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1.
Combined subsidence and thermal 1D modelling was performed on six well-sections located in the north-western Mid-Polish Trough/Swell
in the eastern part of the Central European Basin system. The modelling allowed constraining quantitatively both the Mesozoic
subsidence and the magnitude of the Late Cretaceous–Paleocene inversion and erosion. The latter most probably reached 2,400 m
in the Mid-Polish Swell area. The modelled Upper Cretaceous thickness did not exceed 500 m, and probably corresponded to 200–300 m
in the swell area as compared with more than 2,000 m in the adjacent non-inverted part of the basin. Such Upper Cretaceous
thickness pattern implies early onset of inversion processes, probably in the Late Turonian or Coniacian. Our modelling, coupled
with previous results of stratigraphic and seismic studies, demonstrates that the relatively low sedimentation rates in the
inverted part of the basin during the Late Cretaceous were the net result of several discrete pulses of non-deposition and/or
erosion that were progressively more pronounced towards the trough axis. The last phase of inversion started in the Late Maastrichtian
and was responsible for the total amount of erosion, which removed also the reduced Upper Cretaceous deposits. According to
our modelling results, a Late Cretaceous heat-flow regime which is similar to the present-day conditions (about 50 mW/m2) was responsible for the observed organic maturity of the Permian-Mesozoic rocks. This conclusion does not affect the possibility
of Late Carboniferous–Permian and Late Permian–Early Triassic thermal events. 相似文献
2.
Sorption Model for Dissolved and Leachable Particulate Aluminium in the Great Ouse Estuary, England 总被引:1,自引:0,他引:1
S. Upadhyay 《Aquatic Geochemistry》2012,18(3):243-262
The behaviour of dissolved Al in the Great Ouse estuary, in particular with respect to salinity, is complex. There is, however,
evidence from field data as well as laboratory mixing experiments to suggest that flocculation and sorption mechanisms play
important roles affecting the concentrations of dissolved Al during the early stages of estuarine mixing. In contrast, a near-buffering
of dissolved Al occurs in the entire stretch of the estuary (salinity >0.2) with concentrations varying around 1.4 μg l−1. This distribution and lack of variation with salinity is attributable to sorption processes which might dominate over other
processes in these turbid estuarine waters (suspended particulate load 48–888 mg l−1) impacting dissolved Al levels. Sorption models have been developed for both dissolved and leachable particulate Al concentrations
in these waters. These observations provide compelling evidence of sorption processes that might be important in the geochemistry
of Al in estuarine waters. 相似文献
3.
The Mono estuary is an infilled, microtidal estuary located on the wave-dominated Bight of Benin coast which is subject to very strong eastward longshore drift. The estuarine fill comprises a thick unit of lagoonal mud deposited in a ‘central basin’between upland fluvial deposits and estuary-mouth wave-tide deposits. This lagoonal fill is capped by organic-rich tidal flat mud. In addition to tidal flat mud, the superficial facies overlying the ‘central basin’fill include remnants of spits resting on transgressive/washover sand, an estuary-mouth association of beach, shoreface, flood-tidal delta and tidal inlet deposits, and a thin sheet of fluvial sediments deposited over tidal flat mud. After an initial phase of spit intrusion over the infilled central basin east of the present Mono channel, the whole estuary mouth became bounded by a regressive barrier formed from sand supplied by the Volta Delta during the middle Holocene eustatic highstand. Barrier progradation ceased late in the Holocene following the establishment of an equilibrium plan-form shoreline alignment that allowed through-drift of Volta sand to sediment sinks further downdrift. Over the same period, accretion, from fluvially supplied sediments, of the estuarine plain close to the limit of spring high tides, or, over much of the lower valley, into a fluvial plain no longer subject to tidal flooding, induced marked meandering of the Mono and its tidal distributaries in response to confinement of much of the tidal prism to these channels. The process resulted in erosion of spit/washover and regressive barrier sand, and in reworking of the tidal flat and floodbasin deposits. The strong longshore drift, equilibrium shoreline alignment and the year-round persistence of a tidal inlet maintained by discharge from the Mono and from Lake Ahémé have resulted in a stationary barrier that is reworked by a mobile inlet. The Mono example shows that advanced estuarine infill may result in considerable facies reworking, obliteration of certain facies and marked spatial imbrication of fluvial, estuarine and wave-tide-deposited facies, and confirms patterns of sedimentary change described for microtidal estuaries on wave-influenced coasts. In addition, this study shows that local environmental factors such as sediment supply relative to limited accommodation space, and strong longshore drift, which may preclude accumulation of sediments in the vicinity of the estuary mouth, may lead to infilled equilibrium or near-equilibrium estuaries that will not necessarily evolve into deltas. 相似文献
4.
