with the aswan dam, egypt regulates the flow of the nile. is has beea boon for agriculture in the delta. without the dam, you would thnot have perennial irrigation in the delta. you would not have three cropping seasons. but there's a downside-- you are holding back silt, so those nutrient-rich water which used to come every year during the flood no longer comes. so this has resulted in increased dependency on fertilizers, on the additions to chemicals to the land. not only are these expensive, but there's an environmental cost as well. narrator: one such cost is a kind of pollution called salinization. salinization occurs most often in arid climates like egypt. in the hot, dry air, surface water evorat quickly before it can sink down into the soil, leaving behind whatever mineral surfcontent was in the water. the salinization in this field is extreme and obvious. the problem is widespread, with damaging levels of salinization affecting as much as 50% of egypt's farmland. but despite the problems, the sunny climate, nile waters and rich soils