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1.
The flooded intertidal zone in coastal estuarine systems (e.g., mangroves and salt marshes) is thought to provide nekton with
both food and refuge from predators. The primary aim of this study was to identify the relative contribution of root structure,
shading, and leaf litter, all characteristic features of mangrove forests, in shaping the intertidal distribution of tidally
migrating fishes. We manipulated the structure and shade in 9-m 2 sample plots in a shallow, mangrove-fringed, intertidal embayment in Tampa Bay, Florida. In a separate field experiment,
we compared fish association with standing mangrove leaf litter and bare sand substrate. Shade and leaf litter had a water
depthdependent effect on the distribution of the fish; no effect was associated with the presence of mangrove roots. In shallow
water (<45 cm), fish were captured primarily in plots without shade, but this distribution shifted progressively with increasing
water depth, so that when water was greater than 55 cm most fish were captured in shaded plots. Fish were more frequently
associated with, and feeding in, plots covered in leaf litter than bare sand plots. This relationship did not persist at depths
greater than 15 cm because fish abundance declined gratly. Tethering experiments using Cyprinodon variegatus demonstrated that predation pressure was quadratically correlated with water depth (inflexion point approximately 60 cm).
Our results suggest that small fishes will abandon well-lighted foraging grounds in favor of the potential refuge of shaded
waters as water depth increases. We suggest that studies of intertidal nekton should be carefully interpreted in the context
of water depth. 相似文献
2.
We measured monthly soil surface elevation change and determined its relationship to groundwater changes at a mangrove forest
site along Shark River, Everglades National Park, Florida. We combined the use of an original design, surface elevation table
with new rod-surface elevation tables to separately track changes in the mid zone (0–4 m), the shallow root zone (0–0.35 m),
and the full sediment profile (0–6 m) in response to site hydrology (daily river stage and daily groundwater piezometric pressure).
We calculated expansion and contraction for each of the four constituent soil zones (surface [accretion and erosion; above
0 m], shallow zone [0–0.35 m], middle zone [0.35–4 m], and bottom zone [4–6]) that comprise the entire soil column. Changes
in groundwater pressure correlated strongly, with changes in soil elevation for the entire profile (Adjusted R 2 = 0.90); this relationship was not proportional to the depth of the soil profile sampled. The change in thickness of the
bottom soil zone accounted for the majority (R 2 = 0.63) of the entire soil profile expansion and contraction. The influence of hydrology on specific soil zones and absolute
elevation change must be considered when evaluating the effect of disturbances, sea level rise, and water management decisions
on coastal wetland systems. 相似文献
3.
The cause for prolific seismicity in the Koyna region is a geological enigma. Attempts have been made to link occurrence of
these earthquakes with tectonic strain as well as the nearby reservoirs. With a view to providing reliable seismological database
for studying the earth structure and the earthquake process in the Koyna region, a state of the art digital seismic network
was deployed for twenty months during 1996–97. We present preliminary results from this experiment covering an area of 60
× 80 km 2 with twenty seismic stations. Hypocentral locations of more than 400 earthquakes confined to 11×25 km 2 reveal fragmentation in the seismicity pattern — a NE — SW segment has a dip towards NW at approximately 45°, whilst the
other two segments show a near vertical trend. These seismic segments have a close linkage with the Western Ghat escarpment
and the Warna fault. Ninety per cent of the seismicity is confined within the depth range of 3–10 km. The depth distribution
of earthquakes delimits the seismogenic zone with its base at 10 km indicating a transition from an unstable to stable frictional
sliding regime. The lack of shallow seismicity between 0 and 3 km indicates a mature fault system with well-developed gouge
zones, which inhibit shallow earthquake nucleation. Local earthquake travel time inversion for P- and S-waves show ≈ 2% higher
velocity in the seismogenic crust (0–10 km) beneath the epicentral tract relative to a lower velocity (2–3%) in the adjoining
region. The high P- and S-wave velocity in the seismogenic crust argues against the presence of high pressure fluid zones
and suggests its possible linkage with denser lithology. The zone of high velocity has been traced to deeper depths (≈ 70
km) through teleseismic tomography. The results reveal segmented and matured seismogenic fault systems in the Koyna region
where seismicity is possibly controlled by strain build up due to competent lithology in the seismic zone with a deep crustal
root. 相似文献
4.
