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1.
Seasonal and spatial patterns of aquatic primary production were compared in a tidal creek (Estero Pargo) bordered by mangroves
and open waters of Terminos Lagoon, Mexico. Comparisions were made during a 17-month period in 1990–91 that spanned dry, rainy,
and storm or 'Norte' seasons. Annual net primary productivity was 478 g C m-2 yr-1 in the lagoon and 285 g C m-2 yr-1 in the
tidal creek. In some months, there were significant differences in primary production between the two sites. In both areas,
the highest productivity occurred in summer at the start of the rainy season (June 1991), and the lowest production occurred
during the dry season from February to May. Aquatic primary production was lower during the dry season of 1991 in comparison
to 1990, possibly related to unusually low precipitation during 1991. Seasonal changes in water column productivity were correlated
to variations in light and precipitation. The effect of runoff from mangrove forests was assessed by serial additions of surface
water from a fringe forest to bottle incubations of lagoon water. Small additions of mangrove water stimulated primary production
in lagoon waters during all seasons. The net productivity was extremely sensitive to aliquot volume; small amounts (0.3 and
1.7% of total volume) were stimulatory, increasing rates by > 50% in 7 of 12 experiments. The greatest effect occurred in
September, 1990, when productivity tripled after an amendment with 1 ml (0.3% by volume) of mangrove water. Additions greater
than 3% of total volume generally led to reduction in net productivity probably due to the inhibitory effect of humic substances.
In many tropical systems, tidal exchange of estuarine waters with mangrove forests is likely to be important to enhancing
water column productivity by exporting organic nutrients and other growth-enhancing substances to the estuary.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
2.
Observations made on Heron Island reef flat during the 1970s–1990s highlighted the importance of rapid change in hydrodynamics
and accommodation space for coral development. Between the 1940s and the 1990s, the minimum reef-flat top water level varied
by some tens of centimetres, successively down then up, in rapid response to local engineering works. Coral growth followed
sea-level variations and was quantified here for several coral communities using horizontal two-dimensional above water remotely
sensed observations. This required seven high spatial resolution aerial photographs and Quickbird satellite images spanning
35 years: 1972, 1979, 1990, 1992, 2002, 2006 and 2007. The coral growth dynamics followed four regimes corresponding to artificially
induced changes in sea levels: 1972–1979 (lowest growth rate): no detectable coral development, due to high tidal currents
and minimum mean low-tide water level; 1979–1991 (higher growth rate): horizontal coral development promoted by calmer hydrodynamic
conditions; 1991–2001(lower growth rate): vertical coral development, induced by increased local sea level by ~12 cm due to
construction of new bund walls; 2001–2007 (highest growth rate): horizontal coral development after that vertical growth had
become limited by sea level. This unique time-series displays a succession of ecological stage comprising a ‘catch-up’ dynamic
in response to a rapid local sea-level rise in spite of the occurrences of the most severe bleaching events on record (1998,
2002) and the decreasing calcification rates reported in massive corals in the northern part of the Great Barrier Reef. 相似文献
3.
The aim of this study was to investigate the interactions of natural and anthropogenic variables at different spatial scales related to changes in mangrove distribution during a relatively wet period (1972–1990) and a dry period (1991–2004) in subtropical eastern Australia. Previous research has demonstrated that mangroves are encroaching into salt marsh. Mangrove spatial change in southeast Queensland is related generally to landscape variables especially during the relatively wet period. What has not been explored is the spatial scale of the influence under the two rainfall regimes (wet and dry) and that is the aim of this paper. Ten sites were examined at different levels of resolution including catchment, sub‐catchment and two buffer zones (1000 and 500 m), under the period of relatively higher and lower rainfall. Land use was ascertained from Landsat satellite imagery using Maximum Likelihood Classification techniques. Partial least squares regression analysis was used to study the relationships between the predictor variables and the rate of change in the mangrove distribution. The research has found that the impact of land use/cover on the encroachment of mangrove into saltmarsh can vary and appears to be related to rainfall patterns, which in turn affect hydrological connectivity. A major finding of this research was that the changing spatial patterns of mangroves during the wet period was more a function of land use/cover pattern and population density at the sub‐catchment level, whereas during drier periods it was more affected by the local effects of nearby land use/cover in buffer zones. 相似文献
4.
