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1.
Calvin J. Heusser 《Quaternary Research》1982,17(1):71-92
Fossil pollen identified in the earliest sediments of three cushion bogs in the Cordillera Pelada (40°10′S, 73°30′W) dated 10,425 14C yr B.P. includes the subantarctic species Dacrydium fonckii, Tetroncium magellanicum, Astelia pumila, Gaimardia australis, Donatia fascicularis, and Drosera uniflora. All grow today in the Cordillera Pelada and range poleward to the southernmost Province of Magallanes; one species, Drapetes muscosa, included with the pollen of these plants in the earliest record, is no longer a constituent of the flora but is limited only to subantarctic Chile. Available evidence indicates that plants survived the last glaciation north of the glacial border with the course of postglacial migration southward following the wastage of the glacier complex. Holocene climatic and vegetational changes in the Cordillera Pelada are interpreted in the context of regional reconstructions which show maximum warmth about 9000 yr ago with a pronounced dry period lasting from 9000 to 6500 yr B.P. Maximum precipitation was later reached around 4000 yr ago but has decreased overall since then. The regional decline of the endemic gymnosperm Fitzroya cupressoides, which today is extensively destroyed in the Cordillera Pelada, follows this decrease in precipitation. These climatic data suggest a net south ward shift in the zone of westerly winds that bring rainfall to the region over the past 4000 yr. 相似文献
2.
Dreissena larval fluxes were studied in the lower stretch of the Seine River in 1996–1998. Fluxes reached 150×1012 ind d−1, representing a larval concentration of 5,000 ind l−1 in the Seine estuary. We showed that a sampling frequency with a 3-d interval allowed us to adequately estimate the annual production of larvae. The water residence time in the Seine River and estuary is sufficient for theDreissena larvae to complete their cycle and settlement. High abundance of the larvae in the plankton samples from the Seine River and its estuary showed the existence of a large community of benthic adults, known to be powerful filter-feeders. The progenitor population and the geographical extent of the adultDreissena were estimated from cohort analyses of the planktonic larvae. The maximum density ofDreissena was found in the highly channelized part of the estuary (up to 4,500 ind m−2). Estimated values were compared with concentration of mussels in the benthic traps and samples. Calculated filtration rates of benthic mussels were compared with those of larvae at different stages and with filtration of the zooplankton community. The impact of theDreissena was much higher than that of zooplankton; the filtration of the larvae exceeded that of adults during short periods of maximum larval emission. 相似文献
3.
Calvin J. Heusser 《Quaternary Research》1976,6(2):273-279
In south-central Chile, the Río Ignao nonglacial deposit with a minimal radiocarbon age of 56,000 +2000, ?1700 yr shows the following sequence of pollen assemblages, starting with the oldest: Gramineae (zone 1), Gramineae-Corynabutilon-Lomatia-Ovidia (zone 2), Nothofagus-Embothrium-Gramineae (zone 3A), Nothofagus-Gramineae-Tubuliflorae (zone 3B and D), and Nothofagus-Drimys-Myrtaceae (zone 3A). This sequence implies an initial dry and rather cold climate that later became wetter and somewhat warmer, reached a warm peak, and ultimately became colder and drier. At the warmest time, the Andean tree line is estimated to have been about 900 m lower and average January (summer) temperature about 3–4°C colder than at present. The Río Ignao deposit is believed to represent an early interstade of the last glaciation, known in southern Chile as the Llanquihue Glaciation. 相似文献
4.
A sequence of Triassic rocks is exposed near the town of Concepción, Chile. These clastic strata are interpreted as the deposits of rivers, lakes, playas, and alluvial fans. The deposits comprise conglomerates, arkosic sandstones, and sand-, silt- and mudstones. Four facies associations comprising eight sedimentary facies can be distinguished. Plant fossils from the sedimentary sequence of the Santa Juana Formation indicate a Carnian age. The flora includes ferns (Gleichenites, Cladophlebis, Dictyophyllum, Thaumatopteris, Asterotheca, Saportaea) and seed ferns (Kurtziana, Antevsia, Dicroidium), ginkgophytes (Sphenobaiera), cycads (Pseudoctenis), conifers (Heidiphyllum, Telemachus, Rissikia), and gymnosperms of uncertain affinities (Linguifolium, Gontriglossa). Two new species are presented: Pseudoctenis santajuanensis and Gontriglossa reinerae. 相似文献
5.
