Browsing by Author "Benfield, Ernest F."

Now showing 1 - 20 of 91
  • Thumbnail Image
    Analyses of Two Aspects of Study Design for Bioassessment With Benthic Macroinvertebrates: Single Versus Multiple Habitat Sampling and Taxonomic Identification Level
    Hiner, Stephen W. (Virginia Tech, 2004-02-03)
    Bioassessment is the concept of evaluating the ecological condition of habitats by surveying the resident assemblages of living organisms. Conducting bioassessment with benthic macroinvertebrates is still evolving and continues to be refined. There are strongly divided opinions about study design, sampling methods, laboratory analyses, and data analysis. Two issues that are currently being debated about study design for bioassessment in streams were examined here: 1) what habitats within streams should be sampled; 2) and is it necessary to identify organisms to the species level? The influence of habitat sampling design and level of taxonomic identification on the interpretation of ecological conditions of ten small streams in western Virginia was examined. Cattle watering and grazing heavily affected five of these streams (impaired sites). The other five streams, with no recent cattle activity or other impact by man, were considered to be reference sites because they were minimally impaired and represented best attainable conditions. Inferential and non-inferential statistical analyses concluded that multiple habitat sampling design was more effective than a single habitat design (riffle only) at distinguishing impaired conditions, regardless of taxonomic level. It appeared that sampling design (riffle habitat versus multiple habitats) is more important than taxonomic identification level for distinguishing reference and impaired ecological conditions in this bioassessment study. All levels of taxonomic resolution, which were studied, showed that the macroinvertebrate assemblages at the reference and impaired sites were very different and the assemblages at the impaired sites were adversely affected by perturbation. This study supported the sampling of multiple habitats and identification to the family level as a design for best determining the ecological condition of streams in bioassessment.
  • Thumbnail Image
    Biological and chemical monitoring of three streams in the area of Blacksburg, Virginia
    Hayles, Virginia Mosby (Virginia Tech, 1973-03-15)
    This study compares the sensitivity of biological and chemical parameters for monitoring water quality, examines several methods of analyzing diversity of the aquatic organisms and attempts to assess water quality in the three streams investigated. The Cairns-Dickson DIT diversity index was applied to two trophic levels of aquatic organisms and the results were compared to ascertain whether this diversity index is applicable to all levels of the trophic\structure or of greater use for a particular level. Two diversity indices, Cairns-Dickson DIT and Wilhm-Dorris d̅, were used to analyze the same component of the biological community and the results of these two indices were compared. A correlation test was performed among chemical and biological data and among chemical parameters.
  • Thumbnail Image
    Biotic and abiotic responses to rural development and legacy agriculture by southern Appalachain streams
    Burcher, Chris L. (Virginia Tech, 2005-04-12)
    Streams are integrative systems spanning multiple spatial and temporal scales. Stream researchers, land-use managers, and policy decision makers must consider the downstream displacement of streams when approaching questions about stream ecosystems. The study of how anthropogenic land-use influences streams demands an ecosystem perspective, and this dissertation is an example of applying large scale analyses of stream reach responses, and linking the activity of humans in the landscape to stream structure and function. I investigate whether rural development and agriculture land-cover types influence abiotic and biotic stream responses. I establish a method for considering land-cover as an independent variable at multiple scales throughout a streams' watershed using hydraulic modeling. The travel time required for water to drain from the watershed to a stream reach provided a continuous index to delimit watershed sub portions along a spatial continuum. Within travel time zones (TTZs), I consider land-use at increasingly larger scales relative to a stream reach within which biotic responses are typically measured. By partitioning land-cover in TTZs, I was able to determine the spatial scale at which land-cover was most likely to influence in-stream responses. I quantified a suite of physical and biotic responses typical to the aquatic ecology literature, and found that streams did not respond much to rural development. Rural development influenced suspended and depositional sediments, and likely altered watershed hydrology though I was unable to find significant evidence supporting a hydrologic effect. Subtle differences in assemblages suggest that differences in sediment dynamics influenced macroinvertebrates and fish. Using the Land Cover Cascade (LCC) design, I link the influence of land-cover to biotic responses through a suite of multivariate models, focusing on sediment dynamics in an attempt to capture the subtle influence of hydrology and sediment dynamics. My dissertation provides future researchers with improved methods for considering land-cover as an independent variable, as well as introduces multivariate models that link land-cover to sediment dynamics and biota. My dissertation will assist future research projects in identifying specific mechanisms associated with stream responses to disturbance.
