The purpose of this study is to obtain a better understanding of groundwater contamination processes in an arid environment (precipitation of 50 mm/year) due to cultivation. Additional aims were to study the fate of N, K, and other ions along the whole hydrological system including the soil and vadose zone, and to compare groundwater in its natural state with contaminated groundwater (through the drilling of several wells).A combination of physical, chemical, and isotopic analyses was used to describe the hydrogeological system and the recharge trends of water and salts to the aquifers. The results indicate that intensive irrigation and fertilization substantially affected the quantity and quality of groundwater recharge. Low irrigation efficiency of about 50% contributes approximately 3.5-4 million m 3 /year to the hydrological system, which corresponds to 0.65 m per year of recharge in the irrigated area, by far the most significant recharge mechanism.Two main contamination processes were identified, both linked to human activity: (1) salinization due to circulation of dissolved salts in the irrigation water itself, mainly chloride, sulfate, sodium and calcium, and (2) direct input of nitrate and potassium mainly from fertilizers.The nitrate concentrations in a local shallow groundwater lens range between 100 and 300 mg/l and in the upper sub-aquifer are over 50 mg/l. A major source of nitrate is fertilizer N in the excess irrigation water. The isotopic compositions of d 15 N-NO 3 (range of 4.9-14.8‰) imply also possible contributions from nearby sewage ponds and/or manure. Other evidence of contamination of the local groundwater lens includes high concentrations of K (20-120 mg/l) and total organic carbon (about 10 mg/l). q

The composition of groundwater reclaimed from tertiary soil aquifer treatment systems reflects the dynamic processes taking place in the subsurface, between the infiltration basin and the production wells. At the end of year 2000, following more than a decade of operation, high Mn concentrations (2 micromol L(-1) < or = Mn < or = 40 micromol L(-1)) appeared in the reclaimed effluents of the Dan Region Sewage Reclamation Project (Shafdan), Israel. A mass balance indicates that the high Mn excess originated from the aquifer rocks, most likely following reduction of sedimentary Mn-oxides under suboxic conditions. The subsequent adsorption of the Mn2+ results in a slow Mn2+ front that advances in the direction of groundwater flow only when all the Mn2+ exchangeable sites are saturated. A retardation factor obtained from two independent estimates based on a simple reduction-adsorption-advection model yields a value of about 10. This explains the delayed appearance of the high Mn concentrations at a distance of only -500 m from the infiltration basin.

The ‘seedless’ table grape industry relies mainly on stenospermocarpic cultivars, in which endosperm abortion results in berries with seed rudiments and low levels of bioactive gibberellin (GA). Application of GA to enhance berry sizing in these cultivars is often accompanied by adverse effects, one of which is increased proportions of very small berries (termed shot berries). Manual removal of these berries, which is essential to improve uniformity and market value, increases production cost and exposes the cluster to damage. Unraveling the physiological causes of shot berry formation is thus of both scientific and practical value. This study focuses on understanding the GA-mediated regulation of shot berry formation in Vitis vinifera cv. Early Sweet, known for a high proportion of shot berries, which severely damage cluster appearance. As GA is known to induce the parthenocarpic fruit set, we first tested the assumption that the parthenocarpic nature of a fruitlet is a primary cause for shot berry development. We then examined the consequence of the flower load on the proportion of shot berries in the cluster. Our data suggests that: (1) contrary to prior assumptions, the parthenocarpic nature of a fruitlet is not the primary cause for shot berry development, demonstrated by the fact that parthenocarpic fruitlets develop into a full-size berries; (2) the proportion of shot berries on a cluster is a function of the initial flower load on the inflorescence, with high initial flower load resulting in greater shot berry percentage in the cluster; (3) GA treatment bypasses the natural regulation of flower load, resulting in high fruitlet density and increased competition among fruitlets; (4) variation of flower load within the cluster influences berry size uniformity to a greater extent than does the variation in number of cluster per vine. The identity of the factors that determine the fate of a given flower on a high-load cluster remains an open question.