The physics behind wave-driven mixing of river and ocean waters and current-driven wave breaking are not well understood. The current body of work surrounding river-ocean interactions focuses on large rivers. However, small rivers, which are much more strongly influenced by waves, make up the majority of such systems, and contribute significantly to global riverine discharge. Examining the momentum balance of river flow in opposition to wave-driven forcing from the ocean is necessary to understand how waves influence the travel and mixing of river water. One way to measure this interaction is using instrumental drifting buoys that follow the path of the river water and take temporal measurements of water properties. These leave gaps in our knowledge, as such buoys do not provide a description of the entire system, only specific points. To fill in these gaps, Unmanned Aerial Vehicle (UAV) footage was used to understand broader wave-current interactions at the Quinault River mouth, a small river that feeds directly into the Pacific Ocean. The town of Taholah, WA, is on its banks, and faces challenges due to wave-driven flooding. The size of the surf zone, the nearshore region where waves break at high frequency, was mapped with UAV footage, and related back to local environmental conditions, such as tidal phase. At low water, the momentum from the river is maximized, and so is the cross-shore extent of the surf zone. This decreases salinity around the river mouth, as freshwater is trapped by the surf zone. At high tide, these conditions are reversed, and fresh water streams can be detected past the surf zone, suggesting the river water has escaped from this region of high turbulence. The conditions under which these escapes occur are to be understood by combining analyses of UAV footage with drifter and tidal data.

Drinking water is essential in a person’s everyday life. However, not everyone has access to clean drinking water. This research explored the societal, economical, and environmental issues that are involved in helping a small system deliver clean and safe drinking water. The nearby community of Rollinsford, New Hampshire, was studied and worked with to help understand their issues and solve Rollinsford’s problems. As a small community that has approximately 2,600 people, Rollinsford wrestled with many challenges. Such as a need for optimization of their existing corrosion control due to recent lead and copper rule violations. This research explored the challenges faced by Rollinsford on an everyday basis. By expanding their website to include the latest information on lead and copper as well as answering their frequently asked questions, the community better understood the challenges it faced. To develop the best possible economic and environmental options for Rollinsford’s drinking water, we established a direct partnership with the town water facility operator and assisted him with laboratory research and water analyses. People in Rollinsford may not have the information they need about their water supply and might drink dirty water that could affect them for the rest of their lives. Therefore, this research helped inform a small town and provided the knowledge and experience that can then be applied to communities everywhere.

Every year 26,000 pounds of human waste left by Mt. Everest climbers is disposed in pits near Gorak Shep (elevation 16,942ft.), a village close to Everest Base Camp in Nepal. The Mount Everest Biogas Project (MEBP) is working to build an anaerobic digester (AD) adapted to the extreme conditions of Mount Everest to treat this waste. All project materials must be carried by foot, including the biologic seed for starting the reactors. Thus, identification of a near-by seed is a critical step in the project’s success. Archaeal microbial community from five anaerobic digesters in Nepal were profiled. House-hold digesters and a mid-sized municipal digester in Katmandu were compared. The goal was to determine if methanogenic populations critical for establishing anaerobic digestion were similar among the potential seeds. Between 65,511 and 94,602 archaeal sequences were recovered from each sample. The sequences clustered into 580 operational taxonomic units (OTU). Species richness and Shannon-Weaver diversity indices ranged from 238-320 and 2.38-3.03, respectively. Significantly lower proportions of Methanosaeta, an important genus of acetoclastic methanogens, were detected in the municipal AD sample than in household AD samples (31% and 43%, respectively; t-test p=0.05). Conversely, the other known genus of acetoclastic methanogens, Methanosarcina, represented < 0.2% in all samples. Methanogen populations (phylum Euryarchaeota) dominated all samples (73 to 97%). However, household AD samples contained a significantly higher proportion (21% versus 3%, t-test p=0.007) of poorly characterized archaeal phylum with unknown function in anaerobic digesters. Principle Component Analysis (PCA) revealed that 2 of 3 household AD were similar. Thus, while all systems contained the Methanosaeta and other methanogenic species desired for startup of the MEBP AD, continued study of anaerobic digester is needed to understand how microbial communities evolve in response to the extreme temperatures of Mount Everest to assess the prolonged sustainability of the system.

Traditional geotechnical ground improvement processes oftentimes rely on hazardous chemicals and high energy. Microbially Induced Calcite Precipitation (MICP) offers an eco-friendly alternative and is a bio-mediated cementation method that can improve the shear stiffness and strength of soils by cementing particle contacts. In this process, calcite precipitation is initiated by indigenous bacteria through the hydrolysis of urea, which produces solution alkalinity and ammonium. Following treatment, bio-cemented soils contain high concentrations of ammonium by-products that have the potential to harm environmental and human health. Previous research work has been performed to evaluate the ability of rinse injections to remove nitrogen by-products. In this study a meter-scale bio-cementation experiment was performed and developed rinse techniques were examined. Five 3.7-meter, horizontally oriented, rectangular soil columns were cemented and subsequently rinsed with 13 pore volumes of a high pH, calcium chloride solution. Columns varied in applied treatment techniques and soil types. The first received a standard enrichment stimulation solution to achieve a higher bulk ureolytic activity. The second was treated with a reduced enrichment stimulation solution to reduce ureolytic activity and aim for improved uniformity of cementation over the column length. The third column was augmented with Sporosarcina pasteurii to match the ureolytic rate in the standard enrichment column. Fourth and fifth columns both received the reduced enrichment treatment on different soil types, a marine fine sand and a different alluvial sand, respectively. Shear wave velocities, aqueous samples, pore pressure measurements, and soil samples were collected over the course of the experiment. After injecting 13 pore volumes of rinse solution, aqueous samples suggest that ammonium concentrations were reduced from ~500 mM to less than 2 mM in all columns. After a 24 hour retention period, however, increases in concentrations were observed suggesting the potential for ammonium by-product leaching in time. This work moves MICP closer to field implimentation and wider-use.