Because of the relatively low soil moisture in arid or semi-arid regions, water vapour movement often predominates in the
vadose zone and affects the partitioning of energy among various land surface fluxes. In an outdoor sand bunker experiment,
the soil water content at 10 and 30 cm depth were measured at hourly intervals for 2.5 days during October 2004. It was found
that the soil moisture reached the daily maximum value (5.9–6.1% at 10 cm and 11.9–13.1% at 30 cm) and minimum value (4.4–4.5%
at 10 cm and 10.4–10.8% at 30 cm) at midday (0–1 p.m. for 10 cm and 2–3 p.m. for 30 cm) and before dawn (2–3 a.m. for 10 cm
and 4–5 a.m. for 30 cm), respectively. The modified HYDRUS-1D code, which refers to the coupled water, water vapour and heat
transport in soil, was used to simulate the moisture and water vapour flow in the soil. The numerical analyses provided insight
into the diurnal movement of liquid water and water vapour driven by the gradients of pressure heads and temperatures in the
subsurface zone. The simulated temperature and water content were in good agreement with the measured values. The spatial–temporal
distribution of liquid water flux, water vapour flux and soil temperature showed a detailed diurnal pattern of soil water
dynamics in relatively coarse sand.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users. 相似文献
5.
The objective of this study was to develop an empirical equation for estimating the capillary rise in the saline-sodic soil
area of Songnen Plain in China based on the Averianov formula. The capillary rise was observed under five controlled groundwater
levels by lysimeters. Field experiment results indicated that capillary rise had close relationship with the groundwater table
depth, soil moisture of 10–40 cm soil layer and leaf area index. These factors have been taken into account to develop the
empirical equation for capillary rise simulation. The model parameters for Songnen Plain were derived by Levenberg–Marquardt
and global optimization calculating method. The modeled capillary rise has a good agreement with the observed data ( r
2 = 0.875). With the simulation model, the critical water table depth was identified as 2.5 m, indicating that soil secondary
salinization will not occur when the water table depth is deeper than 2.5 m. Therefore, in the irrigation areas, groundwater
table depth should be controlled to be higher than 2.5 m to prevent the occurrence of soil secondary salinization. The results
from this research will provide useful information for the water sources management and soil secondary salinization control
in Songnen Plain of China, one of the most serious saline-affected areas in the world. 相似文献
6.
Kinmen Island is a small, tectonically stable, granitic island that has been suffering from a scarcity of fresh water resources
due to excessive annual evapotranspiration over annual precipitation. Recent studies further indicate that shallow (0–70 m)
sedimentary aquifers, the major sources of groundwater supply, have already been over-exploited. Therefore, this preliminary
study is to investigate the existence of exploitable water resources that can balance the shortage of fresh water on this
island. Site characterization data are obtained from island-wide geophysical surveys as well as small-scale tests performed
in a study area formed by three deep (maximum depth to 560 m) vertical boreholes installed in mid-east Kinmen northeast to
Taiwu Mountain. Vertical fracture frequency data indicate that the rock body is fractured with a spatially correlated pattern,
from which three major fracture zones (depths 0–70, 330–360, and below 450 m) can be identified. Geologic investigations indicate
that the deepest fracture zone is caused by the large-scale, steeply dipping Taiwushan fault. This fault may have caused a
laterally extensive low-resistivity zone, a potential fractured aquifer, near Taiwu Mountain. The middle fracture zone is
induced by the Taiwushan fault and intersects the fault approximately 21 m southeast of the study area below a depth of 350 m.
