A5003912698- Soil Carbon and Nitrogen Dynamics
- Geology and Paleoclimatology Research
- Isotope Analysis in Ecology
- Soil and Water Nutrient Dynamics
- Atmospheric and Environmental Gas Dynamics
- Groundwater and Isotope Geochemistry
- Peatlands and Wetlands Ecology
- Cryospheric studies and observations
- Soil erosion and sediment transport
- Archaeology and ancient environmental studies
- Climate variability and models
- Pacific and Southeast Asian Studies
- Arctic and Antarctic ice dynamics
- Soil and Unsaturated Flow
- Geochemistry and Geologic Mapping
- Soil Geostatistics and Mapping
- New Zealand Economic and Social Studies
- Rangeland and Wildlife Management
- Hydrology and Watershed Management Studies
- Polar Research and Ecology
- Atmospheric chemistry and aerosols
- Water Quality and Pollution Assessment
- demographic modeling and climate adaptation
- Coastal wetland ecosystem dynamics
- Agriculture Sustainability and Environmental Impact
Motu Economic and Public Policy Research
2023-2025
University of Auckland
2022-2023
University of Waikato
2018-2022
Victoria University of Wellington
2022
GNS Science
2011-2020
Crown Research Institutes
2002-2010
Manaaki Whenua – Landcare Research
2001-2008
Cadre Research
2004-2007
University of California, Berkeley
1998-2003
Massey University
2001-2002
We compiled new and published data on the natural abundance N isotope composition (δ 15 values) of soil plant organic matter from around world. Across a broad range climate ecosystem types, we found that δ values systematically decreased with increasing mean annual precipitation (MAP) decreasing temperature (MAT). Because most undisturbed soils are near steady state, observations suggest an fraction losses N‐depleted forms (NO 3 , 2 O, etc.) MAP MAT. Wetter colder ecosystems appear to be...
Over time scales of thousands to millions years, and in the absence rejuvenating disturbances that initiate primary or early secondary succession, ecosystem properties such as net productivity, decomposition, rates nutrient cycling undergo substantial declines termed retrogression. Retrogression results from depletion reduction availability nutrients, can only be reversed through disturbance resets system; this differs age‐related forest productivity are driven by shorter‐term depression...
We measured 14 C/ 12 C in density fractions from soils collected before and after atmospheric thermonuclear weapons testing to examine soil organic matter (SOM) dynamics along a 3 million year California chronosequence. The mineral‐free particulate (FPOM; <1.6 g cm −3 ) mainly contains recognizable plant material, fungal hyphae, charcoal. Mineral‐associated light (1.6–2.2 display partially or completely humified fine POM, while the dense fraction (>2.2 consists of relatively OM‐free...
Quantifying global patterns of terrestrial nitrogen (N) cycling is central to predicting future primary productivity, carbon sequestration, nutrient fluxes aquatic systems, and climate forcing. With limited direct measures soil N at the scale, syntheses (15)N:(14)N ratio organic matter across gradients provide key insights into understanding cycling. In synthesizing data from over 6000 samples, we show strong relationships among isotopes, mean annual temperature (MAT), precipitation (MAP),...
Abstract The conversion of two‐thirds New Zealand's native forests and grasslands to agriculture has followed trends in other developed nations, except that pastoral grazing rather than cropping dominates agriculture. initial land pasture decreased soil acidity elevated N P stocks, but caused little change organic C stocks. However, less is known about nutrient stock changes during the last two decades under long‐term management. We resampled 31 whole profiles pastures spanning seven orders...
Abstract. Accurate national scale greenhouse gas source and sink estimates are essential to track climate mitigation efforts. Inverse models can complement inventory-based approaches for emissions reporting by providing independent underpinned atmospheric measurements, yet few nations have developed this capability carbon dioxide (CO2). We present results from a decade-long (2011–2020) inverse modelling study New Zealand, which suggests persistent in Zealand’s terrestrial biosphere (-171 ±...
We examine soil organic matter (SOM) turnover and transport using C N isotopes in profiles sampled circa 1949, 1978, 1998 (a period spanning pulse thermonuclear 14 enrichment of the atmosphere) along a 3‐million‐year annual grassland chronosequence. Temporal differences Δ indicate that inputs recently living (OM) occur primarily upper 20–30 cm but suggest OM can below primary rooting zone. A three‐pool SOM model with downward captures most observed variation C, percentages N, δ 13 15...
Abstract. Devising agricultural management schemes that enhance food security and soil carbon levels is a high priority for many nations. However, the coupling between productivity, stocks organic matter turnover rates still unclear. Archived samples from four decades of long-term crop rotation trial were analyzed (SOM) cycling-relevant properties: C N content, bulk composition by nuclear magnetic resonance (NMR) spectroscopy, amino sugar short-term bioavailability assays, modeling...
Predictive understanding of precipitation δ2H and δ18O in New Zealand faces unique challenges, including high spatial variability amounts, alternation between subtropical sub-Antarctic sources, a compressed latitudinal range 34 to 47 °S. To map the isotope ratios across Zealand, three years integrated monthly samples were acquired from >50 stations. Conventional mean-annual maps produced by regressions using geographic annual climate variables. Incomplete data short-term variation sources...
Abstract. High-resolution, well-dated climate archives provide an opportunity to investigate the dynamic interactions of patterns relevant for future projections. Here, we present data from a new, annually dated ice core record eastern Ross Sea, named Roosevelt Island Climate Evolution (RICE) core. Comparison this with reanalysis 1979–2012 interval shows that RICE reliably captures temperature and snow precipitation variability in region. Trends over past 2700 years are shown be distinct...
We characterized the effect of large‐scale (>20 mm) soil physical structure on age and recalcitrance organic carbon (SOC) in upper (A) lower (B) horizons grassland soils from California's Central Valley. The radiocarbon content SOC surfaces interiors structural units (“peds”) was measured order to characterize spatial distribution C pools with distinct residence times. CO 2 released following sieving used identify that is readily respired upon disturbance structure. found longest times...
Hydrologic losses can play a key role in regulating ecosystem nutrient balances, particularly regions where baseline cycles are not augmented by industrial deposition. We used first‐order streams to integrate hydrologic at the watershed scale across unpolluted old‐growth forests New Zealand. employed matrix approach resolve how stream water concentrations of dissolved organic carbon (DOC), and inorganic nitrogen (DON DIN), phosphorus (DOP DIP) varied as function landscape differences climate...
Radiocarbon analysis is an important tool in quantifying soil organic matter (SOM) dynamics within the terrestrial carbon cycle. However, there increasing appreciation that representing SOM as a single, homogeneous pool with mean 14 C concentration inadequate. We investigate whether differing patterns CO 2 release during ramped-temperature oxidation reflect of different ages, and hypothesize thermally labile (combusting at low temperatures) consists younger than resistant matter. Topsoil...