  • Thumbnail Image
    Cellulolytic responses to heavy metal accumulation in Corbicula fluminea and Mudalia dilatata
    Farris, Jerry L. (Virginia Tech, 1986-03-05)
    Cellulolytic responses of the Asiatic clam, Corbicula fluminea and a snail, Mudalia dilatata, to selected constituents of power plant effluents (i.e., zinc, cadmium, acidic and alkaline pH, individually and paired) were investigated in 30-day exposures. Exposures were conducted in both laboratory and field-oriented artificial streams and then validated in the river receiving system of a power plant. Cellulolytic activity was reduced by laboratory and field exposures to cadmium and zinc at all levels tested from 0.012 to 0.10 mg cadmium/L and generally at 0.025 to 1.0 mg zinc/L. Clams detected acute lethal levels of metal and used valve closure as an avoidance mechanism for 14 days. Snails, however, did not effectively avoid exposures and were more sensitive to acute stress during all exposures. These behavioral responses were corroborated by both cellulolytic activity and metal accumulation. Measurements of cellulolytic activity for both test species in laboratory exposures differed from those in field artificial streams. Reduced enzyme activity in controls by day 30 was attributed to artificially induced stress associated with the laboratory environment. This factor precluded any analysis of laboratory responses for periods of exposure longer than 20 days as well as recovery analysis. Field oriented artificial streams provided a sufficient environment to adequately assess long-term stress and recovery as measured by cellulolytic activity and metal accumulation in both clams and snails. Enzyme activity responded to metal exposure with respect to both degree and duration of exposure. Cadmium and zinc combined exposures caused significantly reduced cellulolytic activity at the same concentration as those for cadmium alone. Reduced enzyme activity caused by cadmium and zinc addition at levels that were not detectable suggested that the cellulolytic index was sensitive to sublethal stressors. This was supported by metal uptake patterns in clams and snails. Cellulolytic activity responded to zinc addition at alkaline and acidic pH in a manner that supported pH optima for cellulases and bioavailability of metals. Effects seen in macroinvertebrate assemblages (diversity, richness, and similarity) were compared with cellulolytic activity of caged Corbicula from a site specific power plant discharge. Enzyme activity inhibition was the most sensitive indicator measured. Reductions in cellulolytic activity at stations monitored for total zine content were consistent with effects seen at comparable exposures to zine in field-located artificial streams. A zine concentration of 0.05 mg/L consistently caused the first significant reductions in cellulolytic activity. This concentration is comparable to the U.S. Environmental Protection Agency's Water Quality Criteria value (0.047 mg/L zinc) for protection of aquatic life.
  • Thumbnail Image
    Cellulose digestion and assimilation by three leaf-shredding aquatic insects
    Sinsabaugh, R. L.; Linkins, A. E.; Benfield, Ernest F. (Ecological Society of America, 1985)
    The capacity of three leaf-shredding aquatic insects, Pteronarcys proteus (Plecoptera: Pteronarcidae), Tipula abdominalis (Diptera: Tipulidae), and Pycnopsyche luculenta (Trichoptera: Limnephilidae), to digest and assimilate cellulose was investigated. Pteronarcys numphs collected from two second-order woodland streams over a 14-mo period exhibited high levels of cellulolytic activity in their alimentary tracts, especially in the anterior gut. Similar though slightly lower activity levels were measured in Pycnopsyche guts. Cellulolytic activity in Tipula larvae collected from the streams during the same period was low to absent, and when present, was concentrated in the hindgut. General proteolytic activity was activity was similar in the alimentary tracts of all three species. Assimilation of uniformly labelled 14C-cellulose was determined by a dual-label technique, and assimilation efficiencies were estimated at 11.2% for Pteronarcys, 18.5% for Tipula, and 12.0% for Pycnopsyche. Confirmation that labelled digestion products passed the gut wall in two species was obtained by in vitro label transport experiments. Ion exchange fractionation of labelled digestion products crossing the gut wall showed >90% of the label was transported as organic acid and amino acids in Tipula, while >40% of the label crossing the gut wall in Pteronarcys was neutral sugar. Based on the label experiments and published information, we hypothesize that Tipula relies mainly on microbial endosymbionts for cellulose hydrolysis, while Pteronarcys accomplishes hydrolysis largely by means of acquired microbial enzymes obtained through ingestion of microbially conditioned detritus. This study demonstrates the potential for certain leaf-shredding stream insect to derive nutritional benefit from plant polysaccharides, although not without microbial mediation.
