Controls on Catchment-Scale Patterns of Phosphorous in Soil, Streambed Sediment,and Stream Water

Marcel van der Perk, et al…

Journal of Environmental Quality, 2007

Presentation Outline

1)Overview2)Methods3)Results4)Conclusion5)Discussion/Critique

1. OVERVIEW

1. OVERVIEWGoal of Research:

Attempt to quantify the unique and joint contribution of…

1) Soil type, soil chemical properties, and land use

2) Soil [P], sediment chemical properties, and point source emissions

3) Sediment chemical properties, water chemistry, and point source emissions

Spatial variation of [P] in soil

Spatial variation of [P] in streambed sediments

Spatial variation of [P] in stream water

Independent variables Dependent variables

1. OVERVIEWMotivation for the goal:

Phosphorous is a common limiting nutrient in both aquatic and terrestrial ecosystems

Scientists know it is controlled by climate, geology, topography, and anthropogenic influences

Yet to be successfully quantified/modeled at basin scale

Valid models can be very useful

Geochemical dataset available in the watershed promised possibility of “breaking new ground”

1. OVERVIEWThe Watershed

•Southwest England

•976 km2 (377 mi2)

•72% grassland•6% farmable•17% forest

•50 STW, mostly smalldispersed towns

2. METHODS

2. METHODS

Geochemical survey (2002)

460-495 samples of each of the major top soil type,Stream water, & streambed sediment

Soil-> randomly within every 2nd square kilometer (systematic random)

Streambed-> 1st to 4th order streams (systematic)

Stream water-> same locations as streambed

2. METHODS

Spatial Data

Also made interpolated maps from geochemical survey (conditional simulation)

*******all data re-sampled to 25m resolution

2. METHODS

Statistical Analysis

•Ln transformed if regression residuals not normally distributed

•Only considered variables in regressions if significant (α=0.05, ANOVA)

•Multiple linear regression coefficient must be logical

•Coefficient of Determination (R2) used to partition variation

2. METHODSPartitioning the Variance

2. METHODSPartitioning the Variance

3. RESULTS

3. RESULTSSoil Data

3. RESULTSSoil Data

3. RESULTS

Result of conditional simulation interpolation

Soil Data

3. RESULTSStreambed Data

3. RESULTSStreambed Data

3. RESULTSStream Water

3. RESULTSStream Water

4. CONCLUSION

4. CONCLUSION

1. Soil Parent Material is major factor controlling catchment-scale spatial variation in soil TP and Olsen P, land cover is important too

2. Streambed [P] are correlated with major elements (adsorption).

3. Streambed [P] better predicted by erosion model and land use than upstream soil tests

4. Illustrates complex cascade of P transfer from soil to streambed to stream water under baseflow conditions (long term accumulation/diff sized storms)

5. Problems with spatial data

5. DISCUSSION/CRITIQUE

5. DISCUSSION/CRITIQUE

1. Cluster analysis?

2. GIS techniques

3. Erosion model