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1.
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   

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.
Zebra mussels (Dreissena polymorpha) graze on phytoplankton, and decreased phytoplankton concentrations have been associated with zebra mussels in lakes. It is not known, however, how the zebra mussel will affect phytoplankton in turbid systems such as rivers and the freshwater portions of estuaries. To determine whether zebra mussels can effectively remove phytoplankton in these turbid systems, and to determine what components of the suspended material are removed and at what rates, we conducted a series of grazing and size-selection experiments using ambient Hudson River water and its natural phytoplankton community. Zebra mussels removed both phytoplankton and total suspended weight (TSW) at comparable rates (～115 ml mussel?1 h?1). Variation in filtration rates were not correlated with TSW or chlorophylla (chla) concentration, and did not appear to depend on relative proportions of either component. Mussels removed particles with approximately equal efficiency in all particle size classes measured (0.4 μm to >40 μm). Zebra mussels appear to remove Hudson River phytoplankton effectively in the presence of suspended sediment and do so at rapid rates. Based on our measurements and unpublished estimates of the size of the population, zebra mussels filter a volume equivalent to the entire volume of the tidal freshwater portion of the Hudson River about every 2 d.  相似文献   

4.
Biogeochemical processes were investigated in alpine river—Kamni?ka Bistrica River (North Slovenia), which represents an ideal natural laboratory for studying anthropogenic impacts in catchments with high weathering capacity. The Kamni?ka Bistrica River water chemistry is dominated by HCO3 ?, Ca2+ and Mg2+, and Ca2+/Mg2+ molar ratios indicate that calcite weathering is the major source of solutes to the river system. The Kamni?ka Bistrica River and its tributaries are oversaturated with respect to calcite and dolomite. pCO2 concentrations were on average up to 25 times over atmospheric values. δ13CDIC values ranged from ?12.7 to ?2.7 ‰, controlled by biogeochemical processes in the catchment and within the stream; carbonate dissolution is the most important biogeochemical process affecting carbon isotopes in the upstream portions of the catchment, while carbonate dissolution and organic matter degradation control carbon isotope signatures downstream. Contributions of DIC from various biogeochemical processes were determined using steady state equations for different sampling seasons at the mouth of the Kamni?ka Bistrica River; results indicate that: (1) 1.9–2.2 % of DIC came from exchange with atmospheric CO2, (2) 0–27.5 % of DIC came from degradation of organic matter, (3) 25.4–41.5 % of DIC came from dissolution of carbonates and (4) 33–85 % of DIC came from tributaries. δ15N values of nitrate ranged from ?5.2 ‰ at the headwater spring to 9.8 ‰ in the lower reaches. Higher δ15N values in the lower reaches of the river suggest anthropogenic pollution from agricultural activity. Based on seasonal and longitudinal changes of chemical and isotopic indicators of carbon and nitrogen in Kamni?ka Bistrica River, it can be concluded that seasonal changes are observed (higher concentrations are detected at low discharge conditions) and it turns from pristine alpine river to anthropogenic influenced river in central flow.  相似文献   

5.
Data from sonic tracking during the period 1983–1987 enabled us to define the areas used and the seasonal pattern of movement by adult shortnose sturgeon (Acipenser brevirostrum) in the Delaware River. Tagged adults (n=28) ranged from 544 mm to 871 mm fork length and 1,510 g to 7,125 g. Twenty-six tags were carried for 7–225 d. Most of the tagged sturgeon were relocated in the tidal portion of the river. Sturgeon that overwintered in the upper tidal river near Trenton, New Jersey, began traveling upstream in late March to the nontidal river above Trenton where spawning presumably occurred from late March through April. After spawning, sturgeon traveled rapidly downstream into the tidal portion of the river near Philadelphia, Pennsylvania, where they remained through the end of May. Before the end of June, most sturgeon returned upstream and re-entered the upper tidal river near Trenton, where most apparently remained for the summer and winter. In general, the same pattern was apparent for both sexes. As a result of the intensive use of the river between Philadelphia to just above Trenton, any alterations or additional insults to the river should consider the impact on this endangered species.  相似文献   