Jeremy M. Testa W. Michael Kemp Walter R. Boynton James D. Hagy III 《Estuaries and Coasts》2008,31(6):1021-1037
We conducted a quantitative assessment of estuarine ecosystem responses to reduced phosphorus and nitrogen loading from sewage
treatment facilities and to variability in freshwater flow and nonpoint nutrient inputs to the Patuxent River estuary. We
analyzed a 19-year dataset of water quality conditions, nutrient loading, and climatic forcing for three estuarine regions
and also computed monthly rates of net production of dissolved O2 and physical transport of dissolved inorganic nitrogen (DIN) and phosphorus (DIP) using a salt- and water-balance model.
Point-source loading of DIN and DIP to the estuary declined by 40–60% following upgrades to sewage treatment plants and correlated
with parallel decreases in DIN and DIP concentrations throughout the Patuxent. Reduced point-source nutrient loading and concentration
resulted in declines in phytoplankton chlorophyll-a (chl-a) and light-saturated carbon fixation, as well as in bottom-layer O2 consumption for upper regions of the estuary. Despite significant reductions in seaward N transport from the middle to lower
estuary, chl-a, turbidity, and surface-layer net O2 production increased in the lower estuary, especially during summer. This degradation of water quality in the lower estuary
appears to be linked to a trend of increasing net inputs of DIN into the estuary from Chesapeake Bay and to above-average
river flow during the mid-1990s. In addition, increased abundance of Mnemiopsis leidyi significantly reduced copepod abundance during summer from 1990 to 2002, which favored increases in chl-a and allowed a shift in total N partitioning from DIN to particulate organic nitrogen. These analyses illustrate (1) the value
of long-term monitoring data, (2) the need for regional scale nutrient management that includes integrated estuarine systems,
and (3) the potential water quality impacts of altered coastal food webs. 相似文献
5.
Vertical accretion rates and heavy metal chronologies in wetland sediments of the Tijuana Estuary 总被引:3,自引:0,他引:3
This study represents the first report on sediment accretion rates using137Cs dating for a southern California salt marsh. Vertical accretion rates ranged from 0.7 to 1.2 cm yr−1, which is at the high end of sediment accretion values for coastal wetlands. This has lead to increases in elevation within the estuary from 18 to 35 cm over the last 35 years. Depth profiles of metal concentrations were converted to time-based profiles using vertical accretion rates. Chronologies for most cores indicate a consistent peak in sediment lead (Pb) concentrations in the early to mid 1980s, corresponding to the historic decline in Pb use, which was completed in the U.S. by the early 1980s, but not begun in Mexico until 1991. Sediment Pb levels ranged from about 6–56 μg g−1. Other metals did not show any consistent trends in sediment chronology, except for a single core from a mid-marsh site (east-mid 2), which showed a 2–3-fold increase in levels of Cu, Ni, and Zn during the past two decades. Sediment levels of copper (Cu), nickel (Ni), and zinc (Zn) ranged from 6–34 μg g−1, 11–27 μg g−1, and 42–122 μg g−1, respectively. Despite rapid industrial development of the watershed, a comparison of the sediment metal concentrations in the Tijuana Estuary to other anthropogenically-impacted estuaries in the United States and Europe, shows that metal levels in sediments of the north arm of the estuary are relatively low. 相似文献
6.
