UVM Theses and Dissertations
Format:
Print
Author:
Kaur, Amninder Jit Kaur
Dept./Program:
Plant and Soil Science
Degree:
PhD
Abstract:
Wet soils are generally assumed as nitrate sinks because of increased denitrification potential; however they may be acting as sources of nitrate. The complex nature of hydrology of a site could affect biological N cycling process in the soils. Soils in and around enriched groundwater seeps may be sources or sinks of nitrate, and this role may alternate with wetting and drying conditions.
We investigated the effect of soil moisture and temporal variation on nitrification rates by comparing in-seep soils with nearby well drained soils of two forested watershed of Vermont. The soils at both sites are sandy loams and vegetation comprised of northern hardwoods mainly sugar maple. Gross nitrogen transformation rates of the soils were measured using a ¹⁵N isotopic pool dilution method. Rates were variable but there were many instances of gross nitrification rates being greater in nearly-saturated seep soils compared with drier upland soils. Denitrification rates were calculated by measuring the change in the ¹⁵N of both N₂O and N₂ during the incubation for gross nitrification. Both nitrification and denitrification were occurring in the same cores. Rates varied seasonally and in response to soil moisture. Seep soils were contributing nitrate to the stream and the nitrate flowing through the seep and stream fluctuated with changing seasons.
Disturbance of forest soils, both research-induced and natural, has been found to promote net nitrification. We evaluated the effects of soil sampling disturbance on net nitrification rates in soils from two forested watersheds. Increased gross and net nitrification rates were measured in mixed soils compared to intact cores. Because there were similar gross ammonification rates in both treatments, increased nitrification must have replaced a different pathway of ammonium consumption. Nitrate consumption was decreased somewhat by disturbance but did not account for the large differences in net rates.
We investigated the effect of soil moisture and temporal variation on nitrification rates by comparing in-seep soils with nearby well drained soils of two forested watershed of Vermont. The soils at both sites are sandy loams and vegetation comprised of northern hardwoods mainly sugar maple. Gross nitrogen transformation rates of the soils were measured using a ¹⁵N isotopic pool dilution method. Rates were variable but there were many instances of gross nitrification rates being greater in nearly-saturated seep soils compared with drier upland soils. Denitrification rates were calculated by measuring the change in the ¹⁵N of both N₂O and N₂ during the incubation for gross nitrification. Both nitrification and denitrification were occurring in the same cores. Rates varied seasonally and in response to soil moisture. Seep soils were contributing nitrate to the stream and the nitrate flowing through the seep and stream fluctuated with changing seasons.
Disturbance of forest soils, both research-induced and natural, has been found to promote net nitrification. We evaluated the effects of soil sampling disturbance on net nitrification rates in soils from two forested watersheds. Increased gross and net nitrification rates were measured in mixed soils compared to intact cores. Because there were similar gross ammonification rates in both treatments, increased nitrification must have replaced a different pathway of ammonium consumption. Nitrate consumption was decreased somewhat by disturbance but did not account for the large differences in net rates.