Hydrogen Peroxide Concentration as an Indicator of Environmental Stresses to Relate Hydraulic Quantities and Other Factors

Management of overgrown aquatic macrophytes is an important issue all over the world. The contribution of hydraulics quantities among various environmental factors has not been elucidated yet. Environmental factors affect macrophytes as stresses and regulate their growth, and quantitative comparisons with other types of stressors is important.

When environmental stresses are exerted to organisms, reactive oxygen species are generated in their body, and damage protein, including DNAs, etc., due to oxidative stress.

Among reactive oxygen species, hydrogen peroxide, H₂O₂, generated directly or in the scavenging process of super oxide, is most common.

Laboratory experiments were conducted with Egeria densa with single or combinations of target environmental stressors. Then, the relationship was obtained between H₂O₂ concentration and intensities of the stressors. The results indicate the threshold concentration for the mortality is uniquely determined as 15μmol/gFW. Then, the total H₂O₂ concentration has represented the sum of the stresses generated by each component.

Field observation was conducted for E.densa colony found in a river. E.densa shoots were sampled both in solar radiation exposed and dark adapted (30min shaded) conditions, together with light intensity and flow velocity/turbulence measurements. Then the relationships of each factor with H₂O₂ was obtained, as H₂O₂(μmol/gFW) = 0.1Velocity(cm/s)+3 (H₂O₂μmol/gFW) for velocity and H₂O₂(μmol/gFW) = 0.015Light(μmol/s/m²)-1.5 (H₂O₂μmol/gFW) for light intensity, where H₂O₂ is the hydrogen peroxide concentration of the plant body, Velocity is the average velocity, and Light is the light intensity at the plant canopy depth. Then, the total hydrogen peroxide concentration becomes as　H₂O₂=10/n.h^2/3S^1/2+0.015I₀exp(-kh)+1.5 (H₂O₂μmol/gFW), where h is the depth(cm), S is the channel slope and n is Manning’s coefficient, I₀ the light intensity at the surface, k the light attenuation coefficient.

For different channel slopes, H₂O₂ concentration was simulated for different depths. It was found that the concentration is lowest with 60 to 100cm deep, indicating the largest biomass with the depth, and always higher than the threshold value for higher than 1/100 of the channel slope, revealing no E.densa colony forms with the slope. These results agreed well with the field observation results.

All these results indicate that the hydrogen peroxide concentration becomes a useful indicator of environmental stress intensity and provides the hydraulic condition requiring for the macrophyte colonization.