Brent R. Johnson

Rapid expansion of natural gas development poses a threat to surface waters

Extraction of natural gas from hard-to-reach reservoirs has expanded around the world and poses multiple environmental threats to surface waters. Improved drilling and extraction technology used to access low permeability natural gas requires millions of liters of water and a suite of chemicals that may be toxic to aquatic biota. There is growing concern among the scientific community and the general public that rapid and extensive natural gas development in the US could lead to degradation of natural resources. Gas wells are often close to surface waters that could be impacted by elevated sediment runoff from pipelines and roads, alteration of streamflow as a result of water extraction, and contamination from introduced chemicals or the resulting wastewater. However, the data required to fully understand these potential threats are currently lacking. Scientists therefore need to study the changes in ecosystem structure and function caused by natural gas extraction and to use such data to inform sound environmental policy.

Structural and functional characteristics of natural and constructed channels draining a reclaimed mountaintop removal and valley fill coal mine

Abstract Mountaintop removal and valley fill (MTR/VF) coal mining has altered the landscape of the Central Appalachian region in the USA. Among the changes are large-scale topographic recontouring, burial of headwater streams, and degradation of downstream water quality. The goals of our study were to: 1) compare the structure and function of natural and constructed stream channels in forested and MTR/VF catchments across ephemeral, intermittent, and perennial flow regimes and 2) assess the relationship between leaf litter breakdown and structural measures, such as the habitat assessments currently used by regulatory agencies. Specific conductance of stream water was, on average, 36 to 57× higher at perennial reaches below valley fills than at perennial reaches in forested catchments, whereas pH was circumneutral in both catchment types. Channel habitat and invertebrate assemblages in litter bags differed between forested streams and constructed channels in VF catchments. Invertebrate density, diversity, and biomass were typically higher in litter bags from forested catchments than from VF catchments. No differences in fungal biomass, estimated as ergosterol concentration, were detected between litter bags from forested and VF catchments. Breakdown of oak (Quercus alba) leaves was slower at perennial and intermittent reaches in VF catchments than at perennial and intermittent reaches in forested catchments. However, breakdown rates did not differ between ephemeral reaches on VFs and in forested catchments. Breakdown rates of oak leaves were significantly correlated to conductivity at perennial and intermittent reaches and to shredder diversity across all reaches, but were not correlated with habitat assessment scores currently being used to determine compensatory mitigation. Landuse changes associated with MTR/VF have detrimental consequences to headwater stream function that are not adequately evaluated using the prevalent habitat assessment.

Physical indicators of hydrologic permanence in forested headwater streams

Abstract Recent court cases have questioned whether all headwater streams are jurisdictional waters under the US Clean Water Act. Rapid field-based indicators of hydrologic permanence are needed for making jurisdictional determinations. Our study objectives were to: 1) identify physical characteristics of forested headwater streams that best distinguish perennial, intermittent, and ephemeral reaches and 2) assess the applicability of existing rapid field-based tools for classifying hydrologic permanence across a wide geographic range. We surveyed reach- and drainage-scale characteristics at 113 sites across 10 study forests in the US. Streams in 4 core forests (61 core sites) were sampled over 2 consecutive years and were used in model construction. Streams in 6 satellite forests (72 satellite sites) were used to validate the models over a broader geographic range. Discriminant function models successfully differentiated hydrologic permanence categories at core sites. Drainage area, the Ohio Environmental Protection Agency Headwater Habitat Evaluation Index (HHEI), and the North Carolina Department of Water Quality Stream Classification Method (NCSC) were strongly correlated with the discriminant function that separated ephemeral from perennial and intermittent sites. Entrenchment ratio was the most consistent variable discriminating intermittent from perennial sites across the core forests. The models had mixed results when applied to the validation data set, but did classify correctly most intermittent and ephemeral sites. Classification trees were used to assess broad regional applicability of existing rapid field-based protocols and to identify important metrics. Scores from the Rapid Bioassessment Protocol Habitat Assessment, HHEI, and NCSC all clearly distinguished ephemeral from intermittent and perennial sites, but no differences were detected between intermittent and perennial sites across all sites. However, data from core sites do indicate that a suite of physical variables can be used successfully to identify hydrologic permanence at regional scales.

Long-term resource limitation reduces insect detritivore growth in a headwater stream

We measured larval growth rates of 2 dominant stream detritivore groups to assess the mechanism underlying declines in invertebrate production following exclusion of terrestrial litter inputs to a forested headwater stream. Larval Tallaperla spp. (Plecoptera:Peltoperlidae) were chosen as representative shredders and non-Tanypodinae Chironomidae (Diptera) were selected as representative collector-gatherers. Larval growth rates were measured in the treatment stream and in 2 undisturbed reference streams using in situ growth chambers. Estimates of daily growth rates were derived from change in mean length of larvae over incubation periods. Initial larval length was a significant predictor of growth in each stream for both taxonomic groups (r2 = 0.43–0.72, p < 0.05). Comparison of significant regression lines showed that size-specific growth of both Tallaperla spp. and chironomids was significantly reduced in the litter exclusion stream (ANCOVA, p < 0.05). Lower chironomid growth rates in the treatment stream than in the control streams indicate that production estimates based on the instantaneous growth method are actually lower than previously reported for the site. Mortality of Tallaperla spp. was also significantly higher in the treatment stream than in control streams (ANOVA, p < 0.05). Reduced growth of these representative taxa apparently results from reduced quantity of organic matter food resources. These results show that reduced growth is partially responsible for observed declines in detritivore production in the litter-exclusion stream.

