Diagenetic processes in sedimentary deposits play a central role in the cycling and burial of biogeochemically reactive elements. The activities of marine bottom-dwelling animals dramatically impact early diagenesis, altering material transport and reaction distributions in surface sediments over much of the seafloor. The present research will examine, conceptualize, and quantify specific aspects of these biogenic effects on biogeochemical cycles, and will so within the context of synand autecological characteristics of benthos. Feeding, burrowing, and the irrigation of biogenic structures create complex, time-dependent networks of oxic and anoxic microenvironments. The scaling and macro-geometrical patterns of these microenvironments determines absolute and relative rates of remineralization pathways, microbial abundances and activities, and the coupling between reactions such as nitrification - denitrification or carbonate dissolution - precipitation. Such biogenic heterogeneity is virtually impossible to accurately measure or quantify by traditional methods.
IN this project, researchers at the State University of New York at Stony Brook will continue their observational, experimental, and technological development studies of benthic communities and their two-way relationship with sediment chemistry. A set of planar fluorosensors (planar optodes) designed to measure pH, pCO2, and O2 at high resolution (ca. 30 - 50 um) in single images over areas of 100 - 300 cm2 were developed in part during the previous funding period and will be further optimized. A composite sensor will be developed to allow simultaneous measurement of O2, H+, and CO2. These fluorosensors will be used to directly investigate three-dimensional solute distributions produced by functionally different infauna in laboratory microcosms, and in natural communities in situ using a sediment profiling camera modified for use with planar optodes. The effects of both individual and mixtures of functional types will be examined at multiple densities. Remineralization rates around biogenic structures will be quantified and hypotheses regarding scaling - reaction relationships tested. Direct measures of microbial activity around biogenic structures will be guided by the optically sensed patterns. Diffusion-reaction cells designed to simulate the effect of irrigated burrows will be used together with optical sensors to examine transient and pseudo-steady reaction balances and microbial activity as a function of diffusive transport scale for comparison with natural structures of similar scale. Diffusion cell measurements on mucus secretions will be performed to further constrain semipermeable properties, the fractionation of DOC constituents, and metabolic patterns. Additional experiments on decomposition rates of natural interstitial mucus and tube linings will also be carried out. The implications of semi-permeabilty of pore space and anisotropic transport will be incorporated into conceptual and mathematical models.
Broader Impacts: The present research will advance predictive, mechanistic-based understanding of interactions between benthic communities and sediment chemistry, their effect on biogeochemical cycles of societal importance, and the fate of pollutants. The further development and optimization of planar fluorosensors for biogeochemical applications will substantially improve the basis for conceptual and quantitative models of early diagenesis, aid experimental design, and extend capacity for practical in situ monitoring of biogeochemical processes for management purposes. Real time fluorosensor images provide an effective means to communicate the dynamics and importance of benthic biogeochemical processes, and to engage non-specialists. Planar optode sensor images and the in situ fluorosensor REMOTS system will be incorporated as educational and research tools in the Marine Sciences Research Center REU summer program, a field-oriented undergraduate course, and will also be used as a way to raise general awareness about benthic processes through public forums such as the new Sigma Xi science cafe program. Graduate and undergraduate education and technical training will continue to be intimately integrated with laboratory and field research. Results will be presented at national and international meetings, and in international scientific journals.
