September 2007, Vol. 19, No.9

Research Notes

Geologists Suggest Potential ‘On–Off Switch’ for Atlantic Hurricanes

The frequency of intense hurricanes in the Atlantic Ocean seems to be closely connected to long-term trends in the El Niño–Southern Oscillation and the West African monsoon, according to new research from the Woods Hole Oceanographic Institution (WHOI; Falmouth, Mass.). Geologists Jeff Donnelly and Jonathan Woodruff made that discovery while assembling the longest-ever record of hurricane strikes in the Atlantic basin, according to a WHOI news release.

Donnelly and Woodruff began reconstructing the history of land-falling hurricanes in the Caribbean in 2003 by gathering sediment-core samples from Laguna Playa Grande on Vieques (Puerto Rico), an island extremely vulnerable to hurricane strikes. They examined the cores for evidence of storm surges — distinctive layers of coarse-grained sands and bits of shell interspersed between the organic-rich silt usually found in lagoon sediments — and pieced together a 5000-year chronology of land-falling hurricanes in the region.

In examining the record, they found large and dramatic fluctuations in hurricane activity, with long stretches of frequent strikes punctuated by lulls that lasted many centuries, the news release notes. The team then compared their new hurricane record with existing paleoclimate data on El Niño, the West African monsoon, and other global and regional climate influences. They found the number of intense hurricanes (categories 3, 4, and 5 on the Saffir–Simpson scale) typically increased when El Niño was relatively weak and the West African monsoon was strong.

“The processes that govern the formation, intensity, and track of Atlantic hurricanes are still poorly understood,” said Donnelly, an associate scientist in the WHOI Department of Geology and Geophysics. “Based on this work, we now think that there may be some sort of basinwide ‘on–off switch’ for intense hurricanes.”

Donnelly and Woodruff published their latest results in the May 24 issue of the journal Nature.

For more information, contact Donnelly at  

Pinpointing the Source of Fecal Bacteria

 Excessive levels of fecal bacteria were to blame for almost 60% of Nebraska streams deemed impaired by federal and state environmental laws in 2004, according to a news release from the American Society of Agronomy (ASA; Madison, Wis.). In order to develop effective pollution control strategies, it is important for researchers to identify the source of contamination. By using multiple methods, or a “toolbox” approach, to determine the origin of fecal pollution in streams, researchers were able to identify the source of fecal bacteria with greater certainty than if testing with a single method.

In collaboration with the Nebraska Department of Environmental Quality, the U.S. Environmental Protection Agency (EPA), and the University of Cincinnati, U.S. Geological Survey (USGS) scientists used a toolbox approach when investigating the sources of fecal bacteria within the Plum Creek watershed in south-central Nebraska. The scientists report their findings in the May–June 2007 issue of the Journal of Environmental Quality.

In 2001, monitoring studies by the Nebraska Department of Environmental Quality named Plum Creek the most contaminated tributary to the middle reaches of the Platte River. The researchers used two fecal source-tracking tools to analyze contaminated water and stream-sediment samples in the Plum Creek watershed.

The source-tracking tools use genetic material from bacteria collected in water and sediment samples to determine their source, either by comparing the genetic material with that of known fecal bacteria sources or by looking for a “marker” within the genetic material that is associated with a specific fecal source. The results revealed that cattle and wildlife were the dominant sources of fecal bacteria found in water and stream sediment samples at the main study site, located in an upper reach of the creek, the ASA news release notes.

“While the two methods led to similar overall interpretations, using both methods together gave us a clearer picture of potential sources and the strengths and weaknesses of the methods used,” said USGS hydrologist Jason Vogel, lead author of the study report. “Additionally, results from bacteria found in stream-bottom sediment also suggest that different tools for tracking fecal contamination may have varying relevance to the more specific goal of tracking the sources of E. coli in water or soil within the watershed.”

Ongoing studies at USGS and EPA are testing the use of microorganisms as tools for tracking fecal contamination. Fecal bacteria can enter watersheds from specific sources, such as wastewater treatment outfalls, and from diffuse sources, such as runoff from fields where livestock waste has been applied as fertilizer. Determining the source of the bacteria is necessary to implement appropriate pollution control practices and comply with water quality standards required by the Clean Water Act. Further research is needed to continue to develop and refine existing and new tools for identifying the sources of fecal contamination in water and sediment, according to ASA.

To read the Journal of Environmental Quality article, see;36/3/718.