Showing papers on "Wetland published in 1991"

Sediment and nutrient retention by freshwater wetlands: effects on surface water quality

Abstract: Freshwater wetlands alter surface water quality in ways which benefit downstream use. This review summarizes the mechanisms of freshwater wetland interaction with sediment and nutrients that affect surface water quality. The mechanisms vary in magnitude and reversibility, and differ among wetland types. They include sedimentation, plant uptake, litter decomposition, retention in the soil, and microbial processes. Sedimentation is a relatively permanent retention mechanism whereby particulates and associated contaminants are physically deposited on the wetland soil surface. Plant uptake and litter decomposition provide short‐to long‐term retention of nutrients, depending on rates of leaching, translocation to and from storage structures, and the longevity of plant tissues. Plant litter can also provide a substrate for microbial processing of nutrients. Wetland soils sorb nutrients, and provide the environment for aerobic and anaerobic microorganisms that process nutrients. Wetland storage compartm...

A review of the salt sensitivity of the Australian freshwater biota

Abstract: In Victoria, Australia, both dryland salinity and salinity in irrigation regions are serious agricultural problems. One option to control the latter is to pump groundwater to maintain it below the surface. However, this leaves a saline wastewater for disposal, probably into local streams or wetlands. This review of the salt sensitivity of the biota of Australian streams and wetlands gives information of interest to those responsible for developing controls on these discharges. The review addresses the lethal and sub-lethal effects of salinity on microbes (mainly bacteria), macrophytes and micro-algae, riparian vegetation, invertebrates, fish, amphibians, reptiles, mammals, and birds. Data suggest that direct adverse biological effects are likely to occur in Australian river, stream and wetland ecosystems if salinity is increased to around 1 000 mg L−1. The review highlights a general lack of data on the sensitivity of freshwater plants and animals to salinity increases.

Creating Freshwater Wetlands

Abstract: Marshes, Bogs, Swamps, Sloughs, Fens, Tules, and Bayous Introduction Wetland Definitions Wetland Classification Functions of Natural Wetlands Summary Wetland Regulation Introduction "The Comprehensive Wetlands Conservation and Management Act of 1995" Wetland Categorization Mitigation Three Important Components - Water, Soil, and Vegetation Introduction Hydrology Soils Vegetation Nature's Methods for Creating and Maintaining Wetlands Large Scale: Geologic Small-Scale Factor Maintenance Wetlands: Functions and Values Introduction Life Support Functional Values Water Purification Hydrologic Modification Erosion Protection Open Space and Aesthetics Cultural Resources Recreation and Education Bio-geo-chemical Cycling Defining Your Objectives Creation or Restoration? Objectives Wetlands Functions and Objectives Determining Functional Values Advice and Assistance The Team Approach Technical Assistance Financial Assistance Summary Site Selection and Evaluation Introduction General Considerations Specific Considerations Project Planning Design Selection Specific Designs Major Structures Dikes, Dams, and Berms Water Control Structures Estimating Capacity Structure Comparisons Emergency Spillways Plans and Construction Preparation of Plans Preparation for Construction Construction Plant Selection Introduction Hydrology Substrate Species Characteristics Sources of Plant Materials Summary Planting Vegetation Introduction Natural Methods Planting Vegetation Summary Attracting and Stocking Wildlife Constructed Wetlands-Special Considerations Introduction Design Construction Operation Monitoring A Case History Summary and Comments Operation and Maintenance Introduction First Year Second Year Subsequent Years Bogs and Fens Forested Wetlands Other Considerations Mosquitos System Perturbations Routine Maintenance Monitoring Wetland Restoration and Creation Appendix A. References Appendix B. Common and Scientific Names Appendix C. Sources of Supply Appendix D. Wetland Training Appendix E. Wetland Newsletters and Journals Index

Effects of Nitrogen Loading on Wetland Ecosystems with Particular Reference to Atmospheric Deposition

