סמינר מחלקתי בגאוגרפיה וסביבת האדם: השלכות שינוי אקלים על מפלס אגמים וביטויו בתפקוד המערכת האקולוגית באגמים
פרופ׳ אביטל גזית, בה״ס לסביבה ולמדעי כדור הארץ והמחלקה לזואולוגיה, מדעי החיים, אוניברסיטת תל אביב
Seasonal imbalance between the yearly water input (inflow, direct precipitation) and output (outflow, evaporation) causes seasonal fluctuation of water level in lacustrine systems. The intensity of lake level fluctuation is augmented by water abstraction for human use. Littoral zones are the near-shore, shallow lake areas that are directly affected by water level fluctuations. The bottom of littoral zones often vary with depth and location; changing from rocky formation (pebbles, cobbles, boulders) to fine particles (sand, clay). These structures influences the nature of the habitat and ultimately the biology (species abundance, composition and interactions) of this lake area. Changes of the littoral zone position with the rise and fall of the water, is followed by structural and biotic changes. Climate Change is predicted to modify the hydrologic regime as already evidenced by consecutive drought years interrupted by wet years, intensification of rainstorm events, elevated temperatures and consequently augmented water level fluctuation. Changes occurring in lakes in semi-arid, mediterranean-climate regions can explain what might be expected elsewhere if similar hydrologic changes emanating from CC occur.
For the past 40 years, Lake Kinneret, Israel (~170 km2) portrays a distinct hydrologic signal of accentuated rise and fall of lake level, apparently an impact of CC. The role of CC vs the impact of water abstraction for human use as the key factor in the lowering of the lake level following drought years, is presently contested. At any rate, lowering of the lake level negatively influences fish reproduction by reducing rocky littoral habitats and increasing sandy ones, where shore vegetation rapidly develops (in the exposed shores). Rise of the lake level positively affect fish reproduction by increasing the availability of rocky habitats used by fish breeding in these habitats (e.g. the endemic cyprinid Acanthobrama teraesanctae, known locally as Lavnun Hakinnete), and by providing a new habitat of inundated vegetation. The latter is a favored as a breeding site by cichlid fishes (Amnunim). By modifying the annual and inter-annual intensity of lake level fluctuations, CC can significantly influence fish reproduction success and ultimately fish population size which have a cascading impact on the lakes’ food-web interactions and the ecosystem health.
מרכז הסמינר: פרופ' דרור אבישר