The summer of 2001 was of great interest to OPET, because this was the first summer the Pond's salinity was within the limits of the management plan, which calls for a range of 2-4 parts per thousand (ppt). And salinity was about 2 ppt down to 4 m depth throughout the pond since the Trunk River jetties had been repaired and the Trunk River been dredged. Only the deep south end basin is a trap for the heavy salt water, which, coming across the weir now at the height of the high high tides (but not the low high tides), just seems to flow along the bottom of the pond and settle there. Salinity at 5 and 6 m settled around 12 and 15 ppt, respectively, at those depths.
What happened to dissolved oxygen, the crucial parameter for supporting aerobic life in the pond, this summer? That turns out to be an interesting story. For one, oxygen levels varied with pond area. The sampling site OP1 is located in the north end of the pond. To a depth of 2 m, oxygen was as high as can be expected: about 8 mg/l. But at 3 m, oxygen varied between near 0 and 10mg/l. At 4m, there was no oxygen at any sampling date. In the geographic middle of the pond, at OP2, oxygen at 3m was about 8 mg/l throughout the summer, but at 3.5 m (X--X curve) it was much less during the midsummer. At the south basin, OP3, oxygen was high down to 3 m throughout the summer. At 4m, there was none in June, but it climbed to 8 mg/l by the fall. At greater depths, in the high-salinity water, oxygen was lacking throughout the sampling period. This is expected, because the heavy saltwater does not rise up to mix with the surface water, that gets its oxygen from the air-water interface. For most of the pond, then, fish can thrive down to a depth of 3 m. And, indeed, traps set in August at 3 m caught small white perch and sticklebacks.
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Damsel flies practicing for Valentine's Day at Oyster Pond. Photo by B. Rose |
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