Kesterson Reservoir: Monitoring Vegetation Stress and Trace Element Pollution with Remote Sensing

The Kesterson Reservoir in the San Joaquin Valley of California is the recipient of water drained from agricultural fields. Studies of the freshwater wetlands at Kesterson have shown that the water entering Kesterson has brought with it boron, selenium and other trace elements. These material have accumulated to toxic levels in plant and animal communities. A remote sensing image of Kesterson is shown in Figure 1. The Natural drainage network of the area is visible surrounding the ponds. Water entering the reservoir remains until it evaporates, filters into the ground, or is taken up by plants.

In a recent study, ten plant species were sampled from 140 sites within the reservoir and nearby uncontaminated freshwater wetlands. Digital spectral data from aircraft were acquired at the same time. Analysis of the plant samples showed higher levels of toxic trace elements in the samples from Kesterson. Laboratory spectral analysis of the samples indicated the spectral response of certain plant species - cattails, bullrushes and saltgrass, for example - were affected by the accumulation of toxic materials. Similar changes in the spectral response of these plants were noted in the spectral data obtained in the field by aircraft. Figure 2 is a computer generated image of Kesterson based on the difference in spectral response of the vegetation. The green areas are concentrations of cattail and bullrush. The yellow-green areas have high levels of trace elements; the darker green areas have lower concentrations. The white areas are alkali deposits, and the red areas are algae mats which are generally high in trace element concentrations.

Results of this study indicated that remotely sensed data could be used to map wetland vegetation stress resulting from accumulation of toxic trace elements in agricultural drainage water.

Investigator: Byron L. Wood