Geochemistry of Cu, Co, Ni, Zn, Cd and Cr in the surficial sediments of a tropical estuary, southwest coast of India: a granulometric approach 总被引:3,自引:0,他引:3
Geochemical characteristics of six trace metals – Cu, Co, Ni, Zn, Cd and Cr – in the bulk sediment and sand, silt and clay
fractions of a tropical estuary on the southwest coast of India have been studied and discussed. In bulk sediment, the trace
metal concentration is controlled mainly by the textural composition of the sample. Mud, sandy mud and sandy silt register
higher concentrations of trace metals than that in sand-dominant sediments. The granulometric partitioning studies also re-affirmed
the role of particle size in enriching the trace metals. The silt and clay fractions exhibit 7–8 times the enrichment of Cu
and Cd compared to that in sand. The enrichment factors of Zn, Cr, Ni and Co in the silt and clay fractions, compared to that
in sand, are 5–6, 4–5, 2–5 and 2–3 times, respectively. The trace metals in the sand fraction, particularly Ni and Cr, exhibit
strong positive correlation with the heavy mineral content of the samples. It clearly indicates a heavy mineral pathway to
the trace metals in the sand fraction. Cu and Co in silt and clay fractions exhibit a marked decrease towards the high saline
zones of the estuary. This is attributed to the desorption of Cu and Co from particulate phases during estuarine mixing. Contrary
to Cu and Co, the content of Zn in the clay fraction shows a marginal increase towards the estuarine mouth. This could be
explained by the influx of Zn-rich contaminant discharges from Zn-smelting industries located slightly north of the estuarine
mouth. The released Zn will effectively be held in the lattices of the clay mineral montmorillonite, which also exhibits a
marked increase towards the estuarine mouth. The anomalously high values of Cd in some places of the Central Vembanad estuary
is attributed to the local pollution.
Received: 10 July 1995 · Accepted: 3 June 1996 相似文献
7.
Koen de Jong Chikao Kurimoto Gilles Ruffet 《International Journal of Earth Sciences》2009,98(6):1529-1556
The 218.4 ± 0.4, 228.8 ± 0.9 and 231.9 ± 0.7 Ma 40Ar/39Ar laser probe pseudo-plateau ages (2σ; 49–63% 39Ar-release) of very low-grade meta-pelitic whole-rocks from the Sakaigawa unit date high-P/T metamorphism. We argue that this
event occurred in a subduction–accretion complex, not along the East Asian continental margin, but on the Pacific side of
the proto-Japan superterrane. Proto-Japan was a Permian magmatic arc, presently dispersed in the Japanese islands, which also
contained older subduction–accretion complexes. The arc system was fringing but not yet part of the Eurasian continent. The
Middle to Late Triassic high-P/T tectono-metamorphic event was partly coeval with proto-Japan’s collision with proto-Eurasia
along the southward extension of the Central Asian Orogenic Belt, causing the main metamorphism in the Hida-Oki terrane. It
is possible that this system continued via the Cathaysia block (China) to Indochina. The Late Permian to Middle Triassic Indosinian
event might stem from docking of Pacific-derived terranes with Southeast Asia’s continental margin. The concept of the proto-Japan
superterrane implies that the Qinling-Dabie-Sulu suture zone joined the Central Asian Orogenic Belt to the east of the North
China craton and did not continue to Japan, as commonly assumed. 相似文献
8.
Macrofaunal Spatial Patterns in Relationship to Environmental Variables in the Richibucto Estuary,New Brunswick,Canada 总被引:1,自引:0,他引:1
Estuarine macrobenthos respond to a variety of environmental gradients such as sediment type and salinity, and organic enrichment.
A relatively new influence, organic loading from suspended bivalve culture, has the potential to alter this response. A study
on soft-bottom macrobenthic communities was carried out in the Richibucto estuary (46°40′N, 64°50′W), New Brunswick, Canada,
with samples collected from 18 stations in late September and early October 2006. The site consisted of a large tidal channel
originating upstream in a small river. The channel was punctuated by bag culture of oysters along its length. A total of 88
species were recorded. The mean values of abundance, species richness, and diversity (H′) of macrofauna were 11,199 ind. m−2 (ranged from 4,371 to 19,930 ind. m−2), 23.4 species grab−1 and 3.29 grab−1, respectively. In general species richness and H′ increased from the upper estuary to the estuarine mouth. Multivariate analyses clearly exhibited the spatial distribution
in community structure, which coincided with the locations along the estuary (the upper, the lower and the mouth), as well
as inside and outside the channel. Species richness and diversity H′ showed strong positive correlations with salinity (21.2–25.2 ppt), and abundance was positively correlated with water depth
(1.0–4.5 m). Abundance and species richness were negatively correlated with both of silt–clay fraction (3.3–24.8%) and sorting
(σI). Species richness was also negatively correlated with organic content (1.9–12.7%). The BIO-ENV analyses identified silt–clay
fraction, σI and salinity as the major environmental variable combination influencing the macrofaunal patterns, and silt–clay fraction
as the single best-correlated variable. 相似文献
9.
