Where a springhead becomes a springbrook : a regional zonation of springs

Springs are important freshwater habitats that provide specific abiotic conditions for many species. These conditions may change very rapidly downstream. Limnologists tend to treat spring sources and their adjacent springbrooks as a unity because of the lack of clear criteria to separate these sections. In this study, we investigated the longitudinal distribution of macroinvertebrate assemblages in ten undisturbed springs in north-western Switzerland at three different distances from the source. Using non-metric multidimensional scaling and analysis of similarities, we detected significant differences between the macroinvertebrate assemblages of the investigated sections in all spring ecosystems, even over short distances. These results stress the importance of distinguishing between the sequential habitats in this upper region of headwaters. Although a complex of abiotic factors is responsible for the distribution of macroinvertebrates, we consider temperature to be of special importance. Based on our faunistic data, we propose that the rheocrene-like springs in the Jura Mountains consist of two sections: the springhead and the springbrook, with the springhead consisting of the source and the upper part of the adjacent downstream section. In accordance with literature and our faunistic and temperature data, we place the beginning of the springbrook at approximately 5 m from the springhead. With this distinction, we justify that springheads and springbrooks are unique, discrete ecosystems, and as such must be considered in conservation legislation.