Soil Carbon Dynamics: A Catchment Based

Approach

C. Martinez, G. Hancock, J.D. Kalma & T. Wells

NAFE’06 WorkshopFebruary 13-14, 2006

Introduction

• Significance of terrestrial C fluxes within global C budget• Lack of understanding of C dynamics at hillslope, catchment

& regional scales– particularly lack of studies within Australia– Northern Hemisphere (US, Canada) studies dominate (different

environments/conditions)

• What’s driving catchment soil C dynamics?– textural properties?– soil moisture/temperature?– vegetation?– hillslope/catchment hydrology/ geomorphology?

Introduction cont…

• Traditional methods of soil sampling for estimation of SOC

– attempts to reduce/remove the need for soil sampling

– using remotely sensed data

Project Aims

• Investigate the spatial & temporal patterns of soil C dynamics at hillslope & catchment scales

• Model & predict distribution (temporal & spatial) of soil C within Goulburn River catchment using ground based & remotely sensed data

Data Requirements

• Existing SASMAS network of ground based weather, soil moisture/temperature & stream gauges

• Complement with ground based soil & vegetation sampling & additional water quality instrumentation for quantification of DOC at Stanley

• Data collected at 4 scales:– Hillslope (Stanley transects)– Small catchment (Stanley)– Large catchment (Krui)– Regional (SASMAS & NAFE’05)

Data Requirements cont…

• Remotely sensed data (NDVI)– Use to extrapolate ground based hillslope & sub-catchment

scale data to larger catchment & regional scales

– Satellite vs aircraft vs ground based

• Digital elevation models (DEMs)– 25m LPI DEM

– High resolution 5m DEM (DGPS) for Stanley

– LIDAR (1m)???

Current Study

• Soil C dynamics at hillslope (Stanley) & catchment scales (Stanley = small; Krui = large)– Stanley micro-catchment (C, N & 137Cs)

• 7 SASMAS stations (1 = weather station)• 1 flume• 5m DEM (DGPS)• water quality instrumentation (DOC)

– Krui River catchment (C & N)• 13 SASMAS stations (including Stanley)• NAFE’05 (soil moisture, vegetation, soil C & N)

• Regional SOC dynamics– SASMAS network & NAFE’05

Current Study cont…

• Land use management effects on SOC (C & N)

• Remotely sensed data – Landsat (NDVI) > ground (above-ground biomass [AGB]), aircraft &

satellite• SOC dynamics modelling (RothC, CENTURY)

NAFE’05 Regional Data

• AMSR regional scale sampling (Mondays)

– Week 3 (14/11) & Week 4 (21/11)

– teams collected additional soil samples for C & N determination

– total of 88 soil samples (5cm core depth) collected over Krui & Merriwa River catchments by the 4 teams over 2 days

Catchment Scale• Stanley catchment 1ha grid sampling strategy (Week 4 of NAFE’05)

– 175ha Stanley catchment sampled on a 1ha grid (i.e. sample pt every 100m)

– 133 points sampled (see Figure)

– at each sample point, data collected:• soil core (max. depth 22cm)• AGB sample (0.5m x 0.5m quadrat)• soil moisture via thetaprobe (mV)

Stanley Catchment

Sample Processing• Regional scale samples

– wet & dry weights recorded for all samples (determination of volumetric moisture content)

– oven dried at 400C (Uni of Newcastle)– samples disaggregated using mortar & pestle and passed

through 2mm sieve– 50g acidified samples for C & N analysis (LECO – UWA)– particle size analysis (Malvern); pH; EC; CEC

• Stanley catchment samples (same as above)– *** IN ADDITION remaining <2mm fraction analysed for

137Cs (Uni of Newcastle)• Relationships between SOC & soil redistribution

processes (i.e. erosion & deposition)

Initial ResultsAbove-ground Biomass (t/ha) Volumetric Soil Moisture (%)

Soil Depth Sampled (cm)Vegetation Water Content (kg/m2)

Initial Results cont…• DATA TO COME:

– Process soil samples & analyse for C & N (LECO)

– NAFE’05 aircraft data (NDVI & LIDAR?)

– Landsat OR SPOT NDVI data for sampling period (Nov’05)

– 137Cs analysis

– PSA (Malvern)

– pH

– EC

– CEC

NDVI (Landsat, May’05)

Conclusions

• SOC = key element in global C cycle

• Lack of understanding of SOC dynamics at hillslope and catchment scales

• What’s driving catchment SOC dynamics?

• Need for better & faster (BUT still reliable) methods for quantifying SOC dynamics

Conclusions• NAFE’05

– Regional scale data• Soil moisture/temperature

• Vegetation (NDVI)

• Soil C & N

• LIDAR???

• Stanley catchment scale data– SOC

– 137Cs

– Soil moisture

– Above-ground biomass

Ground-based & remotely sensed (aircraft platform)