Edward Castañeda-Moya Robert R. Twilley Victor H. Rivera-Monroy Keqi Zhang Stephen E. DavisIII Michael Ross 《Estuaries and Coasts》2010,33(1):45-58
The distribution of mangrove biomass and forest structure along Shark River estuary in the Florida Coastal Everglades (FCE)
has been correlated with elevated total phosphorus concentration in soils thought to be associated with storm events. The
passage of Hurricane Wilma across Shark River estuary in 2005 allowed us to quantify sediment deposition and nutrient inputs
in FCE mangrove forests associated with this storm event and to evaluate whether these pulsing events are sufficient to regulate
nutrient biogeochemistry in mangrove forests of south Florida. We sampled the spatial pattern of sediment deposits and their
chemical properties in mangrove forests along FCE sites in December 2005 and October 2006. The thickness (0.5 to 4.5 cm) of
hurricane sediment deposits decreased with distance inland at each site. Bulk density, organic matter content, total nitrogen
(N) and phosphorus (P) concentrations, and inorganic and organic P pools of hurricane sediment deposits differed from surface
(0–10 cm) mangrove soils at each site. Vertical accretion resulting from this hurricane event was eight to 17 times greater
than the annual accretion rate (0.30 ± 0.03 cm year−1) averaged over the last 50 years. Total P inputs from storm-derived sediments were equivalent to twice the average surface
soil nutrient P density (0.19 mg cm−3). In contrast, total N inputs contributed 0.8 times the average soil nutrient N density (2.8 mg cm−3). Allochthonous mineral inputs from Hurricane Wilma represent a significant source of sediment to soil vertical accretion
rates and nutrient resources in mangroves of southwestern Everglades. The gradient in total P deposition to mangrove soils
from west to east direction across the FCE associated with this storm event is particularly significant to forest development
due to the P-limited condition of this carbonate ecosystem. This source of P may be an important adaptation of mangrove forests
in the Caribbean region to projected impacts of sea-level rise. 相似文献
10.
This study examined freshwater discharge of dissolved organic matter (DOM) to the shallow Lavaca–Matagorda (LM) Bay estuarine
system along the central Texas coast and investigated whether chromophoric DOM (CDOM) photochemical reactions have the potential
to stimulate microbial activity within LM estuarine waters. Dissolved organic carbon (DOC) concentrations ranged from 3 to
10 mg C l−1 and CDOM levels (reported as a
305) ranged from 8 to 77 m−1 during April and July, 2007, when the LM system was experiencing very high freshwater inputs. DOC and CDOM levels were well-correlated
with salinities > 3, but exhibited considerable variability at salinities < 3. CDOM photobleaching rates (i.e., decrease in
a
305 resulting from exposure to solar radiation) for estuarine samples ranged from 0.014 to 0.021 h−1, corresponding to photobleaching half-lives of 33–50 h. Our data indicate when Matagorda Bay waters photobleach; dissolved
organic carbon utilization is enhanced perhaps due to enhanced microbial respiration of biologically labile photoproducts
(BLPs). Net ecosystem metabolism calculations indicate that most of the LM system was net heterotrophic during our study.
We estimate that BLP formation could support up to 20% of the daily microbial respiratory C demand in LM surface waters and
combined with direct photochemical oxygen consumption could have an important influence on O2 cycles in the LM system. 相似文献
11.
