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Journal of Environmental Quality 02/2013; 12:263-270. · 2.32 Impact Factor
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ABSTRACT: Re-examination of data distributions from several forested sites in the eastern Sierra Nevada Mountains shows consistent,
positive outliers and skew for NH4
+, NO3
−, and mineral N in resin lysimeters and resin capsules, indicating that most values were low but hotspots of high N flux were
present in most cases. Exact causes of these N flux hotspots is not known, but could include water flux hotspots (e.g., preferential
flowpaths), microbial hotspots, and possibly the entry of N-enriched O horizon interflow. Soil and resin stake (PRS probe)
data from one site (North Lake Tahoe) also showed consistent, positive outliers and skew for NH4
+, NO3
−
, and mineral N, suggesting the presence of microbially produced hotspots. Bicarbonate-P data from soils and ortho-P data from PRS probes also showed highly positive skew and extreme outliers, but Bray (HCl/NH4F-extractable) P in soils did not. Other measured nutrients (extractable Mg2+, K+, SO4
2−, and Ca2+) also showed positive skew and outliers, but less so than NH4
+, NO3
−, and mineral N. Calcium stood out among measured nutrients as the most abundant nutrient with the least outliers and the
lowest (sometimes negative) skew. The differences in distributions of NH4
+, NO3
−, and mineral N and those of Ca2+ may reflect relative abundance: the most abundant ion, Ca2+, shows little evidence of hotspots whereas the much less abundant ions, NH4
+, NO3
− consistently show evidence of hotspots. We hypothesize that the differing distributions of N and Ca reflect the relative
biological competition for these nutrients and that positively-skewed distributions and hotspots will be characteristic of
any other nutrient when it is in limited supply relative to biological demand.
KeywordsNutrients-Soils-Hotspots-Ammonium-Nitrate-Calcium-
Ortho-P-Magnesium-Sulfate-Potassium Sierra Nevada Mountains
Biogeochemistry 04/2012; 101(1):93-103. · 3.07 Impact Factor
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Journal of Plant Nutrition and Soil Science. 01/2012; 175(1):68-77.
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D Obrist, D W Johnson,
S E Lindberg,
Y Luo,
O Hararuk,
R Bracho,
J J Battles,
D B Dail,
R L Edmonds,
R K Monson,
S V Ollinger,
S G Pallardy,
K S Pregitzer,
D E Todd
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ABSTRACT: Results from a systematic investigation of mercury (Hg) concentrations across 14 forest sites in the United States show highest concentrations in litter layers, strongly enriched in Hg compared to aboveground tissues and indicative of substantial postdepositional sorption of Hg. Soil Hg concentrations were lower than in litter, with highest concentrations in surface soils. Aboveground tissues showed no detectable spatial patterns, likely due to 17 different tree species present across sites. Litter and soil Hg concentrations positively correlated with carbon (C), latitude, precipitation, and clay (in soil), which together explained up to 94% of concentration variability. We observed strong latitudinal increases in Hg in soils and litter, in contrast to inverse latitudinal gradients of atmospheric deposition measures. Soil and litter Hg concentrations were closely linked to C contents, consistent with well-known associations between organic matter and Hg, and we propose that C also shapes distribution of Hg in forests at continental scales. The consistent link between C and Hg distribution may reflect a long-term legacy whereby old, C-rich soil and litter layers sequester atmospheric Hg depositions over long time periods. Based on a multiregression model, we present a distribution map of Hg concentrations in surface soils of the United States.
Environmental Science & Technology 05/2011; 45(9):3974-81. · 4.80 Impact Factor
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ABSTRACT: Nutrient distributions, concentrations, and fluxes in two red spruce (Picearubens Sarg.) stands in the Great Smoky Mountains are described and used to evaluate various hypotheses for recent decline of this species. These forests, like others in the southern Appalachians, were relatively rich in N and low in base cation status. The combination of high atmospheric N and S deposition, little or no N or S retention, relatively high N mineralization, and extremely acid soils caused soil solutions to be dominated by NO3−, SO42−, Al, and H+. Soil solution Al in these sites (most of which was in monomeric form) occasionally reached levels noted to inhibit base cation uptake and root growth in solution culture studies. These pulses of Al were driven by pulses of NO3− and, to a lesser extent, SO42− in soil solution. However, fine roots were present at depths of up to 60 cm in the mineral soil, indicating that Al concentrations had not become consistently toxic to roots. Solution fluxes (both throughfall and soil leaching) exceeded litter-fall fluxes for all the macronutrients at both sites, a typical situation for K and S, but most unusual for N, P, Ca, and Mg. There are significant implications of these fluxes and of the apparent net uptake of N by foliage in terms of how vegetation uptake and translocation are calculated. Some new formulations are suggested, but measurement errors in systems with such a predominance of hydrologic fluxes make foliar leaching and, therefore, uptake and translocation calculations extremely uncertain. Although there are no outward signs of decline in these forests (other than balsam fir (Abiesbalsamea (L.) Mill.) mortality due to the balsam woolly adelgid (Adelgespiceae (Ratz.))), the high rates of NO3− leaching rates and the borderline soil solution Al values suggest that these systems are under stress. Whether these factors actually lead to a dieback or growth decline remains to be seen.
