Kenneth Fortino edited ResultsOMMineralization.tex  about 8 years ago

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\subsection{Unleached Litter Experiment}  The sediments added to the mesocosms had an estimated dry bulk density that ranged between 0.25 to 0.26 g ml\textsuperscript{-1} and an organic matter content between 12.7 and 12.9\%. Using this information, we estimate that the sediments in the mesocosms contained between 3.16 and 3.33 g of organic matter. The mesocosms that received leaf litter each received between 0.04 and 0.08 additional g of organic matter with the added leaf litter, which would be the equivelent of 11.3 to 22.7 g coarse organic matter m\textsuperscript{-2}. In the lake from which the sediments were collected we measured between 57.3 and 163.0 g coarse organic matter m\textsuperscript{-2}, so the mesocosms used in the experiment contained at most 40\% of the coarse organic matter of the lake. However in the mesocosms all of the leaf litter was added to the surface of the sediments, while a portion of the leaf litter in the lakes was buried within the sediment.  The dissolved oxygen concentration of the overlying water in the bottles ranged from 80.09 to 275.80 $\mu mols$ O\textsubscript{2} L\textsubscript{-1} with a median of 224.80 $\mu mols$ O\textsubscript{2} L\textsuperscript{-1}. The dissolved oxygen concentration varied significantly over the course of the incubation (p < 0.0001)  and was the lowest on the initial day of the incubation (Fig. \ref{fig:DO_days}). Additionally, the bottles containing leaf litter had significantly  lower dissolved oxygen concentrations in the overlying water (p = 0.002) but this was only evident  on day 0 and day 2 of the incubation (Fig. \ref{fig:DO_days}). Over the course of the 21 days of incubation the total oxygen consumption of the bottles ranged between 360 and 2100 $\mu mols$ O\textsubscript{2} m\textsuperscript{-2} h\textsuperscript{-1}, with a median flux of 920 $\mu mols$ O\textsubscript{2} m\textsuperscript{-2} h\textsuperscript{-1}. Since the treatments with added leaf litter had more organic matter in the sediments than those without leaf litter, we normalized the oxygen flux to the estimated organic matter content of the sediments in the bottles. The organic matter normalized oxygen flux ranged from 7.34 to 42.54 $\mu mols$ O\textsubscript{2} (g organic matter)\textsuperscript{-1} h\textsuperscript{-1}, with a median flux of 18.97 $\mu mols$ O\textsubscript{2} (g organic matter)\textsuperscript{-1} h\textsuperscript{-1}.  Thelinear mixed model evaluating the effect of days of incubation, leaf litter presence, and nutrient enrichment on the organic matter normalized oxygen flux had a REML criteria at convergence of 521.6211. The ANOVA on the model results found that the  only factor that affected organic matter normalized oxygen flux was the presence of leaf litter in the bottles. bottles (Table \ref{tab:SOD_ANOVA}.  Bottles containing leaf litter had a mean oxygen flux of 23.85 $\mu mols$ O\textsubscript{2} (g organic matter)\textsuperscript{-1} h\textsuperscript{-1}, which was significantly greater than the mean oxygen flux of 17.67 $\mu mols$ O\textsubscript{2} (g organic matter)\textsuperscript{-1} h\textsuperscript{-1} in the bottles without leaf litter (p = 0.0005; Fig. (Fig.  \ref{fig:sod}). The patterns in Fig. \ref{fig:sod} suggest that the differences difference  in oxygen flux between the bottles with and without leaf litter may have disappeared by the end of the experiment, but there was no significant interaction between the leaf litter and the days of incubation (p = 0.135). The oxygen consumption of the overlying water alone ranged from -3.5 to 3.1 $\mu mols$ L\textsuperscript{-1} h\textsuperscript{-1}, where the negative flux indicates that the oxygen concentration of the water increased during the incubation. The increases in oxygen concentration occurred primarily during the incubations on the initial and fourteenth day of the experiment (Fig. \ref{fig:waterR}). During the initial incubation the increases in oxygen occurred only in the water that came from bottles containing leaf litter (Fig. \ref{fig:waterR}).