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1.
Analysis of tidal marsh vegetation patterns in two Georgia estuaries using aerial photography and GIS 总被引:1,自引:0,他引:1
Aerial photographs and GIS analysis were used to map the distribution of tidal marsh vegetation along the salinity gradients
of the estuaries of the Altamaha and Satilla Rivers in coastal Georgia. Vegetation maps were constructed from 1993 U.S. Geological
Survey Digital Orthophoto Quarter Quads, 1∶77,000-scale color infrared photographs taken in 1974 and 1∶24,000-scale black
and white photographs taken in 1953, Changes between years were identified using a GIS overlay analysis. Four vegetation classifications
were identified and groundtruthed with field surveys: salt marsh (areas containing primarilySpartina alterniflora), brackish marsh (Spartina cynosuroides andS. alterniflora), Juncus (Juncus roemerianus), and fresh marsh (Zizania aquatica, Zizaniopsis miliacae, and others). There was no evidence for an upstream shift in marsh vegetation along the longitudinal axis of either estuary
over the time frame of this analysis, which implies there has not been a long-term increase in salinity. Although the inland
extent of each marsh zone was further upstream in the Satilla than the Altamaha, they corresponded to similar average high
tide salinities in each estuary: areas classified as salt marsh occurred from the mouth up to where average high tide salinity
in the water was approximately 15 psu;Juncus ranged from 21 to 1 psu; brackish marsh ranged from 15 to 1 psu; and fresh marsh was upstream of 1 psu. Approximately 63%
of the 6,786 ha of tidal marsh vegetation mapped in the Altamaha and 75% of the 10,220 ha mapped in the Satilla remained the
same in all 3 yr.Juncus was the dominant classification in the intermediate regions of both estuaries, and shifts between areas classified asJuncus and either brackish or salt marsh constituted the primary vegetation change between 1953 and 1993 (87% of the changes observed
in the Altamaha and 95% of those in the Satilla). This analysis suggests that the broad distribution of tidal marsh vegetation
along these two estuaries is driven by salinity, but that at the local scale these are dynamic systems with a larger number
of factors affecting the frequently changing borders of vegetation patches. 相似文献
2.
Mirela G. Tulbure Dana M. Ghioca-Robrecht Carol A. Johnston Dennis F. Whigham 《Estuaries and Coasts》2012,35(5):1353-1359
Nonnative Phragmites is among the most invasive plants in the U.S. Atlantic coast tidal wetlands, whereas the native Phragmites has declined. Native and nonnative patches growing side by side provided an ideal setting for studying mechanisms that enable nonnative Phragmites to be a successful invader. We conducted an inventory followed by genetic analysis and compared differences in growth patterns and ventilation efficiency between adjacent native and nonnative Phragmites stands. Genetic analysis of 212 patches revealed that only 14 were native suggesting that very few native Phragmites populations existed in the study area. Shoot density decreased towards the periphery of native patches, but not in nonnative patches. Ventilation efficiency was 300?% higher per unit area for nonnative than native Phragmites, likely resulting in increased oxidation of the rhizosphere and invasive behavior of nonnative Phragmites. Management of nonnative Phragmites stands should include mechanisms that inhibit pressurized ventilation of shoots. 相似文献
3.
Donald P. Hauber Kristin Saltonstall David A. White Craig S. Hood 《Estuaries and Coasts》2011,34(4):851-862
Multiple introductions are believed to play an important role in increasing genetic diversity and adaptability of invasive
species, but there are few well-documented examples. The common reed, Phragmites australis, has dramatically increased in tidal wetlands throughout the USA in the past century due primarily to the introduction of
a Eurasian lineage. In the Mississippi River “Balize” delta, P. australis is the dominant vegetation where monotypic stands of an introduced form blanket the outer marshes. The delta’s interior marshes,
on the other hand, are more vegetatively diverse, serving as important waterfowl foraging habitat. Recent encroachment by
various phenotypic forms of P. australis into the interior marshes led to this study examining genetic variation in these stands. Our results revealed four chloroplast
DNA haplotypes that also segregate based on microsatellite variation. Three of these are closely related and introduced, but
differ relative to time and likely mode of introduction. The “Delta” type (haplotype M1), which is unique to the region and
the most common lineage, displays considerable microsatellite diversity. The Eurasian introduced lineage of P. australis (haplotype M), which is invasive elsewhere in North America, is increasing its distribution in the delta. A novel haplotype,
AD, was also identified which is phenotypically and genetically similar to haplotype M. Despite the close relatedness, we
found no evidence for inter-haplotype gene exchange at the nuclear level, suggesting that intraspecific hybridization is not
a contributing factor to these invasions. The site provides a unique opportunity for researchers to understand the dynamics
of multiple P. australis invasions. 相似文献
4.