Watershed Sciences Faculty Publications. 02/2011;
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ABSTRACT: Potential and actual nitrification were compared between a high and low N fertility Inceptisol in Washington State and between two Tennessee Ultisols to investigate the effect of soil N status and changes in forest floor C/N ratio on NO3-N production. Soil and soil solution data were collected (i) prior to treatment, (ii) after doubling the forest floor C/N ratio with sawdust, and (iii) after doubling the forest floor N content by adding urea N to each of the four forest types. Nitrate N production during aerobic soil incubation before and 1 year after treatment demonstrated significantly higher nitrification capacity of the N-rich Washington soil under alder, the stimulatory effect of N addition, and the suppressing effect of C on nitrification. Our study also indicated that the N fertility status was not as different between the Tennessee soils as originally assumed, that both soils in fact behaved similarly to the N-poor Washingon soil, and that these three soils should be considered in the same category of low N fertility sites. Nitrate concentrations in soil and soil solution samples collected in the field generally agreed with the laboratory findings, but differences in NO3− leaching between the untreated soils and between treatments were often less pronounced. Soil solution NO3− concentrations were <0.01 mmol/L in the two Tennessee soils and the N-poor Washington soil, and differed little between them. In soil that was N enriched by N-fixing alder, the average NO3− solution concentration was 0.4 mmol/L. Spring application of urea N caused an immediate and significant increase in NO3− solution concentration in all four soils, but the treatment effect subsided by the end of the 2nd year in all cases. Adding C to the forest floor did not further reduce already low NO3− solution levels in the two Tennessee soils and the N-poor Washington soil. This treatment did not cause a prolonged reduction in NO3− leaching from the N-rich Washington soil, and it was speculated that this was due to belowground N addition from the root system of the N-fixing alder at this site.
Watershed Sciences Faculty Publications. 02/2011;
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ABSTRACT: Increased belowground labile C inputs under elevated [CO2] could stimulate nonsymbiotic N2 fixation, thereby enhancing growth responses of vegetation to elevated [CO2] on nutrient-poor sites. To test this hypothesis, nonsymbiotic N2 fixation rates in soils planted with 3-year-old Jeffrey pine (Pinus jeffreyi Grev. & Balf.) trees grown under 365 and 700 µL·L1 atmospheric [CO2] were measured by exposing the soil to 15N2-enriched air for 78 d. Nitrogen fixation rates were estimated by measuring 15N content of trees and soil. Compared with the ambient CO2 treatment, the elevated CO2 treatment did not affect biomass, N content, or δ15N of individual plant parts and soils, indicating that elevated [CO2] did not stimulate nonsymbiotic N2 fixation. Because belowground C inputs did not increase under elevated [CO2], the initial hypothesis could not be accepted or rejected. The results from the 15N2 labeling study agree with other studies showing that nonsymbiotic N2 fixation is not likely to provide a large input of N in forest ecosystems. The 15N2 labeling technique was promising for studying N2 fixation in plantsoil systems, but the preliminary nature of this study did not allow for firm conclusions with regard to the effects of elevated [CO2].
Canadian Journal of Forest Research 02/2011; 34(9):1979-1984. · 1.68 Impact Factor
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ABSTRACT: Sulfate was the dominant anion in throughfall and soil solutions from a chestnut oak (Quercuspinus L.) and a yellow poplar (Liriodendrontulipifera L.) forest in eastern Tennessee. Assuming much of this was of anthropogenic origin, cation-leaching rates from foliage and in soils of these forests would have to have been accelerated by acid deposition by two- to three-fold. This acclerated leaching could, in turn, cause changes in the rates of K+, Ca2+, or Mg2+ cycling according to any of a number of possible scenarios explored in this paper. Subsoils beneath the chestnut oak stand adsorbed from atmospheric deposition, which reduced -mediated cation leaching to some extent. In contrast, subsoils from the yellow poplar stand showed a current net output of (perhaps desorbing sulfate adsorbed during previous periods of higher input) and much higher rates of cation leaching. The yellow poplar site showed net annual exports of Ca2+, Mg2+, K+, and Na+, but the chestnut oak site showed a net accumulation of Ca2+ and lower net annual exports of Mg2+ and K+ than the yellow poplar site. Both sites had inexplicably large net exports of Na+.