6.
The benthic fauna of a small cove of the Hudson River containing the aquatic plantMyriophyllum spicatum L. was studied for a one-year period. The fauna was characteristic of oligohaline zones of United States east coast estuaries. Total abundance of invertebrates retained on a 0.12 mm mesh sieve averaged 124,631 organisms m?2 (sediment and plant populations combined) and ranged up to 196,000 m?2. During the May–August period, invertebrates living on the plants comprised 16–35% of the invertebrate fauna in the cove. Chironomid larvae were the most abundant organisms on plants and the third most abundant in the sediments. Two assemblages of chironomid species were recognized; one lived solely in the sediments, the other lived primarily on the plants.Chironomus decorus andTanytarsus sp. dominated the former group andCricotopus sylvestris the latter. The chironomidDicrotendipes modestus utilized both habitats. During the May–August period, chironomid biomass on the plants comprised approximately 50% of total chironomid biomass in the cove. The mean dry-weight biomass of chironomids in the cove (1.6 g m?2) is estimated to be sixteen times greater than that of the fauna in the deeper areas of the river. Because chironomid larvae are eaten by fish and invertebrates, shallow water regions with their rich chironomid (and other fauna) may contribute importantly to the trophic dynamics of estuarine systems. *** DIRECT SUPPORT *** A01BY009 00004  相似文献   

7.
Spatial and temporal dynamics of N and P were examined in the tidal Hudson River between 1992 and 1996. For all seasons and at all locations in the river nutrient concentrations were generally quite high. TN averaged 60 μM and was above 50 μM in 75% of samples. TP averaged 1.7 μM and was above 1.2 μM in 75% of samples. NO3 was the dominant form of N (60% of TN) while PO4 comprised about 40% of TP. Seasonal and spatial variation in most N and P components was quite low but patterns were apparent. Seasonally, forms of N (TN, NO3 and NH4) and PO4 showed opposite patterns. All N components showed summertime decreases, but PO4 increased over the summer. Spatially, along the 200 km fresh to oligohaline stretch, N and P showed similar patterns—declining from upper to mid sections of the river but subsequently increasing in most down river, oligohaline stretches. The down river increase in nutrients is likely caused by a combination of sewage inputs and salinity-related geochemical release of P. A preliminary budget of the upper to the mid section of the river (a 100 km stretch) suggests that the decline in nutrient concentration in this section is due to the net retention of almost 2,000 mT N and 200 mT P per year or about 20% of the N and P input to this section of river. The retention in tidal rivers, like the Hudson, occurs immediately above the estuary and may, therefore, be relatively more significant than retention occurring higher in the watershed.  相似文献   

8.
The tolerance of post yolk-sac American shad Alosa sapidissima larvae to salinities typically seen in estuaries was assessed experimentally. Sixteen-day-old Hudson River (experiment I) and 35-d-old Delaware River (experiment II) larvae were held for 8 d and 9 d respectively in low (0–1‰), medium (9–11‰), and highly (19–20‰) brackish water, and mortality and growth rates were measured. Growth rates did not vary significantly among salinity treatments. Mortality in experiment I did not vary significantly among salinity treatments however, in experiment II, mortality was zero at 10‰ but higher and statistically indistinguishable between 0‰ and 20‰ In experiment II relative condition increased with salinity. These results imply that estuarine salinities neither depress growth rates nor elevate mortality rates of larval American shad when compared with freshwater conditions. We conclude that ecological factors other than the physiological effects of salinity have played more important roles in the evolution of the upriver spawning and nursery preference shown by this species.  相似文献   

