Filters: Tags: Biogeochemistry (X)603 results (243ms)
Role of marine biota in the evolution of terrestrial biota: Gases and genes. Atmospheric composition and evolution of terrestrial biota
Effects of atmospheric change and agriculture on the biogeochemistry and microbial ecology of prairie wetlands
Impact of flash floods on microbial distribution and biogeochemistry in the parafluvial zone of a desert stream
Exchanges between structured canopies and their physical environment: a simple analytical solution for a generic configuration
Snow depth manipulation and its influence on soil frost and water dynamics in a northern hardwood forest
Long-term changes in concentrations of available Ca in soils of red spruce forests have been documented, but remaining questions about the magnitude and regional extent of these changes have precluded an assessment of the current and future status of soil Ca. To address this problem, soil samples were collected in 1992-93 from 12 sites in New York, Vermont, New Hampshire, and Maine to provide additional data necessary to synthesize all available research results on soil Ca in red spruce forests. Sites were chosen to encompass the range of environmental conditions experienced by red spruce. Concentrations of exchangeable Ca ranged from 2.13 to 21.6 cmol(c) kg-1 in the Oa horizon, and from 0.11 to 0.68 cmol(c) kg-1...
Effect of reduced winter precipitation and increased temperature on watershed solute flux, 1988-2002, Northern Michigan
Since 1987 we have studied weekly change in winter (December-April) precipitation, snowpack, snowmelt, soil water, and stream water solute flux in a small (176-ha) Northern Michigan watershed vegetated by 65-85 year-old northern hardwoods. Our primary study objective was to quantify the effect of change in winter temperature and precipitation on watershed hydrology and solute flux. During the study winter runoff was correlated with precipitation, and forest soils beneath the snowpack remained unfrozen. Winter air temperature and soil temperature beneath the snowpack increased while precipitation and snowmelt declined. Atmospheric inputs declined for H+, NO 3- , NH 4+ , dissolved inorganic nitrogen (DIN), and SO...
Multi-scale measurements and modeling of denitrification in streams with varying flow and nitrate concentration in the upper Mississippi River basin, USA
Denitrification is an important net sink for NO3- in streams, but direct measurements are limited and in situ controlling factors are not well known. We measured denitrification at multiple scales over a range of flow conditions and NO3- concentrations in streams draining agricultural land in the upper Mississippi River basin. Comparisons of reach-scale measurements (in-stream mass transport and tracer tests) with local-scale in situ measurements (pore-water profiles, benthic chambers) and laboratory data (sediment core microcosms) gave evidence for heterogeneity in factors affecting benthic denitrification both temporally (e.g., seasonal variation in NO3- concentrations and loads, flood-related disruption and re-growth...
Nitrate reduction in sediments of lowland tropical streams draining swamp forest in Costa Rica: An ecosystem perspective
Nitrate reduction and denitrification were measured in swamp forest streams draining lowland rain forest on Costa Rica's Atlantic slope foothills using the C2H2-block assay and sediment-water nutrient fluxes. Denitrification assays using the C2H2-block technique indicated that the full suite of denitrifying enzymes were present in the sediment but that only a small fraction of the functional activity could be expressed without adding NO3/-. Under optimal conditions, denitrification enzyme activity averaged 15 nmoles cm-3 sediment h-1. Areal NO3/- reduction rates measured from NO3/- loss in the overlying water of sediment- water flux chambers ranged from 65 to 470 umoles m-2 h-1. Oxygen loss rates accompanying NO3/-depletion...