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1.
The rhizocephalanLoxothylacus panopaei parasitizes the estuarine crabRhithropanopeus harrisii. Parasitized crabs are abundant during summers when salinities increase to around 15‰ in the crab–s habitat and scarce when salinities are lower. The two hypotheses that were proposed to explain this pattern were (1) that the parasite interferes with crab osmoregulation causing the host to die in low salinity water and (2) that salinity tolerance of the parasite larvae controls the incidence of parasitism. The first hypothesis was shown to be incorrect because (1) osmoregulation of infected crabs was, not altered by the parasite and (2) crab mortality did not increase in low salinity water down to 1‰. Unparasitized and parasitized crabs and the parasite itself were hypersomotic at low salinities (below 27‰ for the crabs). The parasite became slightly hyperosmotic at high salinities while the crabs were slightly hypoosmotic. The second hypothesis appears correct, becauseL. panopaei larvae survived poorly in salinities below 10‰ but well in salinities from 10 to 15‰. ThusR. harrisii, have a reproductive refuge at salinities below 10‰, because parasite larvae cannot survive and infect the mud crab at these low salinities.  相似文献   

2.
We reared larval zebra mussels,Dreissena polymorpha, and quagga mussels,D. bugensis, through and beyond metamorphosis (settlement) at salinities of 0–8‰. Juvenile zebra mussels gradually acclimated to 8‰ and 10‰ have been reared at these salinities for over 8 mo. Tolerance to both higher temperatures and higher salinities increases with larval age in both species (though zebra mussel embryos and larvae have a greater degree of salinity tolerance than quagga mussel embryos and larvae). Thus, only 6% of 3-day-old zebra mussel veligers survived after exposure to 4‰ for 8 additional days, whereas there was 22% survival of veligers placed in 4‰ at day 13 and grown to settlement 11 d later. Zebra mussel pediveligers, acclimated to increasing salinity in 2‰ increments beginning at day 23, continued to survive and grow in 8‰ after 5-mo exposure, though the growth rates of these juveniles were significantly less than those of juveniles reared in lower salinities. Quagga mussels did not metamorphose and settle as quickly as zebra mussel pediveligers. No quagga mussel pediveligers had settled before exposure to artificial fresh water (AFW), 2‰ 4‰, 6‰, and 8‰ on day 30. Percent settlement of these quagga mussel juveniles (based on 100% survival at the start of experiments on day 30) was 90% in AFW, 67% at 2‰, 69% at 4‰, 46% at 6‰, and 0.1% at 8‰.  相似文献   

3.
The dominant plant in Humboldt Bay salt marshes in Spartina densiflora, a species of cordgrass apparently introduced from South America. At several salt marshes and restoration sites around Humboldt Bay, distribution of this plant has increased significantly. We investigated the relative contributions of vegetative tiller production and seed germination to the establishment and expansion of S. densiflora. Lateral spread of plants surrounded by competitors were compared to areas without competing plant species. Plants growing in areas without competitors had significantly higher rates of vegetative expansion (p<0.0001). Viable seed production, germination rates, seedling survivorship, and growth of adult plants were measured in six salinity treatments. Approximately 1,977±80 viable seeds are produced per plant (0.25–0.5 m2). The number of germinating seeds was inversely related to increases in salinity. Salinity treatments between 19‰ and 35‰ produced significantly lower germination rates than salinities of 0–18‰ (p<0.0001). Seedling survivorship was 50% at ≤4‰ and 8–14% at ≥11‰. Lateral expansion of adult, greenhouse-grown plants occurred in all salinity treatments, with modest decreases in the highest salinity treatments (p<0.05). Our findings indicate that S. densiflora expands primarily by vegetative expansion, and lateral tillers are produced by throughout the year. Spartina densiflora produces prolific amounts of seed, but recruitment in mature salt marshes may be limited by competitors and higher salinities. At restoration sites, planting of native species such as Salicornia virginica, Distichlis spicata, or Jaumea carnosa may prevent monospecific stands of S. densiflora from developing.  相似文献   