  • Thumbnail Image
    Community ecology of aquatic insects in forested headwater streams in the southern Appalachians
    Sokol, Eric R. (Virginia Tech, 2009-09-04)
    Competing paradigms of community assembly emphasize different mechanisms for predicting patterns in biogeography. Niche assembly emphasizes the role of environmental gradients as filters that organize a metacommunity by locally selecting colonizers with similar functional traits, whereas dispersal assembly emphasizes the importance of source pool characteristics and dispersal limitation in organizing a metacommunity. In this study, I developed a framework that uses spatially explicit patterns in taxonomic and functional measures of community composition as diagnostics for community assembly processes for benthic macroinvertebrates in headwater streams in the southern Appalachians. Distance decay in taxonomic and functional similarity was used to determine the scales at which taxonomic turnover occurred within functional niches. Trait-neutral models of community composition were used as null models to assess which functional traits were the best candidates to explain how community composition was influenced by environmental gradients: an assessment of niche-based community assembly. Regional scale patterns suggested that niche-based community assembly was the dominant mechanism organizing community composition in headwater streams at local scales (<30km). Therefore, I compared how well trait-neutral models identified functional traits as relevant to community sorting against how well observed trait distributions correlated with environmental variation at a local scale, in the Ray Branch catchment (<10km study extent). Functional traits exhibiting non-random distributions within the Ray Branch watershed were most strongly correlated with environmental variation. Lastly, I assessed how the influences of niche and dispersal assembly on benthic macroinvertebrate community composition were affected by disturbance (shelterwood logging). Environmental variables defining the habitat template, and macroinvertebrate community composition, were measured before and after the disturbance; and path analysis was used to quantify the disturbance effect. The relationship between environmental variation and functional composition increased following logging, indicating disturbance augmented the influence of environmental filters, and consequently, the importance of niche-based community assembly. My dissertation provides the framework for a novel assessment of taxonomic and functional community composition data to infer the types of ecological dynamics that organize communities in the landscape. Additionally, this work provides a theoretical basis for assessing how dominant ecological processes change, in predictable ways, in response to changes in the habitat template.
  • Thumbnail Image
    Community responses of aquatic macroinvertebrates to heavy metals in laboratory and outdoor experimental streams
    Clements, William H. (Virginia Polytechnic Institute and State University, 1988)
    This research describes aquatic macroinvertebrate community responses to heavy metals (copper, zinc) in experimental streams and at metal-impacted sites in the field. Experiments employed substrate-filled trays which were colonized in the field and then transferred to laboratory or outdoor streams. Laboratory experiments conducted over three seasons showed that acute (96 h) exposure to copper (Cu) at 15-32 μg Cu/L significantly reduced macroinvertebrate abundance and number of taxa during each season. Owing to differences in sensitivity among taxa, the percent composition of dominant groups varied between control and dosed streams. Mayflies were quite sensitive to Cu, particularly during the summer when water temperatures were higher. Community responses to Cu and Zn in outdoor experimental streams were similar to those observed at metal-impacted sites in the field. Control streams and field reference Stations were dominated by mayflies and Tanytarsini chironomids. In contrast, treated Streams and impacted field sites were dominated by net-Spinning caddisflies (Hydropsychidae) and Orthocladiini chironomids. The similarity of these experimental results to those observed in the field suggest that macroinvertebrate community responses to heavy metals are highly predictable. Responses of these communities to Cu were greatly influenced by water quality. Effects were more severe in New River Streams, where water hardness and alkalinity were low, compared to Clinch River Streams, where hardness and alkalinity were higher. In soft water Streams, abundance was reduced by 84% after 10 d exposure to Cu (measured concentration = 13 μg/L). In contrast, abundance was reduced by only 45% in hard water Streams after 10 d at Similar Cu levels. These results demonstrate the importance of accounting for water quality characteristics of receiving systems when establishing site-specific criteria for metals. Chronic exposure (14 d) to sublethal levels of Cu (< 6 μg/L) increased Vulnerability of caddisflies (Hydropsyche morosa and Chimarra sp.) to predation by the Stonefly, Paragnetina fumosa. Caddisflies were also the major component of stonefly diets and were consumed Significantly more frequently in dosed Streams than controls. These results demonstrate that single Species bioassays were inadequate for predicting effects of toxicants on community level processes.