9.
The chemical and isotopic characteristics of the water and suspended particulate materials（SPM） in the Yangtze River were investigated on the samples collected from 25 hydrological monitoring stations in the mainsteam and 13 hydrological monitoring stations in the major tributaries during 2003 to 2007. The water samples show a large variation in both δD（ 30‰ to 112‰） and δ18O（ 3.8‰ to 15.4‰） values. Both δD and δ18O values show a decrease from the river head to the Jinsha Jiang section and then increase downstream to the river mouth. It is found that the oxygen and hydrogen isotopic compositions of the Yangtze water are controlled by meteoric precipitation, evaporation, ice（and snow） melting and dam building. The Yangtze SPM concentrations show a large variation and are well corresponded to the spatial and temporal changes of flow speed, runoff and SPM supply, which are affected by the slope of the river bed, local precipitation rate, weathering intensity, erosion condition and anthropogenic activity. The Yangtze SPM consists of clay minerals, clastic silicate and carbonate minerals, heavy minerals, iron hydroxide and organic compounds. From the upper to lower reaches, the clay and clastic silicate components in SPM increase gradually, but the carbonate components decrease gradually, which may reflect changes of climate and weathering intensity in the drainage area. Compared to those of the upper crust rocks, the Yangtze SPM has lower contents of SiO2, CaO, K2 O and Na2 O and higher contents of TFe2 O3 and trace metals of Co, Ni, Cu, Zn, Pb and Cd. The ΣREE in the Yangtze SPM is also slightly higher than that of the upper crust. From the upper to lower reaches, the CaO and MgO contents in SPM decrease gradually, but the SiO2 content increases gradually, corresponding to the increase of clay minerals and decrease of the carbonates. The δ30SiSPM values（ 1.1‰ to 0.3‰） of the Yangtze SPM are similar to those of the average shale, but lower than those of the granite rocks（ 0.3‰ to 0.3‰）, reflecting the effect of silicon isotope fractionation in silicate weathering process. The δ30SiSPM values of the Yangtze SPM show a decreasing trend from the upper to the middle and lower reaches, responding to the variation of the clay content. The major anions of the river water are HCO 3, SO 4 2, Cl, NO 3, SiO 4 4 and F and the major cations include Ca2＋, Na＋, Mg2＋, K＋ and Sr2＋. The good correlation between HCO3-content and the content of Ca2＋may suggest that carbonate dissolution is the dominate contributor to the total dissolved solid（TDS） of the Yangtze River. Very good correlations are also found among contents of Cl, SO4 2, Na＋, Mg2＋, K＋and Sr2＋, indicating the important contribution of evaporite dissolution to the TDS of the Yangtze River. High TDS contents are generally found in the head water, reflecting a strong effect of evaporation in the Qinghai-Tibet Plateau. A small increase of the TDS is generally observed in the river mouth, indicating the influence of tidal intrusion. The F and NO3 contents show a clear increase trend from the upstream to downstream, reflecting the contribution of pesticides and fertilizers in the Chuan Jiang section and the middle and lower reaches. The DSi shows a decrease trend from the upstream to downstream, reflecting the effect of rice and grass growth along the Chuan Jiang section and the middle and lower reaches. The dissolved Cu, Zn and Cd in the Yangtze water are all higher than those in world large rivers, reflecting the effect of intensive mining activity along the Yangtze drainage area. The Yangtze water generally shows similar REE distribution pattern to the global shale. The δ30SiDiss values of the dissolved silicon vary from 0.5‰ to 3.7‰, which is the highest among those of the rivers studied. The δ30SiDiss values of the water in the Yangtze mainsteam show an increase trend from the upper stream to downstream. Its DSi and δ30SiDiss are influenced by multiple processes, such as weathering process, phytolith growth in plants, evaporation, phytolith dissolution, growth of fresh water diatom, adsorption and desorption of aqueous monosilicic acid on iron oxide, precipitation of silcretes and formation of clays coatings in aquifers, and human activity. The δ34SSO4 values of the Yangtze water range from 1.7‰ to 9.0‰. The SO4 in the Yangtze water are mainly from the SO4 in meteoric water, the dissolved sulfate from evaporite, and oxidation of sulfide in rocks, coal and ore deposits. The sulfate reduction and precipitation process can also affect the sulfur isotope composition of the Yangtze water. The87Sr/86Sr ratios of the Yangtze water range from 0.70823 to 0.71590, with an average value of 0.71084. The87Sr/86Sr ratio and Sr concentration are primary controlled by mixing of various sources with different87Sr/86Sr ratios and Sr contents, including the limestone, evaporite and the silicate rocks. The atmospheric precipitation and anthropogenic inputs can also contribute some Sr to the river. The δ11B values of the dissolved B in the Yangtze water range from 2.0‰ to 18.3‰, which is affected by multifactors, such as silicate weathering, carbonate weathering, evaporite dissolution, atmospheric deposition, and anthropogenic inputs.  相似文献   

