Mosaic Of Wetlands Research Articles

Exploring the links between natural resource use and biophysical status in the waterways of the North Rupununi, Guyana

The North Rupununi District in south-west Guyana is comprised of a mosaic of ecosystems, including savannas, wetlands and forests, and is home to the Makushi Amerindians, who depend on the waterways for their subsistence needs. With logging and mining seen as increasing threats to the region, it is necessary to look at methods for engaging stakeholders in monitoring the status of their natural resources. This paper presents the results of a pilot study carried out to investigate water use by the Makushi Amerindians, and collect baseline data on the hydro-morphological aspects of the waterways. Methods included informal interviews, the use of the River Habitat Survey (RHS), and water quality measurements. The results indicate the heavy reliance of the Makushi on the waterways for their daily lives, particularly on fishing. Although ponds and creeks are important sources of fish, the rivers provide much larger catches of a greater diversity of fish species, both in the wet and dry seasons. The physical characteristics of the water sources used by the Makushi are mainly associated with the surrounding habitat types: the savanna areas containing the more nutrient rich white-water rivers, and the tropical forest areas containing the less nutrient rich black-water rivers. This study indicates that at present there is no direct evidence of adverse impacts on the waterways used by the Makushi in terms of fish catches, habitat conditions and water quality. A monitoring scheme was set up using this study's outputs as a baseline from which any future changes can be compared. Further work is to be carried out over the next three years to produce monitoring and sustainable management procedures for the North Rupununi ecosystems, by linking the physical attributes of the environment to biodiversity and subsequently local livelihoods, and by building capacity of local stakeholders through training.

Spatial and temporal analysis of vegetation mosaics for conservation: poor fen communities in a Cornish valley mire

AbstractAim Biogeographers increasingly realize the importance of seeing plant communities as spatial mosaics and understanding the spatial and temporal heterogeneity of a site is often a key to successful conservation. The aim of this paper is to examine the approaches to the description and analysis of spatial and temporal variation in sub‐communities within patch mosaics of vegetation in order to inform conservation management. The activities of the tin streaming industry in Cornwall over the last century have created a highly varied mosaic of poor fen vegetation on Goss Moor National Nature Reserve (NNR). The wetland mosaics comprise dry hummocks and different sized wet pools. The size and depth of the pools determines the rate and type of vegetation that develops, as does the nature of boundary or edge. The ergodic hypothesis is used to describe the various plant sub‐communities and their boundaries to identify pathways of hydroseral succession. A further aim was to test the use of Ellenberg Indicator (EI) values as a tool for the rapid description of spatial and temporal environmental change on wetland sites with a view to their management.Location Goss Moor National Nature Reserve, Cornwall, UK.Methods An extensive survey of the whole wetland complex was undertaken to identify patches of poor fen vegetation containing Potentilla palustris (L.) Scop. and Menyanthes trifoliata L. At each patch, species abundance data were collected as well as associated environmental information such as depth of the organic layer and standing water depth, patch location, patch size and boundary type. The plant sub‐communities present were defined using techniques of numerical classification [two‐way indicator species analysis (twinspan)] and ordination [detrended correspondence analysis (DCA)] and these were ordered using the ergodic hypothesis in order to characterize the stages of the hydrosere. Floristic and environmental relationships were examined using canonical correspondence analysis (CCA). Further environmental differences between the poor fen sub‐community types were characterized by weighted EI values for acidity (R), moisture (F), nitrogen (N) and light (L).Results and conclusions Twelve poor fen sub‐community types were described and found to be distributed along a primary environmental gradient of organic matter depth, surface water height and bare substrate. Separation of the poor fen communities by a moisture gradient was considered as spatial evidence for hydroseral succession, which begins with the colonization of open‐water pools created by tin excavations. High water levels were associated with the swamp communities, increased organic depth was associated with poor fen, and the type of boundary was shown to affect the resulting community composition. Weighted Community Ellenberg Indicator values for nitrogen, light, reaction and moisture are recommended as an effective tool for indicating differences between plant (sub‐)communities. The importance of examining sub‐community mosaics in the study of hydroseral development is stressed and the manner in which both sets of information may be used to underpin the conservation management of the site is demonstrated.