Michael S. Johnson David Copplestone Winston M. Fox Steve R. Jones 《Estuaries and Coasts》2001,24(2):198-203
The radionuclide burden of vegetation comprising a tide-washed pasture at Ince Marsh in the Mersey Estuary, U.K., derives mainly from adhered external particulates originating as suspended sediments in estuarine water. Radionuclide concentrations are dominated by the growth cycle of the vegetation, with the highest winter levels of contamination activity an order of magnitude greater than the lowest levels in mid-summer. A secondary effect due to sediment transfer during periods of severe flooding produces subsidiary features on this dominant seasonal profile. Radionuclide concentrations on vegetation are in the range137Cs=8–191,134Cs=0.3–0.9,241Am=0.6–46,238Pu=0.1–1.5, and239/240Pu=0.8–44 Bq kg−1. These ranges reflect the relative concentrations of radionuclides in estuarine sediment (137Cs=615,241Am=202, and239/240Pu=104 Bq kg−1) rather than the values in filtered estuary water (137Cs=0.4,241Am=0.001, and239/240Pu=0.001 Bq 1−1). Median Kd values for these radionuclide species are Cs=1,400, Am=200,000, and Pu=80,000 1 kg−1). 相似文献
12.
An ephemeral estuarine turbidity maximum (ETM) occurs at high water in the macrotidal Taf estuary (SW Wales, United Kingdom).
A new mechanism of ETM formation, due to resuspension and advection of material by flood tidal currents, is observed that
differs from classical mechanisms of gravitational circulation and tidal pumping. The flood tide advances across intertidal
sand flats in the main body of the estuary, progressively entraining material from the rippled sands. Resuspension creates,
a turbid front that has suspended sediment concentrations (SSC) of about 4,000 mg I−1 by the time it reaches its landward limit which is also the landward limit of salt penetration. This turbid body constitutes
the ETM. Deposition occurs at high slack water but the ETM retains SSC values up to 800 mg I−1, 1–2 orders of magnitude greater than ambient SSC values in the river and estuarine waters on either side. The ETM retreats
down the estuary during the ebb; some material is deposited thinly across emergent intertidal flats and some is flushed out
of the estuary. A new ETM is generated by the next flood tide. Both location and SSC of the ETM scale on Q/R3 where Q is tidal range and R is river discharge. The greatest expression of the ETM occurs when a spring tide coincides with
low river discharge. It does not form during high river discharge conditions and is poorly developed on neap tides. Particles
in the ETM have effective densities (120–160 kg m−3) that are 3–4 times less than those in the main part of the estuary at high water. High chlorophyll concentrations in the
ETM suggest that flocs probably originate from biological production in the estuary, including production on the intertidal
sand flats. 相似文献
13.
Aerial photographs taken in the 1963 and 2001 and bathymetric charts, in conjunction with coastal processes are analyzed to assess changes in rate of shoreline position, seabed level, and seabed grain sizes along the Tabarka–Berkoukech beach at the north-western Tunisian coastline. The littoral cell of this beach, 12-km-long, is bounded by pronounced embayments and rocky headlands separated by sandy stretches. Although not yet very much undeveloped, this littoral is still experienced degradation and modification, especially along its shoreline, with significant coastal erosion at some places. Results obtained from analysis of shoreline position indicate that El Morjene Beach is experienced a landward retreat of more than −62 m, at a maximum rate of −1.64 m/year, whereas the El corniche beach is advanced about 16–144 m, at an average rate of 0.42 m–3.78 m/year. This beach accretion has been formed on the updrift side of the Tabarka port constructed between 1966 and 1970. Comparison of bottom contours deduced from bathymetric charts surveyed in 1881 and 1996 off the coastline between Tabarka Port and El Morjene Beach identifies erosional areas (sediment source) and accretionary zones (sediment sink). Erosion (0.87–4.35 cm/year) occurs between El kebir River Mouth and El Morjene beach, whereas accretion exists in the zone down wind of the port ranges between 0.87 and 5.21 cm/year. Morphological analyses of the shoreline and the seabed of the study nearshore area indicate that shoreline retreat corresponds to areas of seabed scour (sediment source) while shoreline accretion is associated with areas of seabed deposition (sediment sink). Furthermore, simulation of wave propagation using STWAVE model combined with grain size distributions of the seabed shows that fine sands are much dominated in depositional areas with low wave energy, whereas coarser sands in erosive zones with high wave energy. The results obtained suggest that the change of seabed morphology, wave height pattern and grain size sediment have a great influence on the modification of shoreline morphology and dynamics. 相似文献
14.
