C. Wahl et al., TEMPORAL AND SPATIAL MONITORING OF SOIL SELENIUM AT KESTERSON RESERVOIR, CALIFORNIA, Water, air and soil pollution, 74(3-4), 1994, pp. 345-361
The selenium and salt content of the top 15 cm of the soil profile at
Kesterson Reservoir (Merced County, California) have been monitored an
nually to develop a data set that provides a foundation for: (1) evalu
ating the status of the selenium inventory and biological hazards at K
esterson Reservoir; (2) understanding selenium fluxes near the soil su
rface; and (3) making long-term predictions of the selenium concentrat
ions available for plant uptake and dissolution into rainwater ephemer
al pools. Results of this monitoring program indicate that the soil se
lenium inventory at Kesterson may be categorized in terms of three mai
n patterns: (1) spatial trends associated with historic Reservoir oper
ations; (2) temporal trends due to the oxidation and remobilization of
the selenium inventory and; (3) temporal trends due to seasonal cycle
s. It is evident that the selenium inventory and distribution within t
he soil profile will evolve slowly whereby the fraction of the total i
nventory that is now immobile (est. at 93%) will oxidize to more mobil
e and bioavailable forms. Two major issues with broad importance were
raised concerning sampling the surface soil selenium environment at Ke
sterson which may be helpful to others conducting investigations of si
milar nature. These issues include: (1) the recognition that variation
s in surface soil contaminant concentrations due to seasonal redistrib
ution may obscure long term trends and; (2) large spatial variability
in soil contaminant concentrations make it difficult to obtain large e
nough data sets to detect statistically significant changes in the con
taminant inventory until large changes have already taken place. A com
bination of both process-oriented and synoptic type sampling are recom
mended to better define time trends.