  • Thumbnail Image
    A comparison of techniques for estimating the hazard of chemicals in the aquatic environment
    Niederlehner, Barbara R. (Virginia Polytechnic Institute and State University, 1984)
    Estimates of the concentration of cadmium constituting a threat to aquatic ecosystems were derived from laboratory tests conducted at two levels of the biological hierarchy. A population level estimate was derived from single species toxicity tests and a community level estimate was derived from laboratory tests on microbial communities. Estimates were compared to each other and to an ecosystem level estimate derived from reports of ecological health and ambient cadmium levels in rivers, lakes, and streams. Estimates of permissible levels for short term exposures differed by an order of magnitude. Single species toxicity tests indicated that a level of 46.1 ug Cd/L would affect only 5% of taxa. The corresponding estimate from the community level test was 459.4 ug Cd/L. Similar estimates of permissible levels for chronic exposures were not significantly different (1.02 and 0.20 ug Cd/L, single species arid community level tests, respectively). Both of the laboratory derived estimates of permissible levels for chronic exposure fell within a rational range; the minimum level defined by median cadmium levels reported in healthy aquatic systems (0.05 ug Cd/L), and the maximum level defined by median cadmium levels reported in damaged aquatic systems (9.2 ug Cd/L). However, the community level estimate was obtained more efficiently, permitting an estimate of effects on diversity from a single test. Single species level tests, community level tests, and field studies each contributed unique information to hazard evaluation. Using information from all levels will strengthen predictions.
  • Thumbnail Image
    Comparisons of Secondary Production, Life History, and Mouthpart Functional Morphology Between Two Populations of the Amphipod Gammarus minus
    Haley, Carol J. (Virginia Tech, 1997-01-21)
    In this study, features of ecology, behavior, and functional morphology related to feeding activity of two populations of the amphipod Gammarus minus were compared. The two populations occupied different habitats, and I attempted to determine whether differences observed between the two populations were related to habitat. Annual production and life history of the populations were compared and their relationship to factors such as temperature, water-chemistry, and quantity of available organic matter were examined. Mouthpart and foregut morphology were compared between the two populations and between immature and mature amphipods with light and scanning electron microscopy. Measurements of structure were analyzed by linear regression. A behavioral study, comparing feeding of immature and mature G. minus, was conducted in the laboratory. Annual production of G. minus occupying a habitat characterized by the presence of watercress, gravel substrate, and constant temperature (Site 1) was 3.9 g/m² (95% C.I.: 3.2- 4.5), while that in the habitat characterized by leaf detritus and fluctuating temperatures (Site 2) was 1.8 g/m² (95% C.I.: 1.6-2.1). Breeding occurred throughout the year at Site 1, but there was a yearly cycle at Site 2. The greatest numbers of the smallest size classes of amphipod were present at Site 2 when the quantity of ash-free dry mass (AFDM) of wood and bark was greater than AFDM of leaf detritus. Of nine mouthpart and foregut structures studied, three, the number of cuspidate setae on outer plates of maxillipeds, the length of the dactyl on maxilliped palps, and the number of hook setae on the foregut ampullae, were found to be correlated with body length. Of these, rates of increase in maxilliped setae numbers and hook setae numbers were greater for immature than mature animals, and the number of hook setae for a given sized animal was generally greater for animals at Site 1 than Site 2. Animals presented with ground-up leaf material in the laboratory exhibited twenty-one recognizable behaviors. The frequencies of six behaviors were found to be statistically different between immature and mature animals. The differences suggest that immatures may prefer a food type or size other than that provided in the experiment.
  • Thumbnail Image
    A contribution to the knowledge of the odonata
    Carle, Frank Louis (Virginia Tech, 1982-06-16)
    Theories concerning the origin of insect wings and flight are reviewed and a new scenario for their origin proposed. It is suggested that environmental conditions of the small stream were responsible for the evolution of insect flight, and that thermoregulation as well as respiration was important in the preadaptation of wings. The possibility that the five paired convex-concave vein systems each represented a dorsal-ventral blood channel is suggested. Odonate wing vein homology and nomenclatural systems, and phylogeny are reviewed. The process of vein loss is evaluated in the Palaeoptera and a new system of odonate wing vein homologies proposed. The odonate wing mechanism is analyzed and the heretofore overlooked discal nodus characterized. Reevaluation of the comparative morphology of fossil and recent Odonata indicates that Protozygoptera and Protanisoptera represent evolutionary side branches, that the Anisozygoptera is polyphyletic, and that Isophlebiidae and Calopterygoidea are the most generalized Odonata known. Previous scenarios explaining evolution of the unique odonate copulatory process are reviewed. Considering the copulatory behavior of the Calopterygoidea generalized supports evolutionary trends toward male domination and in-flight completion of the process. Assuming direct sperm transfer the original odonate mode requires that originally oviposition be in tandem and that sperm transfer to and from male anterior abdominal sterna be accidental. In contrast, assuming an original indirect transfer of sperm leads to a copulatory sequence similar to that of the Odonata. The proposed scenario differs from others in that extraordinary postures are not envisioned, the process is completed at rest, and the odonate tandem hold is developed prior to copulation. Anisopteran morphology and phylogeny are reviewed and reliable dentification keys developed for North American families and genera, and for 180 anisopteran species collected in Virginia and vicinity. Each species is described and photographed, including seven new species. The biogeography of Virginia Anisoptera is best explained by overlapping biotic regions, the fauna being a mixture of eastern North American, boreal, and tropical elements. New efficient methods for collecting, preserving, and rearing Odonata are described.
