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Lange, C.L. and S.A. Wittmeyer, 1996. The Contribution of Zebra Mussel (Dreissena SPP.) Feces and Pseudofeces Production to Taste and Odor Episodes in the Niagara River and Lake Erie, Acres International Corporation, Erie Country Water Authority Reprinted from "Zebra Mussels and Other Aquatic Nuisance Species." Ed. by Frank D'itri, Ann Arbor Press, 1996. The Contribution of Zebra Mussel (Dreissena SPP.) Feces and Pseudofeces Production to Taste and Odor Episodes in the Niagara River and Lake ErieINTRODUCTION Studies have identified various taste and odor compounds including methyl-iso-borneal (MIB) and geosmin (trans-dimethyl-trans-9-decalol) (Gerber and Lechevalier, 1965). Certain species of phytoplankton and bacteria are known to produce MIB and geosmin as metabolic byproducts, and have been implicated as the causative agent in taste and odor episodes characterized by earthy-musty tastes and odors (Mallevialle and Suffet, 1987). Organisms most frequently linked to these taste and odor problems have been the Actinomycetes and several genera of the blue-green algae (cyanobacteria). The most common documented taste and odor producing blue-green algae include Oscillatoria spp., Aphanizomenon spp., Anabaena spp., and Microcystis spp. Since 1989, there has been an increase in the number of drinking water taste and odor complaints at the Erie County Water Authority (ECWA). The ECWA uses Lake Erie and Niagara River as its raw water sources, which are both heavily infested with the zebra mussel (Dreissena spp.). As with other water utilities, the onset of increased complaints was coincident with the first occurrence of heavy zebra mussel infestations. Some scientists have proposed that zebra mussels indirectly impact tastes and odors through changes in the phytoplankton community in the pelagic zone (Makarewicz, 1995). Zebra mussels are prodigious filterers, individually capable of filtering up to 16 ml/mg hour for a 15 mm mussel (30 mg Ash Free Dry Weight) or 460 ml/hour (Fanslow et al., 1995). The mussels can filter and retain 100 percent of all particles greater than 1 micron and less than their siphon diameter (Jorgensen et al., 1984). Thus a large colony is capable of profoundly affecting a waterbody by transferring particulates from the pelagic zone to the benthic layer. Food items are digested, and remains expelled as feces. The digestion rate in zebra mussels is poor, as is typical in most bivalves, so much of the food is left undigested or only partially digested (Nichols, 1996). Particulates that are filtered but not ingested, including some algal species, organics and inorganics, are coalesced with mucous into larger solids and expelled through the inhalant siphon as pseudofeces (Reeders and Bij de Vaate, 1990). The size and mass of the pseudofeces limits their resuspension into the pelagic zone, so they generally remain in the interstices of the zebra mussel colony. Living algae produce numerous volatile and non-volatile organic substances that are either simple products of photosynthesis or more complex metabolites. Compounds that cannot be immediately used or stored for future use are excreted and become food for heterotrophic organisms (i.e., bacteria). Many of these extracellular products directly cause tastes and odors in water supplies, and decomposition of these extracellular materials and dead cells constitutes yet another source of taste- and odor-causing compounds in water supplies (Mallevialle and Suffet, 1987). Dead algae can cause taste and odor problems in two ways. First, when algae die and lyse, odorous compounds are released and liberated directly. Secondly, the decaying biomass can produce adequate nitrogen to support bacterial growth, including that of Actinomycetes (MacKenthun and Keup, 1970), which has been implicated as a major taste and odor contributor. Cladophora spp. and Ulothrix spp., although not consumed by the zebra mussels, colonize the zebra mussel beds. Cladophora spp. and Ulothrix spp. are exotic periphytic algae belonging to the division Chlorophyta. Members of this division are documented to be cold tolerant, and algae within this division increase their growth rate in response to increased light intensity and duration, an environment created by the increased water clarity from the filtering activity of zebra mussels. Silvey and Roach (1953) reported finding Actinomycetes inside the cells of Cladophora. Silvey (1953) also reported finding Actinomycetes in the interior of numerous other algae including Chlorella, Nostoc, Anabaena, Melosira, Navicula, and Aphanizomenon, particularly in senescent cells. In 1995, tests were conducted at the ECWA laboratory to investigate a hypothesis that the mussels directly contribute to tastes and odors through feces and pseudofeces production. This production could: 1) concentrate phytoplankton and hasten their degradation, which could result in release of MIB and geosmin; or 2) provide a habitat suitable for taste and odor contributors to flourish, which would result in the increase in MIB and geosmin production. The laboratory study was designed to determine whether the fecal and pseudofecal material itself produced MIB and geosmin. Collected feces/pseudofeces and interstitial material washed from the zebra mussel colony were placed in a series of separate temperature-controlled reactors and monitored over time for MIB and geosmin production.
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