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Sediment from gravel roads has degraded stream health in the southern Appalachians. National Forests initiated road reconstruction projects to reduce stream sedimentation. We monitored runoff water quality, before and after road reconstruction, from a wide variety of roads. Treatments included ditch obliteration, out-sloping, culvert removal, broad-based dips, and hay bales. Pre-treatment sediment yield generally increased with usage levels. Sediment yields following reconstruction were approximately one half of pretreatment levels. We monitored total suspended solids (TSS) and total petroleum hydrocarbons (TPH) from gravel and paved roads to quantify the effects of paving on water quality. While [TSS] tended to be lower on the paved road, they were not significantly lower than those of the maintained gravel roads. [TPH] from the two-year-old surface were just above detection limits (well below standards) at the road edge and not found downstream. TPH from the newly paved road adsorbed to sediments and did not move to the stream.

We characterized structural and functional attributes along hillslope gradients in headwater catchments. We endeavored to identify parameters that described significant transitions along the hillslope. On each of four catchments, we installed eight 50 m transects perpendicular to the stream. Structural attributes included woody and herbaceous vegetation; woody debris and forest floor mass, nitrogen (N) and carbon (C); total soil C and N; litterfall amount and quality by species; and microclimatic conditions. Functional attributes included litter decomposition, soil microarthropods, soil [CO.sub.2] evolution, soil solution chemistry, and soil extractable N. Forest floor mass, N and C, and soil depth increased with distance from the stream and transitioned between 10 and 20 m. In contrast, litterfall N rate (kilograms of nitrogen per hectare per day), downed woody debris, soil A-horizon C and N, and soil solution [NO.sub.3] concentration all decreased with distance, and exhibited significant transitions. Certain overstory species were more abundant in the uplands than near the stream. Herbaceous diversity and richness were similar across the hillslope, but species distributions varied in response to hillslope moisture content. Taken together, these results suggest that at 10-20 m from the stream, transitions occur that separate riparian from upland conditions and may provide valuable insight into riparian zone definition. Resume: Nous avons caracterises les attributs structuraux et fonctionnels le long de gradients de pente dans des bassins versants de tete. Nous avons tente didentifier les parame tres qui caracterisent les zones de transition importante le long des pentes. Dans chacun de quatre bassins versants, nous avons installe huit transects de 50 m perpendiculaires au cours d'eau. Les attributs structuraux incluaient la vegetation ligneuse et herbacee, la teneur en N et C ainsi que la masse des de-bris ligneux et de la couverture morte, la quantite totale de C et N dans le sol, la quantite et la qualite de la chute de litiere par espece et les conditions microclimatiques. Les attributs fonctionnels incluaient la decomposition de la litiere, les microarthropodes du sol, l'evolution du [CO.sub.2] dans le sol, les caracteristiques chimiques de la solution du sol et la quantite de N extractible dans le sol. La teneur en N et C ainsi que la masse de la couverture morte et la profondeur du sol augmentaient avec la distance depuis le cours d'eau et subissaient une transition a une distance de 10 a 20 m. Par contre, le taux de N (kg N*[ha.sup.-1]*[j.sup.-1]) dans la chute de litiere, les debris ligneux au sol, la quantite de C et N dans l'horizon A du sol et la concentration de [NO.sub.3] dans la solution du sol diminuaient avec la distance et connaissaient d'importantes transitions. Certaines especes de letage dominant etaient plus abondantes en terrain eleve qua proximite des cours d'eau. La diversite et la richesse des especes herbacees etaient semblables le long de la pente mais leur distribution variait en fonction de la teneur en humidite le long de la pente. Globalement, ces resultats indiquent qua 10 a 20 m du cours d'eau, des zones de transition separent les conditions riveraines des conditions en terrain eleve et peuvent donner un apercu interessant de la definition de la zone riveraine. [Traduit par la Redaction], Introduction Forested riparian areas mediate a number of terrestrial--aquatic linkages (Karr and Schlosser 1978) through their influence on physical, chemical, and biological dimensions of streams. Riparian zones are three-dimensional areas [...]

•We examined the relationships between stem CO2 efflux ( Es), diameter growth, and nonstructural carbohydrate concentration in loblolly pine trees. Carbohydrate supply was altered via stem girdling during rapid stem growth in the spring and after growth had ceased in the autumn. We hypothesized that substrate type and availability control the seasonal variation and temperature sensitivity of Es. •The Es increased and decreased above and below the girdle, respectively, within 24 h of treatment. Seasonal variation in Es response to girdling corresponded to changes in stem soluble sugar and starch concentration. Relative to nongirdled trees, Es increased 94% above the girdle and decreased 50% below in the autumn compared with a 60% and 20% response at similar positions in the spring. •The sensitivity of Es to temperature decreased below the girdle in the autumn and spring and increased above the girdle but only in the autumn. Temperature-corrected Es was linearly related to soluble sugar ( R2 = 0.57) and starch ( R2 = 0.62) concentration. •We conclude that carbohydrate supply, primarily recently fixed photosynthate, strongly influences Es in Pinus taeda stems. Carbohydrate availability effects on Es obviate the utility of applying short-term temperature response functions across seasons. [ABSTRACT FROM AUTHOR]

