Research Projects

Global Nutrient Transport and Effects

Humans have dramatically altered the Earth’s nitrogen, phosphorus, carbon, and silica cycles.  These changes have had both positiveand negative effects on the Earth System and society.  For example, the increased use of N and P fertilizers has made it possible to produce the foodand energy necessary to support a large and growing human population.  However, much of the increased N and P that is used on land is transported by rivers to coastal marine ecosystems, resulting in considerable environmental degradation (e.g., increased algal growth, alteration and loss of seagrasshabitats, increase in extent and duration of anoxic and hypoxic water, harmful algal blooms, and coral reef degradation).  In addition, nutrient enrichment is also increasing the anthropogenic emissions of nitrous oxide, a trace gas in the atmosphere that contributes to global warming and to the destruction of stratospheric ozone.

Nutrient inputs to coastal ecosystems are not evenly distributed globally.  The uneven spatial pattern is the result of the global distribution of human population, and the activities associated with the production and consumption of food to feed those people and to support their energy needs.  In the next 50 years, further increases in the human population and related activities are predicted.  Relating the global spatial patterns of human activities on land to nutrient enrichment of coastal ecosystems (now and in the future) has been a challenge. However, such information is critical if we are to understand linkages between land-atmosphere and coastal ocean processes.  Such knowledge requires the formulation and application of spatially explicit models appropriate for use at global scales. In our lab we work to develop, apply, and refine such models at regional and global scales. We use these models to answer both basic scientific and management-driven questions.

Modeling Nutrient and Organic Carbon Loads and Sources in California's Central Valley Watersheds: Taking Existing Monitoring Data to the Next Stage 

Concentrations of the nutrients nitrate and phosphorous exceed national guidelines in many of the San Joaquin River’s tributaries, contributing to low dissolved-oxygen levels and a rise in the incidence of algal blooms. In the river’s lower reaches, low oxygen levels create a barrier for migrating salmon. High nutrient and dissolved organic carbon concentrations in water destined for public consumption also pose public health issues. The objective of this research is to use existing data and computer models to quantify the fluxes, sources and controls of nitrate, phosphate, and organic carbon throughout the Sacramento and San Joaquin river systems. Some of the specific research questions we are addressing include: 1) What are relative contributions of various land-based sources of dissolved organic carbon and nutrients? 2) How can the ability to predict sources and fluxes of nutrients be improved? 3) How will changes in climate, population growth and increased water demand influence water quality?

Agriculture and Pollution in the Developing World: Understanding the Link Between Fertilizer Use, Greenhouse Gases, and Coastal Change in Sonora, Mexico

Roughly half of the nitrogen fertilizer that's ever been produced on Earth has been used within the last twenty years. This increase in the use of nitrogen fertilizer has led to massive increases in agricultural yield, the amount of grain per unit area. In fact, it has allowed humans to largely avoid the food shortages people have historically predicted to accompany our recent population boom. In this sense, nitrogen fertilizer has been an enormous boon to humans. However, the recent increase in nitrogen use may have serious drawbacks as well. Two of these potential drawbacks are coastal pollution and the increased production of greenhouse gases, leading to global climate change. Our research in the Yaqui Valley investigates the link between agricultural fertilizer use (the largest human source of reactive nitrogen) and its environmental impacts.

Nutrient Transformation and Retention by Lakes and Reservoirs

Lakes and reservoirs play a key role in trapping and removing reactive N, P and Si as these compounds move downstream through watersheds. Our lab studies nutrient cycling and removal in lakes and reservoirs at various scales. Approaches range from the intensive biogeochemical investigation of a local eutrophic reservoir (Lacamas Lake) to regional and global modeling efforts focused on quantifying N, P, and Si removal by lake and reservoir systems. We are particularly interested in improving understanding of seasonal variation in nutrient dynamics, with the hope that this information may be used to reduce nutrient pollution.

Pacific Northwest Watershed Biogeochemistry

A number of issues are emerging regarding nutrient loading and transport in Pacific Northwest watersheds, including non-point inputs of N and P from natural, agricultural, and urban sources and influence of reservoir management on nutrient dynamics in large rivers. In the months and years to come, we will be developing a focus on understanding relationships between land use and nutrient transport in the streams and rivers of this region.