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C.D. Snyder

Publications and source records attributed to C.D. Snyder.

10 recordsLinked to original sources
USGS2008

The use of local indicators of spatial association to improve LiDAR-derived predictions of potential amphibian breeding ponds

We examined whether spatially explicit information improved models that use LiDAR return signal intensity to discriminate in-pond habitat from terrestrial habitat at 24 amphibian breeding ponds. The addition of Local Indicators of Spatial Association (LISA) to LiDAR return intensity data significantly improved predictive models at all ponds, reduced residual error by as much as 74%, and appeared to improve models by reducing classification errors associated with types of in-pond vegetation. We conclude that LISA statistics can help maximize the information content that can be extracted from time resolved LiDAR return data in models that predict the occurrence of small, seasonal ponds. ?? Springer-Verlag 2008.

Journal of Geographical Systems↗
USGS2006

The use of artificial impoundments by two amphibian species in the Delaware Water Gap National Recreation Area

We compared breeding activity of Ambystoma maculatum (Spotted Salamander) and Rana sylvatica (Wood Frog) in artificial impoundments to patterns in natural wetlands over a three-year period in the Delaware Water Gap National Recreation Area. Rana sylvatica were 5.6 times more likely to use natural bodies of water for breeding than artificial impoundments, while A. maculatum were 2.7 times more likely to use natural bodies of water. Both species were approximately 9 times more likely to breed in fishless bodies of water than in waters with predatory fish. Ambystoma maculatum were 6 times more likely to breed in wetlands with more stable seasonal hydroperiods, while R. sylvatica were only 2 times more likely to do so. We conclude that the high likelihood of fish presence in impoundments was the primary explanation for why both species were less likely to use impoundments than natural wetlands, while the tendency of A. maculatum to avoid natural wetlands with shorter hydroperiods explained why differences in use between pond types was more pronounced for R. sylvatica.

Northeastern Naturalist↗
USGS2006

Macroinvertebrate assemblage recovery following a catastrophic flood and debris flows in an Appalachian mountain stream

In June 1995, heavy rains caused severe flooding and massive debris flows on the Staunton River, a 3rd-order stream in the Blue Ridge Mountains (Virginia, USA). Scouring caused the loss of the riparian zone and repositioned the stream channel of the lower 2.1 km of the stream. Between 1998 and 2001, we conducted seasonal macroinvertebrate surveys at sites on the Staunton River and on White Oak Canyon Run, a reference stream of similar size and geology that was relatively unaffected by the flood. Our study was designed to determine the extent to which flood-induced changes to the stream channel and riparian habitats caused long-term changes to macroinvertebrate community structure and composition. Sites within the impacted zone of the Staunton River supported diverse stable benthic macroinvertebrate assemblages 3 y after the flood despite dramatic and persistent changes in environmental factors known to be important controls on stream ecosystem function. However, significant differences in total macroinvertebrate density and trophic structure could be attributed to the flood. In autumn, densities of most feeding guilds, including shredders, were higher at impacted-zone sites than at all other sites, suggesting higher overall productivity in the impacted zone. Higher shredder density in the impacted zone was surprising in light of expected decreases in leaf-litter inputs because of removal of riparian forests. In contrast, in spring, we observed density differences in only one feeding guild, scrapers, which showed higher densities at impacted-zone sites than at all other sites. This result conformed to a priori expectations that reduced shading in the impacted zone would lead to increased light and higher instream primary production. We attribute the seasonal differences in trophic structure to the effects of increased temperatures on food quality and to the relationship between the timing of our sampling and the emergence patterns of important taxa. ?? 2006 by The North American Benthological Society.

Journal of the North American Benthological Societ↗
USGS2003

Influences of upland and riparian land use patterns on stream biotic integrity

We explored land use, fish assemblage structure, and stream habitat associations in 20 catchments in Opequon Creek watershed, West Virginia. The purpose was to determine the relative importance of urban and agriculture land use on stream biotic integrity, and to evaluate the spatial scale (i.e., whole-catchment vs riparian buffer) at which land use effects were most pronounced. We found that index of biological integrity (IBI) scores were strongly associated with extent of urban land use in individual catchments. Sites that received ratings of poor or very poor based on IBI scores had > 7% of urban land use in their respective catchments. Habitat correlations suggested that urban land use disrupted flow regime, reduced water quality, and altered stream channels. In contrast, we found no meaningful relationship between agricultural land use and IBI at either whole-catchment or riparian scales despite strong correlations between percent agriculture and several important stream habitat measures, including nitrate concentrations, proportion of fine sediments in riffles, and the abundance of fish cover. We also found that variation in gradient (channel slope) influenced responses of fish assemblages to land use. Urban land use was more disruptive to biological integrity in catchments with steeper channel slopes. Based on comparisons of our results in the topographically diverse Opequon Creek watershed with results from watersheds in flatter terrains, we hypothesize that the potential for riparian forests to mitigate effects of deleterious land uses in upland portions of the watershed is inversely related to gradient.

