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William J. Wolfe

Publications and source records attributed to William J. Wolfe.

18 recordsLinked to original sources
USGS2022

A forested wetland at a climate-induced tipping-point: 17-year demographic evidence of widespread tree recruitment failure

Regeneration and survival of forested wetlands are affected by environmental variables related to the hydrologic regime. Climate change, specifically alterations to precipitation patterns, may have outsized effects on these forests. In Tennessee, USA, precipitation has increased by 15% since 1960. The goal of our research was to assess the evidence for whether this change in precipitation patterns resulted in shorter growing seasons and recruitment failure in common canopy trees for a forest wetland. In 2001 and 2018, the density of Quercus lyrata (overcup oak), Liquidambar styraciflua (sweetgum), Quercus phellos (willow oak), and Betula nigra (river birch) seedling, sapling and adult density were mapped in an area of 2.3 ha within a seasonally flooded karst depression. Overall, the percentage of the growing season experiencing inundation was 26% greater in the deep than in shallow areas between 2001 and 2018. Saplings and small adults of all four species were restricted to shallow areas, and their abundance has declined substantially. Overcup oak and sweetgum individuals that were recruited into the adult life history stage were repelled from the deep zone. Overcup oak and sweetgum adults experienced lower mortality across the 2.3-ha study area (11% and 26%, respectively) relative to willow oak (56%) and river birch (64%) over the 17-year study. Growing-season inundation showed no relation to mortality in adult sweetgum and willow oak, a positive relation to mortality among adult river birch across size classes and among small adult overcup oak, and an inverse relation to mortality among large adult overcup oak. In shallow regions, overcup oak and sweetgum adults had greater basal area increment relative to the intermediate and deep regions of the pond. Results of hydrologic modeling for the study area, based on rainfall and temperature records covering 1855–2019, show ponding durations after 1970 considerably longer than the historical baseline, across ponding-depth classes. Our results strongly suggest that climate change is a driving factor suppressing tree regeneration since 1970 in this seasonally flooded karst depression.

Tennessee↗
USGS2021

Increasing hydroperiod in a karst-depression wetland based on 165 years of simulated daily water levels

The hydrology of seasonally inundated depression wetlands can be highly sensitive to climatic fluctuations. Hydroperiod—the number of days per year that a wetland is inundated—is often of primary ecological importance in these systems and can vary interannually depending on climate conditions. In this study we re-examined an existing hydrologic model to simulate daily water levels in Sinking Pond, a 35-hectare seasonally inundated karst-depression wetland in Tennessee, USA. We recalibrated the model using 22 years of climate and water-level observations and used the recalibrated model to reconstruct (hindcast) daily water levels over a 165-year period from 1855 to 2019. A trend analysis of the climatic data and reconstructed water levels over the hindcasting period indicated substantial increases in pond hydroperiod over time, apparently related to increasing regional precipitation. Wetland hydroperiod increased on average by 5.9 days per decade between 1920 and 2019, with a breakpoint around the year 1970. Hydroperiod changes of this magnitude may have profound consequences for wetland ecology, such as a transition from a forested wetland to a mostly open-water pond at the Sinking Pond site. More broadly, this study illustrates the needs for robust hydrologic models of depression wetlands and for consideration of model transferability in time (i.e., hindcasting and forecasting) under non-stationary hydroclimatic conditions. As climate change is expected to influence water cycles, hydrologic processes, and wetland ecohydrology in the coming decades, hydrologic model projections may become increasingly important to detect, anticipate, and potentially mitigate ecological impacts in depression wetland ecosystems.

Tennessee↗
USGS2020

Species richness responses to water withdrawal scenarios and minimum flow levels: Evaluating presumptive standards in the Tennessee and Cumberland River basins

Water resource managers are challenged to balance growing water demand with protecting aquatic ecosystems and biodiversity. Management decisions can benefit from improved understanding of water withdrawal impacts on hydrologic regimes and ecological assemblages. This study used Ecological Limit Functions for fish groups within the Tennessee and Cumberland river basins to predict species richness responses under simulated constant-rate (CR) and percent-of-flow (POF) withdrawals and for different minimum flow level protections. Streamflow characteristics (SFC) and richness were generally less sensitive to POF withdrawals than CR withdrawals among sites, fish groups, and ecoregions. Species richness generally declined with increasing withdrawals, but responses were variable depending on site-specific departures of SFCs from reference conditions, drainage area, fish group, ecoregion, and minimum flow level. Under POF withdrawals, 10% and 20% daily flow reductions often resulted in loss of <1 species and/or ≤5% richness among fish groups. Median ecological withdrawal thresholds ranged from 3.5-31% for POF withdrawals and from 0.01-0.92 m3/s for CR withdrawals across fish groups and ecoregions. Application of minimum flow level cutoffs often resulted in damping effects on SFC and richness responses, indicating that protection of low streamflows may mitigate hydrologic alteration and fish species richness loss related to water withdrawals. Site-specific and regionally summarized responses of flow regimes and fish assemblages under alternative withdrawal strategies in this study may be useful in informing water management decisions regarding streamflow allocation and maintaining ecological flows.

