Floodplains of a regulated southern alpine river (Brenno, Switzerland): ecological assessment and conservation options

Abstract

ABSTRACT1. The fifth-order southern alpine Brenno River and its floodplains are severely impaired by embankments, water abstractions and the construction of dams for hydropower generation. The river's annual mean discharge is reduced to 27% of the natural flow and the number of small (50-100 m 3 s À1) and medium-sized (101-150 m 3 s À1) floods is reduced significantly. 2. Lateral hydrological connectivity has decreased strongly as a result of the flow regulation, whereas the significance of vertical connectivity has increased. The remnants of the middle and lower floodplains still contain springbrooks, ponds, and intermittently connected channels, which are all sustained by emerging groundwater.3. Aquatic floodplain habitats can be classified partially by faunal composition. The lotic/lentic gradient appears to be a dominant compound factor structuring invertebrate assemblages when considering all aquatic habitats. The exfiltration of groundwater in conjunction with a reduced lateral connectivity enables the occurrence of many stenotopic species.4. A comparison of present floodplains with those shown on historical maps shows that the fluvial landscape has changed markedly. The proportions of functional floodplain units characterized by autogenic succession and trends to late successional stages (i.e. senescence) have increased.5. Floodplains of the Brenno river are still considered to represent important ecological areas and they are protected by law. Whilst the legislative protection of floodplains is the basis for conservation, this does not include the restoration of driving hydrological processes. An annual release of small-and medium-sized floods could generate a diversity of disturbances, thereby promoting rejuvenation and counteracting senescence.6. Alternative conservation options that circumvent ongoing contracts of water use, though generally promising, are limited because of the operation of hydropower schemes. At present the exfiltrations of groundwater mitigate the impacts of flow regulation on the ecological integrity of the floodplains.

Distribution of selected macroinvertebrates in a mosaic of temporary and permanent freshwater ponds as explained by autologistic models

“…Indeed, for many species the decline in deviance was only significant at relatively short distances of <200 m, for example A. globulus , L. lunatus , L. peregra and G. pulex . Some of these patterns may reflect the habitat preferences of the species; for example A. globulus is commonly found in spring‐fed pools (Brunke 2002) and this may account for the similarity in pattern with G. pulex . In general, water beetles are good dispersers, although of the four under study A. globulus will have been the poorest.…”

Green hydropower: a new assessment procedure for river management

“…A management plan for preserving valuable landscape features and biotopes should be based on habitat maps and biodiversity analyses. Such a comparative analysis based on the benthic fauna was performed in two floodplain sections of the Brenno (Brunke, 2002;Truffer et al, 2002a). Figure 8 compares the taxa richness and the percentage composition with lotic, lentic, spring and ubiquitous taxa among the Brenno, its tributary, and two flood plains.…”

“…Figure 8 compares the taxa richness and the percentage composition with lotic, lentic, spring and ubiquitous taxa among the Brenno, its tributary, and two flood plains. Two-thirds of all 110 taxa were found exclusively in floodplain habitats but not in the Brenno or the tributary (Brunke, 2002;Truffer et al, 2002a). The floodplains near Grumo (middle course) and near Loderio (lower part of the Brenno) are nature preserves according to Swiss law (Figure 2).…”

Conservation of floodplain wetlands – out of sight, out of mind?

“…Dams capture floods in the river, controlling and diverting flow for human use upstream of the floodplain (Figure (b)). Flooding is marginally reduced in the upper reaches of the river but severely reduced to the floodplain which shrinks because it is mostly downstream of abstractions (Figure (b); Brunke, ). Small privately‐owned off‐river storages also regulate flows to the floodplain (Figure (b)).…”