Fly fishing no-kill zones: a possible way to conjugate conservation issues, sustainable sport enhancement and local development in Alpine areas?

The promotion of sustainable tourism and outdoor sports can represent an important way to couple environmental conservation strategies and economic enhancement in marginal and Alpine areas. In this context catch and release fly fishing zones can represent an interesting tool, although no data is available on the effectiveness of these practices on Alpine salmonid population dynamics. Salmonids are the main group of fish in alpine rivers and they are the only actively targeted by anglers. Aim of this work is filling this gap, with a pilot study on two no-kill zones (Po and Pellice rivers, NW Italy). We conducted a temporal and spatial comparison between free-fishing and catch and release management river sections, with a detailed analysis on the Po River site. Our results support the hypothesis that catch and release management allows a numerical increase in wild trout populations. In particular, we detected a massive and rapid increase in younger individuals, possibly linked to a stop on the removal of large-sized reproducers. Protecting trout by the implementation of this practice can at the same time allow the increase of sustainable economic development and sport in marginal areas.

Experimental Study at the Reservoir Head of Run-of-River Hydropower Plants in Gravel Bed Rivers. Part II: Effects of Reservoir Flushing on Delta Degradation

Run-of-river hydropower plants (RoR HPPs) are capable of interrupting the sediment connectivity of many alpine rivers. Still, there is a lack of systematical investigations of possible sediment management strategies for small and medium sized RoR HPPs. This study deals with the headwater section of an impoundment and the approach of sediment remobilization during drawdown operations. Therefore, a typical medium sized gravel bed river having a width of 20 m, a mean bed slope of 0.005, a mean flow rate of 22 m3/s, and a 1-year flood flow of 104 m3/s is recreated by a 1:20 scaled physical model. Heterogenous sediment mixtures were used under mobile-bed conditions, representing a range of 14–120 mm in nature. During the experiments, the flow rate was set to be 70% of the 1-year flood (HQ1) regarding on the ability to mobilize all sediment fractions. The possibility to remobilize delta depositions by (partial) drawdown flushing within a reasonable period (≈9 h in 1:1 scale) was shown by the results. The erosion of existing headwater delta deposition was found to be retrogressive and twice as fast as the preceding delta formation process. A spatiotemporal erosion scheme points out these findings. This supports the strategy of a reservoir drawdown at flood events of high reoccurrence rate.

Salinization of Alpine rivers during winter months

Human-induced (i.e., secondary) salinization affects aquatic biodiversity and ecosystem functioning worldwide. While agriculture or resource extraction are the main drivers of secondary salinization in arid and semi-arid regions of the world, the application of deicing road salt in winter can be an important source of salts entering freshwaters in cold regions. Alpine rivers are probably affected by salinization, especially in highly populated mountain regions, although this remains to be explored. In this study, we analyzed multi-year conductance time series from four rivers in the European Alps and demonstrated that the application of deicing road salt is linked to peaking rivers’ salinity levels during late winter/early spring. Especially in small catchments with more urban surfaces close to the rivers, conductance increased during constant low-flow periods in late winter and was less correlated with discharge than in summer. Thus, our results suggest that small rivers highly connected to urban infrastructures are prone to considerable salinity peaks during late winter/early spring. Given the low natural level of salinities in Alpine rivers, the aquatic biodiversity might be significantly affected by the recorded changes in conductance, with potential consequences on ecosystem functioning. Thereby, we urge the research community to assess the impact of secondary salinization in Alpine rivers and call for an implementation of management practices to prevent the degradation of these pristine and valuable ecosystems.