Cumberland River basin↗
USGS2016

Stage-discharge relations and annual nitrogen and phosphorus load estimates for stream sites in the Elk River Basin, 2006–2008

The U.S. Geological Survey, in cooperation with the Tennessee Department of Environment and Conservation (TDEC), measured continuous discharge at 4 water-quality monitoring sites and developed stage-discharge ratings for 10 additional water-quality monitoring sites in the Elk River Basin during 2006 through 2008. The discharge data were collected to support stream load assessments by TDEC. Annual nitrogen and phosphorus loads were estimated for the four sites where continuous daily discharge records were collected. Reported loads for the period 2006 through 2008 are not representative of long-term mean annual conditions at the sites in this study, however, because of severe drought conditions in the Elk River Basin during this period.

Alabama, Tennessee↗
USGS2016

Insular ecosystems of the southeastern United States—A regional synthesis to support biodiversity conservation in a changing climate

In the southeastern United States, insular ecosystems&mdash;such as rock outcrops, depression wetlands, high-elevation balds, flood-scoured riparian corridors, and insular prairies and barrens&mdash;occupy a small fraction of land area but constitute an important source of regional and global biodiversity, including concentrations of rare and endemic plant taxa. Maintenance of this biodiversity depends upon regimes of abiotic stress and disturbance, incorporating factors such as soil surface temperature, widely fluctuating hydrologic conditions, fires, flood scouring, and episodic droughts that may be subject to alteration by climate change. Over several decades, numerous localized, site-level investigations have yielded important information about the floristics, physical environments, and ecological dynamics of these insular ecosystems; however, the literature from these investigations has generally remained fragmented. This report consists of literature syntheses for eight categories of insular ecosystems of the southeastern United States, concerning (1) physical geography, (2) ecological determinants of community structures including vegetation dynamics and regimes of abiotic stress and disturbance, (3) contributions to regional and global biodiversity, (4) historical and current anthropogenic threats and conservation approaches, and (5) key knowledge gaps relevant to conservation, particularly in terms of climate-change effects on biodiversity. This regional synthesis was undertaken to discern patterns across ecosystems, identify knowledge gaps, and lay the groundwork for future analyses of climate-change vulnerability. Findings from this synthesis indicate that, despite their importance to regional and global biodiversity, insular ecosystems of the southeastern United States have been subjected to a variety of direct and indirect human alterations. In many cases, important questions remain concerning key determinants of ecosystem function. In particular, few empirical investigations in these ecosystems have focused on possible climate-change effects, despite the well-documented ecological effects of climate change at a global level. Long-term management of these ecosystems could benefit from increased scientific effort to characterize and quantify the linkages between changing environmental conditions and the ecological processes that sustain biodiversity.

Alabama, Arkansas, Florida, Georgia, Kentucky, Lou↗
USGS2016

Model calibration criteria for estimating ecological flow characteristics

Quantification of streamflow characteristics in ungauged catchments remains a challenge. Hydrological modeling is often used to derive flow time series and to calculate streamflow characteristics for subsequent applications that may differ from those envisioned by the modelers. While the estimation of model parameters for ungauged catchments is a challenging research task in itself, it is important to evaluate whether simulated time series preserve critical aspects of the streamflow hydrograph. To address this question, seven calibration objective functions were evaluated for their ability to preserve ecologically relevant streamflow characteristics of the average annual hydrograph using a runoff model, HBV-light, at 27 catchments in the southeastern United States. Calibration trials were repeated 100 times to reduce parameter uncertainty effects on the results, and 12 ecological flow characteristics were computed for comparison. Our results showed that the most suitable calibration strategy varied according to streamflow characteristic. Combined objective functions generally gave the best results, though a clear underprediction bias was observed. The occurrence of low prediction errors for certain combinations of objective function and flow characteristic suggests that (1) incorporating multiple ecological flow characteristics into a single objective function would increase model accuracy, potentially benefitting decision-making processes; and (2) there may be a need to have different objective functions available to address specific applications of the predicted time series.