4.
The brown shrimp,Farfantepenaeus aztecus, is the major component of the Gulf of Mexico shrimp fishery, and it is critical that we understand its environmental requirements. Brown shrimp spend a large portion of their post-larval (PL) and juvenile life within estuaries distributed along salinity gradients and yet our understanding of the salinity tolerance of various age groups is limited. A series of 48-hr bioassays were conducted in which various ages ofF. aztecus (PL-10, PL-13, PL-15, PL-17, PL-20, and PL-23) were acclimated from a salinity of 26‰ to 1‰, 2‰, 4‰, 8‰, 12‰, and 26‰ in order to determine their tolerance to these salinities. Finally, PL-80.F. aztecus were transferred directly from 25‰ to 2‰, 4‰, and 8‰ waters to study the effects of rapid salinity reductions on juvenile survival. Survival of 10-and 13-day-old PLs was significantly, different from the control (26‰) for all salinities tested. Survival of PL-15 shrimp and older was significantly lower than survival of the controls at 1‰ and 2‰ but similar to the control at all other salinities tested. A 4-wk growth trial was conducted with juvenile shrimp at 2‰, 4‰, 8‰, and 12‰. There was no significant difference in survival among treatments, although shrimp maintained at 8‰ and 12‰ grew significantlymore than shrimp maintained at 2‰ and 4‰. There was no growth difference between shrimp at the two low salinities or between shrimp at the two high salinities. Survival of juveniles transferred directly from 25‰ to various salinities were 100% at 25‰, 94.2% at 8‰, 67.3% at 4‰, and 63.5% at 2‰. These results suggest that PL-13 and younger brown shrimp would have a better chance of survival by delaying entry into estuaries susceptible to rapid salinity declines. The brown shrimp juveniles would, be more densely distributed in areas with salinities greater than 4‰ than in salinities less than 4‰. Although food availability, and bottom type also affect shrimp distribution survival and growth, salinity may also greatly affect the shrimp and its fishery.  相似文献   

5.
The rhizocephalan barnacleLoxothylacus panopaei, which parasitizes the mud crabRhithropanopeus harrisii, releases its larvae as nauplii. The nauplii develop through four stages to the cypris stage; both larval forms are lecithotrophs. Parasitized crabs were acclimated in 10‰, 15‰, and 20‰ water during August and the development of releasedL. panopaei larvae was monitored in a range of salinities. After 48–60 h, the nauplii and cyprids in each experimental salinity were counted and the numbers used to calculate a developmental index. The range of salinities in which successful development to cyprids occurred (developmental index >70%) could be shifted as a consequence of the acclimating salinity.L. panopaei larvae can develop successfully over a 10–30‰ salinity range, indicating that settlement onto host crabs and virgin externae is likely to take place in nature within this range.  相似文献   

6.
Species of submerged aquatic vegetation (SAV) are frequently used in the management of estuarine systems to set restoration goals, nutrient load reduction goals, and water quality targets. As human need for water increases, the amount of freshwater required by estuaries has become an increasingly important issue. While the, science of establishing the freshwater needs of estuaries is not well developed, recent attempts have emphasized the freshwater requirements of fisheries. We evaluate the hypothesis that SAV can be used to establish freshwater inflow needs. Salinity tolerance data from laboratory and field studies of SAV in the Caloosahatchee estuary, Florida, are used to estimate a minimum flow required to maintain the salt-tolerant freshwater species,Vallisneria americana, at the head of the estuary and a maximum flow required to prevent mortality, of the marine speciesHalodule wrightii at its mouth. ForV. americana, laboratory experiments showed that little or no growth occurred between 10‰ and 15‰ In the field, lower shoot densities (<400 shoots m?2) were associated with salinities greater than 10‰. Results forH. wrightii were more variable than forV. americana. Laboratory experiments indicated that mortality could occur at salinities <6‰, with little growth occurring between 6‰ and 12‰. Field data indicated that higher blade densities (>600 blades m?2) tend to occur at salinities greater than 12‰ Relationships between salinity in the estuary and discharge from the Caloosahatchee River indicated that flows>8.5 m3 s?1 would produce tolerable salinity (<10‰) forV. americana and flows<89 m3 s?1 would avoid lethal salinities (<6‰) forH. wrightii.  相似文献   