We conducted a laboratory experiment to quantify nutrient (nitrogen and phosphorus) limitation of macroalgae collected along
a gradient in water column nutrient availability in Upper Newport Bay estuary, a relatively nutrient-rich system in southern
California, United States. We collectedEnteromorpha intestinalis and water for use in the experiment from five sites ranging from the lower end of the estuary to the head. Initial algal
tissue N and P concentrations and molar N∶P ratios—as well as water column NO3 and total Kjeldahl nitrogen (TKN)—increased along a spatial gradient from the lower end toward the head. Water column soluble
reactive phosphorus (SRP) varied among sites as well but did not follow a pattem of increasing from the seaward end toward
the head. Algae from each site were assigned to one of four experimental treatments: control (C), nitrogen enrichment (+N),
phosphorus enrichment (+P), and nitrogen and phosphorus enrichment (+N+P). Each week for 3 wk we replaced the water in each
unit with the appropriate treatment water to mimic a poorly flushed estuary. After 3 wk, the degree of nutrient limitation
ofE. intestinalis varied spatially with distance from the head of the estuary. Growth ofE. intestinalis collected from several sites increased with N enrichment alone and increased further when P was added in combination with
N This indicated that N was limiting and that when N was sufficient, P became limiting. Sites from whichE. intestinalis exhibited nutrient limitation spanned the range of background water column NO3 (12.9±0.4 to 55.2±2.1 μM) and SRP (0.8±0.0 to 2.9±0.2 μM) concentrations. Algae that were N limited had initial tissue N
levels ranging from 1.18±0.03 to 2.81±0.08% dry weight and molar N∶P ratios ranging from 16.75±0.39 to 26.40±1.98. 相似文献
5.
Possible long-term seismic behaviour of the Northern strand of the North Anatolian Fault Zone, between western extreme of
the 1999 İzmit rupture and the Aegean Sea, after 400 AD is studied by examining the historical seismicity, the submarine fault
mapping and the paleoseismological studies of the recent scientific efforts. The long-term seismic behaviour is discussed
through two possible seismicity models devised from M
S ≥ 7.0 historical earthquakes. The estimated return period of years of the fault segments for M1 and M2 seismic models along
with their standard deviations are as follows: F4 segment 255 ± 60 and 258 ± 12; F5 segment 258 ± 60 and 258 ± 53; F6 segment
258 ± 60 and 258 ± 53; F7 segment 286 ± 103 and 286 ± 90; F8 segment 286 ± 90 and 286 ± 36. As the latest ruptures on the
submarine segments have been reported to be during the 1754–1766 earthquake sequence, and the 1912 mainshock rupture has been
evidenced to extend almost all over the western part of the Sea of Marmara, our results imply imminent seismic hazard and,
considering the mean recurrence time, a large earthquake to strike the eastern part of the Sea of Marmara in the next two
decades. 相似文献
6.
Christine L. Weilhoefer Walter G. Nelson Patrick Clinton David M. Beugli 《Estuaries and Coasts》2013,36(2):377-389
We investigated whether within wetland environmental conditions or surrounding land cover measured at multiple scales were more influential in structuring regional vegetation patterns in estuarine tidal wetlands in the Pacific Northwest, USA. Surrounding land cover was characterized at the 100, 250, and 1,000 m, and watershed buffer scales. Vegetation communities were characterized by high species richness, lack of monotypic zonation, and paucity of invasive species. The number of species per site ranged between 4 and 20 (mean?±?standard deviation?=?10.2?±?3.1). Sites supported a high richness (mean richness of native species 8.7?±?2.8) and abundance of native macrophytes (mean relative abundance 85 %?±?19 %). Vegetation assemblages were dominated by a mix of grasses, sedges, and herbs with Sarcocornia pacifica and Distichlis spicata being common at sites in the oceanic zone of the estuary and Carex lyngbyei and Agrostis stolonifera being common at the fresher sites throughout the study area. The vegetation community was most strongly correlated with salinity and land cover within close proximity to the study site and less so with land cover variables at the watershed scale. Total species richness and richness of native species were negatively correlated with the amount of wetland in the buffer at all scales, while abundance of invasive species was significantly correlated to within wetland factors, including salinity and dissolved phosphorus concentrations. Landscape factors related to anthropogenic disturbances were only important at the 100-m buffer scale, with anthropogenic disturbances further from the wetland not being influential in shaping the vegetation assemblage. Our research suggests that the traditional paradigms of tidal wetland vegetation structure and environmental determinants developed in east coast US tidal wetlands might not hold true for Pacific Northwest wetlands due to their unique chemical and physical factors, necessitating further detailed study of these systems. 相似文献
7.
