Dynamics of selenium species in a wetland system of Great Salt Lake, Utah, USA

Abstract

The cumulative selenium in the Great Salt Lake via inflow can cause damage to fish and migratory birds at
high concentration. One of the influx passages of selenium to the lake is through wetland systems which can
be a natural method to reduce selenium concentration if favorable conditions are met. A series of nine
integrated ponds was selected to study the lake selenium input and its behavior, receiving flow from the
Jordan River through the Surplus Canal delivering to Farmington Bay at southeast of the lake. The variations
of selenium species in diurnal cycle each in Spring, Summer, and Fall of 2006 were examined. Hourly values
of dissolved oxygen (DO), redox potential (Eh), and pH of each pond were recorded for evaluating
concentration of each of selenium species using the Eh-pH diagram. The accuracy of the diagram was cross
checked by comparison to the hydride-generation atomic absorption spectrometry (HGAAS) which was
found to be less than 2% error. Rising in the morning and dropping at night, the DO, Eh and pH fluctuated for
the whole 24 hours resulting from biochemical effect. Hourly concentration for the selenium species was
determined for all of the nine ponds during each season. The fluctuation patterns of total selenium were
similar for all ponds, higher during 11 am to 5 pm, lower at night and lowest in the morning during 8 to 10 am.
Of the four species, selenate and selenite dominated over elemental selenium and selenide for all three
seasons. Selenate being higher during Spring but lower in Fall and dominated during Summer only at the
upstream of the system whilst Selenite was the dominant species at the mid and downstream system. In total,
the annual average results show total selenium concentration decreases towards the lake from 1.25 ppb at
the first inlet pond to 0.50 ppb at the ninth pond. From this study we should ascertain the appropriate time to
best release the water into the lake.