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

In-stream submerged macrophytes have a complex morphology and several species are not rigid, but are flexible and reconfigure along with the major flow direction to avoid potential damage at high stream velocities. However, in numerical hydrodynamic models, they are often simplified to rigid sticks. In this study hydraulic resistance of vegetation is represented by an adapted bottom friction coefficient and is calculated using an existing two layer formulation for which the input parameters were adjusted to account for (i) the temporary reconfiguration based on an empirical relationship between deflected vegetation height and upstream depth-averaged velocity, and (ii) the complex morphology of natural, flexible, submerged macrophytes. The main advantage of this approach is that it removes the need for calibration of the vegetation resistance coefficient. The calculated hydraulic roughness is an input of the hydrodynamic model Telemac 2D, this model simulates depth-averaged stream velocities in and around individual vegetation patches. Firstly, the model was successfully validated against observed data of a laboratory flume experiment with three macrophyte species at three discharges. Secondly, the effect of reconfiguration was tested by modelling an in situ field flume experiment with, and without, the inclusion of macrophyte reconfiguration. The inclusion of reconfiguration decreased the calculated hydraulic roughness which resulted in smaller spatial variations of simulated stream velocities, as compared to the model scenario without macrophyte reconfiguration. We discuss that including macrophyte reconfiguration in numerical models input, can have significant and extensive effects on the model results of hydrodynamic variables and associated ecological and geomorphological parameters

Editorial: Silicon cycling in agricultural soils under current anthropogenic influences

info:eu-repo/semantics/publishedVersio

Impact of vegetation die-off on spatial flow patterns over a tidal marsh

Large-scale die-off of tidal marsh vegetation, caused by global change, is expected to change flow patterns over tidal wetlands, and hence to affect valuable wetland functions such as reduction of shoreline erosion, attenuation of storm surges, and sedimentation in response to sea level rise. This study quantified for the first time the effects of large-scale (4 ha) artificial vegetation removal, as proxy of die-off, on the spatial flow patterns through a tidal marsh channel and over the surrounding marsh platform. After vegetation removal, the flow velocities measured on the platform increased by a factor of 2 to 4, while the channel flow velocities decreased by almost a factor of 3. This was associated with a change in flow directions on the platform, from perpendicular to the channel edges when vegetation was present, to a tendency of more parallel flow to the channel edges when vegetation was absent. Comparison with hydrodynamic model simulations explains that the vegetation-induced friction causes both flow reduction on the vegetated platform and flow acceleration towards the non-vegetated channels. Our findings imply that large-scale vegetation die-off would not only result in decreased platform sedimentation rates, but also in sediment infilling of the channels, which together would lead to further worsening of plant growth conditions and a potentially runaway feedback to permanent vegetation loss. Citation: Temmerman, S., P. Moonen, J. Schoelynck, G. Govers, and T. J. Bouma (2012), Impact of vegetation die-off on spatial flow patterns over a tidal marsh, Geophys. Res. Lett., 39, L03406, doi: 10.1029/2011GL050502

Flow measurements around a submerged macrophyte patch in an in-situ flume setup

In most aquatic ecosystems, hydrodynamic conditions are a key abiotic factor determining species distribution and aquatic plant abundance. Recently, local differences in hydrodynamic conditions have been shown to be an explanatory mechanism for the patchy pattern of Callitriche platycarpa Kütz. vegetation in lowland rivers. Those patches are often subject to strong hydrodynamic forces as they act as a resistance against the current. A plant‟s ability to tolerate water movement without suffering mechanical damage often relies on minimizing the hydrodynamic forces by avoiding stress. In this paper, we have quantified the behaviour and influence of a C. platycarpa patch in an in situ flume, manipulating the incoming discharge on a single patch. The knowledge obtained helps to understand the plant-flow-sediment interactions that form the basis of the explanatory mechanism for the patchy vegetation pattern

Mapping the Spatio-temporal Distribution of Key Vegetation Cover Properties in Lowland River Reaches, Using Digital Photography

The presence of vegetation in stream ecosystems is highly dynamic in both space and time. A digital photography technique is developed to map aquatic vegetation cover at species level, which has a very-high spatial and a flexible temporal resolution. A digital single-lens-reflex (DSLR) camera mounted on a handheld telescopic pole is used. The low-altitude (5 m) orthogonal aerial images have a low spectral resolution (Red-Green-Blue), high spatial resolution (~1.9 pixels cm-2, ~1.3 cm length) and flexible temporal resolution (monthly). The method is successfully applied in two lowland rivers to quantify four key properties of vegetated rivers: vegetation cover, patch size distribution, biomass and hydraulic resistance. The main advantages are that the method is: (i) suitable for continuous and discontinuous vegetation covers (ii) of very-high spatial and flexible temporal resolution, (iii) relatively fast compared to conventional ground survey methods, (iv) non-destructive, (v) relatively cheap and easy to use, and (vi) the software is widely available and similar open source alternatives exist. The study area should be less than 10 m wide and the prevailing light conditions and water turbidity levels should be sufficient to look into the water. Further improvements of the images processing are expected in the automatic delineation and classification of the vegetation patches