In 2001 and 2002, Georgia salt marshes experienced a dieback event that, affected more than 800 ha throughout the coastal
zone. The dieback event was unprecedented in the state and affected bothSpartina alterniflora andJuncus roemerianus. A transplant study was conducted from May to October 2003 to determine if healthy plants could survive in dieback areas.
Transplants were carried out at two locations on the Georgia coast in areas ofS. alterniflora dieback along the banks of tidal creeks, an area ofS. alterniflora dieback in the mid marsh, and aJ. roemerianus dieback, area in the mid marsh. Transplant survival was nearly 100% and growth (measured as increases in the height of the
5 tallest stems and the number of stems per experimental pot) was observed in both healthy (control) and dieback areas.J. roemerianus grew more slowly thanS. alterniflora, with no, observed increase in stem height and an average 38% increase in stem density as compared to an average 57% increase
in stem height and 137% increase in stem density inS. alterniflora. Differences in growth were inconsistent but in most cases no significant differences were observed between healthy and dieback
areas. Soil characteristics measured over the course of the experiment were generally comparable between healthy and dieback
areas (redox potential averaged 69±123 [SD] across all observations at all sites, pH averaged 6.7 ± 0.3 and salinity averaged
24.9±4.4), but porewater ammonium (NH4) concentration was often higher in dieback areas (overall mean NH4 concentration, was 138±127 μM in dieback areas versus 33±40 μM in healthy areas). These results suggest that the cause of
dieback was no, longer present at the time of this study and that transplants are a possibility for restoring affected areas. 相似文献
8.
Edward Castañeda-Moya Victor H. Rivera-Monroy Robert R. Twilley 《Estuaries and Coasts》2006,29(5):751-764
The structural attributes and zonation patterns of mangrove forests in a dry environmental setting were evaluated in relation
to gradients of soil resources, soil regulators, and hydroperiod between October 2000 and August 2001 in the Gulf of Fonseca,
Honduras. Transects perpendicular to the edge of tidal channels were established at four mangrove sites, each sectioned into
three mangrove zones (fringe, transition, and scrub) based upon distinct tree-height gradients. Porewater sulfide concentrations
among zones were normally below levels of detection (<0.03 mM) and mean redox values ranged from 163.4±9.9 to −42.4±15.8 mv,
indicating slightly reducing conditions in all zones. Mean porewater NOx
− and PO4
3− concentrations were not significantly different among zones and ranged from 3.3±0.5 to 4.5±0.4 μM and from 0.05 ±0.02 to
0.18±0.04 μM, respectively. Soil nitrogen concentrations were 1–3 mg g−1 in all zones, and mean nitrogen:phosphorus atomic ratios were <20 (range: 12.9–14.9), indicative of fertile wetland soils.
Mean basal areas were significantly different among mangrove zones (fringe > transition) and were coupled with differences
in height within species and zones.Avicennia germinans occupied areas with higher elevations associated with higher salinities ranging from 80 to 140 g kg−1 in the dry season.Rhizophora mangle dominated lower elevations where salinities ranged from 38 to 57 g kg−1 in both the dry and wet seasons. Spatial analysis on mangrove seedlings along transects confirmed that seedling distribution
along the intertidal profile was statistically correlated with conspecific adults, indicating that survival and growth of
seedlings in different intertidal locations are closely matched to canopy membership. The sharp transition (<100 m) in forest
structure and distribution of mangrove species along the intertidal zone of subhumid coastal environments demonstrate common
zonation patterns where species distribution and species-specific habitat suitability are mediated closely with tolerance
to soil regulators (high soil salinity) rather than resource availability. 相似文献
9.
