Grantee Research Project Results
1999 Progress Report: Carbon Exchange Dynamics in a Temperate Forested Watershed: A Laboratory and Field Multidisciplinary Study
EPA Grant Number: R824979Title: Carbon Exchange Dynamics in a Temperate Forested Watershed: A Laboratory and Field Multidisciplinary Study
Investigators: Walter, Lynn M. , Teeri, James A. , Meyers, Philip A. , Budai, Joyce M. , Abriola, Linda M. , Zak, Donald R. , Kling, George W.
Institution: University of Michigan
EPA Project Officer: Packard, Benjamin H
Project Period: October 1, 1996 through September 30, 1999 (Extended to September 30, 2000)
Project Period Covered by this Report: October 1, 1998 through September 30, 1999
Project Amount: $800,000
RFA: Water and Watersheds Research (1996) RFA Text | Recipients Lists
Research Category: Watersheds , Water
Objective:
One of the most pressing environmental concerns is the effect that increasing atmospheric carbon dioxide (CO2) from fossil fuel burning will have on earth surface systems. Global CO2 budgets are unbalanced; only two-thirds of the anthropogenic burden can be accounted for by the atmosphere and oceans. The remaining one-third is likely controlled by a terrestrial carbon sink, but this remains an active area of debate and investigation. Our research program addresses, via controlled experiments and watershed-scale study of carbon flow, how carbon stored in temperate forests (as living biomass, litter, and soil organic matter) is transformed via microbial and root respiration to CO2. Although much of the carbon originally fixed by photosynthesis in forest biomass is returned rapidly by respiration, a potentially significant amount of carbon can be solubilized in soil waters during mineral weathering and transported to regional groundwater-surface water systems.Studies of carbon allocation in forests under enhanced and ambient CO2 and nitrogen fertilization growth conditions show that above and below ground carbon storage, as well as root and microbial respiration, all increase at elevated PCO2 and N fertilization. Our multidisciplinary approach integrates experimental and natural system measurements within the Cheboygan watershed, located in the uppermost lower peninsula of Michigan. Like many other forested northern latitude watersheds, it is established on unconsolidated surficial glacial drift deposits that contain significant amounts of calcium carbonate. Carbonate solubility increases strongly with increasing CO2 partial pressure. The CO2 generated within the rooting zone greatly enhances carbonate weathering, which increases carbon fluxes to surface and groundwaters. These geochemical relations contrast sharply with those of carbonate-poor landscapes that dominate the eastern and southern United States.
The investigation was divided into experimental and a natural field components. There are two well studied forest stands (aspen and sugar maple) located within the watershed, and an elevated CO2 open-top chamber experiment with variable N-fertilization protocols has been established at the nearby University of Michigan Biological Station. The experimental chambers contain juvenile aspens and sugar maples cultivated under controlled conditions of CO2- and N- fertilization. One objective was to investigate the soil CO2 profiles and soil water fluxes of carbon as dissolved inorganic carbon (DIC) and as dissolved organic carbon (DOC) from the experimental open-top tree growth chambers to determine what effect CO2 and N fertilization would have on carbon transformation and transport. The other objective was to characterize carbon transformation in natural forest soils to regional groundwater and surface water flow systems, using both direct measurements and well-constrained mathematical modeling of the carbon budget. All of these efforts required study of soil and glacial drift carbon contents and mineral abundances, instrumenting soil water, groundwater and gas sampling arrays, and repeated monitoring/measuring of pertinent chemical and physical parameters over the course of several growth seasons. Modeling and measurements will be integrated to arrive at a quantitative and predictive understanding of how much of the carbon fixed in the temperate forests of Northern Michigan is returned to the atmosphere or transported to surface and groundwater systems.
