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Earthworms and termites, as soil engineers, play a major role in the regulation of biogeochemical processes and the provision of ecosystem services. They create biogenic aggregates on the soil surface, e.g., earthworm casts and termite sheetings, which can influence soil erosion and the downward transfer of fertility. We assessed the effect of the micro-relief generated by earthworms and termites on soil hydrodynamic properties, and soil and nutrient losses. Eighteen 1 m × 1 m plots were established for rainfall simulation experiments (2 runs of 40 min rain, intensity 90 mm h −1 ) in a steep slope fallow in Northern Vietnam. The soil surface of the micro-plots differed in the proportions of earthworm casts and termite sheetings. The results confirmed the importance of soil biostructures in the regulation of pedohydrological properties of soils. Although globular water-stable earthworm casts promote water infiltration in soil and decrease soil and nutrient losses, the unstable termite sheetings break-down rapidly and generate structural crusts which foster water runoff and soil detachment. No relation was observed between the abundance or biomass of earthworms or termites and the pedohydrological properties measured during the rainfall simulations. This therefore suggests that soil engineers can have greater impact on ecosystem functioning through their biogenic structures rather than as a result of their own abundance or biomass.

For the first time, the dual isotope approach was applied to trace the sources of impacts and to identify the governing biogeochemical processes in a river network in the tropical deltaic region of the Red River (Vietnam). Our long term surveys concluded that water in this river network was severely impacted by anthropogenic activities. Analysis has shown strong spatio-temporal variation of nitrate isotopes; ranges of δ15N– and δ18O– were from −5 to 15 ‰ and from −10 to 10 ‰, respectively. Average values of δ15N– and δ18O– in the dry season, when fertilizer is applied, were 3.54 and 3.15 ‰, respectively. In the rainy season, the values changed to 6.41 and −2.23 ‰, respectively. Denitrification and biological assimilation were active throughout the year, but were especially enhanced during fertilization time. Mineralization of domestic organic matter and consequent nitrification of mineralized were the dominant processes, particularly during the rainy period.

For the first time, the dual isotope approach was applied to trace the sources of impacts and to identify the governing biogeochemical processes in a river network in the tropical deltaic region of the Red River (Vietnam). Our long term surveys concluded that water in this river network was severely impacted by anthropogenic activities. Analysis has shown strong spatio-temporal variation of nitrate isotopes; ranges of δ15N– and δ18O– were from −5 to 15 ‰ and from −10 to 10 ‰, respectively. Average values of δ15N– and δ18O– in the dry season, when fertilizer is applied, were 3.54 and 3.15 ‰, respectively. In the rainy season, the values changed to 6.41 and −2.23 ‰, respectively. Denitrification and biological assimilation were active throughout the year, but were especially enhanced during fertilization time. Mineralization of domestic organic matter and consequent nitrification of mineralized were the dominant processes, particularly during the rainy period.