Correlation Assessment of NDVI and Land use Dynamics with Water Resources for the Southern Margin of Mu Us Sandy Land, China

To prevent desertification, countries all over the world have made diversified efforts and vegetation restoration has been proved to be an effective approach. However, for sandy land that has limited water resources, measures such as artificial vegetation, may lead to the increase risk of drought. While affirming the achievements of sand utilization, there are many controversies exist regarding the advantages of turning deserts green, especially considering the water scarcity. Therefore, the long-run and causal relationships between sandy land, water consumption and vegetation coverage are necessary for explorations. Taken the southern margin of the Mu Us Sandy Land as the study area, this study explored the interactions between sandy land, water consumption and NDVI over a period of 2000–2018 with a VAR model approach. In the study area, various revegetation projects have made great achievements, resulting in a significant reduction of the sandy land area. In addition, the NDVI has ascend from 0.196 in 2000 to 0.371 in 2018 with a ratio of 89.3%. Results showed that there exist long-term stable equilibrium and causal relationships between water consumption with sandy land and NDVI. The increase of NDVI is relatively the direct factor causes the increase of water consumption. It could be inferred that those artificial vegetation measures may be based on large amount of water consumption, which may aggravate further water shortage and ecological damage. More scientific and stronger water resources management measures need to be implemented locally to achieve a balance between water resources and revegetation.

Prediction of Transmission Coefficients of Regular Wave Attenuation by Emergent Vegetation

Transmission coefficient (Kt) for wave attenuation by vegetation is essential parameter for predicting the wave height. In this paper, based on the experimental data of three kind of artificial vegetation model, genetic programming (GP), artificial neural networks (ANNs) and multivariate non-linear regression (MNLR) were used to analyze the dimensionless factors including Ursell number (Ur), relative width (RB) relative height (α) and volume fraction (φ). The proposed GP formulae were compared with MNLR and ANNs. The predictions of GP models were in good agreement with measured data, and outperformed MNLR equations. Otherwise, GP and ANNs were used to obtain the weight of each factor. The results can provide a reference for the artificial planting of the three plants.

Influence of the presence of invasive mosquitofish and submerged vegetation on oviposition site selection by gray treefrogs (Hyla versicolor)

Amphibians often select oviposition sites based on a variety of cues that indicate the level of risk in the oviposition habitat. Surprisingly, the role of aquatic vegetation or habitat structure/complexity in anuran oviposition site selection has not been extensively studied even though it might affect perceived risk. We examined the effects of free-ranging invasive western mosquitofish (Gambusia affinis) and artificial vegetation/habitat structure on colonisation of experimental pools by gray treefrogs (Hyla versicolor). Hyla versicolor avoided ovipositing in mesocosms with G. affinis. The presence of artificial vegetation/habitat structure had no effect on oviposition site selection by H. versicolor, whether alone or in interaction with G. affinis. Our experiment provides evidence for the avoidance of fish, and more specifically G. affinis, by ovipositing H. versicolor; but provides no evidence for a role of vegetation/habitat structure.

Bulk drag coefficient of a subaquatic vegetation subjected to irregular waves: Influence of Reynolds and Keulegan-Carpenter numbers

Seagrass meadows are essential for protection of coastal erosion by damping wave and stabilizing the seabed. Seagrass are considered as a source of water resistance which modifies strongly the wave dynamics. As a part of EDF R & D seagrass restoration project in the Berre lagoon, we quantify the wave attenuation due to artificial vegetation distributed in a flume. Experiments have been conducted at Saint-Venant Hydraulics Laboratory wave flume (Chatou, France). We measure the wave damping with 13 resistive waves gauges along a distance L = 22.5 m for the “low” density and L = 12.15 m for the “high” density of vegetation mimics. A JONSWAP spectrum is used for the generation of irregular waves with significant wave height Hs ranging from 0.10 to 0.23 m and peak period Tp ranging from 1 to 3 s. Artificial vegetation is a model of Posidonia oceanica seagrass species represented by slightly flexible polypropylene shoots with 8 artificial leaves of 0.28 and 0.16 m height. Different hydrodynamics conditions (Hs, Tp, water depth hw) and geometrical parameters (submergence ratio α, shoot density N) have been tested to see their influence on wave attenuation. For a high submergence ratio (typically 0.7), the wave attenuation can reach 67% of the incident wave height whereas for a low submergence ratio (< 0.2) the wave attenuation is negligible. From each experiment, a bulk drag coefficient has been extracted following the energy dissipation model for irregular non-breaking waves developed by Mendez and Losada (2004). This model, based on the assumption that the energy loss over the species meadow is essentially due to the drag force, takes into account both wave and vegetation parameter. Finally, we found an empirical relationship for Cd depending on 2 dimensionless parameters: the Reynolds and Keulegan-Carpenter numbers. These relationships are compared with other similar studies.