10.
《Applied Geochemistry》2005,20(4):789-805
Mineralogical, hydrochemical and S isotope data were used to constrain hydrogeochemical processes that produce acid mine drainage from sulfidic waste at the historic Mount Morgan Au–Cu mine, and the factors controlling the concentration of SO4 and environmentally hazardous metals in the nearby Dee River in Queensland, Australia. Some highly contaminated acid waters, with metal contents up to hundreds of orders of magnitude greater than the Australia–New Zealand environmental standards, by-pass the water management system at the site and drain into the adjacent Dee River.Mine drainage precipitates at Mt. Morgan were classified into 4 major groups and were identified as hydrous sulfates and hydroxides of Fe and Al with various contents of other metals. These minerals contain adsorbed or mineralogically bound metals that are released into the water system after rainfall events. Sulfate in open pit water and collection sumps generally has a narrow range of S isotope compositions (δ34S = 1.8–3.7‰) that is comparable to the orebody sulfides and makes S isotopes useful for tracing SO4 back to its source. The higher δ34S values for No. 2 Mill Diesel sump may be attributed to a difference in the source. Dissolved SO4 in the river above the mine influence and 20 km downstream show distinctive heavier isotope compositions (δ34S = 5.4–6.8‰). The Dee River downstream of the mine is enriched in 34S (δ34S = 2.8–5.4‰) compared with mine drainage possibly as a result of bacterial SO4 reduction in the weir pools, and in the water bodies within the river channel. The SO4 and metals attenuate downstream by a combination of dilution with the receiving waters, SO4 reduction, and the precipitation of Fe and Al sulfates and hydroxides. It is suggested here that in subtropical Queensland, with distinct wet and dry seasons, temporary reducing environments in the river play an important role in S isotope systematics.  相似文献   

11.
Atlantic tomcod larvae, hatching in late February and early March 1975 and 1976 into a regime of accelerating river flows, were moved rapidly downriver from milepoint 42–54 (MP 0 is the estuary mouth) to the most seaward reaches of the estuary. This resulted in a spatiotemporal distribution markedly different from that of other Hudson River fish species. Peak tomcod density on posthatch sampling dates was observed most frequently at the George Washington Bridge station (MP 11). Correlation between movements of the 1.0‰ salt front and movements of the age-0 tomcod population was high (r=0.82); and may have been enhanced by high freshwater flows. The population epicenter was always seaward of the 1.0‰ salt front and mean distance between the two was 16–17 km. Moved by tidal and freshwater flows, the tomcod population oscillated between MP 0 and MP 43 during March–May 1973–1976. Location of the population epicenter after mid march was predicted (r2=0.76) to be seaward of the Tappan Zee Bridge (MP 30) when freshwater flows were greater than 450 m3 s?1. During flow regimes greater than 1,290 m3 s?1, the epicenter was predicted to be seaward of the George Washington Bridge (MP 11). An optimum-allocation sampling design for age-0 tomcod showed that 58% of the total effort from mid March to early June should be directed to the river region between MP 0 and MP 24, a region largely ignored in previous studies. *** DIRECT SUPPORT *** A01BY066 00013  相似文献   

12.
From June through September 1983, a survey was conducted to document the occurrence, abundance and distribution of benthic macroinvertebrates in the main channel, Hudson River Estuary. The survey was restricted to a 118-km reach of the limnetic zone from just below Albany to New Hamburg, New York. Results indicated that two crustacean species,Cyathura polita (Stimpson) andChiridotea almyra Bowman, are widely distributed and common throughout the limnetic zone, including areas more than 100 km upstream from the northernmost(=most upstream) intrusion of ocean-derived brackish water.Almyracuma proximoculi Jones and Burbanck was much less common, but also was found in areas well removed from any brackish-water influences. All three species previously have been thought to occur primarily in estuarine waters with at least some salinity. We could find no evidence to suggest that non-ocean derived sources were supplementing the levels of dissolved ions in the river water or sediments. Therefore, it appears that all three species have established permant populations in a truly freshwater habitat.  相似文献   

13.
Benthic macroinvertebrate abundance, taxonomic composition, and surface flooding dynamics were compared among high and low elevation stands of narrow-leaved cattail (Typha angustifolia) and invasive common reed (Phragmites australis) at Iona Island Marsh, an oligohaline wetland, and Piermont Marsh, a mesohaline wetland, within the Hudson River National Estuarine Research Reserve during 1999 and 2000. Overall, the benthic macroinvertebrate community at both sites was similar in composition and abundance to those documented from other low-salinity systems. Macroinvertebrate taxa richness was lowest in mesohaline common reed, but similar among common reed and cattail habitats in oligohaline wetlands. Total macroinvertebrate densities were greater at high-elevation compared to low-elevation reed stands at the mesohaline site during summer 1999 and spring 2000. Total macroinvertebrate densities were similar among both oligohaline vegetation types during all seasons, except for spring 2000, when lower densities were observed in low-elevation common reed. A weak positive relationship between macroinvertebrate density and depth of flooding suggests that surface hydrology may be influencing the observed patterns of macroinvertebrate density among the vegetation stands. These results suggest that benthic macroinvertebrate abundance and diversity may not necessarily be impaired in low-salinity wetlands experiencing invasion by common reed unless the change in vegetation is accompanied by a measurable alteration to physical conditions on the marsh surface (i.e., elevation and flooding dynamics).  相似文献   

