Revaluation of ortho-phosphorus and inorganic nitrogen levels in an antarctic meromictic lake

Recent studies of Lake Bonney, a meromictic Antarctic lake, utilized techniques modified for hypersaline waters and produced results significantly different from those of previous investigators. Notably higher values are reported for ammonia and nitrate, while phosphorus levels tend to be in distinct disagreement with those obtained by other workers except for limited data reported by one author using a technique similar to that used in the current studies. The method of standard additions was employed as a partial solution to salinity interferences.Correspondence: Bruce C. PARKER Biology Department, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061     

Direct and correlated responses to selection for increased postweaning gain in mice

Summary Mass selection for increased body weight gain from 21 to 42 days of age was practiced for 12 generations in four replicate lines of ICR-albino mice. Response to selection averaged 0.56±0.03 g. per generation. This response represented an increase of 7.0 genetic standard deviation units and 3.4 phenotypic standard deviation units in 12 generations. The realized heritability pooled over the four replicates was 0.24±0.02. Sizable positive correlated responses were found for 42 and 56-day weight and gain from 42 to 56 days. Much smaller positive correlated responses were noted for 12-day litter weight and 12-day individual weight. Neither litter size nor weaning weight were significantly altered by selection for increased postweaning gain. Reproductive efficiency measured as percent fertile matings declined significantly in the selected lines.Supported in part by a grant from the Virginia Agricultural Foundation.Published with the approval of the Director of the Research Division, Virginia Polytechnic Institute and State University.     

Soil and plant water stress in an Appalachian oak forest in relation to topography and stand age

Summary A Forest Site Quality Index (FSQI) formulated to predict site quality in Ridge and Valley terrain based on the topographic parameters of aspect, slope inclination and slope position was used to verify moisture gradients along the southeast face of Potts Mountain in Craig County, Virginia. A gradient of site quality index values representing xeric to mesic sites was established in both recently clearcut and adjacent uncut second-growth forest stands. Soil moisture content was determined gravimetrically at ten day intervals from May to October, 1981. Plant moisture stress measurements were taken in conjunction with soil moisture sampling using the pressure chamber technique on three dominant hardwood tree species.For both clearcut and uncut forest stands, a general gradient of increasing soil moisture availability with increasing FSQI was evident, although differences were not large between index values of 8 and 11 in either stand type. Soil water potential and predawn plant water potential exhibited a strong seasonal trend, their direct relationship suggesting that available soil water is probably the critical factor controlling base P levels. Growth limiting stress levels began in late July and continued for the remainder of the growing season.Funding for this research was granted through Cooperative Research Agreement # 18-882, USDA SE Forest Experiment Station and the Forestry Department of Virginia Polytechnic Institute and State University, Blacksburg, VA 24061.     

Geographic variation in patterns of nestedness among local stream fish assemblages in Virginia

Nestedness of faunal assemblages is a multi-scale phenomenon, potentially influenced by a variety of factors. Prior small-scale studies have found freshwater fish species assemblages to be nested along stream courses as a result of either selective colonization or extinction. However, within-stream gradients in temperature and other factors are correlated with the distributions of many fish species and may also contribute to nestedness. At a regional level, strongly nested patterns would require a consistent set of structuring mechanisms across streams, and correlation among species tolerances of the environmental factors that influence distribution. Thus, nestedness should be negatively associated with the spatial extent of the region analyzed and positively associated with elevational gradients (a correlate of temperature and other environmental factors). We examined these relationships for the freshwater fishes of Virginia. Regions were defined within a spatial hierarchy and included whole river drainages, portions of drainages within physiographic provinces, and smaller subdrainages. In most cases, nestedness was significantly stronger in regions of smaller spatial extent and in regions characterized by greater topographic relief. Analysis of hydrologic variability and patterns of faunal turnover provided no evidence that inter-annual colonization/extinction dynamics contributed to elevational differences in nestedness. These results suggest that, at regional scales, nestedness is influenced by interactions between biotic and abiotic factors, and that the strongest nestedness is likely to occur where a small number of organizational processes predominate, i.e., over small spatial extents and regions exhibiting strong environmental gradients.The Virginia Cooperate Fish and Wildlife Research Unit is jointly sponsored by United States Geological Survey, Virginia Polytechnic Institute and State University, and Virginia Department of Game and Inland Fisheries.     

