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Myron J. Mitchell - One of the best experts on this subject based on the ideXlab platform.
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estimating greenhouse gas emissions at the soil atmosphere interface in Forested Watersheds of the us northeast
Environmental Monitoring and Assessment, 2016Co-Authors: Joshua Gomez, Philippe Vidon, Jordan Gross, Colin M Beier, Jesse Caputo, Myron J. MitchellAbstract:Although anthropogenic emissions of greenhouse gases (GHG: CO2, CH4, N2O) are unequivocally tied to climate change, natural systems such as forests have the potential to affect GHG concentration in the atmosphere. Our study reports GHG emissions as CO2, CH4, N2O, and CO2eq fluxes across a range of landscape hydrogeomorphic classes (wetlands, riparian areas, lower hillslopes, upper hillslopes) in a Forested watershed of the Northeastern USA and assesses the usability of the topographic wetness index (TWI) as a tool to identify distinct landscape geomorphic classes to aid in the development of GHG budgets at the soil atmosphere interface at the watershed scale. Wetlands were hot spots of GHG production (in CO2eq) in the landscape owing to large CH4 emission. However, on an areal basis, the lower hillslope class had the greatest influence on the net watershed CO2eq efflux, mainly because it encompassed the largest proportion of the study watershed (54 %) and had high CO2 fluxes relative to other land classes. On an annual basis, summer, fall, winter, and spring accounted for 40, 27, 9, and 24 % of total CO2eq emissions, respectively. When compared to other approaches (e.g., random or systematic sampling design), the TWI landscape classification method was successful in identifying dominant landscape hydrogeomorphic classes and offered the possibility of systematically accounting for small areas of the watershed (e.g., wetlands) that have a disproportionate effect on total GHG emissions. Overall, results indicate that soil CO2eq efflux in the Archer Creek Watershed may exceed C uptake by live trees under current conditions.
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importance of within lake processes in affecting the dynamics of dissolved organic carbon and dissolved organic and inorganic nitrogen in an adirondack Forested lake watershed
Biogeosciences, 2015Co-Authors: Philgoo Kang, Myron J. Mitchell, Charles T Driscoll, Patrick J Mchale, Shreeram Inamdar, Jihyung ParkAbstract:Abstract. Lakes nested in Forested Watersheds play an important role in mediating the concentrations and fluxes of dissolved organic matter. We compared long-term patterns of concentrations and fluxes of dissolved organic carbon (DOC) and dissolved organic (DON) and inorganic nitrogen (DIN) in aquatic ecosystems of the Arbutus Lake watershed to evaluate how a lake nested in a Forested watershed affects the sources (e.g., production) and sinks (e.g., retention) of DOC and DON in the Adirondack Mountains of New York, USA. We observed no significant long-term changes of DOC and DON in the lake outlet since 1983 and 1994, respectively. However, the temporal patterns of DOC and DON concentrations in the lake inlet showed significant seasonality such as increases during the vegetation-growing season along with notable decreases in the dormant season. A comparison of mass balances between inlet and outlet for the period from 2000 to 2009 suggested that the lake was a sink of DOC (mean of influx minus outflux: +1140 mol C ha−1 yr−1). In contrast, the difference of discharge-weighted DON concentrations (mean of inlet minus outlet: −1.0 µmol N L−1) between inlet and outlet was much smaller than the discharge-weighted DOC concentrations (average of inlet minus outlet: + 87 µmol C L−1). DON fluxes showed considerable variation among years (mean of influx minus outflux: +8 mol N ha−1 yr−1; range of differences: −15 to 27 mol N ha−1 yr−1). DON exhibited low percent retention ((influx-outflux)/influx) (mean: 6.9 %, range: −34.8 to +31.2) compared to DOC (mean: 30.1 %, range: +9.2 to +44.1). The resultant increase of DON within the lake was closely linked with a net decrease of DIN through monthly Pearson correlation analysis, suggesting the importance of biotic factors in mediating lake DON dynamics. Our results show different relative retentions of DOC compared with DON, along with a larger retention of DIN than DON, suggesting that DOC and DON might display substantially different biogeochemical relationships in oligo-mesotrophic lakes nested Forested Watersheds and therefore different roles for a sink behavior for DOC compared to a producer of DON.
