Program
Element 4:
Biogeochemical
Dynamics
Fundamental research in dynamic relationships among in situ geochemical,
geological, hydrological, and microbial processes.
PROGRAM OBJECTIVE
To provide a mechanistic understanding of how microorganisms and contaminants
are transported under coupled and interactive physical, geochemical, and microbial
processes and how underlying molecular and interfacial phenomena and natural
heterogeneities control contaminant and nutrient availability and microbial and
rhizosphere activity in contaminated environments.
BACKGROUND
Many bioremedial processes that are effective in small-scale
laboratory experiments fail in field applications.
Many microbial and geochemical processes that are effective in small-scale
laboratory experiments fail in field applications. This can be attributed to factors
such as geochemical and hydrogeological heterogeneity, spatial variability in the
distribution of contaminants, difficulty in characterizing and interpreting the
geological and hydrological setting, lack of control of nutrient or contaminant
availability and moisture content of the soil, or the lack of sufficient
populations or activity of microbial consortia able to biotransform,
biodegrade, or detoxify the contaminants. Recent experience suggests
that successful bioremediation depends on three factors:
All of these factors depend on the complex and dynamic interplay of
hydrological, geochemical, and biological processes within a geological
medium that is spatially and temporally heterogeneous. Knowledge of
these coupled processes -- based on a fundamental understanding at the
molecular, interfacial, and microbiological scales -- is necessary to
assess natural biogeochemical processes and to harness them for either
intrinsic or enhanced bioremediation.
Scientists must evaluate how environmental factors
interact to enhance or interfere with the survival, growth, and
activity of the microbial community needed for
bioremediation.
Over the past several decades, scientists have made significant progress
toward understanding these processes and their interrelationships. For example, the
important role that speciation and complexation of metals and radionuclides play in
their bioavailability and transport properties is now recognized. Similarly, it is now
recognized that geologic environments are heterogeneous on many scales: individual
mineral grains, coatings on their surfaces, aggregates of several grains, and the
macroscopic variations associated with varying depositional environments and post-depositional events (such as fracturing, faulting, and diagenetic alteration). A basic
understanding of the geochemistry of specific mixtures of organic chemicals and
radionuclides, multiphase flow, transport and surface interactions of
colloids/biocolloids, factors influencing bacterial transport, and the microbiology of
deep geologic formations is also emerging. Progress over the past decades provides
an excellent foundation for future research in this area focused on issues crucial
to bioremediation.
To improve the effectiveness of bioremediation, critical research is needed to:
APPROACH
To meet these critical research needs, the Biogeochemical Dynamics program is
closely tied to research in Community Dynamics and Microbial Ecology,
Biotransformation and Biodegradation, Assessment, Acceleration, and System
Integration, and will focus on three areas of scientific research:
Field and laboratory experiments will take place in parallel, using an iterative
process to identify key issues and track progress toward a field-scale understanding
of these processes and their role in bioremediation. Intermediate-scale facilities will
be used for experiments to investigate processes not manifested at the laboratory
scale, such as hydrologic flow regimes and scaled heterogeneities. The goals of
these experiments are (1) to provide a mechanistic understanding of coupled
physical, hydrological, geochemical, and microbiological processes and how
underlying molecular and interfacial phenomena and heterogeneities control
contaminant transport and availability and microbial movement at the field scale;
and (2) to develop a knowledge base sufficient to predict and manipulate the
influence of interfacial phenomena, contaminant and nutrient availability, and in
situ heterogeneities on the effectiveness of intrinsic and enhanced
bioremediation. Information and results from these experiments will be closely
linked to the System Integration, Prediction, and Optimization element.
Subelement 4.1: Interfacial Phenomena
Fundamental research in thermodynamic, mechanistic, and molecular phenomena that operate
at interfaces in the subsurface, including mineral and cell surfaces and immiscible fluid
boundaries.
Objective
To understand coupled geological, geochemical, and biological mechanisms at
interfaces and how these mechanisms influence or control microbial behavior,
biotransformation, and transport.
Goals
Three-Year
Identify the key mechanistic processes operating at mineral, cell, liquid, and gas
interfaces that control or significantly influence microbial adhesion, transport, and
metabolism.
Five-Year
Identify which interfacial phenomena are important for understanding and predicting
the field-scale behavior of complex contaminant mixtures.
Ten-Year
Develop an extensive body of knowledge that will enable measuring and interpreting
of the field-scale biogeochemical processes that affect bioremediation.
Subelement 4.2: Contaminant and Nutrient
Availability
Fundamental research in geochemistry, microbiology, and transport processes focusing on the
sequestration and recalcitrance of contaminants and the availability of nutrients that can limit or
enhance the effectiveness of bioremediation.
Objective
To understand the fundamental processes responsible for physical inaccessibility
(contaminant sequestration), chemical speciation and complexation, nutrient
availability, and the inherent recalcitrance of complex contaminant mixtures and
how these phenomena influence bioremediation processes.
Goals
Three-Year
Identify the mechanisms by which nutrients and compounds that are biodegradable
in culture are sequestered by the solid phase or other mechanisms (i.e., interlayer and
microaggregate transfer, solid phase molecular diffusion, reversible/irreversible
adsorption, precipitation/dissolution).
Five-Year
Understand the fundamental mechanisms of contaminant sequestration and the
inherent recalcitrance of the key components of complex mixtures, and identify
methods for predicting the extent to which these phenomena influence important
contaminant mixtures in the subsurface.
Ten-Year
Identify microbial, physical, and chemical mechanisms to overcome or minimize
sequestration and recalcitrance phenomena to enhance bioremediation potential.
Subelement 4.3: Spatial and Temporal Heterogeneity
Fundamental research in microbiology, geochemistry, geology, and hydrology, focusing on the
spatial and temporal variability observed in soils, sediments, and aquifers and how the variability
of one parameter is coupled to others and reflected at different scales.
Objective
To develop a fundamental understanding of the influence of physical and chemical
heterogeneity and hydrological dynamics on microbial distribution and community
structure and activity, and how these factors influence the effectiveness of
bioremediation.
Goals
Three-Year
Develop the knowledge and methods required to measure and understand spatial
variability in physical, chemical, and biological properties in soils and aquifers
based on laboratory and intermediate-scale scientific research.
Five-Year
Determine which parameters (i.e., physical, chemical, and/or biological
heterogeneities) must be measured and at what scales to predict the field-scale
effects of heterogeneity on contaminant transport processes and microbial
communities.
Ten-Year
Understand how to use information on natural heterogeneity in space and time and
geochemical transport processes in the effective design and deployment of in
situ bioremediation strategies.
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