C. Chang | USGS Science

USGS2009

Pilot- and bench-scale testing of faecal indicator bacteria survival in marine beach sand near point sources

Aim: Factors affecting faecal indicator bacteria (FIB) and pathogen survival/persistence in sand remain largely unstudied. This work elucidates how biological and physical factors affect die-off in beach sand following sewage spills. Methods and Results: Solar disinfection with mechanical mixing was pilot-tested as a disinfection procedure after a large sewage spill in Los Angeles. Effects of solar exposure, mechanical mixing, predation and/or competition, season, and moisture were tested at bench scale. First-order decay constants for Escherichia coli ranged between -0??23 and -1??02 per day, and for enterococci between -0??5 and -1??0 per day. Desiccation was a dominant factor for E. coli but not enterococci inactivation. Effects of season were investigated through a comparison of experimental results from winter, spring, and fall. Conclusions: Moisture was the dominant factor controlling E. coli inactivation kinetics. Initial microbial community and sand temperature were also important factors. Mechanical mixing, common in beach grooming, did not consistently reduce bacterial levels. Significance and Impact of the Study: Inactivation rates are mainly dependent on moisture and high sand temperature. Chlorination was an effective disinfection treatment in sand microcosms inoculated with raw influent. ?? 2009 The Society for Applied Microbiology.

Journal of Applied Microbiology↗

USGS1996

An overview of fire in the Sierra Nevada

Fire, ignited by lightning and Native Americans, was common in the Sierra Nevada prior to 20th century suppression efforts. Presettlement fire return intervals were generally less than 20 years throughout a broad zone extending from the foothills through the mixed conifer forests. In the 20th century, the areal extent of fire was greatly reduced. This reduction in fire activity, coupled with the selective harvest of many large pines, produced forests which today are denser, with generally smaller trees, and have higher proportions of white fir and incense cedar than were present historically. These changes have almost certainly increased the levels of fuel, both on the forest floor and “ladder fuels”—small trees and brush which carry the fire into the forest canopy. Increases in fuel, coupled with efficient suppression of low and moderate intensity fires, has led to an increase in general fire severity. We suggest extensive modification of forest structure will be necessary to minimize severe fires in the future. In high-risk areas, landscapes should be modified both to reduce fire severity and to increase suppression effectiveness. We recommend thinning and underburning to reduce fire-related tree mortality coupled with strategically placed defensible fuel profile zones (DFPZs). DFPZs are areas in which forest structure and fuels have been modified to reduce flame length and “spotting”, allowing effective suppression. This chapter is an overview of work by the fire-subgroup of the Sierra Nevada Ecosystem Project. Details concerning these findings are found in Skinner and Chang 1996; Chang 1996; Husari and McKelvey 1996; McKelvey and Busse 1996; Erman and Jones 1996; van Wagtendonk 1996; and Weatherspoon 1996.

California↗