14.
An investigation using environmental isotopes (δ18O and δD) was conducted to gain insight into the hydrological processes of the Ganga Alluvial Plain, northern India. River-water, shallow-groundwater and lake-water samples from the Gomati River Basin were analyzed. During the winter season, the δ18O and δD compositions of the Gomati River water ranged from ?1.67 to ?7.62 ‰ and ?25.08 to ?61.50 ‰, respectively. Deuterium excess values in the river water (+0.3 to ?13 ‰) and the lake water (?20 ‰) indicate the significance of evaporation processes. Monthly variation of δ18O and δD values of the Gomati River water and the shallow groundwater follows a similar trend, with isotope-depleted peaks for δ18O and δD synchronized during the monsoon season. The isotopically depleted peak values of the river water (δ18O?=??8.30 ‰ and δD?=??57.10 ‰) can be used as a proxy record for the isotopic signature of the monsoon precipitation in the Ganga Alluvial Plain.  相似文献   

15.
Six species of marine fishes, the Atlantic cutlassfish Trichiurus lepturus; planehead filefish, Monacanthus hispidus; guaguanche, Sphyraena guachancho; pigfish, Orthopristic chrysoptera; freckled blenny, Hypsoblenius ionthas; and short bigeye, Pristigenys alta, were observed for the first time in the Hudson River estuary in 1985. Their occurrence was associated with low freshwater runoff and the resulting upstream penetration of the salt front to historic levels. These conditions may have facilitated the dispersal of marine fishes from coastal areas into the lower Hudson River estuary.  相似文献   

16.
During the 1992 spawning season of river herring, three sites in a tributary of the Rappahannock River, Virginia, were studied to characterize spawning and nursery habitats of alewife (Alosa pseudoharengus) and blueback herring (Alosa aestivalis) and to identify differences in habitat use along an upstream to downtream gradient. The sites were sampled (using drift and dip nets and a plankton sampler) and habitat variables were measured on a 5-d, four-time interval rotation: at the end of 5 d, each site had been sampled once at dawn, noon, dusk, and midnight. Considerable non-overlap in spawning seasonality was apparent between species. For both species, densities of river herring adults, eggs, and yolk-sac larvae were highest at the upstream site, indicating 1) that the upstream site is more important for spawning than downstream areas, and 2) these species do not use different spawning areas in this stream. Densities of post-yolk-sac larvae did not differ significantly among sites, indicating post-spawning dispersal to downstream areas. The upstream site was smaller in area, more acidic, had faster water flow, clearer water, more vegetation, and siltier substrate than the downstream sites. At times, pH levels in the upstream site were within the lethal range reported for blueback herring larvae. Possible reasons for selection of the upstream habitat include: 1) adults may migrate as far upstream as possible to avoid predation or potential competition with other species of fish for spawning habitat; or 2) adults may historically enjoy greater spawning success in the upstream habitat due to physicochemical features of this area. More study is needed to determine the reasons for river herring use of upstream habitats in Virginia streams.  相似文献   