Comparison of three zooplankton samplers: a taxon-specific assessment

We compared densities of zooplankton captured by three commonzooplankton samplers during 24 h. A tube sampler generally yieldedzooplankton densities equal to or greater than those from avertical net tow or a Schindler-Patalas trap. Exceptions includedherbivorous rotifers and Diaphanosoma. Because rotifer densityusually was greatest in the deepest stratum sampled (i.e. nearthe bottom of the tube), water loss with lifting probably accountedfor reduced rotifer capture. Why the tube and the Schindler-Patalastrap were less efficient than the net for Diaphanosoma remainsunclear. Because tubes sample the entire water column, providingzooplankton densities comparable with traditional gear, theyare a time-saving alternative for zooplankton sampling in shallowlakes and weedy littoral zones. ²The Unit is sponsored jointly by The United States Fish andWildlife Service, Ohio Department of Natural Resources, TheOhio State University and the Wildlife Management Institute.     

Brain collections at the National Museum of Health and Medicine

Owing in large part to the foresight and efforts of Wally Welker, the National Museum of Health and Medicine has become a major repository for collections of brain specimens vital to the study of neurobehavioral evolution. From its origins in the Armed Forces Institute of Pathology, with the collection of largely pathological specimens assembled by Paul Yakovlev, the museum has added to its resources four additional extensive collections, largely consisting of specimens acquired specifically for comparative and evolutionary studies: Welker's collection from the University of Wisconsin-Madison, John I. Johnson's collection from Michigan State University, the Adolf Meyer Collection from the Johns Hopkins University, and the Elizabeth Crosby collections from the University of Michigan. We describe here the history and contents of each of these five collections, to inform the scientific field of the extent and details of these remarkable resources.     

Spatiotemporal variability of stream habitat and movement of three species of fish

Relationships between environmental variability and movement are poorly understood, due to both their complexity and the limited ecological scope of most movement studies. We studied movements of fantail (Etheostoma flabellare), riverweed (E. podostemone), and Roanoke darters (Percina roanoka) through two stream systems during two summers. We then related movement to variability in measured habitat attributes using logistic regression and exploratory data plots. We indexed habitat conditions at both microhabitat (i.e., patches of uniform depth, velocity, and substrate) and mesohabitat (i.e., riffle and pool channel units) spatial scales, and determined how local habitat conditions were affected by landscape spatial (i.e., longitudinal position, land use) and temporal contexts. Most spatial variability in habitat conditions and fish movement was unexplained by a site’s location on the landscape. Exceptions were microhabitat diversity, which was greater in the less-disturbed watershed, and riffle isolation and predator density in pools, which were greater at more-downstream sites. Habitat conditions and movement also exhibited only minor temporal variability, but the relative influences of habitat attributes on movement were quite variable over time. During the first year, movements of fantail and riverweed darters were triggered predominantly by loss of shallow microhabitats; whereas, during the second year, microhabitat diversity was more strongly related (though in opposite directions) to movement of these two species. Roanoke darters did not move in response to microhabitat-scale variables, presumably because of the species’ preference for deeper microhabitats that changed little over time. Conversely, movement of all species appeared to be constrained by riffle isolation and predator density in pools, two mesohabitat-scale attributes. Relationships between environmental variability and movement depended on both the spatiotemporal scale of consideration and the ecology of the species. Future studies that integrate across scales, taxa, and life-histories are likely to provide greater insight into movement ecology than will traditional, single-season, single-species approaches. The Virginia Cooperative Fish and Wildlife Research Unit is jointly sponsored by the US Geological Survey, Virginia Polytechnic Institute and State University, Virginia Department of Game and Inland Fisheries, and Wildlife Management Institute.     

Predation by rock bass on other stream fishes: experimental effects of depth and cover

Synopsis Effects of water depth and cover availability on predation rates by adult rock bass, Ambloplites rupestris, on juvenile central stoneroller, Campostoma anomalum, pumpkinseed, Lepomis gibbosa, and fantail darter, Etheostoma flabellare, were measured in a laboratory stream. A predation rate experiment and a prey activity experiment were conducted. In the first experiment, each prey type shared experimental chambers with predatory rock bass under all combinations of two depths (shallow and deep) and two cover levels (absent and present). Predation rates after 72 h were greater in deep (35–38 cm) than in shallow (7–10 cm) water for fantail darter and two sizes of central stoneroller, but not for pumpkinseed. Presence of cover (opaque plastic tubes) on the stream bottom had no direct effect on predation rates, which were higher for pumpkinseed and small stoneroller (35–64 mm total length) than for fantail darter and large stoneroller (70–89 mm total length). In the second experiment, diel patterns of small stoneroller activity were monitored under all combinations of two water depths and three levels of predation risk. Small stonerollers were more active during the day and in the absence of rock bass, but were not affected directly by water depth. My results suggest that effects of habitat features (e.g., depth, cover) on predator-prey interactions vary according to the natural history and behavior of particular prey and predators. Future research should integrate habitat-specific responses of prey to predation risk into models that predict the distribution of prey among available habitats.The unit is jointly supported by the U.S. Fish and Wildlife Service, the Virginia Department of Game and Inland Fisheries, the Wildlife Management Institute, and Virginia Polutechnic Institute and State University.     