Elevated major ion concentrations inhibit larval mayfly growth and development

Anthropogenic disturbances, including those from developing energy resources, can alter stream chemistry significantly by elevating total dissolved solids. Field studies have indicated that mayflies (Order Ephemeroptera) are particularly sensitive to high total dissolved solids. In the present study, the authors measured 20-d growth and survivorship of larval Neocloeon triangulifer exposed to a gradient of brine salt (mixed NaCl and CaCl2 ) concentrations. Daily growth rates were reduced significantly in all salt concentrations above the control (363 µS cm(-1) ) and larvae in treatments with specific conductance >812 µS cm(-1) were in comparatively earlier developmental stages (instars) at the end of the experiment. Survivorship declined significantly when specific conductance was >1513 µS cm(-1) and the calculated 20-d 50% lethal concentration was 2866 µS cm(-1) . The present studys results provide strong experimental evidence that elevated ion concentrations similar to those observed in developing energy resources, such as oil and gas drilling or coal mining, can adversely affect sensitive aquatic insect species.

Part 2: Sensitivity comparisons of the mayfly Centroptilum triangulifer to Ceriodaphnia dubia and Daphnia magna using standard reference toxicants; NaCl, KCl and CuSO4.

Criteria for establishing water quality standards that are protective for 95% of the native species are generally based upon laboratory toxicity tests. These tests utilize common model organisms that have established test methods. However, for invertebrates these species represent mostly the zooplankton community and are not inclusive of all taxa. In order to examine a potential under-representation in emerging aquatic invertebrates the US Environmental Protection Agency has cultured a parthenogenetic mayfly, Centroptilum triangulifer (Ephemeroptera: Baetidae). This study established a 48h acute and a 14-day short-term chronic testing procedure for C. triangulifer and compared its sensitivity to two model invertebrates, Ceriodaphnia dubia and Daphnia magna. Toxicity tests were conducted to determine mortality and growth effects using standard reference toxicants: NaCl, KCl and CuSO4. In 48-h acute tests, the average LC50 for the mayfly was 659mgL(-1) NaCl, 1957mgL(-1) KCl, and 11μgL(-1) CuSO4. IC25 values, using dry weight as the endpoint, were 228mgL(-1) NaCl, 356mgL(-1) KCl and 5μgL(-1) CuSO4. C. triangulifer was the most sensitive species in NaCl acute and chronic growth tests. At KCl concentrations tested, C. triangulifer was less sensitive for acute tests but was equally or more sensitive than C. dubia and D. magna for growth measurements. This study determined C. triangulifer has great potential and benefits for use in ecotoxicological studies.

Part 1: Laboratory culture of Centroptilum triangulifer (Ephemeroptera: Baetidae) using a defined diet of three diatoms.

Development of methods for assessing exposure and effects of waterborne toxicants on stream invertebrate species is important to elucidate environmentally relevant information. Current protocols for freshwater invertebrate toxicity testing almost exclusively utilize cladocerans, amphipods or chironomids rather than the more typical aquatic insect taxa found in lotic systems. Centroptilum triangulifer is a parthenogenetic mayfly occurring in depositional habitats of streams and rivers of the Eastern U.S. and Canada. C. triangulifer is an ideal stream insect for toxicity testing under field and laboratory conditions because of its short life cycle, parthenogenetic mode of reproduction, and it represents a group considered sensitive to environmental stressors. In this study, a colony of C. triangulifer was reared using a defined diet of three diatoms, Mayamaea atomus var. permitis, Nitzschia cf. pusilla, and Achnanthidium minutissimum. Percent survival (⩾80%), fecundity measurements (⩾1000 eggs) and pre-egg laying weights were used as indicators of overall colony health and fitness in our laboratory water (Lab-line) and in Moderately Hard Reconstituted Water (MHRW). Lab-line reared C. triangulifer had average survival rate of 92.69% for eleven generations and 82.99% over thirteen generations. MHRW reared C. triangulifer had an average survival rate of 80.65% for four generations and three generations of fecundities greater than 1000 eggs per individual. Pre-egg laying weight and fecundity were highly correlated and a best-fit model equation was derived to estimate egg counts for future generations. Establishment of this culturing protocol provides a more ecologically relevant species for toxicity testing and aids in further stressor identification for stream bioassessments.

Macroinvertebrate and organic matter export from headwater tributaries of a Central Appalachian stream

Headwater streams export organisms and other materials to receiving streams, and macroinvertebrate drift can shape colonization dynamics in downstream reaches while providing food for downstream consumers. Spring-time drift and organic matter export was measured once monthly (February–May) over a 24-h period near the outlets of 12 eastern Kentucky (USA) streams to document and explore factors governing downstream transport. We compared drift measures as loads (day−1) and concentrations (volume−1) including drift density, biomass, richness, composition, and particulate organic matter across catchment area, month, reach scale factors, and network proximity. Aquatic invertebrate drift densities were roughly 10 times greater than terrestrial invertebrate densities; aquatic richness ranged from 18 to 45 taxa with Ephemeroptera, Plecoptera, Trichoptera, and Diptera genera dominating drift sample richness and abundance. Ordination revealed that assemblages clustered by month and catchment area; organic matter exports (loads or concentrations) also varied by month and catchment area factors. While drift measures were correlated with catchment area and sample date, local factors (e.g., substrate composition, riffle length, channel slope, and network proximity) were generally non-influential. The findings can be used to inform preservation and restoration strategies where headwater streams serve as sources of colonizers and provide food subsidies to receiving streams.