Surface water sampling |
Three Teflon* sampling lines were set at an upper, mid, and lower depth in the water column in an undisturbed area about 50 feet from the dock (not shown). Using a peristaltic pump, samples were collected at specified time intervals and sampled immediately for sulfide using a portable spectrophotometer (1). |
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Hydrolabs (2) were placed at upper, mid, and lower depths in the water column and DO was recorded hourly. |
Porewater sampling |
Six mini-piezometers were secured to an acrylic disc and set at 2, 4, 6, 8, 10, and 40 cm below the sediment/water interface (3). The piezometers were connected to gas-impermeable tubing (4) and run through a modified multi-channel peristaltic pumphead (5) (flow rate: 10 ml/min) to a syringe reservoir (6). Only 60 ml of sample was collected at each depth during each sampling to avoid draw from depths above and below specified sampling interval. |
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A microelectrode system (7) was used to monitor DO in the porewaters. Samples (<10 ml) were pumped to a syringe and injected into a flow-through chamber (8). The mV reading was recorded from an OM-4 meter hourly and later converted to mg/l concentrations. |
Sulfide measurements: Hach DR2000 portable spectrophotometer ( range: 0.001-0.6 mg/l ) Methylene Blue Method (adapted from Standard Methods for the Examination of Water and Wastewater). Procedure is equivalent to the USEPA method 376.2
DO measurements: Surface water: Hydrolab Minisonde and Scout II polarographic 1 mil Teflon membrane sensor ( range: 0-20 mg/l; accuracy:+/-0.2 mg/l; resolution: 0.01 mg/l ) Porewater: Microelectrode Flow-thru Oxygen Electrode 8-730 Polarographic 1 mil Teflon membrane (drift = 1 mV/hr or 0.3% of mV reading)
*The use of trade names does not constitute endorsement by the USGS.