Distribution of copper, zinc, lead and cadmium concentrations in stream sediments from the Mapocho River in Santiago, Chile 总被引:17,自引:0,他引:17
The Mapocho river, which crosses downtown Santiago, is one of the most important rivers in contact with a population of about six million inhabitants. Anthropogenic activities, industrialization, farming activities, transport, urbanization, animal and human excretions, domestic wastes and copper mining have affected the river, contaminating it and its sediments with heavy metals. Concentration and distribution of Cu, Zn, Pb and Cd were studied with the purpose of determining their bioavailability and their relation with the characteristics of the sediments. Freshly deposited seasonal sediments were collected from 0–8 cm depths from 6 locations (S1 to S6) along the 30-km long channel length, in the four seasons of year on the following dates: May 2001 (D1, autumn); August 2001 (D2, winter); October 2001 (D3, spring) and January 2002 (D4, summer). The dried samples were sifted to obtain the < 63-μm sediment fraction, since it has been shown that large amounts of heavy metals are bound in the fine-grained fraction of the sediment. Cu and Zn were analyzed by atomic absorption spectrophotometry and Pb and Cd by square wave anodic stripping voltammetry. The highest concentrations of Cu (2850 μg g− 1) were found in the northern part of the river (S1, average D1–D4), near the mountains and a copper mine, and then decreased downstream to 209 μg g− 1 (S6). Total Zn showed an irregular variation, with higher values at S1 (1290 μg g− 1) and high values in some winter sampling (1384 μg g− 1 S4, S5–D2). Pb showed different trends, increasing from S1 to S6 (17 to 61 μg g− 1), with the highest values in the summer samples (83 μg g− 1, S4–S6, D4), and total Cd increased slightly from mean values of 0.2 and 0.5 μg g− 1. Partition into five fractions was made using Tessier's analytical sequential extraction technique; the residue was treated with aqua regia for recovery studies, although this step is not part of the Tessier procedure. The results show that Cu, Zn and Pb in the sediments were dependent on the sampling places along the river, and variation in two years was low (D1–D4). The highest values of total organic matter, carbonate and conductivity were found in S6, which has the smallest size particles, while at S1 the sediments were predominantly sand and contain larger amounts of silica. Cu associated with carbonate decreased gradually from 58% (1771 μg g− 1, S1) to 16% (32 μg g− 1, S6); Cu bonded to reducible fraction was almost constant (33% to 37%), and Cu associated with oxidizable fraction increased from 7% (S1) to 34% (S6), but copper content was lower (214 to 68 μg g− 1). Zn had a similar fractionation profile. However, Pb bound to oxidizable fraction did not show significant percent variation along the river (20% to 19%), but the amount bounded was 4 to 12 μg g− 1. The residual fraction increased from 24% to 41% (5 to 25 μg g− 1, S1 to S6). The distribution of Cd in the sediment was almost independent of the sampling stations and was bound to carbonate, reducible and residual fraction in similar proportion. Cu and Zn at S1 were mainly bound to carbonates and reducible phases with 91% and 73% (2779 and 965 μg g− 1, respectively), and with a change in the pH and/or the redox potential of the sediment–water system, these contaminants could easily enter the food chain. In S6 the amount of Cu and Zn in these phases was 50% and 53% (100 to 313 μg g− 1, respectively). 相似文献
6.
