1. Colloid Mobilization and Biogeochemical Cycling Of Organic Carbon, Nitrogen and Phosphorous in Wetlands

Wetlands, because of their ability to remove nutrients and pollutants before they enter downstream waters, are a valuable component of integrated approaches to manage impairing water resources at the urban-agricultural interface. The biogeochemical processes that control the retention, transformation, and transport of nitrogen (N), phosphorous (P), dissolved organic matter (DOM) and how these processes are affected by colloid mobilization need to be systematically evaluated. The goal of the project is to provide a comprehensive investigation on the mechanisms and processes that control the fate and transport of N, P, and DOM in the unique wetland environment subject to a large range of hydrological and redox conditions; with a special emphasis in the role of colloid mobilization in these processes. Our specific objectives include: (1) To quantify the amount of inorganic N, dissolved and colloidal forms of P, DOM and colloidal OM at the hydrologic inlet and outlet of wetlands; (2) to quantify the amount of colloids mobilized and evaluate their role in the cycling of N, P and DOM in wetlands; (3) to elucidate the mechanisms and dynamic interplay between colloid mobilization and stability, redox conditions, and DOM concentration; and (4) to assess the impact of wetland hydroperiod fluctuations and hydrodynamics on these processes. The objectives will be accomplished through extensive ground water and surface water sampling at three selected freshwater wetland sites (where we have long-term monitoring data) which represent a range in hydroperiod and hydrodynamics, and complimentary laboratory experiments.

2. Bioavailability And Fate Of Articulate And Colloidal Phosphorus Released From Agricultural Sources: A Case Study In The Chesapeake Bay Watershed

The Chesapeake Bay and its watershed suffer from varying degrees of water quality issues fueled by both point and non–point nutrient sources. We believe that the incomplete understanding of the different colloidal and particulate P forms and their corresponding bioavailability in the continuum from source to sink coupled with methodological limitations to track P sources and identify the specific P pools that can be biologically cycled (or remain recalcitrant) in both short and long terms are the major obstacles preventing accurate assessment of the nutrient loads released to open waters. To address this limitation, we apply colloid sciences paired with isotope techniques along with a suite of mineralogical (XRD), microscopic (SEM, TEM, and confocal), elemental, and spectroscopic (1H, 13C, and 31P NMR) methods to quantify particulate and colloidal P in samples collected along the physicochemical and hydrodynamic gradients in the agriculture-source runoff dominated Deer Creek that drains to the lower Susquehanna River and river estuary in the Chesapeake Bay as well as from controlled laboratory experiments. A thorough understanding of the physicochemical and biological mechanisms underpinning mobilization and transport (with or without biological cycling) of colloidal and particulate P in the downstream continuum will provide the scientific foundation for re-assessing current nutrient management plans, existing models on total maximum daily load (TMDL), and widen colloidal/particulate source-based research to identify the extent to which colloidal and particulate P from agricultural sources have contributed to the impaired water quality in the Chesapeake Bay and other watersheds.

3. Hydro-Biophysical Processes Shaping Microbial Contamination in Fresh Produce

Fresh fruits and vegetables have been increasingly associated with outbreaks of foodborne illness. What are the mechanisms that allow foodborne pathogens to attach, survive, colonize or grow on produce surfaces? What are the critical factors affecting pathogen attachment and colonization? We aim to address these questions a cross-disciplinary effort that bring recent advances in the areas of colloid and microbial attachment and transport processes in porous media and individual/agent-based modeling of microbial growth, communication and social behavior and microbial ecology, to the relevant field of food safety. The goal of the project is to provide critical mechanistic understanding of early-stage pathogen contamination in fresh produce by linking surface properties (e.g., hydrophobicity and microscale morphology), hydro-physical conditions (hydration status and aqueous-phase configuration), and the resulting nutrient fluxes with pathogen attachment and in situ microbial population establishment. We use laser scanning confocal microscopy to experimentally quantify microbial attachment and growth to identify the key surface properties and biophysical factors influencing bacterial attachment and colonization on fresh produce. We will develop an individual-based modeling platform that explicitly takes into account microscale geometrical features and aqueous-phase configurations and connectivity that shapes microbial attachment and colonization. This research will improve assessment of risks associated with pathogen contamination of fresh produce as well as new insight into modern food pathogen control protocols and provide additional scientific basis for improving the protocols.