Wetland Edge Research Articles

Landscape as a predictor of wetland condition: an evaluation of the Landscape Development Index (LDI) with a large reference wetland dataset from Ohio

Recent approaches to wetland assessment have advocated a multilevel approach which incorporates assessments based on landscape (remote sensing) data, on-site but "rapid" methods, and intensive methods where quantitative data is collected. Brown and Vivas (2004) recently pro- posed an assessment method that uses remote sensing information (Landscape Development Index or LDI) and propose that it may also be usable as a quantified human disturbance gradient. The LDI was evaluated using a large reference wetland data set from Ohio using land use percentages within a 1 km radius circle of the wetlands. The LDI had interpretable and significant relationships with another human disturbance gradient (the Ohio Rapid Assessment Method for Wetlands or ORAM) and with most metrics and scores from the Vegetation Index of Biotic Integrity (VIBI) developed for use in the State of Ohio. Metrics from emergent wetlands had the most significant correlations with the LDI (10 of 10 metrics), followed by forested wetlands (8 of 10 metrics) and shrub wetlands (4 of 10). Poor correlation for VIBI scores and metrics of shrub wetlands was due to differences in attainable LDI scores based on ecoregion and natural buffers shielding the wetland from otherwise intensive land uses. The ORAM and VIBI were developed for use in wetlands in Ohio completely independent of the LDI. It is an important test of the LDI concept that so many interpretable and significant relationships occurred between the VIBI scores, VIBI metric values, and the ORAM scores. For the purposes of VIBI development, the LDI is an independent, quantified disturbance gradient that has provided an additional test of the VIBI. Given its theoretical underpinnings and the fact that it uses quantified land use percentages, the LDI has many advantages over more qualitative human disturbance gradients. Using land use percentages from increasingly smaller distances from the wetland edge (100-200 m) may improve the resolution of the LDI to detect on-site disturbances to a wetland which degrade its ecological condition. The LDI should be evaluated with other large reference data sets in other regions to evaluate its validity and usefulness as an assessment tool.

Controlling Phalaris arundinacea (reed canarygrass) with live willow stakes: A density-dependent response

We tested the use of live willow stakes to manage reed canarygrass ( Phalaris arundinacea L.) invasions on a wetland site. We planted willow at densities of 0.60 m (2 ft) centers, 0.91 m (3 ft) centers, 1.21 m (4 ft) centers, and control (no plantings) on a sloping wetland edge at Lake Washington, Seattle, U.S.A., where reed canarygrass dominated prior to the experiment. Soil moisture content was measured along the slope gradient, resulting in three soil moisture classes per replicate. Willow leaf area index and reed canarygrass aboveground biomass were measured after each of two consecutive growing seasons and analyzed using ANCOVA. Relative to the controls, the willows reduced total biomass of reed canarygrass by 44.9% with 0.60 m spacing in the first year and by 68.0% with 0.60 m spacing and 56.1% with 0.91 m spacing in the second year. Differences in soil moisture did not affect reed canarygrass aboveground biomass or effects of willow on reed canarygrass, but did affect willow growth, perhaps through reed canarygrass competition under lower soil moisture conditions. We recommend the 0.60 and 0.91 m spacings for wetland restoration projects attempting to manage reed canarygrass through live willow staking.

Limitations of regulated “buffer zones” for the conservation of marbled salamanders

Most amphibians that breed in seasonal wetlands are predominantly terrestrial animals that require “upland” habitats for the majority of their life cycles. However, wetland regulations aimed partially at protecting wildlife values are often limited to the wetland basins and small terrestrial “buffer zones” that typically extend 30 m or less from the wetland edge. In this study, we assessed whether a common buffer zone (i.e., 30 m) is sufficient for the conservation of marbled salamanders (Ambystoma opacum). We installed and monitored two concentric and continuous drift fence arrays (3 m and 30 m from the pond margin) around each of three seasonal ponds in western Massachusetts, USA. We quantified the numbers and percentages of breeding adults and emerging juvenile salamanders that immigrated from and/or emigrated beyond the 30-m fences. In addition, we recorded incidental year-of-emergence captures of juveniles at more distant drift fences that were in place for a broader study. Of the breeding adults captured immigrating to the basins at 3-m fences, 84–96% were first captured at 30-m fences, and corrections for capture probabilities suggested that nearly 100% of these individuals originated beyond 30 m from their breeding sites. Of the newly emerging juveniles captured emigrating from the basins at 3-m fences, 58–85% were subsequently captured at 30-m fences and 284 juvenile captures were recorded at distances between 111 and 1,230 m (median = 269.2 m) from natal ponds. Our findings highlight the dramatic limitations of existing wetland regulations with regard to upland habitat use by mole salamanders (family Ambystomatidae) and the need to approach conservation of these animals both at broader scales and with more comprehensive and innovative strategies.

