Methods

Methods sections for the threats processes

Sediment Modeling — by Matthew Perry — last modified 28-12-2006 17:15

Rivers contribute 95% of sediment entering the ocean. A river’s sediment load is related to many watershed-based processes generally consisting of erosion and deposition. Previous global sediment studies use coarse resolution (0.5 degree) spatial data and empirical models based on area, relief and temperature to derive estimates. Using global datasets of soils, rainfall, elevation and vegetation at a 30 arc-second (approximately 1km) spatial resolution, we were able to use the RUSLE model to predict a global erosion potential map. By summing the erosion potential by basin, we derived estimates of annual sediment load for each river. The estimates for 121 rivers were compared to observed sediment loads and were found to predict within 2 orders of magnitude in all but 3 cases. Techniques were explored to adjust the estimates for the effects of dams, reservoirs and other depositional factors but these did not increase the predictive power of the model.

Dasymetric Mapping — by Matthew Perry — last modified 28-12-2006 15:11

National-level fertilizer and pesticide statistics can be represented in a GIS through the traditional approach of choroplethic mapping. This techqnique falsely assumes that values are even distributed across the entire polygon making it insufficient for making watershed-level estimates of fertilizer and pesticide consumption. Using a dasymetric mapping technique, we were able to use ancillary land cover data to better represent the true heterogeneous distribution of these phenomenon.

Basins — by Matthew Perry — last modified 01-12-2006 12:03

 

Aggregating Land Based Data by Basin — by Matthew Perry — last modified 01-12-2006 12:07

Basin statistics

Plume Modeling — by Matthew Perry — last modified 01-12-2006 12:08

 

Sediment Model Diagram — by Matthew Perry — last modified 01-12-2006 16:47

 

Dasymetric Model Flowchart — by Matthew Perry — last modified 20-12-2006 11:00