ABSTRACT
To address concerns expressed about the possible effects of drilling mud discharges on shallow, low-energy estuarine ecosystems, a 12-month study was designed to detect alterations in water quality, sediment geochemistry, and the benthic community. A relatively pristine, shallow (1.2 m) estuary ( Christmas Bay, Texas) without any drilling activity for the last 30 years was chosen for the study site. After a 3-month baseline study, three stations were selected. At each treatment station (muddy-sand or seagrass community), mesocosms were constructed to enclose a 3%5 m3 water column. Each in situ mesocosm, except the controls, was successively dosed at a mesocosm-specific concentration with 4 field-collected muds (spud, nondispersed, lightly-treated, and heavily-treated lignosulfonate ) over a 1.5-month time period to simulate discharges from a drilling rig. Twenty-four hours after each dose, water exchange was allowed until the next treatment. After the last treatment, the enclosures were removed and the site monitored for 6 months. One additional site was similarly dosed with clean sediment from Christmas Bay for comparison. Analysis of the water samples and field data showed that water quality was impacted during the discharges, primarily at the highest dose (1: 100), but that elevated levels returned to ambient levels immediately after water exchange was allowed. Barium, from the barite, was used as a tracer during the study to confirm the estimated doses. Barium levels returned to ambient or only slightly elevated levels at the end of the 6-month monitoring period due to sediment deposition, resuspension and
*Present address: ENSR Environmental Laboratory, 2400 West Loop South, Suite 300, Houston, Texas 77027-4206, USA.
