Decomposition of cattail and bulrush plant parts in a constructed wetland treating pulp mill effluent Public Deposited

http://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/70795c370

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  • Dried cattail and bulrush plant pieces in mesh bags were incubated in the constructed wetland treating Pope & Talbot pulp mill effluent. Two ponds planted with each species and two depth ranges in each pond were chosen, to determine decomposition rates. Bags were withdrawn and analyzed at five time points for the cattail and three for the bulrush. Also a laboratory study was conducted, where ground cattail and bulrush material was incubated aerobically and anaerobically. Both species and control were sampled at five time points. The remaining dry mass and the contents of hemicellulose, cellulose, lignin, and silica was examined. Decomposition rates were determined by fitting the data to the single exponential model with the intercept fixed in 1 (100%). An asymptotic model was used to obtain better fit. The sum of squared errors (SSE) was used as a measure of fit. In the field study the ANOVA revealed no change in decomposition with depth. Neither was there a difference between cattail and bulrush ponds. During the first two days only the cell compounds are drastically reduced. Cellulose and hemicellulose start to decline later. Lignin increased slightly during the first half of the experiment. Decay rates from the single exponential model with the intercept fixed were higher than the ones listed for wetlands by Webster & Benfield (1986). The asymptotic model indicates, that there is a fraction, which does not decompose significantly during the time frame of the experiment. It predicts 36% cattail and 53% bulrush material to be left after one year of decomposition. All samples in the laboratory incubation showed strong leaching during the first day (26.5% for cattail, 23% for bulrush). After this the t-test (95% confidence) showed a significant decay coefficient only for the aerobic cattail samples the model with the best fit. These same samples had an increased cell component, and a very small particle size at the last sampling time (120 days). Neither bulrush nor the anaerobic cattail incubations showed the same effect. Cattail and bulrush plants in the field were labeled to observe the senescence. Their height and in the case of cattail the amount of green and dry leaves was recorded monthly. Plants were harvested once a month until February, and the fiber composition was measured. Cattail was completely dry in January, while bulrush still showed green spots in February. Cattail entered the aquatic system mainly by dropping pieces of leaf tips, less by breaking off and losing the outside leaves. In February the average height of cattail plants was 64.7% of the maximum average height in August. Bulrush plants shortened to 84.1% of the maximum average height from September. Most of the bulrush plants died through nutria, a rodent, which is chopping off the plants. Less material was lost by dropping small pieces off the plant tips.
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