Trade‐off between drag reduction and light interception of macrophytes: comparing five aquatic plants with contrasting morphology

Abstract

Summary1. Macrophytes in running waters experience an often dynamic and harsh environment. To avoid breakage, plants have to reduce the experienced drag force. However, by reducing leaf area, photosynthetic production is less. Aquatic plants therefore have to find a balance between reducing drag and maintaining photosynthetic capacity. 2. In the experiments in this study, we assessed to what extent different morphological strategies (emergent vs. submerged) were able to minimize drag while maximizing leaf area. 3. From our measurements, it is clear that with increasing water velocities, emergent plant species have a drag value three to four times higher than submerged species. 4. To test the versatility of leaves, leaves were removed and their effect on drag and bending was investigated. Almost 60% of the drag is contributed by the leaves, and stems bend less when leaves are removed. 5. Because high submerged leaf area increases not only plant drag but also photosynthetic yield, a trade-off between both parameters was investigated in the function of stream velocity. Emerged species had a more favourable trade-off at low stream velocities. However, with increasing stream velocity, submerged species could reduce their drag more in comparison with blunt objects. Within these submerged species, a clear distinction was seen between those (Potamogeton natans) concentrating their leaf area on or just beneath the water surface (Stuckenia pectinata) and those with more or less evenly distributed biomass (Callitriche platycarpa and Ranunculus penicillatus). 6. These results indicate that aquatic plants with an emergent strategy are able to take better advantage of zones with reduced hydraulic forces than submerged plants. Additionally, this plant occurrence will be determined by the relationship between total plant drag and root strength.

Resistance and reconfiguration of natural flexible submerged vegetation in hydrodynamic river modelling

“…Firstly, in order to simulate the variation in vegetation canopy height, as a function of upstream depth-averaged velocity, a relationship between the bending angle and upstream depth-averaged velocity is used. The bending angle is defined as the angle between the horizontal bed and the shoot [13] ( Fig. 1).…”

“…These mutual plant-flow interactions have important effects on the hydraulic, ecological and geomorphic functioning of lowland rivers [7][8][9] and it is therefore crucial to implement plant-flow interactions in hydrodynamic models. Plant-flow interactions have been relatively well studied in recent years through numerical modelling [10,11], laboratory experiments [12][13][14][15] and field measurements [8,16]. Vegetation resistance can be quantified via empirical relationships or with Environ Fluid Mech hydrodynamic models.…”

Does the canopy mixing layer model apply to highly flexible aquatic vegetation? Insights from numerical modelling

“…It is therefore likely that plant-flow interactions will reflect that. Aquatic vegetation must find a balance between drag reduction and photosynthetic capacity [59,60]. Therefore, aquatic vegetation commonly has substantial foliage with a large surface area to maximize light capture.…”

Extending the canopy flow model for natural, highly flexible macrophyte canopies

“…Aquatic vegetation must find a balance between drag reduction and photosynthetic capacity (Albayrak et al, 2011, Bal et al, 2011. Therefore, aquatic vegetation commonly has substantial foliage with a large surface area to maximize light capture.…”