Home Ranges, Movements, and Habitat Selection of Oregon Spotted Frogs (Rana pretiosa)

Abstract From 1997–1999 we studied one of four known populations of Oregon Spotted Frogs (Rana pretiosa) in Washington State to investigate patterns of range use, movements, and habitat selection. Sixty telemetered frogs occupied a range that was a mosaic of wetlands (15.6 ha) and upland pasture (13.2 ha) grazed by dairy cows. Mean (± SE) home-range size for four frogs was 2.2 ± 1.0 ha. Patterns of spatial use, determined from 654 telemetry locations, were closely related to season and changing surface water conditions. During the breeding season (February to May), frogs occupied ≥50% of the area they used the entire year, and oviposited in shallow pools (depth = 16.9 ± 0.6 cm) on the margins of an ephemeral creek. In the dry season (June to August), frogs moved down stream to deeper, permanent pools (depth = 23.6 ± 1.0 cm), significantly reduced their movements, and occupied the smallest ranges of any season. During the wet season (September to January), frogs moved back up stream and reoccupied the bree...

Waterbird responses to experimental drawdown: implications for the multispecies management of wetland mosaics

Summary The loss and human modification of wetlands world‐wide underscores the importance of efficient management. For wetlands that provide habitats for non‐breeding waterbirds, such management often aims to support a rich and abundant waterbird community. Among the world's many seasonal, moist‐soil managed wetlands, annual winter flooding is followed by spring drawdown to encourage germination of waterfowl food plants. Recommendations on how best to maintain flooded wetlands for multiple species are mostly theoretical, and drawdown management typically focuses on spring for migrating shorebirds. The benefits and drawbacks of shallow‐water management in winter have not been examined, especially where sizeable populations of wintering shorebirds and waterfowl occur together. We considered The Grasslands Ecological Area in California's Central Valley, USA, as a model wetland complex in which to assess optimal winter flood‐depth for multispecies use. We also examined the relative benefits for each waterbird group (e.g. shorebirds and waterfowl) of drawdowns conducted in winter and spring. We experimentally dewatered wetlands of measured topography in the winter and spring of 1994–95, documenting changes in waterbird species richness and abundance associated with daily changes in habitat diversity and availability. Results indicated limited regional availability of shallow‐water habitat across the landscape in winter but not spring, as use by shorebirds and teal increased on drawndown wetlands in winter only. Use by deeper‐water dabbling ducks and diving waterbirds declined during the later stages of drawdown in both seasons, but not until use by shorebirds and teal had peaked. The maximum diversity and abundance of waterbirds occurred at average depths of 10–20 cm on wetlands with topographic gradients of 30–40 cm. This study has important implications for the winter management of seasonal wetland complexes, especially moist‐soil systems where managers provide habitat for different waterbird groups (from shorebirds to diving waterbirds) simultaneously. In general, where topography is variable (e.g. a difference of 30–40 cm between the deepest and shallowest zones), wetlands flooded to average depths of 15–20 cm should accommodate the greatest richness and abundance of waterbirds.

Typology of arid-zone floodplain wetlands of the Paroo River (inland Australia) and the influence of water regime, turbidity, and salinity on their aquatic invertebrate assemblages

Typologies of arid-zone wetlands tend to be based on basin geomorphology, hydrology and vegetation because these parameters are readily surveyed at a broad scale. However, there has been little work confirming that these typologies are relevant at finer scales to aquatic macroinvertebrate and zooplankton assemblages whose composition may be responses to more proximate features of water regime, turbidity, and salinity. Furthermore, the practical difficulties of sampling these wetlands (e.g., distance, harsh working conditions, unpredictable filling) mean that we have little understanding of the interactions among these variables and the effects on the fauna of arid-zone wetlands. Based on several intensive collections trom the Paroo floodplain over a decade spanning highly variable flows, we explore the match between present wetland typologies and invertebrate assemblage structure. Statistical relationships of assemblage structure with salinity, turbidity and water regime indicate differential responses, typical of the temporal and spatial mosaic of wetlands and their filling patterns in this arid zone. Salinity, turbidity and water regime also serve to distinguish among the wetland types on the Paroo River floodplain, indicating that a general typology that applies to vegetation, basin morphology and invertebrate community structure can be used for classification and land management purposes in this arid-zone.

