GEOSMIN AND 2-METHYLISOBORNEOL PRODUCTION IN A MAJOR AQUEDUCT SYSTEM

The California Aqueduct supplies water from Northern California to Sou thern California, dividing into the West and East branches above Pyram id Lake. In July and August 1990, elevated geosmin levels (10-48 ng/l) occurred in the East Branch of the aqueduct, which extends along the southern edge of the Mojave Desert. The geosmin episode was associated with attached algal growths on the sides of the aqueduct. A geosmin-p roducing cyanobacterium, possibly a Microcoleus sp., was isolated from both water and periphyton. In the summer of 1991, elevated levels of 2-methylisoborneol (MIB) occurred in the East Branch of the aqueduct ( up to 78 ng/l), along with lower levels of geosmin. In July 1992, a re currence of MIB production led to a severe off-flavor problem for a wa ter agency that receives water directly from the aqueduct, resulting i n numerous complaints from consumers. In both episodes, a Lyngbya sp. was isolated from periphyton and mud collected near the water's edge. These isolates were strong MIB producers in culture, yielding 240 and 260 mu g/l, respectively. Beginning in 1992, a second, relatively weak MIB producer, a Hyella sp., was isolated from membrane-filter plates inoculated with aqueduct water. These off-flavor episodes - associated with low flows during a drought period - showed that previously untai nted water sources can be affected by these problems when conditions c hange.