Canadian Journal of Forest Research 02/2011; 15(5):773-782. · 1.68 Impact Factor
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ABSTRACT: The presence of nitrogen (N) fixing vegetation can have significant deleterious effects on water quality and also soil leaching. This study investigates the effects of snowbrush (Ceanothus velutinus Dougl.), a common post-disturbance N fixer in the western United States, on water quality and soil leaching. We compared mineral N concentrations in soil solution, runoff, O horizon leachates and resin lysimeters in adjacent snowbrush and Jeffrey pine (Pinus jeffreyii Grev. & Balf) stands in one site in the eastern Sierra Nevada Mountains in Nevada. Soil solutions from snowbrush had slightly but not significantly greater NO3− concentrations than those from Jeffrey pine. Leaching rates of NO3− and NH4+ measured by resin lysimeters were lower in snowbrush than in Jeffrey pine, and leaching rates in mineral soil (15 cm) were not significantly different. Nitrate and NH4+ concentrations in runoff were greater in the snowbrush than Jeffrey pine, and ancillary field column studies confirmed that snowbrush litter was the primary source of this elevated mineral N. Cutting, followed by mastication and herbicide treatments had no effect on mineral N leaching in a snowbrush stand growing on a recently burned (1994) site in the eastern Sierra Nevada Mountains of California. We conclude from this and previous studies that snowbrush, unlike some other post-disturbance N-fixing species, has minimal and inconsistent effects on water quality in the eastern Sierra Nevada Mountains. Copyright © 2009 John Wiley & Sons, Ltd.
Ecohydrology 12/2009; 3(1):79 - 87. · 2.13 Impact Factor
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ABSTRACT: As the interface between air and rock, the critical zone integrates
everything from the biologically-mediated breakdown of minerals to the
effects of climate change and tectonics on soil formation and sediment
transport. River incision into rock provides a crucial, first-order link
between extrinsic forcing factors (such as climate change and tectonic
uplift) and the hillslope processes that shape the critical zone by
changing soil thickness, geochemistry, and ultimately topographic form.
Theoretical considerations and experimental studies indicate that there
is great potential for feedbacks between hillslope and channel
processes. For example, bedrock river incision should be regulated in
part by both the quantity and caliber (i.e., grain-size distribution) of
sediment supply, which together affect the availability and persistence
of bed-scouring tools in channels. Although sediment supply rates and
grain-size distributions can be readily measured in many landscapes
(e.g., using cosmogenic nuclides and traditional soil sampling
techniques), the importance of measuring them together, to help unravel
and understand the complex linkages among hillslope and channel
processes, has been overlooked until recently. Here we compile and
analyze data from nearly 200 soil pits arrayed across a nearly uniform
grid of sampling localities within the Southern Sierra Nevada Critical
Zone Observatory (CZO). The CZO is part of the Kings River Experimental
Watershed, where measurements of sediment and solute yields are an
integral part of an ongoing, multi-decadal effort to monitor stocks and
flows of biogeochemical cycles. Our quantitative data on rock fragment
abundance, regolith density, and bulk geochemistry represents a range of
topographic conditions, from convex ridgelines to positions at the toes
of slopes, next to stream channels. Our results indicate that the
percentage of coarse (>2 mm) material—which presumably becomes
the bedload that abrades and thus lowers channels—varies
significantly in soils across the 4 CZO watersheds, from an average of
15% in one extreme case to 50% in another. Rock fragment abundance is
lowest in the catchment that also exhibits both the highest sediment
yield and the lowest percent coverage by bare rock outcrops. This may
indicate that both sediment yield and the physical breakdown of rock are
limited by percent coverage of bare rock, consistent with a decades-old
hypothesis that was developed to explain relationships among weathering,
erosion, outcrop density, and topographic form in the region.
AGU Fall Meeting Abstracts. 11/2009; -1:02.
