The influence of soil biodiversity on hydrological pathways and the transfer of materials between terrestrial and aquatic ecosystems

The boundaries between terrestrial and aquatic ecosystems, known as critica l transition zones (CTZ), are dynamic interfaces for fluxes of water, sedim ent, solutes, and gases. Moreover, they often support unique or diverse bio tas. Soils, especially those of riparian zones, have not been recognized as CTZ even though they play a critical role in regulating the hydrologic pat hways of infiltration and leaching, or runoff and erosion, which can cumula tively affect biogeochemical processes and human livelihoods at landscape s cales. In this review, we show how the processes that regulate hydrologic f luxes across and through soil CTZ are influenced by the activities of soil biota. Our message is fourfold. First, there are a variety of ways in which soil biodiversity, in terms of richness and dominance, can influence hydro logical pathways in soil and thus the transfer of materials from terrestria l to aquatic ecosystems. Second, the influence of soil organisms on these h ydrological pathways is very much interlinked with other environmental, soi l biophysical, and vegetation factors that operate at different spatial and temporal scales. Third, we propose that the influence of soil biodiversity on hydrological pathways is most apparent (or identifiable), relative to o ther factors, in situations that lead to the dominance of certain organisms , such as larger fauna. Fourth, soils are buffered against environmental ch ange by biophysical properties that have developed over long periods of tim e. Therefore, the effects of changes in soil biodiversity on hydrological p rocesses at the ecosystem scale might be delayed and become most apparent i n the long term.