Dryland environments are estimated to cover around 40% of the global land surface, and are home to approximately 2.4 billion people. Many of these areas have recently experienced extensive land degradation. This study focuses on semi-arid areas in the US Southwest, where degradation over the past 150 years has been characterized by the invasion of woody vegetation into areas previously dominated by grasslands. This vegetation change has been associated with increases in soil erosion and water quality problems, including the loss of key nutrients such as carbon from the soil to adjacent fluvial systems. Such loss of resources may impact heavily upon the amount of carbon that is lost as the land becomes more heavily degraded.
Therefore, understanding these vegetation transitions is significant both for sustainable land use and global biogeochemical cycling. This study uses an ecohydrological approach to develop an understanding of the relationship between structure and function across these transitions. This is done via the monitoring of rainfall-runoff events across instrumented runoff plots with different vegetation characteristics to investigate fluvial sediment fluxes during intense summer monsoon season rainfall events.
Each study area consisted of a 10m wide, 30m long, downslope runoff plot, bound at the top and sides with aluminum flashing and fitted with water collecting guttering at the bottom so inputs and outputs could be quantified. The guttering fed water into a flume fixed into the ground at 4⁰ allowing water leaving the plot as runoff to be quantified.
The flumes were instrumented with a pump sampler to collect runoff samples leaving the plot and a bubbler module to measure discharge. In addition all runoff and associated sediment was collected in a covered stock tank (560 gallons for study area 1&2, 1000 gallons for study are 3). Rainfall onto the plot was measured using tipping-bucket rain gauges connected to the pump sampler. Following rainfall events all data was downloaded from the sampler using Flowlink v3.2 software.
Eroded sediment was collected from stock tank following rainfall events, coarse organic matter was removed via flotation, samples were oven dried at 60⁰C, weighed and sieved for particle size analysis using US. standard sieves at the Sevilleta LTER field station.
Setting up plots:
Plots were selected on comparable planar slopes in areas believed to be representative of endmember vegetation habitats.
Instrument Name: Pump samplers fitted with bubbler modules
Model Number: Model 6700 pump samplers and attached model 730 bubbler modules
Instrument Name: Tipping-bucket rain gauges
Model Number: 674
Instrument Name: Flowlink software
Model Number: Version 3.2
Instrument Name: Sieve set and shaker
Manufacturer: unknown/various (from Sevilleta LTER field station)
Model Number: US. Standard: 12mm, 4mm, 2mm, 1mm, 0.5mm, 0.063mm
This data was collected and analyzed by Alan Puttock as part of the PhD project: ‘Developing an understanding of vegetation change and fluvial carbon fluxes in semi-arid environments’. This project is supervised by Dr Richard Brazier, Dr Jenifer Dungait and Dr Kit Macleod. Analysis of samples/data is being carried out at the University of Exeter and North Wyke Research, United Kingdom.
This data was collected under USFWS permit number: 22522 10-026