Grantee Research Project Results
1998 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, 1997 through September 30, 1998
Project Amount: $800,000
RFA: Water and Watersheds Research (1996) RFA Text | Recipients Lists
Research Category: Watersheds , Water
Objective:
The role of temperate forests in modulating buildup of anthropogenic carbon dioxide (CO2) has been of continuing interest. Most recently, a large midlatitude CO2 sink has been inferred by modeling suggesting that these landscapes may already be active in modulating the anthropogenic CO2 flux. 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 N2 fertilization. A portion of this additional organic carbon is rapidly recycled via respiration to the atmosphere. However, organic carbon fixed in the rooting zone may also be transported in dissolved form as soil waters migrate to the water table. Our research goal is to track how carbon fixed in temperate forest biomass may be transformed via microbial processing and mineral weathering at landscape and shallow subsurface spatial scales. In forested watersheds established on surficial deposits containing carbonate minerals, CO2 enhanced mineral dissolution may provide an important feedback loop between carbon storage capacity of groundwaters and an additional carbon reservoir to that stored in biomass and soils.
Our multidisciplinary approach integrates experimental and natural system measurements on a hydrologically and physiographically constrained catchment within the Cheboygan watershed, located in the uppermost lower peninsula of Michigan. Here, temperate and boreal forests stands have reestablished themselves after logging off in the 1800s. These forests are established atop relatively recent glacial deposits (<10,000 years old), which comprise a large unconfined regional aquifer system. Importantly, the glacial drift deposits contain variable amounts of reactive carbonate minerals (calcite, dolomite) and unstable aluminosilicates, making this an ideal site for investigating soil and rooted zone carbon transformations and fluxes to groundwater systems. The CO2 generated within the rooting zone greatly enhances mineral weathering of very soluble carbonates, which greatly increases carbon transferring from rooting zones to groundwaters relative to carbonate-poor landscapes which dominate the eastern and southern United States. The carbon flux is also manifest in streams and rivers that are largely groundwater fed in this watershed. Our research program addresses how carbon fixed in temperate forests is: (1) transformed via microbial processing, (2) solubilized by mineral weathering, and (3) transported to regional groundwater systems. There are two well studied forest stands (aspen and sugar maple) and an elevated CO2 open-top chamber experiment with variable N-fertilization protocols located within the catchment. The experimental chambers contain juvenile aspens and sugar maples cultivated under controlled conditions of CO2- and N-fertilization. Studies of the natural forest systems permit us to place the experimental chamber carbon transfer mechanisms into a regional C budget.
Progress Summary:
One important component of the project was the characterization of the two natural forest systems and the geochemical fluxes across the study area landscape and subsurface groundwater systems. System characterization required establishment of sampling points for soil and groundwaters across the catchment spanning upland to lowland ecosystems. A regional sampling array of the surface water flow system from the uplands out through the lake reservoir systems also has been established. A water budget and hydrologic model have been made for the upper flow system, including soil moisture and recharge to the unconfined glacial drift aquifers. Detailed measurements of various chemical processes are being made for these sample sites (surface water, groundwater, soil waters, and gases). Geochemical characterization of soil profiles and mineral abundances with depth also have been made across the catchment. Controlled soil leaching experiments show how rapidly carbonate mineral dissolution proceeds in these soil profiles and how closely coupled the process is to ambient CO2 partial pressures. A field level experiment of the biogeochemical response of trees grown in experimental open-top chambers under conditions of varying soil fertility and CO2 partial pressures is another project component. These experimental open-top chambers utilize natural soils and saplings from trees within the catchment (maples, aspens). Each chamber has been equipped with lysimeters and gas wells to sample soil water and gases. A unique aspect of our project is the response of soil PCO2, soil water dissolved inorganic carbon (DIC) and dissolved organic carbon (DOC) fluxes, and mineral weathering rates in the various chamber treatments. Chemistry of soil water, gas, and groundwaters has now been characterized over two field seasons for natural forest and the experimental growth. Soil waters exhibit large vertical chemical variations, generally grading from dilute, dissolved organic carbon-rich solutions in the upper 20 cm into mineralized solutions chemically similar to regional groundwaters by 4 m depth. The CO2 partial pressures determined from soil gas wells show a strong vertical and seasonal gradient; the partial pressures increase from the surface to the base of the rooting zone (about 100 cm), then decline with depth. The decline is strongly related to the depth to the water table. Similar values of CO2 partial pressure were observed within the rooting zones of the unfertilized experimental growth chamber. Nitrogen fertilization greatly increased the CO2 partial pressures and carbonate mineral weathering fluxes from the experimental chambers. Elevated versus ambient PCO2 in the chamber had no discernible effect on soil water chemical fluxes from mineral dissolution.
Mass balance among dissolved carbon species suggests that DOC originating from reactions in the upper rooted zone is transformed to DIC via respiration and coupled mineral solubilization reactions. Dissolved silica and aluminum increase rapidly in soil waters suggesting that aluminosilicates, as well as carbonates, dissolving as DOC (especially organic acid anions) are transformed to DIC. Carbon processing in upper soil horizons is closely linked to mineral dissolution (DIC transport) and related cation fluxes to groundwaters. The significant solute acquisition and carbon transformation evident in soil water profiles suggest that organic processes in the upper soil horizons are closely linked to mineral dissolution (DIC transport) and, in turn, to the overall rate of solute transport to unconfined glacial drift aquifers. The surface water system provides an interesting integrator of seasonal and spatial changes in the balance of respiration/photosynthesis and mineral weathering reactions. Importantly, the DIC content of the system through all of its portions remains at values of 3 mM, close to groundwater values, suggesting that the carbon flux from soil water to groundwater is exported from the catchment without carbonate mineral back precipitation.
Future Activities:
Geochemical and isotopic budget for water and solute sources and chemical fluxes with season and forest environment are still being assessed. Analyses are underway to determine how these systematics vary between the two natural forest sites and with the behavior of the elevated and ambient CO2 open-top chamber tree growth experiments. Modeling efforts will extend the results from nature and the experimental chambers to larger spatial and temporal scales, permitting assessment of how much carbon storage can be accomplished by enhanced mineral weathering and fluxes to regional groundwater systems.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:
hydrology, geology, watershed., 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.