Waterfowl–habitat associations during winter in an urban North Atlantic estuary

Coastal habitats near urban centres in North Atlantic estuaries often support substantial numbers of wintering waterfowl, but little is known of the effects of landscape setting and urbanisation on habitat use. We conducted surveys of waterfowl at 32 wintering sites in Narragansett Bay, Rhode Island, to identify characteristics that may influence habitat use. Sites were chosen along a gradient of urbanisation and reflected the dominant habitat types used by waterfowl in the Bay. Mean waterfowl abundance was 206.7 ± 209.5 birds per site, and sites in the inner part of the estuary had higher overall waterfowl abundances ( r 2 = 0.40, p = 0.021). Species richness ranged from 3.2 to 13.0 and decreased with increasing hunting activity ( r 2 = 0.36, p = 0.040). Hunting activity and habitat characteristics (e.g., latitude, shoreline configuration, prey density) explained 13–27% of the variation in waterfowl abundance and species richness among sites, but landscape characteristics (e.g., surrounding residential development, vegetated land, or wetland surrounding the sites and the extent of wetland edge) explained an additional 1–26%. The landscape characteristics extent of adjacent residential development and vegetated upland were the most common variables entering into the models; most species were more abundant at sites with more adjacent vegetated upland and less adjacent residential development. Our results suggest that landscape setting may be influencing the distribution of wintering waterfowl, and should be considered when developing strategies for the conservation for these species in urban North Atlantic estuaries.

The Ups and Downs of Life on the Edge: The Influence of Water Level Fluctuations on Biomass Allocation in two Contrasting Aquatic Plants

Plant communities at wetland edges typically exhibit strong zonation along water depth gradients, although community structure is not as simple as this common observation may suggest. Water levels fluctuate at many temporal scales and in varied patterns. Understanding of how water regime controls plant community structure requires information on how individual species are affected by water regime. The allocation of biomass to roots, tillers, stolons and inflorescences was measured over 16 weeks in two species of aquatic plants with contrasting life histories. Juncus articulatus L. produces large numbers of small seeds while Glyceria australis C. E. Hubb produces small numbers of large seeds. Both species also reproduce vegetatively. Changes in biomass allocation were measured in response to duration, frequency and amplitude of water level fluctuations. The fluctuations in water level were achieved by suspending plants in pots from chains and raising and lowering the pots in and out of water in replicate tanks. There were complex responses to water regime components. As is common to many emergents, both species increased allocation to above ground vegetative structures in response to increasing water depth. Differences between the species in overall patterns of allocation reflected differences in life history. Juncus articulatus showed greater overall biomass production and greater proportional resource allocation to inflorescences than Glyceria australis. There were other differences in response to components of water regime that distinguished the species, mainly in allocation to reproduction in response to the range of depths (amplitude) and extended dry periods. These different functional responses to aspects of water level fluctuations indicate it may be possible to manipulate species composition if water levels are controllable. The most important characteristics of water regime were threshold events such as extremes of depth and dry periods. These may not be captured in measures of water regime such as average water levels.

Early and mid Holocene tool-use and processing of taro ( Colocasia esculenta), yam ( Dioscorea sp.) and other plants at Kuk Swamp in the highlands of Papua New Guinea

Recent multidisciplinary investigations document an independent emergence of agriculture at Kuk Swamp in the highlands of Papua New Guinea. In this paper we report preliminary usewear analysis and details of prehistoric use of stone tools for processing starchy food and other plants at Kuk Swamp. Morphological diagnostics for starch granules are reported for two potentially significant economic species, taro ( Colocasia esculenta) and yam ( Dioscorea sp.), following comparisons between prehistoric and botanical reference specimens. Usewear and residue analyses of starch granules indicate that both these species were processed on the wetland margin during the early and mid Holocene. We argue that processing of taro and yam commences by at least 10,200 calibrated years before present (cal BP), although the taro and yam starch granules do not permit us to distinguish between wild or cultivated forms. From at least 6950 to 6440 cal BP the processing of taro, yam and other plants indicates that they are likely to have been integrated into cultivation practices on the wetland edge.