7.
Environmental characteristics were measured and recorded in the Skagit Marsh, a brackish intertidal marsh on Puget Sound, Washington. Four transects were placed perpendicular to a known gradient of increasing salinity which began with fresh water at the bank of one of the outlets of the Skagit River and reached a surface water salinity of 22‰ at a point alongshore 5 km north of the outlet. The environmental characteristics which were measured varied along gradients (soil texture, organic carbon in fines, soil column temperature, free soil water salinity) or had a patchy distribution (soil redox potential, soil macro-organic matter). Growth and production vary across the marsh. The maximum aboveground standing crop (1,742 g m?2 dry weight) was measured at a site with 0–4‰ free soil water salinity, dominated by the sedgeCarex lyngbyei. In more saline areas (8–12‰), the bulrushScirpus americanus was dominant and standing crop values dropped to a third of the maximum. Species performance varied in a complex manner as did the environment.C. lyngbyei had diminished growth and decreased standing crop in areas where salinity was higher.S. americanus was equally productive in low elevation, high salinity sites and in high elevation, low salinity sites. An increase in shoot density for dominant species occurred in saline areas as individual shoot weights and leaf areas decreased. Because species responded differently, environmental variation was magnified in the population and community responses of the marsh vegetation.  相似文献   

8.
Despite·a paucity of available prey, little feeding competition occurred between juvenile American shad,Alosa sapidissima, juvenile blueback herring,Alosa aestivalis, and pumpkinseed,Lepomis gibbosus, in the Connecticut River below Holyoke Dam. Pumpkinseed differed from clupeids in pronounced selection for chironomid larvae, and bottom feeding. Feeding conflicts between the twoAlosa species were reduced by: 1) more opportunistic feeding by shad; 2) differential selection for cladoceran prey; 3) higher utilization of copepods by herring.  相似文献   

9.
A greenhouse experiment was conducted to examine the effects of salinity, nitrogen, and aeration on the growth of Spartina alterniflora Loisel. The experiment was conducted in a factorial arrangement of treatments with salt marsh substrate at three salinity levels (15, 30, 45‰), at two nitrogen levels (0 and 168 kg/ha) and at two aeration levels (zero and oxygen saturation). The maximum biomass was found in the low salinity, nitrogen enhanced, aerated treatment which had 11 times more biomass than the highest (45‰) salinity, nitrogen poor, unaerated treatment. the average effect of nitrogen over the three salinity levels was a 2.01, 1.47, 1.25, and 1.52 times increase in aerial biomass, density, height, and belowground biomass of the plants, respectively. The main effect of aeration was a 2.49, 2.01, 1.57, and 1.85 times increase in the same variables. The combination effect of aeration and nitrogen additions enhanced biomass by 453%. An increase in salinity from 15‰ to 45‰ decreased biomass, density, height and belowground biomass of S. alterniflora by 66, 53, 38, and 61%, respectively. The effect of salinity was more pronounced between 30 and 45‰ than it was between 15 and 30‰. N, P, K, Ca, Mg, Na, Fe, Mn, Zn, Cu, and S concentrations in the aerial living biomass were also examined. There was no evidence to suggest that elemental concentrations (on a per gram basis) were consistently correlated with increased or decreased growth. In relation to salinity, correlations between growth and elemental concentrations were negative while for nitrogen enhanced and/or aerated systems, the correlations were positive.  相似文献   