Dissolved and particulate trace metals and their partitioning in a hypoxic estuary: The Tanshui Estuary in Northern Taiwan 总被引:1,自引:0,他引:1
The distribution and partitioning of trace metals (Co, Cu, Fe, Mn, Ni, and Zn) between dissolved and particulate phases were studied in the Tanshui Estuary. The upper reach of the estuary is hypoxic and heavily polluted due to domestic and industrial discharges. The concentration ranges of dissolved and leachable particulate trace metals in the Tanshui Estuary were: Co: 0.3–6.1 nM, 1.8–18.6 mg kg−1; Cu: 5–53 nM, 22–500 mg kg−1; Fe: 388–3,364 nM, 1.08–6.67%; Mn: 57–2,914 nM, 209–1,169 mg kg−1; Ni: 7–310 nM, 6–108 mg kg−1; and Zn: 12–176 nM, 62–1,316 mg kg−1; respectively. The dissolved concentrations of the metals were 2–35 times higher than the average values of the world river water. The distributions of dissolved and particulate studied metals, except Mn, in the estuary showed scattering, which could be attributed to the discharges from many industrial wastewater disposal works located in the upper tributaries. The daily input of dissolved metals from the disposal works to the Tanshui Estuary ranged from 0.1–0.4 tons. Dissolved Mn was nearly conservative in the region with salinity higher than 10 psu, while particulate Mn decreased in the region with salinity of 10–15 psu. The concentration increased significantly seawards, corresponding with the distribution of dissolved oxygen. The distribution coefficient (KD) for Mn in the lower estuary was nearly three orders of magnitude higher than in the upper estuary. This phenomenon may be attributed to the diffusion of Mn from the anoxic sediment in the upper estuary and gradual oxidation into particulate Mn in the middle and lower estuary as the estuarine water became more oxygenated. The distribution coefficient for Cu decreased with increasing salinity. The percentages of trace metals bound by suspended particulate matter decreased in the following order: Fe>Zn, Cu>Co>Mn>Ni. 相似文献
15.
Natural and anthropogenic influences in the northeastern coast of the Nile delta,Egypt 总被引:4,自引:0,他引:4
Landsat enhanced thematic mapper imagery (ETM) of 2002 and aerial photography of 1955, combined with published charts and
field observations were used to interpret coastal changes in the zone between Kitchener drain and Damietta spit in the northeastern
Nile delta, previously recognized as a vulnerable zone to the effects of any sea level rise resulting from global warming.
The interpretation resulted in recognition of several changes in nine identified geomorphological land types: beach and coastal
flat, coastal dunes, agricultural deltaic land, sabkhas, fish farms, Manzala lagoon, saltpans, marshes and urban centers.
Reclamation of vast areas of the coastal dunes and of Manzala lagoon added about 420 km2 to the agricultural deltaic land.
About 48 km2 of backshore flats, marshes, salt pans and Manzala lagoon have been converted to productive fish farms. The main
urban centers have expanded; nearly 12.1 km2 have been added to their areas, and new urban centers (Damietta harbor and the New Damietta city) with total area reach of
~35.3 km2 have been constructed at the expense of vast areas of Manzala lagoon, coastal dunes, and backshore flats. As a consequence
of human activities, the size of Manzala lagoon has been reduced to more than 65%. Shoreline changes have been determined
from beach profile survey (1990–2000), and comparison of 1955 aerial photographs and ETM satellite image of 2002 reveal alongshore
patterns of erosion versus accretion. The short-term rate of shoreline retreat (1990–2000) has increased in the downdrift
side of Damietta harbor (≃14 m/year), whereas areas of accretion exist within the embayment of Gamasa and in the shadow of
Ras El Bar detached breakwaters system, with a maximum shoreline advance of ~15 m/year. A sandy spit, 12 km long, has developed
southeast of Damietta promontory. These erosion/accretion patterns denote the natural processes of wave-induced longshore
currents and sediment transport, in addition, the impact of man-made coastal protection structures. 相似文献
16.