LANDSCAPE COMPOSITION, PATCH SIZE, AND DISTANCE TO EDGES: INTERACTIONS AFFECTING DUCK REPRODUCTIVE SUCCESS

Prairies and other North American grasslands, although highly fragmented, provide breeding habitat for a diverse array of species, including species of tremendous economic and ecological importance. Conservation and management of these species requires some understanding of how reproductive success is affected by edge effects, patch size, and characteristics of the landscape. We examined how differences in the percentage of grassland in the landscape influenced the relationships between the success of nests of upland‐nesting ducks and (1) field size and (2) distance to nearest field and wetland edges. We collected data on study areas composed of 15–20% grassland and areas composed of 45–55% grassland in central North Dakota, USA during the 1996 and 1997 nesting seasons. Daily survival rates (DSRs) of duck nests were greater in study areas with 45–55% grassland than with 15–20% grassland. Within study areas, we detected a curvilinear relationship between DSR and field size: DSRs were highest in small and large fields and lowest in moderately sized fields. In study areas with 15–20% grassland, there was no relationship between probability of hatching and distance to nearest field edge, whereas in study areas with 45–55% grassland, there was a positive relationship between these two variables. Results of this study support the conclusion that both landscape composition and configuration affect reproductive success of ground‐nesting birds. We are prompted to question conservation strategies that favor clustering moderately sized patches of nesting habitat within agricultural landscapes because our results show that such patches would have low nest success, most likely caused by predation. Understanding the pattern of nest success, and the predator–prey mechanisms that produce the pattern, will enable design of patch configurations that are most conducive to meeting conservation goals.

Changes in biotic communities developing from freshwater wetland sediments under experimental salinity and water regimes

Summary1. Reduction in diversity of both freshwater aquatic and terrestrial ecosystems has been attributed to salinity increase and such increases are a symptom of changes to land use. Hydrological alteration to ground and surface water are likely to be associated with salinity increase and its influence on biodiversity. However the combined effects of salinity and hydrology on aquatic biodiversity have not been elucidated fully in either field or experimental situations.2. The effect of salinity and water regime on the biota in sediments from seven wetlands from inland south‐eastern Australia was tested experimentally using germination of aquatic plant seeds (five salinity and two water levels) and emergence of zooplankton eggs (five salinity levels). Salinity levels were <300, 1000, 2000, 3000, 5000 mg L−1 and water regimes were damp (waterlogged) and submerged.3. Aquatic plant germination and zooplankton hatching was not consistent for all seven wetland sediments. Four of the wetland sediments, Narran Lakes, Gwydir Wetlands, Macquarie Marshes and Billybung Lagoon showed similar responses to salinity and water regime but the other three wetland sediments from Lake Cowal, Great Cumbung Swamp and Darling Anabranch did not.4. As salinity increased above 1000 mg L−1 there was a decrease in the species richness and the abundance of biota germinating or hatching from sediment from four of the wetlands.5. Salinity had a particularly strong effect in reducing germination from sediments in damp conditions when compared to the flooded conditions. In parallel, salts accumulated in the sediment in damp conditions but did not in flooded conditions.6. There is potential for increasing salinity in freshwater rivers and wetlands to decrease the species richness of aquatic communities and thus of the wetland community as a whole, resulting in loss of wetland biodiversity. This reduction in diversity varies between wetlands and is at least partly related to hydrology. For aquatic plants the reduction in diversity will be more marked for plants germinating from seed banks at the edges of wetlands where plants are not completely submerged than for the same seed bank germinating in submerged conditions.

Foraging by a Red-tailed Hawk along a Wetland Edge: How Large a Duck can be Captured?

