Freshwater spring indicator taxa of benthic invertebrates

Abstract

Groundwater and subsurface water have important roles in river ecosystems: e.g., stabilizing flow regime and water temperature, supplying nutrients, and increasing biodiversity. However, detection of springs and quantitative estimation of groundwater contribution to the surface water ecosystems are not easy in the field. Although some indirect measurements combing simulations and models have been widely used to estimate the groundwater flow, they require certain assumptions, thus it is rather difficult to estimate the discharge of groundwater on a local scale. Direct field-scale measurement of groundwater flow is also difficult particularly for researches of ecology and environmental science.In this study, we present biological indicators of benthic invertebrates to evaluate the contribution of groundwater to surface water bodies. Because the benthic invertebrates show distribution patterns reflecting habitat scale environmental conditions in a sensitive manner, they are expected to serve as a biological indicator of groundwater spring sites. We collected data of benthic invertebrates from literature in a global scale and additional field research in Japan. By analyzing their taxonomic features and biological habits, we identified spring indicator taxa of benthic invertebrates based on the degree of dependency to groundwater environment.A total of 1,448 aquatic invertebrate species representing 58 orders were found from 249 research sites. The spring indicators were identified as spring dependent species including groundwater species (Stygobites and Stygophiles), cave species (Troglobites and Troglophile), and stenothermal species. Considering the geographical distribution patterns of the spring indicator taxa, stenothermal species were classified into "cold stenothermal species" which evolutionarily originate in more boreal regions and "warm stenothermal species" derived from more tropical regions. Ecological interpretation of these stenothermal species was discussed in relation to climatic zones and altitude of the basin concerned. Based on the variations of spring contribution into river ecosystems suggested by the spring indicator species, we proposed an application procedure of the spring indicators for environmental assessment and nature conservation works in river management.