Lucas R.M. Ellison J.C. Mitchell A. Donnelly B. Finlayson M. Milne A.K. 《Wetlands Ecology and Management》2002,10(2):159-173
The study investigated the use of aerial photographs, acquired in 1950 and1991, for assessing the temporal dynamics of mangroves along the WestAlligator River in Australia's Northern Territory. For both years,mangrove extent was mapped using an unsupervised classification of thedigital orthomosaic and Digital Elevation Models (DEMs), or height maps,of the mangrove canopy were derived from stereo pairs. Helicopter andfield observations in 1998 and 1999 respectively provided ground truthfor interpreting the derived datasets. The comparison of mangrove extentrevealed a substantial movement over the 41-year period, perhaps inresponse to hydrological changes that have resulted in a landward extensionof saline conditions. Changes in the height of mangroves were observedbut were difficult to quantify due to the reduced quality of the 1950 DEM. The study demonstrated the viability of using time-series of aerialphotography for monitoring and understanding the long-term response ofmangroves to environmental change, including hydrological variations andsea level rise. 相似文献
5.
Philip W. Stevens Sandra L. Fox Clay L. Montague 《Wetlands Ecology and Management》2006,14(5):435-444
The interplay between mangroves and saltmarshes at the temperate to subtropical transition in Florida results in dramatic
changes to the appearance of the coastal landscape. In the 1980s, freezes killed entire mangrove forests dominated by black
mangroves, Avicennia germinans (L.). Following the freezes, saltmarshes dominated by smooth cordgrass, Spartina alterniflora Loisel, revegetated the intertidal zone. After a decade of mild winters, however, mangroves are beginning to reclaim the
area. The rate of mangrove expansion was determined by comparing aerial photography (change from 1995 to 1999), and from monitoring
transects (over a 3 year period) on three of the Cedar Keys, Florida (Lat. 29°08′). The rate of mangrove expansion varied
among islands, and the mechanism of expansion ranged from propagule-trapping by saltmarshes along the edges of mangrove clumps
to widespread dispersal and growth of existing or newly imported propagules. A freeze occurred during the study, which may
have set back mangrove expansion by defoliating mangrove trees and resetting mangrove reproduction. Mangrove expansion was
projected to take 20–30 years for complete seedling cover. Given the possibility of global climate change and its potential
influence on the distribution of coastal vegetation, the timeframes and implications to coastal wetland ecosystems involved
in this regular interplay will provide valuable baseline information for future studies. 相似文献
6.
A field based statistical approach for validating a remotely sensed mangrove forest classification scheme 总被引:1,自引:0,他引:1
John M. Kovacs Yali Liu Chunhua Zhang Francisco Flores-Verdugo Francisco Flores de Santiago 《Wetlands Ecology and Management》2011,19(5):409-421
Amongst the most threatened ecosystems on Earth, mangrove forests are also one of the more difficult to work in due to their
growth in mud and open water coastal zones and their dense tangled stems, branches and prop roots. Consequently, there has
been an impetus to employ remotely sensed imagery as a means for rapid inventory of these coastal wetlands. To date, the majority
of mangrove maps derived from satellite imagery utilize a simple mangrove classification scheme which does not distinguish
mangrove species and may not be useful for conservation and management purposes. Although more elaborate satellite based mangrove
classification schemes are being developed, given their enhanced complexity they deserve additional justification for end
users. The purpose of this study was to statistically examine the appropriateness of one such classification scheme based
on an inventory of field data. In January of 2007 and May of 2008, 61 field sample plots were selected in a stratified random
fashion based on a previous classification of a degraded mangrove forest of the Isla La Palma (Sinaloa, Mexico) using Landsat
TM5 data. Unlike other previous Landsat TM based classifications of this region, which simply identified the mangrove forests
as one class, the mangroves were classified (i.e. mapped) according to four conditions; healthy tall, healthy dwarf, poor
condition, and dead mangroves. Within each sample plot, all mangroves of diameter of breast height (dbh) greater than 2.5 cm
were identified and their height, condition and dbh recorded. An estimated Leaf Area Index (LAI) value also was obtained for
each sample and the shortest distance from the center of each sample plot to open flowing water was determined using a geographic
information system (GIS) overlay procedure. These data were then used to calculate mean values for the four classes as well
as to determine stem densities, basal areas, and the Shannon–Wiener diversity index. In order to assess the appropriateness
of this mangrove classification scheme a discriminant analysis approach was then applied to these field data. The results
indicate this forest has undergone severe degradation, with decreasing mean tree heights, mean dbh and species diversity.
