4 results for Pendall, E

  • Surface soil organic carbon pools, mineralization and CO2 efflux rates under different land-use types in Central Panama

    Schwendenmann, Luitgard; Pendall, E; Potvin, C (2007-03-22)

    Book item
    The University of Auckland Library

    The chapters in this book cover a broad range of topical research areas, from impacts of different forest-use intensities, sustainable management of ...

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  • Land use and season affect fluxes of CO2, CH4, CO, N2O, H-2 and isotopic source signatures in Panama: evidence from nocturnal boundary layer profiles

    Pendall, E; Schwendenmann, Luitgard; Rahn, T; Miller, JB; Tans, PP; White, JWC (2010-10)

    Journal article
    The University of Auckland Library

    Conversion of tropical rainforests to pastures and plantations is associated with changes in soil properties and biogeochemical cycling, with implications for carbon cycling and trace gas fluxes. The stable isotopic composition of ecosystem respiration (??13CR and ??18OR) is used in inversion models to quantify regional patterns of CO2 sources and sinks, but models are limited by sparse measurements in tropical regions. We measured soil respiration rates, concentrations of CO2, CH4, CO, N2O and H2 and the isotopic composition of CO2, CH4 and H2 at four heights in the nocturnal boundary layer (NBL) above three common land-use types in central Panama, during dry and rainy seasons. Soil respiration rates were lowest in Plantation (average 3.4 ??mol m???2 s???1), highest in Pasture (8.3 ??mol m???2 s???1) and intermediate in Rainforest (5.2 ??mol m???2 s???1). ??13CR closely reflected land use and increased during the dry season where C3 vegetation was present. ??18OR did not differ by land use but was lower during the rainy than the dry season. CO2 was correlated with other species in approximately half of the NBL profiles, allowing us to estimate trace gas fluxes that were generally within the range of literature values. The Rainforest soil was a sink for CH4 but emissions were observed in Pasture and Plantation, especially during the wet season. N2O emissions were higher in Pasture and Plantation than Rainforest, contrary to expectations. Soil H2 uptake was highest in Rainforest and was not observable in Pasture and Plantation during the wet season. We observed soil CO uptake during the dry season and emissions during the wet season across land-use types. This study demonstrated that strong impacts of land-use change on soil???atmosphere trace gas exchange can be detected in the NBL, and provides useful observational constraints for top-down and bottom-up biogeochemistry models.

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  • Response of soil organic matter dynamics to conversion from tropical forest to grassland as determined by long-term incubation

    Schwendenmann, Luitgard; Pendall, E (2008-09)

    Journal article
    The University of Auckland Library

    Understanding soil organic carbon (SOC) responses to land-use changes requires knowledge of the sizes and mean residence times (MRT) of specific identifiable SOC pools over a range of decomposability. We examined pool sizes and kinetics of active and slow pool carbon (C) for tropical forest and grassland ecosystems on Barro Colorado Island, Panama, using long-term incubations (180 days) of soil and stable C isotopes. Chemical fractionation (acid hydrolysis) was applied to assess the magnitude of non-hydrolysable pool C (NHC). Incubation revealed that both grassland and forest soil contained a small proportion of active pool C (<1%), with MRT of ~6 days. Forest and grassland soil apparently did not differ considerably with respect to their labile pool substrate quality. The MRT of slow pool C in the upper soil layer (0???10 cm) did not differ between forest and grassland, and was approximately 15 years. In contrast, changes in vegetation cover resulted in significantly shorter MRT of slow pool C under grassland (29 years) as compared to forest (53 years) in the subsoil (30???40 cm). The faster slow pool turnover rate is probably associated with a loss of 30% total C in grassland subsoil compared to the forest. The NHC expressed as a percentage of total C varied between 54% and 64% in the surface soil and decreased with depth to ~30%. Grassland NHC had considerably longer MRTs (120 to 320 years) as compared to slow pool C. However, the functional significance of the NHC pool is not clear, indicating that this approach must be applied cautiously.

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  • Effects of forest conversion into grassland on soil aggregate structure and carbon storage in Panama: evidence from soil carbon fractionation and stable isotopes

    Schwendenmann, Luitgard; Pendall, E (2006-10)

    Journal article
    The University of Auckland Library

    Land-use and land-cover strongly influence soil properties such as the amount of soil organic carbon (SOC), aggregate structure and SOC turnover processes. We studied the effects of a vegetation shift from forest to grassland 90 years ago in soils derived from andesite material on Barro Colorado Island (BCI), Panama. We quantified the amount of carbon (C) and nitrogen (N) and determined the turnover of C in bulk soil, water stable aggregates (WSA) of different size classes ( < 53 ??m, 53???250 ??m, 250???2000 ??m and 2000???8000 ??m) and density fractions (free light fraction, intra-aggregate particulate organic matter and mineral associated soil organic C). Total SOC stocks (0???50 cm) under forest (84 Mg C ha^???1) and grassland (64 Mg C ha^???1) did not differ significantly. Our results revealed that vegetation type did not have an effect on aggregate structure and stability. The investigated soils at BCI did not show higher C and N concentrations in larger aggregates, indicating that organic material is not the major binding agent in these soils to form aggregates. Based on ??^13C values and treating bulk soil as a single, homogenous C pool we estimated a mean residence time (MRT) of 69 years for the surface layer (0???5 cm). The MRT varied among the different SOC fractions and among depth. In 0??? 5 cm, MRT of intra-aggregate particulate organic matter (iPOM) was 29 years; whereas mineral associated soil organic C (mSOC) had a MRT of 124 years. These soils have substantial resilience to C and N losses because the >90% of C and N is associated with mSOC, which has a comparatively long MRT.

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