Comparative effects of methazole and two of its degradation products in plants on the metabolism of enzymatically isolated leaf cells of velvetleaf (Abutilon theophrasti Medic)

Effects of methazole [2-(3,4-dichlorophenyl)-4-methyl-1,2,4-oxadiazolidine-3,5-dione] and of its plant degradation products, DCPMU [3-(3,4-dichlorophenyl)-1-methylurea] and DCPU [3-(3,4-dichlorophenyl)urea], on photosynthesis, protein synthesis, ribonucleic acid (RNA) synthesis, and lipid synthesis of enzymatically isolated leaf cells of velvetleaf (Abutilon theophrasti Medic) were compared. Photosynthesis and protein, RNA, and lipid synthesis were assayed by the incorporation of NaH¹⁴CO₃, [¹⁴C]-leucine, [¹⁴C]-uracil, and [¹⁴C]-acetate, respectively, into the isolated cells. Time-course and concentration studies included incubation times of 30, 60, and 120 min and concentrations of 0.1, 1, 10, and 100 μM of all three chemicals. DCPMU was a more potent inhibitor of the four metabolic processes examined than either the parent herbicide methazole or DCPU. The sensitivity of the four metabolic processes to DCPMU decreased in the order: photosynthesis>lipid>RNA >protein synthesis. Inhibition of all metabolic processes by methazole was time-dependent, increasing in magnitude with concomitant increases in incubation time. It is probable that the observed effects of methazole were caused by DCPMU, formed through metabolism of methazole by the isolated leaf cells of velvetleaf rather than by methazole itself. DCPU was less active than the parent herbicide methazole and DCPMU and seems to be a terminal metabolite of methazole with limited phytotoxicity. Contribution No. 470, Department of Plant Pathology and Physiology, Virginia Polytechnic Institute and State University, Blacksburg, Virginia 24061, USA.     

Differential effects of BCNU on T cell,macrophage, natural killer and lymphokine-activated killer cell activities in mice bearing a syngeneic tumor

Summary Chloroethylnitrosoureas have been used widely to treat human and experimental animal tumors. We have earlier observed that >90% of the mice transplanted with syngeneic tumors survive following treatment with nitrosoureas such as 1,3-bis(2-chloroethyl)-1-nitrosourea (BCNU) and furthermore, they resist subsequent challenge with the same tumor. The present investigation was initiated to determine the mechanism by which BCNU brings about this effect. Treatment of tumor cell targets in vivo or in vitro with BCNU, increased their susceptibility to macrophage (MØ)-mediated cytotoxicity as measured in a direct cytotoxicity assay or in an antibody-dependent cell-mediated cytotoxicity (ADCC) assay. In contrast, the antitumor cytotoxicity caused by cytotoxic T lymphocytes (CTL), natural killer (NK) cells, or lymphokine-activated killer (LAK) cells, was not altered following BCNU treatment of tumor targets. Studies were also conducted to investigate the direct effect of BCNU in vivo on various cytotoxic effector cells. For this purpose, MØ, NK, LAK, and CTL activities from BCNU-treated-tumor-bearing mice were screened for cytotoxicity against untreated tumor targets in vitro. It was observed that tumor-specific CTL and LAK cell activity increased in BCNU-treated tumor-bearing mice when compared to untreated controls while the cytotoxic potential of NK cells and MØs was not altered. The present study suggests that antitumor drugs such as BCNU are not only tumoricidal but also selectively act in a variety of ways at both the effector and target cell level, leading to overall enhanced antitumor immunity and high rate of cures from the syngeneic tumor challenge.The work at Virginia Polytechnic Institute and State University was supported by NIH grants CA45009 and CA45010 and by a Biomedical Research Support Grant. The work at University of Kentucky was supported by NIH grants CA34052 and CA33629 and by a grant from the Tobacco and Health Institute     

