首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 31 毫秒
1.
Atrazine (2-chloro-4-ethylamino-6-isopropylamine-s-triazine) concentrations of 1,000 ppm either killed or eliminated the escape response (considered to be analogous to death) ofUca pugnax in laboratory experiments in August 1977. Adverse effects were observed at concentrations as low as 100 ppm and the severity was dependent on size and sex of the crab. However, in subsequent experiments, each with a new group of crabs, the effects of atrazine became smaller and smaller until a November experiment when no deleterious effects were observed even when exposed to 1,000 ppm. Experiments in August, 1978 confirmed the data obtained 1 year earlier. Ecological and physiological considerations of this seasonal variation in response are discussed. Crabs fed for 20 days with detritus wetted with 10?4 M atrazine were not adversely affected. Crabs exposed to a single application of 0, 100, 1,000, and 10,000 ppm atrazine in the field and in microecosystems were adversely affected only by the 10,000-ppm rate. Toxicity of atrazine to the larval stage of the crab was not investigated.  相似文献   

2.
We investigated spatial and temporal changes in spectral irradiance, phytoplankton community composition, and primary productivity in North Inlet Estuary, South Carolina, USA. High concentrations of colored dissolved organic matter (CDOM) were responsible for up to 84 % of the attenuation of photosynthetically available radiation (PAR). Green-yellow wavelengths were the predominant colors of light available at the two sampling sites: Clam Bank Creek and Oyster Landing. Vertical attenuation coefficients of PAR were 0.7–2.1 m?1 with corresponding euphotic zone depths of 1.5–6.7 m. Phytoplankton biomass (as chlorophyll a [chl a]) varied seasonally with a summer maximum of 16 μg chl a l?1 and a winter minimum of 1.4 μg chl a l?1. The phytoplankton community consisted mainly of diatoms, prasinophytes, cryptophytes and haptophytes, with diatoms and prasinophytes accounting for up to 67 % of total chl a. Changes in phytoplankton community composition showed strongest correlations with temperature. Light-saturated chl a-specific rates of photosynthesis and daily primary productivity varied with season and ranged from 1.6 to 14 mg C (mg chl a) ?1?h?1 (32–803 mg C m?3?day?1). Calculated daily rates added up to an annual carbon fixation rate of 84 g C m?3?year?1. Overall, changes in phytoplankton community composition and primary productivity in North Inlet showed a strong dependence on temperature, with PAR and spectral irradiance playing a relatively minor role due to short residence times, strong tidal forcing and vertical mixing.  相似文献   

3.
Although top-down control of plant growth has been shown in a variety of marine systems, it is widely thought to be unimportant in salt marshes. Recent caging experiments in Virginia and Georgia have challenged this notion and shown that the dominant marsh grazer (the periwinkle,Littoraria irrorata) not only suppresses plant growth, but can denude marsh substrate at high densities. In these same marshes, our field observations suggest that the black-clawed mud crab,Panopeus herbstii, is an abundant and potentially important top-down determinant of periwinkle density. No studies have quantitatively examinedPanopeus distribution or trophic interactions in marsh systems, and its potential impacts on community structure remained unexplored. We investigated distribution and feeding habits ofPanopeus in eight salt marshes along the Mid-Atlantic seashore (Delaware-North Carolina). We found that mud crabs were abundant in tall (4–82 ind m?2), intermediate (0–15 ind m?2), and short-form (0–5 ind m?2)Spartina alterniflora zones in all marshes and that crab densities were negatively correlated with tidal height and positively correlated with bivalve density. Excavation of crab lairs r?utinely produced shells of plant-grazing snails (up to 36 lair?1) and bivalves. Lab experiments confirmed that mud crabs readily consume these abundant marsh molluscs. To experimentally examine potential community effects of observed predation patterns, we manipulated crab and periwinkle densities in a 1-mo field experiment. Results showed thatPanopeus can suppress gastropod abundance and that predation rates increase with increasing snail density. In turn, crab suppression of snail density reduces grazing intensity on salt marsh cordgrass, suggesting presence of a trophic cascade. These results indicate that this previously under-appreciated consumer is an important and indirect determinant of community structure and contribute to a growing body of evidence challenging the long-standing notion that consumers play a minor role in regulating marsh plant growth.  相似文献   