Book chapter↗
USGS2014

Freshwater mussel population status and habitat quality in the Clinch River, Virginia and Tennessee, USA: a featured collection

The Clinch River of southwestern Virginia and northeastern Tennessee is arguably the most important river for freshwater mussel conservation in the United States. This featured collection presents investigations of mussel population status and habitat quality in the Clinch River. Analyses of historic water- and sediment-quality data suggest that water column ammonia and water column and sediment metals, including Cu and Zn, may have contributed historically to declining densities and extirpations of mussels in the river's Virginia sections. These studies also reveal increasing temporal trends for dissolved solids concentrations throughout much of the river's extent. Current mussel abundance patterns do not correspond spatially with physical habitat quality, but they do correspond with specific conductance, dissolved major ions, and water column metals, suggesting these and/or associated constituents as factors contributing to mussel declines. Mussels are sensitive to metals. Native mussels and hatchery-raised mussels held in cages in situ accumulated metals in their body tissues in river sections where mussels are declining. Organic compound and bed-sediment contaminant analyses did not reveal spatial correspondences with mussel status metrics, although potentially toxic levels were found. Collectively, these studies identify major ions and metals as water- and sediment-quality concerns for mussel conservation in the Clinch River.

Tennessee, Virginia↗
USGS2014

Hydrologic data for the Obed River watershed, Tennessee

The Obed River watershed drains a 520-square-mile area of the Cumberland Plateau physiographic region in the Tennessee River basin. The watershed is underlain by conglomerate, sandstone, and shale of Pennsylvanian age, which overlie Mississippian-age limestone. The larger creeks and rivers of the Obed River system have eroded gorges through the conglomerate and sandstone into the deeper shale. The largest gorges are up to 400 feet deep and are protected by the Wild and Scenic Rivers Act as part of the Obed Wild and Scenic River, which is managed by the National Park Service. The growing communities of Crossville and Crab Orchard, Tennessee, are located upstream of the gorge areas of the Obed River watershed. The cities used about 5.8 million gallons of water per day for drinking water in 2010 from Lake Holiday and Stone Lake in the Obed River watershed and Meadow Park Lake in the Caney Fork River watershed. The city of Crossville operates a wastewater treatment plant that releases an annual average of about 2.2 million gallons per day of treated effluent to the Obed River, representing as much as 10 to 40 percent of the monthly average streamflow of the Obed River near Lancing about 35 miles downstream, during summer and fall. During the past 50 years (1960–2010), several dozen tributary impoundments and more than 2,000 small farm ponds have been constructed in the Obed River watershed. Synoptic streamflow measurements indicate a tendency towards dampened high flows and slightly increased low flows as the percentage of basin area controlled by impoundments increases.

Tennessee↗
USGS2013

Ecological limit functions relating fish community response to hydrologic departures of the ecological flow regime in the Tennessee River basin, United States

Ecological limit functions relating streamflow and aquatic ecosystems remain elusive despite decades of research. We investigated functional relationships between species richness and changes in streamflow characteristics at 662 fish sampling sites in the Tennessee River basin. Our approach included the following: (1) a brief summary of relevant literature on functional relations between fish and streamflow, (2) the development of ecological limit functions that describe the strongest discernible relationships between fish species richness and streamflow characteristics, (3) the evaluation of proposed definitions of hydrologic reference conditions, and (4) an investigation of the internal structures of wedge-shaped distributions underlying ecological limit functions. Twenty-one ecological limit functions were developed across three ecoregions that relate the species richness of 11 fish groups and departures from hydrologic reference conditions using multivariate and quantile regression methods. Each negatively sloped function is described using up to four streamflow characteristics expressed in terms of cumulative departure from hydrologic reference conditions. Negative slopes indicate increased departure results in decreased species richness. Sites with the highest measured fish species richness generally had near-reference hydrologic conditions for a given ecoregion. Hydrology did not generally differ between sites with the highest and lowest fish species richness, indicating that other environmental factors likely limit species richness at sites with reference hydrology. Use of ecological limit functions to make decisions regarding proposed hydrologic regime changes, although commonly presented as a management tool, is not as straightforward or informative as often assumed. We contend that statistical evaluation of the internal wedge structure below limit functions may provide a probabilistic understanding of how aquatic ecology is influenced by altered hydrology and may serve as the basis for evaluating the potential effect of proposed hydrologic changes.

