Macrophytes respond to reach‐scale river restorations

Abstract

Summary1. In recent years, river restoration science has been searching for biological indicators of improvement in the physical habitats of streams. To date, research has mainly focused on the use of fish and macroinvertebrates as indicators. Despite their importance in aquatic ecosystems, the response of macrophytes to habitat restoration has been rarely studied. 2. We investigated the macrophyte communities of 40 restored river reaches in the lowland and lower mountainous areas of Germany. Each restored reach was compared to an upstream, unrestored reach using a space-for-time-substitution approach. At each reach, a 100 m stretch was surveyed for submerged and emergent macrophytes, recording the quantity, abundance and growth form of each species. Additionally, microhabitat patterns (substrate, depth, current velocity) and channel parameters (mean and bankfull width, number of channel elements) were recorded. 3. Restored reaches had a significantly higher macrophyte cover, richness, diversity and number of growth forms. Macrophyte diversity and richness were both positively correlated with depth, current and substrate. 4. The analysis of growth forms showed that Lemnids, Helodids, Parvopotamids, Elodids, Peplids and Juncids are all significant indicators of restoration. These species all responded directly to the restoration measures either by highly increasing in abundance or by being present in the restored reaches and absent in the unrestored reaches. While the restored reaches of the lowland rivers were characterized by a high abundance of Peplids and Parvopotamids, the restored reaches of the mountain rivers showed a significantly higher presence and abundance of Lemnids and Helodids. 5. Three macrophyte species (Lemna minor, Persicaria hydropiper, Potamogeton crispus) were regarded as significant indicators of restoration. No species were found to be indicators of unrestored reaches. 6. Synthesis and applications. Macrophyte communities benefit from river restoration by showing increased cover, abundance and diversity. The main drivers of this enhancement are more natural and diverse substrates and an increased floodplain area in the restored reaches, as well as a greater variability of current and depth patterns. Monitoring of macrophytes could thus be an easy and cost-effective means to gauge the success of river restoration measures.

The River Gelså restoration revisited: Habitat specific assemblages and persistence of the macroinvertebrate community over an 11-year period

“…Very rarely has this fluvial dynamism been taken into consideration in the design of restoration projects and temporal data documenting restoration effects on fluvial processes are missing. Even though the number of river restorations has increased over the last several decades in both Europe and North America (Bernhardt et al, 2005;Feld et al, 2011;Lorenz et al, 2012), studies providing conclusive empirical evidence of its effects are lacking (Bernhardt and Palmer, 2011). Several published reviews provide almost no evidence of a long-term (+5 years) positive effect of river restoration on biotic communities (Roni et al, 2008;Miller et al, 2010;Feld et al, 2011), albeit Lorenz et al (2012) in a recent study found a longer term positive response of macrophytes to restoration measures.…”

Morphological forms of two macrophytes (yellow water-lily and arrowhead) along velocity gradient

“…Flexible forms ensure colonization of unoccupied spaces, unavailable for other species of macrophytes (O'Hare et al 2011). Moreover, submerged vegetation has a significant impact on the accumulation of fine sediments, reduces erosion, increases retention, preserves water clarity and improves its quality (Horippila & Nurminen 2003;Kleeberg 2010;O'Hare et al 2011;Lorenz et al 2012). We showed the relationships between water velocity and other environmental factors, such as the depth of water and type of substrate.…”

“…Furthermore, morphological adaptations, such as reduction in the leaf number, are the result of aquatic plant response to hydrodynamic stress (Puijalon et al 2007). Growth forms of aquatic plants can be used as tools for the habitat modification assessment and monitoring of ecological status of different rivers types (Gurnell et al 2010;Lorenz et al 2012;Vukov et al 2012).…”

Native submerged macrophyte distribution in seasonally-flowing, south-western Australian streams in relation to stream condition

“…Although recolonisation of macrophytes is a common goal of restoration in Europe (Lorenz et al 2012), they are rarely considered in this context in Australian streams. This study indicates the potential for positive growth response of some submerged native macrophyte species to stream degradation in seasonally-flowing streams, and demonstrates that these plant assemblages can support a more abundant and diverse aquatic fauna in reaches where riparian vegetation is degraded or absent.…”