4.
N2 fixation associated with the epiphytic community on standing dead Spartina alterniflora shoots was examined in both a natural and transplanted salt marsh in North Carolina. Acetylene reduction (AR) assays were conducted over a 24-mo period to estimate N2 fixation rates on standing dead stems and leaves. In the natural salt marsh, mean AR rates ranged from 0.5 nmol C2H4 cm?2 h?1 to 14 nmol C2H4 cm?2 h?1, while in the transplanted marsh mean AR rates ranged from 1 nmol C2H4 cm?2 h?1 to 33 nmol C2H4 cm?2 h?1. Diel AR activity of epiphytic communities in both marshes varied seasonally. Midday incubations yielded higher AR rates than nighttime incubations in the spring, while midday incubations in late summer and fall generally yielded AR rates equal to or lower than nighttime incubations. Desiccation during low tides occasionally repressed AR activity, although AR rates quickly rebounded with wetting. AR activity was localized in the epiphytic community, rather than in the underlying Spartina stem material. Based on the measured AR rates and the density of standing dead stems, the annual input of new N to the natural salt marsh via epiphytic N2 fixation is estimated to be 2.6 g N m?2 yr?1. The estimate of annual input of new N to the transplanted marsh is 3.8 g N m?2 yr?1. These estimates should be added to previous estimates of N2 fixation in marsh sediments to estimate the total contribution of new nitrogen to salt marsh nitrogen budgets.  相似文献   

5.
Recent (6–12 month) marsh sediment accretion and accumulation rates were measured with feldspar marker horizons in the vicinity of natural waterways and man-made canals with spoil banks in the rapidly subsiding environment of coastal Louisiana. Annual accretion rates in aSpartina alterniflora salt marsh in the Mississippi deltaic plain averaged 6 mm in marsh adjacent to canals compared to 10 mm in marsh adjacent to natural waterways. The rates, however, were not statistically significantly different. The average rate of sediment accretion in the same salt marsh region for a transect perpendicular to a canal (13 mm yr?1) was significantly greater than the rate measured for a transect perpendicular to a natural waterway (7 mm yr?1). Measurements of soil bulk density and organic matter content from the two transects were also different. This spatial variability in accretion rates is probably related to (1) spoil bank influences on local hydrology; and (2) a locally high rate of sediment input from lateral erosion associated with pond enlargement. In a brackishSpartina patens marsh on Louisiana’s Chenier plain, vertical accretion rates were the same along natural and canal waterways (3–4 mm yr?1) in a hydrologically restricted marsh region. However, the accretion rates for both waterways were significantly lower than the rates along a nonhydrologically restricted natural waterway nearby (11 mm yr?1). The vertical accretion of matter displayed semi-annual differences in the brackish marsh environment.  相似文献   

6.
Primary production by algal epiphytes of dead Spartina alterniflora shoots in a Georgia salt marsh was measured using the 14C technique. A 23 factorial design was used to quantify the effects of light intensity and inundation frequency (stem height) on carbon fixation at two sites along a salt marsh creek. Algae inundated daily fixed carbon more rapidly than those which had dried for several days, but this may have been the results of greater biomass on more frequently immersed stems. This result corroborates studies showing desiccation is not always a severe stress for intertidal algae. Similarity of epiphyte algal productivity to that of salt marsh benthic diatoms suggests that, given adequate substrate, the epiphytes may be an important source of primary production during some seasons of the year.  相似文献   

7.
This paper documents the role of salt marsh algal mats in the productivity of a southern California tidal wetland. The productivity of the mats, which are composed of filamentous bluegreen and green algae and diatoms, varies both temporally and spatially in relation to tidal inundation and overstory vegetation. The estimates of net primary productivity (NPP) were highest under the canopy ofJaumea carnosa (Less.) Gray (341 g C m?2 yr?1) at low elevation. Elsewhere, NPP appeared to be limited by low light (276 g C m?2 yr?1 underSpartina foliosa Trin.) and desiccation (185 g C m?2 yr?1 underBatis martima L. and 253 g C m?2 yr?1 underMonanthochloe littoralis Engelm). Algal NPP was from 0.8 to 1.4 times that of the vascular plant overstory NPP. It is hypothesized that the arid environment of southern California and resulting hypersaline soils reduce vascular plant cover, which leads to high algal productivity.  相似文献   

