VERTICAL DISTRIBUTION OF NITRATE IN THE SEDIMENTS OF SILVER LAKE

  Heather Bailey, Chad Fields, Ariana Houge, Mohammad Iqbal, and Edward Brown 

   Silver Lake in Northeast Iowa is a biologically restricted lake that does not support its designated use as a recreational facility.  Due to the concern for the future of the lake by the area residents, an extensive investigation on the lake was conducted in the summer of 2001.  The main objective of this study was to see if a vertical gradient of nitrate was present in the sediments of the lake. 

   In June 2001, sediment cores were taken from 15 sites in Silver Lake.  Nitrate was detected in 12 of the 15 sites.  Five of these cores (41.7%) show a concentration gradient decreasing downward, which is not enough evidence to show a lake-wide distribution of nitrate.  The average NO₃ concentration in the top 5 cm of sediment is 93.39965 mg/gm (range: 1.803 mg/gm to 733.087 mg/gm).  At 7 of these sites the average NO₃ concentration between 5 and 10 cm is 197.13677 mg/gm (range: 4.429 mg/gm to 538.66 mg/gm).  At 11 of these sites the average NO₃ concentration between 10 and 15 cm is 104.1797 mg/gm (range: 2.261 mg/gm to 331.057mg/gm).  The results indicate that there are pockets of high NO₃ concentrations in the sediments.  The highest concentration is located in an area that is adjacent to a livestock farm.  These studies suggest that any strategy for restoring Silver Lake should include dredging the sediments.

This research was supported, in part, by the Roy J. Carver Charitable Trust and the Iowa Space Grant Consortium.