Pradeep K. Rawat P. C. Tiwari C. C. Pant A. K. Sharama P. D. Pant 《Natural Hazards》2011,59(3):1277-1297
Assessment and inventory on soil erosion hazard are essential for the formulation of successful hazard mitigation plans and
sustainable development. The objective of this study was to assess and map soil erosion hazard in Lesser Himalaya with a case
study. The Dabka watershed constitutes a part of the Kosi Basin in the Lesser Himalaya, India, in district Nainital has been
selected for the case illustration. The average rate of erosion hazard is 0.68 mm/year or 224 tons/km2/year. Anthropogenic and geo-environmental factors have together significantly accelerated the rate of erosion. This reconnaissance
study estimates the erosion rate over the period of 3 years (2006–2008) as 1.21 mm/year (398 tons/km2/year) in the barren land having geological background of diamictite, siltstone and shale rocks, 0.92 mm/year (302 tons/km2/year) in the agricultural land with lithology of diamictite, slates, siltstone, limestone rocks, while in the forest land,
it varies between 0.20 mm/year (66 tons/km2/year) under dense forest land having the geology of quartzwacke and quartrenite rocks and 0.40 mm/year (132 tons/km2/year) under open forest/shrubs land having geological setup of shale, dolomite and gypsum rocks. Compared to the intensity
of erosion in the least disturbed dense forest, the erosion rate is about 5–6 times higher in the most disturbed agricultural
land and barren land, respectively. The erosion hazard zones delineated following scalogram modelling approach. Integrated
scalogram modelling approach resulted in severe classes of soil erosion hazard in the study area with numerical values of
Erosion Hazard Index (EHI) ranging between 01 (very low hazard) and 5 (very high hazard). 相似文献
17.
Jean-Clair Duchesne Jean-Paul Liègeois Viorica Iancu Tudor Berza Dmitry I. Matukov Mihai Tatu Sergei A. Sergeev 《International Journal of Earth Sciences》2008,97(4):705-723
The Sichevita and Poniasca plutons belong to an alignment of granites cutting across the metamorphic basement of the Getic
Nappe in the South Carpathians. The present work provides SHRIMP age data for the zircon population from a Poniasca biotite
diorite and geochemical analyses (major and trace elements, Sr–Nd isotopes) of representative rock types from the two intrusions
grading from biotite diorite to biotite K-feldspar porphyritic monzogranite. U–Pb zircon data yielded 311 ± 2 Ma for the intrusion
of the biotite diorite. Granites are mostly high-K leucogranites, and biotite diorites are magnesian, and calcic to calc-alkaline.
Sr, and Nd isotope and trace element data (REE, Th, Ta, Cr, Ba and Rb) permit distinguishing five different groups of rocks
corresponding to several magma batches: the Poniasca biotite diorite (P1) shows a clear crustal character while the Poniasca granite (P2) is more juvenile. Conversely, Sichevita biotite diorite (S1), and a granite (S2*) are more juvenile than the other Sichevita granites (S2). Geochemical modelling of major elements and REE suggests that fractional crystallization can account for variations within
P1 and S1 groups. Dehydration melting of a number of protoliths may be the source of these magma batches. The Variscan basement, a
subduction accretion wedge, could correspond to such a heterogeneous source. The intrusion of the Sichevita–Poniasca plutons
took place in the final stages of the Variscan orogeny, as is the case for a series of European granites around 310 Ma ago,
especially in Bulgaria and in Iberia, no Alleghenian granitoids (late Carboniferous—early Permian times) being known in the
Getic nappe. The geodynamical environment of Sichevita–Poniasca was typically post-collisional of the Variscan orogenic phase. 相似文献
18.
Isotopic Determination of Food Web Origins in Restoring and Ancient Estuarine Wetlands of the San Francisco Bay and Delta 总被引:1,自引:0,他引:1
We compared the extent to which ancient and restoring wetlands in three estuary regions of San Francisco Bay support estuarine
ecosystems through food web contributions. In comparison to mature marshes, we hypothesized that food webs of increasingly
younger restoration sites would display increased dependency upon allochthonous subsidies due to nominal internal production.
