The Experts below are selected from a list of 16491 Experts worldwide ranked by ideXlab platform
Madeleine M. Mineau - One of the best experts on this subject based on the ideXlab platform.
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an invasive riparian tree reduces Stream Ecosystem efficiency via a recalcitrant organic matter subsidy
Ecology, 2012Co-Authors: Madeleine M. Mineau, Colden V. Baxter, Amy Marcarelli, Wayne G MinshallAbstract:A disturbance, such as species invasion, can alter the exchange of materials and organisms between Ecosystems, with potential consequences for the function of both Ecosystems. Russian olive (Elaeagnus angustifolia) is an exotic tree invading riparian corridors in the western United States, and may alter Stream organic matter budgets by increasing allochthonous litter and by reducing light via shading, in turn decreasing in-Stream primary production. We used a before-after invasion comparison spanning 35 years to show that Russian olive invasion increased allochthonous litter nearly 25-fold to an invaded vs. a control reach of a Stream, and we found that this litter decayed more slowly than native willow. Despite a mean 50% increase in canopy cover by Russian olive and associated shading, there were no significant changes in gross primary production. Benthic organic matter storage increased fourfold after Russian olive invasion compared to pre-invasion conditions, but there were no associated changes in st...
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An invasive riparian tree reduces Stream Ecosystem efficiency via a recalcitrant organic matter subsidy
Ecology, 2012Co-Authors: Madeleine M. Mineau, Colden V. Baxter, Amy Marcarelli, G. Wayne MinshallAbstract:A disturbance, such as species invasion, can alter the exchange of materials and organisms between Ecosystems, with potential consequences for the function of both Ecosystems. Russian olive (Elaeagnus angustifolia) is an exotic tree invading riparian corridors in the western United States, and may alter Stream organic matter budgets by increasing allochthonous litter and by reducing light via shading, in turn decreasing in-Stream primary production. We used a before-after invasion comparison spanning 35 years to show that Russian olive invasion increased allochthonous litter nearly 25-fold to an invaded vs. a control reach of a Stream, and we found that this litter decayed more slowly than native willow. Despite a mean 50% increase in canopy cover by Russian olive and associated shading, there were no significant changes in gross primary production. Benthic organic matter storage increased fourfold after Russian olive invasion compared to pre-invasion conditions, but there were no associated changes in Stream Ecosystem respiration or organic matter export. Thus, estimated Stream Ecosystem efficiency (ratio of Ecosystem respiration to organic matter input) decreased 14%. These findings show that invasions of nonnative plant species in terrestrial habitats can alter resource fluxes to Streams with consequences for whole-Ecosystem functions.
Walter R. Hill - One of the best experts on this subject based on the ideXlab platform.
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The Role of Periphyton in Mediating the Effects of Pollution in a Stream Ecosystem
Environmental Management, 2010Co-Authors: Walter R. Hill, John G. Smith, Michael G Ryon, S. Marshall Adams, Harry L. Boston, Arthur J. StewartAbstract:The effects of pollutants on primary producers ramify through Ecosystems because primary producers provide food and structure for higher trophic levels and they mediate the biogeochemical cycling of nutrients and contaminants. Periphyton (attached algae) were studied as part of a long-term biological monitoring program designed to guide remediation efforts by the Department of Energy’s Y-12 National Security Complex on East Fork Poplar Creek (EFPC) in Oak Ridge, Tennessee. High concentrations of nutrients entering EFPC were responsible for elevated periphyton production and placed the Stream in a state of eutrophy. High rates of primary production at upStream locations in EFPC were associated with alterations in both invertebrate and fish communities. Grazers represented >50% of the biomass of invertebrates and fish near the Y-12 Complex but
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Stream Ecosystem responses to the 2007 spring freeze in the southeastern United States: unexpected effects of climate change
Global Change Biology, 2009Co-Authors: Patrick J Mulholland, Walter R. Hill, Brian J. Roberts, John G. SmithAbstract:Some expected changes in climate resulting from human greenhouse gas emissions are clear and well documented, but others may be harder to predict because they involve extreme weather events or heretofore unusual combinations of weather patterns. One recent example of unusual weather that may become more frequent with climate change occurred in early spring 2007 when a large Arctic air mass moved into the eastern United States following a very warm late winter. In this paper, we document effects of this freeze event on Walker Branch, a well-studied Stream Ecosystem in eastern Tennessee. The 2007 spring freeze killed newly grown leaf tissues in the forest canopy, dramatically increasing the amount of light reaching the Stream. Light levels at the Stream surface were sustained at levels considerably above those normal for the late spring and summer months due to the incomplete recovery of canopy leaf area. Increased light levels caused a cascade of ecological effects in the Stream beginning with considerably higher (two– three times) rates of gross primary production (GPP) during the late spring and summer months when normally low light levels severely limit Stream GPP. Higher rates of Stream GPP in turn resulted in higher rates of nitrate (NO3 ) uptake by the autotrophic community and lower NO3 concentrations in Stream water. Higher rates of Stream GPP in summer also resulted in higher growth rates of a dominant herbivore, the snail Elimia clavaeformis. Typically, during summer months net NO3 uptake and snail growth rates are zero to negative; however, in 2007 uptake and growth were maintained at moderate levels. These results show how changes in forest vegetation phenology can have dramatic effects on Stream productivity at multiple trophic levels and on nutrient cycling as a result of tight coupling of forest and Stream Ecosystems. Thus, climate change-induced changes in canopy structure and phenology may lead to large effects on Stream Ecosystems in the future.