17.
The geochemical and isotopic compositions of river water are controlled by different factors. The seasonal and spatial variations in the geochemical composition, δD, δ18O, and δ15N–NO3 of the Kumho River were investigated to reveal the geochemical processes occurring at different seasons. The Kumho River, which runs through different geologic terrains with different land use characteristics, is the largest tributary of the Nakdong River, the longest river in South Korea. The data varied significantly according to the land use and the season. Each monitoring station showed the lowest concentrations of various ions during July, the rainy season, due to the increase of precipitation rate. The ionic concentrations gradually increased downstream by the mineral weathering and anthropogenic activity. At the upper regions of the river, Ca and HCO3, which are closely associated with mineral weathering, were the most dominant cation and anion, respectively. The relatively high Si concentration of the headwater samples, caused by the weathering of volcanic rocks, also showed the importance of weathering in the upper regions mainly composed of volcanic rocks. The downstream regions of the Kumho River are mainly influenced by sedimentary rocks. At the lower reaches of the river, especially near the industrial complexes in Daegu, the third largest city in Korea, Na, Cl, and SO4 became the dominant ions, indicating that the anthropogenic pollution became more important in regulating the chemical composition of the river. The increasing (Ca + Mg + Na + K)/HCO3 ratio downstream also indicates that the anthropogenic effects became more important as the river flows downstream. The isotopic compositions of δD and δ18O indicate that the river waters were significantly affected by evaporation during May and July, but the evaporation effect was relatively low during October. The isotopic composition of δ15N–NO3 increased downstream, also confirming that anthropogenic effects became more significant at the lower reach of the river and near Daegu.  相似文献   

18.
We studied the macroinvertebrate fauna of a rocky shore in the freshwater tidal Hudson River during 1992–1994, the early years of the zebra mussel (Dreissena polymorpha) invasion. The macroinvertebrate community was numerically dominated by chironomids, nematodes, oligochaetes, gastropods, zebra mussels, and planarian flatworms. The community was a mixture of species typical of stony warm water rivers and lake shores, freshwater generalists, and semiterrestrial species. Overall macroinvertebrate densities were moderate to low (2,800–14,600 m−2). Density was a strong function of season and elevation, with consistently low densities in the early spring and in the intertidal zone. This pattern suggests that physical harshness (alternating submergence and desiccation;ice and low temperatures) limits the distribution of invertebrates at this site. Zebra mussels occurred at our study site chiefly below the low tide mark, but only at moderate abundance (usually <1,000 m−2). A weak correlation between the densities of zebra mussels and those of other macroinvertebrates nonetheless suggests that the zebra mussel invasion may have affected community structure.  相似文献   

19.
Zooplankton assemblages in relation to water quality parameters at lentic and lotic habitats of Air Itam Reservoir, Penang, Malaysia, were analysed. Five sampling stations were designated, including three stations located in the reservoir (Stations A, B, and C) and two stations in the upstream inflow and downstream outflow (Stations D and E, respectively). The most common and dominant zooplankton found in the lake were Polyarthra vulgaris, Ceriodaphnia cornuta, Mesocyclops leuckarti, and Thermocyclops crassus. Water Quality Index, calculated as recommended by the Malaysian Department of Environment, ranged between 88.46 and 93.6, showed that the reservoir was clean. Low numbers of species and value of the Shannon–Wiener Diversity Index were recorded at stations located upstream and downstream of the reservoir. Cluster analysis based on the abundance of zooplankton species distinguished the sampling stations into two groups (lentic and lotic groups, comprised of Stations A, B, and C; and Stations D and E, respectively). This study showed that zooplankton occurrence and abundance were associated with the quality of their environment, and zooplankton community provides information about the reservoir ecosystem, thus reflecting the importance of biomonitoring in lake assessment and management.  相似文献   

20.
Inter-basin water transfer projects (IBWTPs) can involve basins as water donors and water receivers. In contrast to most studies on IBWTPs, which mainly impact the surface-water eco-environment, this study focuses on the impacts of an IBWTP on groundwater and its eco-environment in a water donor basin in an arid area, where surface water and groundwater are exchanged. Surface water is assumed to recharge groundwater and a groundwater numerical simulation model was constructed using MODFLOW. The model was used to quantitatively evaluate the impact of an IBWTP located in the upstream portion of Nalenggele River (the biggest river in the Qaidam basin, Northwest China). The impact involved decrease in spring flow, drawdown of groundwater, reduction in oasis area, and an increase in species replacement of oasis vegetation in the midstream and downstream of the river. Results show that the emergence sites of springs at the front of the oasis will move 2–5 km downstream, and the outflow of springs will decrease by 42 million m3/a. The maximum drawdown of groundwater level at the front of the oasis will be 3.6 m and the area across which groundwater drawdown exceeds 2.0 m will be about 59.02 km2, accounting for 2.71% of the total area of the oasis. Under such conditions, reeds will gradually be replaced by Tamarix, shrubs, and other alternative plant species. These findings have important implications for the optimization of water resource allocation and protection of the eco-environment in arid regions.  相似文献   

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