Response of macrophyte communities to flow regulation in mountain streams

Abstract

River macrophytes are widely used in freshwater ecosystem assessment because of their sensitivity to anthropogenic pressures, even if there are only a few studies that investigated how macrophytes respond to water regime alterations. In this study, we analyzed the effects of dams on river macrophyte communities through a comparison between upstream and downstream sides from 18 dams located in Alps and Apennines. A co-inertia analysis and a Mantel test were applied to assess if the analysis of environmental parameters could be effective in predicting macrophyte community structure. We analyzed morphological and physicochemical inter-site differences and tested the influence of dams on various aspects of community structure (composition, richness, diversity, dominance, coverage) using multivariate randomized block permutation procedure. Plant similarity between sites was evaluated at the level of phylum, and indicator species analysis was performed to identify the taxa most sensitive or tolerant to water regulation. We found that the overall environmental setting overwhelms the dam impact and that the influence of hydrological alteration became apparent when comparing upstream and downstream assemblages at the same dam. In particular, we found that most of taxa had a higher affinity with the downstream side and that in general, stream regulation increases plant richness and coverage, but reduces community evenness. Analyses based on higher taxonomic groups (phyla) demonstrated that this community can be effectively used in bioassessment even at phylum level analysis. In particular, we found that bryophytes, strictly linked with changes in substrate stability, show particular sensitivity to water regulation in mountain streams.

Impacts of artificial barriers on the connectivity and dispersal of vascular macrophytes in rivers: A critical review

“…Discontinuities in community composition have been associated with dams, with assemblages exhibiting a shift from a composition similar to the drifting hydrochorous propagule bank upstream, to communities derived from local seed‐bearing plants downstream (Andersson et al, ; Jansson, Nilsson, Dynesius, et al, ). Decreases in macrophyte diversity and abundance have been reported downstream of dams (Casado, García de Jalon, Delolmo, Barcelo, & Menes, ; García de Jalon, Sanchez, & Camargo, ), while in other cases an increase in macrophyte abundance has been reported (Abati, Minciardi, Ciadamidaro, Fattorini, & Ceschin, ; Goes, ; Tena, Vericat, Gonzalo, & Batalla, ), although in these studies, changes in macrophyte population structure were not directly linked to disruptions of hydrochory, and probably related to differences in hydrological regime. However, other studies have found evidence that the richness of riverine plant communities was linked to hydrochorous seed input, with free‐flowing rivers showing higher richness (Merritt, Nilsson, & Jansson, ; Nilsson, Ekblad, et al, ; Nilsson, Gardfjell, et al, ).…”

“…Many of the observed changes in macrophyte community have been associated with the hydrological effects of dams, rather than their role in disrupting hydrochory. Stable flow conditions often found downstream of dams can increase aquatic plant cover in affected reaches (Abati et al, ; Goes, ; Ibáñez, Caiola, Rovira, & Real, ). Moderate disturbance caused by hydropeaking (frequent, short duration, artificial flow events) can also lead to increased macrophyte richness and abundance, compared to unregulated rivers (Bernez, Daniel, Haury, & Ferreira, ; Bernez, Haury, & Ferreira, ).…”

Aquatic Plant Diversity in Italy: Distribution, Drivers and Strategic Conservation Actions

“…Despite this, at national level a remarkable revival of interest in aquatic flora was stimulated by the enactment of the WFD ( Bolpagni et al, 2017a ). It has resulted into a renewed attention for inland aquatic habitats in general, and it has favored the integration of the available aquatic plant knowledge ( Testi et al, 2009 ; Ceschin et al, 2010 ; Azzella et al, 2013 , 2014 ; Villa et al, 2015 ; Abati et al, 2016 ; Bolpagni et al, 2016 ). Nevertheless, much work has to be done in order to facilitate the comparison and sharing of information gathered by the various institutional actors involved in the monitoring programs.…”

A river vegetation quality metric in the eco‐hydromorphology philosophy

“…However, Szoszkiewicz et al () also report that although macrophyte metrics developed to indicate ecological status respond strongly to total phosphorus concentrations in terms of nutrient response in both rivers and lakes, substrate was most important in structuring macrophyte species composition and abundance in rivers. Many widely used metrics including the Macrophyte Biological Index for Rivers, the Macrophyte Index for Rivers, the River Nutrient Macrophyte Index, and the Reference Index respond negatively to increased shading by the tree canopy (Wiegleb, Gebler, van de Weyer, & Birk, ), but macrophyte communities also respond strongly to changes in hydrological and morphological parameters (Abati, Minciardi, Ciadamidaro, Fattorini, & Ceschin, ; Ceschin, Tombolini, Abati, & Zuccarello, ).…”

“…Many widely used metrics including the Macrophyte Biological Index for Rivers, the Macrophyte Index for Rivers, the River Nutrient Macrophyte Index, and the Reference Index respond negatively to increased shading by the tree canopy (Wiegleb, Gebler, van de Weyer, & Birk, 2016), but macrophyte communities also respond strongly to changes in hydrological and morphological parameters (Abati, Minciardi, Ciadamidaro, Fattorini, & Ceschin, 2016;Ceschin, Tombolini, Abati, & Zuccarello, 2015).…”