Flow Intermittency Affects Leaf Decomposition and Benthic Consumer Communities of Alpine Streams: A Case Study along the Po River

Michele Freppaz,Alberto Doretto,Elisa Falasco,Francesca Bona,Laura Gruppuso,Mark Eric Benbow,Stefano Fenoglio

doi:10.3390/w14020258

Michele Freppaz, Alberto Doretto + Show 5 more

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https://doi.org/10.3390/w14020258

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Abstract

Streams and rivers are becoming increasingly intermittent in Alpine regions due to the global climate change and related increases of local water abstractions, making it fundamental to investigate the occurrence of supraseasonal drying events and their correlated effects. We aimed to investigate leaf litter decomposition, the C:N ratio of the litter, and changes in associated macroinvertebrate communities in three reaches of the Po River: One upstream, consistently perennial, a perennial mid-reach with high hydrological variability, and an intermittent downstream reach. We placed leaf litter bags of two leaf types—chestnut and oak; both showed comparable decomposition rates, but the remaining litter mass was different and was attributed to the C:N ratio and palatability. Furthermore, (1) in perennial reaches, leaf litter decomposed faster than in the intermittent ones; (2) in intermittent reaches, the C:N ratio showed a decreasing trend in both leaf types, indicating that drying affected the nitrogen consumption, therefore the conditioning phase; (3) associated macroinvertebrate communities were richer and more stable in perennial reaches, where a higher richness and abundance of EPT taxa and shredders was observed. Our results suggest that the variations in the hydrology of mountain streams caused by global climate change could significantly impact on functional processes and biodiversity of benthic communities.

Highlights

Introduction iationsOver the last few decades, the phenomenon of riverbed drying in mountain streams has gained increasing attention from researchers [1,2,3]
We evaluated the effect of supraseasonal dry events, which occur mainly in winter when the input of allochthonous material is higher, on the leaf litter decomposition process [52]
Research attention has been shifted to those streams that were previously considered perennial but which are facing dry events more frequently

Summary

Introduction

Introduction iationsOver the last few decades, the phenomenon of riverbed drying in mountain streams has gained increasing attention from researchers [1,2,3]. In the Italian Alps, effects of climate change such as increasing temperatures and decreasing winter precipitation are coupled with anthropogenic pressures (i.e., water abstraction) [4,5]. This phenomenon is quite recent in those streams that were previously considered perennial, and its effects must be investigated to fully understand the potential short- and long-term ecological consequences to river and watershed ecosystems. Riverbed drying events can negatively affect ecological processes from primary instream production to allochthonous coarse particulate organic matter (CPOM) decomposition [6].

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