Abstract: Wetlands fulfill an important role in global biogeochemical cycles. For example, they transfer to the atmosphere globally significant quantities of CH4 (60, 61) and reduced sulfur gases (127). Coastal marshes may function as net sinks for N20 (46). Because of the anaerobic nature of their soils, wetlands act as sinks for organic carbon. It has been estimated that wetlands once sequestered a net of 57 to 83 x 106 metric tons of carbon per year worldwide, but recent widespread drainage of wetland soils has shifted the carbon balance (7). Although this rate of carbon uptake is small in comparison to other global carbon fluxes, such as the annual release of carbon from combustion of fossil fuel (5-6 x 109 metric tons yr1) (112) or the net uptake of C02-C by the ocean (1.6 x 109 metric tons yr-1) (129), it is important when the net balance between large fluxes is considered, and it is certainly important over geologic time scales. Locally, wetlands function as habitats for wildlife, as flood control systems, as stabilizers and sinks for sediments, as storage reservoirs for water, and as biological filters that maintain water quality. For example, riparian

Are Spartina Marshes a Replaceable Resource? A Functional Approach to Evaluation of Marsh Creation Efforts

Abstract: Marsh creation has come into increasing use as a measure to mitigate loss of valuable wetlands. However, few programs have addressed the functional ecological equivalence of man-made marshes and their natural counterparts. This study addresses structural and functional interactions in a man-made and two natural marshes. This was done by integrating substrate characteristics and marsh utilization by organisms of two trophic levels. Sediment properties, infaunal community composition, andFundulus heteroclitus marsh utilization were compared for a man-madeSpartina salt marsh (between ages 1 to 3 yr) in Dills Creek, North Carolina, and adjacent natural marshes to the east and west. East natural marsh and planted marsh sediment grain-size distributions were more similar to each other than to the west natural marsh due to shared drainage systems, but sediment organic content of the planted marsh was much lower than in either natural marsh. This difference was reflected in macrofaunal composition. Natural marsh sediments were inhabited primarily by subsurface, deposit-feeding oligochaetes whereas planted marsh sediments were dominated by the tube-building, surface-deposit feeding polychaetesStreblospio benedicti andManayunkia aestuarina. Infaunal differences were mirrored inFundulus diets. Natural marsh diets contained more detritus and insects, because oligochaetes, though abundant, were relatively inaccessible. Polychaetes and algae were major constituents of the planted marshFundulus diet. Though naturalmarsh fish may acquire a potentially less nutritive, detritus-based diet relative to the higher animal protein diet of the planted marsh fish,Fundulus abundances were markedly lower in the planted marsh than in the natural marshes, indicating fewer fish were being supported. LowerSpartina stem densities in the planted marsh may have provided inadequate protection from predation or insufficient spawning sites for the fundulids. After three years, the planted marsh remained functionally distinct from the adjacent natural marshes. Mitigation success at Dills Creek could have been improved by increasing tidal flushing, thereby enhancing, access to marine organisms and by mulching withSpartina wrack to increase sediment organic-matter content and porosity. Results from this study indicate that salt marshes should not be treated as a replaceable resource in the short term. The extreme spatial and temporal variability inherent to salt marshes make it virtually impossible to exactly replace a marsh by planting one on another site.

Land degradation: development and breakdown of terrestrial environments.

Abstract: Preface Acknowledgements 1. Land degradation: an overview 2. Why is land degradation occurring? 3. Land degradation through global pollution: the 'greenhouse effect' 4. Land degradation through global pollution: stratospheric ozone depletion, acid deposition and tropospheric ozone increase 5. Degradation of tropical rainforests, tropical/subtropical seasonally dry and tropical/subtropical upland forests, woodlands and scrublands 6. Degradation of seasonally dry tropical/subtropical and Mediterranean woodlands and scrublands, temperate and high-latitude forests 7. The degradation of wetlands, tundra, uplands and islands 8. Land degradation in drylands 9. Non-erosive soil degradation 10. Erosive soil degradation 11. Land degradation through warfare, mineral extraction, industrial and urban development and increased movement of organisms 12. Conclusion: conservation and preventative/remedial strategies References Index.

The concept of a hydrophyte for wetland identification

Abstract: deepwater aquatic systems and terrestrial systems. Although often found along rivers, lakes, ponds, and estuaries, wetlands also exist on gentle slopes or in isolated depressions surrounded by uplands. Wetlands can be considered to occur along a natural soil-moisture gradient between permanently flooded deepwater areas and dryland (Figure 1). Wetland hydrologic conditions, therefore, range from permanent inundation by shallow water or permanent soil saturation to periodic inundation or soil saturation.

Nitrogen mineralization, nitrification and denitrification in upland and wetland ecosystems.

