Showing papers in "Wetlands Ecology and Management in 2001"

Depletion of the mangroves of Continental Asia

Abstract: The mangroves located around the Bay of Bengal and along the coast ofSouth China Sea are of special interest for many reasons. This coastlinereceives three major tropical rivers (Ganges, Irrawaddy, Mekong) and it hasthe world's largest mangrove stands in a single block (the Sunderbans). Thecontrasted climatic conditions from sub-arid (southeastern India), to moist(coastal Cambodia), and the extreme diversity of human impacts in one ofthe world's highest population densities (West Bengal in India andBangladesh), have created a mosaic of mangrove types that are floristicallyrich and with different histories, different ecological frameworks and distinct evolutionary trends.For the first time, we draw together remote sensing data along withessential structural and physiognomic parameters of mangrove forest areas.We have devised a sufficiently accurate coastal mapping methodologyproviding statistics on the actual areal extent of mangrove types andsub-types, both at local and continental scales. Some results are entirelynew, and others provide comparison with existing data. The exact extentof mangroves in Myanmar was previously unknown. Using remote sensingwe also demonstrate the magnitude of the ongoing deforestation in thiscountry. The current location and status of mangrove forests in the affectedarea are described using the methodology which is also being applied inother sites around the world.

Estimating above-ground biomass and production in mangrove communities of Biscayne National Park, Florida (U.S.A.)

Abstract: Total above-ground production isusually estimated by a combination of allometry andlitter collection. However, in coastal sites that aretidally influenced, or in juvenile or dwarf forestswhere the crown bases of dominant individuals maybegin within a few decimeters of ground level,estimates of community leaf production that depend onlitter collection may not be feasible. Thus, in thispaper, we present 1) allometric equations that allowaccurate estimation of total above-ground biomass ofthree mangrove species (Rhizophora mangle, Laguncularia racemosa, and Avicennia germinans)in very small to medium size classes, and 2) analternative method of estimating total above-groundproduction that overcomes the limitations of littercollection. The method we employ to estimate mangroveproductivity is an adaptation for woody plantcommunities of a procedure introduced by Dai andWeigert (1996) for grasslands. It incorporates adetailed census of all individuals within fixedsampling plots, along with periodic observations ofmarked leaf cohorts. The method allows the comparisonof biomass allocation patterns among forests thatdiffer widely in physiognomy and physiographicsetting.The method was applied to a South Florida fringemangrove forest in the early stages of recovery fromHurricane Andrew (August 1992), and an adjacent dwarfforest which was not substantially damaged by thestorm. Total above-ground production in the fringeforest from July 1996 through June 1997 was about 3times higher than dwarf forest production,26.1 Mg·ha-1·yr-1 vs.8.1 Mg·ha-1·yr-1, respectively. Furthermore, when compared to the dwarf forest, fringeproduction rates were approximately eight, six, six,and two times as high as dwarf forest rates forproproots, branches, stems, and leaves, respectively. Calculations of leaf production were based on mean redmangrove leaf longevities that ranged from about 189days to 281 days, depending on cohort and site.Repeated measures analysis of variance indicated thatleaf life spans did not differ significantly betweendwarf and fringe forests, but did differ among leafcohorts.Based on reported values for similar mangrove forests,the method provided reasonable estimates ofabove-ground biomass and production, while furnishingrelevant auxiliary information on spatial and temporalvariation in leaf demographic patterns. Furthermore,the partitioning of annual production between woodytissues and leaves followed the reported trend in mostforest ecosystems.

Gap creation and regenerative processes driving diversity and structure of mangrove ecosystems

Abstract: Turnover within both mangrove and terrestrial forests is driven by stand development in conjunction with factors influencing tree death and replacement at various temporal and spatial scales Development in terrestrial forests appears comparable with that in mangroves but turnover seems to differ considerably between these broad forest types The most important difference is in the character of small forest gaps Gaps are common in terrestrial forests but those in mangroves rarely involve falls of large older trees in the first instance Instead, mangrove trees usually die standing in small clusters of mixed age cohorts Identifying a common cause for gap creation in mangroves might be important towards understanding what drives forest turnover but there is a greater need to quantify this process Small-scale disturbance in mangrove forests is poorly quantified but preliminary evidence implies that its' importance may have been greatly under-estimated Based on available observations, a conceptual model of mangrove forest development and gap regeneration is proposed The model helps explain the peculiar characteristics and structure of mangrove forests and how these forests might respond to changing environmental conditions and disturbance at various landscape scales

Growth and nutrient dynamics of soft-stem bulrush in constructed wetlands treating nutrient-rich wastewaters