Implementing plant growth of flexible aquatic vegetation into a hydrodynamic model (TELEMAC2D)

Water Qualit

Enhanced Weathering and related element fluxes - A cropland mesocosm approach

The weathering of silicates is a major control on atmospheric CO2 at geologic timescales. It was proposed to enhance this process to actively remove CO2 from the atmosphere. While there are some studies that propose and theoretically analyze the application of rock powder to agricultural land, results from field experiments are still scarce. © 2020. This work is distributed under the Creative Commons Attribution 4.0 License

Ecosystem engineering by plants on wave-exposed intertidal flats is governed by relationships between effect and response traits

In hydrodynamically stressful environments, some species—known as ecosystem engineers—are able to modify the environment for their own benefit. Little is known however, about the interaction between functional plant traits and ecosystem engineering. We studied the responses of Scirpus tabernaemontani and Scirpus maritimus to wave impact in full-scale flume experiments. Stem density and biomass were used to predict the ecosystem engineering effect of wave attenuation. Also the drag force on plants, their bending angle after wave impact and the stem biomechanical properties were quantified as both responses of stress experienced and effects on ecosystem engineering. We analyzed lignin, cellulose, and silica contents as traits likely effecting stress resistance (avoidance, tolerance). Stem density and biomass were strong predictors for wave attenuation, S. maritimus showing a higher effect than S. tabernaemontani. The drag force and drag force per wet frontal area both differed significantly between the species at shallow water depths (20 cm). At greater depths (35 cm), drag forces and bending angles were significantly higher for S. maritimus than for S. tabernaemontani. However, they do not differ in drag force per wet frontal area due to the larger plant surface of S. maritimus. Stem resistance to breaking and stem flexibility were significantly higher in S. tabernaemontani, having a higher cellulose concentration and a larger cross-section in its basal stem parts. S. maritimus had clearly more lignin and silica contents in the basal stem parts than S. tabernaemontani. We concluded that the effect of biomass seems more relevant for the engineering effect of emergent macrophytes with leaves than species morphology: S. tabernaemontani has avoiding traits with minor effects on wave attenuation; S. maritimus has tolerating traits with larger effects. This implies that ecosystem engineering effects are directly linked with traits affecting species stress resistance and responding to stress experienced

The effects of dunite fertilization on growth and elemental composition of barley and wheat differ with dunite grain size and rainfall regimes

Enhanced weathering (EW) of silicate rocks is a negative emission technology that captures CO2 from the atmosphere. Olivine (Mg2SiO4) is a fast weathering silicate mineral that can be used for EW and is abundant in dunite rock. In addition to CO2 sequestration, EW also has co-benefits in an agricultural context. Adding silicate minerals to soils can significantly improve crop health and growth as the weathering releases elements such as silicon (Si) that can stimulate crop growth and increase stress resistance, a co-benefit that is becoming increasingly important as global warming proceeds. However, dunite also contains heavy metals, especially nickel (Ni) and chromium (Cr), potentially limiting its use in an agricultural context. In this study, we investigate the influence of dunite addition on growth of barley and wheat in a mesocosm experiment. We amended the soil with the equivalent of 220 ton ha-1 dunite, using two grain sizes (p80 = 1020 µm and p80 = 43.5 µm), under two rainfall regimes (each receiving the same amount of 800 mm water y−1 but at daily versus weekly rainfall frequency). Our results indicate that the amendment of fine dunite increased leaf biomass but only with daily rainfall. Aboveground biomass was significantly reduced with weekly rainfall compared to daily rainfall, but this reduction was slightly alleviated by fine dunite application for wheat. This indicates a positive effect of dunite during drying-rewetting cycles. For barley the negative effect of reduced rainfall frequency was not counterbalanced by dunite application. Contrary to our expectations, calcium (Ca) and Si concentrations in crops decreased with fine dunite application, while, as expected, magnesium (Mg) concentration increased. Coarse dunite application did not significantly affect crop nutrient concentrations, most likely due to its lower weathering rate. In contrast to what was expected, plant Ni and Cr concentrations did not increase with dunite application. Hence, despite high dunite application in our experiment, plants did not accumulate these heavy metals, and only benefited from the released nutrients, albeit dependent on grain size and rainfall frequency