Conservation value of variable connectivity: aquatic invertebrate assemblages of channel and floodplain habitats of a central Australian arid-zone river, Cooper Creek

Rapidly expanding water resource development in arid and semi-arid zones of Australia threatens the flow regime and ecological integrity of the few large dryland rivers and their immense floodplains. Efforts to manage and conserve the surface waters of these rivers are hampered by limited scientific data on the ecology of their flora and fauna and on their responses to the high natural variability of flow regime that typifies dryland rivers. Irregular floods connect channel and floodplain wetlands to differing degrees and for varying periods of time but the ecological significance of this connectivity is poorly understood. On Cooper Creek, a large dryland river in central Australia, we explored the degree to which assemblage composition varied with connectivity and hydrological regime. Shortly after protracted regional flooding, we sampled aquatic macroinvertebrate assemblages from the principal microhabitats in 12 channel and floodplain wetlands. Ephemeral and temporary lakes tended to have fewer taxa than semi-permanent channel or terminal lake habitats. Although hydrological connection had only recently been lost for some wetlands, there was already evidence of divergence in aquatic macroinvertebrate assemblage composition. Disruption of the natural variability in connectivity and hydrological regime by excessive water abstraction or river-flow regulation threatens the ecological integrity and aquatic macroinvertebrate biodiversity of dryland rivers. Preservation of the irregular flow regime and sporadic connectivity underpins conservation of the mosaic of floodplain wetlands that play such a crucial role in the ecosystem functioning of rivers such as Cooper Creek.

Mapping a forest mosaic – A comparison of vegetation and bird distributions using geographic boundary analysis

Many areas of ecological inquiry require the ability to detect and characterize change in ecological variables across both space and time. The purpose of this study was to investigate ways in which geographic boundary analysis techniques could be used to characterize the pattern of change over space in plant distributions in a forested wetland mosaic. With vegetation maps created using spatially constrained clustering and difference boundary delineation, we examined similarities between the identified boundaries in plant distributions and the occurrence of six species of songbirds. We found that vegetation boundaries were significantly cohesive, suggesting one or more crisp vegetation transition zones exist in the study site. Smaller, less cohesive boundary areas also provided important information about patterns of treefall gaps and dense patches of understory within the study area. Boundaries for songbird abundance were not cohesive, and bird and vegetation difference boundaries did not show significant overlap. However, bird boundaries did overlap significantly with vegetation cluster boundaries. Vegetation clusters delineated using constrained clustering techniques have the potential to be very useful for stratifying bird abundance data collected in different sections of the study site, which could be used to improve the efficiency of monitoring efforts for rare bird species.

Wetland Loss and Biodiversity Conservation

Abstract: Most species of wetland‐dependent organisms live in multiple local populations sustained through occasional migration. Retention of minimum wetland densities in human‐dominated landscapes is fundamental to conserving these organisms. An analysis of wetland mosaics was performed for two regions of the northeastern United States to assess the degree to which historical wetland loss alters the metrics of wetland mosaics and to assess potential future effects mediated by differently structured wetland regulations. These analyses indicated that profound reductions in wetland density and proximity are associated with increased human populations and that protections for all wetlands >1 acre (0.4 ha) are likely required to retain wetland densities minimally sufficient to sustain the wetland biota.

A comparison between saline and freshwater wetlands on Bloodwood Station, the Paroo, Australia, with special reference to their use by waterbirds

Bloodwood Station, 130 km NW of Bourke, NSW, has a diverse array of intermittently flooded wetlands raging from salinas to fresh waters, either clear, opaque or very turbid, and from relatively large (820 ha) to quite small (<1 ha). A study during 1995 followed the filling of 22 wetlands after heavy rain in January to subsequent drying or recession, and looked at the relationship between physicochemical features, aquatic plants, zooplankton, littoral invertebrates, tadpoles, and waterbirds. Wetlands were delineated into two major groups: saline and fresh, with the latter subdivided into five types — clear fresh waters, artificial tanks, vegetated pans, turbid pans, and miscellaneous. The saline lakes developed extensive beds of macrophytes some months after filling which attracted large number of waterbirds. Later, abundant Zooplankton were feed for many Pink-eared Duck. Most of the fresh waters developed large initial populations of phyllopodous crustaceans, Zooplankton and tadpoles, but these waters attracted few waterbirds. Clearer fresh waters later grew macrophytes which attracted many waterbirds, but the turbid claypans remained unattractive to waterbirds during their existence, despite harbouring a host of invertebrates. The vegetated pans, artificial tanks and miscellaneous sites attracted only a few waterbirds, but the tanks along with the persistent clear fresh waters become important as feeding and resting sites as other wetlands dried towards the year end. Few waterbirds bred on these wetlands during 1995. However, many were important as major feeding sites and formed part of a mosaic of intermittent wetlands for Australia's inland waterbirds.

