Measuring ecological change of aquatic macrophytes in Mediterranean rivers

Abstract

a b s t r a c tA metric was developed for assessing anthropogenic impacts on aquatic macrophyte ecology by scoring macrophyte species along the main gradient of community change. A measure of ecological quality was then calculated by Weighted Averaging (WA) of these species scores at a monitoring site, and comparison to a reference condition score. This metric was used to illustrate the difficulties of developing aquatic macrophyte indices based on indicator species in Mediterranean rivers. The response of the metric to a nutrient gradient was examined within two different river typologies: the national typology designed for the Water Framework Directive and a typology that segregates the environmental variables to produce maximum species similarity within a river type. Both typologies showed the strong north-south climatic divide in Portugal, with southern rivers having long periods without rainfall and often without flowing water in the summer. Overall, the metric responded well to nutrient impacts however it performed poorly in some southern lowland river types. This was thought to be due to low numbers of aquatic macrophytes in temporary rivers. Non-aquatic species that establish in the river channel of temporary rivers may have to be included in indices to improve performance. Also, simple Weighted Averaging (WA) metrics may be insensitive to abundance changes and loss of rarer indicators in lowland Mediterranean rivers. More sophisticated methods of using WA are suggested, as well as further research into developing assessment methods specific to the character of Mediterranean rivers.

Is the macrophyte diversification along the trophic gradient distinct enough for river monitoring?

“…The occurrence of many rare species in clean waters has already been reported in the literature (Schaumburg et al 2004; Steffen et al 2014). In turn, the disappearance of rare sensitive taxa in watercourses with increased nutrient content was described by Dodkins et al (2012), who investigated lowland rivers in the UK. Changes in macrophyte species and their population size under the influence of water habitat disturbance have also been reported by other authors (e.g., Kohler 1975; Steffen et al 2013, 2014; Wiegleb et al 2015).…”

“…A particularly significant part of the analyzed data is the physicochemical dataset where samples were taken monthly during the whole year, for each river site. The quality of our physicochemical data is exceptional within the field of research into aquatic plant ecology, since most studies are typically based on data from a single water sampling (Hering et al 2006; Szoszkiewicz et al 2006; Dodkins et al 2012; Chappuis et al 2014; Steffen et al 2014; Jusik et al 2015) or several samplings at most (Thiébaut et al 2002; Birk and Willby 2010). Analyses of large scale macrophyte development in relation to comprehensive hydrochemical data obtained from environmental monitoring were carried out by Marzin et al (2012), but the typological differentiation was not respected in their analysis.…”

“…It is assumed that the most important of them are nutrient concentrations (Westlake 1975; Robach et al 1996; Schneider et al 2000; Thiébaut et al 2002; Szoszkiewicz et al 2006; Dodkins et al 2012), flow velocity (Westlake 1975; Dawson 1988; Fennessy et al 1994), hydrological conditions (Westlake 1975; Haslam 1987; Baattrup-Pedersen and Riis 1999), pH (Tremp and Kohler 1995), carbonate hardness, shading (Westlake 1975; Dawson and Kern-Hansen 1979), hydromorphological modifications (O’Hare et al 2006), and landscape pattern (Wiegleb et al 2015). A significant and apparent response of vegetation provides a useful indication of persistent and long-term habitat changes in aquatic ecosystems, which have been widely used as indicators of water quality in streams and rivers for many decades (Wiegleb 1979; Haslam 1982; Holmes et al 1999; Ceschin et al 2010).…”

Application of Aerial Digital Photography for Macrophyte Cover and Composition Survey in Small Rural Streams

“…In both altered and natural conditions, dense macrophyte patches can lead to a reduction in water velocity and are likely to cause high water levels, bank overtopping and consequential flooding (Sand-Jensen and Pedersen, 1999;Green, 2005a;2005b). The sensitivity of aquatic vegetation to water quality and habitat modification makes this group suitable to be used as a biological assessment tool (Hering et al, 2006;Szoszkiewicz et al, 2006;Kuhar et al, 2011;Lorenz et al, 2012;Dodkins et al, 2012) and as an early indicator of water quality and ecosystem integrity (Swanson et al, 2012). The more commonly used methodologies for identification and mapping of macrophytes employ ground level surveys (Dawson, 2002), such as grid analysis (e.g.…”

“…The more commonly used methodologies for identification and mapping of macrophytes employ ground level surveys (Dawson, 2002), such as grid analysis (e.g. Collier et al, 1999;Champion and Tanner, 2000;Demars and Harper, 2005;Szoszkiewicz et al, 2006), or surveying a stream section by pacing along a known stream stretch (Dawson, 2002;Dodkins et al, 2012;Lorenz et al, 2012). While such methodologies can provide detailed information on plant community and species, applying them over large sections can be rather difficult and highly time consuming, and subject to the surveyor experience.…”