10.
A granite‐related scheelite deposit has been recently discovered in the Wuyi metallogenic belt of southeast China. The veinlet–disseminated scheelite occurs mainly in the inner and outer contact zones of the porphyritic biotite granite, spatially associated with potassic feldspathization and silicification. Re–Os dating of molybdenite intergrowths with scheelite yield a well‐constrained isochron age of 170.4 ± 1.2 Ma, coeval with the LA–MC–ICP–MS concordant zircon age of porphyritic biotite granite (167.6 ± 2.2 Ma), indicating that the Lunwei W deposit was formed in the Middle Jurassic (~170 Ma). We identify three stages of ore formation (from early to late): (I) the quartz–K‐feldspar–scheelite stage; (II) the quartz–polymetallic sulfide stage; and (III) the quartz–carbonate stage. Based on petrographic observations and microthermometric criteria, the fluid inclusions in the scheelite and quartz are determined to be mainly aqueous two‐phase (liquid‐rich and gas‐rich) fluid inclusions, with minor gas‐pure and CO2‐bearing fluid inclusions. Ore‐forming fluids in the Lunwei W deposit show a successive decrease in temperature and salinity from Stage I to Stage III. The homogenization temperature decreases from an average of 299 °C in Stage I, through 251 °C in Stage II, to 212 °C in Stage III, with a corresponding change in salinity from an average of 5.8 wt.%, through 5.2 wt.%, to 3.4 wt.%. The ore‐forming fluids have intermediate to low temperatures and low salinities, belonging to the H2O–NaCl ± CO2 system. The δ18OH2O values vary from 1.8‰ to 3.3‰, and the δDV‐SMOW values vary from –66‰ to –76‰, suggesting that the ore‐forming fluid was primarily of magmatic water mixed with various amounts of meteoric water. Sulfur isotope compositions of sulfides (δ34S ranging from –1.1‰ to +2.4‰) and Re contents in molybdenite (1.45–19.25 µg/g, mean of 8.97 µg/g) indicate that the ore‐forming materials originated mainly in the crust. The primary mechanism for mineral deposition in the Lunwei W deposit was a decrease in temperature and the mixing of magmatic and meteoric water. The Lunwei deposit can be classified as a porphyry‐type scheelite deposit and is a product of widespread tungsten mineralization in South China. We summarize the geological characteristics of typical W deposits (the Xingluokeng, Shangfang, and Lunwei deposits) in the Wuyi metallogenic belt and suggest that porphyry and skarn scheelite deposits should be considered the principal exploration targets in this area.  相似文献   

11.
Zoeae of three species of temperate zone fiddler crabs, Uca pugnax, U. minax, and U. pugilator, were reared in the laboratory. The zoeae of each species were placed individually in artificial salinity gradients and observed for specific salinity preferences. Each species of zoeae displayed a salinity preference that reflected the salinity patterns of the adult crabs of the same species. Zoeae of U. pugnax and U. pugilator, like the adult crabs, displayed a preference for higher salinities (i.e., 20.6‰±3.5 and 21.5‰±3.0, respectively). Zoeae of U. minax, like the adult crabs, displayed a preference for lower salinities (i.e., 9.8‰±2.9).  相似文献   

12.
Monthly growth of the fouling community at eight test panel sites in the Loxahatchee River Estuary was related to salinity and temperature. Growth was lowest in January 1981 (averaging 23 g per m2, dry weight), and increased during spring and early summer with increasing water temperature. Maximum growth occurred during early or midsummer at upstream locations, before river or canal discharge substantially reduced salinity, and in late summer at downstream locations. Growth was greatest at salinities slightly less than that of seawater and decreased at salinities less than about 10‰. Growth was suppressed throughout the estuary in August 1981, probably because of the sudden decrease in temperature and salinity, and perhaps the increase in physical scouring, caused by runoff from Tropical Storm Dennis. Large loads of nutrients transported to the estuary from storm runoff, however, may have subsequently stimulated growth, which increased in September 1981 to the maximum for the year (averaging 683 g per m2, dry weight).  相似文献   

13.
Large, recreationally or commercially important populations of Atlantic sturgeon (Acipenser oxyrinchus), American shad (Alosa sapidissima), and striped bass (Morone saxatilis) occur in the Hudson River. Members of the Hudson River populations of these fishes also occur over a broad range along the Atlantic coast where they mix with conspecifics from other anadromous populations. For management purposes, it is imperative to be able to discriminate among individual stocks so that weak stocks may be protected and harvest may be allocated equitably. Because of their sensitivity and resistance to environmentally-induced temporal variation, molecular approaches have been increasingly employed in stock identification studies. However, post-Pleistocene recolonization of the Hudson River must have occurred less than 10,000 years ago—a relatively brief period for genetic divergence among populations. We tested whether various measures of DNA variation between Hudson River populations and adjacent populations of Atlantic sturgeon, American shad, and striped bass were sufficient to discriminate among their conspecific populations. American shad populations surveyed for mtDNA variation were highly diverse genotypically, but genotypic frequencies among the populations of the Connecticut, Hudson, and Delaware rivers were statistically homogenous (p>0.05). In contrast, Atlantic sturgeon (surveyed for mtDNA variation) and striped bass (surveyed for mtDNA and nuclear DNA variation) populations of the Hudson River were not genotypically diverse, but they were differentiated from northern and southern populations. Our results suggest higher gene flow (and lesser homing fidelity) among American shad populations in comparison with the two other species.  相似文献   