  • Thumbnail Image
    Contributions to the autecology and ecosystematics of immature ceratopogonidae (Diptera), with emphasis on the tribes heteromyiini and sphaeromiini in the middle atlantic United States
    Knausenberger, Walter Ingolf (Virginia Tech, 1986-12-05)
    Biological and systematic study of the immature stages of the biting midges (Diptera: Ceratopogonidae) has been infrequent, although the family is one of the largest in the order, with over 4,000 species worldwide, and is ubiquitous among aquatic/semiaquatic environments. An ecosystematic analysis is presented here of the Ceratopogonidae in Virginia and contiguous states based mainly on a diversified biological field survey, with particular attention to associating immature stages with adults, and acquisition of ecological data. I emphasized (a) extraction of larvae and pupae; (b) two methods of rearing, developed for this study: individual rearing(IR) with an agar-nematode technique, and collective rearing from the habitat substrate in rearing cartons(RC); and (c) field trapping of adults at the habitats. In Section I, a faunistic assessment - the first of its sort - is provided of the total Virginia-region ceratopogonid fauna, in all developmental stages, with a focus on Culicoides, including a comparative evaluation of the relative abundance of the ceratopogonid genera with respect to methods of collecting and extracting. High taxonomic richness of the ceratopogonid fauna in the Middle Atlantic states is reflected in the 150 described and 42 undescribed (new) species recovered. A detailed geographic checklist for the 222 species of Virginia and the five contiguous states is presented and interpreted. At least 54 Culicoides species are present in the Middle Atlantic u.s. About half of the larval species can be determined in Virginia. With the results of this study, 93% of breeding sites for the genus are known in Virginia, more than for any other state. Section II assembles and synopsizes data on the autecology, life history, habitat, morphology, systematics, as well as geographic and seasonal occurrence of 28 species (3 new) and 10 genera in two related tribes of predaceous biting midges, Heteromyiini and Sphaeromiini (subfamily Ceratopogoninae). Shorelines are the "archetypical arena" in which these larvae thrive, typically above and below the water line. Their habitats and substrates are characterized in detail. The greatest diversity of larvae in these tribes consistently occurs in and along mid-reach streams{Order: 3 to 5). Mechanisms of ecological partitioning by sympatric species, and the differential adaptive significance of larval, pupal and adult morphological characters are evaluated. Taxonomic and ecological diversity in these groups are clearly related.
  • Thumbnail Image
    Control strategies for the zebra mussel, Dreissena polymorpha, and the Asian clam, Corbicula fluminea: comparative stress responses and nontarget impact
    Bidwell, Joseph R. (Virginia Tech, 1993-09-04)
    The studies described herein focused on the use of intermittent halogenation to control biofouling of water intake systems by the zebra mussel, Dreissena polymorpha, the comparative response of zebra mussels and the Asian clam, Corbicula fluminea, to a surfactant -based chemical control agent, the nontarget impact associated with the control agent, and the use of the Asian clam as a biomonitor of the control agent. Effects of intermittent (2-4 hr/day) treatments with chlorine or bromine at levels of 0.5 and 1.0 mg/L (total residual oxidant) upon settling of zebra mussel veligers were examined in studies conducted in a field laboratory on western Lake Erie. Veliger densities in the water column at the field site peaked at 530/L, while mussel densities on settling monitors reached 147,083/m² over the course of the study period. Zebra mussel settling in test systems treated with the halogens was reduced by as much as 91 % in comparison with controls, although mussel densities of up to 6,044/m² still occurred. Treated mussels which remained settled had growth rates similar to controls, and reached 2-4 mm length over 30 days. The intermittent halogen treatments had no significant impact on either adult zebra mussels or Asian clams. The studies indicate that while the treatment regimes may reduce zebra mussel densities within intake systems, the threat of eventual fouling due to cumulative settling remains.