Landscape Ecology↗
USGS2002

A terrain-based paired-site sampling design to assess biodiversity losses from eastern hemlock decline

Biodiversity surveys are often hampered by the inability to control extraneous sources of variability introduced into comparisons of populations across a heterogenous landscape. If not specifically accounted for a priori, this noise can weaken comparisons between sites, and can make it difficult to draw inferences about specific ecological processes. We developed a terrain-based, paired-site sampling design to analyze differences in aquatic biodiversity between streams draining eastern hemlock (Tsuga canadensis) forests, and those draining mixed hardwood forests in Delaware Water Gap National Recreation Area (USA). The goal of this design was to minimize variance due to terrain influences on stream communities, while representing the range of hemlock dominated stream environments present in the park. We used geographic information systems (GIS) and cluster analysis to define and partition hemlock dominated streams into terrain types based on topographic variables and stream order. We computed similarity of forest stands within terrain types and used this information to pair hemlock-dominated streams with hardwood counterparts prior to sampling. We evaluated the effectiveness of the design through power analysis and found that power to detect differences in aquatic invertebrate taxa richness was highest when sites were paired and terrain type was included as a factor in the analysis. Precision of the estimated difference in mean richness was nearly doubled using the terrain-based, paired site design in comparison to other evaluated designs. Use of this method allowed us to sample stream communities representative of park-wide forest conditions while effectively controlling for landscape variability.

Environmental Monitoring and Assessment↗
USGS2002

Influence of eastern hemlock (Tsuga canadensis) forests on aquatic invertebrate assemblages in headwater streams

We conducted a comparative study in the Delaware Water Gap National Recreation Area to determine the potential long-term impacts of hemlock forest decline on stream benthic macroinvertebrate assemblages. Hemlock forests throughout eastern North America have been declining because of the hemlock woolly adelgid, an exotic insect pest. We found aquatic invertebrate community structure to be strongly correlated with forest composition. Streams draining hemlock forests supported significantly more total taxa than streams draining mixed hardwood forests, and over 8% of the taxa were strongly associated with hemlock. In addition, invertebrate taxa were more evenly distributed (i.e., higher Simpson's evenness values) in hemlock-drained streams. In contrast, the number of rare species and total densities were significantly lower in streams draining hemlock, suggesting that diversity differences observed between forest types were not related to stochastic factors associated with sampling and that streams draining mixed hardwood forests may be more productive. Analysis of stream habitat data indicated that streams draining hemlock forests had more stable thermal and hydrologic regimes. Our findings suggest that hemlock decline may result in long-term changes in headwater ecosystems leading to reductions in both within-stream (i.e., alpha) and park-wide (i.e., gamma) benthic community diversity.

Canadian Journal of Fisheries and Aquatic Sciences↗
USGS1997

Genetic responses of Isonychia bicolor (Ephemeroptera: Isonychiidae) to chronic mercury pollution

The relationship between allozyme genotype and survival of nymphs of the mayfly Isonychia bicolor (Walker) when exposed to acute mercury concentrations was tested in laboratory experiments. The probability of survival and individual times-to-death were found to be significantly different among genotypes at the glucose phosphate isomerase locus, but not at the phosphoglucomutase locus. This pattern was consistent for both summer and winter temperatures and for populations from 2 separate, unpolluted streams. Subsequent field surveys were conducted to determine if results of these acute laboratory tests could be extrapolated to the more chronic, sublethal conditions present in the South River, Virginia. Genotypes identified as sensitive and tolerant in the laboratory experiments showed no consistent relationship with environmental mercury levels in the South River. In fact, one heterozygote identified as tolerant was found to be more frequent at the reference site than at contaminated sites, and no significant between-site differences were observed in the frequencies of the most sensitive genotype. Consequently, despite fitness differences to mercury exposure among allozyme variants, we were unable to attribute any between-site differences in genetic structure in I. bicolor populations to adaptation to mercury pollution.

Journal of the North American Benthological Societ↗
USGS1995

Effect of seasonally changing feeding habits on whole-animal mercury concentrations in Hydropsyche morosa (Trichoptera: Hydropsychidae)

Food habits, net-spinning activity, and whole-animal mercury concentrations in Hydropsyche morosa Hagan were examined monthly over a one year period on the South River, Virginia. Gut content analysis revealed seasonal patterns in the consumption of food that was correlated with net-spinning activity. Between April and October, when feeding nets were widespread, detritus represented between 72 and 94% of the total volume of food material found in the guts, while algae represented less than 18%. However, between November and March, when feeding nets were rare or absent, the relative contribution of each of the three food types ( i.e. , detritus, algae, and animal) changed significantly. Detritus declined to between 51 and 60%, and algae increased to between 39 and 47% of the total food volume. Whole-animal mercury concentrations ranged from 0.14 to 1.20 µg g −1 and were significantly higher in the summer. Seasonal differences were not related to environmental mercury levels and only weakly related to body size. In contrast, whole-animal mercury levels were strongly related to seasonal changes in diet. In summer, when H. morosa larvae were filtering highly contaminated seston, whole-animal mercury levels were high. Conversely, in winter, when larvae were grazing less contaminated algae, whole-animal mercury levels were significantly lower. The primary component of seston was detritus (>81%) throughout the year. Therefore, the high mercury concentration in seston was probably associated with detritus. As a result, a significant relationship was observed between whole-animal mercury concentration and the relative amount of detritus consumed. These patterns indicate that in streams with highly productive hydropsychid populations, the rate of processing of mercury and other heavy metals may be related to seasonal changes in feeding behavior.

Hydrobiologia↗