Slug testing results yield fracture transmissivity varying from 4.8 × 10 −7 to 2.2 × 10 −4 m 2/s. Cross-hole tests have confirmed that hydraulic connectivity of the deeper rock body is controlled by the Taiwushan fault
and the middle fracture zone. This connectivity may extend vertically to the sedimentary aquifers through high-angle joint
sets. Despite the presence of a flow barrier formed by doleritic dike at about 300 m depth, the existence of fresh as well
as meteoric water in the deeper rock body manifests that certain flow paths must exist through which the deeper fractured
aquifers can be connected to the upper rock body. Therefore, groundwater stored within the Taiwushan fault and the associated
low-resistivity zone can be considered as additional fresh water resources for future exploitation. 相似文献
7.
In order to shed light on upper crustal differentiation of mantle-derived basaltic magmas in a subduction zone setting, we
have determined the mineral chemistry and oxygen and hydrogen isotope composition of individual cumulus minerals in plutonic
blocks from St. Vincent, Lesser Antilles. Plutonic rock types display great variation in mineralogy, from olivine–gabbros
to troctolites and hornblendites, with a corresponding variety of cumulate textures. Mineral compositions differ from those
in erupted basaltic lavas from St. Vincent and in published high-pressure (4–10 kb) experimental run products of a St. Vincent
high-Mg basalt in having higher An plagioclase coexisting with lower Fo olivine. The oxygen isotope compositions (δ 18O) of cumulus olivine (4.89–5.18‰), plagioclase (5.84–6.28‰), clinopyroxene (5.17–5.47‰) and hornblende (5.48–5.61‰) and hydrogen
isotope composition of hornblende (δD = −35.5 to −49.9‰) are all consistent with closed system magmatic differentiation of
a mantle-derived basaltic melt. We employed a number of modelling exercises to constrain the origin of the chemical and isotopic
compositions reported. δ 18O Olivine is up to 0.2‰ higher than modelled values for closed system fractional crystallisation of a primary melt. We attribute this
to isotopic disequilibria between cumulus minerals crystallising at different temperatures, with equilibration retarded by
slow oxygen diffusion in olivine during prolonged crustal storage. We used melt inclusion and plagioclase compositions to
determine parental magmatic water contents (water saturated, 4.6 ± 0.5 wt% H 2O) and crystallisation pressures (173 ± 50 MPa). Applying these values to previously reported basaltic and basaltic andesite
lava compositions, we can reproduce the cumulus plagioclase and olivine compositions and their associated trend. We conclude
that differentiation of primitive hydrous basalts on St. Vincent involves crystallisation of olivine and Cr-rich spinel at
depth within the crust, lowering MgO and Cr 2O 3 and raising Al 2O 3 and CaO of residual melt due to suppression of plagioclase. Low density, hydrous basaltic and basaltic andesite melts then
ascend rapidly through the crust, stalling at shallow depth upon water saturation where crystallisation of the chemically
distinct cumulus phases observed in this study can occur. Deposited crystals armour the shallow magma chamber where oxygen
isotope equilibration between minerals is slowly approached, before remobilisation and entrainment by later injections of
magma. 相似文献
8.
Excessive arsenic concentrations above the Argentinean and WHO guidelines for drinking water (10 μg L −1) affects shallow aquifers of the southern Pampean Plain (Argentina) hosted in the Pampean and the Post Pampean formations
(loess and reworked loess; Plio-Pleistocene–Holocene). Health problems related to high As concentrations in drinking waters
are known as Endemic Regional Chronic Hydroarsenicism. Hydrochemistry of shallow groundwaters and soil geochemistry were investigated
aiming to (1) understand the partition of As in the solid phase and its relationship with unacceptable As concentrations in
waters, (2) identify the provision source of As to groundwaters. Only 5% of the samples had As concentrations <10 μg L −1; in 27% As concentrations ranged from 10 to 50 μg L −1 and in 58% it reached 60–500 μg L −1. The coarse fraction (50–2,000 μm) hosts about 27% of the total As in the solid phase, being positively correlated to Ba
( p < 0.01; r
2 = 0.93). About 70% is included in the <2 μm fraction and had positive correlations of As–Fe ( p < 0.05; r
2 = 0.85) and As–Cr ( p < 0.05; r
2 = 0.68). Soils and sediment sand fractions of vadose zones are the primary sources of As in shallow groundwater while adsorption–desorption
processes, codisolution–coprecipitation, and evaporation during the dry seasons raise As concentrations in waters exceeding
the guideline value for drinking water. 相似文献
9.