  • Thumbnail Image
    December 2006 Report Of The Academic Advisory Committee To Virginia Department Of Environmental Quality: Freshwater Nutrient Criteria For Rivers And Streams
    Zipper, Carl E.; Yagow, Eugene R.; Walker, Jane L.; Smith, Eric P.; Shabman, Leonard A.; Smock, Leonard A.; Hershner, Carl H.; Younos, Tamim M.; Benfield, Ernest F.; Bukaveckas, Paul A.; Garman, Greg C.; Kator, Howard I.; Lung, Wu-Seng; Stephenson, Stephen Kurt (Virginia Water Resources Research Center, 2007-01-10)
    This report reviews activities conducted by the Academic Advisory Committee to the Virginia Department of Environmental Quality (DEQ) between July and December 2006. Activities were conducted for the purpose of developing recommendations for DEQ regarding nutrient criteria for freshwater rivers and streams.
  • Thumbnail Image
    December 2006 Report of the Academic Advisory Committee to Virginia Department of Environmental Quality: Freshwater Nutrient Criteria for Rivers and Streams
    Zipper, Carl E.; Yagow, Eugene R.; Walker, Jane L.; Smith, Eric P.; Shabman, Leonard A.; Smock, Leonard A.; Hershner, Carl H.; Younos, Tamim M.; Benfield, Ernest F.; Bukaveckas, Paul A.; Garman, Greg C.; Kator, Howard I.; Lung, Wu-Seng; Stephenson, Stephen Kurt (Virginia Water Resources Research Center, 2007-01-10)
    This report reviews activities conducted by the Academic Advisory Committee to the Virginia Department of Environmental Quality (DEQ) between July and December 2006. Activities were conducted for the purpose of developing recommendations for DEQ regarding nutrient criteria for freshwater rivers and streams.
  • Thumbnail Image
    The development and assessment of an automated biological monitoring system using crayfish locomotor activity to detect toxic stress
    Maciorowski, Anthony F. (Virginia Tech, 1978-06-15)
    In-plant biomonitors, controlled by dedicated microcomputers, may ultimately provide detection of developing toxicity and hazardous spills in industrial effluents rapidly enough to prevent serious damage to receiving waters. A computer automated system was developed to continuously monitor spontaneous locomotor activity of eight crayfish. Electric potentials generated by muscular movements of untethered crayfish were detected by external electrodes, amplified, digitized, and analyzed by a hybrid computer network. A microcomputer evaluated the number of peaks produced in the waveforms of eight individual C. acuminatus for successive one-hour intervals. The resultant counts were directly related to locomotor activity. The effectiveness of the crayfish biomonitor in detecting simulated spills of cadmium in the laboratory was determined by 7 experiments with 56 crayfish. Results indicated that crayfish responded to 2.5 and 0.5 mg Cd⁺⁺/l with increased activity, which was detected by the crayfish biomonitor two hours after exposure. A simulated spill of 0.1 mgCd⁺⁺/l was detected by the biomonitor within 113 hours. These results support the assumption that the crayfish activity monitor may be used as a potential tool for water quality management.
  • Thumbnail Image
    The diet and growth of a leaf-shredding caddisfly, Pycnopsyche, in streams of contrasting disturbance histories
    Hutchens, John Jehu (Virginia Tech, 1994-06-28)
    This study investigated the diet and growth of a leaf-eating caddisfly, Pycnopsyche, in streams draining a >60 year-old reference forest and a 16-year-old c1earcut (disturbed) forest at Coweeta Hydrologic Laboratory in southwestern North Carolina. The objective was to examine whether Pycnopsyche larvae grew better on fast-decaying leaf types more prevalent in the disturbed streams (e.g., black birch) because leaf-eating insects (shredders) in a previous study were more productive in these streams despite having less food available. Larvae consumed mostly unidentified plant material in streams of both forest types over three seasons (fall, winter, and spring) which suggested larvae did not consume higher quality foods (e.g., algae) in disturbed streams. When fed 2-mo "conditioned" black birch and white oak leaves, lab experiment larvae grew significantly faster on birch leaves. However, when larvae were fed the same leaf types after 3 mo of conditioning, larvae grew significantly faster on oak leaves. A field growth experiment conducted for 42 d using leaf diets representative of both forest types and conditioned for 2 mo found Pycnopsyche grew better on the diet representative of the reference forest. found Pycnopsyche grew better on the diet representative of the reference forest.