Using multiple stable isotopes (δ13C, δ15N, δ34S) in a mixing model, we traced links among primary producers and estuarine consumers. Results indicate that food webs of
estuarine marshes are heavily dependent upon autochthonous marsh materials (76 ± 17%), even within the youngest restoration
marshes (11 years). Nearly all sampled organisms relied upon autochthonous marsh materials, with the exception of Neomysis kadiakensis, a mysid shrimp, which derived the majority of its support from freshwater-produced phytoplankton. Marsh-derived organic
matter (OM) support was consistent both temporally throughout the year and spatially along the three estuary regions, but
evidence suggests that the specific type of OM supporting estuarine consumers depends on position along the estuarine gradient
and on seasonal shifts in freshwater flow. These results indicate that wetland restoration rapidly provides important contributions
to marsh consumers and potentially bolsters food web linkages in shallow-water ecosystems. 相似文献
19.
An Idealized Model and Systematic Process Study of Oxygen Depletion in Highly Turbid Estuaries 总被引:1,自引:0,他引:1
The sensitivity of oxygen depletion in turbid estuaries to parameters like freshwater discharge, depth, and sediment availability
is investigated using an idealized model. The model describes tidally averaged circulation and suspended sediment concentration
(SSC), which are input into an advection–diffusion sink module of dissolved oxygen (DO). Based on the analysis of field data
collected in the Ems estuary, the modeled oxygen depletion rates are proportional to SSC. The model is calibrated to the observed
variation of DO with SSC and temperature. Modeled DO closely tracks changes to the estuarine turbidity zone (ETZ): increased
channel depth, decreased freshwater discharge, and decreased mixing move the ETZ upstream, amplify SSCs, and decrease DO.
Summertime temperatures produce lower DO than cooler periods. Model results are consistent with historical measurements in
the Ems, which indicate that hypoxic events (DO concentrations < 2 mg l−1) have occurred more frequently after deepening from 5 to 7 m. 相似文献
20.
In the Patía River delta, the best-developed delta on the western margin of South America, a major water diversion started in 1972. The diversion of the Patía flow to the Sanquianga River, the latter a small stream draining internal lakes from the Pacific lowlands, shifted the active delta plain from the south to the north and changed the northern estuarine system into an active delta plain. The Sanquianga Mangrove National Park, a mangrove reserve measuring 800 km2, lies in this former estuary, where major hydrologic and sedimentation changes are occurring. Overall, major environmental consequences of this discharge diversion in terms of geomorphic changes along distributary channels and ecological impacts on mangrove ecosystems are evidenced by: (1) distributary channel accretion by operating processes such as sedimentation, overbank flow, increasing width of levees, sedimentation in crevasses, interdistributary channel fill, and colonization of pioneer mangrove; (2) freshening conditions in the Sanquianga distributary channel, a hydrologic change that has shifted the upper estuarine region (salinity <1%) downstream; (3) downstream advance of freshwater vegetation, which is invading channel banks in the lower and mixing estuarine zones; (4) die-off of approximately 5200 ha of mangrove near the delta apex at Bocas de Satinga, where the highest sediment accumulation rates occur; and (5) recurrent periods of mangrove defoliation due to a worm plague. Further analyses indicate strong mangrove erosion along transgressive barrier islands on the former delta plain. Here tectonic-induced subsidence, relative sea-level rise, and sediment starving conditions due to the channel diversion, are the main causes of the observed retreating conditions of mangrove communities. Our data also indicate that the Patía River has the highest sediment load (27 × 106 t yr−1) and basin-wide sediment yield (1500 t km−2 yr−1) on the west coast of South America. Erosion rates from the Patía catchment have been more pronounced during the decades of 1970–1980 and 1990–2000, as a result of land degradation and deforestation. The high sediment and freshwater inputs into the mangrove ecosystem create additional stress (both at ongoing background levels and, occasionally, at dramatic levels), which may periodically push local environmental parameters beyond the thresholds for mangrove survival. The future environmental state of the Sanquianga Mangrove National Reserve deserves more scientific and governmental attention. 相似文献