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comparison of sample preparation methods for stable isotope analysis of dissolved sulphate in Forested Watersheds
Isotopes in Environmental and Health Studies, 2012Co-Authors: Philgoo Kang, Bernhard Mayer, Myron J. MitchellAbstract:Pretreatment methods for measuring stable sulphur (δ34S) and oxygen (δ18O) isotope ratios of dissolved sulphate from Watersheds have evolved throughout the last few decades. The current study evaluated if there are differences in the measured stable S and O isotope values of dissolved sulphate from Forested Watersheds when pretreated using three different methods: Method 1 (M1): adsorb sulphate on anion exchange resins and send directly to isotope facility; Method 2 (M2): adsorb sulphate on anion exchange resins, extract sulphate from anion exchange resins, and send the produced BaSO4 to the isotope facility; and Method 3 (M3): directly precipitate BaSO4 without anion exchange resins with the precipitates being sent to the isotope facility. We found an excellent agreement of the δ34Ssulphate values among all the three methods. However, some differences were observed in the δ18Osulphate values (M1 versus M2:−1.5 ‰; M1 versus M3:−1.2 ‰) associated with possible O contamination before isotope measurement. Se...
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Nitrate dynamics of Forested Watersheds: spatial and temporal patterns in North America, Europe and Japan
Journal of Forest Research, 2011Co-Authors: Myron J. MitchellAbstract:The relationships of nitrogen biogeochemistry are reviewed, focusing on Forested Watersheds in North America, Europe and Japan. Changes in both local and global nitrogen cycles that affect the structure and function of ecosystems are described. Within northeastern United States and Europe, atmospheric deposition thresholds of ~8 and ~10 kg N ha^−1 year^−1, respectively, result in enhanced mobilization of nitrate. High nitrate concentrations and drainage water loss rates up to 22 kg N ha^−1 year^−1 have also been found near Tokyo. Although atmospheric deposition may explain a substantial portion of the spatial pattern of nitrate in surface waters, other factors also play major roles in affecting the spatial patterns of nitrogen biogeochemistry. Calcium availability influences the composition of the vegetation and the biogeochemistry of nitrogen. The abundance of sugar maple is directly linked to soil organic matter characteristics and high rates of nitrogen mineralization and nitrification. Seasonal patterns of nitrate concentration and drainage water losses are closely coupled with differences in seasonal temperature and hydrological regimes. Snow-dominated Forested catchments have highest nitrate losses during snowmelt. Watersheds in the main island of Japan (Honshu) with high summer temperatures and precipitation inputs have greatest losses of nitrate occur during the late summer. Understanding future changes in nitrate concentrations in surface waters will require an integrated approach that will evaluate concomitantly the influence of both biotic and biotic factors on nitrogen biogeochemistry.
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Hydrological flow paths controlling stream chemistry in Japanese Forested Watersheds
Hydrological Processes, 1999Co-Authors: Kiyokazu Ohrui, Myron J. MitchellAbstract:Water sources and flow paths contributing to stream chemistry were evaluated in four Japanese Forested Watersheds with steep topography (slopes ≥30°). Stream chemistry during periods without rainfall and during events with less than 100 mm of precipitation was similar to seepage water chemistry, but markedly different from that of soil water which had higher concentrations of NO−3 and Ca2+ and lower concentrations of Na+ and HCO−3. Also, stream Cl− concentrations in a Cl−-treated watershed did not increase either during events with less than 100 mm of total rainfall or at baseflow conditions, even three years after the Cl− treatment. These results suggest that groundwater within bedrock fissures of Paleozoic strata had a long residence time and was a major contributor to steam water under baseflow conditions and even during small precipitation events (≤100 mm). In contrast, for large precipitation events (≥100 mm), stream chemistry became more similar to soil water chemistry, especially within the steepest watershed. Also, for large precipitation events, stream Cl− concentrations in the Cl−-treated watershed increased markedly. These results suggest that soil water was a major contributor to stream waters only during these large events. Copyright © 1999 John Wiley & Sons, Ltd.