Silvia E. Ibarra-Obando Miriam Poumian-Tapia Hem Nalini Morzaria-Luna 《Estuaries and Coasts》2010,33(3):753-768
Disturbance is an important factor influencing plant species composition and diversity. We addressed changes in plant composition
and soil characteristics in Estero de Punta Banda, Baja California, Mexico following 22 years of disturbance by tidal exclusion.
Currently, sediments in the non-tidal site are dry, 26 ± 1% moisture, and hypersaline, 143 ± 12; while those at the tidal
marsh are wet, 36.2 ± 1% moisture, with 40.3 ± 2.6 salinity. The non-tidal site has lost seven species including annuals,
short- and long-lived perennials, ephemerals, and parasites. Current dominants are the perennials Batis maritima and Sarcocornia pacifica. Average species richness at the non-tidal site is 4.4 ± 0.32 vs.10 ± 0.18 species per square meter at the tidal site. Average
species diversity index is lower at the diked area. The general biodiversity loss that results from tidal exclusion in arid
estuaries, contrasts with the species-rich communities that develop in diked humid-climate estuaries. 相似文献
10.
Trends in phosphatase activity along a successional gradient of tidal freshwater marshes on the Cooper River South Carolina 总被引:1,自引:0,他引:1
Phosphatase activity was measured in sediments from tidal freshwater habitats adjacent to the Cooper River in South Carolina
representing different stages of ecological succession. It was found that sediment (0–5 cm) acid phosphatase activity, alkaline
phosphatase activity and phosphodiesterase activity increased with increasing successional stage and phytomass. Acid phosphatase
activity in creased from 7.5±1.2 (±1 SD) in subtidal sediment from a shallow open water habitat without vegetation to 61.2±4.9
μmol g−1 hr−1 (μmol of p-nitrophenol released per gram of dry sediment per hour) in intertidal sediments colonized by emergent macrophytes,
while alkaline phosphatase activity increased from 2.1±0.1 to 19.01±1.5 μmol g−1 hr−1. Phosphodiesterase activity increased from 1.8±0.1 to 20.2±2.0 μmol g−1 hr−1 along the same gradient. Acid phosphatase activity was highly correlated (R2=0.92, P<0.001) with the organic matter content of the sediment. A study of phosphatase kinetics showed that Vmax of all phosphatases also increased along the successional gradient. Trends in phosphatase activity and Vmax correlated positively with plant biomass and negatively with concentrations of soluble reactive phosphorus in porewater,
sediment extractable phosphorus, and total phosphourus. The porewater N∶P atom ratio decreased along the succession gradient
from 25.3 in an early stage, open water community to 13.0 in a community dominated by emergent vegetation. The data also show
that the distribution of the forms of phosphorus changed with successional stage. The change in distribution and the increased
biological demand for phosphorus that paralleled succession were mediated by the activity of phosphatase enzymes. 相似文献
11.
Summary Transmission M?ssbauer spectra of synthetic Ca-free P21/c Mg0.22Fe0.78SiO3 clinopyroxene were collected at temperatures in the range 4.2 to 745 K and in an external magnetic field of 60 kOe at 180 K.
The magnetic order-disorder transition temperature was determined by M?ssbauer thermoscanning to be 21 ± 3 K. Above this temperature,
all M?ssbauer spectra consist of a superposition of two doublets, respectively produced by Fe2+ ions at an almost regular octahedral M1 site and at a more distorted octahedral M2 site. The temperature variation of the
Fe2+ center shifts were analyzed using the Debye model for the lattice vibrations. The characteristic M?ssbauer temperatures were
found to be 356 K ± 35 K for M1 and 333 K ± 25 K for M2. From the external field (60 kOe) M?ssbauer spectrum recorded at 180 K,
the principal component V
zz of the electric field gradient (EFG) was determined to be positive for both sites but precise values for the magnitudes of
the asymmetry parameters η of the EFG could not be determined. The temperature variations of the M1 and M2 quadrupole splittings
ΔE
Q(T ) are consistent with the higher distortion of the M2 octahedra. Using the crystal-field model to interpret ΔE
Q(T ), the energy gaps δ1 and δ2 of the first excited electronic states within the 5D orbital term were estimated to be 410 ± 50 cm−1 and 730 ± 50 cm−1 for M1, and δ1 = 1050 ± 75 cm−1 for M2.
Received May 29, 2000;/revised version accepted July 13, 2001 相似文献
12.