Edward R. Long M. Jawed Hameedi Gail M. Sloane Lorraine B. Read 《Estuaries and Coasts》2002,25(4):622-637
A large-scale survey of sediment quality in Biscayne Bay, Florida, was conducted in 1995–1996 to characterize the relative degree, geographic patterns, and spatial extent of degraded sediment quality. Chemical analyses and multiple toxicity tests were performed on 226 surficial sediment samples collected over an area of 484 km2 in greater Biscayne Bay, including saltwater reaches of several tributaries. Benthic samples were collected and analyzed at one-third of the locations. One or more chemical concentrations exceeded effects range median (ERM) values in 35 samples, representing an area of 5.4 km2 (1.1% of the survey area). Highly toxic conditions in amphipod survival tests occurred in 24 of the samples, representing 62 km2 (13% of the area). Highly significant results were more frequently observed in three sub-lethal tests: sea urchin fertilization (affecting 47% of the area), sea urchin embryological development (84% of the area), and microbial bioluminescence (51% of the area). The highest levels of chemical contamination (range in mean ERM quotients of 0.2 to 2.0, average 0.76) were observed in samples from the lower Miami River. The high degree of contamination in the river contrasted sharply with conditions in the bay, where chemical concentrations generally were much lower (range in mean ERM quotients of 0.005 to 0.21, average 0.04). Amphipod survival tests showed a very high degree of correspondence with a gradient in chemical contamination in the river and adjoining reaches of the bay. Correlation analyses, scatter plots, and principal component analyses indicated that both amphipod survival in the laboratory tests and the abundance and diversity of the benthos decreased sharply with increasing concentrations of mixtures of organic compounds and trace metals in the sediments. The triad of analyses provided a strong weight of evidence of pollution-induced degradation of sediment quality in the riverine locations. 相似文献
7.
Results of the microscopic study of sandy rocks from the Bugrovaya and lower Khvalynian sequences at the lower course of the Volga River are discussed. The terrigenous material of these deposits represents a mixture of clasts of two types: argillic (clayey) and nonargillic. The argillic component (clasts of chocolate clays) predominates in the clastic material and imparts the brownish red color to sands and sandstones of the Bugrovaya sequence. The nonargillic component includes fragments of crystals and rocks, the assemblage of which is similar to the clastic material of the underlying Khvalynian sand. The combination of clay clasts, which are not prone to long-range transport, with redeposited crystallo-and lithoclasts indicates the presence of different provenances. Their thin banding (lamination) related to differentiation of the clastic material by composition and grain size and the presence of glauconite grains testify to the aqueous origin of the Bugrovaya sequence. 相似文献
8.
Yves de Lafontaine 《Estuaries and Coasts》1990,13(1):43-50
The species composition and relative abundance of ichthyoplankton were investigated during summer 1986 at four stations along the salinity gradient in the Manicouagan River estuary, a tributary of the lower St. Lawrence estuary. Physical characteristics of water masses indicated the presence of a strong saline front (>10‰ per km) delineating the freshwater and marine section of the Manicouagan estuary. The estuary supports a depauperate ichthyoplankton community, including four species of pelagic fish eggs and eight species of fish larvae. Species richness increased with salinity. The ichthyoplankton fauna can be divided into two distinct groups: freshwater and marine. These two groups result initially from spawning preferences exhibited by the different species abundance of freshwater larvae was maximal at the head of the estuary and marine larvae were most abundant at the most saline station. The length frequency distribution suggests that marine larvae are not effectively retained within the estuary. The Manicouagan estuary cannot be considered as a major spawning site nor an important nursery zone for any fish found in this area. 相似文献
9.
<正> 辽南复州湾地区本溪组出露较好,以往在上部即三棱山灰岩及以上层位研究较详,而下部研究甚少,未见古生物方面的报道,其地质时代总是同上部一起看作相当莫斯科期,有人曾怀疑该段地层有属早石炭世的可能(辽宁区域地质志,1989)。本文对复州湾区本溪组下部地层测制了两条剖面,三棱山剖面在以往资料中常见涉及,此处不再赘述,而位于三棱山西北约400m、丁屯村东的水泥厂附近(新开大路两侧),下部层位发育、出露甚好(图1),自上而下详述如下: 相似文献
10.
