Hydrogeological characterization of an altered wetland

SummarySpatiotemporal changes in the hydrogeology of the Hula altered wetland may influence the water quality of Lake Kinneret, which provides up to 30% of the potable water for the state of Israel. The main objectives of this work were to study the groundwater-flow characteristics in this wetland and assess the potential impact on downstream water quality. We constructed variograms of hydraulic heads, computed decision-tree models of major ions, and determined the hydraulic conductivity (K) and δ2H/δ18O ratios, to ascertain the spatial and vertical distribution of hydrogeological parameters. We also performed large-scale field experiments (⩾1 km2) to assess the connectivity between the waterways and the wetland’s aquifer. The aquifer is fragmented by three parent materials: deep peat, shallow peat/marl complex and marl. The decision-tree-based model, the isotopic ratios and K determinations suggest that the deep peat subaquifer is composed of one homogeneous layer characterized by low K (0.001 m d−1). The two other subaquifers consist of three hydrostratigraphic layers: (i) the vadose zone, (ii) a layer with well-developed macropores at a depth of 1.5–4 m and (iii) an aquitard layer at a depth of 4–15 m. The temporal head fluctuations, the high K values of the second layer (>170 m d−1), and the large volume of water flowing into and out of the two subaquifers during large-scale field experiments all attest to excellent connectivity with the waterways. These results support the concept of critical source area which claims that most of the P loss in a catchment derives from small areas in which specific P release and transport mechanisms coincide with high connectivity. We conclude that the high connectivity of this Mediterranean altered wetland to waterways, coupled with the high P release that has occurred in recent years following soil flooding, provides the loading mechanism that partially explains the observed P increase in the Jordan River.