In regards to the discriminant analysis procedure, further classification of these field plots and cross-validation based
on these significant variables provided high classification accuracy thus validating the appropriateness of the satellite
based image classification scheme. Moreover, the discriminant analysis indicated that the estimated LAI, mean height, and
mean dbh are significant in the separation of the classification of mangrove forest condition along these field sample plots. 相似文献
7.
Edward Castañeda-Moya Robert R. Twilley Victor H. Rivera-Monroy Brian D. Marx Carlos Coronado-Molina Sharon M. L. Ewe 《Ecosystems》2011,14(7):1178-1195
Patterns of mangrove vegetation in two distinct basins of Florida Coastal Everglades (FCE), Shark River estuary and Taylor
River Slough, represent unique opportunities to test hypotheses that root dynamics respond to gradients of resources, regulators,
and hydroperiod. We propose that soil total phosphorus (P) gradients in these two coastal basins of FCE cause specific patterns
in belowground biomass allocation and net primary productivity that facilitate nutrient acquisition, but also minimize stress
from regulators and hydroperiod in flooded soil conditions. Shark River basin has higher P and tidal hydrology with riverine
mangroves, in contrast to scrub mangroves of Taylor basin with more permanent flooding and lower P across the coastal landscape.
Belowground biomass (0–90 cm) of mangrove sites in Shark River and Taylor River basins ranged from 2317 to 4673 g m−2, with the highest contribution (62–85%) of roots in the shallow root zone (0–45 cm) compared to the deeper root zone (45–90 cm).
Total root productivity did not vary significantly among sites and ranged from 407 to 643 g m−2 y−1. Root production in the shallow root zone accounted for 57–78% of total production. Root turnover rates ranged from 0.04
to 0.60 y−1 and consistently decreased as the root size class distribution increased from fine to coarse roots, indicating differences
in root longevity. Fine root biomass was negatively correlated with soil P density and frequency of inundation, whereas fine
root turnover decreased with increasing soil N:P ratios. Lower P availability in Taylor River basin relative to Shark River
basin, along with higher regulator and hydroperiod stress, confirms our hypothesis that interactions of stress from resource
limitation and long duration of hydroperiod account for higher fine root biomass along with lower fine root production and
turnover. Because fine root production and organic matter accumulation are the primary processes controlling soil formation
and accretion in scrub mangrove forests, root dynamics in the P-limited carbonate ecosystem of south Florida have a major
controlling role as to how mangroves respond to future impacts of sea-level rise. 相似文献
8.
Xavier López‐Medellín Exequiel Ezcurra Charlotte González‐Abraham Jon Hak Louis S. Santiago James O. Sickman 《植被学杂志》2011,22(1):143-151
Question: Although mangrove forests are generally regarded as highly threatened, some studies have shown that mangrove canopies in the Pacific coast of Mexico have been increasing in recent decades. We investigated the possible causes driving this reported mangrove expansion. Location: The mangrove lagoons of Magdalena Bay in Baja California, Mexico. Methods: We used 50‐year‐old aerial photographs and 24‐year‐old satellite images to compare long‐term vegetation change, surveyed a coastal vegetation transect to analyse flooding levels, compiled six decades of tidal and oceanographic information, as well as hurricane data to analyse changes in storm frequency or sea‐level conditions, and used isotopic analysis to date the age of trees along the gradient. Results: A significant increase in mangrove cover has occurred in backwaters of the lagoons during the last 40 years, and especially during the El Niño anomalies of the 1980s and 1990s, while at the same time the mangrove fringe has been receding. Conclusions: The observed change can be attributed to the combined action of the warm surface waters of El Niño events and sea‐level rise. Jointly, these two effects are sufficient to flood large areas of previously non‐flooded salt flats, dispersing mangrove seedlings inland. The inland expansion of mangroves, however, does not ease conservation concerns, as it is the seaward fringes, and not the inland margins, that provide the most valuable environmental services for fisheries and coastal protection. 相似文献
9.