8.
In order to test the assumption that accretion rates of intertidal salt marshes are approximately equal to rates of sea-level rise along the Rhode Island coast,210Pb analyses were carried out and accretion rates calculated using constant flux and constant activity models applied to sediment cores collected from lowSpartina alterniflora marshes at four sites from the head to the mouth of Narragansett Bay. A core was also collected from a highSpartina patens marsh at one site. Additional low marsh cores from a tidal river entering the bay and a coastal lagoon on Block Island Sound were also analyzed. Accretion rates for all cores were also calculated from copper concentration data assuming that anthropogenic copper increases began at all sites between 1865 and 1885. Bulk density and weight-loss-on-ignition of the sediments were measured in order to assess the relative importance of inorganic and organic accumulation. During the past 60 yr, accretion rates at the eight low marsh sites averaged 0.43±0.13 cm yr?1 (0.25 to 0.60 cm yr?1) based on the constant flux model, 0.40±0.15 cm yr?1 (0.15 to 0.58 cm yr?1) based on the constant activity model, and 0.44±0.11 cm yr?1 (0.30 to 0.59 cm yr?1) based on copper concentration data, with no apparent trend down-bay. High marsh rates were 0.24±0.02 (constant flux), 0.25±0.01 (constant activity), and 0.47±0.04 (copper concentration data). The cores showing closest agreement between the three methods are those for which the excess210Pb inventories are consistent with atmospheric inputs. These rates compare to a tide gauge record from the mouth of the bay that shows an average sea-level rise of 0.26±0.02 cm yr?1 from 1931 to 1986. Low marshes in this area appear to accrete at rates 1.5–1.7 times greater than local relative sea-level rise, while the high marsh accretion rate is equal to the rise in sea level. The variability among the low marsh sites suggests that marshes may not be poised at mean water level to within better than ±several cm on time scales of decades. Inorganic and organic dry solids each contributed about 9% by volume to low marsh accretion, while organic dry solids contributed 11% and inorganic 4% to high marsh accretion. Water/pore space accounted for the majority of accretion in both low and high marshes. If water associated with the organic component is considered, organic matter accounts for an average of 91% of low marsh and 96% of high marsh accretion. A dramatic increase in the organic content at a depth of 60 to 90 cm in the cores from Narragansett Bay appears to mark the start of marsh development on prograding sand flats.  相似文献   

9.
A series of seasonal cores was taken in a high marsh near the terminus of Delaware Bay, U.S.A. A seasonal harmonic diffusion model was successfully fit to the concentration profiles of chloride ion in the salt marsh pore waters yielding a calculated sedimentary diffusion coefficient.Virtually all other chemical reactions within salt marsh sediments are directly linked to the rate and stoichiometry of organic decomposition. The rich organic input from the grass Spartina alterniflora is oxidized anaerobically through the process of sulfate reduction. Over 90% of this net decomposition of organic matter takes place in the uppermost 20 cm. The model for sulfate reduction proposed yields an internally consistent set of both pore water (HCO?3, NH+4, HPO2?4, HS?, SO2?4) and solid phase (FeS2) distribution profiles for these sediments. Steady state assumptions and the use of mean annual constants can be employed to model the net rates of diagenetic processes in salt marshes. The pore water concentrations of sulfate ion as well as those ions released by sulfate reduction (HCO?3, NH+4, HPO2?4, HS?) are modeled by a system composed of an upper zone, where extensive reconsumption of these metabolite ions occurs, and a lower zone where steady state production and no ion reconsumption occurs.A major product of the sulfate reduction is pyrite, whose accumulation rate is greatest between 7 and 9 cm depth, where it equals the net rate of sulfate reduction. Above this zone little pyrite accumulates due to extensive reoxidation. Below 9 cm the rate of pyritization is controlled by the rate of sulfidation of a refractory iron phase.  相似文献   