Ahmed I. Rushdi Ali A. DouAbul Sama Samir Mohammed Bernd R. T. Simoneit 《Environmental Geology》2006,50(8):1171-1181
The concentrations of polar organic compounds including n-alkanoic acids, n-alkanols, steroids and triterpenoids were determined in extracts of shallow sediments from the Mesopotamian marshlands of Iraq. The sediments were collected by a stainless steel sediment corer, extracted with a dichloromethane and methanol mixture (3:1 v:v) by ultrasonic agitation and then analyzed by gas chromatography–mass spectrometric (GC–MS). The analysis results showed that the n-alkanoic acids ranged from C8 to C20 with concentrations of 7.8 ± 1.2 μg/g sample, whereas the concentrations of n-alkanols, which ranged from C12 to C39 were from 28.6 ± 4.3 to 121.7 ± 18.3 μg/g sample. The steroids and triterpenoids included stenols, stanols, stenones, stanones, tetrahymanol, tetrahymanone and extended ββ-hopanes. The total concentrations of steroids and triterpenoids ranged from 26.8 ± 4.1 to 174.6 ± 26.2 μg/g and from 0.74 ± 0.11 to 11.2 ± 1.7 μg/g sample, respectively. The major sources of these lipids were from natural vegetation, microbial (plankton) residues and bacteria in the sediments, with some contribution from anthropogenic sources (livestock, sewage and petroleum). Further studies of these wetlands are needed to characterize the input rate, transformation and diagenesis of the organic matter and to assess its various sources. 相似文献
13.
Michael G. LaMontagne Valeria Astorga Anne E. Giblin Ivan Valiela 《Estuaries and Coasts》2002,25(2):272-281
To determine the removal of regenerated nitrogen by estuarine sediments, we compared sediment N2 fluxes to the stoichiometry of nutrient and O2 fluxes in cores collected in the Childs River, Cape Cod, Massachusetts. The difference between the annual PO4 3− (0.2 mol P m−2 yr−1) and NH4 + (1.6 mol N m−2 yr−1) flux and the Redfield N∶P ratio of 16 suggested an annual deficit of 1.5 mol N m−2 yr−1. Denitrification predicted from O2∶NH4 + flux ratios and measured as N2 flux suggested a nitrogen sink of roughly the same magnitude (1.4 mol N m−2 yr−1). Denitrification accounted for low N∶P ratios of benthic flux and removed 32–37% of nitrogen inputs entering the relatively highly nutrient loaded Childs River, despite a relatively brief residence time for freshwater in this system. Uptake of bottom water nitrate could only supply a fraction of the observed N2 flux. Removal of regenerated nitrogen by denitrification in this system appears to vary seasonally. Denitrification efficiency was inversely correlated with oxygen and ammonium flux and was lowest in summer. We investigated the effect of organic matter on denitrification by simulating phytoplankton deposition to cores incubated in the lab and by deploying chambers on bare and macroaglae covered sediments in the field. Organic matter addition to sediments increased N2 flux and did not alter denitrification efficiency. Increased N2 flux co-varied with O2 and NH4 + fluxes. N2 flux (261±60 μmol m−2 h−1) was lower in chambers deployed on macroalgal beds than deployed on bare sediments (458±70 μmol m−2 h−1), and O2 uptake rate was higher in chambers deployed on macroalgal beds (14.6±2.2 mmol m−2 h−1) than on bare sediments (9.6±1.5 mmol m−2 h−1). Macroalgal cover, which can retain nitrogen in the system, is a link between nutrient loading and denitrification. Decreased denitrification due to increasing macroalgal cover could create a positive feedback because decreasing denitrification would increase nitrogen availability and could increase macroalgae cover. 相似文献
14.