Abstract: The growth characteristics and nutritional status ofSchoenoplectus tabernaemontani (CC Gmelin)Palla (soft-stem bulrush or lake clubrush) wereinvestigated during the second and third growthseasons in four equivalent subsurface-flow, gravel-bedconstructed treatment wetlands Each wetland wassupplied with a different hydraulic loading rate ofagricultural wastewater, covering the range commonlyapplied to such systems Harvest and demographictechniques were combined to determine seasonalpatterns and gradients of growth and nutrientallocation, and net annual primary productivity(NAPP) Marked seasonal patterns of early springemergence, summer growth and autumn senescence wereobserved, with little over-wintering of liveabove-ground biomass Starch, the dominant long-termstorage substance, comprised ∼20% of rhizome dryweight (DW) in autumn Mobilization during springreduced concentrations by around half, with a trend ofincreasing depletion in the higher loaded wetlandsNAPP, including above-ground mortality, during thesecond growth season ranged between ∼25 and 35 kg DWm-2, with 10-23% allocated to below-groundgrowth Mean above-ground live and dead biomass rangedbetween ∼175 and 265 kg DW m-2 by mid-summer,with below to above-ground biomass ratios similar inall wetlands at between 06 and 07 Rhizomes, whichcomprised around 80% of the below-ground biomass,were generally restricted to the upper 10 cm of thesubstratum and over half the root biomass alsooccurred in this zone, with very few roots penetratingbelow 30 cm depth High culm concentrations of N,P, Mg and Zn in spring declined markedly over thegrowth season, while S and Ca showed generalincreases, and K, Fe and Cu remained relativelystable Gradients of decreasing tissue concentrationof most macronutrients were noted with increasingdistance from wastewater inflows Plant accumulationof N rose by 20-35 g m-2 and P by 4-9 g m-2with seasonal re-growth of above-ground shoots Netplant N and P uptake rates rose to maximum values of03 g N m-2 d-1 and 01 g P m-2d-1 in early summer, declining markedly duringlate summer and autumn Mass balance assessments of Nand P accumulation in plants at near maximum seasonalbiomass, after three growth seasons, showed that only6 to 11% of the N removal and 6 to 13% of the Premoval recorded from wastewaters applied to thewetlands could be ascribed to plant uptake andaccumulation

Halophytes – A resource for the future

Abstract: One of the more urgent global problems, particularly in arid and semi-arid regions of the world, is finding enough water and land to support the world’s growing food needs. By some estimates, an additional 500 million acres of new croplands are required over the next thirty years to feed burgeoning populations of the tropics and subtropics. Yet only 230 million acres are available in these areas for farming to expand. And, much of this land is forested and should realistically be preserved to maintain the integrity of remaining natural stands and ecosystem functioning. Furthermore, saline soils are a major problem of cultivated lands in semi-arid and arid areas. About 23% of the world’s 1.5 × 10 9 ha of cultivated land is saline and 37% is sodic. Approximately one third of the world’s irrigated land is salt-affected due chiefly to unsustainable irrigation practices. Freshwater resources are also being rapidly depleted and current agricultural irrigation practices are steadily increasing salinity levels in many regions. Rapid increases in population pressure are leading to greater utilization of remaining meager freshwater supplies for drinking, leaving even less for agriculture. In this complex scenario, it has become imperative to consider development of non-conventional agricultural technologies which might more effectively utilize degraded, marginal and saline lands for agriculture by using, the ‘so-called’, poor quality water (brackish water, seawater, and wastewater). An attractive option is the use of seawater or brackish water agriculture, and this has worked well in both inland and coastal sandy soils of some desert environments. Saline water aquifers exist in many arid lands of the world but these have been greatly under-utilized. This brackish water could be a major resource in saline agriculture to produce food, feed, and fiber and oil seeds on currently non-productive, saline arid lands. In further support of saline agriculture, there would be no shortage of water since seawater in the oceans makes up 97% of water on earth. Desert land is also plentiful, with around 43% of the earth’s total land surface being arid or semi-arid. A small portion of this (about 15%) is close to the sea and this would be convenient for growing crops using saline agriculture. This amounts to 130 million hectares of ‘new’ land that could arguably be brought into human or animal food production – without cutting down more forests or diverting scarce fresh water resources from current agricultural and community needs. Salt tolerant plants (halophytes, including salt marsh and mangrove plants) are highly evolved and specialised organisms with well-adapted morphological and physiological characteristics allowing them to proliferate in the soils possessing high salt concentrations. It is tempting to think we might exploit these plants for the better utilization of saline water, and for the rehabilitation of highly saline soils. Saline agriculture, however, must fulfill two conditions to be cost-effective. First, it must produce useful crops at yields high enough to justify the expense of pumping salty water. Second, researchers must develop successful agronomic techniques for growing saline, water-irrigated crops in a sustainable manner. These methods must also not contribute to further damage of natural environments. If applied successfully, this approach would lead to the domestication of wild, salttolerant plants for use as food, forage, and oilseed crops.

History and biogeography of the mangrove ecosystem, based on a critical reassessment of the paleontological record

Abstract: The geological record of mangrove plants is based on comparablemorphological characteristics of pollen, fruits and wood, of fossil andmodern species. But this record relies on the assumption that the ecologicaland habitat preferences of ancestral taxa have remained similar throughages. A reexamination of fossil evidence of Avicennia, Pelliciera,Sonneratia, Rhizophora, Bruguiera, Ceriops, etc.reveals that the modern mangrove flora was pantropic by the Eocene, andappears to have originated during Paleocene times. Earlier Paleozoic andMesozoic candidates for a mangrove ecology lack conclusive evidence oftheir exclusive association with tidal environments. It is therefore clear thatcontinental drift had a limited role in the dispersal and development ofmodern mangrove floras. The Eocene/Oligocene boundary crisis appears toherald a beginning of the biogeographic split between the current-dayeastern and western provinces of mangrove plants. But, while the climaticorigins of this major disjunction is not clearly understood, our reassessmentof Tertiary paleoclimates suggests that the major cooling events of themiddle Paleocene, the end of the Eocene and the middle Pliocene were themost likely influences on the evolution of mangrove floras. The associatedinvertebrates, especially molluscs, further support our assertion that amodern mangrove ecosystem was established only during the earliestEocene times. We summarize our interpretation in a set of 9 palinspasticmaps of fossil mangrove genera through their evolution ending with thecurrent, bipartite distribution of present day taxa.