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ABSTRACT: Interactions between forest health variables and mensurational characteristics in an uneven-aged eastern Sierra Nevada mixed conifer stand were examined. The stand was located in the Lake Tahoe Basin on a site featuring a coarsely textured granitic soil and numerous rock outcrops. Its composition was dominated by California white fir (Abies concolor var. lowiana [Gord.] Lemm.), with Jeffrey pine (Pinus jeffreyi Grev. & Balf.) and sugar pine (Pinus lambertiana Dougl.) less prominent and incense-cedar (Libocedrus decurrens Torr.) and mountain alder (Alnus tenuifolia Nutt.) the most minor constituents. The majority of saplings and seedlings were white fir. The stand exhibited no evidence that its development had been influenced by fire and, overall, it consisted of numerous small trees accruing little radial growth. Nearly one-quarter of all standing stems pole size or larger were dead, with mortality concentrated in white fir. Forest-floor fuel accumulations were excessive, and coarse debris was especially prominent. A fir engraver beetle (Scolytus ventralis LeConte) epidemic in white fir contrasted against apparent endemic population levels of the Jeffrey pine (Dendroctonus jeffreyi Hopkins) and red turpentine (Dendroctonus valens LeConte) beetles in Jeffrey pine and of the mountain pine beetle (Dendroctonus ponderosae Hopkins) in sugar pine. The severity of fir engraver attack on white fir was weakly related to overall tree size and to the proportion of composition consisting of this host species, while in Jeffrey pine and sugar pine, bark beetle attacks were strongly correlated with the individual proportions of these 2 hosts. Across all species, basal area explained a substantial proportion of the variation in overall attack severity. We found light infestations of true fir dwarf mistletoe (Arceuthobium abietinum Engelm. ex Munz f. sp. concoloris) in white fir and western dwarf mistletoe (Arceuthobium campylopodum Engelm.) in Jeffrey pine, plus an early stage of infection by the white pine blister rust (Cronartium ribicola J.C. Fischer) in sugar pine. Collectively, this case study characterized and quantified many of the conditions, symptoms, and causative agents inherent in a decadent mixed conifer stand in the eastern Sierra Nevada.
Western North American Naturalist 09/2009; · 0.40 Impact Factor
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J.A. Arnone III,
P.S.J. Verburg, D.W. Johnson,
J.D. Larsen,
R.L. Jasoni,
A.J. Lucchesi,
C.M. Batts,
C. von Nagy,
W.G. Coulombe,
D.E. Schorran,
P.E. Buck,
B.H. Braswell,
J.S. Coleman,
R.A. Sherry,
L.L. Wallace,
Y. Luo,
D.S. Schimel
Nature. 01/2008; 455:383-386.
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Journal of Sustainable Forestry 01/2008; 26(4):241-283.
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Journal of Sustainable Forestry 01/2008; 26(1):19-60.
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ABSTRACT: Conventional soil solution lysimeters and snowmelt solution collectors suffer from a number of limitations when used to estimate yearly nutrient fluxes. This study describes an alternative technique to directly measure soil and snowmelt solution fluxes utilizing ion exchange resin-based collectors. Resin-lysimeters were constructed by enclosing a layer of resin between two layers of nutrient-free silica sand within a polyvinyl chloride tube. Nitrogen (N) and phosphorus (P) fluxes from resin based collectors were compared against buried resin bags, ceramic cup lysimeters, and traditional snowmelt solution collectors co-located in an eastern Sierra Nevada forest. Ammonium and P accumulation in resin lysimeters were one- to two orders of magnitude smaller than in buried resin bags placed in direct contact with the soil. Resin lysimeters and resin snowmelt collectors measured NH4–N and P fluxes that were three times greater than those estimated from ceramic cup lysimeters and solution snowmelt collectors. We hypothesize that this difference was due to spoilage of the solution sample in solution collectors between collections. Resin lysimeters are easy to construct, provide a direct measurement of nutrient fluxes, and are an alternative to solution snowmelt collectors and ceramic cup lysimeters, especially in areas where poor winter accessibility precludes constant maintenance.
Commun. Soil Sci. Plant Anal. 08/2006; 33(7&8)(pp. 1261–1275 (2002)):1261-1275.
