Factors shaping submerged bryophyte communities: A conceptual model for small mountain streams in Germany

Abstract

a b s t r a c tSeveral models explaining species composition of aquatic bryophytes are available for specific regions. However, a more general, conceptual model applicable to a broader range of regions is lacking.We present a conceptual model ranking environmental factors determining submerged bryophyte communities in small mountain streams. It was tested on a dataset of 54 stream sections after removing the effect of stream size and altitude. Species responses were modeled with pH as predictor variable based on 97 stream sites covering six mountain regions all over Germany. Multiple regressions revealed the importance of primary growth factors (light, Ep(CO 2 )) and substrate for the total submerged bryophyte coverage.The known distinction of hard-and softwater bryoflora was clearly supported. The floristic composition of headwaters was predominantly determined by the bicarbonate/ionic strength complex. Species response to pH values supported this result and thus our conceptual model. The primary growth resources light, Ep(CO 2 ) and availability of coarse streambed material explained one third (R adjusted 2 = 0.34) of total submerged bryophyte cover. Disturbances, predominantly spates, reduce biomass but do not affect the basic floristic structure.In conclusion, conceptual models and monitoring methods focusing on aquatic bryophytes need to clearly distinguish "aquatic" from "submersed by chance". All "aquatic bryophytes" found in Germany can also occur at least temporarily at non-submerged sites. Therefore, a distinction between primary growth factors and additional resources is recommended to disentangle factors determining aquatic bryophyte communities.

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

“…This factor enabled the distinguishing of alpine-like rivers with considerable river slopes, high kinetic energy, turbulent flow and coarse-grained riverbed material (boulders, stones), from submontane rivers with smaller riverbed slopes, low kinetic energy and fine-grained bottom material (cobbles, pebbles). The environmental variation reflected in our database is large enough to analyse sources of biological variation, as water velocity and substrate are considered to be primary factors affecting biological communities in mountain streams (Lorenz et al, 2004;Baattrup-Pedersen et al, 2006;Brabec & Szoszkiewicz, 2006;Szoszkiewicz et al, 2006;Callanan et al, 2012;Langhammer et al, 2012;Tremp et al, 2012;Vieira et al, 2014;Ceschin et al, 2015).…”

Which environmental factors best explain variation of species richness and composition of stream bryophytes? A case study from mountainous streams in Madeira Island

“…They reflect anthropogenic influences as well as the disturbance regime (or the streambed stability) and they have been shown to be important for bryophyte species composition in various types of streams (Englund, 1991;Muotka and Virtanen, 1995;Suren and Ormerod, 1998;Scarlett and O'Hare, 2006;Lang and Murphy, 2012;Tremp et al, 2012;Manolaki and Papastergiadou, 2013). The physical-chemical variables were of particular importance in the instream habitat where they explained approximately one third of the variation in the species composition.…”

“…For example, velocity of the water or the kind of substrates available (e.g. blocks, sand) strongly influence bryophyte communities (Muotka and Virtanen, 1995;Tremp et al, 2012). Effects of these variables on bryophyte communities are mostly indirect by determining or modulating disturbance regimes.…”

“…Generally, community ecology of stream bryophytes has been in the focus of a number of studies (Söderström, 2006;Richardson and Danehy, 2007;Lang and Murphy, 2012;Tremp et al, 2012). However, there is considerable bias in these studies with respect to the type of streams studied as emphasized by Lang and Murphy (2012).…”

Environmental effects on species richness of macrophytes in Slovak streams

“…The effort of detecting causes of differences in the macrophyte composition resulted in numerous studies of macrophyte-environment relationship. Several papers have focused on species composition in streams in relation to ecological variables [5][6][7][8][9] or human impact and management [10]. The acquired knowledge is applicable under the Water Framework Directive [11] where macrophytes are used as one group of the indicators of ecological status in different types of surface waters [cf.…”