Pamela J. Edwards

Hydrology under change: an evaluation protocol to investigate how hydrological models deal with changing catchments

Abstract Testing hydrological models under changing conditions is essential to evaluate their ability to cope with changing catchments and their suitability for impact studies. With this perspective in mind, a workshop dedicated to this issue was held at the 2013 General Assembly of the International Association of Hydrological Sciences (IAHS) in Göteborg, Sweden, in July 2013, during which the results of a common testing experiment were presented. Prior to the workshop, the participants had been invited to test their own models on a common set of basins showing varying conditions specifically set up for the workshop. All these basins experienced changes, either in physical characteristics (e.g. changes in land cover) or climate conditions (e.g. gradual temperature increase). This article presents the motivations and organization of this experiment—that is—the testing (calibration and evaluation) protocol and the common framework of statistical procedures and graphical tools used to assess the model performances. The basins datasets are also briefly introduced (a detailed description is provided in the associated Supplementary material).

Indicators of nitrate export from forested watersheds of the mid‐Appalachians, United States of America

Soil net nitrogen mineralization and nitrification rates were studied on nine undisturbed, forested watersheds in an effort to explain large variations in nitrate export in streamflow within the mid-Appalachian region. Rates of soil net nitrogen mineralization and net nitrification were measured in the upper 10 cm of mineral soil over a 5-week summer incubation period (June–July) using nine buried bags in each of the three major soil types on each watershed. Watersheds with high, medium, and low nitrate export rates exhibited high, medium, and low mean net nitrogen mineralization and net nitrification rates, respectively. Exchangeable calcium (an index to site fertility), C/N ratios, and soil moisture content together explained 63% of the variation in soil nitrogen mineralization rates, and exchangeable calcium and soil moisture content explained 61% of the variation in soil nitrification rates using multiple regression analysis. The variation in watershed nitrate export was best explained by total nitrogen in the upper 10 cm of mineral soil (explained 46%) and the percentage of mineralization due to nitrification (explained 42%). Estimated rates of wet and dry atmospheric deposition of nitrogen were not significantly correlated with watershed nitrate export. Results from this study demonstrate that soil nitrogen pools and dynamics are the most critical factors controlling nitrate export from forested watersheds in the mid-Appalachians. Long-term changes in site fertility, C/N ratios, and soil moisture, which largely control microbial nitrogen cycling, should have a significant effect on long-term trends in nitrate leaching.

Comparison of methods for calculating annual solute exports from six forested appalachian watersheds

Six methods were compared for calculating annual stream exports of sulfate, nitrate, calcium, magnesium and aluminum from six small Appalachian watersheds. Approximately 250–400 stream samples and concurrent stream flow measurements were collected during baseflows and storm flows for the 1989 water year at five Pennsylvania watersheds and during the 1989–1992 water years at a West Virginia watershed. Continuous stream flow records were also collected at each watershed. Solute exports were calculated from the complete data set using six different scenarios ranging from instantaneous monthly measurements of stream chemistry and stream flow, to intensive monitoring of storm flow events and multiple regression equations. The results for five of the methods were compared with the regression method because statistically significant models were developed and the regression equations allowed for prediction of solute concentrations during unsampled storm flows. Results indicated that continuous stream flow measurement was critical to producing exports within 10% of regression estimates. For solutes whose concentrations were not correlated strongly with stream flow, weekly grab samples combined with continuous records of stream flow were sufficient to produce export estimates within 10% of the regression method. For solutes whose concentrations were correlated strongly with stream flow, more intensive sampling during storm flows or the use of multiple regression equations were the most appropriate methods, especially for watersheds where stream flows changed most quickly. Concentration–stream flow relationships, stream hydrological response, available resources and required level of accuracy of chemical budgets should be considered when choosing a method for calculating solute exports.

SOIL LEACHATE RESPONSES DURING 10 YEARS OF INDUCED WHOLE-WATERSHED ACIDIFICATION

Soil solution was collected from zero-tension lysimeters for 10 yr on two small central Appalachian watersheds in West Virginia, U.S.A. Ammonium sulfate fertilizer was applied to onecatchment 3 times per year during each year. The other watershedwas used as a reference to account for ambient baseline conditions. Ca and Mg concentrations collected below the A- andB-horizons of the treated watershed increased and then decreasedover time as a result of the treatment. By contrast, Ca and Mgconcentrations in the C-horizon continued to increase throughoutthe study period. The depletion in Ca and Mg that occurred inthe upper levels apparently occurred due to charge pairing andleaching of those base cations with NO3 and SO4. Theprogressively greater amounts of Ca and Mg carried through thesoil with these acid anions provided their continued increasingconcentrations in the C-horizon. NO3 concentrations increased progressively with depth due to both the assimilationof NO3 by vegetation and microorganisms in the upper soillayers and leaching of NO3 into deeper soils by mesoporeflow. NO3 became a more important ion over time with respectto pairing and leaching with base cations because its concentrations continued to increase in all soil layers, whereasSO4 became retained in all soil layers after after severalyears of treatment, presumably induced by adsorption from increasing SO3 concentrations.