Predation, habitat complexity, and distribution of the crayfishProcambarus alleni within a wetland habitat mosaic

The crayfishProcambarus alleni is abundant in densely vegetated habitats within the freshwater wetland mosaics of central and southern Florida. We performed laboratory experiments to determine whether habitat preference and/or predation could account for habitat use by this species. First, groups of crayfish were placed into tanks divided evenly into vegetated and non-vegetated sides, and habitat use was measured during the day and night. Crayfish preferred vegetated habitats during both the day and night, although use of non-vegetated habitats increased significantly at night. Next, different size classes of crayfish were exposed to predatory largemouth bass (Micropterus salmoides) in experimental tanks of varying habitat complexity (i.e., plant biomass). Bass reduced survival of small-sized crayfish but had no effect on larger crayfish. Larger crayfish also seemed to prey upon smaller crayfish. Susceptibility of crayfish to predation decreased with increasing habitat complexity. Experimental results are consistent with field observations and indicate that predators and habitat complexity play important roles in determining the distribution and daily activity ofP. alleni within wetland habitat mosaics.

Spatial ecology of the crayfishProcambarus alleni in a Florida wetland mosaic

We investigated patterns of differential habitat occupation by the crayfishProcambarus alleni, a numerically abundant and trophically important species in freshwater marsh systems of southern Florida. Crayfish were collected from emergent wet prairies and sloughs in marshes forming the headwaters of the St. Johns River, Florida between August 1992 and December 1993. In addition to differences in plant species composition, wet prairies had greater plant biomass and lower water depths than sloughs. Mean density and biomass of crayfish were significantly higher in the densely vegetated wet prairies (28 per m2; 26.9 g per m2) than in aquatic sloughs (3 per m2; 1.5 g per m2). Crayfish density increased with increasing plant biomass (i.e., habitat complexity) in wet prairies, whereas crayfish density decreased with increasing water levels (i.e., hydroperiod) within slough habitats. Recruitment occurred throughout the study, and the majority of crayfish collected were small in size (<1.0 g). Ovigerous females were rarely collected and were found only in wet prairies. Differences in relative risk of predation, food availability, or a combination of these factors are likely generating differences in habitat occupation by the crayfishP. alleni in this wetland habitat mosaic. Efforts to restore and manage freshwater marshes in southern Florida (e.g., Everglades, Lake Okeechobee, Kissimmee River, St. Johns River) would benefit by considering spatial aspects of the ecology of indicator taxa such as crayfish.

Conservation of Large, Nomadic Populations of White Ibises (Eudocimus albus) in the United States

We compiled published and unpublished records of large nestings of White Ibises (Eudocimus albus) in the United States between 1930 and 1993. The resulting database provides evidence of at least four major geographic shifts of the breeding population of White Ibises during the period. Banding returns and colony histories demonstrate that the movements were not migratory. The extremely fast growth of most White Ibis breeding colonies indicates that local recruitment could not have fueled the large increases in breeding numbers in colonized areas. Ibises seem to colonize wetland areas that have good feeding resources and to abandon areas that lose the ability to supply this resource. Mechanisms of attraction to new sites and repulsion from degraded ones may work alone or in tandem. Degradation of breeding sites frequently occurs through natural processes, such as hurricanes, stochastic weather patterns, and wetland conditions, and the nomadic behavior of White Ibises appears to be an obligate life‐history feature. Although surveys throughout the range of the U.S. population of White Ibises have never been comprehensive, available records indicate minimum breeding populations of 125,000 pairs in 1933, 170,000 pairs in 1976, and 51,000 pairs in 1991. The U.S. population as a whole appears to be decreasing. White Ibises share a suite of population, social, and movement characteristics with a number of nomadic species. Conservation strategies for these species may differ fundamentally from those targeting more sedentary species. Nomadic species may typically depend on large populations to find food and to stimulate breeding and are therefore likely to decline abruptly and unpredictably as habitat is lost or degraded. Rapid population declines may occur at population levels well above those predicted by genetic and minimum viability models. Because of its nomadic habit, the survival of this species may depend on a regional planning approach. To conserve this species we recommend a continuing commitment to the monitoring, assessment, and preservation of a mosaic of fresh and estuarine wetlands in the southeastern U.S.; the maintenance of natural disturbances needed to produce pulses of food in these wetlands, and the coordination of management efforts throughout the US., as well as between the U.S. and Cuba.