14.
Crabs (Grapsidae,Sesarma) are the dominant macrofaunal group of mangrove forest soils in northern Australia. Little is known about the ecology of these crabs or the factors that influence their distribution in mangrove forests. Pitfall traps were used to sample grapsid crabs in the Murray River estuary in north Queensland. Sampling was conducted at five sites along a salinity gradient from <1‰ at upstream sites to >35‰ at the river mouth. At each site, trapping was done in both low and high intertidal forests. We characterized the sediments at each site by measuring percent sand, silt, clay and organic matter, Eh, pH, and soil pore-water salinity. Four species of grapsids dominated the crab fauna along the Murray River (Sesarma semperi-longicristatum, S. messa, S. brevicristatum, andS. brevipes). Distinct zonation patterns were found along the salinity gradient and between high and low intertidal forests.S. messa was dominant in high intertidal, downstream forests, high and low intertidal forests in the middle to downstream portion of the river, and in low intertidal forests in the central reach of the river.S. brevipes was dominant in both low and high intertidal zone forests at low salinity upstream sites.S. brevicristatum was most abundant in the central reaches of the river and only in the high intertidal zone.S. semperi-longicristatum was found only in the low intertidal zone, downstream forest. Subsequently, tests of salinity tolerances of these crabs were carried out in the laboratory. These indicated very wide tolerances over salinities from completely fresh to hypersaline (60‰). The osmoregulatory abilities of the crabs were also found to vary. However, neither their salinity tolerance nor osmoregulatory ability adequately explain the zonation patterns were measured in the field. For example,S. brevicristatum had the most restricted distribution, but it had the second broadest salinity tolerance and osmoregulatory ability. Sediment characteristics explained a significant amount of the variation in abundance for two of the crab species. Pore-water salinity provided no explanatory power for any of the species. Individual species abundances are probably influenced by additional factors such as interspecific competition and predation.  相似文献   

15.
Variable recruitments of striped bass were hypothesized to be caused by factors influencing growth and survival of larvae. Eggs and larvae were collected in the Potomac River from 1987 to 1989 and in the Upper Chesapeake Bay in 1988 and 1989 to estimate abundances, larval growth and survival rates, and environmental variability. Larval batch dates, ages, and growth and mortality rates were estimated from analysis of otolith daily increments. A retrospective analysis of Potomae River ichthyoplankton data from 1974–1977 and 1980–1982 provided additional estimates of larval abundances and vital rates for comparative purposes. Significant correlations betweens vital rates (growth and mortality) and abundances of striped bass larvae, and the Maryland juvenile recruitment index indicated that recruitment level may be fixed during the larval stage. The ratio of mean daily growth and mortality rates (G:Z) of larvae in the Potomac River for 1987–1989 was highest in 1987 when the juvenile index was relatively high, and was lower in 1988 and 1989 when juvenile indices were low. In the Upper Bay, mean larval growth rate, survival rate, and the G:Z ratio were highest in 1989 when the juvenile index also was high. In both tributaries, abundances of late-stage larvae (8 mm SL) were correlated with juvenile-stage recruitment indices. The retrospective analysis provided additional evidence that Potomac River larval abundances and G:Z ratios were positively correlated with juvenile recruitment indices in the 1974–1977 and 1980–1982 periods. Conditions favoring striped bass larval abundance and potential recruitment differed between the Potomac River and the Upper Bay. In the Potomac, late-stage larval abundances coincided with late-season water temperatures that were relatively warm, low river discharges and high, late-season densities of zooplankton prey, which favored larval growth. In the Upper Bay, the high abundance of late-stage larvae in 1989 relative to 1988 was attributed to a higher egg production that was coincident with high zooplankton abundances.  相似文献   