10.
No pre-1977 quantitative data exist that describe phytoplankton biomass in the water column of Lake Suwa, a Japanese eutrophic lake, although several studies have been conducted since. To assess recent environmental changes with time in the lake, phytoplankton composition was determined from analysis of photosynthetic pigments in the sediment core. Specifically, the total chlorophyll a (TCh-a) concentration in the water column before 1977 was estimated for comparison with that of the water column and sediment deposited since 1977. The depth profile of zeaxanthin, a potential indicator of cyanobacteria activity, substantially increased from 1960 to 1973 (from 9.53 to 76.7?nmol?g?1). Additionally, the concentration of fucoxanthin, diadinoxanthin and diatoxanthin, originating from diatoms and dinoflagellates, increased slightly during this period (from 1.64 to 4.90, 1.86 to 3.54, and 4.00 to 3.26?nmol?g?1). Cyanobacteria have been the major algal species in the lake since 1949; however, the ratio of fucoxanthin versus total algal carotenoids has gradually increased since 1981 indicating diatoms have increased relative to cyanobacteria since 1979, and that organic matter inflow and nutrient concentrations have resulted in changes in the phytoplankton composition. Since 1977, the chlorophyll a concentration in water in the lake had a very similar pattern as the TCh-a concentration in the sediment. The concentration in the water column also corresponds to those in the sediment even before 1977. These results indicate that it might be possible to predict the phytoplankton biomass of the water column based on the TCh-a in the water and sediment in this lake.  相似文献   

11.
Phaeosphaeria spartinicola is known to be an important fungal (ascomycetous) secondary producer in the smooth-cordgrass (Spartina alterniflora) decomposition system of western Atlantic salt marshes, yet its degree of predominance among the ascomycete assemblages of salt marshes and the concentration of its sexual reproductive structures (ascomata) have been largely unknown. During May–June, we measured by direct microscopy the percent occupancy of leaf abaxial area and concentrations of ascomata in leaf blades of smooth cordgrass at three elevations in three drainage systems within the marshes of Sapelo Island, Georgia, United States. We also measured in water-saturation chambers the rates at which the ascomata expelled ascopoores (sexual propagules) out of decaying leaves from marsh sites containing or not containing shredder gastropods.P. spartinicola ascomata were found at averages of 36% to 93% of grid-circles (3-mm radius) on decaying leaf blades, with lower values at points directly adjacent to the leaf sheath, on leaves at earlier stages of decay, and at elevational subsites where shredder snails were more active. Marsh elevation had no effect of its own on percent occupation. No other species of ascomycetes were found at overall avarage frequencies greater than 3%. Average concentration of ascomata along the intervascular rows where they were located was 1 ascoma per 0.5 mm row (～1000 cm?2 abaxial leaf surface, translating to production of 1.6×107 ascomata m?2 intermediate-height marsh per standing crop of living stems). The fraction of total fungal production allocated to ascomata is speculatively and crudely estimated at about 9%, without taking into account potential loss to invertebrate shredders. At sites with abundances of snails >-50 m?2 peaks of ascospore expulsion (about 50–75 spores cm?2 leaf h?1, 3–5× the overall average rate) observed at snail-free sites were absent. Our measured rate of ascospore expulsion (averaged over snail-free and high-snail sites, and possibly an underestimate) translated to 6.5×104 spores m?2 marsh h?1 for times of freshwater saturation of leaves, and one-third that value for times of saltwater wetting.  相似文献   

