What we do
The Ward Lab largely studies four processes that transform organic carbon in aquatic ecosystems. First, microbes use organic carbon as a food source and respire it to carbon dioxide (CO2; green arrow). Second, sunlight converts organic carbon to CO2 in a process known as photomineralization or complete photochemical oxidation (red arrow). Third, sunlight transforms organic carbon into new, oxygenated compounds in a process known as partial photochemical oxidation (orange arrow). Lastly, some of these partially photo-oxidized compounds are more labile to microbes and can be respired to CO2 in a process known as coupled photo-bio degradation (yellow arrow). We study these processes for a wide range of organic carbon types, including naturally derived organic carbon, like dissolved organic matter, and organic pollutants, like crude oil and plastics. We work in fresh and saline surface waters from the Arctic to the Gulf of Mexico.
Sunlight changes the physical and chemical properties of oil spilled into the ocean. We discovered that over half of the oil floating on the Gulf of Mexico after the 2010 Deepwater Horizon disaster was partially oxidized by sunlight in less than one week. This oxidation has important implications for the long-term fate of the oil and how to effectively respond to oil spills. For example, sunlight oxidation negatively impacted the performance of aerial dispersants that were applied to floating oil after the spill. Expanding on this work, we are currently studying how sunlight oxidation impacts the physical properties of oil, such as aqueous solubility, interfacial tension, density, and viscosity, which collectively influence the behavior of oil at sea.
Our goal is to provide an enhanced understanding of the timescales, products, and controls of the degradation of plastic goods in the environment. We have multiple projects that collectively work towards achieving this goal. Two projects funded by The Seaver Institute and NSF Environmental Chemical Sciences focus on identifying what controls the fate of common consumer products in the sunlit surface ocean. Another project, funded by Eastman Chemical, aims to identify sustainably sourced plastics that demonstrably degrade in the environment. Finally, a project funded by the Gerstner Family Foundation focuses on understanding the potential toxicity of consumer plastic photodegradation products.
We are actively exploring new ways to quantify the degradation of organic carbon in surface waters. Technologies we are developing include (i) LED based methods to probe the wavelength dependence of photochemical reactions, and (ii) a prototype to measures in-situ rates of photochemical oxidation, microbial respiration, and primary production.
Dissolved Organic Matter
Dissolved organic matter (DOM) is a key intermediate in the global carbon cycle. Sunlight alters the chemical composition and fate of DOM in surface waters. We study the rates, pathways, and controls of these light-driven reactions, with focus on photochemical oxidation (O2 consumption) and mineralization (CO2 production).