediments from Zeekoevlei, the largest freshwater
lake in South Africa. Typical C/N (10–12), H/C ratios (≥1.7) and δ 13C organic values (−22 to −19‰) together with the increase in TOC concentration indicate elevated primary productivity in lower middle
(18–22 cm) and top (0–8 cm) sections of the sediment cores. Seepage of nutrients from a nearby waste water treatment plant,
rapid urbanization and heavily fertilized farming in the catchments are responsible for the increased productivity. Consistent
with this, measured δ 15N organic values (∼11‰) indicate increased raw sewage input towards the top-section of the core. Although cyanobacterial blooms are
evident from the low δ 15N values (∼3‰) in mid-section of the core, they did not outnumber the phytoplankton population. Low N/P ratio (∼0) and high
TP (100–2,200 mg l −1) support cyanobacterial growth under N limited condition, and insignificant input of macrophytes towards the organic matter
pool. Dredging in 1983, caused sub-aerial exposure of the suspended and surface sediments, and affected organic matter preservation
in the upper mid-section (12–14 cm) of the core. 相似文献
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