Abstract: Nitrogen mineralization, nitrification, denitrification, and microbial biomass were evaluated in four representative ecosystems in east-central Minnesota. The study ecosystems included: old field, swamp forest, savanna, and upland pin oak forest. Due to a high regional water table and permeable soils, the upland and wetland ecosystems were separated by relatively short distances (2 to 5 m). Two randomly selected sites within each ecosystem were sampled for an entire growing season. Soil samples were collected at 5-week intervals to determine rates of N cycling processes and changes in microbial biomass. Mean daily N mineralization rates during five-week in situ soil incubations were significantly different among sampling dates and ecosystems. The highest annual rates were measured in the upland pin oak ecosystem (8.6 g N m−2 yr−1), and the lowest rates in the swamp forest (1.5 g N m−2 yr−1); nitrification followed an identical pattern. Denitrification was relatively high in the swamp forest during early spring (8040 μg N2O−N m−2 d−1) and late autumn (2525 μg N2O−N m−2 d−1); nitrification occurred at rates sufficient to sustain these losses. In the well-drained uplands, rates of denitrification were generally lower and equivalent to rates of atmospheric N inputs. Microbial C and N were consistently higher in the swamp forest than in the other ecosystems; both were positively correlated with average daily rates of N mineralization. In the subtle landscape of east-central Minnesota, rates of N cycling can differ by an order of magnitude across relatively short distances.

Chamaecyparis thyoides wetlands and suburbanization : effects on hydrology, water quality and plant community composition

Abstract: (1) Atlantic white cedar (Chamaecyparis thyoides) wetlands in the New Jersey Pinelands were studied along a gradient of suburban development defined by increasingly intrusive road and house construction close to the site. Water table level, water chemistry, plant species composition and community structure were recorded to assess the effects of increasing levels of upland disturbance on the adjacent wetlands. (2) Some increases in nitrogen, phosphorus, and chloride occurred in both surface and groundwater within wetlands beside septic system drain fields. Much larger increases in these parameters, plus increases in heavy metal concentrations, occurred in sites receiving both septic tank drainage and road run-off. (3) Hydrology was only affected by the presence of dams on the streams traversing the wetlands, and by ditches dug in association with stormwater sewer outfalls. (4) With increasing levels of suburban disturbance, there was an increasing loss of indigenous herbaceous species and an increasing incursion of upland and exotic species. Ground cover by Sphagnum spp. and cedar seedling densities all declined with increasing suburban development. Woody plant community composition and structure showed little change over the gradient. Changes in water quality were more important in determining changes in community composition and structure than were changes in hydrology. (5) The changes in species composition associated with changes in water quality support the theory that species-richness follows an optimization curve with respect to nutritional quality of the wetland. (6) The results suggest that the maximum buffer width provided for by law be required for all upland development adjacent to white cedar wetlands.

Global warming and prairie wetlands: potential consequences for waterfowl habitat

Abstract: In this article, the authors discuss current understanding and projections of global warming; review wetland vegetation dynamics to establish the strong relationship among climate, wetland hydrology, vegetation patterns and waterfowl habitat; discuss the potential effects of a greenhouse warming on these relationships; and illustrate the potential effects of climate change on wetland habitat by using a simulation model.

Estimating primary productivity of forested wetland communities in different hydrologic landscapes

Abstract: Five forested wetland sites in western Kentucky with hydrologic regimes varying from seasonally to continuously flooded were investigated for net above-ground biomass productivity (litterfall plus biomass growth) and for possible indicators of that productivity, including abiotic (flooding frequency and depth, phosphorus concentrations in water and sediments) and biotic (biomass, tree density, basal area, structural complexity, and mean height) indices. Net biomass productivity ranged from 205 g m-2y-1 for a stagnant semipermanently flooded Taxodium swamp to 1,334 g m-2y-1 in a bottomland forest along the Ohio River. Productivity was highest in wetlands with pulsing hydroperiods, intermediate with slowly flowing systems, and lowest with stagnant conditions. Surface water flooding of the wetlands during the growing season ranged from 17 to 100 percent of the year and did not predict productivity. Phosphorus concentrations in water and in sediments were not correlated to one another and did not, by themselves, predict productivity. No single abiotic variable predicted the exact ranking of productivity of the sites. Of the biotic variables, average tree diameter was inversely related to productivity.