  • Thumbnail Image
    Ecological studies of benthic macroinvertebrates for determining sedimentation impacts in Chattahoochee National Forest streams
    Longing, Scott Douglas (Virginia Tech, 2006-04-07)
    Understanding sedimentation impacts to benthic macroinvertebrates in headwater, mountain streams is a top priority of watershed management programs in the Chattahoochee National Forest. Five studies involving the analysis of historical, biological survey data and current data were conducted to improve our understanding of macroinvertebrate response to sedimentation and to support the development of biological information for sediment load models to be applied in the Chattooga River watershed. An initial analysis of historical data involving a composited, macroinvertebrate reach-scale sample revealed weak relationships between assemblage metrics and sedimentation, which was similar to results of two recent macroinvertebrate studies that found biological ratings of good or excellent with reported physical impact attributed to sedimentation. Those findings and field reconnaissance in the Chattooga River watershed revealed that patchy, coarse sands may be the primary issue of concern regarding sedimentation impact to benthic macroinvertebrates. Therefore, a modified sampling approach was used to investigate relationships of macroinvertebrates and environmental conditions that included micro-habitat patches containing coarse sands, a product of erosion associated with Southern Blue Ridge, silicate parent geology. At the microhabitat, patch scale, flow velocity was the main environmental factor associated with a macroinvertebrate assemblage gradient, and was significantly correlated with percent deposited sediment across 264 samples. The high dominance of just a few macroinvertebrate genera, and the majority lack of individual macroinvertebrate associations with dominant substrate types may suggest that the dominant macroinvertebrates utilize a multi-microhabitat portion of the streambed at any given time, which may be due to the homogenization of streambeds due to sand (providing ease of movement) and its immobility (low bedload volume and sand patch shift). Because flow was the only significantly correlated environmental variable on an assemblage gradient produced by ordination (and was individually correlated with dominant substrate and percent deposited sediment), a subsequent study was conducted to determine macroinvertebrate sensitivity to deposited sediments among two flow-differentiated habitat types. Results showed that more taxa were related to a gradient of percent deposited sediment in fast water habitats, and no taxa were positively correlated with percent deposited sediment. Indicator species analysis found a number of taxa that were associated with a four-level grouping of percent deposited sediment levels. Therefore, a final study involved calculating deposited sediment tolerance values using indicator species associations and individual cumulative abundances across percent deposited sediment levels. The final index developed from cumulative abundances showed a relationship with deposited sediment within the range 0 – 30%, and that low range was due to the low deposited sediment levels at which all 50% cumulative abundances fell (1 - 10%). The sedimentation index produced from indicator species analysis produced a reach-scale index that was related to percent pool embeddedness. Key findings from these studies are: (1) sand is the primary deposited sediment type, with most streambed comprised of cobble-sand substrate, (2) few taxa are associated with deposited sand substrate, (3) there are high numbers of a relatively few dominant taxa across samples and streams, (4) macroinvertebrate response to deposited sediments is greatest in fast water habitats, and (5) the developed sedimentation biotic index is a potential, assemblage-level indicator of increasing sedimentation in these headwater systems. The functional and habit organization of the four most dominant taxa determined in recent studies suggest that they may be utilizing sand patches for crawling and collecting food, therefore structurally adapting to long-term, press disturbances due to historical and contemporary anthropogenic activities and natural erosion. In addition, macroinvertebrate assemblage composition in these streams indicates overall good "health" and suggests streambed stability in the presence of a large portion of coarse sand. However, an important question that remains involves sand movement along streambeds and the ecological consequences of continued sediment inputs to these headwater systems.
  • Thumbnail Image
    Ecosystem Function in Appalachian Headwater Streams during an Active Invasion by the Hemlock Woolly Adelgid
    Northington, Robert M.; Webster, Jackson R.; Benfield, Ernest F.; Cheever, Beth M.; Niederlehner, Barbara R. (PLOS, 2013-04-22)
    Forested ecosystems in the southeastern United States are currently undergoing an invasion by the hemlock woolly adelgid (HWA). Previous studies in this area have shown changes to forest structure, decreases in canopy cover, increases in organic matter, and changes to nutrient cycling on the forest floor and soil. Here, we were interested in how the effects of canopy loss and nutrient leakage from terrestrial areas would translate into functional changes in streams draining affected watersheds. We addressed these questions in HWA-infested watersheds at the Coweeta Hydrologic Laboratory in North Carolina. Specifically, we measured stream metabolism (gross primary production and ecosystem respiration) and nitrogen uptake from 2008 to 2011 in five streams across the Coweeta basin. Over the course of our study, we found no change to in-stream nutrient concentrations. While canopy cover decreased annually in these watersheds, this change in light penetration did not translate to higher rates of in-stream primary production during the summer months of our study. We found a trend towards greater heterotrophy within our watersheds, where in-stream respiration accounted for a much larger component of net ecosystem production than GPP. Additionally, increases in rhododendron cover may counteract changes in light and nutrient availability that occurred with hemlock loss. The variability in our metabolic and uptake parameters suggests an actively-infested ecosystem in transition between steady states.