We measured diel patterns of stem surface CO2 efflux ( Es, µmol m−2 s−1), sap velocity ( vs, mm s−1) and xylem CO2 concetration ([CO2]) ( Xs, %) in 8-year-old loblolly pine trees during the spring to determine how vs and Xs influence Es. All trees showed a strong diel hysteresis between Es and stem temperature, where at a given temperature, Es was lower during the day than at night. Diel variations in temperature-independent Es were correlated with vs ( R2 = 0.54), such that at maximum vs, Es was reduced between 18 and 40%. However, this correlation may not represent a cause-and-effect relationship. In a subset of trees, vs was artificially reduced by progressively removing the tree canopy. Reducing vs to near zero had no effect on Es and did not change the diel hysteretic response to temperature. Diel Xs tended to decrease with vs and increase with Es, however, in defoliated trees, large increases in Xs, when vs ≈ 0, had no effect on Es. We conclude that at this time of the year, Es is driven primarily by respiration of cambium and phloem tissues and that sap flow and xylem transport of CO2 had no direct influence on Es. [ABSTRACT FROM AUTHOR]

Trichloroethene (TCE) was detected in cores of trees growing above TCE-contaminated ground at three sites: the Carswell Golf Course in Texas, Air Force Plant PJKS in Colorado, and Naval Weapons Station Charleston in South Carolina. This was true even when the depth to water was 7.9 m or when the contaminated aquifer was confined beneath -3 m of clay. Additional ground water contaminants detected in the tree cores were cis--1,2-dichloroethene at two sites and tetrachloroethene at one site. Thus, tree coring can be a rapid and effective means of locating shallow subsurface chlorinated ethenes and possibly identifying zones of active TCE dechlorination. Tree cores collected over time were useful in identifying the onset of ground water contamination. Several factors affecting chlorinated ethene concentrations in tree cores were identified in this investigation. The factors include ground water chlorinated ethene concentrations and depth to ground water contamination. In addition, differing TCE concentrations around the trunk of some trees appear to be related to the roots deriving water from differing areas. Opportunistic uptake of infiltrating rainfall can dilute prerain TCE concentrations in the trunk. TCE concentrations in core headspace may differ among some tree species. In some trees, infestation of bacteria in decaying heartwood may provide a TCE dechlorination mechanism within the trunk. [ABSTRACT FROM AUTHOR]

We measured seasonal fine root respiration rate in situ while controlling chamber temperature and [CO2]. Atmospheric [CO2] ([CO2]a) and measured soil [CO2] ([CO2]s) were alternately delivered to a cuvette containing intact fine roots of eastern white pine (Pinus strobus L.). Respiration rates were consistently higher in [CO2]a than in [CO2]s and were almost three times higher during midsummer. Respiration rates were immediately reversed after returning to the alternate [CO2] (i.e., [CO2]a → [CO2]s → [CO2]a, and vice versa) suggesting a direct effect of elevated [CO2] on apparent respiration. Soil-[CO2]-based respiration rates decreased with increasing [CO2] on a dry mass and tissue [N] basis. We conclude that estimates of soil CO2 flux and soil carbon budgets may be improved by more completely accounting for the rhizosphere microclimate (i.e., soil temperature and [CO2]s) during measurement of fine root respiration. [ABSTRACT FROM AUTHOR]

The use of plants to remediate polluted groundwater is becoming an attractive alternative to more expensive traditional techniques. In order to adequately assess the effectiveness of the phytoremediation treatment, a clear understanding of water-use habits by the selected plant species is essential. We examined the relative uptake of surface water (i.e., precipitation) vs. groundwater by mature Populus deltoides by applying irrigation water at a rate equivalent to a 5-cm rain event. We used stable isotopes of hydrogen (D) and oxygen (18O) to identify groundwater and surface water (irrigation water) in the xylem sap water. Pretreatment isotopic ratios of both deuterium and 18O, ranked from heaviest to lightest, were irrigation water > groundwater > xylem sap. The discrepancy in preirrigation isotopic signatures between groundwater and xylem sap suggests that in the absence of a surface source of water (i.e., between rain events) there is an unknown amount of water being extracted from sources other than groundwater (i.e., soil surface water). We examined changes in volumetric soil water content (%), total hourly sapflux rates, and trichloroethene (TCE) concentrations. Following the irrigation treatment, volumetric soil water increased by 86% and sapflux increased by as much as 61%. Isotopic signatures of the xylem sap became substantially heavier following irrigation, suggesting that the applied irrigation water was quickly taken up by the plants. TCE concentrations in the xylem sap were diluted by an average of 21% following irrigation; however, dilution was low relative to the increase in sapflux. Our results show that water use by Populus deltoides is variable. Hence, studies addressing phytoremediation effectiveness must account for the relative proportion of surface vs. groundwater uptake.