Colin Hill discusses in silico modeling of human cells

Colin Hill is the founder of Gene Network Sciences (GNS; http://www.gnsbiotech.com) and serves as President and Chief Executive Officer. He has extensive scientific experience in the areas of gene network modeling, pioneering the application of methods based in statistical physics and non-linear dynamics to the stochastic dynamics of gene expression. He is the co-founder of a multidisciplinary research effort at Cornell University dedicated to combining computational and experimental approaches to the study of signal transduction pathways. Hill is the co-creator of the Digital Cell™ software environment for the modeling of complex gene networks and biochemical pathways. He earned his BS degree in Physics from Virginia Polytechnic and State University and his MS degrees in Physics from McGill University and Cornell University.     

An assessment of the sources of error in estimations of bulk sedimentary pigment concentrations and its implications for trophic status assessment

Rates of leaf litter processing and densities of macroinvertebrates in leaf packs were compared at two sites that differed in catchment logging history. The processing rate of leaves of sugar maple (Acer saccharum Marsh.) was significantly faster in a stream draining a catchment that had been logged about 20 years ago than in one that had been undisturbed for 80 years. The faster processing rate was accompanied by significantly higher leaf pack densities of total macroinvertebrates, shredders, and collector-gatherers. The higher densities of leaf pack macroinvertebrates were apparently a result of differences in tree species between the two catchments. These differences resulted in greater inputs of fast-decomposing leaf litter to the stream draining the disturbed catchment and in smaller amounts of leaf litter remaining in the stream draining the disturbed catchment by spring when this study was conducted. The Unit is jointly sponsored by the West Virginia Department of Natural Resources, West Virginia University, the U.S. Fish and Wildlife Service, and the Wildlife Management Institute. The Unit is jointly sponsored by the West Virginia Department of Natural Resources, West Virginia University, the U.S. Fish and Wildlife Service, and the Wildlife Management Institute.     

Effects of wastewater treatment plant effluents on freshwater mollusks in the upper Clinch River,Virginia, USA

Field and laboratory studies were conducted to determine mollusk distributions in proximity to waste-water treatment plants (WTP's) in the upper Clinch River and to test the tolerance of two mollusk species to monochloramine and unionized ammonia, the major toxicants in domestic effluent. River reaches up to 3.7 km downstream of WTP's were devoid of freshwater mussels (Unionidae), and tolerance to effluents varied among snails, sphaeriid clams, and the asian clam Corbicula fluminea. Residential communities with septic systems had no measurable impact on mollusk assemblages downstream.Laboratory bioassays with glochidia of Villosa iris yielded the following results: 24 h EC₅₀ and LC₅₀ values of 0.042 mg l^–1 and 0.084 mg l^–1 monochloramine, respectively; and 24 h EC₅₀ and LC₅₀ of 0.237 mg l^–1 and 0.284 mg l^–1 unionized ammonia, respectively. Glochidia rank among the most sensitive invertebrates in their tolerance to these toxicants. The snail Pleurocera unciale unciale was moderately sensitive, with 96 h LC₅₀ values of 0.252 mg l^–1 monochloramine and 0.742 mg l^–1 unionized ammonia. Monitoring of monochloramine and unionized ammonia concentrations 0.1 km below WTP outfalls indicated that monochloramine was the toxicant likely inhibiting mollusk recovery below these plants.The Unit is jointly supported by the U.S. Fish and Wildlife Service, Virginia Department of Game and Inland Fisheries, The Wildlife Management Institute and Virginia Polytechnic Institute and State University.     

Development and feeding of <Emphasis Type="Italic">Tetraphleps galchanoides</Emphasis>, a predator of the hemlock woolly adelgid

Tetraphleps galchanoides Ghauri (Hemiptera: Anthocoridae) nymphs were collected from hemlock woolly adelgid (HWA) Adelges tsugae Annand (Hemiptera: Adelgidae) infested Tsuga sp. in Baoxing, Sichuan, China. First and second stage nymphs collected from foliage shipped from China; were reared to adults and tested for feeding rates and host preferences. They were reared at 5, 8, 12, and 15 ± 1 °C from November to December, January to March, April, and May to June, respectively, in the quarantine laboratory at Virginia Polytechnic Institute and State University. At 8 °C, development time was 15, 20, and 40 days for the N-III, IV, and V nymphal stages, respectively. Adult males lived 83 days with a range of 21–147 days. A single adult female lived for 21 days. At 5 °C, second stage T. galchanoides nymphs consumed 0.8 HWA nymphs per day, and 2.0 HWA nymphs per day at the N-V stage. At 8 °C, consumption of HWA nymphs ranged from 1.3 to 3.4 nymphs per day for the N-III to N-V stages, respectively. Adult T. galchanoides consumed more HWA eggs than HWA adults, pine bark adelgid (PBA) Pineus strobi (Hartig) (Hemiptera: Adelgidae) adults, and eggs in no-choice tests. In choice tests with HWA eggs and PBA eggs, more HWA eggs were eaten. Adult and nymph body measurements are presented for determination of nymphal instars.     