  • Thumbnail Image
    An Ecotoxicological Assessment of a Treated Coal-mining Effluent in the Leading Creek Watershed, Meigs County, Ohio
    Kennedy, Alan James (Virginia Tech, 2002-12-13)
    The majority of research studying the ecological impacts of the coal mining industry on freshwater systems has focused on abandoned-mined land, and the associated acid drainage and metals toxicity. Treated discharges from active mining and preparation facilities, however, can also impair lotic ecosystems through total dissolved solids (TDS) toxicity, caused primarily by the reagents used for pH modifications and the oxidation of reduced sulfur. Such impairment was best detected through application of (1) benthic macroinvertebrate surveys using metrics of biotic impairment such as relative Ephemeroptera abundance and Ephemeroptera-Plecoptera-Trichoptera (EPT) minus the tolerant caddisfly family Hydropsychidae (2) in situ growth of Corbicula fluminea during 96-d exposure and (3) laboratory testing using Ceriodaphnia dubia. Traditional metrics such as total taxa richness, EPT, diversity and biotic indices were not sensitive to elevated TDS levels. Further study using strength of evidence, regression analysis and manipulation of laboratory formulated media, indicated that the mine effluent was the primary causal agent of the observed biotic impairment, and its toxicity could be attributed to sodium/sulfate-dominated TDS, which is significantly ameliorated by water hardness. Finally, although testing with lentic cladocerans, such as Ceriodaphnia, is consistent, cost-effective and sensitive to TDS related toxicity, the ecological relevance and protective capability of such testing is questionable when assessing contaminant effects on sensitive macroinvertebrates indigenous to lotic systems. A more ecologically relevant laboratory bioassay using the mayfly, Isonychia bicolor, in simulated lotic microcosms provided more sensitive endpoints than Ceriodaphnia and Pimephales promelas. Although the heartiness of Isonychia in laboratory conditions is poorly understood relative to standardized test organisms, these results, along with potential toxic impacts from numerous sodium/sulfate-dominated wastewaters discharging into freshwater systems, may have important implications to future national pollution discharge and elimination system (NPDES) permit testing. Currently, however, strong recommendations can only be made using Ceriodaphnia endpoints. Potential acute toxicity to aquatic organisms in high hardness solution (~790 mg/L as CaCO₃) is possible where sodium/sulfate-dominated TDS levels exceed ~7000 uS/cm (5167 mg/L), with potential chronic toxicity occurring at ~3200 uS/cm (2342 mg/L). These endpoints were significantly reduced in solutions of lower hardness (88 mg/L as CaCO₃), with acute and chronic toxicity occurring at 5100 uS/cm (3754 mg/L) and ~2100 uS/cm (1523 mg/L), respectively. Point source discharges causing instream TDS concentrations to exceed these levels risk impairment to aquatic life.
  • Thumbnail Image
    The effects of cattle exclusion on stream structure and function
    Hughes, April Heather (Virginia Tech, 2008-07-08)
    Stream ecosystems can be influenced by cattle grazing in the riparian zone due to sediment input, nutrient loading, and soil compaction, which lead to alterations of macroinvertebrate and microbial activity. Recently government programs, such as the Conservation Reserve Enhancement Program (CREP), have provided funding for farmers to exclude cattle from streams and riparian zones. Funding for CREP is limited and does not allow for post exclusion assessment. The objectives for this study were; 1) to explore whether CREP and other cattle exclusion initiatives help restore functional integrity to streams; 2) and if they do, to evaluate the time required for integrity to be restored. I predicted leaf processing (a fundamental ecosystem level function) in streams would be influenced by excluding cattle from the riparian zone due to changes in nutrient availability, sediment abundance, shredding macroinvertebrates, and microbial activity. I tested this prediction by measuring leaf processing at sites that had cattle excluded for <1 to 15 years. Breakdown rates did not correspond linearly to time since cattle exclusion. This was probably due to the opposing effects of elevated sediment versus nutrients on leaf breakdown at recently grazed sites. Leaf breakdown and shredder density were strongly correlated with riparian vegetation density. This study suggests that in addition to cattle exclusion, reforestation of woody riparian vegetation may be essential to restore functional integrity to agricultural streams.