Restoration principles emerging from one of the world's largest tidal marsh restoration projects

Abstract: One of the world’s largest tidal wetland restoration projects was conceived to offset the loss of nekton to oncethrough cooling at a power plant on Delaware Bay, USA. An aggregated food chain model was employed to estimate the area of tidal salt marsh required to replace these losses. The 5040 ha was comprised of two degraded marsh types – Phragmites-dominated marshes and diked salt hay farms – at eleven locations in oligo-mesohaline and polyhaline reaches of the estuary. At a series of ‘summits’ convened with noted experts in the field, it was decided to apply an ecological engineering approach (i.e., ‘self design’, and minimal intrusion) in a landscape ecology framework to the restoration designs while at the same time monitoring long-term success of the project in the context of a ‘bound of expectation’. The latter encompassed a range of reference marsh planforms and acceptable end-points established interactively with two advisory committees, numerous resource agencies, the permitting agency and multiple-stakeholder groups. In addition to the technical recommendations provided by the project’s advisors, public health and safety, property protection and public access to the restored sites were a constant part of the dialogue between the utility, its consulting scientists and the resource/permitting agencies. Adaptive management was used to maintain the restoration trajectories, ensure that success criteria were met in a timely fashion, and to protect the public against potential effects of salt intrusion into wells and septic systems, and against upland flooding. Herbicide spray, followed by prescribed burns and altered microtopography were used at Phragmites-dominated sites, and excavation of higher order channels and dike breaching were the methods used to initiate the restorations at the diked salt hay farms. Monitoring consisted of evaluating the rate of re-vegetation and redevelopment of natural drainage networks, nekton response to the restorations, and focused research on nutrient flux, nekton movements, condition factors, trophic linkages, and other specific topics. Because of its size and uniqueness, the Estuary Enhancement Program as this project is known, has become an important case study for scientists engaged in restoration ecology and the application of ecological engineering principles. The history of this project, and ultimately the Restoration Principles that emerged from it, are the subjects of this paper. By documenting the pathways to success, it is hoped that other restoration ecologists and practitioners will benefit from the experiences we have gained.

Changes in the distribution of mangroves and saltmarshes in Jervis Bay, Australia

Abstract: The decline of saltmarsh in Currambene Creek andCararma Inlet, in Jervis Bay, eastern Australia, inthe period 1944–1999 has been documented through photogrammetric analysis. The area of saltmarsh hasdeclined in Currambene Creek by approximately 52.5%and in Cararma Inlet by approximately 35%. InCurrambene Creek the decline of saltmarsh is primarilydue to the landward encroachment of mangroves, whilein Cararma Creek the seaward encroachment of Melaleuca and Casuarina have more significantlycontributed to losses of saltmarsh. Regional sea-levelrise is excluded as a primary cause of thistransgression. A more plausible hypothesis involvesan increase in the delivery of freshwater andnutrients to the intertidal environments in responseto higher rainfall and catchment modifications.

Biogeochemical cycling of methylmercury at Barn Island Salt Marsh, Stonington, CT, USA

Abstract: Monomethylmercury (MMHg) is toxic, and is the primary form of Hg thatbioaccumulates in the food web. An understanding of its distribution,production, and transport is needed. Prior investigations indicate thatmethylation is mediated by sulfate-reducing bacteria, yet limited in highsulfate environments. High rates of microbial respiration and strong oxygengradients are found in salt marshes. It is hypothesized that significant in situ methylation takes place in the redox transition zone of sulfate rich(≥ 28 mM) salt marsh sediment. Results from a water column surveyof Barn Island Salt Marsh in October 1996 showed that ca. 61pmol m-2 d-1 of dissolved MMHg were discharged toadjacent coastal waters, while 16 pmol m-2 d-1 ofparticulate MMHg were entrained in the marsh, implying an in situsource. In-sediment MMHg production rates were determined by203Hg radiotracer studies. At the surface, methylation rates variedover both long (i.e., 100's m; 11–1120 pmol m-2 d-1) andshort (i.e., 10 cm; 11–108 pmol m-2 d-1) spatial scales. Methylation rate profiles from both low and high MMHg production sitesexhibited an exponential decrease below the redox transition zone. Porewater was collected with multi-chambered in situ dialysis (30 kDa)samplers [Peepers] and analyzed for MMHg. Temporal differences in porewater MMHg accumulation (i.e., May > September > November)were found. Results from May showed a significant gradient at thesediment water interface. The transport out of the sediments estimated byFick's Law (ca. 390 pmol MMHg m-2 d-1) suggeststhat MMHg entered the marsh water by diffusion. This workdemonstrates the potential for elevated in situ Hg methylation in highsulfate environments.

