Seasonal variations of heat flux at the water-sediment interface in very shallow lagoons

Temperature measurements were taken at five levels in a homogeneous zone of silty sediments and very shallow water (1m) in the Lagoon of Venice. Temperature decreased with depth. A penetration depth of 230 cm and a phase lag between temperature maxima at various levels are observed and confirmed by typical values of thermal diffusivity for silty muds. The energy stored in the water from late winter to late summer is about 2 X 10 super(3) cal cm super(-1) while in the same period, the energy stored in the sediment down to the penetration depth is about 1.7 X cal cm super(-1). The theoretical value of energy stored in the whole sediment is 2.1 X 10 super(-1) cal cm super(-1). Simple calculations based on the assumed conductivity of silty mud indicate that the heat flux through the water-sediment interface is on the order of 10 super(-4) cal cm super(-2) sec. super(-1), that is, 1/10 of the annual excursion of the incident solar flux at Venice's latitude