Selenium and the Kesterson Reservoir

Kayla Carpenter

San Joaquin Valley:

•Lots of farming

•Poorly drained

•Built drain to the San Francisco Bay

San Luis DrainSan Luis Drain• Built 1968-1975 by Bureau of Built 1968-1975 by Bureau of

ReclamationReclamation• Originally from Five Points, CA, to BayOriginally from Five Points, CA, to Bay• Reservoir = controlling reservoir, Reservoir = controlling reservoir,

midpointmidpoint

SELENIUM!SELENIUM!

• Water: 300 ppb from drain vs. <10ppb natural

• Soil: above 100 ppm in evaporation ponds

Deformity and death of waterfowl

leads to closure

1988• 500 ha site, 60% filled in• 15-150 cm uncontaminated soil• Wetland upland grassland• PHYTOREMEDIATION!

– Inexpensive, enviro friendly, rather effective– Brought in over 20 spp common weedy

plants– Volatilized to atmosphere, dimethyl

selenide– Aided by microorganisms, esp. in

rhizosphere

4 Depositional 4 Depositional EnvironmentsEnvironments

• Dryer northern pondsDryer northern ponds– Saltgrass Saltgrass (Distichlis(Distichlis) ) && alkali weed ( alkali weed (CressaCressa))– Accumulates loose layer of organic detriusAccumulates loose layer of organic detrius

• ““Playas”Playas”– Flooded in winter & spring, little organic Flooded in winter & spring, little organic

mattermatter– RuppiaRuppia spp then filamentous algae spp then filamentous algae

• Flooded & wetFlooded & wet– Cattails (Cattails (TyphaTypha) & alkali bulrush () & alkali bulrush (Scirpus Scirpus spp)spp)– Stay wet Stay wet peat-like material peat-like material

• SubmergedSubmerged– Algae dominant (Algae dominant (Chara,Chara, then filamentous & then filamentous &

diatoms)diatoms)– Thick organic ooze deposits in open watersThick organic ooze deposits in open waters

Miscellaneous Findings

• pH 6.5 –8.0• Selenate, selenite, organic Se• Amount & speciation changed over time• Sharp decrease in water-extractable soil Se, esp top soil• Correlation between vegetation & water extractable Se• Plant roots can take up Se from lower soil profile

good news for aquifer• Food chain contamination less with upland than

wetland • Plants in irrigated soils have higher Se concentrations• More volatilization in warm months & wet areas

Rate of Removal• At current conditions, volatilization

of 1-5% total selenium in top 60 cm• 5%: half gone 14 yrs, all gone 46 yrs• 1%: half gone 69 years, all gone 230

yrs• Further aided by irrigation,

application of carbon & protein source (glucose & casein), aerobic conditions, and pH 8.0

Conclusions

•It is working•It’s slow•Still impacts food chain•Volatilized selenium

QuestioQuestions?ns?