Todd M Scanlon - One of the best experts on this subject based on the ideXlab platform.
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particulate and dissolved mercury export in streamwater within three mid appalachian Forested Watersheds in the us
Journal of Hydrology, 2013Co-Authors: Ami L Riscassi, Todd M ScanlonAbstract:Summary Forested uplands retain Hg in soils from atmospheric deposition and are a potential long-term source of Hg to downstream waters. Accurate estimates of dissolved and particulate mercury (HgD and HgP, respectively) streamwater fluxes are needed to track the movement and storage of Hg in these ecosystems. It is well established that frequent sampling during high-flow events, when Hg concentrations can vary by orders of magnitude, is necessary to quantify Hg export in these systems. However, in part due to the difficulties of consistently sampling during these short-duration periods, and lack of alternative surrogate measures, no studies have quantified HgD and HgP export during storm flow relative to the total annual flux. At three mid-Appalachian Forested Watersheds, we sampled streamwater bi-weekly and hourly during storm events using both manual and automated techniques for 18 months and investigated the feasibility of using turbidity measured with an in situ sonde as a surrogate measure for HgP. We determined turbidity had a much stronger correlation to HgP (r2 = 0.78–0.98) as compared to specific discharge (r2 = 0.36–0.55), making it an effective high-frequency surrogate at each site. For the year-long study, we found that approximately 80% of the total Hg (HgT) flux was exported during the high-flow periods corresponding to approximately 1% of the time. Particulate Hg accounted for the majority of annual HgT fluxes at all three sites (58–85%) as a consequence of being more strongly flow-activated relative to the dissolved form. Despite being associated with relatively low dissolved organic carbon (DOC) concentrations, the HgT fluxes from these Forested Appalachian Watersheds, which ranged from 1.26 to 3.71 μg m−2 yr−1, were comparable to fluxes reported in other regions of the world
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nitrate variability in hydrological flow paths for three mid appalachian Forested Watersheds following a large scale defoliation
Journal of Geophysical Research, 2009Co-Authors: Ami L Riscassi, Todd M ScanlonAbstract:[1] Nitrate (NO3−) leakage from Forested Watersheds due to disturbance is a well documented but not well understood process that can contribute to the degradation of receiving waters through eutrophication. Several studies have shown that large-scale defoliation and deforestation events in small Forested Watersheds in the eastern United States cause immediate and dramatic increases in NO3− flux to steams, with large differences in recovery time. Water quality and discharge data collected from 1992 to 2004 following a large-scale gypsy moth defoliation were used to investigate hydrological controls on long-term NO3− leakage from three Forested Watersheds in Shenandoah National Park, Virginia. During storm events, a conventional two-component hydrograph separation in conjunction with an inverse solution technique was employed to determine the concentrations of NO3− in groundwater and soil water. Following defoliation, groundwater NO3− concentrations declined exponentially with a distinct seasonal pattern. A rank-order relationship between the rate constants associated with the exponential declines in groundwater NO3− concentrations and groundwater recession constants indicates a hydrological control on long-term watershed recovery for these defoliated systems. Comparisons to deForested systems in Hubbard Brook, New Hampshire, and Coweeta, North Carolina, indicate hydrological controls are similarly present. Biogeochemical differences, however, need to be considered to account for the more attenuated recovery observed in defoliated systems. No long-term trend was found in the model-derived soil water NO3− concentrations, which suggests the presence of some form of rate limitation on the transformation of the nitrogen pool introduced during the disturbance and/or reduced nutrient uptake due to tree mortality.
Karl W J Williard - One of the best experts on this subject based on the ideXlab platform.