Extension-growth responses and expression of flavonoid biosynthesis genes in the Arabidopsis hy4 mutant

The hy4 mutant of Arabidopsis thaliana(L.) Heynh. was previously shown to be impaired in the suppression of hypocotyl extension specifically by blue light. We report here that hy4 is altered in a range of blue-light-mediated extension-growth responses in various organs in seedlings and mature plants: it shows greater length of bolted stems, increased petiole extension and increased leaf width and area in blue light compared to the wild type. The hy4 mutant shows decreased cotyledon expansion in both red and blue light compared to the wild type. Anthocyanin formation and the expression of several flavonoid biosynthesis genes is stimulated by blue light in the wild type but to a much lower extent in hy4. The results indicate that the HY4 gene product is concerned with the perception of blue light in a range of extension-growth and gene-expression responses in Arabidopsis.Abbreviations DFR dihydroflavonol reductase - CHS chalcone synthase - CHI chalcone isomerase We thank the UK Agricultural and Food Research Council for supporting this work through the award of a research grant to G.I.J. We are grateful to Robert Brown for excellent technical assistance and Drs B.W. Shirley (Department of Biology, Virginia Polytechnic Institute and State University, Blacksburg, USA), C.D. Silflow (Department of Genetics and Cell Biology, University of Minnesota, St. Paul, USA) and I.E. Somssich (Department of Biochemistry, Max-Planck-Institut, Köln, Germany) for providing plasmid DNA.     

Zooplankton of a swamp water ecosystem

The Great Dismal Swamp, located in southeastern Virginia and extending into northeastern North Carolina, is a unique ecosystem which has undergone severe alteration over the last 200 years due to agricultural, municipal and timbering development. The swamp is presently about 50% of its late 1700 size when George Washington commissioned the construction of the first of a series of drainage ditches that have subsequently reduced the swamp aquatic environs to a ditch network draining into Lake Drummond located near the swamp's center. The swamp waters are characterized by a brown color, high suspended organic matter, high acidity and low nutrient levels. This paper presents the first comprehensive study of the zooplankton assemblages of the Great Dismal Swamp.Zooplankton was collected for one year at 14 stations and was dominated by rotifers. Of the 84 species identified, 61 were rotifers, 18 were Cladocera and 5 were copepods. Many of the species collected were cosmopolitan and acid tolerant forms. Dominant lake rotifers included Polyarthra vulgaris, Conochiloides dossuarius, Keratella cochlearis, Trichocerca similis, Synchaeta longipes and Microcodon clavus. Dominant crustaceae included Bosmina longirostris, Diaphanosoma leuchtenbergianum, Mesocyclops edax, and Tropocyclops prasinus.Usually the ditch zooplankton was the same as that of the lake. Of the seven ditches studied, the most unique chemically and biologically were Interior, Washington, and Portsmouth. Measurable alkalinity was detected in Interior and Washington Ditches. Alkaline water rotifers such as Brachionus, Mytilina, Filinia, Notholca Platyias and Keratella earlinae were found in these ditches. The rotifer, Keratella valga, was only found from Portsmouth Ditch, during a period when water was flowing into the lake and it contained high nutrient levels.Research funded in part by the Virginia Academy of Sciences and the Center for Environmental Studies, Virginia Polytechnic Institute and State University.     