12.
A pot experiment was conducted to monitor the dynamic response of photosynthesis of Amorpha fruticosa seedlings to different concentrations of petroleum-contaminated soils from April to September. The results showed that the photosynthetic rates, stomatal conductance and transpiration rate of seedlings significantly decreased in 5–20 g kg?1 petroleum-contaminated soil during the three given sampling period of July 31 (early), August 30 (mid-term) and September 29 (late). However, the intercellular CO2 concentration significantly increased in 10 g kg?1 contaminated soil, while declined in 20 g kg?1 contaminated soil during the early sampling period as well as in 20 g kg?1 contaminated soil during the late sampling period. The leaf relative water content of seedlings significantly increased in 20 g kg?1 contaminated soil during the early sampling period, while it dropped dramatically in 15–20 g kg?1 contaminated soil during the late sampling period. The contents of chlorophyll a, chlorophyll b and the total chlorophyll of seedlings showed a sharp decline during the three sampling periods in contaminated soil. Comprehensively, considering the negative effects of petroleum on the photosynthesis, growth performance and remediation effect on petroleum of A. fruticosa seedlings, this plant was tolerant of petroleum-contaminated soil and was potentially useful for the phytoremediation of petroleum-contaminated sites in northern Shaanxi, China.  相似文献   

13.
In many southern California salt marshes, increased freshwater inflows have promoted the establishment of exotic plant species. A comparative study showed that a native, perennial, high marsh dominant,Salicornia subterminalis, and an invasive, exotic annual grass,Polypogon monspeliensis, responded differently to soil salinity and saturation.Salicornia subterminalis seeds and young plants were more salt tolerant, and the native grew best at high salinities (23 g 1?1 and 34 g 1?1) in greenhouse experiments. In contrast, the exotic had reduced growth at high salinities relative to nonsaline controls. The native,S. subterminalis, grew poorly as the duration of soil saturation increased from 2 wk to 32 wk, butP. monspeliensis grew equally well for all durations tested. The response ofS. subterminalis andP. monspeliensis to increased salinity indicated that salt applications might be used to protect native vegetation in salt marshes where salt-sensitive exotics are a problem. A field experiment verified that a salt application of 850 g m?2 mo?1 for 3 mo was sufficient to control the exotic, while not noticeably affecting the native. Thus, salt applications may be a practical method for controllingP. monspeliensis invasions in areas receiving urban runoff or other unwanted freshwater inflows.  相似文献   

14.
The presence of the C30 sterol gorgosterol (22,23-methylene-23,24-dimethylcholest-5-en-3ß-ol) and its analogues in some marine and freshwater environments is generally associated with invertebrate animals or dinoflagellates since there have been no reports of them in other microalgal classes. Here we show that two unialgal cultures of different species of the marine diatom Delphineis contain gorgosterol in addition to sterols more commonly found in diatoms. Our findings suggest that some reports of gorgosterol in seawater and marine sediments may well have an origin, at least in part, from diatoms.  相似文献   

15.
Studies of photosynthesis and respiration in the sheet-like green macroalgaUlva lactuca L. have typically made use of cut discs or individual thalli. Because this species accumulates in layered mats in the field, its structure has the potential to significantly alter metabolic rates compared to those measured for a single layer. The effect of biomass layering on photosynthesis and respiration inU. lactuca was assessed by incubating stacks of 1, 2, 4, and 8 thalli across a range of surface irradiance and in the dark. The photosynthesis-irradiance curve for a single thallus was hyperbolic in shape with maximum photosynthetic rates of 16–24.5 mg O2 g?1 dry weight h?1, a photosynthetic efficiency of 0.18 mg O2 g?1 dry weight h?1 (μE m?2 s?1)?1, and dark respiration rates of 0.95–1.2 mg O2 g?1 dry weight h?1. Weight-specific photosynthesis and respiration rates decreased as the amount of layering increased, with rates approximately twice as high in a single layer as for 8 layers. A simple model revealed that the reduced photosynthetic rates were due to attenuation of light through the stack. Each layer ofUlva reduced the light available to the next layer by approximately 55%, and variability in this absorption was directly related to thallus chlorophyll content. Model runs suggested that acclimation of the thalli by changes in chlorophyll content has the potential to reduce some, but not all of the effect of layering. Reduced respiration rates were atributed to the depletion of oxygen from the interstices between the layers. Results were incorporated into a model of anUlva mat, which predicted decreasing rates of weight-specific total mat production with increasing mat thickness as additional layers are added to the bottom of the mat that neither produce nor consume significant amounts of oxygen. The model predicted area-weighted mat production to increase up to a thickness of 10 layers, after which the rate was constant with increasing mat thickness for the same reason. SinceUlva has a tendency to accumulate in layers under natural conditions, these results improve upon metabolic measurements made with single thalli and will be useful for calculations of macroalgal production as well as in ecosystem models in whichUlva is an important primary producer.  相似文献   