Ecology of heterotrophic dinitrogen fixation in the rhizosphere of mangrove plant community at the Ganges river estuary in India 总被引:7,自引:0,他引:7
Summary Heterotrophic dinitrogen fixation in root associations of successional stages of the tropical mangrove plant community at
the Ganges river estuary in India was investigated by excised-root acetylene reduction assay, and enumeration and identification
of diazotrophic bacteria from sediment, root and tidal water samples. High to very high rates of nitrogenase activity (64–130
nmol C2H4/g dry root/h) were associated with washed excised roots of seven common early-successional mangrove species at the inundated
swamps. Declining, late-successional mangroves at the occasionally inundated ridges had considerably lower values and the
“declined” mangroves and other non-littoral species at embankment protected highlands had very low to insignificant values
of root nitrogenase activity. Total and inorganic nitrogen contents of the mangrove sediments were low and were positively
related to the stages of physiographic succession. Plant-associated sediments of particularly the old formation swamps had
very high C/N ratios. Nine isolates of nitrogen-fixing bacteria belonging to all known O2 response groups were distinguished from a large population of diazotrophs associated with roots of mangroves and other associate
plant species of the community. The isolates differed with respect to their N2-fixation efficiency and halotolerance in pure culture. There was no specificity of any of the bacterial isolates to any of
the plant species of the community but a higher number of efficient isolates were seen to be associated with mangroves at
the swampy succession. Sediment-free tidal water also contained a large population of microaerophilic and anaerobic N2-fixing bacteria. 相似文献
10.
From half a million hectares at the turn of the century, Philippine mangroves have declined to only 120,000 ha while fish/shrimp
culture ponds have increased to 232,000 ha. Mangrove replanting programs have thus been popular, from community initiatives
(1930s–1950s) to government-sponsored projects (1970s) to large-scale international development assistance programs (1980s
to present). Planting costs escalated from less than US$100 to over $500/ha, with half of the latter amount allocated to administration,
supervision and project management. Despite heavy funds for massive rehabilitation of mangrove forests over the last two decades,
the long-term survival rates of mangroves are generally low at 10–20%. Poor survival can be mainly traced to two factors:
inappropriate species and site selection. The favored but unsuitable Rhizophora are planted in sandy substrates of exposed coastlines instead of the natural colonizers Avicennia and Sonneratia. More significantly, planting sites are generally in the lower intertidal to subtidal zones where mangroves do not thrive
rather than the optimal middle to upper intertidal levels, for a simple reason. Such ideal sites have long been converted
to brackishwater fishponds whereas the former are open access areas with no ownership problems. The issue of pond ownership
may be complex and difficult, but such should not outweigh ecological requirements: mangroves should be planted where fishponds
are, not on seagrass beds and tidal flats where they never existed. This paper reviews eight mangrove initiatives in the Philippines
and evaluates the biophysical and institutional factors behind success or failure. The authors recommend specific protocols
(among them pushing for a 4:1 mangrove to pond ratio recommended for a healthy ecosystem) and wider policy directions to make
mangrove rehabilitation in the country more effective. 相似文献
11.
Will mangrove encroachment into saltmarshes affect saltwater mosquito habitats? To address this, we synthesized information from two perspectives: 1) at a detailed level, the immature mosquito habitat within mangroves; 2) at a more general or regional level, changes due to mangrove expansion into saltmarshes. This is a synthesis of two research projects. One showed that mosquito larval habitats in mangroves are complex, related to the detailed interactions between topography and tidal patterns and that not all parts of a mangrove forest are suitable habitat. The other, based on remote sensing and analysis of rainfall data, showed that mangrove encroachment in eastern Australia is related to both climate and human land use over several decades (1972–2004). An important question emerged: when mangroves encroach into saltmarshes will they displace saltmarsh immature mosquito habitats or will they replace them with mangrove ones? There is no simple answer: it will vary with climate change and sea level scenario and how these affect the system. We conclude that mosquito management, which is locally implemented, needs to be integrated with land use planning systems, which often operate at a more general level. 相似文献
12.