Tennessee River basin↗
USGS2012

Predicting ecological flow regime at ungaged sites: A comparison of methods

Nineteen ecologically relevant streamflow characteristics were estimated using published rainfall–runoff and regional regression models for six sites with observed daily streamflow records in Kentucky. The regional regression model produced median estimates closer to the observed median for all but two characteristics. The variability of predictions from both models was generally less than the observed variability. The variability of the predictions from the rainfall–runoff model was greater than that from the regional regression model for all but three characteristics. Eight characteristics predicted by the rainfall–runoff model display positive or negative bias across all six sites; biases are not as pronounced for the regional regression model. Results suggest that a rainfall–runoff model calibrated on a single characteristic is less likely to perform well as a predictor of a range of other characteristics (flow regime) when compared with a regional regression model calibrated individually on multiple characteristics used to represent the flow regime. Poor model performance may misrepresent hydrologic conditions, potentially distorting the perceived risk of ecological degradation. Without prior selection of streamflow characteristics, targeted calibration, and error quantification, the widespread application of general hydrologic models to ecological flow studies is problematic. Published 2012. This article is a U.S. Government work and is in the public domain in the USA.

Kentucky, Tennessee↗
USGS2011

Modelling ecological flow regime: an example from the Tennessee and Cumberland River basins

Predictive equations were developed for 19 ecologically relevant streamflow characteristics within five major groups of flow variables (magnitude, ratio, frequency, variability, and date) for use in the Tennessee and Cumberland River basins using stepbackward regression. Basin characteristics explain 50% or more of the variation for 12 of the 19 equations. Independent variables identified through stepbackward regression were statistically significant in 78 of 304 cases (α > 0.0001) and represent four major groups: climate, physical landscape features, regional indicators, and land use. Of these groups, the regional and climate variables were the most influential for determining hydrologic response. Daily temperature range, geologic factor, and rock depth were major factors explaining the variability in 17, 15, and 13 equations, respectively. The equations and independent datasets were used to explore the broad relation between basin properties and streamflow and the implication of streamflow to the study of ecological flow requirements. Key results include a high degree of hydrologic variability among least disturbed Blue Ridge streams, similar hydrologic behaviour for watersheds with widely varying degrees of forest cover, and distinct hydrologic profiles for streams in different geographic regions. Published in 2011. This article is a US Government work and is in the public domain in the USA.

Alabama;Georgia;Kentucky;Mississippi;North Carolin↗
USGS2011

If the creeks don't rise: the May 2010 Flood in Nashville

The aftermath, recovery, and lessons of the future following a major flood that inundated the greater Nashville area one year ago are the subjects of this article. The authors discuss what led up to the event, its impacts, and what, if anything, can be done to prevent or diminish the reoccurrence of such flooding in the future.

Tennessee↗
USGS2011

Regression models of ecological streamflow characteristics in the Cumberland and Tennessee River Valleys

Predictive equations were developed using stepbackward regression for 19 ecologically relevant streamflow characteristics grouped in five major classes (magnitude, ratio, frequency, variability, and date) for use in the Tennessee and Cumberland River watersheds. Basin characteristics explain 50 percent or more of the variation for 10 of the 19 equations. Independent variables identified through stepbackward regression were statistically significant in 81 of 304 coefficients tested across 19 models (⬚ < 0.0001) and represent four major groups: climate, physical landscape features, regional indicators, and land use. The most influential variables for determining hydrologic response were in the land-use and climate groups: daily temperature range, percent agricultural land use, and monthly mean precipitation. These three variables were major explanatory factors in 17, 15, and 13 models, respectively. The equations and independent datasets were used to explore the broad relation between basin properties and streamflow and its implications for the study of ecological flow requirements. Key results include a high degree of hydrologic variability among least disturbed Blue Ridge streams, similar hydrologic behavior for watersheds with widely varying degrees of forest cover, and distinct hydrologic profiles for streams in different geographic regions.

Tennessee and Cumberland Rivers↗
USGS2010

Suspended-sediment concentration regimes for two biological reference streams in Middle Tennessee

Temporal patterns of suspended-sediment concentration (SSC) duration and frequency (SSC regimes) were characterized and compared with biological impairment thresholds for two headwater streams in the Western Highland Rim of Tennessee. The SSC regimes were plotted as curves showing concentrations and durations of the annual longest and tenth-longest SSC excursions above 18 concentrations for water years 2005-2008 in Copperas Branch and water years 2006 and 2008 in Kelley Creek. Both streams have fish communities remarkably diverse for their small drainage basin areas (420 and 565 ha, respectively), and represent biological reference conditions with respect to SSC. SSC-regime curves were similar for the two sites across water years. The measured SSC regimes reached or exceeded published experimentally based SSC impairment thresholds and plotted below a proposed long-term SSC reference regime for the Interior Plateau ecoregion (Ecoregion 71), suggesting that neither the experimentally based thresholds nor the proposed SSC reference regime adequately reflect the relation between SSC and biological impairment for Western Highland Rim headwater streams. The SSC regimes of the two study streams were similar to the estimated SSC regime of an unimpaired East Tennessee trout stream. Additional field studies are needed to describe SSC regimes in streams of varying basin scale, level of impairment, and region.