Stratigraphy and geologic history of a southeastern salt marsh basin, North Inlet, South Carolina, USA

Abstract: Forty seven vibracores and fifteen radiocarbon dates have beenobtained to outline the Holocene history of the North Inlet saltmarsh basin. Marsh deposits date from about 3500 years BP and havetransgressed over a Late Pleistocene beach-ridge terrain that waspartly eroded by Late Holocene tidal channel meandering. Marsh mudalso has prograded southward over shallow subtidal estuarine Macomamuds which date from about 4500 years BP and which are stillaccumulating in adjacent Winyah Bay. The southward migration of themarsh environment probably is due to the southward migration ofboth North Inlet and the mouth of Winyah Bay. The stratigraphy ofthe North Inlet basin offers no evidence for Late Holocene sea-level oscillations.Application of this model of marsh history to the study long-term ecosystem succession driven by slowly rising sea level isdiscussed.

Salinity tolerance in some mangrove species from Pakistan

Abstract: Growth, ionic and water relations of three mangrove species viz. Avicennia marina, Ceriops tagal and Rhizophora mucronata werestudied in different seawater concentrations (0, 25, 50, 75 and 100%).All mangrove species showed optimal growth at 50% seawater. Relativelymore biomass was accumulated by R. mucronata while C. tagalhad the tallest individuals. Tissue water potential became more negativewith the increase in salinity and stomatal conductance was decreased in allplants. Higher stomatal conductance was noted in R. mucronata,followed by A. marina and C. tagal. Sodium and chloride ionsincreased with the increase in salinity and this accumulation was muchhigher in A. marina.

Seed banks and seed population dynamics of halophytes

Abstract: In this review I will describe the importance of seed banks and thepopulation dynamics of seeds on the distribution of species in salinehabitats. The main questions being examined in this review include: 1.Does the seed bank represent the flora of the entire salinity gradient or isit restricted to the species in each zonal community? 2. Is the size andspecies composition of the persistent seed bank regulated by the degree ofsalt stress in habitats along an environmental gradient? 3. Does thepopulation dynamics of seeds influence the temporal and spatial distributionof plant species in saline habitats? Seed banks may be transient orpersistent depending upon the physiological responses of species and thesoil environment in which the seeds are found. The formation of zonalcommunities in salt marsh environments is affected by changes in soilsalinity and flooding along an elevational gradient. Population dynamics ofseeds have been found to determine the spatial and temporal distributionof species along salinity gradients. The flora and relative density of speciesof zonal communities are significantly dependent upon the stress toleranceof species at different stages of development and the presence of transientor persistent seed banks. The occurrence of a seed bank is related to thesalinity tolerance of species at the germination stage of development, aseeds ability to tolerate hypersaline conditions and flooding, and whetheror not species are able to maintain a persistent seed bank until hypersalineconditions are alleviated.

Influence of salinity and temperature on the germination of Kochia scoparia

Abstract: Kochia scoparia is one of the most common annual halophytes foundin the Great Basin Seeds were collected from a population growing in asalt playa at Faust, Utah and were germinated at 5 temperature regimes(12 h night/12 h day, 5–15 °C, 10–20 °C, 15–25 °C,20–30 °C and 25–35 °C) and 6 salinities (0, 200, 400,600, 800 and 1000 mM NaCl) to determine optimal conditions forgermination and recovery of germination from saline conditions after beingtransferred to distilled water Maximum germination occurred in distilledwater, and an increase in NaCl concentration progressively inhibited seedgermination Few seeds germinated at 1000 mM NaCl A temperatureregime of 25 °C night and 35 °C day yielded maximumgermination Cooler temperature 5–15 °C significantly inhibited seedgermination Rate of germination decreased with increase in salinityGermination rate was highest at 25–35 °C and lowest at5–15 °C Seeds were transferred from salt solutions to distilled waterafter 20 days and those from high salinities recovered quickly at warmertemperature regimes Final recovery germination percentages in high salttreatments were high, indicating that exposure to high concentration ofNaCl did not inhibit germination permanently

Population genetic structure of Ceriops tagal (Rhizophoraceae) in Thailand and China

Abstract: Knowledge of the amount and patterns of genetic variation within and among populations of mangrove trees is essential for devising optimum genetic management strategies for their conservation and sustainable utilization. Ceriops tagal is a widespread viviparous mangrove. Genetic diversity in the species was examined with inter-simple sequence repeat (ISSR). Nine natural populations were collected from Thailand and China. The estimates of genetic variation were extremely low (HT = 0.0179 ± 0.005, HS = 0.0084 ± 0.001), and only 47% of the total gene diversity was maintained within populations (GST = 0.529). The eastern coastal populations of Thailand were more similar to populations from China than to populations from the western coastline of Thailand. A high level of Nei's genetic identity exists between populations of C. tagal (I = 0.989), suggesting their common ancestry. The low levels of genetic diversity in the species may result from a series of genetic bottlenecks during several glacial epochs.