A Red-tailed Hawk (Buteo jamaicensis; estimated mass 1,000–1,200 g) failed to kill a Red-breasted Merganser (Mergus serrator; estimated mass 1,150 g) that it captured in shallow water (<25 cm), but evidently dispatched a starving Red-necked Grebe (Podiceps grisegena; mass 645–660 g). These observations are pertinent to estimating the upper mass limit for successful foraging in water.

The interpretation of fen carr pollen diagrams: pollen–vegetation relationships within the fen carr

Sediments deposited in fen carr environments are frequently used in pollen-based reconstructions of vegetation history, although few studies of modern pollen–vegetation relationships in fen carr have been undertaken to aid the interpretation of fossil assemblages. It is often assumed that the wetland pollen signal will reflect the overall composition of the fen carr system although, given the closed canopy context, it may actually be dominated by local vegetation elements. This paper seeks to determine whether the vegetation heterogeneity within a modern fen carr is reflected in the pollen signal of the wetland taxa. Vegetation composition was recorded around a series of moss polster sample points at Calthorpe and Wheatfen, two areas of fen carr in the Norfolk Broadland, UK. The spatial interrelationship between the wetland components of the vegetation and their palynological equivalents in the moss polster pollen assemblages is explored through trend surfaces and a correlation based statistical test (the Mantel Test). The representation of the major vegetation components in the pollen record is highly variable. Values for Alnus glutinosa, a dominant canopy species, range from 5.3% to 73% of total land pollen (TLP) at Calthorpe and 2.5–61% TLP at Wheatfen. In part, this variation reflects the enhanced input of pollen from dry land sources close to the wetland edge although the variation recorded at points equidistant from the dry land margin suggests that other processes are also influential. The strongest positive associations in the Mantel Test are for under-storey and ground flora elements that are poorly represented in the pollen record. Taxa for which there is no association include those with few vegetation occurrences and those for which a large proportion of the pollen appears to have been derived from outside the study areas. We conclude that modern pollen samples collected from fen carr broadly reflect the vegetation composition of the study areas. However, the input of pollen from fen carr species is spatially inconsistent. Differences between the sample points can be attributed to the distribution and pollination biology of the under-storey and ground flora elements and the structure of the vegetation around sites. The results caution against assuming that changes in the pollen representation of wetland taxa, in fossil sequences constructed from fen carr deposits, necessarily reflect changes in the overall composition of the community.

Habitat use by breeding Tree Sparrows Passer montanus

Tree Sparrows Passer montanus showed a strong preference for nest‐sites adjacent to wetland habitats, and avoidance of sites on intensively managed mixed farmland distant from Rutland Water. A variety of wetland edge habitats were frequently used by foraging adult birds when provisioning nestlings, and invertebrate prey of aquatic origin was frequently recorded in chick diet. We suggest that the wetland edge habitats at the study sites played a key role in providing adequate diversity and availability of suitable invertebrate prey to allow successful chick rearing throughout the long breeding season of this multi‐brooded passerine. It is possible that large areas of formerly occupied farmland in the UK no longer provide these invertebrate resources due to the effects of intensification in the late 20th century. There was no evidence that the availability of supplementary seed food within 1 km of the nest‐site influenced nest‐site choice, or affected productivity. It is probable that the importance of seed food resources to the persistence of Tree Sparrow populations operates on a larger spatial scale than that tested in this study, due to the greater mobility of Tree Sparrows in the non‐breeding season, when seed resources are most likely to be a key limiting factor. When considering conservation management aimed at recovering breeding populations of Tree Sparrows, the key resources of seed food, invertebrate food and nest‐sites must be made available at appropriate spatial scales.

Buffer zone and windbreak effects on spray drift deposition in a simulated wetland

The amount of agricultural spray that drifts into a wetland from an adjacent crop field is influenced by vegetation along the field boundary or any intentional setback distance (buffer zone) between the sprayer and the edge of the arable field. In this study, spray tracer drift deposits were measured in a simulated wetland area under different conditions of wind speed and buffer zone width. The effect of an artificial windbreak at the upwind edge of the simulated wetland was also evaluated. A level of tolerance of 0.1% of the in-swath spray deposition was established as a no-effect level for the response of aquatic plants to common herbicides. Our results indicate that a vegetated 10-m field margin (eg a fencerow) alone provides adequate protection from herbicide drift into a wetland area under wind conditions normally considered acceptable for spraying. For high winds (> 4m s(-1)) when field spraying would not normally be advised, adequate protection was afforded by the same 10-m margin plus a dense windbreak (25% porosity) or by the margin plus a 20-m buffer zone.

