Date of Award

Winter 1981

Project Type


Program or Major


Degree Name

Doctor of Philosophy


The upper 12 cm of sediment from two shallow water locations were sampled for 13 months to examine the interactions among bacterial activity, geochemistry and bioturbation. The upper 8-10 cm of sediments near the Jackson Estuarine Laboratory (JEL) were bioturbated actively from June to December. Sediments at the mouth of the Lamprey and Squamscott rivers (SQUAM) were not bioturbated actively.

Microbial activity was monitored radiometrically as glucose turnover and sulfate reduction rates. Analyses of pore water concentrations of sulfate, chloride, iron and organic carbon, sedimentary concentrations of acid-volatile sulfides, and the abundance of sulfate-reducing bacteria were also made.

Average annual sulfate reduction at JEL was 5 times more rapid than at SQAUM (140 vs 30 nmoles(.)ml('-1)(.)d('-1)) and influenced by bioturbation-mediated transport of organic matter. JEL sediments accumulated a larger concentration of acid-volatile sulfides than at SQUAM (47.4 vs. 8.3 (mu)moles(.)ml('-1)). The oxidation of these sulfides during winter maintained greater anoxia at JEL.

The distribution of glucose decomposition products varied vertically, horizontally and temporally. Most notable was a temperature controlled decrease in the glucose respiration percentage from summer to winter at JEL.

Comparisons of dissolved iron concentrations with the percentage of ('35)S precipitated as acid-volatile sulfides demonstrated that factors other than sulfide precipitation were important in controlling the concentrations of dissolved iron in the winter and spring.

Increased sediment temperature caused a rapid chain of events. In early spring heterotrophic activity increased, DOC was consumed, iron dissolved while sulfate reduction remained slow. The onset of sulfate reduction in May produced an increase in DOC and the removal of iron as a sulfide precipitate. Rapid bioturbation commenced in early June and was accompanied by a three-fold increase in sulfate reduction, a two-fold increase in glucose turnover, a 5-fold increase in dissolved iron and a decrease in DOC. The combined effects of changes in microbial activity and bioturbation resulted in an oscillation in pore water chemistry.

Bioturbation influences were demonstrated by a comparison of sulfate reduction rates calculated from ('35)S, jar experiments, and diagenetic models. A comparison also was made between theoretical nutrient regeneration rates and actual nutrient concentrations. Nutrient pools in bioturbated sediments were turned over 7 times faster than in non-bioturbated sediments.