| Popis: |
The displacement and recovery of surface-applied 15 NO 3 , 2 H and Cl − in the unsaturated zone of the British Upper Chalk was followed over a 4 year period. Recovery of Cl − in the chalk matrix under the treated plot was equivalent to 110% of that applied. That of 2 H was 57% in the treated plot. Lateral flow of 2 H was evident from cores taken outside the plot, and if this is included, together with 2 H estimated to have been lost by evapotranspiration, the recovery approached 100%. Recovery of 15 NO 3 was 100% 1 year after tracer application, falling to 9.4% after 4 years. No evidence of denitrification was obtained from background NO 3 cores, and it was concluded that the shortfall in NO 3 recovery was due to uptake by grass from depths of 50–70 cm. The tracer profiles and recoveries were not consistent with significant vertical macrofissure flow, but the lack of seasonal periodicity in background 2 H profiles suggested that some microfissure flow could be occurring. The displacement of the tracer peaks, when considered with the estimates of recharge, indicated that only 50% of the water-filled matrix was conducting flow. |