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influence of bedrock geology and tree species composition on stream nitrate concentrations in mid appalachian Forested Watersheds
Water Air and Soil Pollution, 2005Co-Authors: Karl W J Williard, David R Dewalle, Pamela J EdwardsAbstract:Although the large variations in nitrate export from Forested Watersheds have been at- tributed to a variety of natural and disturbance-related factors, baseflow nitrate concentrations in 49 mid-Appalachian Forested Watersheds were most strongly related to differences in bedrock geol- ogy. Within the mid-Appalachian region of Pennsylvania, Maryland and West Virginia, Watersheds dominated by Pottsville and Allegheny sandstone (PVA), Catskill, Chemung, and Pocono shale and sandstone (CCP), and Mauch Chunk shale and Greenbrier limestone (MCG), respectively, exhibited significantly different low, intermediate, and high mean stream nitrate concentrations. Soil pH, soil percent N concentration (%N), soil C:N mass ratio, soil exchangeable Ca, watershed slope, and the occurrence of white ash (Fraxinus americana L.), sugar maple (Acer saccharum Marsh.), and eastern hemlock (Tsuga canadensis L.) were related significantly to bedrock geology type as well as stream nitrate levels. Other factors such as past land disturbances (fire and agriculture) and stand age (old- growth) typically were associated with only one bedrock geology type. However, within a bedrock geology type, past agriculture and the presence of old-growth forest may be important in explaining stream nitrate concentrations on an individual watershed basis. The basal area of black locust (Robinia pseudoacacia L.), a species that enhances soil nitrogen levels via nitrogen fixation, showed a moderate positive correlation with stream nitrate concentrations. Bedrock geology explained the most variation in winter (49%) and summer (32%) stream nitrate concentrations. Bedrock geology may have been a better predictor of stream nitrate concentrations than soil chemistry, because the geologic variation was better assessed at the regional scale of this study compared to soil chemistry, which varies at the micro-scale due to topographic, vegetation, microbial, and climatic influences. Results of this study suggest that bedrock geology is an important factor to consider when assessing forest nitrogen dynamics at a broad landscape scale.
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sampling considerations for establishment of baseline loadings from Forested Watersheds for tmdl application
Environmental Monitoring and Assessment, 2004Co-Authors: Pamela J Edwards, Karl W J Williard, James N KochenderferAbstract:Five methods for estimating maximum daily and annual nitrate (NO3) and suspended sediment loads using periodic sampling of varying intensities were compared to actual loads calculated from intensive stormflow and baseflow sampling from small, Forested Watersheds in north central West Virginia to determine if the less intensive sampling methods were accurate and could be utilized in TMDL development. There were no significant differences between the annual NO3 load estimates using non-intensive sampling methods and the actual NO3 loads. However, maximum daily NO3 loads were estimated less accurately than annual loads. The ability to estimate baseline NO3 loads fairly accurately with non-intensive concentration data is attributed to the small fluctuation in NO3 concentrations over flow and time, particularly during storms. By contrast, suspended sediment exports determined by any of the non-intensive methods varied significantly and widely from and compared poorly to the actual exports for both daily and annual methods. Weekly sampling better approximated actual annual exports, but there were no significant statistical differences among weekly, monthly, and quarterly estimates. Suspended sediment concentrations varied widely within and among storm events, so that accurate estimates of total annual or maximum daily loads could not be obtained from infrequent sampling.
