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Blowing dust

Reduction of visibility by strong winds blowing across dry ground with little or no vegetation. Visibilities of 1/8 mile or less over a widespread area are criteria for a Blowing Dust Advisory.

Blueschist

Metamorphic rock formed under great pressures, but not so great temperatures.

BOD5

The biochemical oxygen demand of wastewater during decomposition occurring over a 5-day period. A measure of the organic content of wastewater. See biological oxygen demand.

Boreal

Of or relating to the forest areas of the northern North Temperate Zone, dominated by coniferous trees such as spruce, fir, and pine.

Borehole

Any exploratory hole drilled into the Earth or ice to gather geophysical data. Climate researchers often take ice core samples, a type of borehole, to predict atmospheric composition in earlier years. See ice core.

Botanical pest.

Pesticides whose active ingredients are plant-produced chemicals such as nicotine, rotenone, or strychnine. Also called plant-derived pesticides. Being "natural" pesticides, as distinct from synthetic ones, they are typically acceptable to organic farmers.

Bovine spongiform encephalopathy (BSE)

Commonly known as "mad cow disease," BSE is a slowly progressive, incurable disease affecting the central nervous system of cattle, first diagnosed in Britain in 1986. Consumption by cattle of BSE-contaminated ruminant proteins in animal feed has been cited as one possible means of transmission. Scientists have confirmed a link between BSE in cattle and several dozen recent European cases of a human variant of BSE, Creutzfeldt-Jacob disease. More than 77,000 cattle suspected of having been exposed to the disease have been slaughtered in Great Britain, and a ban on ruminant protein-containing feeds was imposed in 1988. To date, no BSE has been found in U.S. cattle, although other BSE-like animal diseases are found in the United States, including scrapie in sheep and goats. USDA banned the importation of live cattle from Great Britain in 1989, and imposed a partial ban on using ruminant protein in animal feed in 1997.

Braiding of river channels

Successive division and rejoining (of riverflow ) with accompanying islands is the important characteristic denoted by the synonymous terms, braided or anastomosing stream. A braided stream is composed of anabranches.

British thermal unit (Btu)

The quantity of heat required to raise the temperature of one pound of water one degree of Fahrenheit at or near 39.2 degrees Fahrenheit.

Broadcast application

The spreading of pesticides or fertilizers over an entire area (see band application).

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