Based on shipboard and satellite observations, the characteristics of upwelling in Lake Baikal in the period of direct temperature
stratification have been determined for the first time. Coastal upwellings appear annually under the effect of run-down and
alongshore winds and are traced along the coast to a distance of up to 60–100 km and up to 250 km in North Baikal. Analogous
to the way it occurs in seas, water rises from the depths of 100–200 m (350 m as a maximum) at the velocity of 0.1 × 10 −2−6.5 × 10 −2 cm/s. Divergence in the field of intràbasin cyclonic macrovortices produces upwelling in the Baikal pelagic zone and downwelling
in the vicinity of shores; this lasts from 7 to 88 days and covers the depth interval of 80–300 m in August and up to 400–800
m in early-mid November. The area of upwellings occupies up to 20–60% of the separate basins of the lake. Vertical circulation
of water in the field of pelagic upwellings leads to intensification of coastal currents and to formation of the thermobar
with a heat inert zone in the central part of the lake in November, and this thermobar is not observed in other lakes, at
that. 相似文献
10.
Groundwater vulnerability is a cornerstone in evaluating the risk of groundwater contamination and developing management options
to preserve the quality of groundwater. Based on the professional model (DRASTIC model) and geographical information system
(GIS) techniques, this paper carries out the shallow groundwater vulnerability assessment in the Zhangye Basin. The DRASTIC
model uses seven environmental parameters (depth to water, net recharge, aquifer media, soil media, topography, impact of
vadose zone, and hydraulic conductivity) to characterize the hydrogeological setting and evaluate aquifer vulnerability. According
to the results of the shallow groundwater vulnerability assessment, the Zhangye Basin can be divided into three zones: low
groundwater vulnerability risk zone (risk index <120); middle groundwater vulnerability risk zone (risk indexes 120–140) and
high risk zone (risk index >140). Under the natural conditions, the middle and high groundwater vulnerability risk zones of
the Zhangye Basin are mainly located in the groundwater recharge zones and the important cities. The high, middle and low
groundwater vulnerability risk zones of the Zhangye Basin cover around 17, 21 and 62% of study area, respectively. 相似文献
11.
Subsurface-water flow pathways in three different land-use areas (non-irrigated grassland, poplar forest, and irrigated arable land) in the central North China Plain were investigated using oxygen (18O) and hydrogen (2H) isotopes in samples of precipitation, soils, and groundwater. Soil water in the top 10 cm was significantly affected by both evaporation and infiltration. Water at 10–40 cm depth in the grassland and arable land, and 10–60 cm in poplar forest, showed a relatively short residence time, as a substantial proportion of antecedent soil water was mixed with a 92-mm storm infiltration event, whereas below those depths (down to 150 cm), depleted δ18O spikes suggested that some storm water bypassed the shallow soil layers. Significant differences, in soil-water content and δ18O values, within a small area, suggested that the proportion of immobile soil water and water flowing in subsurface pathways varies depending on local vegetation cover, soil characteristics and irrigation applications. Soil-water δ18O values revealed that preferential flow and diffuse flow coexist. Preferential flow was active within the root zone, independent of antecedent soil-water content, in both poplar forest and arable land, whereas diffuse flow was observed in grassland. The depleted δ18O spikes at 20–50 cm depth in the arable land suggested the infiltration of irrigation water during the dry season. Temporal isotopic variations in precipitation were subdued in the shallow groundwater, suggesting more complete mixing of different input waters in the unsaturated zone before reaching the shallow groundwater. 相似文献
12.
The purpose of this study is to investigate the quality and usage possibility of groundwater in the Çavuşçayı basin and suggest the best water structure for the groundwater use. Results from hydrochemical analyses reveal that groundwater is mostly affected by salty (Na +–Cl −) waters of the Incik Formation and brackish (Ca 2+, Mg 2+–SO
4
2−
) waters of the Bayındır Formation. The Alibaba saltpan discharged (2 l/s) from the Incik Formation is used for salt production. In the basin, salinity risk increases with depth and along the groundwater flow direction. Therefore, shallow water and trenches opened in the alluvium aquifer at the east of the basin were determined to yield suitable water with no Na + and Cl − contamination. Following the heavy rainy period, waters of less salinity and conductivity are possibly used for agriculture. 相似文献
13.
