Assessment of capybara (Hydrochoerus hydrochaeris) populations in the wetlands of Corrientes,Argentina

Ten sampling sites were selected to represent six distinct habitat types used by capybaras (clean lagoons, dirty lagoons, cutwaters, fens and marshes, gallery forests, and erosion ditches). The sites were sampled during winter (July and August); densities were expressed as number of capybaras per linear km of shoreline (C/LKS). The sites were classified as protected from poachers (P), under light hunting pressure (LHP), and under heavy hunting pressure (HHP). Clean protected (P) lagoons had three times as many capybaras as LHP ones (30.7 and 10.9 C/LKS, respectively), and thirty times those under HHP (1.0 C/LKS). Protected marshes and dirty lagoons had even higher capybara densities (52.5 and 50.0 C/LKS, respectively). Gallery forests under LHP had low densities (6.3 C/LKS), and protected cutwaters intermediate densities (27.5 C/LKS). Erosion ditches had exceptionally high densities (900 C/LKS), probably because cattle were fenced out, reducing forage competition. These densities, when converted to the standard unit area measurement (individuals/ha), were similar to those obtained by other researchers in the Brazilian Pantanal, and somewhat smaller than those in the Venezuelan Llanos. Mean number of capybaras per group remained relatively constant in all habitats (averages ranged between 9.2 and 11.8 individuals/group) but its coefficient of variation was much higher in LHP sites, probably because social structure was altered severely by hunting. The overall ratio of young to adults and juveniles was 1:7.4. In one of the sites, 13 of 34 groups (38.2%) were with young (average of 17 capybaras per group, 4.7 of which were young), confirming that this species can reproduce all year long.Requests for reprints should be sent to: Dr. J. Rabinovich.     

Use of Restored Small Wetlands by Breeding Waterfowl in Prince Edward Island, Canada

Abstract Since 1990 under the Eastern Habitat Joint Venture over 100 small wetlands have been restored in Prince Edward Island, Canada. Wetlands were restored by means of dredging accumulated sediment from erosion to emulate pre‐disturbance conditions (i.e., open water and extended hydroperiod). In 1998 and 1999 we compared waterfowl pair and brood use on 22 restored and 24 reference wetlands. More pairs and broods of Ring‐necked Ducks, Gadwall, Green‐winged Teal, and American Black Ducks used restored versus reference wetlands. In restored wetlands waterfowl pair density and species richness were positively correlated with wetland/cattail area, percent cattail cover, and close proximity to freshwater rivers. In addition, a waterfowl reproductive index was positively correlated with percent cattail cover. Green‐winged Teal pair occurrence in restored wetlands was positively correlated with greater amounts of open water and water depths. American Black Duck pairs occurred on most (86%) restored wetlands. Restored small wetlands likely served as stopover points for American Black Duck broods during overland or stream movements, whereas they likely served as a final brood‐rearing destination for Green‐winged Teal broods. We suggest that wetland restoration is a good management tool for increasing populations of Green‐winged Teal and American Black Ducks in Prince Edward Island.     

A Comparison of Remote Sensing and Ground-Based Methods for Monitoring Wetland Restoration Success

Abstract Efficient and accurate vegetation sampling techniques are essential for the assessment of wetland restoration success. Remotely acquired data, used extensively in many locations, have not been widely used to monitor restored wetlands. We compared three different vegetation sampling techniques to determine the accuracy associated with each method when used to determine species composition and cover in restored Pacific coast wetlands dominated by Salicornia virginica (perennial pickleweed). Two ground‐based techniques, using quadrat and line intercept sampling, and a remote sensing technique, using low altitude, high resolution, color and color infrared photographs, were applied to estimate cover in three small restoration sites. The remote technique provided an accurate and efficient means of sampling vegetation cover, but individual species could not be identified, precluding estimates of species density and distribution. Aerial photography was determined to be an effective tool for vegetation monitoring of simple (i.e., single‐species) habitat types or when species identities are not important (e.g., when vegetation is developing on a new restoration site). The efficiency associated with these vegetation sampling techniques was dependent on the scale of the assessment, with aerial photography more efficient than ground‐based sampling methods for assessing large areas. However, the inability of aerial photography to identify individual species, especially mixed‐species stands common in southern California salt marshes, limits its usefulness for monitoring restoration success. A combination of aerial photography and ground‐based methods may be the most effective means of monitoring the success of large wetland restoration projects.     