Development of an automated micrometeorological method for measuring the emission of mercury vapor from wetland vegetation

Abstract: The ability of green plants to act as conduits to enhance the transport ofHg from soils to the atmosphere is now established, but the data base isseverely limited. The potential role of this process in mobilizing Hg inglobal and regional cycles makes it imperative that automated methods bedeveloped to increase our capability to measure and understand the processin a variety of ecosystems. We previously published a tower-basedmicrometeorological gradient method for measuring gas-phase Hg°fluxes in terrestrial systems based on the Modified Bowen ratio (MBR)approach. The method relied on demanding and time-consuming manualsampling of Hg gradients. Automated Hg sampling methods now exist, andwe describe here applications of the Tekran Hg analyzer to automatednear-real-time measurements of Hg gradients over wetland vegetation. Weuse these data with MBR to compute fluxes of Hg from those of othertrace gases. From 1996 to 1998 we sampled Hg fluxes over emergentmacrophytes in the Florida Everglades, beginning with manual methods, butlater deploying automated methods for most of the study to collect morethan 500 30-min fluxes over 2 y. The limitations of the manual methodresulted in considerable uncertainly in our earlier observations, even to theextent that we initially doubted that vegetation emissions were real. However, the automated method allowed us to quantify the actualdevelopment of Hg emission gradients over wetland vegetation. Followingsunrise Hg fluxes show diel patterns similar to those of CO2 andH2O, providing information on the possible mechanisms of Hgemission. Our data suggest mean daytime emission rates of Hg over thesewetlands on the order of 30 ng m-2 h-1. Fluxes wereinfluenced by temperature, solar radiation, and atmospheric turbulence. There exists a significant biotic re-emission of Hg° from the oceans,and our data provide the first direct evidence of a similar process insubtropical wetlands.

Patterns of natural and anthropogenic disturbance of the mangroves on the Pacific Island of Kosrae.

Abstract: Mangroves in many parts of the world are subjected to frequent, large-scaledisturbances. A possible exception is Kosrae, Federated States of Micronesia(FSM), a small volcanic island in the west-central Pacific Ocean. Relativesea level has been stable for most of the last 1000 years and the last tropical cyclone to affect the island was in 1905. Many trees on Kosrae,especially individuals of the species Sonneratia alba, thereforeappear to die only after reaching advanced ages and exceptional sizes. Themost widespread anthropogenic disturbance is harvesting of trees for fuelwoodand poles, which is done selectively and generally creates small, dispersedgaps. Other forms of anthropogenic disturbance, such as modifications ofcoastal landforms, alterations of freshwater inflows road construction andconversion to residential or agricultural uses, are still relatively minorbut have led to some irreversible losses. The economy of Kosrae is basedto a large degree on income derived from a Compact of Free Association betweenthe FSM and the United States, an agreement that has an uncertain future.Many of the funding provisions of the Compact expire in 2001 and, if notrenewed, may have dramatic impacts on resource use. This in turn may leadto a much greater level of anthropogenic disturbance of what are now someof the world's most intact mangrove swamps.

Variability in Flood Disturbance and the Impact on Riparian Tree Recruitment in Two Contrasting River Systems

Abstract: The vegetation within the riparian zone performs animportant ecological function for in-stream processes.In Australia, riparian zones are regarded as the mostdegraded natural resource zone due to disturbancessuch as river regulation and livestock grazing. Thisstudy looks at factors influencing vegetation dynamicsof riparian tree species on two contrasting riversystems in Western Australia. The Blackwood River insouth-western Australia is influenced by aMediterranean type climate with regular seasonalwinter flows. The Ord River in north-western Australiais characterized by low winter base flows andepisodic, extreme flows influenced by monsoon rains inthe summer. For both rivers, reproductive phenology ofstudied overstory species is timed to coincide withseasonal river hydrology and rainfall. An evendistribution of size classes of trees on the BlackwoodRiver indicated recruitment into the population iscontinual and related to the regular predictableseasonal river flows and rainfall. In contrast, on theOrd River tree size class distribution was clustered,indicating episodic recruitment. On both rivers treeestablishment is also influenced by elevation abovethe river, microtopography, moisture status and soiltype. In terms of vegetation dynamics riparianvegetation on the Ord River consists of long periodsof transition with short lived stable states incontrast to the Blackwood river where tree populationstructure is characterized by long periods of stablestates with short transitions.

The mangrove palm Nypa in the geologic past of the New World

Abstract: The paleontological history of Nypa, known today as the mangrovepalm, is traced through geological time back to the Late Cretaceous. Emphasis is laid on the New World occurrences, especially in NorthAmerica, where Nypa is known from fossil fruits and pollen. In SouthAmerica, the stratigraphic range of this palm extends from theMaastrichtian to the late Eocene, whereas in North America, Nypa isrestricted to only the Eocene. Nypa occurs as pollen all along theAmerican Gulf Coast from the early Eocene (Ypresian) to the late Eocene(Priabonian), while fruit records come from the early and middle Eoceneof Maryland and Texas, respectively. The floristics of these Eocenemangroves, including possible mangrove associates, and the developmentof mangrove vegetation in the neotropics through the Tertiary andQuaternary, are discussed. New paleobotanical evidence from a middleEocene faunal and floral assemblage in Texas, the Casa Blanca flora (LaredoFormation, Claiborne Group), which contains fossil Nypa pollen andfruits, is described in detail.

