Selected Projects

The chemistry of drainage basins: The Pulse-Shunt Concept

Abstract Excerpt:

The transfers of carbon, nutrients and pollutants from the land to streams and their changes as they move through river networks are issues that motivate environmental scientists and water resource managers. Dissolved organic matter (DOM) is a central chemical in streams and rivers that affects the forms and movements of contaminants, light penetration through the water, metabolism of life in the streams, pH, and the efficiency of water treatments by municipalities. This study aims to improve predictions of DOM formation and movement from small headwater streams and our understanding of the factors that change the amount and forms of DOM during as it moves downstream. One goal of this research is to greatly improve a computer model of DOM transport and transformation as it moves through a watershed and into the headwater streams. This model links rainfall and runoff that generate streamflow to the biological and chemical processes that lead to changes in the amount and forms of DOM. The model will be tested against actual measurements of DOM made in several headwater streams of the Connecticut River along its length. Measurements will then also be made in larger parts of the Connecticut River downriver that will help explain how DOM changes along the entire drainage network. This project challenges a long standing picture of how streams and rivers work, called the River Continuum Concept, proposing that a newer view may be required, referred to as the Pulse-Shunt Concept. 


Watersheds Rules of Life

Part of the NSF "Understanding the Rules of Life" Big Ideas initiative.

Abstract Excerpt:

Rivers are the circulatory systems of the continents, delivering land-derived water, pollutants and elements to the ocean. They are also sites with unique organisms, food webs, and microbial communities that can transform these materials during transport to the ocean. Microbes are the engines for these transformations, with considerable capacity to remove or alter important elements (e.g., carbon, nitrogen, phosphorus, mercury, arsenic), produce greenhouse gasses, and support food webs. However, due to large changes in water flow from day to day, and the big differences in the types of streams and rivers across the landscape, understanding how riverine microbes impact the chemistry of rivers is difficult. This project will research a set of "Watershed Rules of Life" that govern the establishment of riverine water column microbial communities that are critical to understanding rivers as circulatory systems. The researchers have proposed a set of hypotheses that adds microbial ecology into the scaffolding of hydrology and geomorphology in order to research these Watershed Rules of Life. The hypothesis will be tested by field work and modeling in a diverse set of watersheds throughout the United States. The knowledge gained by these studies will allow for a broader understanding of rivers in both the U.S. and other temperate regions of the world. 



Microbial diversity and organic matter in major rivers

Abstract Excerpt:

Rivers and streams are the major conduits for transporting of Earth's carbon from the land to the oceans. Much of the carbon is in a dissolved organic form, and it serves as food for aquatic microorganisms. The challenge is that the chemical diversity of dissolved organic carbon is very great, and the genetic diversity of aquatic microbes is also immense. Accordingly, this project will use state-of-the art genomic methods to study the diversity and specific functions of these microorganisms. The results will fill a critical gap in understanding the specific metabolic capabilities of these microbes and how they carry out the key ecosystem function of transforming and metabolizing highly complex, riverborne dissolved organic carbon. The data that will be collected are important for predicting the impacts of land-use change, nutrient use, and shifting climate on freshwater quality across the USA. The research involves a collaboration with the Yale Peabody Museum Evolution program for inner-city New Haven high-school students to train interns and develop an interactive museum exhibit on U.S. rivers. The project will also train a postdoctoral researcher, and undergraduate and graduate students, including members of underrepresented groups in science.

Greenhouse gas evasion from streams and rivers

Abstract Excerpt:

Inland waters cover a small area of the planet and thus their impact on global budgets has received limited systematic study. Nevertheless, idiosyncratic approaches, have, in recent years, suggested that inland waters are key "hot spots" that control the processing of carbon at the global scale. The study of the roles of both the ocean and the terrestrial biosphere have made stunning achievements by launching systematic large regional- to- global networks. In contrast, the study of inland waters has lagged, largely due to lack of any centralized coordination and synthesis.

The proposed synthesis activities will launch a systematic program to refine and scale-up inland water fluxes. The proposal will catalyze an international group of scientists with specialties ranging from geomorphology to remote sensing to biogeochemistry. The lead PI, Raymond, led a grass-roots effort to include inland waters in regional and global fluxes as part of the Global Carbon Project's (GCP) REgional Carbon Cycle Assessment and Processes (RECCAP) project. One of the conclusions of the RECCAP work is that sustained, organized study would be highly beneficial moving forward. The proposed work consists of a number of research activities in Years 1 and 2 that have already been defined as major shortcomings coupled with a series of workshops to continue and broaden synthesis activities, with emphasis on engaging scientists in tropical regions that have little data.