Forms and distribution of inorganic phosphorus in sediments of two shallow eutrophic lakes in Florida

Physicochemical attributes were measured and aquatic macroinvertebrates were collected from six wetlands near Perth, Western Australia at three weekly intervals over a 13 month period from August 1988 to September 1989. The six wetlands encompassed a range of depths, pH, concuctivities, nutrient concentrations and colours. Temporal changes in the macroinvertebrate communities appeared to be related to seasonal changes in the physical and chemical characteristics of the wetlands. Community composition differed more between the less enriched wetlands then the higly enriched wetlands where communities were generally similar. High species richness was associated with seasonal drying. High macro invertebrate abundance appeared to be associated with the presence of either green algal or cyanobacterial blooms in the enriched wetlands. The highest macroinvertebrate biomass was recorded in wetlands with both cyanobacterial blooms and abundant macrophytes present.     

Use of inexpensive pressure transducers for measuring water levels in wells

Frequent measurement of below ground water levels at multiple locations is an important component of many wetland ecosystem studies. These measurements, however, are usually time consuming, labor intensive, and expensive. This paper describes a water-level sensor that is inexpensive and easy to construct. The sensor is placed below the expected low water level in a shallow well and, when connected to a datalogger, uses a pressure transducer to detect groundwater or surface water elevations. Details of pressure transducer theory, sensor construction, calibration, and examples of field installations are presented. Although the transducers must be individually calibrated, the sensors have a linear response to changing water levels (r ² .999). Measurement errors resulting from temperature fluctuations are shown to be about 4 cm over a 35°C temperature range, but are minimal when the sensors are installed in groundwater wells where temperatures are less variable. Greater accuracy may be obtained by incorporating water temperature data into the initial calibration (0.14 cm error over a 35C temperature range). Examples of the utility of these sensors in studies of groundwater/surface water interactions and the effects of water level fluctuations on tree growth are provided.     

A geomorphic approach to global classification for natural inland wetlands and rationalization of the system used by the Ramsar Convention – a discussion

Globally, the most widely used wetland classification is that adopted by the contracting parties of the Ramsar Convention, which is the Convention on Wetlands of International Importance especially as Waterfowl Habitat. A review of the Inland Wetland component of this system shows that mixed criteria are used to separate the wetlands, and that not all natural inland wetlands have been addressed. A classification system using landform and hydro-period, which results in 13 primary geomorphically non-emergent types for natural wetlands, is proposed to describe the full variety of wetlands at a primary level around the globe, and is suggested to be incorporated as the first-tier of the Ramsar classification.The proposed classification has been designed so wetlands can be described, classified and compared systematically. This paper attempts to reconcile the Ramsar Classification system with the proposed approach. The intention in this paper is not to displace the Ramsar Classification, but rather to indicate its inherent underlying geomorphic structure, and hence re-order its hierarchical framework. This adjustment to the existing classification system would highlight underlying similarities between wetlands so that global comparisons can be more readily made. It also has considerable advantages for a staged, systematic discrimination and classification of the vast array of differing wetlands globally.The use of geomorphic and hydrologic elements as the primary and secondary divisions with the more commonly used Ramsar Classification terms as a tertiary division, provides a logical structure to compare and contrast wetlands globally.     

Reducing acidic discharges from coastal wetlands in eastern Australia

Much of eastern Australia's coastal lowlands are underlain by Holocene sulfidic sediments. Large areas have been drained for agriculture. Drained, sulfidic sediments oxidize and produce highly acidic discharge (pH<4) with significant impacts on estuarine ecosystems. The rate of production of acid from drained floodplains is between 100 to 300 kg H₂SO₄ /ha/y and hundreds of tonnes of H₂SO₄ can be discharged in a single flood from the floodplain. Generation and export of acidity is controlled by the water balance of the floodplain, the characteristics of the drainage system and the distribution of sulfides. Evapotranspiration by native plants and crops plays a dominant role in the oxidation of sediments in dry periods. In wet periods, upland discharges to floodplains dominate the water balance. Drain spacing and drain depth are critical factors in the export of acidity into coastal streams. Amelioration of acidic outflows requires an understanding of the interaction between chemical and hydrological processes in sulfidic landscapes. Redesign of drainage systems to manage surface waters and reduce drain density with the treatment of drains with lime offer promise for treating acidic discharge and reducing impacts. Reflooding of drained, partially oxidized floodplains with freshwater may not be a panacea because of the large volumes of acid stored in the soil, a lack of labile organic matter in the sediments needed to reduce sulfate and irreversible changes to the soil due to oxidation. Tidal brackish water reflooding of unproductive acidified lowlands offers promise for rehabilitating wetlands. Sulfidic wetlands which are still undrained should remain so unless all acidic discharge can be treated.     

