Browsing by Subject "Soil carbon"

Now showing 1 - 3 of 3
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    Carbon-mineral interactions and bioturbation: an earthworm invasion chronosequence in a sugar maple forest in Northern Minnesota
    (2013-05) Lyttle, Amy Marie
    European earthworm species have been introduced into previously glaciated hardwood forests in North America over the past centuries. The invasive earthworms reorganize soil structure, losses of carbon and nitrogen, and the reduction in abundance and diversity of understory communities. One of the direct impacts of earthworms on soils is increased bioturbation, which has domino effects on soil properties that include decrease in litter layer and thickening and increasing bulk density of the A horizons. Such enhanced interactions between organic matter and minerals due to invasive earthworms and earthworms in general have been studied in the context of soil carbon cycle. In this study we attempt to better understand exotic earthworms' impacts on the sorption of organic matter on mineral surfaces and how this fundamental process determining the soil carbon storage and turnover is affected by bioturbation and different earthworm functional groups. Despite the reduction of total C inventory with the arrival of endogeic species, such reduction is largely derived by the loss of light density fraction C. In contrast, the C inventory in heavy density fraction - which we associate with mineral-sorbed - shows little change, which is consistent with likewise stable inventories of mineral surface areas and C-covered mineral surface areas. Mineral-sorbed C pool appears to be in dynamic equilibrium across the diverse ecological stages of earthworm invasion. Our study suggests that the direction and size of changes in soil C inventory in response to bioturbators in general and invasive earthworms specifically will be strongly dependent upon the soil depth profiles of mineralogy and texture.
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    Hillslope redistribution of soil organic carbon in the depressional landscape in Minnesota
    (2014-07) Wu, An-Min
    Agricultural tillage has been estimated to cause a loss of 30-50% of the pre-settlement soil organic carbon (SOC) through enhanced decomposition and loss to the atmosphere or through erosion and subsequently loss to surface waters or burial in lower landscape positions. However, measures of whole landscape redistribution and fate of sediments and SOC are lacking. This research seeks to estimate change in SOC storage since agricultural settlement using soil-terrain modeling techniques in closed-depressional landscapes. The overall quantity of SOC in depressional landscapes may have not been lost to the atmosphere through enhanced decomposition but rather is redistributed downslope.I conducted field observations and soil sampling in hillslope transects in Lake Rebecca Park Reserve in East-Central Minnesota. The thickness of re-deposited sediments (termed post-settlement alluvium, or PSA) was identified by morphological indicators in the field. The spatial distribution of PSA presence and its thickness were modeled with local and regional terrain attributes using a two-stage regression approach. The current SOC inventory (1.119 Pg) in top 1-m soil at the Lake Rebecca site was estimated by spatial predictive models of SOC contents at four soil depths (0-10 cm, 10-30 cm, 30-60 cm, 60-100 cm). I estimated pre-settlement SOC inventory for erosional uplands with spatial predictive models for an uncultivated grassland in Morristown, Minnesota; for depositional lowlands, I calculated pre-settlement SOC inventory by applying models for soil profiles below the PSA depth at the study site. Erosional losses and depositional gains were determined by subtracting current SOC inventory from pre-settlement values.The results showed high SOC contents in surface soils at lower landscape positions, especially in wetlands near the surrounding marsh. Total SOC in the uppermost meter of this 6-ha study site was estimated as 1.528 Gg. The change in SOC density since European settlement was highly overestimated (36.7% increase). The prediction error is likely due to the lack of a mechanism to constrain the prediction of PSA under natural sedimentation patterns at the very bottom of the hillslope beyond the zone where PSA was observed. The model improvement is required to more accurately predict whole landscape SOC distribution and change over time.
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    Impacts of agricultural management and landscape factors on soil carbon and nitrogen
    (2011-12) Van Vleck, Harriet E.
    Agricultural management has altered soil carbon (C) and nitrogen (N) inputs, losses, and turnover rates. Understanding how management interacts with landscape factors to regulate soil C and N losses is essential to addressing climate change. Through research conducted in agricultural systems in Minnesota I investigated: (1) how the loss of corn root-derived C as carbon dioxide (CO2), and N as nitrous oxide (N2O) differed among five management systems, and (2) how hillslope position and soil moisture affected the size and turnover of soil C pools. In a field study using stable isotope techniques, I found that the fraction of root-derived C and N emitted as CO2 and N2O, the C and N emission factors, were 35% and less than 1% respectively. Individually, each emission factor was lower in systems with increased rotation diversity. Conversely, the relationship between C and N emission factors differed with tillage and fertilization intensity, not with rotation diversity. The magnitude of root-derived C and N emission factors has agricultural policy implications. Currently an emission factor of 1% is used for all N inputs to agricultural systems. My research suggests that a lower emission factor would better reflect N2O emissions from belowground N sources.In a laboratory study, both position and soil moisture significantly impacted the size and mean residence time of soil C pools along a low slope hillslope. Intact core sections of the upper four horizons from three hillslope positions were incubated at 50, 75, 90 and 100% water-filled pore space (WFPS) for 355 days. Total soil C (TC), N, and the resistant fraction of TC (64%) increased downslope. Under saturated conditions, 100% WFPS treatment, the size and mean residence time of the labile C fraction (<1% of TC) increased. Increased moisture, between 50% and 90% WFPS, also lengthened the mean residence time of slow C. In this low slope landscape I found effects of both position and moisture on C pool dynamics; soil moisture had the most significant impacts on labile C pool size and the slow C pool mean residence time.