The distribution and intensity of hypoxia (low dissolved oxygen) in estuaries is increasing worldwide due to cultural eutrophication.
This study quantifies the strength of associations between the duration of diel-cycling severe hypoxia (≤2 mg O 2 l −1) in bottom water (∼15 cm above bottom) of a shallow (<2 m) coastal lagoon estuary (Delaware, USA) and abiotic environmental
variables (water temperature, insolation, tide, streamflow, and wind) and predicts the duration of severe hypoxia given different
combinations of these variables. The intensity and spatial extent and dynamics of diel-cycling severe hypoxia events were
defined. Vertical variability in dissolved oxygen (DO) concentration during the daytime was also determined. During the summers
of 2001–2005, bottom DO data were collected for periods of weeks to months at multiple sites using automated sondes. Multiple
linear regression (MLR) and regression tree analysis (RTA) were used to determine the relative importance of the environmental
variables in predicting the number of hours of severe hypoxia per day. Key findings of the study were that severe hypoxia
events of minutes to hours in duration occurred frequently in all four tributaries sampled, primarily between 0200 and 1000
hours. Severe hypoxia duration and diel-cycling amplitudes of DO concentration increased in the up-tributary direction. Hierarchically,
the duration of severe hypoxia was influenced mostly by the mean daily water temperature, then by preceding days’ total insolation,
percentage of morning hours (02:00 to 10:00 a.m.) ebb tide, and daily streamflow. Collectively, the variables examined by the MLR and the RTA approaches accounted for 62%
and 65% of the variability in the duration of severe hypoxia, respectively. RTA demonstrated that daily mean water temperature
above 26.3°C and previous day’s total insolation below 13.6 kW m −2 were associated with the longest lasting severe hypoxic events (9.56 h). The environmental variables and combinations of
conditions that modulate or augment diel-cycling hypoxia presented in this paper enhance understanding of this widespread
and growing phenomenon and provide additional insight regarding the extent to which it can impact food webs in very shallow
estuarine waters that often serve as nursery habitat. 相似文献
14.
Biogeochemical processes occurring near the sediment-water interface of shallow (≈20 m) water sediments lying beneath the Mississippi River plume on the Louisiana shelf were studied using benthic chambers and sediment cores. Three sites were chosen with distinctly different characteristics. One was overlain by oxic water where aerobic respiration dominated organic matter remineralization. The second site was overlain by oxic water but organic matter remineralization was dominated by sulfate reduction. The third site was overlain by hypoxic water and aerobic remineralization was of minor significance. Major differences were observed in the fluxes of CO 2(17–56 mmol m −2 d −1), O 2(2–56 mmol m −2 d −1) and nutrients (e.g., NH 4 +, 2.6–4.2 mmol m −2 d −1) across the sediment-water interface, and the relative importance of different electron acceptors, even though the sites were in close proximity and at nearly the same water depth. Large variations in the efficiency of organic-C burial (3%–51%) were also calculated based on a simplified model of the relationships between the fraction of organic matter remineralized by sulfate reduction and the fraction of sulfide produced that is buried as pyrite. These observations demonstrate the high degree of spatial heterogeneity of benthic biogeochemistry in this important near-deltaic environment. 相似文献
15.
Fish-habitat relationships on the shallow inner continental shelf were quantified with video sled and metered beam trawl on
Fenwick and Weaver shoals offshore of Maryland and Delaware, U.S. These areas provide megascale physical relief and habitat
complexity, but for juvenile fishes, mesoscale and microscale habitat is very important particularly as refuge from predation.
