DYNAMICS OF UV-DRIVEN HYDROGEN-PEROXIDE FORMATION ON AN INTERTIDAL SANDFLAT

Photochemically produced H2O2 was found to accumulate at micromolar co ncentrations in intertidal Wadden Sea areas. Annual amplitudes of sola r radiation lead to variations of the intertidal H2O2 accumulation wit h concentrations between 1 and 4 mu mol liter(-1) during summer, while winter concentrations were mostly <0.5 mu mol liter(-1). Diurnal vari ations of H2O2 accumulation over daily low-tide periods in intertidal environments are determined by the incident solar radiation, the conce ntration of UV-absorbing dissolved organic carbon in the water, as wel l as the concomitant biological and chemical H2O2 degradation within t he sediment surface. The efficiency of photosynthetic available radiat ion (PAR), UVA and UVB photons for photochemical H2O2 production was a ssessed using cut-off filters in the UVB and in different UVA ranges. UVB photons (295-320 nm) displayed an 11-fold higher efficiency compar ed to UVA (335-370 nm) and a 340-fold higher efficiency compared to PA R photons (>400 nm). A 10% ozone reduction leads to a doubling of UVB surface irradiance at 300 nm, which entails a 30 and 40% increase of t he apparent intertidal H2O2 concentrations. Progressive stratospheric ozone depletion via UVB-induced H2O2 formation will have yet unpredict able effects on boreal and Antarctic intertidal ecosystems.