Marsh Foraminifera and Arcellaceans of the Lower Mississippi Delta - Controls on Spatial Distributions

Abstract: Foraminifera and arcellaceans ("thecamoebians") were examined from 73 surface samples collected to represent four vegetation zones (I-IV) that have been defined in the Mississippi Delta Plain. Previous studies of benthonic foraminifera had not differentiated these environments. Saline marshes (I) are characterized by a vertical zonation typical of most marshes, with a variety of estuarine species in the low marsh and trochamminids in the upper marsh. Brackish marshes (II) are dominated by a completely different set of species, all agglutinated, but the vertical zonation is weak, probably because of the low vertical gradient. Emergent freshwater or intermediate marshes (III) are dominated by arcellaceans but there are significant numbers of foraminifera, indicating episodic marine incursions. The freshwater floating marsh zone (IV) has only arcellaceans. A previous study of arcellaceans living in the lacustrine environment below the floating marsh reveals a different arcellacean fauna than that observed above it. These data suggest that marsh foraminifera have potential application as sea-level indicators in the delta region and that fossil remains of these protozoans can be used to differentiate coastal vegetation zones in the fossil record. INTRODUCTION The lower Mississippi delta region is one of the most intensively studied Quaternary sections in the world and benthonic foraminifera have been used frequently by various investigators. Surprisingly, although some overall distribution patterns are known, detailed relations between wetland benthonic foraminiferal assemblages and vegetation assemblages within and between regions is not well known. All previous workers have listed a group of species referred to as "marsh" species but have not tried to subdivide them. Also, with the exception of Haman (1982, 1990), arcellaceans (or "thecamoebians") have been virtually ignored in investigations of freshwater areas of the lower delta. We have carefully sampled most of the major vegetation zones and, in marine marshes, we were careful to sample the entire vertical range of the salt marshes to detect vertical zonations that have been observed elsewhere (Scott and Medioli 1980a). Previous cores from the delta, examined several years ago (unpublished student data from Dalhousie University and Collins 1988), indicated the presence of discrete assemblages of marsh species. However, without data on their modem distribution little interpretation of the core assemblages was possible; this is what prompted the present study. Using data from other areas, it was possible to speculate on assemblage characteristics (i.e. elevation, salinity requirements); however, because the Mississippi delta region is much more complex than most regions with the low elevation gradient and the many vegetation types, it was not possible to have confidence in our interpretations. PHYSIOGRAPHY Physiographically, this system is a low lying coastal plain with an extremely small vertical gradient, which has promoted the development of an extensive wetland system ranging from saline to freshwater. In this study, we have attempted to sample each of the wetlands except the freshwater cypress swamps. Salinities and temperatures in the wetlands are strongly influenced by atmospheric conditions and one time measurements of these parameters are not so useful; however salinity values were obtained where possible during the sampling. The tidal range is low (30cm) but storm surges generated by hurricanes can raise the sea level from .5m to over 7m (Penland et al. 1988). These authors also state that the average wind-generated waves are low-energy, such that the coastline is considered a storm-dominated system.

Approaches to the Conservation of Coastal Wetlands in the Western Hemisphere

Abstract: Coastal wetlands rank among the most productive and ecologically valuable natural ecosystems on Earth. Unfortunately, they are also some of the most disturbed. Because they are productive and can serve as transportation arteries, coastal wetlands have long attracted human settlement. More than half of the U.S. population currently lives within 80 km of its coasts, and one estimate places 70% of all humanity in the coastal zone. Human impacts to coastal wetlands include physical alteration of hydrological processes; the introduction of toxic materials, nutrients, heat, and exotic species; and the unsustainable harvest ofnative species. Between 1950 and 1970, coastal wetland losses in the U.S. averaged 8 100 ha/year. In Central and South America, development pressures along the coastal zone rank among the most serious natural resource problems in the region. Here, we (1) briefly describe coastal wetland avifauna, (2) discuss the threat of global warming on coastal wetlands, (3) use several Western Hemisphere wetlands as site-specific examples of development pressures facing these habitats, and (4) provide synopses of non- governmental and governmental approaches to wetland conservation. Overall, we provide a socio-economic context for conservation of coastal wetlands in the Western Hemisphere. We suggest that efforts aimed at conserving sites of particular importance for their biological diversity should be pursued within a framework of wise use that addresses the broader issues of human population growth and economic development.