Seasonal sulfate deposition and export patterns for a small Appalachian watershed

Sulfate deposition and exports from 1988–92 were analyzed for a small headwater catchment in north-central West Virginia. Annual sulfate inputs, estimated by applying throughfall-adjusted ratios to bulk deposition values, and outputs were approximately equal for the five years. Annual mean throughfall-adjusted deposition and export loads were 55.78 and 55.48 kg ha-1, respectively. While these results indicate the watershed has reached sulfate equilibrium relative to current deposition levels, seasonal sulfate accumulations and deficits were evident. Deposition and exports averaged 5.61 and 2.49 kg ha-1 mo-1, respectively, during the growing season, and 3.69 and 5.22 kg ha-1 mo-1 during the dormant season. Sulfur accumulated within the soil during the growing season because inputs of wet and dry sulfur deposition were high while outputs were negligible. The latter was due largely to the lack of runoff resulting from high evapotranspirational demands. By contrast, net sulfate losses occurred during dormant seasons, primarily due to high runoff, even though inputs declined during this season. Researchers working on other watersheds have interpreted similar input/output patterns to mean that sulfate accumulated during the growing season is the source of sulfate exported during the dormant season. However, radioisotopic evidence from a companion study on this watershed showed that some labeled sulfate applied to the watershed more than a year earlier was still present in the organic and mineral soil layers at the point of application (with some as soluble sulfate), and in soil water dispersed throughout the watershed. Its presence indicates that dormant season exports can originate from sulfate deposited over longer periods than just the previous growing season or even previous year. Volume-weighted concentrations in soil leachate suggest that dormant-season sulfate losses resulted from progressive depletion of the anion through the soil profile. During the fall and early winter, soluble sulfate was depleted in the upper soil horizons; in later winter, depletion occurred in the lower horizons.

The characterization of ozone exposures in rural West Virginia and Virginia.

Ozone (O3) is suspected of being the most significant air pollutant affecting vegetation in the United States. Ozone concentrations measured at Bearden Knob and Parsons, located in a remote forested region of northcentral West Virginia, were characterized and compared with exposures experienced at other sites in the region. From 1988 to 1992, 1988 was one of the highest O3 exposure years in the region, while 1992 was the lowest. At almost all sites in 1992, few hourly average concentrations were > or = 0.10 ppm, while in 1988 several sites had more than 100 hourly average concentrations > or = 0.10 ppm. These instances occurred at both high- and low-elevation sites. In 1992, the high-elevation Bearden Knob site experienced a flat-type diurnal pattern, while the nearby low-elevation Parsons site experienced a changing diurnal pattern, indicative of scavenging. Using several indices, O3 exposures at Parsons were less than those at Bearden Knob. Evaluation of hourly averaged data for all sites in the region from 1988 to 1992 showed that Horton Station experienced the highest W126 O3 exposures. Horton Station is a high-elevation site in the mountains of southwestern Virginia. Square-wave exposures have been used under artificial conditions in vegetation experiments. If square-wave exposures are observed under ambient conditions, then the vegetation data collected under artificial conditions may be relevant for predictive purposes. Square-wave exposures were characterized for two high-elevation sites. In 1992, Horton Station experienced 25 episodes for which the hourly average concentrations remained near 0.05 ppm for eight hours or longer; there were 18 episodes for which the hourly average concentrations remained near 0.06 ppm, and three episodes for which the concentrations remained near 0.07 ppm. Bearden Knob experienced 31 episodes of eight hours or longer for hourly average concentrations near 0.05 ppm, 13 episodes at or near 0.06 ppm, and three episodes at or near 0.07 ppm. Until experiments are performed to determine the relative importance of hourly average concentrations above 0.03 ppm for assessing vegetation effects, using single-parameter exposure indices to predict effects may produce inconsistent results.