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18o isotopic separation of stream nitrate sources in mid appalachian Forested Watersheds
Journal of Hydrology, 2001Co-Authors: Karl W J Williard, David R Dewalle, Pamela J Edwards, William E SharpeAbstract:Abstract The δ 18 O values of atmospheric nitrate deposition, microbe-produced nitrate, and stream nitrate were measured to determine the dominant source of stream nitrate in 27 mid-Appalachian headwater Forested Watersheds (12–771 ha) with varying bedrock geologies, land disturbance histories, and stand ages. The 12 monthly composite nitrate δ 18 O values of wet deposition and throughfall exhibited similar pronounced seasonal trends, with relatively depleted δ 18 O values during the summer. Wet deposition and throughfall nitrate δ 18 O values were not significantly different between northern (Leading Ridge, PA) and southern (Fernow, WV) regional sampling sites, indicating that δ 18 O values were spatially similar across the study area. Atmospheric nitrate δ 18 O values were significantly greater than microbe-produced nitrate δ 18 O values, allowing the two sources of stream nitrate to be separated. During four baseflow and three stormflow sampling periods, microbe-produced nitrate was the dominant (>70%) source of nitrate in the study streams. This result does not mean atmospheric nitrogen deposition should be discounted as a source of Forested stream nitrate, because atmospheric deposition is the primary external contributor to the long-term soil nitrogen pool that ultimately drives soil nitrate production rates. Stream nitrate δ 18 O values were greater during stormflow periods compared to baseflow periods, indicating greater contributions of atmospheric nitrate during storm events. Neither microbe-produced nitrate δ 18 O values from incubated forest soil samples nor stream nitrate δ 18 O values showed strong relationships with land disturbance history or stand age. However, Watersheds dominated by Pottsville/Allegheny bedrock and associated extremely acid soils had greater summer stream nitrate δ 18 O values than Watersheds containing predominantly Catskill/Chemung/Pocono and Mauch Chunk/Greenbrier bedrock. Inhibited microbial nitrate production by low soil pH could account for the greater proportions of atmospheric nitrate deposition in streams draining Pottsville/Allegheny bedrock.
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indicators of nitrate export from Forested Watersheds of the mid appalachians united states of america
Global Biogeochemical Cycles, 1997Co-Authors: Karl W J Williard, David R Dewalle, Pamela J Edwards, Ronald R SchnabelAbstract: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.
David R Dewalle - One of the best experts on this subject based on the ideXlab platform.
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influence of bedrock geology and tree species composition on stream nitrate concentrations in mid appalachian Forested Watersheds
Water Air and Soil Pollution, 2005Co-Authors: Karl W J Williard, David R Dewalle, Pamela J EdwardsAbstract:Although the large variations in nitrate export from Forested Watersheds have been at- tributed to a variety of natural and disturbance-related factors, baseflow nitrate concentrations in 49 mid-Appalachian Forested Watersheds were most strongly related to differences in bedrock geol- ogy. Within the mid-Appalachian region of Pennsylvania, Maryland and West Virginia, Watersheds dominated by Pottsville and Allegheny sandstone (PVA), Catskill, Chemung, and Pocono shale and sandstone (CCP), and Mauch Chunk shale and Greenbrier limestone (MCG), respectively, exhibited significantly different low, intermediate, and high mean stream nitrate concentrations. Soil pH, soil percent N concentration (%N), soil C:N mass ratio, soil exchangeable Ca, watershed slope, and the occurrence of white ash (Fraxinus americana L.), sugar maple (Acer saccharum Marsh.), and eastern hemlock (Tsuga canadensis L.) were related significantly to bedrock geology type as well as stream nitrate levels. Other factors such as past land disturbances (fire and agriculture) and stand age (old- growth) typically were associated with only one bedrock geology type. However, within a bedrock geology type, past agriculture and the presence of old-growth forest may be important in explaining stream nitrate concentrations on an individual watershed basis. The basal area of black locust (Robinia pseudoacacia L.), a species that enhances soil nitrogen levels via nitrogen fixation, showed a moderate positive correlation with stream nitrate concentrations. Bedrock geology explained the most variation in winter (49%) and summer (32%) stream nitrate concentrations. Bedrock geology may have been a better predictor of stream nitrate concentrations than soil chemistry, because the geologic variation was better assessed at the regional scale of this study compared to soil chemistry, which varies at the micro-scale due to topographic, vegetation, microbial, and climatic influences. Results of this study suggest that bedrock geology is an important factor to consider when assessing forest nitrogen dynamics at a broad landscape scale.