Estimating the ‘critical’ distance at which adjacent land-use degrades wetland water and sediment quality

Conversion of forested lands to agriculture or urban/residential areas has been associated with declines in stream and lake water quality. Less attention has been paid to the effects of adjacent land-uses on wetland sediment and water quality and, perhaps more importantly, the spatial scales at which these effects occur. Here we address these issues by examining variation in water and sediment nutrient levels in 73 southeastern Ontario, Canada, wetlands. We modeled the relationship between water and sediment nutrient concentrations and various measures of adjacent land-use such as forest cover and road density, measured over increasing distances from the wetland edge. We found that water nitrogen and phosphorous levels were negatively correlated with forest cover at 2250 meters from the wetland edge, while sediment phosphorous levels were negatively correlated with wetland size and forest cover at 4000 meters and positively correlated with the proportion of land within 4000 meters that is itself wetland. These results suggest that the effects of adjacent land-use on wetland sediment and water quality can extend over comparatively large distances. As such, effective wetland conservation will not be achieved merely through the creation of narrow buffer zones between wetlands and more intensive land-uses. Rather, sustaining high wetland water quality will require maintaining a heterogeneous regional landscape containing relatively large areas of natural forest and wetlands.

ANALYSIS OF PREDATOR MOVEMENT IN PRAIRIE LANDSCAPES WITH CONTRASTING GRASSLAND COMPOSITION

Mammalian predation influences waterfowl breeding success in the U.S. northern Great Plains, yet little is known about the influence of the landscape on the ability of predators to find waterfowl nests. We used radiotelemetry to record nightly movements of red foxes (Vulpes vulpes) and striped skunks (Mephitis mephitis) in two 41.4-km 2 study areas in North Dakota. Study areas contained either 15‐20% grassland (low grassland composition) or 45‐55% grassland (high grassland composition). Grasslands included planted cover, pastureland, and hayland. We predicted that the type and composition of cover types in the landscape would influence both predator movement across the landscape (as measured by the fractal dimension and displacement ratio) as well as localized movement (as measured by the rate of movement and turning angle between locations) within patches of different cover types. Red fox movements were straighter (lower fractal dimensions and higher displacements) across landscapes with a low grassland composition, indicating directed movement between the more isolated patches of planted cover. Striped skunk movements did not differ between landscape types, illustrating their movement along wetland edges, which had similar compositions in both landscape types. The high variability in turning angles by red fox in planted cover and pastureland in both landscape types is consistent with restricted-area foraging. The high rate of movement by red foxes in planted cover and by striped skunks in wetland edges suggests that spatial memory may influence movement patterns. Understanding the behavior of predators in fragmented prairie landscape is essential for managing breeding habitat for grassland birds and for predicting the spatial and temporal dynamics of predators and their prey.

BREEDING ABUNDANCE AND NEST-SITE DISTRIBUTION OF THE ALTAMIRA ORIOLE AT SANTA ANA NATIONAL WILDLIFE REFUGE, TEXAS

The distribution of the Altamira oriole (Icterus gularis) in the United States is restricted to the Lower Rio Grande Valley of southernmost Texas. Our objective was to assess the current breeding status of this species at and near Santa Ana National Wildlife Refuge (SANWR), a principal nesting area in the region. During each breeding season from 1997 to 1999, we attempted to find and monitor all Altamira oriole nests in and within 0.5 km of SANWR to determine annual breeding-pair abundance, annual nest-site distribution, and nest distribution among tree species. We estimated that there were 6 or 7, 8 or 9, and 6 or 7 breeding pairs in 1997, 1998, and 1999, respectively. Of the 26 nests found, 12 (46%) were next to the Rio Grande and 7 (27%) were at the edge of a major wetland within the refuge. Only 1 of the other 7 nests was more than 115 m inside the refuge. Nests (n = 26) were distributed among Salix nigra (39%), Fraxinus berlandieriana (23%), Acacia minuata (19%), Celtis laevigata (8%), Ulmus crassifolia (8%), and Chloroleucon ebano (4%). Comparisons of results with historical accounts suggest a decline in annual breeding abundance and nest-site availability at SANWR since the early 1970s.

