## 4 Discussion
### The Enzyme Activity as Affected by Soil Horizons and Microsites
The latter is important in the context of our study, given that specific enzyme activity increased primarily in mineral soils where enzyme interactions with mineral particles would be most likely to occur [56]. Higher pH has also been shown to enhance enzyme activity [57] and we found a positive correlation between pH and enzyme activity rates expressed per unit mass of SOC or MBC but not per unit mass of soil weight (which exhibited a negative correlation with some enzymes). Shifts in microbial community structure with soil depth, and between natural and drained wetlands, may have played a role in determining enzyme activity, but detailed soil microbial community analysis was not an objective of this study. Soil depth effects on enzyme activity also appear dependent on the type of enzyme, with some studies showing decreases in hydrolytic enzyme activity and no change or increases in oxidative enzymes with depth in northern wetlands, tropical swamp peat soils [34; 36] andarable soils [53]. In our study, hydrolytic enzyme activity in the natural wetland tended to be higher compared to the drained wetland in the organic soil horizons. This may result from the higher SOC content of organic soils of these freshwater forested wetlands ([PERSON] et al., 2019) and high levels of plant and microbial belowground activity [6; 24]. We also found an increase in the activity with soil depth of the oxidative enzyme PER when normalized by SOC and MBC. The presence of higher concentrations of lignin at depth in wetland soils [39] would also elicit increased activity of lignin-degrading enzymes, reflecting the different availability of C substrates in subsurface compared to surface soil horizons [53], and PER activity was previously shown to be of importance to wetland C cycling [9]. In regard to oxidative enzymes, previous studies have reported greater activity of enzymes utilizing oxygen as the electron acceptor in drained wetland soils compared to intact, frequently submerged wetland soils [19]. In addition to oxygen concentration, the concentration of phenolic materials (as suggested by 'enzyme latch hypothesis') or iron content (iron can increase the stability of soil organic carbon) can modify enzyme activities. On the contrary, we found that enzyme activity at the natural wetlands tended to be higher than the drained wetland. This could be attributed to the dynamic hydroperiod at our site supplying ample O\({}_{2}\) to support the functioning of oxidative enzymes, even at depth within the soil profile where anaerobic conditions have traditionally been presumed to dominate [36]. Peroxidase appears to be an especially important oxidative enzyme in these freshwater wetland soils given its high rate of activity, no change or increases with soil depth [36], enhanced activity under freshwater compared to saltwater conditions [9] and exhibiting the highest activity rates of all enzymes measured in this study. Previous work at our site has suggested that PER activity may also be of importance to methane production as higher rates of PER activity correlated with greater methane production from incubated soils [9; 58]. Enzyme activity normalized per unit mass of SOC and MBC was lower in the organic soil horizons of the drained wetland compared to the natural wetland, which was partially contradictory to our hypothesis that drainage would increase microbial activity given previous findings of enhanced organic matter breakdown and microbial activity in drained wetland soils [12; 59]. This suggests that microbes are investing more energy into production of extracellular enzymes responsible for degradation of C compounds with fast to slow turnover times in the Oi and Ooi soil horizons of the natural wetland, potentially as a mechanism to maximize breakdown of SOC or to increase the likelihood that under stressful environmental conditions at least some minimal amount of C will become available for microbial assimilation.