Using photographic image analysis to assess ground cover: a case study of forest road cutbanks

Road prisms, including cutbanks, road surfaces, and fillslopes, can be important contributors of sediment to streams in forested watersheds. Following road construction, cutbanks and fillslopes are often seeded, mulched, and sometimes fertilized to limit erosion and sedimentation. Assessing the success of vegetation establishment on cutbanks and fillslopes is a common task of forested land managers. This study developed and applied a photographic image analysis method to assess percent ground cover along an entire cutbank of a cut-and-fill haul road in the Monongahela National Forest in Tucker County, West Virginia. Variable-sized sections were employed to quantify the vegetative cover. Measurements obtained by this technique were similar to more commonly applied fixed-area plots, and it proved to be a useful tool for land managers who require a more repeatable quantification of ground cover than is possible through visual assessments. Cutbank slope and aspect also were analyzed to determine their potential impact on cutbank vegetation establishment. Slope was not a significant variable in explaining differences in vegetation cover; however, aspect did affect vegetation establishment. South-facing aspects had significantly lower percent vegetation cover than northeast, east, northwest, and north northwest aspects after the first year following seeding and throughout the entire study. Mean percent cover on the south-facing cutbanks was 32% over all time periods, compared to 60% to 73% for the other represented aspects. This result was expected since south-facing slopes generally are drier in the growing season and are subject to more freeze–thaw cycles in the winter. Timber felled onto the cutbank also decreased vegetative cover in the short term on north and north northwest aspects, but vegetation quickly became reestablished on these aspects with their favorable growing conditions.

Turbidity and suspended-sediment changes from stream-crossing construction on a forest haul road in West Virginia, USA

A forested headwater watershed in West Virginia was monitored to examine changes to in-stream turbidity following the construction of a 0.92 km (0.57 mi) haul road. Due to the design of the study, most of the sediment that entered the stream following road construction was known to result from the stream crossings and approaches to the crossings. Stream-water samples collected daily and sequentially during stormflow from 1999 through 2005 were used to interpret the effects of stream-crossing construction on turbidity and suspended-sediment concentrations (SSC). Daily and stormflow turbidity and SSC values increased as a result of the construction. Average sediment loads (kg per storm) and total annualized sediment loads (kg per year) also increased significantly, both by a factor of about 1.8. Sediment delivery to the stream was caused by mechanical introduction of soil during stream-crossing culvert installation and fill-slope construction in the crossing approaches, and by erosion of those areas due to delays in vegetation re-establishment. Inputs from stream-crossing construction affected the overall sediment regime of the stream; the turbidity-discharge hysteresis changed from the normal clockwise pattern to a counter-clockwise pattern for about seven months. As the crossing fills and approach fill slopes became re-vegetated, they stabilized, and annualized sediment loads declined. However, at the end of the study, sediment exports remained above pre-disturbance levels.

Effects of development of a natural gas well and associated pipeline on the natural and scientific resources of the Fernow Experimental Forest

Development of a natural gas well and pipeline on the Fernow Experimental Forest, WV, raised concerns about the effects on the natural and scientifi c resources of the Fernow, set aside in 1934 for long-term research. A case study approach was used to evaluate effects of the development. This report includes results of monitoring projects as well as observations related to unexpected impacts on the resources of the Fernow. Two points are obvious: that some effects can be predicted and mitigated through cooperation between landowner and energy developer, and that unexpected impacts will occur. These unexpected impacts may be most problematic.

Characterization of Ozone during consecutive drought and wet years at a rural West Virginia site

Ozone concentrations at a rural-remote site in a forested region of north-central West Virginia were monitored during 1988 and 1989, a drought and wet year, respectively. During 1988, the absolute maximum average concentration for a single hour was 156 ppb, while it was only 107 ppb in 1989. Overall, the frequency of high concentrations was greater during 1988; the 120 ppb National Ambient Air Quality Standard was exceeded 17 times. The 7-h period encompassing the highest growing season concentrations for this site over the 2-yr period is 1100- 1759 h EST, rather than the period 0900-1559 h originally used by the National Crop Loss Assessment Network. The 7-h growing season means (0900-1559 h) of 52.6 ppb and 47.1 ppb for 1988 and 1989, respectively, compare well to those reported for the Piedmont/Mountain/Ridge-Valley area, but are higher than those for other surrounding areas. The diurnal ozone patterns, as well as the distribution of concentration ranges and timing of seasonal maxima, suggest that long...