Biomechanical properties of aquatic plants and their effects on plant–flow interactions in streams and rivers

Abstract

We analysed the biomechanical properties of aquatic plant stems of four common submerged river macrophyte species with bending, tension and cyclic loading/ unloading tests and related these properties to the hydraulic habitats of the plants. The studied species included Glyceria fluitans, Ranunculus penicillatus, Myriophyllum alterniflorum and Fontinalis antipyretica. Habitat assessment shows that these species occur in a range from low to high flow velocities, respectively. G. fluitans is a semi-aquatic species with stems of a high flexural rigidity and high breaking force and breaking stress that enable them to carry their own weight and balance gravity when growing upright in slow flowing rivers. G. fluitans may also grow horizontally often producing emerged terrestrial stems. In contrast, F. antipyretica grows in fierce water flow. Its stems have the highest flexibility, a significantly higher 'tension' Young's modulus, breaking stress and work of fracture and a lower plastic deformation compared to M. alterniflorum and R. penicillatus. These traits enable F. antipyretica to survive even in swift flowing streams and constrict the growth of M. alterniflorum and R. penicillatus to the river reaches with moderate flow velocities. R. penicillatus has a weak bottom part with a low breaking force and breaking stress acting as a predetermined breaking point and enabling seasonal regrowth from root parts.

Adaptation of submerged macrophytes to both water depth and flood intensity as revealed by their mechanical resistance

“…This result indicates that the upper shoots of the five submerged macrophytes were prone to damage by hydraulic forces, but H. verticillata and P. maackianus can withstand drag force for a considerably longer time. Such variations were also observed in ripe aquatic plants (Usherwood et al, 1997;Schutten et al, 2005;Puijalon et al, 2011;Miler et al, 2012). These differences are related to stem tissue structure and cellulose content (Denny, 1988;Sand-Jensen, 2003;Schutten et al, 2004;Zhu et al, 2012).…”

“…Each intact main stem was divided into three parts, namely, the lower, middle, and upper segments (Madsen & Owens, 1998;Patterson et al, 2001;Miler et al, 2012). The diameters of each segment were measured at the middle parts with dial calipers to the nearest 0.1 mm.…”

“…In terms of the mechanical resistance of aquatic plants, root anchorage strength avoids uprooting (Schutten et al, 2005), stem tensile force and tensile strain represent the capability of the stem to deal with drag force in terms of how strongly and how long it can last before breaking, and tensile stress is as function of material mechanical strength (Brewer & Parker, 1990;Usherwood et al, 1997;Miler et al, 2012).…”

“…These traits facilitate the adaptation of C. demersum and P. maackianus to rapidly rising water levels. Aquatic plants grown in slow flows and/ or shallow water generally possess less flexible, but stronger stems than those inhabiting fast running water or deep waters (Brewer & Parker, 1990;Usherwood et al, 1997;Bociag et al, 2009;Miler et al, 2010Miler et al, , 2012. Additionally, the canopy-forming species generally have much higher growth rate than species with other growth forms in lakes with low-light availability (Keddy, 1983;Chambers & Prepas, 1988;Hudon et al, 2000).…”

High-resolution numerical modelling of flow—vegetation interactions

“…It is these three forces which must be balanced to ascertain the plant movement and position. it is likely that most vegetation stalks will also differ in diameter along the stalk (Miler et al 2012). This would lead to an -dependence in both flexural rigidity and mass per unit length.…”