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Summary  

At the estuary-ocean boundary, it has heretofore been assumed that the ocean is a sink and that flood tide waters assist in the dilution of nutrient levels in the estuary. However, measurements of the flux at this boundary have been difficult to accumulate because the only way to determine whether a particular substance is imported to or exported from an estuary over a long period of time and to detect any episodic event is to conduct continuous long-term monitoring. This Sea Grant-supported project is the first study that monitors the nitrogen import and export at the estuary-ocean boundary continuously and over a long-term, using a piece of newly-developed in situ equipment.

The in situ nutrient analyzer and current meter were successfully deployed from March 17 to April 11, 2000. A set of long-term continuous nitrate concentration and flow data were recorded. A major event was detected and recorded during this monitoring period.

High concentration of nitrate occurred in water that was exchanged through Barnegat Inlet from April 18 to April 24, 2000. This concentration was two to ten times greater than normally recorded levels.

Preliminary results indicate that nutrients can enter Barnegat Bay from the ocean as well as from the mainland and that continuous long-term monitoring is necessary to detect episodic events such as freshwater flow from the watershed or ocean upwelling. It is also necessary to quantify net import and export of nitrogen to an estuary across its several boundaries. Future water quality/eutrophication modeling must consider these dynamic boundary conditions.

Graphs

In Situ Current Meter

In Situ Nutrient Analyzer

Variation of Ammonia Concentration at Barnegat Bay Inlet on 7/19/99

Variation of Nitrate Concentration at Barnegat Bay Inlet on 7/19/99

Time Variation of Nitrate Concentration (March 17 to April 11, 2000)

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