Applying remote sensing techniques to monitor shifting wetland vegetation: A case study of Danshui River estuary mangrove communities,Taiwan 总被引:1,自引:0,他引:1
The purpose of this study is to apply different remote sensing techniques to monitor shifting mangrove vegetation in the Danshui River estuary in Taipei, Taiwan, in order to evaluate a long-term wetland conservation strategy compromising between comprehensive wetland ecosystem management and urban development. In the Danshui estuary, mangrove dominated by Kandelia candel is the major vegetation, and a large area of marsh with freshwater grasses has been protected in three reserves along the river shore. This study applied satellite imagery from different remote sensors of various resolutions for spectral analysis in order to compare shifting wetland vegetation communities at different times. A two-stage analytical process was used for extracting vegetation area and types. In the first-stage, a normalized difference vegetation index (NDVI) was adopted to analyze SPOT, Landsat, and QuickBird imagery to obtain the spatial distribution of vegetation covers. In the second stage, a maximum likelihood classification (MLC) program was used to classify mangrove and non-mangrove areas. The results indicated that the spatial distribution of mangroves expanded 15.18 and 40 ha in two monitoring sites in 10 years, demonstrating the success of establishing reserves for protecting mangrove habitats. The analytical results also indicated that satellite imagery can easily discern the difference in characteristics between imagery of mangrove and other vegetation types, and that the logistical disadvantages of monitoring long-term vegetation community changes as well as evaluating an inaccessible area may be overcome by applying remote sensing techniques. 相似文献
13.
Holmer M. Andersen F.Ø. Holmboe N. Kristensen E. Thongtham N. 《Wetlands Ecology and Management》2001,9(2):141-158
Benthic primary production and nutrient dynamics were examined along a transect in the Bangrong mangrove forest in Thailand.
Six stations were established extending from a high-intertidal site within the mangrove forest to low-intertidal flats and
seagrass beds in front of the mangrove forest. Benthic processes (O2 and CO2 fluxes) and nutrient dynamics (mineralization, sediment-water fluxes, pore water and sediment pools) were measured under
light and dark conditions during wet and dry seasons over a 2-yr period. The sediments were mostly autotrophic, only the mangrove
forest sites were net heterotrophic during the wet season. Maximum daily net primary production was found at the non-vegetated
tidal flats (40–75 mmol O2 m-2d-1), where light and nutrient availability were highest. The variation in benthic mineralization along the transect was minor
(1.6–4.3 mmol CO2 m-2h-1) and did not reflect the large changes inorganic matter content (organic carbon: 0.7–4.2% DW) and quality (C:N ratio varied
from 25 to 100), suggesting that the mineralizable pool of organic matter was of similar magnitude at all sites. There was
only minor seasonal variation in rates of mineralization. The net primary production showed more variation with lower rates
in the mangrove forest (reduced with 74%) and higher rates at the tidal flats (increased with 172%) and in the seagrass beds
(increased with 228%) during the wet season. The nutrient pools and fluxes across the sediment-water interface were generally
low along the transect, and the sediments were efficient in retaining nitrogen in the nutrient limited mangrove/seagrass environment.
Pools and fluxes of phosphorus were generally very low suggesting that benthic primary production was phosphorus limited along
the transect.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献
14.
The diffuse attenuation coefficient, K (m− 1), is a measure of the effective attenuation of light in the water column. It characterizes water clarity and is used as a
proxy for water quality. Mapping of shallow water benthic habitats using optical means, including daytime visible satellite
imagery, requires knowledge of K to correct for water column effects such as light absorption and scattering. Traditionally, K is derived from imagery using a priori knowledge of bottom types at different depths and specific locations, and assuming that light attenuates exponentially with
depth. This technique is applied to three Landsat 7 satellite images (February, May, and July 2000) from the Florida Keys
Reef Tract between Key Largo and Key West. Interpolated depth data, initially from NOAA vector chart data, with uncertainties
of ±0.5 m, were draped over 30 m spatial resolution Landsat satellite imagery. K was derived for 27 sites where bright sand could be observed at depths between 3 and 20 m. The blue and green bands (Landsat
bands 1 and 2 at 450–520 nm and 520–600 nm, respectively) provided K values consistent with time and location. Average K values for bands 1 and 2, respectively, were 0.029 and 0.043 m− 1 (Lower Keys), 0.050 and 0.072 m− 1 (Middle Keys), and 0.063 and 0.082 m− 1 (Upper Keys). The red band (band 3, 630–690 nm) provided more ambiguous and erroneous results with several negative K values, attributed primarily to three factors use of a simple atmospheric correction, the high absorption and rapid attenuation
of red light in water, and low radiometric sensitivity of the Landsat ETM + sensor. Despite the fact that these observations
were a snapshot in time, trends were observed for the Upper, Middle, and Lower Keys, possibly due to the influence of more
turbid Florida Bay waters. 相似文献
15.