Constructed wetlands to control nonpoint source pollution

Abstract: The construct containing in hydraulic order a sediment basin, level-lip spreader, grassy filter, wetland, and deep pond can be used to remove pollutants from nonpoint source runoff. Wetlands are planted with vegetation that encourages growth of aerobic and anaerobic bacteria which are helpful in removing and detoxifying contaminants.

Treatment of polluted water using wetland plants in a floating habitat

Abstract: An apparatus for treating waste water including a waste water basin and a number of wetland plants in floating containers adapted to float on the surface of waste water in the waste water basin such that the root systems of the wetland plants treat the waste water. The floating containers are constructed so that they retain soil and/or another particulate solid required to sustain and nourish the wetland plants and also so that they permit the root systems of the wetland plants to grow outwardly into the waste water to be treated. The root systems produce aerobic zones within the waster water in the waste water basin. The extent of the growth of the root systems is controlled, preferably by an adjustable platform associated with each floating container, so that the aerobic and anaerobic zones within the waste water basin are controlled and can be adjusted or varied as required.

Wigeongrass (Ruppia maritima): A Literature Review.

Abstract: : Wigeongrass (Ruppia maritima L.) is a submersed macrophyte of nearly cosmopolitan distribution and worldwide importance as a waterfowl food. Unfortunately, the plant no longer inhabits vast areas disturbed by human activities. Taxonomic status of the plant is uncertain, especially in North America. In mild climates, in habitats subject to environmental extremes, the plant behaves as an annual (vegetation perishes), or as a perennial in deeper, more stable habitats (some vegetative parts grow year round). Drupelets (seeds) provide a mechanism for wigeongrass to survive periods of drought and excessive water salinity. These sexual propagules can be washed ashore or carried by birds or fish for long distances. Wigeongrass mostly occurs in temporarily to permanently flooded mesohaline-hyperhaline estuarine wetlands, but it also occurs inland in fresh to hypersaline palustrine and lacustrine wetlands. Most populations inhabit warm, relatively unpolluted, and well lit waters <2.0 m deep where fetches and wave action are not great. The species is probably best adapted to stable water levels but can tolerate significant water level fluctuations, including periodic exposure in tidal areas. Robust growth occurs in areas of slow current. Wigeongrass is alone among the submersed North American angiosperms in tolerance to high salinity, but it is likely at a competitive disadvantage among specialist taxa in soft or acidic waters. The species grows in nearly all common bottom substrates, but growth is favored by aerobic and low H2S conditions. Turbidity frequently limits wigeongrass growth in waters overlying easily suspendible bottom substrates. Wigeongrass often occurs in monotypic stands, yet grows with many other submersed and emergent macrophytes.

Beaver population fluctuations and tropospheric methane emissions in boreal wetlands

Abstract: Measurements of net methane flux were made during the 1988 ice-free season (May–October) at a beaver-meadow complex in northern Minnesota, USA. The site included upland boreal forest, sedge meadow, submerged aquatic plants, and the open water of a beaver pond. Annual fluxes were 8–11 g C/m2 in the permanently wetted zones and 0.2–0.4 g C/m2 at the occasionally inundated meadow and forest sites. These data, when coupled with long-term (46 yr) data on beaver (Castor canadensis) population size and habitat alteration, suggest that about 1% of the recent rise in atmospheric methane may be attributable to pond creation by beaver in North America.

Wetland Plants in New Zealand.

Abstract: Of all the strange places where plants grow, wetlands are among the most diverse. This field guide illustrates both native and naturalized plants of New Zealand's bogs, swamps, estuaries and lakes. Line drawings complement the text describing key features, distribution and habitats. The volume covers the New Zealand botanical region, that is, the three main islands, the Kermadec and Three Kings Islands, the Chatham Islands, and the sub-antarctic islands as far as Macquarie Island. With the exception of stoneworts, only vascular plants are included, that is, the ferns and their allies, conifers and flowering plants. Mosses, liverworts and lichens are not treated.

Riparian vegetation along current-exposure gradients in floodplain wetlands of the River Murray, Australia

Abstract: (1) This paper develops a simple conceptual model of riparian vegetation applicable to floodplain wetlands of a regulated river. The vegetation was studied with respect to two gradients: current and exposure to wave action. The study area was the Chowilla floodplain on the River Murray in the semi-arid zone of South Australia. (2) Four vegetation types were distinguished by cluster analysis and by separation on three ordination axes. Each was strongly and significantly associated with a particular category of wetland on the floodplain. (3) The first ordination axis represented a gradient in vegetation structure. It separated vegetation types dominated by trees from those dominated by sedges and/or grasses; the former had higher species richness and greater range of growth forms. (4) The second ordination axis was a current-related gradient, having a significant regression on current; the vegetation type with the swiftest currents and steepest banks was riparian grasses. (5) The third axis was a gradient related to exposure to wave action. (6) Application of a simple model to vegetation of the Chowilla floodplain suggested how river regulation might have changed wetland vegetation.