16.
The relationships between egg production (spawning behavior), larval growth and survival, and environmental conditions that larvae encounter were investigated in the Patuxent River tributary of Chesapeake Bay in 1991. Striped, bass (Morone saxatilis) eggs and larvae occurred predominantly above the salt front where conductivity was ≤800 μmhos cm?1. There were three prominent peaks in egg production, each coinciding with increasing temperatures. Estimated growth rates of 6-d, otolith-aged cohorts, which ranged from 0.15 mm d?1 to 0.22 mm d?1 (mean=0.17 mm d?1), were not demonstrated to differ significantly from each other. Observed zooplankton densities and temperature did not significantly affect growth rates. Stage-specific cumulative mortalities of combined cohorts were calculated for eggs (Zstage=0.20=18.1%), yolk-sac larvae (Zstage=5.80=99.7%), and first-feeding larvae (Zstage=2.95=94.8%). The very high mortality of yolk-sac larvae suggests that dynamic during this stage may have had a major impact on subsquent recruitment. Cohort-specific mortality rates of larvae were variable, ranging from Z=0.045 d?1 to 0.719 d?1, and were strongly temperature-dependent. Cohorts that experiented average temperature <15°C or >20°C during the first 25 d after hatching had significantly higher mortality rates than those which experienced intermediate temperatures. Estimated hatch-date frequencies of larvae ≥8 mm SL indicated goo, very good, and very low potential recruitments for cohorst spawned during early-season (April 2–11), mid-season (April 12–24) and late-season (April 25–May 5), respectively. Because seasonal temperature trends and fluctuations are unpredictable, striped bass females cannot select a spawning time that guarantees their offspring will be exposed to optimum temperatures. Consequently, selection may have occured for spawning over a broad range of temperatures and dates, a behavior insuring that some larval cohorts will encounter favorable temperatures.  相似文献   

17.
From 1977 to 1980, samples of barnacles were collected (as opportunities arose) from 61 subtidal locations (mostly oyster beds) around Chesapeake Bay, Maryland. Three species were identified from the area.Balanus improvisus dominated, comprising 83% of the 8,231 barnacles identified, and was collected at all locations but one. It occurred over a collection salinity range of 0.8‰ to 17.9‰.Balanus subalbidus (14% of the barnacles identified) was collected over the same salinity range, but mainly in lower salinity waters.Balanus eburneus was scarce (2% of the barnacles identified) and was collected at higher salinities (8.5‰ to 17.1‰).  相似文献   

18.
目前关于恰功矽卡岩型铁矿床的流体演化过程及成矿机制,尤其是铁-铅矿体的成矿作用尚缺研究.对不同阶段的主要矿物进行包裹体均一温度-盐度、激光拉曼光谱分析以及H-O同位素测试.进矽卡岩阶段包裹体均一温度为400~550℃;盐度为15.5%~20.9% NaCleqv,其中S型盐度高达56.5% NaCleqv;气液相成分均为H2O.退化蚀变阶段包裹体均一温度为350~420℃;盐度集中于14.1%~16.6% NaCleqv,少量为2%~8% NaCleqv,而S型包裹体盐度亦高达55.8% NaCleqv;气液相成分均为H2O,液相富含HCO3-和CO32-.石英-方铅矿阶段包裹体均一温度范围为238~343℃,对应盐度为3.1~13.9% NaCleqv,其中含CO2三相包裹体完全均一温度集中在290~310℃,盐度为1.6%~11.2% NaCleqv.石英-方解石阶段包裹体均一温度与盐度分别为242~360℃和1.7%~11.8% NaCleqv,气液相成分均为H2O.H-O同位素显示:进矽卡岩阶段δDH2O为-106.4‰~-113.2‰,δ18OH2O为6.2‰~8.0‰;退化蚀变阶段δDH2O为-84.8‰~-130.1‰,δ18OH2O为2.7‰~5.5‰,退化蚀变阶段δ18OH2O值相对进矽卡岩阶段低;石英-方铅矿阶段δDH2O为-95.3‰~-103.8‰,δ18OH2O为-1.6‰~-0.7‰;石英-方解石阶段δDH2O为-67.4‰~-101.0‰,δ18OH2O为-0.8‰~0.6‰.结果表明流体整体具有从高温、中-高盐度逐渐向低温、低盐度演化的特征,矽卡岩期成矿流体来源于岩浆出溶;矽卡岩期流体的不混溶作用并与围岩发生反应是磁铁矿沉淀的重要机制,石英-方铅矿阶段流体温压下降是方铅矿沉淀的根本原因.   相似文献   