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Stream Ecosystem responses to forest leaf emergence in spring
Ecology, 2001Co-Authors: Walter R. Hill, Patrick J Mulholland, E R MarzolfAbstract:Streams in deciduous forests undergo marked transitions from light-replete to light-limited Ecosystems every spring when leaves emerge on Streamside trees. During the course of leaf emergence and enlargement, shade from leaves on Streamside trees can reduce photosynthetically active radiation (PAR) falling on the Streambed from >1000 to <30 Vmol.m-2*s-l. In this study, we examined the effects of leaf emergence at multiple levels in two headwater Streams in eastern Tennessee. Primary production estimated from both photosynthesis-irradiance measurements of periphyton in the laboratory and whole- steam diurnal oxygen measurements decreased dramatically over the course of canopy closure. Monthly carbon fixation estimates for periphyton in White Oak Creek declined from 354 pg C/cm2 in April to 66 pg C/cm2 in June, while carbon fixation in Walker Branch declined from 495 to 168 pg C/cm2. Periphyton photosynthesis became increasingly efficient at low irradiances (ox increased more than threefold) as ambient Streambed irradiances declined, but this increase in efficiency only partially compensated for the photon scarcity caused by riparian shade. Ecological photosynthetic efficiency (percentage of incident PAR energy fixed by photosynthesis) estimated from static models, whole-Stream measurements, and ambient PAR was a negative exponential function of incident PAR, increasing from <0.3% to 2% during canopy closure. This increase was attributable to (1) inefficient use of the relatively high irradiances before leaf emergence, and (2) greater photoefficiency (increased ox) at low irradiances after leaf emergence. Nutrient concentrations (dissolved nitrate and phosphate) in both Streams increased coincident with leaf emergence, implying a cascade of shade effects through primary producers to abiotic components of the eco- system. Shade effects also propagated to higher trophic levels: growth rates of grazing snails (Elimia clavaeformis) in both Streams decreased substantially from April to June, consistent with modeled decreases in the productivity of their food resource (periphyton). Snail growth rates were almost zero in White Oak Creek and were negative in Walker Branch during summer when Streambed PAR was lowest. The multilevel effects of leaf emergence reported in this study accentuate the importance of light variation in aquatic Ecosystems and illustrate the close coupling between Streams and their surrounding terres- trial Ecosystems.