Stable carbon isotope variation in C 3 and C 4 plants along the Amazon River

Abstract: ALL plants assimilate 12C in preference to 13C. As a result of this isotope fractionation, the tissues of subaerial plants have lower 13C/12C ratios than that of atmospheric CO2. By contrast, plant respiration and tissue decomposition are accompanied by little, if any, fractionation and hence release 13C-depleted biogenic CO2 back into the atmosphere. If this biogenic CO2 is reassimilated before it is thoroughly mixed into the atmosphere, a further depletion of 13C in the plant tissue will result. This recycling effect has been found most often in vertical variations of stable isotope composition in tropical forests where plant tissues near the forest floor are more depleted in 13C (refs 1–5). Here we show that the intensity of biogenic CO2 recycling in flood plain forests of the Amazon systematically increases inland, in the western Amazon basin. We also show that a similar recycling mechanism affects the 13C composition of semiaquatic grasses owing to evasion of biogenic CO2 from the Amazon river. But in this case the degree of recycling is more pronounced in the eastern basin because the flux of 13CO2 out of the river is smaller there. Our data indicate that significant spatial carbon isotope gradients can exist across the same general ecosystem, both between different species and also within a single species. Recycling effects therefore need to be taken into account in studies that try to relate plant carbon composition to animal and human diet, and in those attempting to determine the carbon isotope composition of the ancient atmosphere from preserved plant tissues.

The dynamics, distribution and classification of swamp vegetation in Peruvian Amazonia

Abstract: Swamp vegetation was surveyed in the western Amazon lowlands (<500 m above sea level) using Landsat MSS and TM imagery, radar maps and ground truth surveys. Four categories of swamp vegetation were recog nized on the basis of the physiognomy: (I) herbaceous swamp, (II) shrub swamp, (HI) palm swamp and (IV) forest swamp. The total coverage of the swamp vegetation recognized was 24 900 km2 or 3.4% of the study area. Of these swamps, 19% are situated in flood basin areas, 8% in blocked valleys, and 73% belong to the "Maranon wetland complex", where no detailed swamp classification was carried out The largest swamp areas are located in the central parts of the intra-foreland basins Pastaza-Mara non and Ucayali, which are characterized by widespread inundations and aggradation. Mobile river channels cause alterations in inundation con ditions, which lead to local forest destruction and succession. The insta bility of the swamp site physiography makes swamp vegetation classi fication difficult. The suggestion is made that future studies on swamp vegetation should also contain descriptions of the swamp site geo morphology, the type of flood water received (rivers, rain) and the hydrology (flood regime).

A comparison of the hydrology of moorland under natural conditions, agricultural use and forestry

Abstract: Long term research has been conducted into the hydrological effects of different land usage of a wetland mire in southern Germany. Drainage for agriculture lowered the water table and reduced evaporation from about 110% of open water losses to just under the Penman short grass potential rate. The runoff regime was altered and peak flows increased. Afforestation of agricultural land increased evaporation losses to much higher levels than open water evaporation, and annual runoff was nearly halved. Forest growth reduced soil water and baseflows. Peak flows became smaller; the rate of reduction was particularly rapid in the early years of tree growth.

Growth rates of American alligators in estuarine and palustrine wetlands in Louisiana

Abstract: A comparative study of American alligator (Alligator mississippiensis) growth rates was made in estuarine and palustrine wetlands in southwestern Louisiana. In the estuarine wetlands, where characteristic salinity levels were ≤5%, alligators grew faster and therefore reached sexual maturity earlier than did those in palustrine wetlands, which are characterized by shallow, freshwater marsh vegetation. Slower growth rates in palustrine wetlands appeared to be related to prey density, indicated by previous studies to be lower than in estuarine wetlands. Males grew faster than females and therefore reached sexual maturity at an earlier age in both habitats. This study revealed a major limitation in using total lengths as an index upon which population age structure can be based even when alligators are in the same geographic region.