The Sedgwick Hillslope Monitoring Site
An Overview


Location and Geology

In the spring of 1996, the Soil Sciences Group launched a long-term hydro-ecological study at the University of California, Sedgwick Natural Reserve. The hillslope study site is 150 m wide by 200 m long near the bottom of Lisque watershed (Image 7, Figure b). Extending 30 meters in elevation from valley-bottom to ridge-top the site is situated on the southwest-facing slope of a slightly dissected, planar fluvial terrace. The geological formation underlying the terrace and flooring the hillslope catena is the Paso Robles formation, a weakly consolidated early Pleistocene alluvium composed largely of Monterey Shale. Hillslope geomorphology encompasses a range of convex (hydrologically divergent) and concave (hydrologically convergent) landform components. The surface is extensively burrowed by gophers that leads to very high infiltration rates. There is no incised drainage and no indication of overland fluvial transport on the site.

Vegetation

The hillslope study site contains several blue oaks (Quercus douglasii) and two large coast live oaks (Quercus agrifolia). The grassland vegetation is dominated by annual Mediterranean grasses such as rip-gut brome (Bromus diandrus Roth), soft chess brome (B. hordeaceus L.), wild oats (Avena barbata Link and A. sativa L.), and rat-tail fescue [Vulpia myuros (L.) C. Gmelin]. Herbaceous annuals are primarily exotic species that include filaree [Erodium cicutarium (L.) LíHur], black mustard [Brassica nigra (L.) Koch], tocolote (Centauria melitensis L.), and a biennial mustard [Hirschfeldia incana (L.) Lagr.-Fossat]. Extremely well-drained sites contain the native shrub saw-toothed goldenbush [Hazardia squarrosa (Hook. & Arn.) E. Greene]. Other native herbs include vinegar weed (Trichostema lanceolatum Benth.) and chia sage (Salvia columbariae Benth). Boundary enclosures have been preventing cattle grazing on the site since 1996 and foot traffic has been greatly curtailed.

Digital Elevation Model (DEM)

A DEM spanning from ridge-top to valley-bottom was established for quantitative terrain characterization. A Trimble GPS 4400 Total Station Survey System was used to develop a 2-m grid-point spacing DEM (Figure b). Primary and secondary terrain attributes that quantify landform were computed using the TAPES-G and UPSUMG software programs (Moore et al., 1993, Gessler et al. 1995: Gallant and Wilson, 1996).

Instrumentation and Monitoring

Nine soil profiles (Figure b) were instrumented for long-term monitoring of biogeochemical fluxes and continual testing and refinement of ecosystem process hypotheses. To measure volumetric soil-water content in the nine profiles, buriable three-pronge Time Domain Reflectometer (TDR) probes were placed in all major horizons down to rock (or 3-m, whichever occurred first). Small holes were either drilled or carefully excavated parallel to the soil surface upslope direction of the soil profile for placement of these monitoring probes. At the same intervals, gas samples were taken using air-tight syringes for subsequent measurement in a gas chromatograph. Soil thermocouples were also inserted for measuring soil temperature. Each soil profile was then back-filled around a vertically-oriented PVC conduit protecting the instrumentation tubes and wires (Image 9). Data collection was initiated in April 1997.

Database

The database was originally developed in a Microsoft Access, a relational database management system (RDBMS). Recently we have been working on creating a dynamic and queriable database which could be accessed via this website. The database contains the following information:

  • Meterological data

  • Soil-moisture data
  • Soil-temperature data
  • Soil-CO2 concentration data
  • Soil physical and chemical data
  • Net Primary Productivity (NPP)

Some useful references:

Gallant, J.C. and Wilson, J.P. 1996. TAPES-G: A grid-base terrain analysis program for the environmental sciences. Computers and Geosciences. 22(7): 713-722.

Gessler, P.E, Moore, I.D., McKenzie, N.J, and Ryan, P.J. 1995. Soil-landscape modelling and spatial prediction of soil attributes. Int. J. Geographical Information Systems. 4:421-432.

Moore, I.D., Gessler, P.E., and Nielson, G.A. 1993. Soil attribute prediction using terrain analysis. Soil Sci. Soc. Am. J. 57: 443-452.


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