Chu-fa Tsai M. Nazrul Islam Rezaul Karim MD K. U. M. Shahidur Rahman 《Estuaries and Coasts》1981,4(2):127-138
Spawning biology and spawn fishery of three valuable species of Indian major carps,Catla catla, Labeo rohita andCirrhinus mrigala, in the lower Halda River, Bangladesh, were studied in 1978. The major carps spawned only in the Sonairchar oxbow-bend from April to June on or near the dates of the full moon and the new moon. The tide was then at its highest level, and there was heavy flood water runoff from the hill region with sharp increases in water level, turbidity and current velocity, as well as decreases in water temperature, dissolved oxygen, and hydrogen ion concentration. These three heterogeneric species, as a result of parallelism or convergence in evolution, overlap in their environmental requirements for spawning. The nursery ground of the major carp fry spawned in the Halda River was found to be in the Bay of Bengal. The brood stock origin is suspected to be at the Shankha River, 40 miles south of the Karnafuli River. The spawn fishery in the Halda River was intensive but inefficient. Engineering works and water management schemes are threatening the spawning habitat. 相似文献
11.
Sediment dynamics and hydrodynamics in the lower course of a river highly regulated by dams: the Ebro River 总被引:1,自引:0,他引:1
The lowest part of the Ebro River is a microtidal salt-wedge estuary. Penetration of the salt-wedge is largely controlled by the fluvial discharge and the morphology of the river bed, although sea level variations caused by tides and atmospheric conditions can also play significant roles. The concentration and distribution of suspended particulate matter in this part of the river and the fluvial sediment discharge are strongly influenced by the dynamics of the salt-wedge. Damming of the river has caused sediment to be trapped in reservoirs and has regulated the fluvial discharge. Intrusion of the salt wedge has thus also been regulated. At present, sediment discharge is between 1 and 1·5 × 105 tons per year, which is less than 1% of the sediment that the Ebro River discharged into the sea before construction of the dams. This extreme reduction in sediment supply has allowed marine erosional processes to dominate in the delta. 相似文献
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15.
Dissolved oxygen concentration below 5 mg 1−1 has characterized the lower tidal portion of the San Joaquin River downstream of Stockton, California, during the summer
and fall for the past four decades. Intensive field research in 2000 and 2001 indicated low dissolved oxygen concentration
was restricted to the first 14 km of the river, which was deepened to 12 m for shipping, downstream of Stockton. The persistent
low dissolved oxygen concentration in the shipping channel was not caused by physical stratification that prevented aeration
from vertical mixing or respiration associated wigh high phytoplankton biomass. The low dissolved oxygen concentration was
primarily caused bynitrification that produced up to 81% of the total oxygen demand. Stepwise multiple regression analysis
isolated dissolved ammonia concentration and carbonaceous oxygen demand as the water quality variables most closely associated
with the variation in oxygen demand. Between these two sources, dissolved ammonia concentration accounted for 60% of the total
variation in oxygen demand compared with a maximum of 30% for carbonceous oxygen demand. The Stockton wastewater treatment
plant and nonpoint sources upstream were direct sources of dissolved ammonia in the channel. A large portion of the dissolved
ammonia in the channel was also produced by oxidation of the organic nitrogen load from upstream. The phytoplankton biomass
load from upstream primarily produced the carbonaceous oxygen demand. Mass balance models suggested the relative contribution
of the wastewater and nonpoint upstream load to the ammonia concentration in the shipping channel at various residence times
was dependent on the cumulative effect of ammonification, composition of the upstream load, and net downstream transport of
the daily load. 相似文献
16.
