The effects of animal-sediment interactions on biogeochemical processes at the sediment -water interface

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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 and sediment-water exchange over much of the seafloor. In this project, researchers at the State University of New York at Stony Brook will continue to examine, conceptualize, and quantify specific aspects of these biogenic effects on biogeochemical cycles using newly developed optical sensors and models, and will do so within the context of syn- and 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 biogenic microenvironments determine absolute and relative rates of remineralization pathways, microbial abundances and activities, the coupling between reactions such as sulfate reduction/sulfide oxidation or carbonate dissolution - precipitation, and elemental burial. Such biogenic heterogeneity is virtually impossible to accurately measure or quantify by traditional methods. A set of planar optical sensors designed to measure pH, pCO2, O2 , H2S, simultaneous H2S / O2, and Fe2+ at high resolution (~50 - 100 ìm) in single 2-D images over areas of ~ 100 - 300 cm2 were developed as part of recently funded research, and will be further optimized and applied. The ongoing development of new exoenzyme and Ca2+ sensors will be completed. These sensors will be used to directly investigate three-dimensional solute distributions produced by functionally distinct infauna in laboratory microcosms, and in natural communities in situ, using sediment profiling cameras designed for use with planar optodes. Building on previous microcosm experiments with Nephtys incisa, the effects of selected additional individual species and mixtures of functional types will be examined at multiple densities and constant biomass or biovolume. Biogenic structure and associated remineralization rate patterns will be quantified and hypotheses regarding scaling ? redox 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 at multiple scales will be used together with optical sensors to examine transient and pseudo-steady redox reaction balances and microbial activity as a function of diffusive transport scale for comparison with natural structures of similar scale. The composition, structure, and degradation patterns of representative macrofaunal tube materials, which represent a significant but understudied pathway of sedimentary C, N, P, and metal cycling, will be examined in laboratory and field experiments. Experimental results will be incorporated into integrative 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 optical sensors integrated with 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. Agricultural and soil research may also benefit from planar sensor applications. These capabilities will continue to be promoted and shared through interdisciplinary collaborations. Real time optical sensor images also provide an effective means to communicate the dynamics and importance of benthic biogeochemical processes, and to engage nonspecialists. Planar optode sensor images and in situ Chem-SPI systems will be incorporated as educational and research tools and will also be used as a way to raise general awareness about benthic processes in public forums. 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 peer-reviewed international scientific journals.