Hydrological control of phosphorus mobility in altered wetland soils

Ground water transport of P from the altered wetland soils of the Hula Valley may influence the water quality of Lake Kinneret, which provides up to 30% of the potable water for the state of Israel. We hypothesized that land use change in these altered wetland soils is the cause for the reported increase in particulate P loading to the Jordan River, which empties to Lake Kinneret. To test this hypothesis we evaluated the P mobility from the Hula's wetland soils to waterways under various hydrological conditions using a field-scale experiment (0.8 km²) with well-monitored boundary conditions. The spatiotemporal changes in hydraulic head across the study area were measured using automated monitoring stations installed in eight observation wells. The hydraulic conductivity (K) of the near-surface peat/marl layers (179 m d ^-1) was significantly larger than the K values (0.001 to 0.03 m d^-1) measured in the marl layers at 5 to 15 m below surface. The large K values of the near-surface layers result from the drainage of this wetland in the late 1950s followed by the oxidation of the peat layers and dissection of the lower peat and upper silt-clayey marl layers. Using a simple water-budget approach, the large field experiment yielded a discharge of 0.27 Mm³ and a loading of 306 kg P transported from the altered peat soils to the waterways, in just 7 wk. Most of the P loading was in the form of particulate P (>0.45 μm) rather than dissolved P.