Natural variation of macrophyte vegetation of lowland streams at the regional level

Abstract

a b s t r a c tIn the present study, we present a synopsis of two macrophyte surveys of physiographic units in northwest Germany carried out over one decade. Data were used to test a set of hypotheses on macrophyte distribution at the regional level. Rank-frequency curves resembled the broken stick model. Twentyone species of the 59 most frequent species occurred at high frequencies above 15%. Helophytes made up a high percentage (12 of 21) of the frequent species. Phalaris arundinacea was the most frequent species in both sampling periods. Most species showed no considerable change in frequency over time, among them the core hydrophytes. Spatial variation of species frequencies among physiographical units showed a unimodal distribution in relation to frequency. Spatial variation of frequencies of functional groups was significantly lower. Most uneven distribution among physiographical units was found in cryptogams. DCA ordinations of physiographical units showed a spatial gradient from alluvial plains to higher grounds units, which remained constant over time. CCA ordination of physiographical units in relation to environmental parameters identified two main axes, an altitudinal gradient and an alkalinity gradient. Species composition of units corresponded to the main landscape pattern of alluvial plains, glacial lowlands, and higher grounds on Mesozoic rock. Species diversity showed a complex behavior. Diverse units were found both in alluvial plains and glacial lowlands of intermediate elevation. The study may help defining regionally differentiated reference states for stream management, benchmarking indicator scores of species and avoiding application of assessment methods outside their range of applicability.

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

“…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. In the study by Wiegleb et al (2015), the gradient was only three classes long (comparable to classes II–IV in this paper), and thus, many assessment methods did not work well.…”

“…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).…”

“…Some skeptical arguments also concerned the idea of macrophyte indication (Demars and Edwards 2009; Demars et al 2012a; Wiegleb et al 2014a), in view of the difficulty of statistical detection of important ecological gradients, particularly trophy (as well as altitude and alkalinity), due to collinearity of ecological gradients as well as insufficiency of databases to estimate spatial and temporal variation of macrophyte metrics. Moreover, Wiegleb et al (2015) raised questions on the idea that a classification-independent single metrics method can yield reasonable results under complex conditions. By means of stratification of sampling or classification of rivers, better results are achieved.…”

Fragmentation and groundwater supply as major drivers of algal and plant diversity and relative cover dynamics along a highly modified lowland river

“…Generally, a high DIC availability tends to support high algal diversity levels (Graham et al, 1996;Wyatt and Stevenson, 2010). A recent regional study performed by Wiegleb et al (2015) reinforced the preeminent importance of inorganic carbon availability on aquatic vascular plant distribution, if compared with reduced nitrogen or phosphorus levels, thereby integrating previous observations (Demars and Edwards, 2009;Demars et al, 2012). Alkalinity clearly emerges as a key discriminator in large-scale analyses, as was initially suggested by Wiegleb (1984).…”

Macrophyte and macroinvertebrate patterns in unimpacted mountain rivers of two European ecoregions

“…Geographical location was also identified as one of the major factors influencing macroinvertebrate communities, which should be taken into consideration in the assessment of river typology based on biotic elements. Some differentiation of vegetation between adjacent physiographic units was detected by Wiegleb et al (2015) in northwest Germany, but on the other hand, the limited role of ecoregional criteria in explaining the macrophyte distribution has been revealed by other studies, for instance Jusik et al (2015) in Poland, Vieira et al (2016) in Mediterranean Europe as well as BaattrupPetersen et al (2006BaattrupPetersen et al ( , 2008, who have undertaken relevant multivariate analyses of the macrophyte sites recorded across several European ecoregions. In the case of macroinvertebrate distribution patterns, the apparent impact of a geographical factor was detected in headwater streams by Astorga et al (2014).…”