Seed-bank dynamics of Eleocharis: can spatial and temporal variability explain habitat segregation?

Four Eleocharis species exhibit habitat partitioning in both extant vegetation and in the soil seed bank of upland temporary wetlands on the Northern Tablelands of New South Wales. Explanations for this partitioning were sought in seed-bank dynamics at three shore levels in two wetlands. Habitat partitioning (zonation) was explained in part by seedling recruitment but not by either persistence of seeds in the soil or by dormancy patterns. All four species recruited at wetland edges but only the deepwater species, Eleocharis sphacelata, recruited in deeper water. Viability of buried seeds was consistently high and species had very low decay rates and half-lives greater than 50 years. Two types of dormancy patterns with burial were shown. Most seeds of Eleocharis sphacelata and E. pusilla were non-dormant after a 3-month burial, whereas for E. acuta and E. dietrichiana seed germination percentages gradually increased over a number of years. These two dormancy patterns may contribute to coexistence, since coexistence is enhanced by a long-lived resistant phase in the life history of species and by temporal variability in germination. There were also spatial inconsistencies in patterns of dormant fractions. Burial in the deeper zones of the marsh-like Billybung Lagoon had an inhibitory effect both on germinability and on germination rates of E. acuta and E. dietrichiana seeds. All but E. acuta showed some degree of seasonal dormancy, but this pattern was also not consistent in space. Explanations for zonation should concentrate on other life-history phases, such as dispersal and seedling survival.

Maya Sites and Monuments in SE Campeche, Mexico

Four seasons of archaeological surveys in the SE part of the Mexican federal state of Campeche are summarized. The area is located in the archaeologically little-known central part of the Yucatan peninsula. More than 60 unreported Maya sites were recorded, including major urban centers with large architectural complexes, sculpted monuments with hieroglyphic inscriptions, and caves with vestiges of ritual activities. Settlements are regularly located on elevated ground and major centers are on the edges of low wetlands. While most sites are from the Classic period (ca. A.D. 250–900), earlier complexes of monumental architecture indicate that a large population density and social and political complexity were attained as early as the Late Preclassic (ca. 300 B.C.–A.D.250), paralleling the developments documented in northern Guatemala. The existence of formerly unknown regional seats of power is revealed by large urban centers with functionally diverse types of monumental architecture, and particularly by hieroglyphic inscriptions on stelae and other stone monuments, which shed light on the Classic-period political organization in the area. A stela found at Los Alacranes, for example, mentions a 6th-century lord enthroned under the auspices of the king of Calakmul, while an altar from Altar de los Reyes contains references to a number of Late Classic Lowland Maya polities.

Predator Selection of Prairie Landscape Features and Its Relation to Duck Nest Success

Mammalian predation is a major cause of mortality for breeding waterfowl in the U.S. Northern Great Plains, and yet we know little about the selection of prairie habitats by predators or how this influences nest success in grassland nesting cover. We selected 2 41.4-km 2 study areas in both 1996 and 1997 in North Dakota, USA, with contrasting compositions of perennial grassland. A study area contained either 15-20% perennial grassland (Low Grassland Composition LGC]) or 45-55% perennial grassland (High Grassland Composition [HGC]). We used radiotelemetry to investigate the selection of 9 landscape cover types by red fox (Vulpes vulpes) and striped skunk (Mephitis mephitis), while simultaneously recording duck nest success within planted cover. The cover types included the edge and core areas of planted cover, wetland edges within planted cover or surrounded by cropland, pastureland, hayland, cropland, roads, and miscellaneous cover types. Striped skunks selected wetland edges surrounded by agriculture over all other cover types in LGC landscapes (P-values for all pairwise comparisons were <0.05). Striped skunks also selected wetland edges surrounded by agriculture over all other cover types in HGC landscapes (P < 0.05), except for wetland edges within planted cover (P = 0.12). Red foxes selected the edge and core areas of planted cover, as well as wetland edges within planted cover in LGC landscapes (i.e., they were attracted to the more isolated patches of planted cover). However, in HGC landscapes, red foxes did not select interior areas of planted cover (i.e., core areas of planted cover and wetland edges in planted cover) as frequently as edges of planted cover (P< 0.05). Red foxes selected core areas of planted cover more frequently in LGC than in HGC landscapes (P< 0.05) and selected pastureland more frequently in HGC than in LGC landscapes (P< 0.05). Furthermore, red foxes selected the isolated patches of planted cover more than pastureland in LGC landscapes (P< 0.05). Duck nest success was greater in HGC landscapes than in LGC landscapes for planted-cover core (P < 0.0001), planted-cover edge (P< 0.001) and planted cover-wetland edge (P< 0.001). Both the increased amount of planted-cover core area and the increased pastureland selection in HGC landscapes may have diluted predator foraging efficiency in the interior areas of planted cover and contributed to higher nest success in HGC landscapes. Our observations of predator cover-type selection not only support the restoration and management of large blocks of grassland but also indicate the influence of alternative cover types for mitigating nest predation in the Prairie Pothole Region.

