Penetration of bog peats and lake sediments by tritium from atmospheric fallout

PEAT SAMPLES WERE COLLECTED WITH LIVINGSTONE AND JENKINS SAMPLERS AND BY DIVERS FROM THE GREAT WETLAND COMPLEX NORTH OF UPPER RED LAKE AND FROM THE DEEPEST PARTS OF FOUR LAKES IN THE FORESTED PART OF MINNESOTA TO INVESTIGATE: (1) HOW DEEPLY TRITIUM PENETRATES PEATS AND LAKE SEDIMENTS AND (2) WHETHER PAST INPUT PULSES HAVE BEEN PRESERVED IN PEAT AND SEDIMENT PROFILES. LAKE WATER SAMPLES WERE ALSO COLLECTED FOR COMPARISON. TRITIUM IN THE SURFACE BOG PEATS OF THE RED LAKE WETLAND EXHIBITED ABOUT THE SAME CONCENTRATION AS IN ATMOSPHERIC PRECIPITATION, WHICH IS STILL APPRECIABLY ENRICHED BY TRITIUM FROM NUCLEAR WEAPON TESTING. PAST INPUT PULSES ARE NOT PRESERVED IN THE PEAT PROFILE, AND THE PATTERN OF SUBSURFACE DECLINE SUGGESTS THAT MOST OF THE MODERN PRECIPITATION RICH IN TRITIUM IS REMOVED RAPIDLY BY EVAPOTRANSPIRATION AND BY LATERAL RUNOFF WITHIN THE TOP 1.5 M OF THE 3.5-M THICKNESS OF LITTLE-DECOMPOSED SPHAGNUM PEAT AT THE CREST OF THE RAISED BOG. HOWEVER, SOME BOMB TRITIUM HAS PENETRATED DOWN TO THE DISCONTINUITY BETWEEN THE HIGHLY PERMEABLE SPHAGNUM PEAT AND THE UNDERLYING WELL-DECOMPOSED AND MUCH LESS PERMEABLE FEN PEAT. IN PROFUNDAL LAKE SEDIMENTS THE INFLUENCE OF HIGHLY ENRICHED PRECIPITATION HAS LIKEWISE BEEN LARGELY TRANSITORY AND OF MAJOR SIGNIFICANCE ONLY IN SEDIMENT DEPTHS OF LESS THAN 1 M. THE LAKE WATER SAMPLES CONTAINED TRITIUM CONCENTRATIONS THAT WERE DISTINCTLY GREATER THAN MOST OF THOSE FOR ATMOSPHERIC PRECIPITATION. SUCH RESULTS ARE NOT UNEXPECTED SINCE ANNUAL RATES OF PRECIPITATION AND EVAPORATION WERE RATHER SIMILAR. (HOLOMAN-BATTELLE)