Benthic invertebrate assemblages and leaf-litter breakdown along the eucrenal–hypocrenal ecotone of a rheocrene spring in Central Italy: Are there spatial and seasonal differences?

To better understand the pattern of variation in biocomplexity of springs and first-order streams, it is essential to explore how the characteristics of spring communities may vary from the spring source (eucrenal) to the first reach of the originating springbrook (hypocrenal). For these reasons, we assessed spatial and temporal variation of crenic assemblages and leaf-litter breakdown along a 45-m reach of a spring–springbrook system in Central Italy. We found that physicochemical and hydrological parameters of Vera Spring did not vary significantly along the 45-m reach investigated. In contrast, total richness of assemblages was significantly higher at 20 and 45 m from the spring source, while abundances were more variable and did not show significant differences between seasons and among sites. The composition of assemblages did not show significant temporal trends in all sites investigated, while spatial differences along the eucrenal–hypocrenal ecotone were more prominent. The functional organization of assemblages was relatively stable in both space and time, and no spatial differences were observed in the rate of leaf-litter breakdown, though the dry mass loss of poplar leaves was slightly higher at the most downstream site. We conclude that immediately after groundwater emergence, spring communities are less stable and more variable while they tend to be better organized at short distance downstream. Small and gradual spatial changes in the strength of competitive interactions and predation pressures may have a fundamental role in structuring spring communities more than variation in abiotic parameters and/or differences in quantity and quality of food resources.