Soil and Water Conservation Zones for Pollution Control

This paper reports the preliminary results obtained from an FAO/IAEA coordinated research project (CRP) involving eight countries. Results obtained are discussed with respect to sources and sinks of water and nutrients in water conservation zones that help farmers to use water when it is required. Three types of water conservation zones, namely farm ponds, wetlands and riparian buffer zones were studied using stable isotopes of oxygen-18 (δ18O) and hydrogen-2 (δ2H) to trace the movement of water, and nitrogen-15 (15N) to trace nitrogen (N) and determine N use efficiency. Preliminary results showed that δ18O and δ2H effectively identified sources of water in water conservation zones and the interactions between water conservation zones and water from the catchment. Approximately 90 percent of water in water conservation zones was provided by runoff from the catchment while the remainder came from sub-surface flows and/or direct rainfall inputs. Water balance estimations showed that these water conservation zones with a surface area of less than three percent of the catchment area were able to capture more than 90 percent of water generated as runoff. Besides water retention, one water conservation zone in Estonia trapped N in the runoff water (up to 60 percent) effectively and converted nitrate into N2 gas (170 to 350 kg·ha/yr) through denitrification, thus potentially reducing nitrate inputs into downstream receiving waters. The nitrate and ammonium trapped in water conservation zones could also be used to provide N for crops through irrigation.