Steven L. Huntley Richard J. Wenning Steave H. Su Nancy L. Bonnevie Dennis J. Paustenbach 《Estuaries and Coasts》1995,18(2):351-361
In an attempt to characterize localized rates of sediment accretion, 10 sediment cores were collected from the lower reach of the Passaic River, a major tributary of Newark Bay, New Jersey. Sediments were assayed for 210Pb activity at predetermined depths and the rate of sediment accretion (cm yr?1) was estimated from the least squares regression of the log of unsupported activity versus depth. Sediment accretion rates, derived from 210Pb measurements (RPb) were used to predict the depth interval within the core containing sediments deposited around 1954; subsequent 137Cs analyses were focused on this depth interval. Sediment accretion rates derived from 137Cs measurements (RCs) were extrapolated from the depth of the 1954 horizon. Lead-210 derived sediment accretion rates in cores collected from a sediment bench extending along the inside bend on the southern shore of a meander in the river, ranged from 4.1 cm yr?1 to 10.2 cm yr?1 and averaged 6.8 cm yr?1. The RCs estimates for cores from this area ranged from 3.8 cm yr?1 to 8.9 cm yr?1 and averaged 6.6 cm yr?1. The RCs for cores collected in a more hydrologically dynamic reach of the river upstream of the sediment bench, were only 0.41 cm yr?1 and 0.66 cm yr?1. The results of this investigation indicate that this reach of the lower Passaic River is an area of high sediment accumulation, retaining much of the sediment load deposited from upstream and downstream sources. The rates of sediment accretion in the lower Passaic River are among the highest reported anywhere in the Newark Bay estuary. 相似文献
17.
N. Janardhana Raju Prahlad Ram Sangita Dey 《Journal of the Geological Society of India》2009,73(2):178-192
The lower Varuna River basin in Varanasi district situated in the central Ganga plain is a highly productive agricultural
area, and is also one of the fast growing urban areas in India. The agricultural and urbanization activities have a lot of
impact on the groundwater quality of the study area. The river basin is underlain by Quaternary alluvial sediments consisting
of clay, silt, sand and gravel of various grades. The hydrogeochemical study was undertaken by randomly collecting 75 groundwater
samples from dug wells and hand pumps covering the entire basin in order to understand the sources of dissolved ions, and
to assess the chemical quality of the groundwater through analysis of major ions. Based on the total dissolved solids, two
groundwater samples are considered unsuitable for drinking purpose, but all samples are useful for irrigation. Graphical treatment
of major ion chemistry by Piper diagram helps in identifying hydro-geochemical facies of groundwaters and the dominant hydrochemical
facies is Ca-Mg-HCO3 with appreciable percentage of the water having mixed facies. As per Wilcox’s diagram and US Salinity laboratory classification,
most of the groundwater samples are suitable for irrigation except two samples (No’s 30 and 68) which are unsuitable due to
the presence of high salinity and medium sodium hazard. Irrigation waters classified based on residual sodium carbonate, have
revealed that all groundwaters are in general safe for irrigation except one sample (No. 27), which needs treatment before
use. Permeability index indicates that the groundwater samples are suitable for irrigation purpose.
Although the general quality of groundwater of the lower Varuna River basin is suitable for irrigation purpose, fifty seven
percent of the samples are found having nitrate content more than permissible limit (>45 mg/l) which is not good for human
consumption. Application of N-Fertilizers on agricultural land as crop nutrients along the Varuna River course may be responsible
for nitrate pollution in the groundwater due to leaching by applied irrigation water. The other potential sources of high
nitrate concentration in extreme northern, southern and southwestern parts of study area are poor sewerage and drainage facilities,
leakage of human excreta from very old septic tanks, and sanitary landfills. The high fluoride contamination (>1.5 mg/l) in
some of the samples may be due to the dissolution of micaceous content in the alluvium. Nitrate and fluoride contamination
of groundwater is a serious problem for its domestic use. Hence an immediate protective measure must be put into action in
the study area. 相似文献
18.