Using aquatic invertebrates to delineate seasonal and temporary wetlands in the prairie pothole region of North America

Tillage can destroy or greatly disturb indicators of hydric soils and hydrophytic vegetation, making delineation of tilled wetlands difficult. The remains of aquatic invertebrates (e.g., shells, drought-resistant eggs, and trichopteran cases) are easily identifiable and persist in wetland substrates even when wetlands are dry. Additionally, these remains are not easily destroyed by mechanical tillage. To test the feasibility of using invertebrate remains to delineate wetlands, we used two methods to identify the wetland edge of ten seasonal and ten temporary wetlands, evenly divided between grassland and cropland landscapes. First, we identified the wetland edge using hydric soil and vegetation indicators along six evenly spaced transects in each wetland (our “standard” delineation). We then identified the wetland edge along the same transects using aquatic invertebrate remains as our indicator. In grassland landscapes, delineations of the wetland edge made using invertebrate remains were consistently at the same location or closer to the wetland center as the standard delineations for both seasonal and temporary wetlands. In cropland landscapes, however, many of our invertebrate delineations of seasonal and temporary wetlands were on the upland side of our standard delineations. We attribute the differences to movement of remains during tillage, increased maximum pool levels in cropland wetlands, and disturbance of hydric soils and plants. We found that the elevations of the wetland edge indicated by invertebrate remains were more consistent within a wetland than elevations determined by standard delineations. Aquatic invertebrate remains can be useful in delineating wetlands when other indicators have been destroyed or severely disturbed by tillage.

Degradation of trichloroethylene in wetland microcosms containing broad-leaved cattail and eastern cottonwood

Remediation of aquifers containing trichloroethylene (TCE) relies primarily on physical extraction of contaminated groundwater and soil. Unfortunately, this is typically expensive and does not always attain the desired treatment goals. In situ bioremediation via natural attenuation is an alternative treatment process in which TCE is transformed by indigenous microorganisms and plants. In this study, TCE was observed in a surficial aquifer that discharges into a wetland. Experiments were undertaken to determine whether natural attenuation of TCE in the wetland was possible. Microcosms were constructed using sandy soil±eastern cottonwoods (Populus deltoides) from the wetland's edge and organic soil±broad-leaved cattails (Typha latifolia) from the wetland's interior. [14C] TCE was added to each microcosm (1.27μCi). Overtime, 14C was recovered from four microcosm compartments: (1) as 14C bound to soil and water, (2) as volatilized [14C] TCE, (3) as [14C] CO2 produced by mineralization of [14C] TCE, and (4) as 14C incorporated into the plants. Total recoveries of the 14C-label ranged from 73.6% to 95.8%. Volatilized [14C] TCE accounted for the majority (>50%) of the recovered label. In microcosms without plants, [14C] CO2 represented 3.2% (organic soil) to 15.6% (sandy soil) of the recovered 14C, indicating that TCE was mineralized by indigenous microorganisms. The presence of the broad-leaved cattail resulted in increased production of [14C] CO2 to 5.3% in the organic soil. The data thus suggest that natural attenuation is a potential bioremediative strategy for TCE-contaminated wetlands.