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Effects of log storage on water quality and microbiology in experimental enclosures in Babine Lake, British Columbia Wentzell, Paula Lanette


The environmental impacts of log storage on water quality and microbiology in Babine Lake, B.C. were studied in experimental enclosures. The enclosure work was a two phase study, with data collected during the summers of 1984 and 1985. The experiments performed in the field season of 1984 involved the addition of mixed lodgepole pine (Pinus contorta) and white spruce (Picea glauca) bark debris, in different amounts, to the enclosures to examine effects on water quality (dissolved oxygen, lignins-tannins, total organic carbon, total inorganic carbon, pH, and alkalinity), bacterial activity (heterotrophy), and phytoplanktonic primary production. The 1985 study attempted to simulate a shallow water log storage facility by adding logs to the enclosures. A comparison was made of differences in water quality (including the above measurements plus chemical oxygen demand, nutrients, volatile fatty acids, and carbohydrates), and sestonic bacterial and phytoplanktonic algal populations (enumeration and biomass calculations) between (i) lodgepole pine and white spruce, and (ii) the number of logs per enclosure. The bark enclosure study resulted in organic enrichment of the enclosure ecosystem. More than 50% of the total organic carbon (TOC) was attributed to leached lignins and tannins. The leachate was capable of modifying microorganism production. Phytoplanktonic algal biomass, measured by chlorophyll ɑ, was completely eliminated at high concentrations of bark. Short term laboratory studies with bark leachate inhibited microbial activity of natural aquatic bacteria, however, from the enclosure experiments, it was apparent that with time a population of microbes would develop to utilize the chemically complex leachate. The presence of utilizable organic material (i.e. wood sugars) and an active microbial community resulted in a significant decrease in the dissolved oxygen levels. The results of the log study found significant decreases in the amount of organic extractives leached from logs compared to the TOC concentration in the bark experiment. For example, the TOC concentrations in the 5 log enclosures were approximately 20 mg/l by the end of the 25 day test period (≤ 10% was lignin and tannin carbon) ; this value was significantly smaller compared to the bark experiments, where the TOC levels in the heavy bark treatment (20 kg) reached ≃ 400 mg/l after 25 days. A comparison between the bark and log experiments (on an equivalent bark dry weight basis) found water quality degradation by bark leachates more severe than log leachates. The log leachate stimulated bacterial production and did not adversely affect phytoplankton biomass. The increase in bacterial production, a direct result of (i) an available carbon source, determined by TOC measurements and the very low concentrations of volatile fatty acids and reduced carbohydrates (rapidly utilized), and (ii) an increase in water temperature caused a decrease in dissolved oxygen levels. The spruce log enclosures for both June and July had higher heterotrophic uptake rates than the pine log enclosures. This indicated a difference in the chemical composition of the spruce and pine log leachates. This chemical difference was detected in the TOC and COD measurements and the microbial uptake kinetics experiment. These measurements found that the pine log leachate was more readily degraded (high affinity, Vmax/Kt) by a heterotrophic population than the spruce leachate, and that this difference could account for the higher dissolved oxygen demand of the pine log enclosures compared to the spruce logs. Detailed chemical analyses of the leachates in the presence of microbial inhibitors may help to delineate this discrepancy between the spruce heterotrophic uptake rates and the chemical and bacterial measurements of the pine log leachates. The enclosure studies indicated that log storage in a shallow, poorly flushed, littoral area of a lake would possibly result in an accumulation of organic components leached from the log and bark debris. The organic enrichment of the aquatic ecosystem would contribute to a potential decrease in dissolved oxygen, thus, negatively affecting fish habitat, but could increase microbial production.

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