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ABSTRACT: The objectives of this study were to quantify the effects of prescribed fire on forest floor C and nutrient content, soil chemical properties, and soil leaching in a Jeffrey pine (Pinus jeffreyi [Grev. and Balf.]) forest in the eastern Sierra Nevada Mountains of California. The study included a prescribed fire and three timber harvest treatments: whole-tree (WT) thinning, cut-to-length (CTL) thinning, and no harvest (CONT). Prescribed fire resulted in significant decreases in forest floor C (-8 to -23 mg ha-1, or 39% to 61% decrease), N (-114 to -252 kg ha-1, or -31% to 51% decrease), S (0 to -15 kg ha-1, or 0% to 48% decrease), and K (-3 to -45 kg ha-1, or 12% to 51% decrease) contents but no significant change in Ca or Mg contents. In each case, the decreases were greatest in the CTL treatment, where slash accumulation before burning was greatest. Burning caused statistically significant effects on soil total nitrogen, C:N ratio, pH, water-extractable ortho-P, and water-extractable SO42- in some cases, but these effects were generally small, inconsistent among harvest treatments and horizons, and in the case of ortho-P much less than the temporal variation in both burned and unburned plots. There were no statistically significant effects of burning on total C, Bray-extractable P, bicarbonate-extractable P, and exchangeable Ca2+, K+, or Mg2+. Burning had no significant effect on soil solution pH, ortho-P, SO42-, NO3-, or NH4+ as measured by ceramic cup lysimeters and no effect on the cumulative leaching of ortho-P, NO3-, or NH4+ as measured by resin lysimeters. Burning had no effect on needle weight or nutrient contents as measured by the vector analysis. We conclude that prescribed fire had minimal effects on soils or water quality at this site, and that the most ecologically significant effect was the loss of N from the forest floor.
Soil Science 02/2006; 171(3):181-199. · 1.14 Impact Factor
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ABSTRACT: The effects of elevated CO2 (ambient, +175, and +350μll−1) and nitrogen fertilization (0, 100, and 200kg Nha−1yr−1 as ammonium sulfate) on C and N accumulations in biomass and soils planted with ponderosa pine (Pinus ponderosa Laws) over a 6-year study period are reported. Both nitrogen fertilization and elevated CO2 caused increases in C and N contents of vegetation over the study period. The pattern of responses varied over time. Responses
to CO2 decreased in the +175μll−1 and increased in the +350μll−1 after the first year, whereas responses to N decreased after the first year and became non-significant by year six. Foliar
N concentrations were lower and tree C:N ratios were higher with elevated CO2 in the early years, but this was offset by the increases in biomass, resulting in substantial increases in N uptake with
elevated CO2. Nitrogen budget estimates showed that the major source of the N for unfertilized trees, with or without elevated CO2, was likely the soil organic N pool. There were no effects of elevated CO2 on soil C, but a significant decrease in soil N and an increase in soil C:N ratio in year six. Nitrogen fertilization had
no significant effect on tree C:N ratios, foliar N concentrations, soil C content, soil N content, or soil C:N ratios. There
were no significant interactions between CO2 and N treatments, indicating that N fertilization had no effect on responses to CO2 and that CO2 treatments had no effect on responses to N fertilization. These results illustrate the importance of long-term studies involving
more than one level of treatment to assess the effects of elevated CO2.
Biogeochemistry 01/2006; 77(2):157-175. · 3.07 Impact Factor
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Journal of Sustainable Forestry 01/2006; 23(2):99-115.
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Journal of Sustainable Forestry 01/2006; 23(4):35-59.
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ABSTRACT: It is generally held that surface runoff in heavily forested ecosystems is minimal and therefore nutrient fluxes via runoff are unimportant. This is based in large measure on the absence of direct observation or remnant physical evidence. It is further held that protected forests with heavy understory and litter serve as a nutrient sink due to maximum uptake and interception. Our Sierran studies have detected the presence of surface runoff at several sites in the form of both overland and litter interflow with concentrations of NH4-N as high as 87.2 mg L−1, NO3-N as high as 95.4 mg L−1, and PO4-P as high as 24.4 mg L−1. Data suggest that nutrients are derived from the mature O-horizons, and that there has been little contact with the mineral soil or root zone where strong retention and/or uptake of these ions would be expected. Such contributions from overland/interflow could be particularly important in areas where ultra-oligotrophic lakes (e.g., Lake Tahoe) are now trending towards meso-oligotrophic status. We believe that fire exclusion in these systems may have exacerbated N and P inputs to Lake Tahoe and elsewhere by allowing unnatural buildups of O-horizons that are apparently a source of nutrients to surface runoff.
Water Air and Soil Pollution 04/2005; 163(1):3-17. · 1.63 Impact Factor
