Seasonal and Spatial Distribution of N & P Substances in the Hula Valley (Israel) Subterranean

Abstract

Until the late 1950s the Hula Valley, located between altitude of 170 masl in the northern part and 61 masl in the southern part, was covered by the old shallow Lake Hula (1.5 m mean depth; 1400 ha water surface); and 4500 ha of swamps partly or permanently were water covered. During 1950-1957 the old Lake Hula and the wetlands were drained and converted into agricultural usage. As a result of inappropriate agricultural management, a reclamation project (Hula Project, HP, 1990-1997) was implemented. A vertical plastic sheet (4.5 m deep) was placed along 2.8 km across the valley aimed at reduction of pollutants migration. This plastic barrier divided the valley into northern, organic, and southern mineral soil blocks. The HP was aimed at agricultural renovation together with prevention of water quality deterioration in the downstream Lake Kinneret. The chemical composition of the underground waters was monitored on a monthly basis in 14 drills and ground water table observation wells over the valley during 14 months. The Ground Water Table (GWT) in the northern part of the valley was shallower than in the south and seasonal fluctuation amplitudes were smaller in the north. Higher levels of TP, TDP, P-Ortho and particulate Phosphorus, TN and ammonium were documented in the southern underground waters. The level of nutrient concentrations in the south was probably enhanced by three factors: 1) accumulation by underground water migration; 2) eroded substances from the southern mineral soil; 3) intensive Evapo-Transpiration in the south. Due to the lower level of organic content in the south and in spite of possible underground accumulation no significant difference between southern and northern blocks was indicated for Nitrate (NO3) concentrations. Not like nitrates, the reduced nitrogen form of ammonium concentration in the undergrounds was higher in the south. It was suggested that the nutrient concentrations (dissolved and suspended) in the Southern underground waters were higher than those in the North as a result of water migration, which took over the plastic barrier underneath and/or aside while moving from north to south was resulted by the hydraulic gradient. This gradient was partly due to the topographic slope and partly to the intensive Evapo-Transpiration in this part of the valley, which also contributed to the decline of GWT.