Flow routing in mangrove forests: field data obtained in Trang, Thailand

Mangroves grow in the intertidal parts of sheltered tropical coastlines, facilitating coastal stabilization and wave attenuation. Mangroves are widely threatened nowadays, although past studies have indicated their contribution to coastal safety. Most of these studies were based on numerical modeling however and a proper database with field observations is lacking yet. This paper presents part of the results of an extensive field campaign in a mangrove area in Trang Province, Thailand. The study area covers the outer border of an estuarine mangrove creek catchment. Data have been collected on elevation, vegetation, water levels, flow directions and flow velocities throughout this study area. Due to the tough conditions in the field, developing a suitable method for data collection and processing has been a major challenge in this study. Analysis of the hydrodynamic data uncovers the change of flow directions and velocities throughout a mangrove creek catchment over one tidal cycle. In the initial stages of flooding and the final stages of ebbing, creeks supply water to the lower elevated parts of the mangroves. In between these stages, the entire forest bordering the estuary is flooded and flow directions are perpendicular to the forest fringe. Flow velocities within the creeks are still substantially higher than those within the forest, as the creeks also supply water to the back mangroves. These insights in flow routing are promising for the future analysis of sediment input and distribution in mangroves

Utilization of respiratory energy in higher plants : requirements for 'maintenance' and transport processes

Quantitative knowledge of both photosynthesis and respiration is required to understand plant growth and resulting crop yield. However, especially the nature of the energy demanding processes that are dependent on dark respiration in full-grown tissues is largely unknown. The main objective of the present study was to establish the identity and energy requirements of the most important of these (maintenance) processes, and to gain insight in methods of determining the rates and specific costs of these processes. Developing such methods is more important than obtaining data on the rates of maintenance processes for certain crops, as these rates are likely to vary as a function of e.g. the environmental conditions, developmental stage and species.Leaf respiration rates of 15 potato cultivars (Solanum tuberosum L.) differed significantly (chapter 2). To examine whether growth and maintenance requirements differed, two cultivars were compared. After synchronizing their development, leaf protein content, shoot and leaf respiration, photosynthetic light response curves and the growth parameters (i.e. RGR, LAR, SLA, and LWR) were similar, thus excluding potential differences in growth and maintenance respiration. It was concluded that it is important to study the physiological cause of respiratory differences, before starting to select genotypes for low respiration rate.Protein turnover is generally regarded as an important maintenance process. The component of dark respiration rate associated with overall protein turnover of tissues was quantified in vivo by the use of an inhibitor of cytosolic protein synthesis (chapter 3). The in vivo effect of this inhibitor was assessed by monitoring the inhibition of the induction of the ethyleneforming enzyme activity. The respiratory costs of protein turnover were maximally 17 - 35% of total respiration. The maximum degradation constants (i.e. K d -values) derived for growing and full-grown leaves were up to 2.42 x 10 -6and 1. 12 x 10 -6s -1, respectively.Nocturnal carbohydrate export is another process requiring respiratory energy. The potential contribution of the energy requirements associated with nocturnal carbohydrate export to i) the fraction of dark respiration affected by leaf nitrogen concentration and ii) the dark respiration of mature source leaves, was explored (chapter 4). The estimate of the specific energy cost involved in carbohydrate export (0.70 mol C0 2 [mol sucrose]-1), agrees well with both literature data (0.47 to 1.26) and the theoretically calculated range for starch-storing species (0.40 to 1.20). Maximally 42 to '107'% of the effect of the leaf organic nitrogen concentration on the dark respiration of primary bean leaves, is ascribed to the energy costs associated with nocturnal export of carbohydrates. Total energy costs associated with export account on average for 29% of the dark respiration rate for various starch-storing species.The respiratory energy requirements of maintaining ion gradients were quantified on plant roots (chapter 5). Combining the anion efflux rate (35 neq [g dry weight] -1s -1) with literature data on the specific costs of ion transport, suggests that energy costs associated with re-uptake of ions may account for up to 66% of the total respiratory costs involved in (an)ion influx. A value of 34% of the total respiratory costs involved in (an)ion influx was obtained if the net uptake rate was based on the relative growth rate observed for potato, and assuming phosphate and sulfate to be both 10% of nitrate in- and efflux. Comparison of relative values of the respiration of root and shoot is not useful, as in both tissues other processes add to the total.Estimating the respiratory energy requirements of maintaining ion gradients is complicated by lack of knowledge on efflux kinetics. Therefore, efflux kinetics was studied, using a dynamic simulation model (chapter 6). Simulations showed that the overall efflux kinetics observed in the medium may differ significantly, even if actual efflux rates (and thus costs involved in maintaining ion gradients) in the simulations were equal. Similarly, the relative contribution of ions originally located in the apoplast, cytoplasm and vacuole of different cell layers to these efflux kinetics and the observed cumulative efflux originating from the symplast were different. All these differences were due to the presence or absence of an endodermis, different pathways involved in net uptake and different number of cell layers involved in efflux.Integration of the available knowledge on maintenance, growth and uptake processes enabled to explain the respiration of potato roots. The costs calculated for protein turnover could explain total maintenance requirements (10.2 to 14.8 nmol O 2 [g DW] -1s -1). It was deduced that overall costs for maintaining solute gradients (i.e. re-uptake balancing efflux) account for up to 33% of the overall costs of nitrate influx (i.e. 1/U is up to a factor 1.5 higher if efflux takes place). This agrees well with the results of chapter 5

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

Patches in a side-by-side configuration: a description of the flow and deposition fields

In the last few decades, a lot of research attention has been paid to flow-vegetation interactions. Starting with the description of the flow field around uniform macrophyte stands, research has evolved more recently to the description of flow fields around individual, distinct patches. However, in the field, vegetation patches almost never occur in isolation. As such, patches will influence each other during their development and interacting, complex flow fields can be expected. In this study, two emergent patches of the same diameter (D = 22 cm) and a solid volume fraction of 10% were placed in a side-by-side configuration in a lab flume. The patches were built as an array of wooden cylinders, and the distance between the patches (gap width Delta) was varied between Delta = 0 and 14 cm. Flow measurements were performed by a 3D Vectrino Velocimeter (Nortek AS) at mid-depth of the flow. Deposition experiments of suspended solids were performed for selected gap widths. Directly behind each patch, the wake evolved in a manner identical to that of a single, isolated patch. On the centerline between the patches, the maximum velocity U-max was found to be independent of the gap width Delta. However, the length over which this maximum velocity persists, the potential core L-j, increased linearly as the gap width increased. After the merging of the wakes, the centerline velocity reaches a minimum value U-min. The minimum centerline velocity decreased in magnitude as the gap width decreased. The velocity pattern within the wake is reflected in the deposition patterns. An erosion zone occurs on the centerline between the patches, where the velocity is elevated. Deposition occurs in the low velocity zones directly behind each patch and also downstream of the patches, along the centerline between the patches at the point of local velocity minimum. This downstream deposition zone, a result of the interaction of neighbouring patch wakes, may facilitate the establishment of new vegetation, which may eventually inhibit flow between the upstream patches and facilitate patch merger

Cross-shore gradients of physical disturbance in mangroves: Implications for seedling establishment

10.5194/bg-10-5411-2013Biogeosciences1085411-541