H. N. McKellar D. L. Tufford M. C. Alford P. Saroprayogi B. J. Kelley J. T. Morris 《Estuaries and Coasts》2007,30(6):989-1006
Tidal freshwater sections of the Cooper River Estuary (South Carolina) include extensive wetlands, which were formerly impounded
for rice culture during the 1,700s and 1,800s. Most of these former rice fields are now open to tidal exchange and have developed
into productive wetlands that vary in bottom topography, tidal hydrography and vegetation dominants. The purpose of this project
was to quantify nitrogen (N) transport via tidal exchange between the main estuarine channel and representative wetland types
and to relate exchange patterns to the succession of vegetation dominants. We examined N concentration and mass exchange at
the main tidal inlets for the three representative wetland types (submerged aquatic vegetation [SAV], floating leaf vegetation,
and intertidal emergent marsh) over 18-21 tidal cycles (July 1998–August 2000). Nitrate + nitrite concentrations were significantly
lower during ebb flow at all study sites, suggesting potential patterns of uptake by all wetland types. The magnitude of nitrate
decline during ebb flow was negatively correlated with oxygen concentration, reflecting the potential importance of denitrification
and nitrate reduction within hypoxic wetland waters and sediments. The net tidal exchange of nitrate + nitrite was particularly
consistent for the intertidal emergent marsh, where flow-weighted ebb concentrations were usually 18–40% lower than during
flood tides. Seasonal patterns for the emergent marsh indicated higher rates of nitrate + nitrite uptake during the spring
and summer (> 400 μmol N m-2 tide-1) with an annual mean uptake of 248 ± 162 μmol m–2 tide–1. The emergent marsh also removed ammonium through most of the year (207 ± 109 μmol m–2 tide–1), and exported dissolved organic nitrogen (DON) in the fall (1,690 ± 793 μmol m–2 tide–1), suggesting an approximate annual balance between the dissolved inorganic N uptake and DON export. The other wetland types
(SAV and floating leaf vegetation) were less consistent in magnitude and direction of N exchange. Since the emergent marsh
site had the highest bottom elevation and the highest relative cover of intertidal habitat, these results suggest that the
nature of N exchange between the estuarine waters and bordering wetlands is affected by wetland morphometry, tidal hydrography,
and corresponding vegetation dominants. With the recent diversion of river discharge, water levels in the upper Cooper estuary
have dropped more than 10 cm, leading to a succession of wetland communities from subtidal habitats toward more intertidal
habitats. Results of this study suggest that current trends of wetland succession in the upper Cooper River may result in
higher rates of system-wide inorganic N removal and DON inputs by the growing distributions of intertidal emergent marshes. 相似文献
15.
Estuaries located in the northern Gulf of Mexico are expected to experience reduced river discharge due to increasing demand for freshwater and predicted periods of declining precipitation. Changes in freshwater and nutrient input might impact estuarine higher trophic level productivity through changes in phytoplankton quantity and quality. Phytoplankton biomass and composition were examined in Apalachicola Bay, Florida during two summers of contrasting river discharge. The <20 μm autotrophs were the main component (92?±?3 %; n?=?14) of phytoplankton biomass in lower (<25 psu) salinity waters. In these lower salinity waters containing higher dissolved inorganic nutrients, phycocyanin containing cyanobacteria made the greatest contribution to phytoplankton biomass (69?±?3 %; n?=?14) followed by <20 μm eukaryotes (19?±?1 %; n?=?14), and phycoerythrin containing cyanobacteria (4?±?1 %; n?=?14). In waters with salinity from 25 to 35 psu that were located within or in close proximity to the estuary, >20 μm diatoms were an increasingly (20 to 70 %) larger component of phytoplankton biomass. Lower summer river discharges that lead to an areal contraction of lower (5–25 psu) salinity waters composed of higher phytoplankton biomass dominated by small (<20 μm) autotrophs will lead to a concomitant areal expansion of higher (>25 psu) salinity waters composed of relatively lower phytoplankton biomass and a higher percent contribution by >20 μm diatoms. A reduction in summer river discharge that leads to such a change in quantity and quality of estuarine phytoplankton available will result in a reduction in estuarine zooplankton productivity and possibly the productivity of higher trophic levels. 相似文献
16.
Michael T. League Erin P. Colbert Denise M. Seliskar John L. Gallagher 《Estuaries and Coasts》2006,29(2):269-276
Phragmites australis (common reed), a clonal grass, has expanded from a minor component of the mid-Atlantic wetlands to a dominant species. It
has been suggested that invasive populations ofPhragmites are an exotic haplotype responsible for the dramatic increase in the distribution of the species. We used field observations
and measurements and a greenhouse assay to compare native (haplotype F) and exotic (haplotype M) populations, growing adjacent
to one another in a brackish marsh near Odessa, Delaware. In the marsh, shoots of the exotic strain emerged from the rhizomes
earlier than those of the native and by March there was an order of magnitude more new shoots of the exotic strain than the
native. In August, the exotic strain was 30% taller than the native, had twice the leaf biomass, and twice the total biomass.
Nine of ten morphological and biomass characteristics measured differed significantly between the native and exotic strains.
