Concentrated waste plumes from fish farms could travel significant distances to reach coastlines, according to a study co-authored by Roz NaylorOliver Fringer and Jeffrey Koseff of Stanford's Woods Institute for the Environment. The study, published in the journal Environmental Fluid Mechanics, found that relatively high concentrations of dissolved waste from fish pens do not consistently dilute immediately.

The paper provides the first detailed look at how real-world variables - such as tides, currents, the Earth's rotation and the physical structure of the pens themselves - influence the flow of waste from fish farms. The research, which was funded by the Lenfest Ocean Program, can serve as an important tool for determining the impacts of aquaculture discharge on waterways and surrounding shorelines, the authors said. "This study suggests that we should not simply assume 'dilution is the solution' for aquaculture pollution," said Koseff, professor of civil and environmental engineering and co-director of the Woods Institute. "We discovered that the natural environment around fish pens can dramatically affect how far waste plumes travel from the source."

VIDEO: Concentrated waste from fish farms could travel significant distances to reach coastlines, according to a study co-authored by Woods Institute senior fellows Rosamond Naylor and Jeffrey Koseff (2:48)

Waste plumes

Dissolved substances from feces, undigested food and other forms of discharge amass near fish pens. In multiple modeling scenarios in which these factors were varied to study how each one affected the behavior of such pollution, effluent was characterized by plumes of highly concentrated waste that held together for great distances from the source (see video animation of the pollutant plumes).

The findings suggest that regulators need to consider the full range of possible influences on the movement of pollution plumes - and accurately identify the dominant factors - when designing water quality regulations for and monitoring waste from aquaculture.

"Our approach to aquaculture is at an important juncture right now," said Naylor, director of the Program on Food Security and the Environment. She noted that the National Oceanic and Atmospheric Administration is inviting public comments through April 11, 2011, on its draft national aquaculture policy, and that the state of California is implementing new aquaculture regulations.

"As the aquaculture industry grows, so will the number of pens that create pollution," added Naylor, professor of environmental Earth system science and senior fellow at the Woods and Freeman Spogli institutes. "The models that we developed for this study can help regulators determine how waste from proposed fish farms might impact the waterways and coastlines both near and far from the pens."

Oliver Fringer is an assistant professor of civil and environmental engineering at Stanford. Other co-authors are Subhas Venayagamoorthy and Hyeyun Ku of Colorado State University; and Alice Chiu, aquaculture research assistant with Stanford's Program on Food Security and the Environment.

The Lenfest Ocean Program supports scientific research aimed at forging solutions to the challenges facing the global marine environment. The program was established in 2004 by the Lenfest Foundation and is managed by the Pew Environment Group.

The foundation has prepared a two-page summary of the study.