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18o isotopic separation of stream nitrate sources in mid appalachian Forested Watersheds
Journal of Hydrology, 2001Co-Authors: Karl W J Williard, David R Dewalle, Pamela J Edwards, William E SharpeAbstract:Abstract The δ 18 O values of atmospheric nitrate deposition, microbe-produced nitrate, and stream nitrate were measured to determine the dominant source of stream nitrate in 27 mid-Appalachian headwater Forested Watersheds (12–771 ha) with varying bedrock geologies, land disturbance histories, and stand ages. The 12 monthly composite nitrate δ 18 O values of wet deposition and throughfall exhibited similar pronounced seasonal trends, with relatively depleted δ 18 O values during the summer. Wet deposition and throughfall nitrate δ 18 O values were not significantly different between northern (Leading Ridge, PA) and southern (Fernow, WV) regional sampling sites, indicating that δ 18 O values were spatially similar across the study area. Atmospheric nitrate δ 18 O values were significantly greater than microbe-produced nitrate δ 18 O values, allowing the two sources of stream nitrate to be separated. During four baseflow and three stormflow sampling periods, microbe-produced nitrate was the dominant (>70%) source of nitrate in the study streams. This result does not mean atmospheric nitrogen deposition should be discounted as a source of Forested stream nitrate, because atmospheric deposition is the primary external contributor to the long-term soil nitrogen pool that ultimately drives soil nitrate production rates. Stream nitrate δ 18 O values were greater during stormflow periods compared to baseflow periods, indicating greater contributions of atmospheric nitrate during storm events. Neither microbe-produced nitrate δ 18 O values from incubated forest soil samples nor stream nitrate δ 18 O values showed strong relationships with land disturbance history or stand age. However, Watersheds dominated by Pottsville/Allegheny bedrock and associated extremely acid soils had greater summer stream nitrate δ 18 O values than Watersheds containing predominantly Catskill/Chemung/Pocono and Mauch Chunk/Greenbrier bedrock. Inhibited microbial nitrate production by low soil pH could account for the greater proportions of atmospheric nitrate deposition in streams draining Pottsville/Allegheny bedrock.
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indicators of nitrate export from Forested Watersheds of the mid appalachians united states of america
Global Biogeochemical Cycles, 1997Co-Authors: Karl W J Williard, David R Dewalle, Pamela J Edwards, Ronald R SchnabelAbstract: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.
Pamela J Edwards - One of the best experts on this subject based on the ideXlab platform.
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influence of bedrock geology and tree species composition on stream nitrate concentrations in mid appalachian Forested Watersheds
Water Air and Soil Pollution, 2005Co-Authors: Karl W J Williard, David R Dewalle, Pamela J EdwardsAbstract:Although the large variations in nitrate export from Forested Watersheds have been at- tributed to a variety of natural and disturbance-related factors, baseflow nitrate concentrations in 49 mid-Appalachian Forested Watersheds were most strongly related to differences in bedrock geol- ogy. Within the mid-Appalachian region of Pennsylvania, Maryland and West Virginia, Watersheds dominated by Pottsville and Allegheny sandstone (PVA), Catskill, Chemung, and Pocono shale and sandstone (CCP), and Mauch Chunk shale and Greenbrier limestone (MCG), respectively, exhibited significantly different low, intermediate, and high mean stream nitrate concentrations. Soil pH, soil percent N concentration (%N), soil C:N mass ratio, soil exchangeable Ca, watershed slope, and the occurrence of white ash (Fraxinus americana L.), sugar maple (Acer saccharum Marsh.), and eastern hemlock (Tsuga canadensis L.) were related significantly to bedrock geology type as well as stream nitrate levels. Other factors such as past land disturbances (fire and agriculture) and stand age (old- growth) typically were associated with only one bedrock geology type. However, within a bedrock geology type, past agriculture and the presence of old-growth forest may be important in explaining stream nitrate concentrations on an individual watershed basis. The basal area of black locust (Robinia pseudoacacia L.), a species that enhances soil nitrogen levels via nitrogen fixation, showed a moderate positive correlation with stream nitrate concentrations. Bedrock geology explained the most variation in winter (49%) and summer (32%) stream nitrate concentrations. Bedrock geology may have been a better predictor of stream nitrate concentrations than soil chemistry, because the geologic variation was better assessed at the regional scale of this study compared to soil chemistry, which varies at the micro-scale due to topographic, vegetation, microbial, and climatic influences. Results of this study suggest that bedrock geology is an important factor to consider when assessing forest nitrogen dynamics at a broad landscape scale.