A greenhouse assay was conducted by planting rhizomes collected in March in shallow trays and growing them for 70 d followed
by shoot harvest (Harvest 1). Rhizomes were measured, replanted, and grown for 35 d after which time they were measured and
shoots were harvested (Harvest 2). At Harvest 1, shoot height was approximately 80% greater in the exotic strain, shoot biomass
was three times higher, aboveground to belowground biomass ratio was twice as high, and rhizome internode length was 50% greater
in the exotic strain than the native. These traits, in addition to number of shoots, were also greater in the exotic strain
at Harvest 2. The number of rhizome buds at Harvest 1 was three times greater in the native than in the exotic strain. The
greater number of rhizome buds in the native would seem to be an advantage, but it did not result in more shoot production.
Buds were maintained in an inactive state that does not allow this strain to compete well in a wetland environment inhabited
by a more efficient spreader. The earlier emergence of new shoots from the rhizomes, the greater aboveground structure, the
greater rhizome internode length, and the quick transition of rhizome buds to shoot or rhizome explain in part the exotic
strain's advantage over the native and the mechanisms for its invasive nature. 相似文献
17.
Data from the revised Geneva-Copenhagen catalog are used to study the influence of radial migration of stars on the age dependences
of parameters of the velocity ellipsoids for nearby stars in the thin disk of the Galaxy, assuming that the mean radii of
the stellar orbits remain constant. It is demonstrated that precisely the radial migration of stars, together with the negative
metallicity gradient in the thin disk, are responsible for the observed negative correlation between the metallicities and
angular momenta of nearby stars, while the angular momenta of stars that were born at the same Galactocentric distances do
not depend on either age or metallicity. The velocity components of the Sun relative to the Local Standard of Rest derived
using data for stars born at the solar Galactocentric distance are (U
⊙, V
⊙, W
⊙)
LSR
= (5.1 ± 0.4, 7.9 ± 0.5, 7.7 ± 0.2) km/s. The two coordinates of the apex of the solar motion remain equal to 〈l
⊙〉 = 70° ± 7° and 〈b
⊙〉 = 41° ± 2°, within the errors. The indices for the power-law age dependences of them ajor, middle, and minor semi-axes become
0.26±0.04, 0.32±0.03, and 0.07±0.03, respectively. As a result, with age, the velocity ellipsoid for thin-disk stars born
at the solar Galactocentric distance increases only in the plane of the disk, remaining virtually constant in the perpendicular
direction. Its shape remains far from equilibrium, and the direction of the major axis does not change with age: the ellipsoid
vertex deviation remains constant and equal to zero within the errors (〈L〉 = 0.7° ± 0.6°, 〈B〉 = 1.9° ± 1.1°). Such a small increase in the velocity dispersion perpendicular to the Galactic plane with age can probably
be explained by “heating” of the stellar system purely by spiral density waves, without a contribution from giant molecular
clouds. 相似文献
18.
The Malanjkhand copper ( + molybdenum) deposit, India: mineralization from a low-temperature ore-fluid of granitoid affiliation 总被引:2,自引:0,他引:2
Copper and subordinate molybdenum mineralization at Malanjkhand occurs within a fracture-controlled quartz-reef enclosed
in a pink granitoid body surrounded by grey-granitoids constituting the regional matrix. Sulfide-bearing stringers, pegmatites
with only quartz + microcline and sulfide disseminations, all within the pink-granitoid, represent other minor modes of occurrences.