16.
Phytoplankton chlorophyll a concentration, biovolume, cell diameter, and species composition differed across the narrow, low salinity zone between 0.6‰ to 4‰ and may influence copepod food availability in the northern San Francisco Bay Estuary. The highest chlorophyll a concentrations (range 3.2–12.3 μg 1?1), widest cell diameters (>5 μm diam), highest diatom densities and highest production rates of >10 μm diam cells occurred at the landward edge of the salinity zone in April during a strong spring tide and May during a strong neap tide. Near optimum predator/prey ratios, large prey estimated spherical diameters, and high chlorophyll a concentrations suggest these phytoplankton communities provided good food quantity and quality for the most abundant copepods, Eurytemora affinis, Sinocalanus doerrii, and Pseudodiaptomus forbesi. At the center of the zone, chlorophyll a concentrations, diatom densities, and production rates of >10 μm diam cells were lower and cell diameters were smaller than upstream. Downstream transport was accompanied by accumulation of phytoplankton with depth and tide; maximum biomass occurred on spring tide. The lowest chlorophyll a concentrations (1.4–3.6 μg 1?) and consistently high densities (3,000–4,000 cells ml?1) of <5 μm diam cells occurred at the seaward edge of the zone, where the green alga Nannochloris spp. and the bluegreen alga Synechococcus spp. were the most abundant phytoplankton. Low chlorophyll a concentrations and production rates of >10 μm diam cells, small prey estimated spherical diameters, and high predator/prey ratios suggested the seaward edge of the zone had poor phytoplankton food for copepodids and adult copepods. The seaward decrease in phytoplankton chlorophyll a concentration and cell diameter and shift in species composition in the low salinity zone were probably a function of an estuary-wide decrease in chlorophyll a concentration, cell diameter, and diatom density since the early 1980s that was enhanced in the low salinity zone by clam herbivory after 1987. *** DIRECT SUPPORT *** A01BY090 00008  相似文献   

17.
Planimetry studies of coastal geology maps prepared by the Maine Geological Survey show that there is more than an order of magnitude more tidal marsh area in the state of Maine than documented in previously published estimates. The highly convoluted coast of Maine, which is approximately 5,970 km long, contains almost 79 km2 of salt marsh, far more than any other New England state, New York, or the Bay of Fundy region. Reasonable estimates for the per-unit primary productivity of salt marshes lead to projections of total marsh productivity on the order of 1010 g dry weight yr?1 for the Maine coast and 1011 g dry weight yr?1 for the Gulf of Maine as a whole. Distribution of tidal marsh area is strongly controlled by coastal geomorphology, which varies considerably along the coast of Maine. The salt marsh area is concentrated in the southwestern coastal region of arcuate bays, where marshes have developed behind sandy beaches. A series of long islands and bedrock peninsulas in the south-central portion of the coast also provides sheltered areas where large marshes occur. Northeast of Penobscot Bay salt marshes become more numerous and smaller in average areal extent. A lack of protection from waves, along with limited sources of glacio-fluvial and glacio-marine sediments, restricts the occurrence of salt marshes in that region to the frignes of coves and tidal rivers.  相似文献   