19.
The Tonglushan Cu–Fe deposit (1.12 Mt at 1.61% Cu, 5.68 Mt at 41% Fe) is located in the westernmost district of the Middle–Lower Yangtze River metallogenic belt. As a typical polymetal skarn metallogenic region, it consists of 13 skarn orebodies, mainly hosted in the contact zone between the Tonglushan quartz-diorite pluton (140 Ma) and Lower Triassic marine carbonate rocks of the Daye Formation. Four stages of mineralization and alterations can be identified: i.e. prograde skarn formation, retrograde hydrothermal alteration, quartz-sulphide followed by carbonate vein formation. Electron microprobe analysis (EMPA) indicates garnets vary from grossular (Ad20.2–41.6Gr49.7–74.1) to pure andradite (Ad47.4–70.7Gr23.9–45.9) in composition, and pyroxenes are represented by diopsides. Fluid inclusions identify three major types of fluids involved during formation of the deposit within the H2O–NaCl system, i.e. liquid-rich inclusions (Type I), halite-bearing inclusions (Type II), and vapour-rich inclusions (Type III). Measurements of fluid inclusions reveal that the prograde skarn minerals formed at high temperatures (>550°C) in equilibrium with high-saline fluids (>66.57 wt.% NaCl equivalent). Oxygen and hydrogen stable isotopes of fluid inclusions from garnets and pyroxenes indicate that ore-formation fluids are mainly of magmatic-hydrothermal origin (δ18O = 6.68‰ to 9.67‰, δD = –67‰ to –92‰), whereas some meteoric water was incorporated into fluids of the retrograde alteration stage judging from compositions of epidote (δ18O = 2.26‰ to 3.74‰, δD= –31‰ to –73‰). Continuing depressurization and cooling to 405–567°C may have resulted in both a decrease in salinity (to 48.43–55.36 wt.% NaCl equivalent) and the deposition of abundant magnetite. During the quartz-sulphide stage, boiling produced sulphide assemblage precipitated from primary magmatic-hydrothermal fluids (δ18O = 4.98‰, δD = –66‰, δ34S values of sulphides: 0.71–3.8‰) with an extensive range of salinities (4.96–50.75 wt.% NaCl equivalent), temperatures (240–350°C), and pressures (11.6–22.2 MPa). Carbonate veins formed at relatively low temperatures (174–284°C) from fluids of low salinity (1.57–4.03 wt.% NaCl equivalent), possibly reflecting the mixing of early magmatic fluids with abundant meteoric water. Boiling and fluid mixing played important roles for Cu precipitation in the Tonglushan deposit.  相似文献   

20.
Our objective was to quantify the contribution of autochthonous, locally-produced phytoplankton, and allochthonous, terrestrial-derived organic matter (OM) to the production of young-of-year (YOY) American shad(Alosa sapidissima) using stable isotopes. We measured the carbon and nitrogen stable isotope composition of YOY American shad in the tidal fresh water of the Mattaponi River, a tributary in the York River estuary, during three consecutive years. The isotopic ratios of larval American shad varied among years, indicating a switch from reliance on a primarily autochthonous food web pathway during low and moderate discharge years (50–90%; 2002, 2004) to a primarily allochthonous pathway during a high discharge year (< 35% phytoplankton; 2003). Reliance on phytoplankton by larval fish declined exponentially with increasing Mattaponi River discharge. In 2003, juvenile production was also supported by allochthonous OM, though autochthonous phytoplankton accounted for an increasingly large fraction during June through August, up to 40–55%. We also found a long-term, positive relationship between the duration of above average flow during April through June in the Mattaponi River and a corresponding index of juvenile American shad abundance. The largest American shad cohort recorded since 1967 was observed in 2003, a high discharge year. The production of this cohort was largely supported by allochthonous OM. The results suggest an important link between river discharge, energy flow, and recruitment, wherein high discharge favors reliance on terrestrial carbon by YOY American shad, owing to changes in zooplankton diet, macroinvertebrate abundance, or both, and also favors high American shad abundance.  相似文献   

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