Abstract
Forestry-related land use can cause increasing instream sedimentation, burying and eradicating stream bryophytes, with severe ecological consequences. However, there is limited understanding of the relative roles and overall importance of the two frequently co-occurring stressors, increased fine sediments and loss of bryophytes, to stream biodiversity and ecosystem functions. By using random forest modeling and partial dependence functions, we studied the relative importance of stream bryophytes and fine sediments to multiple biological endpoints (leaf-decaying fungi, diatom, bryophyte, and benthic macroinvertebrate communities; leaf decomposition) using field survey data from headwater streams. Stream bryophyte abundance and richness were negatively related to fine sediment cover, highlighting the detrimental effect of sedimentation on bryophytes. However, bryophyte abundance was consistently more important a determinant of variation in community composition than was fine sediment cover. Leaf decomposition was influenced by shredder abundance, water temperature and, to a lesser degree, stream size. Our results suggest that the loss of stream bryophytes due to increasing sedimentation, rather than fine sediments per se, seems to be the key factor affecting multiple biological responses. Enhancing the re-establishment of bryophyte stands could partly compensate for the negative impacts of sedimentation on bryophytes and, consequently, on several other components of boreal stream ecosystems.
Highlights
In many stream ecosystems, aquatic macrophytes modify erosion and sedimentation regimes and create habitat for other organisms (Sand-Jensen, 1998; SandJensen & Pedersen, 1999)
Water color (% increase in mean squared error (MSE) = 12.1) (Fig. 2a), bryophyte cover (MSE = 9.3) (Fig. 2b), and water temperature (MSE = 6.8) (Fig. 2c) were the most important variables, explaining 36.1% of the variability in Non-parametric Multidimensional Scaling (NMDS) axis 1 scores. Species such as Ulnaria danica (Kutzing) Compere & Bukhtiyarova, Ulnaria ulna (Nitzsch) Compere, Planothidium lanceolatum (Brebisson & Kutzing) Bukhtiyarova, Aulacoseira ambigua (Grunow) Simonsen, Diatoma mesodon (Ehrenberg) Kutzing, Staurosira pinnata Ehrenberg and Achnanthidium minutissimum (Kutzing) Czarnecki were associated with the beginning of the NMDS 1 gradient whereas Eunotia mucophila (Lange-Bertalot, Norpel-Schempp & Alles) Lange-Bertalot, Eunotia rhomboidea Hustedt, Eunotia incisa W.Smith ex W.Gregory, Frustulia rhomboids (Ehrenberg) De Toni, Pinnularia perirrorata Krammer, Navicula arvensis Hustedt and Tabellaria flocculosa (Roth) Kutzing were associated with the end of the gradient (Online resource 3)
Diatom communities exhibited a change in response to water temperature between 6 and 7°C but the effect of temperature was much weaker than that of water color and bryophyte cover (Fig. 2c)
Summary
Aquatic macrophytes modify erosion and sedimentation regimes and create habitat for other organisms (Sand-Jensen, 1998; SandJensen & Pedersen, 1999). Macrophytes generally increase habitat heterogeneity and support diverse and abundant invertebrate communities (e.g., Taniguchi et al, 2003; Suurkuukka et al, 2014; Turunen et al, 2018). Macrophytes provide refuge from predation and harsh environmental conditions such as floods or droughts (Rantala et al, 2004; Huttunen et al, 2017). Bryophytes and mosses often dominate macrophyte communities. While it is known that bryophytes provide important habitat for stream invertebrates (Suren, 1993) and buffer invertebrate communities against variability (Huttunen et al, 2017) their importance to other ecosystem components, such as microbial communities and stream ecosystem functions remains poorly understood
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