Gear type,species composition and economic value of fisheries in the mangroves of Pak Phanang,Thailand 总被引:1,自引:0,他引:1
Fishing gear and methods, catch composition, annual catch numbers and the monetary value of fisheries based in the mangroves
of Pak Phanang, Nakhon Si Thamarat province, Thailand, were studied from September 2004 to February 2005. The fishing gear
and methods were surveyed by visual observation and interviews. Sample catches were taken for each type of fishing gear and
method. Semi-closed questionnaire surveys were conducted among fishers, local traders, local administrative officers and related
organizations to derive information on utilized species, gear and methods, fisher and fishery status, and trading and catch
price. The Pak Phanang mangrove fishery has three types of multi-species capture gear: channel traps, gill nets and lift nets.
It also has three kinds of single-species (group) gear/methods: crab traps, catfish hooks and hand capture using a long tail
fishing boat. A total of 57 fish species in 27 families, and 23 shell fish species in 8 families were recorded from the catch
samples. Penaeid shrimp (25%), and ambassid (31%) and mugilid (24%) fishes were the abundant groups in the channel traps,
while ariid (36%) and mugilid (19%) fishes were abundant in the lift net catches. Ambassid (42%) fish dominated the gill net
catches. Species richness (number of species) varied depending on sampling month and type of fishing gear. The total annual
catch and its monetary value were estimated to be 442–551 tons and US $368,038–733,973, respectively. The estimated annual
catch per unit area of mangrove was 63–79 kg ha−1, which generated a market value of US $368,038–733,973, respectively. The estimated annual
catch per unit area of mangrove was 63–79 kg ha−1, which generated a market value of US 52–105. 相似文献
16.
17.
This research uses Landsat Multi-Spectral Scanner of 1973, Thematic Mapper of 1989, Advance Earth Observing Satellite of 1996,
and Enhanced Thematic Mapper of 2003 imagery to examine the effects of socioeconomic and demographic factors on land use and
forest cover dynamics in the Bara district of the Central Tarai Region of Nepal for 1973–2003. These satellite images are
used to generate three transition matrices for 1973–1989, 1989–1996, and 1996–2003; and the outcomes of the final transition
matrix are compared with the land use and cover patterns seen on the IKONOS (1 × 1 m) 2003 images. This paper contributes
to our understanding of how land use and cover dynamics correspond to national-level socioeconomic developments, demographic
changes, and environmental awareness as envisioned by Ecological Modernization Theory. It also demonstrates how such a set
of transition matrices generated from different resolution images helps assess these explanatory relationships at different
temporal and spatial scales. 相似文献
18.
The digital airborne sensor, CASI (Compact Airborne Spectrographic Imager) has considerable potential for mapping marine
habitats. Here we present an account of one of the first coral reef applications. The CASI was flown over reefs of the Turks
and Caicos Islands (British West Indies) and set to view 1 m pixels in 8 spectral bands. In addition, reef habitats were sampled
in situ by visual assessment of percent cover in 1 m quadrats. Seagrass standing crop was assessed using a calibrated visual scale.
Benthic habitats were classified using hierarchical cluster and similarity percentage analyses of the field survey data. Two
levels of habitat discrimination were assessed: a coarse level (corals, algae, sand, seagrass) and a fine level which included
nine reef habitats. Overall accuracies of CASI-derived habitat maps were 89% and 81% for coarse and fine levels of habitat
discrimination, respectively. Accuracies were greatest once CASI data had been processed to compensate for variations in depth
and edited to take account of generic patterns of reef distribution. These overall accuracies were significantly (P<0.001) better than those obtained from satellite imagery of the same site (Landsat MSS, Landsat TM, SPOT XS, SPOT Pan, merged
Landsat TM/SPOT Pan). Results from CASI were also significantly better than those from interpretation of 1:10 000 colour aerial
photographs of reefs in Anguilla (Sheppard et al. 1995). However, the studies may not have been entirely comparable due to
a disparity in the areas mapped.