Despite this diversity in mode of occurrence, the mineralogy of ores is quite consistent and conform to a common paragenetic
sequence comprising an early `ferrous' stage of precipitation of magnetite (I) and pyrite (I) and, the main-stage chalcopyrite
mineralization with minor sphalerite, pyrite (II), magnetite (II), molybdenite and hematite. Both stages witnessed continuous
precipitation of quartz ± microcline ± (chlorite, biotite and epidote). The enclosing pink-granitoid and the regional grey-granitoids
display alteration features such as saussuritization of plagioclase, breakdown of hornblende and chloritization of biotite
on a regional scale, indicating interaction with a pervasive fluid. Quartz and microcline precipitation mostly restricted
within the pink granitoid, postdates this alteration. Four types of primary inclusions were encountered in quartz from ore samples: (1) type-I – aqueous-biphase(L + V) inclusions, the commonest variety in all ore types; (2) type-II – aqueous-carbonic(Laq + Lcarb ± Vcarb); (3) type-III – pure-carbonic(Lcarb ± Vcarb) – type-II and III being restricted to stringer and pegmatitic ores, and (4) rare polyphase (Laq + Vaq + calcite/gypsum) inclusions. Quartz in granitoids contain primary type-I inclusions only. Type-I inclusions from ore samples furnish a temperature range (after a rough pressure
correction to the T
H
-maxima of 140–180 °C) of 150–275 °C and a moderately low salinity of 4–12 wt.% NaCl equivalent. This is inferred to represent
the signature of the major component (F2) of the ore fluid. A few type-I inclusions of higher T
M
(up to 380 °C) and low salinity and density represent the other (F1) identifiable component of the ore fluid present in low
proportion. The T
H
-maxima and the total range in salinity of type-I inclusions in quartz from granitoids are strikingly similar to those from the ore samples. Composition of syn-ore chlorites furnished a temperature range of 185–327
°C, which conforms to the fluid inclusion microthermometric data. Pressure estimates using standard fluid inclusion geobarometric
methods, vary from 550 to 1790 bar in the stringer ores. Observed temperature-salinity/density relationships are best explained
by a two-stage evolution model of the ore fluid: the first stage witnessed mixing of the two components, F1 and F2 in unequal
proportion, bringing about mineralization. The second stage of evolution was marked by the separation of a carbonic component
on continued sulfide precipitation and attendant increase in salinity of the fluid. The F1 component emerged as a distinct,
heated and (CO2 + S)-charged entity due to steam-heating and contamination of the early-ingressed F2 fluid at the fracture zone. The pervasive
fluid phase in the surrounding granitoids contributed the F2 component.
Received: (10 August 1994), 15 August 1995 / Accepted: 12 January 1996 相似文献
19.
Through their physiological effects on ion, oxygen, and carbon balance, respectively, salinity, sulfide, and prolonged flooding
combine to constrain the invasion and spread ofPhragmites in tidal wetlands. Initial sites of vigorous invasion by seed germination and growth from rhizome fragments appear limited
to sections of marsh where salinity is <10‰, sulfide concentrations are less than 0.1 mM, and flooding frequency is less than
10%. In polyhaline tidal wetlands the invasion sites include the upland fringe and some high marsh creek banks. The zones
of potential invasion tend to be larger in marshes occupying lower-salinity portions of estuaries and in marshes that have
been altered hydrologically. Owing to clonal integration and a positive feedback loop of growth-induced modification of edaphic
soil conditions, however, a greater total area of wetland is susceptible toPhragmites expansion away from sites of establishment. Mature clones have been reported growing in different marshes with salinity up
to 45‰, sulfide concentration up to 1.75 mM, and flooding frequency up to 100%. ForPhragmites establishment and expansion in tidal marshes, windows of opportunity open with microtopographic enhancement of subsurface
drainage patterns, marsh-wide depression of flooding and salinity regimes, and variation in sea level driven by global warming
and lunar nodal cycles. To avoidPhragmites monocultures, tidal wetland creation, restoration, and management must be considered within the context of these different
scales of plant-environment interaction. 相似文献
20.
Sulfide Inhibition of Nitrate Removal in Coastal Sediments 总被引:1,自引:0,他引:1
Microbial nitrate (NO3−) removal via denitrification (DNF) at high sulfide (H2S) concentrations was compared in sediment from a coastal freshwater pond in a developed area that receives salt-water influx
during storm events, and a saline pond proximal to an undeveloped estuary. Sediments were incubated with added SO42− (1,000 μg per gram dry weight basis (gdw)) to determine whether acid volatile sulfides (AVS) were formed. DNF in the sediments
was measured with NO3–N (300 μg gdw−1) alone, and with NO3–N and H2S (1,000 μg S2− gdw−1). SO42− addition to the freshwater sediments resulted in AVS formation (970 ± 307 μg S gdw−1) similar to the wetland with no added SO42− (986 ± 156 μg S gdw−1). DNF rates measured with no added H2S were greater in the freshwater than the wetland site (10.6 ± 0.6 vs. 6.4 ± 0.1 μg N2O–N gdw−1 h−1, respectively). High H2S concentrations retained NH4–N in the undeveloped wetland and retained NO3–N in the developed freshwater site, suggesting that potential salt-water influx may reduce the ability of the freshwater
sediments to remove NO3–N. 相似文献