Effects of land-use practice on wetland soil hydrology, salinity, and biogeochemistry in the prairie pothole region
Date
2020-09-21
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
ORCID
0000-0001-6559-0548
Type
Thesis
Degree Level
Doctoral
Abstract
Land-use practice shift to short rotation willow (SRW) can accelerate vegetation linked alterations in the shallow groundwater table (GWT), salinity, and nutrient availability in the hydrologically dynamic wetland riparian zones. Additionally, SRW has higher potentials to sequester soil organic carbon (SOC) and can further impact greenhouse gas (GHG) emissions and extracellular enzyme activities (EEAs). In a field experiment, the effects of SRW were evaluated by measuring the depth to GWT; groundwater and soil electrical conductivity (EC), nutrients (N, P, K, and S), and SOC content with different fractions and chemical compositions in soils (60-cm depth) collected along transects during the first rotation (3-year cycle) and compared with adjacent annual crop (AC), and pasture (PA) in two (site A and B) semi-arid prairie pothole region (PPR) wetland systems. In a microcosm experiment, GHG (CO2, CH4, and N2O) emissions and EEAs [β-glucosidase (BG), N-acetyl glucosaminidase (NAG), and alkaline phosphatase (AP)] were measured in intact soil cores (30-cm depth) collected from the same field sites, and treated with declining water tables (2 to 26 cm depth), and salinity levels (S0 = control, S1 = 6 mS cm-1, and S2 = 12 mS cm-1).
The GWT responded to precipitation patterns. Both groundwater and soil EC varied significantly (p < 0.05), but no consistent land-use patterns were observed between sites. Land-use practices only impacted the GWT depth significantly (p < 0.001) in site B. Soil EC did not vary significantly (p > 0.05) for depths, years, and months. Under SRW, soil NH4+-N and K+ contents were lower, whereas NO3--N, PO43--P, and SO42--S were higher. The groundwater NH4+-N, NO3--N, K+, and SO42--S were significantly higher (p < 0.05) under SRW, whereas PO43--P did not differ significantly (p > 0.05) across land-uses. Total SOC was higher in PA in both sites, but significant (p < 0.05) only in site B. The light fraction organic carbon (LFOC) and particulate organic carbon (POC) followed a similar land-use pattern (i.e., PA > SRW = AC). The SOC and water extractable organic carbon (WEOC) were significantly higher (p < 0.05) at 0-15 cm across land-uses. The ratios of phenolic and amides to polysaccharides were significantly higher (p < 0.05) under SRW than AC and PA in site A. The higher alkyl-C to O-alkyl-C ratio suggested a higher degree of decomposition and better stability of SOC at 15-30 cm. The GHG emissions were significantly (p < 0.001) affected by the soils from different land-uses in the order of PA > AC = SRW. Compared to control, emissions of CO2 and CH4 were significantly lower (p < 0.05), while N2O was significantly higher (p < 0.05) under higher salinity treatments (i.e., S1 and S2). Emissions under declining GWT were significantly (p < 0.001) variable and specific to each gas. The SRW soils had significantly lower (p < 0.05) global warming potential (GWP) than AC and PA. Soil EEAs significantly (p < 0.05) impacted by different land-uses (i.e., PA > AC = SRW), suggested that the effects resulted from background SOC. Soil EEAs were significantly (p < 0.05) reduced under higher depth to GWT except reverse for BG in site B. However, they did not differ significantly among salinity treatments. This research demonstrates that land-use linked variation in GWT and salinity can have a consequential effect on the riparian wetland soil nutrients, SOC, GHG emissions, and EEAs in the PPR.
Description
Keywords
Land-use practice, Short rotation willow, Wetland soil, Prairie pothole region, Hydrology, Groundwater table, Groundwater salinity, Soil nutrients, Soil organic carbon, Soil organic carbon chemical composition, Greenhouse gas emissions, Extracellular enzyme activities, Biogeochemistry
Citation
Degree
Doctor of Philosophy (Ph.D.)
Department
Soil Science
Program
Soil Science