At these smaller scales, much of the relief on the inner continental shelf is contributed by bedforms or sand waves and biogenic
structures such as tubes, shell beds, or pits. A quantitative association for juvenile fishes between and within benthic habitats
was found and related primarily to bedform size and amount of biogenic structure. The incidence of fishes was about four-times
higher for large bedforms (> 30 cm wavelength and about 10 cm crest height) relative to smaller bedforms (<30 cm wavelength
and about 5 cm crest height). For biogenic structure, going from high patch-mat tube densities to lower densities or no biogenic
structure increased fish incidence by 5.4 and 3.3 times, respectively. The significant relationships of fishes with bedform
size and density of biogenic structure indicated that seemingly small differences in physical structure of a habitat can make
the difference between unacceptable and essential habitat for juvenile fishes. Proximity of complex and simple habitats was
important in the diel use of habitat and in balancing pressure of refuge from predation provided by complex habitats with
foraging for increased resources available in simpler habitats. During the day, spatially complex habitats comprised of Diopatra and Asabellides tube mats had about twice as many fishes relative to bare sandy habitats (8.3–9.9 versus 4.0–4.1 fishes 100 m −2, respectively). At night, the pattern was reversed with more fishes present in the bare sandy habitats (12.4–13.5 versus
5.6–8.7 fishes 100 m −2). Some fish, such as Ammodytes spp., were very habitat specific and occurred only on dynamic coarser sands near the top of the shoals. Others, such as Urophycis regia, showed less habitat preference and occurred in all habitats during both day and night. Combining the effects of physical
relief and biogenics, the habitat with the highest incidence of fishes had large bedforms with some biogenic structure. More
emphasis needs to be placed on quantifying the relationship between fishes and their habitats for the fisheries management
concept of essential fish habitat to develop into an effective tool on the inner continental shelf. The juvenile life history
stages need to be emphasized because fish-habitat interactions are the strongest for these stages and may be the most ecologically
important. 相似文献
16.
According to the field experiment in the sodic saline soil region in the Songnen Plain, the dynamics of the soil water and
solute affected by the shallow groundwater were explored during the growing season in 2004. The results presented that, influenced
by the strongly evaporative demand, the soil water tended to transport to the upper soil layer with salt. The layered soil
water balance model (LSWB model) revealed that the ratio of the water exchange between the groundwater and upper layer of
the soil was 11.7:1. The groundwater discharge was 53.86 mm, but the groundwater recharge from the upper layer of soil was
only 5.04 mm from 11 July to 06 September, which indicated that the groundwater could discharge to upper layer of soil and
influence the soil salinization through capillary rise. The observed values of the salt content from July to mid-October presented
that the soil solute was more changeable influenced by the climatic condition at 30 cm depth. As the field saturated hydraulic
conductivity was low, the salts mainly accumulated in about 50–70 cm depth soil layer and hardly leached into deeper soil
layer. Furthermore, the salt content was mainly controlled by the groundwater in the subsoil below 100 cm depth, the salt
content decreased with the groundwater level receding. As influenced by the shallow groundwater and freeze-thaw action, further
studies should be performed on the mechanism of soil salinization in the sodic saline soil region in the Songnen Plain of
China. 相似文献
17.
Palaeoclimate and palaeoecological study was carried out using palynological and thecamoebian evidences buried in ∼4 m vertically
exposed sediment section (12 km inland from the present shoreline) of Late Holocene age along the banks of Gautami-Godavari
River and from three shallow cores from its Nilarevu tributary, Andhra Pradesh. Inferred climatic periods include (1) a basal
cold/arid period (∼3000-2000 yrs BP) with dominance of Botryococcus and other fresh water algal remains coupled with abundance of 25 species of thecamoebians indicating shallow and lentic ecosystem
during most of the period and (2) a relatively warm/wet conditions (since ∼2000 yrs BP) reveal lotic fresh water ecosystem
characterized by the evidences of tree palynotaxa and low percentage of thecamoebians. The three shallow cores (0.5–1 m) near
the mouth (∼8 km stretch) of the Nilarevu tributary reveal fluvio-marine deposition in the top 50–80 cm sediment unlike the
deeper fresh water depositional environment suggesting sea water ingression in the recent decades. The study illustrates that
the Gautami-Godavari River delta gradually prograded since ∼3000 yrs BP until 100–150 yrs unlike the intermittent relative
sea level rise and fall recorded during the same period in the contemporary south-east deltaic areas. 相似文献
18.
