Environmental control of macrophyte traits and interactions with metabolism and hydromorphology in a groundwater‐fed river

Abstract

Macrophytes are important organisms in running water systems, having a decisive role in ecological processes and interactions. Their temporal and spatial distribution in streams can be highly variable, and this is often determined by flow velocity. In this study, macrophyte growth, morphology and nutrient stoichiometry were studied monthly during one growing season in reaches with different flow velocity and flow velocity distribution and, as a result, different distributional plant patterns in an Austrian lowland stream, dominated by evergreen macrophyte species, Berula erecta. Flow velocity, water depth, fine sediment layer depth and metabolism were measured in the stream and the correlation with plant biomass and morphological traits was tested. We aimed to study differences between reaches with different distributional plant patterns and whether common interactions between macrophytes and flow velocity can also be observed when vegetation is evergreen. Plant biomass showed seasonal variation, with the highest values in June and the lowest in February. In the reach with low flow velocity and homogeneous macrophyte distribution, biomass peaked in summer and plant morphology changed with the seasons, whereas biomass and morphology in the reach with high flow velocity and patchy distribution were more constant throughout the year. Plant carbon, nitrogen and phosphorus content were higher in spring and autumn than in summer, whereas biogenic silica accumulated over the course of the growth season. Stream metabolism was strongly correlated with macrophyte biomass, and this correlation was stronger in the reach with homogeneous macrophyte distribution than in the reach with a patchy distribution. Moreover, average leaf area and stem length were positively correlated with fine sediment layer depth, and negatively with flow velocity. The results stress the importance of macrophyte growth and morphology in river processes like metabolism, hydromorphology and nutrient dynamics: especially plant morphology plays an important role in macrophyte–flow interactions.

Juncus Bulbosus Tissue Nutrient Concentrations and Stoichiometry in Oligotrophic Ecosystems: Variability with Seasons, Growth Forms, Organs and Habitats

“…There were no temporal differences in C, N, P and C:N:P between samples collected in early versus late summer (2008 survey) but large differences in P, C:P and N:P ratios between samples collected in late spring versus autumn (2006 survey). Such seasonal shifts in plant stoichiometry have been reported before for other species and are known to vary between species and elements [29][30][31][32]. In Lobelia dortmanna (an isoetid), N accumulation occurred under low light availability and slow growth in the autumn for possible use in the following spring and summer growth spurt [18].…”

Scale-dependent effects of vegetation on flow velocity and biogeochemical conditions in aquatic systems

“…Further studies should investigate threshold lengths in different flow conditions in order to establish general, non-dimensional models predicting thresholds for the modification of sediment properties and nutrient conditions inside patches. Thresholds could also be strongly dependent on plant and patch characteristics, such as the capacity to release oxygen in roots, plant flexibility, and the density of the canopy (Barcelona et al, 2021b;Reitsema et al, 2021), as well as on large-scale canopy organization (Folkard, 2019;Barcelona et al, 2021a). Depending on the morphological and architectural characteristics of plants and patches, it seems plausible that different aquatic plant species will have different effects on hydrodynamics and in turn the characteristics of accumulated sediments, which will induce corresponding effects on biogeochemical conditions, emphasizing the importance of considering plant traits in addition to vegetation biomass alone when studying the role of vegetation at the ecosystem scale (Su et al, 2019;Dalla Vecchia et al, 2020).…”

“…As a result, inside plant patches, the potential for resuspension and erosion is reduced Schulz et al, 2003;Hendriks et al, 2009), and fine sediment tends to accumulate compared to bare areas Biggs et al, 2021), whereas flow acceleration next to the patch contributes to particle entrainment and transport Schoelynck et al, 2013). As a consequence, plant growth and thus patch expansion could be locally enhanced inside or immediately downstream of a patch due to reduced hydrodynamic stress, a lower risk of mechanical damage for plants (breakage, uprooting) and accumulation of fine particles (Wharton et al, 2006;Jones et al, 2012;Biggs et al, 2021;Reitsema et al, 2021), which in turn increases nitrogen and phosphorus concentrations Clarke and Wharton, 2001;Sanders and Trimmer, 2006;Schoelynck et al, 2017) and enhances nutrient availability for plants. Reciprocally, plant growth and thus patch expansion could be inhibited next to the patch due to higher hydrodynamic stress and coarser sediment, leading to the formation of regular patterns Schoelynck et al, 2012;Cornacchia et al, 2019).…”

Riverine landscapes: Challenges and future trends in research and management

“…Revisions of temperature optima are needed to model future shifts in species distributions induced by global warming, as was undertaken for benthic invertebrates in alpine regions (Niedrist & Füreder, 2021). The study by Reitsema et al (2021) highlights the importance of macrophytes in riverine metabolism, hydromorphology, and nutrient dynamics. The authors show the strong correlation between stream hydromorphology and macrophyte morphology, indicating that morphological traits need to be considered in addition to biomass assessments to fully understand the relationship between environmental changes and macrophyte development in rivers.…”