Student Projects on Oyster Pond

WHOI PROJECT: WATER FLOW IN THE CULVERT

Jason Hyatt, a graduate student in the WHOI-MIT Joint Program in Oceanography and a resident of Ransom Road, completed a project for the class "Principles of Oceanographic Instruments Systems - Sensors and Measurements", for which he built a hydrometer from scratch. The goal of the project (entitled OPSaFE, for Oyster Pond Salt Flux Experiment) was to measure flow rate and salinity of water entering or leaving the pond, and correlate it with influencing factors such as precipitation and tides. Life in the pond is sensitive to the pond's salinity, so identifying and understanding factors that change it are important. Working with his professors, Drs. Sandy Williams and Jim Irish, Jason created a hydrometer (normally a several thousand-dollar instrument) entirely from spare parts, though he confessed that getting it to work was quite a challenge. The 10-ft instrument was installed in the culvert just downstream of the weir. He found that flow in the culvert was nearly always seaward, even during rising tides in Vineyard Sound. Correspondingly, measured salinity remained very low during these times. Exceptions occurred during times of spring tides, the stronger tides associated with full and new moons. Then, flow was towards the pond and high levels of salinity were recorded. Does this mean all the high-salinity water measured actually reached the pond? Jason does not think so: the instrument and its sensors were near the bottom of the culvert, but the flow on the bottom of the culvert is not the same as that at the surface or as that across the weir. First, water coming from the pond will always be less salty and thus be lighter than water coming in from the lagoon, and hence may flow near the surface with different velocity than the heavier bottom water. Second, in a sort of vertical eddy effect, the incoming water may get deflected upward by the weir and be swept along by the water leaving the pond across the weir. The instrument would log flow towards the pond in the bottom layer, but the incoming water would be circling right back out into the lagoon, flowing in the opposite direction on the surface. Thus, to measure the salinity flux actually entering Oyster Pond, instruments need to be installed upstream of the weir as well. Though the class for which Jason started this project is long over, he plans to continue with the experiment, expanding to include such measurements on the other side of the weir. But first, he's off to Antarctica on the Research Vessel Palmer (an ice-breaker) for about seven weeks. Good luck, Jason and keep warm!
By Mindy Hall

DAUGHTER/FATHER TEAM STUDIES POND SALINITY
BEFORE & AFTER THE DREDGING OF TRUNK RIVER

Falmouth Academy 7th grader Emily Tietje chose to study salin-ity of Oyster Pond for her science project and won honorable mention for her work. OPET's Bob Livingstone offered guidance on location, instrumentation, collection method, and analysis of water samples. Emily's dad, Jim Tietje, who, like Emily's mom, grew up on Oyster Pond, did not want to be left out and Emily graciously allowed him to assist in the data collection. In fact, when the school project was finished, Jim continued to sample Oyster Pond for OPET. From Nov-ember to February, Emily took samples at the weir, at 2 or 3 locations in the pond and in the lagoon. The weather was cold, the pond froze over - no deterrent for this hardy trio! Dad would chip a hole in the thick ice for Emily to take samples and readings and Bob was there to take pictures and give advice. Salinity at all pond locations and at the weir was about 0 parts per thousand (ppt) in November and December. Work on Trunk River began December 21, the pond level fell 9 inches and now storm-related high tides reached the pond and Emily measured an increase in pond salinity to 1.0 ppt. Samplings in February and March by Bob and Jim showed a further gradual increase to the current 2.0 ppt. OPET is grateful to Emily and Jim for their careful and rather heroic study under adverse winter conditions, and to Bob, for his unfailing contributions to OPET's projects!

Emily Tietje, collecting samples, assisted by her father Jim. Photo by R. Livingstone

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