Progress Summary:
A water budget and hydrologic model have been made for the upper glacial drift aquifer flow system. Detailed geochemical measurements (major elements, DIC, DOC, gas compositions, and stable C, O, and H isotopes of water and DIC) have been made for natural system surface water, groundwater, soil waters, and gases over three seasons. Soil waters exhibit large vertical chemical variations, generally grading from dilute, DOC-rich solutions in the upper 20 cm into DIC-rich solutions by 4 m soil depth. The CO2 partial pressures determined from soil gas wells show strong vertical and seasonal gradients; the partial pressures increase from the surface to the base of the rooting zone (about 100 cm), then decline with depth.After two full seasons of growth, trees in the experimental open top chambers were sacrificed in June 1999, and samples of soil were obtained to compare with those of the initial materials. Analyses of soil water chemistries from the open top chambers were completed in September 1999. They reveal that carbonate mineral dissolution proceeds to near equilibrium rapidly in these disturbed soil profiles, with close coupling between soil CO2 and solubility. Nitrogen fertilization greatly increased the CO2 partial pressures and carbonate mineral weathering fluxes from experimental chamber soil waters. Elevated versus ambient PCO2 in the chamber had no discernible effect on soil water chemical fluxes from mineral dissolution.
Mass balance and kinetic/equilibrium constraints for dissolved carbon species suggest that DOC originating in the rooted zone is transformed to inorganic carbon (DIC) via respiration and coupled mineral solubilization reactions. Carbon processing in upper soil horizons is linked closely to mineral dissolution (DIC transport) and related cation fluxes to groundwaters. The mass balance suggests that for every 100 moles of organic carbon returned to the atmosphere via respiration, one mole is transported to regional groundwaters. The surface water system provides an interesting integrator of seasonal and spatial changes in the balance of respiration/photosynthesis and mineral weathering reactions across the watershed. Importantly, the DIC content at the mouth of the Cheboygan River, which drains the entire watershed, remains at values of 3 mM, close to groundwater values, suggesting that the carbon flux from soil water to groundwater is exported largely from the catchment without carbonate mineral back precipitation. This suggests that "greening" of high latitude forests likely will be accompanied by increased belowground carbon storage, and enhanced DIC and DOC fluxes to regional hydrologic systems.
Future Activities:
In the final year of the project, most effort will be devoted to integrating the various database components from natural and experimental soil horizons. The importance of different carbon transformation processes and pathways will be assessed. These include: soil respiration, DOC and DIC generation and transport from the soil horizons in different forest ecosystems, groundwater DOC/DIC concentrations and mass transport rates, and surface water H2O and carbon fluxes from the watershed. Models of CO2 generation and transport out of the soil system to the atmosphere will be generated, using measurements of soil respiration and CO2 profiles as validation tests on modeling parameters.Journal Articles on this Report : 2 Displayed | Download in RIS Format
Other project views: | All 10 publications | 3 publications in selected types | All 3 journal articles |
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Type | Citation | ||
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Walter LM, Budai JM, Ku TCW, Meyers PA, Baptist K, Abriola LM, Chen Y-M, Zak DR, Kling GW. Carbon exchange dynamics and mineral weathering in a temperate forested watershed (Northern Michigan): links between forest ecosystems and groundwaters. Mineralogical Magazine 1998;62A:1625-1626. |
R824979 (1998) R824979 (1999) R824979 (Final) |
not available |
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Zak DR, Pregitzer KS, King JS, Holmes WE. Elevated atmospheric CO2, fine roots and the response of soil microorganisms: a review and hypothesis. New Phytologist, July 2000;147(1):201-222. |
R824979 (1998) R824979 (1999) R824979 (Final) |
not available |
Supplemental Keywords:
global climate, chemical transport, ecosystem, aquatic, environmental chemistry, engineering, ecology, hydrology, geology, Great Lakes, EPA Region 5, Michigan, MI., RFA, Scientific Discipline, Water, Waste, Ecosystem Protection/Environmental Exposure & Risk, Water & Watershed, Hydrology, Geochemistry, Fate & Transport, Biochemistry, Ecology and Ecosystems, Watersheds, fate and transport, bioassessment, biogeochemical study, soil water chemistry, predictive model, aquatic ecosystems, carbon exchange, carbon flux, ecology assessment models, forested watershedProgress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.