SEICHE-INDUCED MIXING - ITS IMPACT ON LAKE PRODUCTIVITY

Analysis of temperature and oxygen data at an inshore station in Lake Kinneret (Israel) indicates that cross-isopycnal mixing occurs at the littoral zone as a consequence of seiche activity. We suggest that nea r-bottom mixing at the lake periphery is highly important for nutrient supply from the hypolimnion to the epilimnion. Temperature and temper ature gradient distribution patterns along a cross-lake transect indic ate horizontal transport via the metalimnion of the mixed water from t he littoral toward deeper parts of the lake. Inshore localization of m ixing and dilution of the mixed water during its transport cause the h ypolimnetic water supply into the epilimnion to be higher nearshore th an in the middle of the lake. Addition (5-10%) of hypolimnetic water t o epilimnetic water in laboratory experiments results in enhanced prim ary production and increased algal biomass. The stimulating effect of hypolimnetic water on primary producers (algae) and the deduced patter n of nutrient-rich hypolimnetic water supply are consistent with obser ved spatial distributions of algae and fish (mainly planktivorous), wh ich are more abundant in the lake periphery. We suggest that the impor t of hypolimnetic waters into the epilimnion enhances biological produ ctivity of the lake.