VIVASSEN – VATTENUTBYTE, SYRE- OCH NÄRSALTSFÖRHÅLLANDEN / The Embayment of Vivassen – Water Exchange, Oxygen and Nutrients
The Vivassen is a small embayment (1 km2) on the Swedish east coast with a narrow sound connecting it to the Baltic archipelago. We have measured the supply of nitrogen and phosphorus from waste disposal and from runoff and compared those sources with the supply of nutrients from the Baltic dividing between spring bloom nutrient pool, surface and deep water supply, respectively. Considering the inorganic N/P supply ratio, there is a reasonably large surplus of nitrogen to the bay. Summer nutrient concentrations, in the other hand, indicate that nitrogen is the limiting nutrient. We have calculated the oxygen consumption in the deep water and found a value of approximately 0.3 l/m2 day, which was also in accordance with the supply of nutrients. With normal deep water supply there is no risk for oxygen deficit. During warm summers, however, the deep water supply may cease due to a thick warm water layer on top of the Baltic. This situation prevents intermittent coastal upwelling, which usually supplies the Vivassen with new deep water.