Total nitrogen (TN), total phosphorus (TP), and total suspended solids (TSS) loadings [log (kg ha −1 yr −1)] were regressed against seagrass depth limits (percent of depth-limit targets) to back-predict the load limits or allocations
(kg ha −1 yr −1 or kg yr −1) necessary to meet targeted seagrass depth limits in the Indian River and Banana River (IRBR) lagoons, Florida. Because the
load allocations can be applied as total maximum daily loads (TMDL) for the IRBR (U.S. Environmental Protection Agency mandate),
the method and results are developed and presented toward that end. The regression analyses indicate that the range of surface-discharge
load limits (nonpoint + point source), per watershed area, required to achieve the desired depth limits for seagrass in the
IRBR are approximately 2.4–3.2 kg ha −1 yr −1 TN, 0.41–0.64 kg ha −1 yr −1 TP, and 48–64 kg ha −1 yr −1 TSS. This simple regression method may have application to other shallow estuarine lagoons or bays where seagrass growth
is limited by light and water transparency, water transparency is strongly affected by watershed pollutant loadings, water
residence times are sufficiently long to allow seagrass coverage to respond to and covary with total load inputs, and multiyear
monitoring has yielded sufficient variability in both pollutant loadings and seagrass coverages to develop a statistically
meaningful relationship. 相似文献
19.
According to the characteristics of groundwater in arid area, this paper proposes DRAV model for groundwater vulnerability
assessment, where D is groundwater depth, R is the net recharge of aquifer, A is the aquifer characteristics, and V is the lithology of vadose zone. As a case study, the paper assesses the vulnerability of pore phreatic water in Tarim Basin
of Xinjiang, China by using the DRAV model. The results indicate that the areas of phreatic water with vulnerability index
ranges of 2–4, 4–6, 6–8 and >8 accounting for 10.1, 80.4, 9.2 and 0.2% of the total plain area of the Tarim Basin respectively,
and the areas with the latter two vulnerability ranges (6–8 and >8) are mainly located in the irrigation districts with thin
soil layer (20–30 cm thick surface soil of vadose zone, mainly with underlying sandy gravel) and with silty and fine sand
layer. Such vadose zone generally lacks sandy loam and clayey soil and has larger recharge by infiltration of irrigation water. 相似文献
20.
The Laguna Madre of South Texas is a shallow coastal lagoon whose dominant primary producers shifted from seagrasses to phytoplankton with the onset of the Texas brown tide, which persisted from 1990 through 1997. Acartia tonsa is the dominant component of the mesozooplankton and forms an important link in both the phytoplankton and detritus-based pelagic food webs. Stable carbon isotope ratios of A. tonsa, as well as the two major primary producers: phytoplankton (as particulate organic carbon) and seagrasses, were measured from March 1989 to October 1991. Zooplankton samples were collected at four locations in the Laguna Madre: two in shallow water (c. 1 m) over seagrass beds and two in slightly deeper water (c. 2–3 m) over a muddy bottom in a secondary bay without seagrasses. We found seasonal trends in the isotopic composition of A. tonsa collected within both habitats as well as distinct differences between the average {ie995-1} values of individuals collected in the two regions. Isotopic ratios of animals collected during the summer months were generally 4–8‰ enriched in 13C compared with those collected in the winter, at all stations. A. tonsa collected over seagrass beds were 2–5‰ more enriched in 13C than those collected over muddy bottoms. These observations suggest carbon derived from seagrasses can be an important source of nutrition for these copepods in summer, especially for copepods living over seagrass beds. The effects of the persistent brown tide decreased the contribution of seagrasses as a carbon source for A. tonsa during the summer of 1991. The pathway by which seagrass carbon enters the diet of A. tonsa is unclear, but the two pathways considered most likely are through copepods feeding on microzooplankton that have fed on bacteria nourished on seagrass carbon, or by copepods feeding directly on particles of seagrass detritus. 相似文献
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