18.
Experiments were performed seasonally to estimate grass shrimp,Palaemonetes pugio, grazing on the epiphytic microalgae of cordgrass,Spartina alterniflora, and to determine if grass shrimp have the potential to regulate epiphyte abundance. Grass shrimp were given access to live culms with low and high epiphytic abundance and standing dead culms collected from the streamside levee of a Louisiana salt marsh. Plexiglas frames were used to hold culms upright in aquaria and to restrict grass shrimp access to one half of each culm. We compared epiphyte biomass on the sides of culms exposed to shrimp with the corresponding unexposed sides. Epiphytes were removed from the lowest 10 cm of culms on days 0, 3, and 10, and chlorophylla (chla) measurements on each culm half were made by fluorometry. Chla biomass on culm halves not exposed to grass shrimp significantly increased over time. Percent reductions in chla on culm halves exposed to grass shrimp (calculated by subtraction from the corresponding half not exposed to shrimp) significantly increased over time for at least one culm type in all seasons. Grass shrimp caused an average 30% reduction of epiphyte biomass over 3 d and a 40% reduction over 10 d, suggesting that grass shrimp have the capability of consuming a substantial proportion of the daily production of epiphytes. Epiphytes from standing-dead culms may be more important than those from live culms at the marsh edge to the diet of grass shrimp because chla biomass was, on average, high, and standing-dead culms were seasonally abundant. Diagnostic photosynthetic pigments from selected culms, grass shrimp gut contents, and fecal pellets were identified by high performance liquid chromatography and were used to quantify the taxonomic groups of epiphytic microalgae. Results suggested that diatoms, brown algae, green algae, red algae, and cyanobacteria were present on all culms. Similarities in the pigment content of grass shrimp gut contents and fecal pellets suggested that all algal groups were ingested. Pigment data analysis could not detect a change in the composition of the microalgal assemblage associated with grass shrimp grazing. Assuming that the reduction in chla was due exclusively to grazing, grass shrimp consumed an average of 0.5–1.5 g epiphyte carbon shrimp?1 d?1, suggesting that grass shrimp benefit significantly from the consumption ofS. alterniflora epiphytic algae.  相似文献   

19.
For determination of atrazine isotherms in agricultural soils of Fars Province, composite soil samples from 0 to 5 cm depth with textures of silty clay loam, clay loam and loam were collected. In order to form the atrazine isotherms, 10, 50 and 100 µg atrazine g?1 soil was added to the soil samples. Soluble atrazine in water:soil ratios of 10:1, 50:1 and 200:1 was measured after 3-h shaking. Finally, for each cases of applied atrazine, water extractable atrazine was determined and quantified using gas chromatography instrument. The results indicated that there was a linear relationship between the logarithms of water extractable atrazine and added atrazine for different water:soil ratios. A general equation of WEA = K(WS) α (AA) β is obtained experimentally between water extractable atrazine, µg g?1(WEA), and added atrazine, µg g?1 (AA), where K, α and β are absorption constants; WS is the water:soil ratio, g g?1. For the loam, silty clay loam and clay loam soil textures, the α were 0.49, 0.23 and 0.13, respectively, the β were 0.55, 0.806 and 0.21, respectively, and the K were 1.44, 0.78 and 25.38, respectively.  相似文献   

20.
The goal of this study was to evaluate the soil properties and their modifications within the rhizosphere of spontaneous vegetation as key factors to assess the phytomanagement of a salt marsh polluted by mining wastes. A field survey was performed based on a plot sampling design. The results provided by the analyses of rhizospheric soil (pH, electrical conductivity (EC), organic carbon, total nitrogen, etc.) and metal(loid)s’ phytoavailability (assessed by EDTA) were discussed and related to plant metal uptake. The averages of pH and EC values of the bulk soil and rhizospheric samples were in the range of neutral to slightly alkaline (pH 7–8) to saline (>2 dS m?1), respectively. Heavy metal and As concentrations (e.g. ~600 mg kg?1 As, ~50 mg kg?1 Cd, ~11,000 mg kg?1 Pb) were higher in the rhizosphere for both total and EDTA-extractable fraction. Phragmites australis uptaked the highest concentrations in roots (e.g. ~66 mg kg?1 As, ~1,770 mg kg?1 Zn) but not in shoots, for which most of plant species showed low values for Zn (<300 mg kg?1) but not for Cd (>0.5 mg kg?1) or Pb (~20–40 mg kg?1). Vegetation distribution in the studied salt marsh looked to be more affected by salinity than by metal pollution. The free availability of water for plants and the incoming nutrient-enriched effluents which flow through the salt marsh may have hindered the metal(loid)s’ phytotoxicity. The phytomanagement of these polluted areas employing the spontaneous vegetation is a good option in order to improve the ecological indicators and to prevent the transport of pollutants to nearby areas.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号