Comparison of biogeochemical functions between restored and natural bottomland hardwood wetlands.

摘要

The purpose of this research was to compare biogeochemical functions of restored and natural bottomland hardwood (BLH) wetlands to determine if re-establishment of hydrology and vegetation is equivalent to restoration of ecosystem function. Three wetland types were studied: natural BLH (NAT), restored with hydrology re-established (RWH), and restored without hydrology re-established (RWOH). Denitrification potential (DEA), soluble organic carbon (SOC), soil moisture, readily mineralizable carbon (RMC), and heterotrophic microbial activity were measured seasonally from 1997--99. Leaf litter mass, total carbon and nitrogen concentrations, moisture, and microbial activity were also measured at three soil depths in study wetlands. The effect of organic matter amendments on microbial activity and denitrification rates was determined during a one-month incubation. Mean ng nitrous oxide evolved/g soil/day for NAT, RWH, and RWOH were 657, 372, and 162, respectively, with a significant difference among wetland types measured in fall. During the two-year period, average soil saturation in the upper 15 cm was 4, 4.25, and 2 months, for NAT, RWH, and RWOH, respectively. Carbon amendments added to restored wetland soils significantly increased denitrification rates and microbial activity but there were no differences in measured parameters among wetland types. Although no significant differences were detected among wetland types for RMC, SOC, and three of the four seasons for heterotrophic microbial activity, values were consistently highest in NAT and lowest in RWOH. Litter mass was significantly higher on NAT soils than on restored, corresponding to higher microbial activities in NAT soils than in restored. Because parameters measured in the RWH wetland soils were much higher than those in RWOH soils, these results illustrate that changes in hydrology will effect changes in soil characteristics and microbial dynamics. Therefore, a BLH wetland restored without re-establishing hydrology will not have biogeochemical functions comparable to those of a natural BLH wetland. Although RWOH soils have the capability to denitrify, because these wetlands are not connected to the surface hydrology of the watershed they will not be in contact with nitrate and thus will not be important in removing nutrients from agricultural runoff water.