Monitoring, classification, and characterization of interior Alaska forests using AIRSAR and ERS-1 SAR

AbstractAt the Bonanza Creek Experimental Forest (BCEF), past ecological research has been directed at forest successional processes on the floodplain of the Tanana River and adjacent uplands. Research at the Bonanza Creek site continues on the mosaic of forests, shrublands, and wetlands in a wide variety of successional stages on the Tanana floodplain. This paper reviews research since 1988 into the capabilities of Synthetic Aperture Radar (SAR) for monitoring, classification, and characterization of these forests using radar remote sensing and modelling techniques. Classifications of successional stages, obtained by use of different classifiers on multi-frequency and multi-polarimetric AIRSAR data, are contrasted; these classifications have been used to predict classification accuracies obtained with ERS-1 data, and to estimate the utility of an ERS-1 and RADARSAT combination for classification. Forest classifications, used in combination with ground-truth data for more than 50 forest stands, are used to summarize the distribution of biomass on the landscape. This will allow projections of future biomass. Monitoring of forest phenology, seasonality of flooding, and freeze–thaw transitions is ongoing. Also, direct monitoring of dominant tree species is demonstrating diurnal variation and interrelationships among environmental, physiological, and backscatter measurements.

Importance of small wetlands for the persistence of local populations of wetland-associated animals

I simulated loss of small, legally unprotected freshwater wetlands in a 600 km2 area of Maine, USA to examine how loss of small wetlands altered the geometry of the wetland mosaic and thereby might affect the dynamics of metapopulations of wetland-associated organisms. Loss of small wetlands resulted in total wetland area declining by 19% (from 2032 to 1655 ha), total wetland number declining by 62% (from 354 to 136 wetlands), and average inter-wetland distance increasing by 67% (from 0.6 to 1.0 km). Also, average upland-wetland proximity decreased by 50% (0.5 to 1.0 km), such that just 54% of the landscape was within the maximum migration distance (1000m) of terrestrial-dwelling and aquatic-breeding amphibians after loss of small wetlands, versus 90% before loss. A spatially-structured demographic model revealed that local populations of turtles, small birds, and small mammals, stable under conditions of no wetland loss, faced a significant risk of extinction (P > 5%) after loss of small wetlands. No change in metapopulation extinction risk was evident for salamanders or frogs, largely because high rates of population increase buffered these taxa against local extinction. These results suggest that small wetlands play a greater role in the metapopulation dynamics of certain taxa of wetland animals than the modest area comprised by small wetlands might imply.

Wetland effects on lake water quality in the Minneapolis/St. Paul metropolitan area

A method developed to evaluate the cumulative effect of wetland mosaics on water quality was applied to 33 lake watersheds in the seven-county region surrounding Minneapolis-St. Paul, Minnesota. A geographic information system (GIS) was used to record and measure landscape variables derived from aerial photos. Twenty-seven watershed land-use and land-cover variables were reduced to eight principal components which described 85% of the variance among watersheds. Relationships between lake water quality variables and the first six principal components plus an index of lake mixis were analyzed through stepwise multiple regression analysis. A combination of three landscape components (wetland/watershed area, agriculture/wetlands, and forest/soils components) explained 49% of the variance in a trophic state index, even though most of the lakes examined were already highly eutrophic, and thus were influenced by internal loading. The regression equations explained a range of 14 to 76% of the variation in individual water quality variables. Forested land-use was associated with lower lake trophic state, chloride, and lead. High lake trophic state was associated with agricultural land-use and with wetland distance from the lake of interest. The extent of wetlands was associated with low total lead and high color in lakes downstream. Wet meadows or herbaceous, seasonally-flooded wetlands contributed more to lake water color than did cattail marshes.

The cumulative effect of wetlands on stream water quality and quantity. A landscape approach

A method was developed to evaluate the cumulative effect of wetland mosaics in the landscape on stream water quality and quantity in the nine-county region surrounding Minneapolis—St. Paul, Minnesota. A Geographic Information System (GIS) was used to record and measure 33 watershed variables derived from historical aerial photos. These watershed variables were then reduced to eight principal components which explained 86% of the variance. Relationships between stream water quality variables and the three wetland-related principal components were explored through stepwise multiple regression analysis. The proximity of wetlands to the sampling station was related to principal component two, which was associated with decreased annual concentrations of inorganic suspended solids, fecal coliform, nitrates, specific conductivity, flow-weighted NH4 flow-weighted total P, and a decreased proportion of phosphorus in dissolved form(p < 0.05). Wetland extent was related to decreased specific conductivity, chloride, and lead concentrations. The wetland-related principal components were also associated with the seasonal export of organic matter, organic nitrogen, and orthophosphate. Relationships between water quality and wetlands components were different for time-weighted averages as compared to flow-weighted averages. This suggests that wetlands were more effective in removing suspended solids, total phosphorus, and ammonia during high flow periods but were more effective in removing nitrates during low flow periods.