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Stream Ecosystem responses to forest leaf emergence in spring
Ecology, 2001Co-Authors: Walter R. Hill, Patrick J Mulholland, E R MarzolfAbstract:Streams in deciduous forests undergo marked transitions from light-replete to light-limited Ecosystems every spring when leaves emerge on Streamside trees. During the course of leaf emergence and enlargement, shade from leaves on Streamside trees can reduce photosynthetically active radiation (PAR) falling on the Streambed from >1000 to
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light limitation in a Stream Ecosystem responses by primary producers and consumers
Ecology, 1995Co-Authors: Walter R. Hill, Michael G Ryon, Elizabeth M SchillingAbstract:Heavy shade presents serious challenges for primary producers and food- limited herbivores in forest Streams. In this study, we examined the response of periphyton and grazing snails (Elimia clavaeformis) to summer shade in White Oak Creek (WOC), a second-order Stream in a Tennessee deciduous forest. Three experiments were performed: (1) in situ manipulation of light and snail density to test the effects of light limitation and grazing; (2) construction of photosynthesis-irradiance (P-I) curves to test for shade ad- aptation by periphyton; and (3) measurements of snail growth vs. irradiance, to quantify the indirect relationship between grazers and an abiotic constraint on photosynthesis. In the first experiment, light and snail densities were manipulated in a 2 X 2 factorial design: two light treatments were created by removing Streamside vegetation from four sites in WOC and by pairing each of these sites with an adjacent, shaded site; two snail density treatments at each site were created by adding snails at normal (970 individuals/) and low (50 individuals/) density to the two sides of Plexiglas channels. Snails at normal densities cropped periphyton biomass to low levels regardless of light regime, but periphyton productivity was higher at the open sites where snails grew faster and accumulated more lipid. Snail growth and lipid accumulation were strongly affected by intraspecific com- petition in both light regimes. In the second experiment, photosynthesis-irradiance curves for periphyton from shaded and open sites illustrated considerable shade adaptation: shaded periphyton was 2 times more efficient at low irradiance than was periphyton from open sites. Despite the greater efficiency of shaded periphyton at low irradiance, integrated primary production estimated with photosynthetic models was 4 times greater in the open because shade adaptation provided only partial compensation for the very low irradiances in the shade. In the third experiment, in situ snail growth again increased with decreasing shade. The growth vs. irradiance response resembled a P-I curve: snail growth increased almost linearly with increased light and then leveled off at a photon flux density of -'~7 mol.m-2.d-l. If this curve primarily reflects rates of food supply, then periphyton production and grazer growth in WOC and similar Streams is light-limited at a photon flux density <7 mol.m-2-d-'. Bottom-up effects of light limitation were propagated very strongly in WOC, where the invertebrate fauna is dominated by a grazer that appears to escape top-down control.
Amy Marcarelli - One of the best experts on this subject based on the ideXlab platform.
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an invasive riparian tree reduces Stream Ecosystem efficiency via a recalcitrant organic matter subsidy
Ecology, 2012Co-Authors: Madeleine M. Mineau, Colden V. Baxter, Amy Marcarelli, Wayne G MinshallAbstract:A disturbance, such as species invasion, can alter the exchange of materials and organisms between Ecosystems, with potential consequences for the function of both Ecosystems. Russian olive (Elaeagnus angustifolia) is an exotic tree invading riparian corridors in the western United States, and may alter Stream organic matter budgets by increasing allochthonous litter and by reducing light via shading, in turn decreasing in-Stream primary production. We used a before-after invasion comparison spanning 35 years to show that Russian olive invasion increased allochthonous litter nearly 25-fold to an invaded vs. a control reach of a Stream, and we found that this litter decayed more slowly than native willow. Despite a mean 50% increase in canopy cover by Russian olive and associated shading, there were no significant changes in gross primary production. Benthic organic matter storage increased fourfold after Russian olive invasion compared to pre-invasion conditions, but there were no associated changes in st...
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An invasive riparian tree reduces Stream Ecosystem efficiency via a recalcitrant organic matter subsidy
Ecology, 2012Co-Authors: Madeleine M. Mineau, Colden V. Baxter, Amy Marcarelli, G. Wayne MinshallAbstract:A disturbance, such as species invasion, can alter the exchange of materials and organisms between Ecosystems, with potential consequences for the function of both Ecosystems. Russian olive (Elaeagnus angustifolia) is an exotic tree invading riparian corridors in the western United States, and may alter Stream organic matter budgets by increasing allochthonous litter and by reducing light via shading, in turn decreasing in-Stream primary production. We used a before-after invasion comparison spanning 35 years to show that Russian olive invasion increased allochthonous litter nearly 25-fold to an invaded vs. a control reach of a Stream, and we found that this litter decayed more slowly than native willow. Despite a mean 50% increase in canopy cover by Russian olive and associated shading, there were no significant changes in gross primary production. Benthic organic matter storage increased fourfold after Russian olive invasion compared to pre-invasion conditions, but there were no associated changes in Stream Ecosystem respiration or organic matter export. Thus, estimated Stream Ecosystem efficiency (ratio of Ecosystem respiration to organic matter input) decreased 14%. These findings show that invasions of nonnative plant species in terrestrial habitats can alter resource fluxes to Streams with consequences for whole-Ecosystem functions.
Wayne G Minshall - One of the best experts on this subject based on the ideXlab platform.
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an invasive riparian tree reduces Stream Ecosystem efficiency via a recalcitrant organic matter subsidy
Ecology, 2012Co-Authors: Madeleine M. Mineau, Colden V. Baxter, Amy Marcarelli, Wayne G MinshallAbstract:A disturbance, such as species invasion, can alter the exchange of materials and organisms between Ecosystems, with potential consequences for the function of both Ecosystems. Russian olive (Elaeagnus angustifolia) is an exotic tree invading riparian corridors in the western United States, and may alter Stream organic matter budgets by increasing allochthonous litter and by reducing light via shading, in turn decreasing in-Stream primary production. We used a before-after invasion comparison spanning 35 years to show that Russian olive invasion increased allochthonous litter nearly 25-fold to an invaded vs. a control reach of a Stream, and we found that this litter decayed more slowly than native willow. Despite a mean 50% increase in canopy cover by Russian olive and associated shading, there were no significant changes in gross primary production. Benthic organic matter storage increased fourfold after Russian olive invasion compared to pre-invasion conditions, but there were no associated changes in st...
