Research Projects

Project at a Glance

Project Status: complete

Title: Vegetation process studies. a final report to the California Air Resources Board integrated watershed study

Principal Investigator / Author(s): Rundell, Philip W

Contractor: Laboratory of Biomedical and Environmental Sciences, UCLA

Contract Number: A6-081-32


Research Program Area: Ecosystem & Multimedia Effects

Topic Areas: Acid Deposition, Ecosystem Impacts


Abstract:

In this final project report, preceded by two final contract reports in previous years, we have focused on aluminum specifically as potentially significant trace element in the terrestrial mineral fluxes of the Emerald Lake basin, and additionally dealt more broadly with the pool sizes and fluxes for all of the major macronutrients, cations and trace elements in the terrestrial vegetation of this basin. The 1206 conifers in the basin are scattered in occurrence, but form the major part of the plant biomass. These conifers comprise 90% of the above-ground biomass in the basin, 73% of the below-ground biomass, and are associated with 5% of the litter biomass. Overall, conifers comprise 85% of the 25.65 metric tons of biomass present. In terms of net annual productivity, the conifers are somewhat less important but still comprise the dominant vegetation unit in terms of biological activity. Conifers account for 62% of net above-ground productivity, more than four times the values for the willow and wet meadow communities which are also significant. Together these three communities account for 90% of the basin-wide, above-ground, net primary productivity. Our below-ground values of net productivity remain with a high uncertainty value, and almost certainly overestimate the levels of growth, particularly for the willow community. Investigations of biogeochemical aspects of aluminum cycling through the terrestrial compartments of the Emerald Lake watershed have established that several communities appear to be rapidly aggrading and accumulating aluminum. Aluminum is released into the soil primarily by the weathering of gibbsite and hydroxy interlayer vermiculite in acid soils. Free A13+ in the soil solution is controlled by weathering and release reactions, but some of this A13+ is absorbed by vegetation. Most of the observed net accumulation of aluminum in vegetation is associated with below-ground tissues, rather than above-ground tissues, this may represent some degree of soil contamination. Overall, aluminum cycling in the watershed is conservative. No evidence exists to suggest that soil acidity itself is adversely affecting plant growth in the basin. Soil pH in the basin range from 4.0 to 5.5 for the typic cryorthod unit comprising much of the Pinus monticola stands. This value seems to be within the pH tolerance range for these conifers. Acidity may, however, have the potential to cause a secondary effect on aluminum solubility which could impact conifer roots. Laboratory experiments with red fir suggest that growth rates of conifer roots may be suppressed in the presence of A13+ levels similar to those measured in soils of the Emerald Lake basin. Field studies and laboratory analyses have been used to quantify standing biomass, net annual primary production, vegetation mineral pool sizes, and vegetation mineral flux rates for nine major plant communities in the Emerald Lake watershed. For conifers, these data are based on a complete census of all trees in the basin. For the other eight communities data were calculated per unit area of that community type and for the basin as a whole. Data for biomass and nutrient pool sizes have been estimated from a variety of both direct measurements and extrapolations from other data (see text). Productivity and nutrient flux data are considered to be accurate for above-ground tissues, but less reliable for below-ground tissues because of inherent problems in sampling these tissues. Root tissues are a very important component of the biological activity of the basin. Although they comprise less than 30% of the existing biomass, we estimate that such tissues comprise 60-70% of the net primary production.


 

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