Lake Kinneret sediments: Nutrient composition of the pore water and mud water exchanges1

Various elements of the pore water of Lake Kinneret scdimcnts have been analyzed and their fluctuations observed during 20 months at four stations, with concomitant measurements of bottom currents, temperature, and benthic flora. Dissolved iron reaches its maximum solubility at the beginning of turnover. The exchangeable phosphorus stems to be the iron-bound fraction and its concentration in the pore water increases simultaneously with the reduction of sulfates and precipitation of iron sulfide, but its release is controlled by the calcium phosphate equilibria. This mechanism explains how the rate of release of phosphorus is only 0.8 mg m-2day-” and how the Kinneret sediments play the role of a sink as far as phosphorus is concerned. Ammonia is produced by an intense process of ammonification and its rate of release reaches 25 mg mM2 day-l. The internal nutrient load is compared to the external one. Since there is evidence that the winter-spring Peridinium bloom can be supported solely by the internal load, working hypotheses are provided concerning the relationshiD between the release of nutrients from the mud and the nature of the Goom. The importance of regeneration of nutricnts in the epilimnion of lakes has been noted ( Klccrckopcr 1953; Lawacz 1969). However, a certain amount of trypton reaches the bottom and undergoes additional mineralization. In stratified and productive lakes, the “internal nutrient load” due to bottom regeneration may compctc with the amount of nutrients brought to the lake from the drainage area (Bachofen 1960; B urns and Ross 1971) and the qualitative composition of the internal load certainly plays a role in algal productivity and the predominance of certain species, The rcgcneration of nutrients in the sediments is a two step process: the first one, which includes bacterial activity an d physicochemical reactions, determines the concentration of nutrients in the pore water ’ Contribution of the Israel Oceanographic & Limnological Research Ltd., Kinneret Limnological Laboratory. (PW) ; the second one governs their release through the mud-water interface. Our purpose here is to show the fluctuations of nutrient concentration in pore water of Lake Kinneret sediments as a function of the bottom conditions, currents, temperature, flora, and of the sedimentation rate and composition of the trypton at different stations. We thank M. Hatab for his help in fieldwork. WC are grateful to H. L. Goltcrman for reviewing the manuscript. Methods and procedures The composition of the pore water of the sediments of four stations at different depths (A, 42 m; C, 30 m; F and G, 25 m: Fig. 1) was measured for 20 months (January 1971 to August 1972). Stations A, C, and G were sampled about twice a month ( 37 sets of data). Station F was sampled more frequently, especially at the turnover period ( 55 sets of data). The mud and water were sampled with LIMNOLOGY AND OCEANOGRAPI-IY 489 MAY 1974, V. 19(3)