Jackson R. Webster - One of the best experts on this subject based on the ideXlab platform.
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recovery of Stream Ecosystem metabolism from historical agriculture
Journal of The North American Benthological Society, 2007Co-Authors: Matthew E. Mctammany, Ernest F. Benfield, Jackson R. WebsterAbstract:AbstractAgriculture has influenced southern Appalachian Streams for centuries, but recent socioeconomic trends in the region have led to extensive reforestation of agricultural land. Stream Ecosystem metabolism might recover from agricultural influence as watersheds undergo reforestation, particularly when shade from terrestrial vegetation is restored. We determined historical (1950) and current (1993) forest cover in 2nd- and 3rd-order watersheds in 4 counties of the southern Appalachians using a geographic information system. Streams were placed into landuse categories based on % forested land cover in watersheds and riparian zones. Categories included forested (FOR; >98% forested) and 3 levels of agriculture (AG; ranging from 95% forest to <60% forest) with no change in % forest over the past 50 y, and 2 levels of recovery from agriculture (REC) indicated by reforestation after land abandonment. We selected 3 Streams from each category and measured gross primary production (GPP) and 24-h respiration (R...
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Recovery of Stream Ecosystem metabolism from historical agriculture
Journal of the North American Benthological Society, 2007Co-Authors: Matthew E. Mctammany, Ernest F. Benfield, Jackson R. WebsterAbstract:AbstractAgriculture has influenced southern Appalachian Streams for centuries, but recent socioeconomic trends in the region have led to extensive reforestation of agricultural land. Stream Ecosystem metabolism might recover from agricultural influence as watersheds undergo reforestation, particularly when shade from terrestrial vegetation is restored. We determined historical (1950) and current (1993) forest cover in 2nd- and 3rd-order watersheds in 4 counties of the southern Appalachians using a geographic information system. Streams were placed into landuse categories based on % forested land cover in watersheds and riparian zones. Categories included forested (FOR; >98% forested) and 3 levels of agriculture (AG; ranging from 95% forest to
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the role of macroinvertebrates in Stream Ecosystem function
Annual Review of Entomology, 1996Co-Authors: J B Wallace, Jackson R. WebsterAbstract:This review focuses on some of the roles of macroinvertebrate functional groups, i.e. grazers, shredders, gatherers, filterers, and predators, in Stream-Ecosystem processes. Many Stream-dwelling insects exploit the physical characteristics of Streams to obtain their foods. As consumers at intermediate trophic levels, macroinvertebrates are influenced by both bottom-up and top-down forces in Streams and serve as the conduits by which these effects are propagated. Macroinvertebrates can have an important influence on nutrient cycles, primary productivity, decomposition, and translocation of materials. Interactions among macroinvertebrates and their food resources vary among functional groups. Macroinvertebrates constitute an important source of food for numerous fish, and unless outside energy subsidies are greater than in-Stream food resources for fish, effective fisheries management must account for fish-invertebrate linkages and macroinvertebrate linkages with resources and habitats. Macroinvertebrates a...
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The role of macroinvertebrates in Stream Ecosystem function.
Annual Review of Entomology, 1996Co-Authors: J B Wallace, Jackson R. WebsterAbstract:This review focuses on some of the roles of macroinvertebrate functional groups, i.e. grazers, shredders, gatherers, filterers, and predators, in Stream-Ecosystem processes. Many Stream-dwelling insects exploit the physical characteristics of Streams to obtain their foods. As consumers at intermediate trophic levels, macroinvertebrates are influenced by both bottom-up and top-down forces in Streams and serve as the conduits by which these effects are propagated. Macroinvertebrates can have can important influence on nutrient cycles, primary productivity, decomposition, and translocation of materials. Interactions among macroinvertebrates and their food resources vary among functional groups. Macroinvertebrates constitute an important source of food for numerous fish, and unless outside energy subsidies are greater than in-Stream food resources for fish, effective fisheries management must account for fish-invertebrate linkages and macroinvertebrate linkages with resources and habitats. Macroinvertebrates also serve as valuable indicators of Stream degradation. The many roles performed by Stream-dwelling macroinvertebrates underscore the importance of their conservation.