The role of salt marshes in the Mira estuary (Portugal)

Abstract: The Mira estuary is a narrow entrenched pristine estuary of the Ria type, about 30 km long. It comprises an area of 285 ha of salt marsh, of which250 ha have been proposed for reclamation for aquaculture. Dredging, village and recreation development menace the yet undisturbed estuarine ecosystem. To assess the biological importance of this wetland, a multidisciplinary study was conducted in apart of the salt marsh, considered as being representative of the whole area. Halophytic vegetation covering 75% of the total salt marsh site is dominated by Spartina maritima (28% of total vegetation area). Total primary production attains63,766 kg/yr (dw). A net export of 1541 kg/yr of COM to the relatively oligotrophic adjacent waters was also found. Insects and birds are described for the first time in the saltmarsh. Macrobenthic communities are dominated by Hediste diversicolor, Nepthys caeca and Scrobicularia plana. The fiddler crabUca tangeri attains here its north distribution limit. The mud flats and creeks associated with the salt marsh act as a nursery for 40.8% of the fish species present. The food web is dominated by detritivorous species like the grey mullets. The results obtained in this study support the need for an effective conservation of this area.

Low salinities adversely affect photosynthetic performance of the mangrove, Avicennia marina

Abstract: Photosynthetic performance of the highly salt tolerant mangrove, Avicennia marina, was compared at two sites differing insubstrate soil salinities. Carbon dioxide exchange and chlorophyll fluorescence weremonitored at a high salinity site in Durban Bay (35‰) and at a low salinitysite in Beachwood (< 12‰). Mean CO2 exchange, conductanceand transpiration were consistently higher at the high salinity site. Carbondioxide response curves indicated that carboxylation efficiency was higherand stomatal limitation lower at the Durban Bay site. PSII quantum yield,electron transport rates (ETR) and intrinsic PSII efficiency(Fv/Fm) were significantly higher at the high salinity site.Quenching analysis indicated a higher degree ofphotoinhibition/photoprotection in leaves at the low salinity site. Predawnand midday leaf water potentials were –1.6 and –3.1 MPa at Beachwood,compared to –2.6 and –3.8 MPa, respectively, at Durban Bay. Leafconcentrations of Na+, K+, Ca2+, Mg2+,Cl- and N were significantly higher at Durban Bay. Photosyntheticperformance is apparently impaired at the low salinity site in Beachwood asa result of K+ and N deficiencies in the leaves.

Gas space and oxygen exchange in roots of Avicennia marina (Forssk.) Vierh. var. australasica (Walp.) Moldenke ex N. C. Duke, the Grey Mangrove

Abstract: Aerenchyma pervades the cortex of the whole root system in Avicenniamarina var. australasica plants grown for 3 to 5 years in artificial-tidaltanks. The gas spaces appear to be schizogenous in all but the finest roots,where some apparently lysigenous gas spaces develop. Gas spaces in thepith are small. Pneumatophores examined at the time the tips are growingpossess subrisules on the tips as well as lenticels on mature regions. At othertimes subrisules are not seen. When the tide floods the pneumatophores,gas pressure and oxygen concentration go down – pressure by 1.7 kPa orless, but oxygen by as much as 3 mol m-3, or more in some cases.On draining, pressure recovers immediately to atmospheric, but oxygenslowly rises to a plateau below the concentration in the atmosphere. Thechanges in oxygen concentration are consistent with oxygen supply bydiffusion. The contribution of oxygen made by the small influx of air onpressure recovery is only a minor fraction of the respiratory oxygenrequirement. Wet weather at low tide restricts gas exchange, affecting bothpressure and oxygen. The pressure and oxygen changes are repeated overmany tidal cycles. The results are compared with those for other speciesand situations in the literature.

Mercury accumulation in sediment cores and along food chains in two regions of the Brazilian Pantanal