M. J. Dagg T. S. Bianchi G. A. Breed W. -J. Cai S. Duan H. Liu B. A. McKee R. T. Powell C. M. Stewart 《Estuaries and Coasts》2005,28(5):664-674
During June 2003, a period of mid level discharge (17,400 m−3 s−1), a parcel of water in the lower Mississippi River was sampled every 2 h during its 4-d transit from river km 362 near Baton
Rouge to km 0 at Head of Passes, Louisiana, United States. Properties measured at the surface during each of the 48 stations
were temperature, salinity, dissolved organic carbon (DOC), total dissolved nitrogen, dissolved macronutrients (NO3+NO2, PO4, Si(OH)4), chlorophylla (chla; three size fractions: < 5 μm, 5–20 μm, and > 20 μm) pigment composition by HPLC, total suspended matter (TSM), particulate
organic carbon (POC), and particulate nitrogen (PN). Air-water CO2 flux was calculated from surface water dissolved inorganic carbon and pH. During the 4 d transit, large particles appeared
to be settling out of the surface water. Concentrations of chla containing particles > 20 μm declined 37%, TSM declined 43%, POC declined 42% and PN declined 57%. Concentrations of the
smaller chla containing particles did not change suggesting only large particulate materials were settling. There was no measurable loss
of dissolved NO3, PO4, or Si(OH)4, consistent with the observation that chla did not increase during the 4-d transit. DOC declined slightly (3%). These data indicate there was little autotrophic or
heterotrophic activity in the lower Mississippi River at this time, but the system was slightly net heterotrophic. 相似文献
19.
Gennady G. Boeskorov Peter A. Lazarev Andrei V. Sher Sergei P. Davydov Nadezhda T. Bakulina Marina V. Shchelchkova Jonas Binladen Eske Willerslev Bernard Buigues Alexey N. Tikhonov 《Quaternary Science Reviews》2011,30(17-18):2262-2272
A nearly complete frozen mummy of a woolly rhinoceros (Coelodonta antiquitatis Blum., 1799) was discovered in a gold mine on the lower reaches of the Kolyma River, north–eastern Siberia. This is the first find of the whole body of woolly rhino in permafrost. A large part of the mummified body was preserved, including the left part of the body, covered by skin, including skin of the head and ear, fore and hind legs. The skull with 2 horns and the lower jaw were also preserved. Most of the internal organs were lost, except the intestines, stomach, and their contents. A rib fragment from this individual was dated by AMS-radiocarbon method to 39,140 ± 390 years BP (OxA-18755). Spore and pollen analyses of the stomach contents indicate that grasses and sagebrushes formed the main part of the diet of C. antiquitatis in this region of Arctic Siberia. 相似文献
20.
Jennifer L. Klug 《Estuaries and Coasts》2006,29(5):831-840
One of the most serious threats to freshwater and marine ecosystems is high rates of anthropogenic nutrient loading, particularly
nitrogen (N) and phophorus (P). One of the major freshwater sources of nutrients to Long Island Sound (LIS) is the Housatonic
River (HR). Current management plans that call for reducing N inputs without reducing P inputs may change the N: P ratio in
the water column and the pattern of algal nutrient limitation and species composition in the tidal portion of the river. To
assess the current pattern of algal nutrient limitation in the HR estuary, nutrient bioassays were conducted in spring, summer,
and fall at 5 sites throughout the tidal portion and adjacent LIS. Diatoms were a dominant taxon at all sites throughout the
sampling period. Other seasonally important taxa include cyanobacteria, cryptophytes, and euglenoids. Phytoplankton in LIS
were always strongly N limited and were co-limited by P in spring. During low flow (summer), phytoplankton in the lower HR
estuary were N limited. Phytoplankton in the middle reaches showed no evidence of N or P limitation and were likely limited
by other factors. In spring, phytoplankton in the upper HR estuary were P limited. Periods of N or P limitation were better
correlated with periods of lower concentrations of nitrate or phosphate than with differences in N: P ratio. These results
suggest that decreases in N concentration could increase the prevalence of N limitation throughout the estuary that in turn
may reduce phytoplankton biomass and alter species composition of the phytoplankton. 相似文献