Adaptation of wastewater surface flow wetland formulae for application in constructed stormwater wetlands

Over the past 30 years, the use of constructed wetlands for wastewater treatment has been a topic of significant research culminating in a good data base from which simplistic equations have been derived to aid in the design of these facilities to meet long term water quality treatment performance criteria. Over the past decade, the use of treatment wetlands has extended to stormwater and combined sewer overflow (CSO) management applications. Designing constructed wetlands for stormwater and CSO applications have unique challenges stemming from the highly stochastic nature of the hydraulic and pollutant loading on a stormwater wetland compared with wastewater treatment systems. This paper explores the possibility of adapting the simplistic models for wastewater wetlands for interim use in developing design guidelines for stormwater wetland systems. A procedure that takes into account the unsteady intermittent nature of stormwater inflows to these wetlands has been incorporated into one of these simplistic models and a case study presented to demonstrate the application of the procedure.     

Influence of temperature on hatching of eggs of Lepidurus couesii (Crustacea,Notostraca)

Tadpole shrimps (Notostraca) occur sporadically in temporary ponds and their survival there depends largely upon the drought-resistant eggs they produce. Environmental conditions conducive to hatching of eggs of Lepidurus couesii were investigated in the laboratory. Almost all eggs hatched best at 20 °C, whether desiccated for a short or long period, with a prior freezing shock or without such a shock, with intact shells. Eggs that endured a longer period of desiccation and eggs with abraded shells displayed a more equivocal response to different temperatures for hatching. Long-term hatchability of eggs was demonstrated. Time required for successful hatching was shortest at 20 °C, with no discernible difference between 17 °C and 25 °C. Both short- and long-term survival of populations of the species appears to be fostered by the adaptive response to temperature shown by the eggs.     

The dilution and loss of wetland function associated with conversion to open water

Some degree of wetland loss characterizes most coastal systems of the United States. This loss is generally reported as a decrease in wetland area, but most coastal land loss entails wetland submergence and conversion to open water. This concurrent increase in the area of aquatic habitat decreases the wetland:open water ratio, effectively diluting the area of remaining wetland relative to the aquatic system. The functional loss of intertidal wetlands to the ecosystem associated with this dilution effect may significantly alter ecological functions dependent on the interactive coupling of wetland and aquatic habitats. The magnitude of functional loss is strongly dependent on the wetland:water ratio of an estuary. In estuaries with open bay-type morphologies, the open water area is already large and functional loss of wetland by additional dilution may be only slightly greater than the areal wetland loss. Where estuaries are wetland-dominated, however, conversion of even a small percentage of wetland to water drastically alters the wetland:water ratio. In these cases, functional losses by dilution are much greater than the rate of areal wetland loss.In the Barataria Basin estuary, Louisiana, between 1967 and 1987, 15.4% of the salt marsh was lost (assuming a loss rate of 0.8% y^–1 of the remaining marsh). We estimated that this 15% loss of salt marsh, by conversion to open water, may have resulted in a 27% reduction in the supply of inorganic nutrients and organic matter to the estuarine water column by the marsh, simply due to the dilution effects of the changed wetland:open water ratio. Functional losses of this magnitude may have serious implications to the estuarine ecosystem where intertidal wetlands support aquatic productivity by exporting nutrients and energy or where intertidal wetlands buffer aquatic eutrophication by importing excess nutrients and organic matter. It is conceivable that an estuary characterized by wetland loss may reach a point where, although some wetland remains, its functional value to the ecosystem is essentially gone.