Abstract: The Pantanal is a 140,000 km2 floodplain wetland stretching acrosswestern Brazil and parts of Bolivia and Paraguay. Gold mining withmercury (Hg) amalgamation has thrived since 1980 along its northern rim. We quantified Hg accumulation in sediment cores (N = 5) and food chainsin this general region of the northern Pantanal and in a reference region,200 km deeper into the wetland (Acurizal). Cores were dated with210Pb and 137Cs using direct gamma-assay. Total Hg wasanalyzed by cold-vapor atomic fluorescence using a gold-meshpre-concentration trap. Average pre-1940 Hg accumulation in cores wasnot significantly different (N = 5, p= 0.14) between both regions andcomparable with rates calculated for global reference sites. Post gold-rushHg (post-1980) deposition averaged 55 ± 11.3 μg m-2yr-1 in the northern impacted region and was more than 1.5 timeshigher than the post-1980 rate in Acurizal, implying a regional Hg effectof gold mining. Post-1980 Hg accumulation in Acurizal, in turn, was 2.1times the rate reported for a global reference during that time period,suggesting an additional basin-wide effect over such reference sites. Bycombining our core data with assessments of the size of the impacted areaand the amount of Hg released to the region since 1980, we estimated thatonly 2–8% of this Hg was recovered as a sedimentary signal. Theremainder of the Hg was lost to the atmosphere, downstream areas, orstored in biota. Hg concentrations in surface sediments in the northernPantanal (45.5 ± 5.5 ng gdry -1) were significantlyhigher than those in our reference region (29.1 ± 0.7ng gdry -1). Hg levels in primary producers were alsoelevated in the northern Pantanal. Eichhornia crassipes rootscontained 2.7–3.0 times more mercury than shoots in both regions and Salvinia auriculata, suggested as a biological monitor for Hg pollution,contained almost four times more mercury in the northern Pantanal (90.7± 9.1 ng gdry -1) than in Acurizal (24.5 ± 3.3ng gdry -1). Plant grazers and scavengers, such as apple snails(Pomacea sp.) and adult water beetles (Fam. Hydrophilidae), werelow in Hg, confirming previous data showing that the channeling of mercuryfrom lower to higher trophic levels along herbivorous links was inefficientcompared to transfer along carnivorous links. Collections of 12–16individuals of four species of Characidae (Aphyocharax sp., Tetragonopterus sp., Serrasalmus spiropleura and Pygocentrisnattereri) in both regions showed elevated Hg body burdens in bothpiranhas S. spiropleura and P. nattereri from the northernPantanal (149.9 ± 84.2 and 302.2 ± 159.1ng gdry -1, respectively). Fish length for each species was notstatistically different between regions. P. nattereri length correlatedsignificantly (p<0.001) with Hg content in both regions, but the slopeof the regression in the northern Pantanal was 2.6 times the slope for theAcurizal collection, indicating an elevated rate of biomagnification in theHg-impacted region. Signals of Hg use in mining can be quantified insediment core chronologies and biological tissues, although species atdifferent trophic levels show dissimilar impacts. Mechanisms involved in Hgmagnification along food chains deserve more attention, particularly intropical regions where the threat of chronic exposure to this neurotoxinmay have the greatest implications for biodiversity.

Effects of salinity and nitrogen on growth, ion relations and proline accumulation in Triglochin bulbosa

Abstract: The effects of salinity and nitrogen on growth, ion relations and prolineaccumulation in the monocotyledonous halophyte, Triglochin bulbosa,was investigated in hydroponic culture over 5 months. The experimentaldesign was a 3 × 3 factorial with three salinity treatments (0, 150 and 300 mol m-3 NaCl) and three levels of N (5, 10 and 20 μgml-1 N as NaNO3). Total and root dry biomass accumulationwere significantly affected by salinity, but not by N or N × salinityinteraction. Increase in NaCl from 0 to 150 mol m-3 had no effecton total or root dry biomass, while further increase in salinity to 300mol m-3 significantly reduced biomass by 21% and 25%respectively. Shoot dry biomass, which was significantly affected by N andnot by salinity, increased with increase in N from 5 to 10 μgml-1. Ion concentrations in roots and shoots were significantlyaffected by salinity, but not by N or N × salinity interaction. Theconcentration of Na+ and Cl- in roots and shoots increasedprogressively with an increase in salinity, while that of K+ decreased. Under non-saline conditions, Na+/K+ ratios were low (0.41to 0.44) and increased significantly with an increase in salinity in both rootsand shoots. Shoot sap osmotic potentials decreased progressively with anincrease in salinity. Increase in N in the hydroponic solution from 5 to20 μg ml-1 significantly increased root and shoot N by 66%and 41% respectively. Tissue concentrations of proline were significantlyaffected by salinity and substrate N but not by N × salinity interaction. Theconcentration of proline in roots and shoots increased significantly by334% and 48%, respectively, with an increase in salinity from 0 to 300mol m-3 NaCl. Increase in substrate N from 5 to 20 μg ml-1 significantly increased proline in roots and shoots by 66% and41% respectively. The significance of substrate N on the accumulationof proline is discussed in relation to salt tolerance.

Effects of tadpole grazing on periphytic algae in ponds

Abstract: Tadpole impact on periphytic algae was estimated with an exclosure experiment in the field. Algae growth on control (exposed) and experimental (netted-in) Perspex plates was measured in 12 ponds in 1991 and 8 in 1993.An index of snail (Lymnea and Planorbis)presence in the ponds was used to correct their effect. Grazing pressure (difference in amount of algae between control and experimental plates)differed between ponds. The difference was correlated to amount of Rana tadpoles present in the pond. At the higher densities of tadpoles observed in the study ponds, the algae standing crop on exposed plates was about 50–75% of that on netted-in plates. These result demonstrate that there is potential for effects of exploitation competition in ponds with a high tadpole density.

Spatial and temporal variability in benthic processes along a mangrove-seagrass transect near the Bangrong Mangrove, Thailand

Abstract: 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.