Genetic systems development in the clostridia

Abstract: This review describes recent developments in the genetic manipulation of the solventogenic clostridia, Clostridium acetobutylicum and C. beijerinckii . It is to be noted that our laboratory stock of C. acetobutylicum ATCC 824, which was obtained from the American Type Culture Collection, has recently been re-identified as C. beijerinckii NCIMB 8052 based on DNA similarity studies using the S1 nuclease method (personal communication, Dr. Jiann-Shin Chen, Virginia Polytechnic Institute and State University). Reference to our laboratory 824 culture has been changed to C. beijerinckii NCIMB 8052 throughout this paper in order to be consistent with this finding. The focus of this review specifically involves the characterization of an M13-like genetic system for the clostridia based on the pCAK1 phagemid, as well as preliminary work on development of a plasmid-based vector based on the indigenous pDM11 plasmid recovered from C. acetobutylicum NCIB 6443. The construction of a C. beijerinckii strain with amplified endoglucanase activity was achieved by inserting the engB gene from C. cellulovorans into C. beijerinckii . The successful expression of a heterologous engB gene from C. cellulovorans in C. beijerinckii NCIMB 8052 has important industrial significance for the eventual utilization of cellulose by this acetone-butanol-ethanol fermentation microorganism.     

Variation in polychlorinated biphenyl levels in common carp from a primarily agricultural drainage

Concentrations of polychlorinated biphenyls (PCBs) in common carp, Cyprinus carpio, from the Des Moines River, Iowa, were assessed for variability related to sampling location, sampling period, fish age, and fat content. Concentrations were highest at a location near the City of Des Moines; they were substantially lower in 1981 than in 1980. Age and fat content had little influence on PCB concentrations in carp. Overall concentrations were some of the lowest recorded in the United States and Canada in recent times.The Unit is jointly supported by Iowa State University, the Iowa State Conservation Commission, and the U.S. Fish and Wildlife Service.Journal Paper No. 10754 of the Iowa Agriculture and Home Economics Experiment Station, Ames, Iowa. Project No. 2465. Financed by a grant from the U.S. Department of Defense Army Corps of Engineers and made available through the Engineering Research Institute, Iowa State University.     

Comparison of sleds versus plankton nets for sampling fish larvae and eggs

Fish larvae and fish eggs were sampled from the inshore waters of eastern Lake Michigan from 1978 through 1980, using a benthic sled and a plankton net towed within 0.5 m of the lake bottom. Differences between estimates of ichthyoplankton abundance based on the benthic sled and those based on the plankton net towed near bottom were examined along with interactions between gear, bottom depth, and time of day. Time of day was determined to be an important factor in comparing these two gear, but data were inconclusive as to the effect of depth on gear differences. Abundance of fish eggs calculated using sled tow data was significantly higher than that for the plankton net. For nighttime collections, density of alewife Alosa pseudoharengus larvae sampled in the plankton net significantly exceeded that for the sled, whereas density of spottail shiner Notropis hudsonius larvae based on sled data was significantly higher than that based on the plankton net for day sampling. Overall, the plankton net appeared to be adequate for sampling abundance of alewife larvae, while the sled was preferred for sampling fish eggs, spottail shiner larvae, and the following less common, but apparently demersal larvae: trout-perch Percopsis omiscomaycus, johnny darter Etheostoma nigrum, ninespine stickleback Pungitius pungitius, and slimy sculpin Cottus cognatus.     

Detrital processing in streams exposed to acidic precipitation in the Central Appalachian Mountains

Continuing high rates of acidic deposition in the eastern United States may lead to long-term effects on stream communities, because sensitive catchments are continuing to lose anions and cations. We conducted a two-year study of the effects of pH and associated water chemistry variables on detrital processing in three streams with different bedrock geology in the Monongahela National Forest, West Virginia. We compared leaf pack processing rates and macroinvertebrate colonization and microbial biomass (ATP concentration) on the packs in the three streams. Breakdown rates of red maple and white oak leaf packs were significantly lower in the most acidic stream. The acidic stream also had significantly lower microbial and shredder biomass than two more circumneutral streams. Shredder composition differed among streams; large-particle detritivores dominated the shredder assemblages of the two circumneutral streams, and smaller shredders dominated in the acidic stream. Within streams, processing rates for three leaf species were not significantly different between the two years of the study even though invertebrate and microbial communities were different in the two years. Thus, macroinvertebrate and microbial communities differed both among streams that differed in their capacity to buffer the effects of acidic precipitation and among years in the same stream; these differences in biotic communities were not large enough to affect rates of leaf processing between the two years of the study, but they did significantly affect processing rates between acidic and circumneutral streams.The Unit is jointly sponsored by the National Biological Service, the West Virginian Division of Natural Resources, West Virginia University, and the Wildlife Management Institute.The Unit is jointly sponsored by the National Biological Service, the West Virginian Division of Natural Resources, West Virginia University, and the Wildlife Management Institute.