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sampling considerations for establishment of baseline loadings from Forested Watersheds for tmdl application
Environmental Monitoring and Assessment, 2004Co-Authors: Pamela J Edwards, Karl W J Williard, James N KochenderferAbstract:Five methods for estimating maximum daily and annual nitrate (NO3) and suspended sediment loads using periodic sampling of varying intensities were compared to actual loads calculated from intensive stormflow and baseflow sampling from small, Forested Watersheds in north central West Virginia to determine if the less intensive sampling methods were accurate and could be utilized in TMDL development. There were no significant differences between the annual NO3 load estimates using non-intensive sampling methods and the actual NO3 loads. However, maximum daily NO3 loads were estimated less accurately than annual loads. The ability to estimate baseline NO3 loads fairly accurately with non-intensive concentration data is attributed to the small fluctuation in NO3 concentrations over flow and time, particularly during storms. By contrast, suspended sediment exports determined by any of the non-intensive methods varied significantly and widely from and compared poorly to the actual exports for both daily and annual methods. Weekly sampling better approximated actual annual exports, but there were no significant statistical differences among weekly, monthly, and quarterly estimates. Suspended sediment concentrations varied widely within and among storm events, so that accurate estimates of total annual or maximum daily loads could not be obtained from infrequent sampling.
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18o isotopic separation of stream nitrate sources in mid appalachian Forested Watersheds
Journal of Hydrology, 2001Co-Authors: Karl W J Williard, David R Dewalle, Pamela J Edwards, William E SharpeAbstract:Abstract The δ 18 O values of atmospheric nitrate deposition, microbe-produced nitrate, and stream nitrate were measured to determine the dominant source of stream nitrate in 27 mid-Appalachian headwater Forested Watersheds (12–771 ha) with varying bedrock geologies, land disturbance histories, and stand ages. The 12 monthly composite nitrate δ 18 O values of wet deposition and throughfall exhibited similar pronounced seasonal trends, with relatively depleted δ 18 O values during the summer. Wet deposition and throughfall nitrate δ 18 O values were not significantly different between northern (Leading Ridge, PA) and southern (Fernow, WV) regional sampling sites, indicating that δ 18 O values were spatially similar across the study area. Atmospheric nitrate δ 18 O values were significantly greater than microbe-produced nitrate δ 18 O values, allowing the two sources of stream nitrate to be separated. During four baseflow and three stormflow sampling periods, microbe-produced nitrate was the dominant (>70%) source of nitrate in the study streams. This result does not mean atmospheric nitrogen deposition should be discounted as a source of Forested stream nitrate, because atmospheric deposition is the primary external contributor to the long-term soil nitrogen pool that ultimately drives soil nitrate production rates. Stream nitrate δ 18 O values were greater during stormflow periods compared to baseflow periods, indicating greater contributions of atmospheric nitrate during storm events. Neither microbe-produced nitrate δ 18 O values from incubated forest soil samples nor stream nitrate δ 18 O values showed strong relationships with land disturbance history or stand age. However, Watersheds dominated by Pottsville/Allegheny bedrock and associated extremely acid soils had greater summer stream nitrate δ 18 O values than Watersheds containing predominantly Catskill/Chemung/Pocono and Mauch Chunk/Greenbrier bedrock. Inhibited microbial nitrate production by low soil pH could account for the greater proportions of atmospheric nitrate deposition in streams draining Pottsville/Allegheny bedrock.
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indicators of nitrate export from Forested Watersheds of the mid appalachians united states of america
Global Biogeochemical Cycles, 1997Co-Authors: Karl W J Williard, David R Dewalle, Pamela J Edwards, Ronald R SchnabelAbstract: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.