Effects of hydrology on spatial patterns of soil development in created riparian wetlands

Abstract: Surficial soil development was studied in four wetland basins created on the floodplain of the Des Plaines River near Chicago, Illinois, USA. These studies determined changes in the spatial distribution of plant-available nutrients as a result of establishing two different wetland hydrologic regimes. Three wetland basins had mineral soils and one an organic soil. A geostatistical analysis including kriging of collected data indicated that all soil parameters showed significant changes in their spatial structure as a result of the water inputs and unidirectional flows. The degree of spatial variability as indicated by autocorrelation in the soil data (i.e., points closer to one another are more similar than points further apart due to the influence of landscape processes) declined for all parameters except Mg+2. Temporal changes in the spatial patterns of extractable phosphorus (P) and percent organic carbon (OC) tended to be inverse; P declined in areas where OC increased and vice versa. The spatial pattern of these changes was dissimilar in the mineral soils as compared to the organic soil and was related to patterns of primary productivity. Zones of P uptake and OC accumulation were also related to wetland hydrology and primary productivity. Changes in the distribution of nutrients, particularly P, may be viewed as a result of nutrient spirals within the wetlands. By comparison, the reorganization in the concentrations of K+ and Ca+2 appear to have been mediated by cation exchange processes. The formation of new concentration gradients was strongly related to both flow pathways and the different water inflow rates. The formation of concentration gradients in exchangeable cations was not reflected in the average concentrations within each basin. Mean values changed significantly in only a few instances. Reducing data in this way missed important biogeochemical changes occurring within the experimental wetland basins.

Storage and export of mercury from a contaminated bay (Ria de Aveiro, Portugal)

Abstract: Mercury has been determined in water, suspended particulate matter (SPM)and sediments (solid fraction and pore water) collected in a heavilycontaminated confined area (Largo do Laranjo) of the Ria de Aveiro.Mercury has been analysed in seabass (Dicentrarchus labrax) capturedin several locations of the lagoon. The levels of mercury in water and SPMin the contaminated sampled places fluctuated daily with the tide (from 10to 53 ng.dm-3 and 3.5 to 26 μg.g-1, respectively),indicating the export at the tidal rhythm. Bottom sediments exhibitedhigher concentrations, the maximum (48 μg.g-1) occurringnear the anthropogenic source at depths corresponding to the periods ofhigher industrial discharges. Mercury concentrations in pore waters (max.80 ng.dm-3) exceed the values found in the water column and werehigher at depths where Acid Volatile Sulphides (AVS) presented broadmaximums. This implies a remobilization at anoxic conditions. However theexport across the sediment-water interface predicted through moleculardiffusion is low (between 1 to 4 × 10-3 ng.cm-2.h-1) incomparison to the industrial input. The anthropogenic mercury appears tobe rapidly accumulated in seabass, a predator fish that enter seasonally inLargo do Laranjo.

Growth and establishment of mangrove ( Avicennia marina ) on the coastlines of Kuwait

Abstract: Mangrove (Avicennia marina) communities constitute an importantcomponent of the renewable natural vegetation resources of the coastalzones of the Arabian Gulf south of Kuwait. Attempts to introduce themangrove into the intertidal zones of the coastline of Kuwait are underwaybecause of the expected favorable environmental impact of this plant, andbecause of its moderating influence on the local climate and enhancementof the aesthetic and recreational value of the coastlines and fisheryresources. Propagules were collected from natural stands of mangrove inBahrain and the United Arab Emirates. Silvicultural practices were followedto produce healthy plants after growing of propagules in the greenhouse.Observations indicated that there is a positive correlation betweenpropagule weight and the length of the seedling stem. Outplanting wasdone in two sites in the intertidal zone around the Sulabikhat Bay, Kuwait.Data on plant survival showed that the most suitable level for successfulestablishment of mangrove was around or below the 3-meter contour tidalline. After 7 years of growth, plants reached a mean height of 250 cm,which is close to the height of their parent trees in Bahrain. The U.A.E.stock plants reached 288 cm after 5 years of growth in Kuwait. Plantsflowered and produced viable seeds. The biological feasibility ofestablishing mangrove plantations in the intertidal flats of Kuwait's coastlineswas documented from the field observation of the experimental plantations.Studies to document the environmental impact of the introduction areunderway.

The effects of iron ore dust on mangroves in Western Australia: Lack of evidence for stomatal damage

Abstract: Anecdotal evidence suggests that iron ore dust derived from industrialshiploading activities in north-western Australia may be more injurious tomangroves than is naturally-derived dust, because of its more angularstructure and presumed ability to damage stomatal cells Abaxial hairs onthe most common mangrove, Avicennia marina (Forfk) Vierh, havebeen thought to exacerbate this effect through trapping and retaining dustThis study examined this hypothesis Leaves were collected from dustyindustrial areas and natural environments Leaves in dusty environmentswere chosen on the basis of their thick coating of iron ore dust on both leafsurfaces Approximately 3,000 stomata were examined in detail using lightmicroscopy Hair density, stomatal aperture, cell condition and presence ofdust were also noted Despite there often being a visible layer of dust onthe abaxial and adaxial surfaces of the leaf, evidence for dust of any kindwithin stomatal spaces was noted, in total, only three times The lack ofvisible dust in stomata was attributed to three factors; the density andmorphology of the abaxial hairs, which prevent dust from enteringthe space between the hairs, and the improbability of dust circulating in thestagnant air within that space and moving against gravity past the guardcells It was concluded that if iron ore dust affects mangroves, it must doso by some other mechanism, such as either increased temperature, shadingor a restriction of transpiration by the thickness of the dust on the abaxialsurface