Tennessee↗
USGS2010

Suspended-sediment concentration regimes in Tennessee biological reference streams

Suspended-sediment-concentration (SSC) regimes of five biological reference streams in Tennessee were characterized from 15-minute SSC records spanning 1 to 4 water years (October 1 through September 30) between 2004 and 2008. These streams represent least disturbed conditions for their respective ecoregions and have exceptional biodiversity in terms of fish or aquatic invertebrates. SSC regimes in streams, when plotted in terms of duration above a given SSC at a given annual frequency such as the annual maximum or the annual tenth longest duration, can be compared directly to published biological impairment thresholds derived from experimental trials. Based on such comparison, the SSC regimes of all five reference streams reached published impairment thresholds at least 10 times per water year for all years of record. The results suggest that the published impairment thresholds are not directly applicable to streams in Tennessee and, by extension, the southeastern United States.

Tennessee↗
USGS2007

Soil gas screening for chlorinated solvents at three contaminated karst sites in Tennessee

Soil gas was sampled using active sampling techniques and passive collectors at three sites in Tennessee to evaluate the effectiveness of these techniques for locating chlorinated solvent sources and flowpaths in karst aquifers. Actively collected soil gas samples were analyzed in the field with a portable gas chromatograph, and the passive soil gas collectors were analyzed in the lab with gas chromatography/mass spectrometry. Results of the sampling indicate that the effectiveness of both techniques is highly dependent on the distribution of the contaminants in the subsurface, the geomorphic and hydrogeologic characteristics of the site, and, in one case, on seasonal conditions. Both active and passive techniques identified areas of elevated subsurface chlorinated solvent concentrations at a landfill site where contamination remains concentrated in the regolith. Neither technique detected chlorinated solvents known to be moving in the bedrock at a manufacturing site characterized by thick regolith and an absence of surficial karst features. Passive soil gas sampling had varied success detecting flowpaths for chloroform in the bedrock at a train derailment site characterized by shallow regolith and abundant surficial karst features. At the train derailment site, delineation of the contaminant flowpath through passive soil gas sampling was stronger and more detailed under Winter conditions than summer.

Tennessee↗
USGS2004

Tree-regeneration and mortality patterns and hydrologic change in a forested karst wetland--Sinking Pond, Arnold Air Force Base, Tennessee

Multiple lines of evidence point to climate change as the driving factor suppressing tree regeneration since 1970 in Sinking Pond, a 35-hectare seasonally flooded karst depression located on Arnold Air Force Base near Manchester, Tennessee. Annual censuses of 162-193 seedling plots from 1997 through 2001 demonstrate that the critical stage for tree survival is the transition from seedling to sapling and that this transition is limited to shallow (less than 0.5 meters) ponding depths. Recruitment of saplings to the small adult class also was restricted to shallow areas. Analysis of the spatial and elevation distribution of tree-size classes in a representative 2.3-hectare area of Sinking Pond showed a general absence of overcup oak saplings and young adults in deep (ponding depth greater than 1 meter) and intermediate (ponding depth 0.5-1 meter) areas, even though overcup oak seedlings and mature trees are concentrated in these areas. Analysis of tree rings from 45 trees sampled in a 2.3-hectare spatial-analysis plot showed an even distribution of tree ages across ponding-depth classes from the 1800s through 1970, followed by complete suppression of recruitment in deep and intermediate areas after 1970. Trees younger than 30 years were spatially and vertically concentrated in a small area with shallow ponding depth, about 0.5 meter below the spillway elevation. Results of hydrologic modeling, based on rainfall and temperature records covering the period January 1854 through September 2002, show ponding durations after 1970 considerably longer than historical norms, across ponding-depth classes. This increase in ponding duration corresponds closely with similar increases documented in published analyses of streamflow and precipitation in the eastern United States and with the suppression of tree regeneration at ponding depths greater than 0.5 meter indicated by tree-ring analysis. Comparison of the simulated stage record for Sinking Pond with the ages and elevations of sampled trees shows that prolonged (200 days or more per year) inundation in more than 2 of the first 5 years after germination is inversely related to successful tree recruitment and that such inundation was rare before 1970 and common afterwards.

Water-Resources Investigations Report↗