Accepted: 26 May 1997 相似文献
19.
The semi-diurnal tidal regime (≥2 m) in the Paria Gulf on the Atlantic coast of Venezuela, and the flat landscape of the region,
allow the penetration for tens of km of marine waters into the rivers draining the northeastern coastal plain of the country.
The levels of salinity, tidal flooding, and sedimentation decrease perpendicularly from the river channel toward the back
swamps. The vegetation varies sequentially from fringe mangroves along the river margins, to back swamps containing forests
dominated by Pterocarpus officinalis, herbaceous communities of Lagenocarpus guianensis, and palm swamps with Mauritia flexuosa, Chrysobalanus icaco, and Tabebuia spp. This environmental structure was used to test the hypotheses that: (a) mangrove distribution is strongly associated
with salinity of interstitial water, and (b) they occupy areas where tidal influence and sediment dynamics determine a relatively
open N cycle. Analyses of soil, water, and plants along a 1.5 km transect located near the confluence of the Guanoco and San
Juan Rivers (Sucre and Monagas States, Venezuela) revealed that: (a) conductivity decreased from 11 to 0.2 mmhos cm−1 from the river fringe to the internal swamp, whereas Na in the same stretch decreased from 100 to 2 μM; (b) average leaf
tissue concentrations of Na, P, and N decreased significantly along the transect; (c) P. officinalis showed a large Na-exclusion capacity indicated by positive K/Na ratios from 8 to 200, and Crinum erubescens counteracted Na by accumulating K above 1,000 mmol kg−1; (d) leaves varied widely in δ 13C (−25.5 to −32‰) and δ 15N (4 to −10.5‰) values. Samples were aggregated according to soil carbon content corresponding to those of the mangrove forest
belt (5–28 mol C kg−1; 0–650 from river fringe) and those of the back swamps (40–44 mol C kg−1; 700–1,500 m from river fringe). The concentrations of Na, P, and N (in mmol kg−1) and δ 15N values (in ‰) were significantly higher in the mangrove forest compared to the back swamp (Na 213 vs. 88; P 41 vs. 16; N
1,535 vs. 727; δ 15N 1.5 vs. −3.7), indicating that the fringe forest was not nutrient limited. These results support the hypotheses that mangroves
are restricted to the more-saline sections of the transect, and that the fringe forest has a more open N cycle, favoring 15N accumulation within the system. 相似文献
20.
Using expert knowledge and modeling to define mangrove composition,functioning, and threats and estimate time frame for recovery 下载免费PDF全文
Nibedita Mukherjee William J. Sutherland Md Nabiul I. Khan Uta Berger Nele Schmitz Nico Koedam 《Ecology and evolution》2014,4(11):2247-2262
Mangroves are threatened worldwide, and their loss or degradation could impact functioning of the ecosystem. Our aim was to investigate three aspects of mangroves at a global scale: (1) their constituents (2) their indispensable ecological functions, and (3) the maintenance of their constituents and functions in degraded mangroves. We focused on answering two questions: “What is a mangrove ecosystem” and “How vulnerable are mangrove ecosystems to different impacts”? We invited 106 mangrove experts globally to participate in a survey based on the Delphi technique and provide inputs on the three aspects. The outputs from the Delphi technique for the third aspect, i.e. maintenance of constituents and functions were incorporated in a modeling approach to simulate the time frame for recovery. Presented here for the first time are the consensus definition of the mangrove ecosystem and the list of mangrove plant species. In this study, experts considered even monospecific (tree) stands to be a mangrove ecosystem as long as there was adequate tidal exchange, propagule dispersal, and faunal interactions. We provide a ranking of the important ecological functions, faunal groups, and impacts on mangroves. Degradation due to development was identified as having the largest impact on mangroves globally in terms of spatial scale, intensity, and time needed for restoration. The results indicate that mangroves are ecologically unique even though they may be species poor (from the vegetation perspective). The consensus list of mangrove species and the ranking of the mangrove ecological functions could be a useful tool for restoration and management of mangroves. While there is ample literature on the destruction of mangroves due to aquaculture in the past decade, this study clearly shows that more attention must go to avoiding and mitigating mangrove loss due to coastal development (such as building of roads, ports, or harbors). 相似文献