Runoff Processes in Southeast Asia: Role of Soil, Regolith, and Rock Type

Changing climate and nutrient transfers: Evidence from high temporal resolution concentration-flow dynamics in headwater catchments

“…The nitrate peak that followed dilution or extended the response suggested a slower subsurface pathway connected to an old nitrate source such as displacement of nitrate in sub-surface pore water. However, the response time of this pathway is still relatively fast (hours rather than days), thus, according to Chappell et al (2007), again suggesting a shallow pathway. Nitrate levels are known to be high, and rising, in the sandstone aquifer in the bottom of the Eden Valley (Butcher et al, 2006) and whilst the hydrogeology of the catchments (Allen et al, 2010) suggests that the deep groundwater does not contribute to the outflow of these study catchments, it is possible that some nitrate leaves the catchments through the soil and rock and may eventually contribute to the nitrate in the sandstone aquifer, which may subsequently return to the surface further down the larger Eden catchment.…”

“…The sediment and TP responses were almost concurrent with discharge (highest cross correlation with discharge at time lag of 0 h), and approximately three hours behind peak rainfall, indicating fast pathways such as surface runoff or tile drains, both of which have been observed in the catchments. Chappell et al (2007) suggest that information about the dominant flow pathways can be deduced from knowledge on the presence or absence of four types of strata (topsoil, subsoil, permeable regolith, permeable rock). For example, a thin layer of topsoil over impermeable rock would result in a very fast response time in the hydrograph (time constant of minutes to hours), whereas the water movement through all four layers would show as a very damped and slow response in the hydrograph (time constant of weeks to months).…”

Overview: oxidant and particle photochemical processes above a south-east Asian tropical rainforest (the OP3 project): introduction, rationale, location characteristics and tools

“…Usually over two thirds of the upper canopy comprises tree species not contributing more than 1% to the total number (Whitmore, 1998). The soils typically associated with the occurrence of this forest formation in tropical Asia are the Ultisol group, and within western Amazonia the Oxisol group (Baillie, 1996;Chappell et al, 2007).…”

The role of climatic and terrain attributes in estimating baseflow recession in tropical catchments

“…By contrast, lower recession coefficients (slower drainage) were found for most of the humid tropics. Although there were no good quality data to account for the effects of soil depth and aquifer porosity, deep soils and permeable regoliths are widely present in tropical landscapes; and are likely to represent an important source of baseflow (Chappell et al, 2007). A recent three-year study in a small catchment underlain by very deep soils in the central Amazon Basin by Tomasella et al (2008) showed an important contribution to the groundwater system by the extended unsaturated zone.…”