Marianna Soler

Quantified distribution of diatoms during the stratified period of Boadella reservoir

We collected data and samples, from June to November of 1999 and 2000, to in situ quantify the abundance of phytoplankton in Boadella reservoir. Samples were taken at different stations along the reservoir and diatoms were persistent in the epilimnion and were the main phytoplankton component, with a peak of abundance up to ∼5 105 particles ml−1. The diatom growth during the initiation of the summer bloom was high in the reservoir upstream concurrent with maximum Chlorophyll a concentrations. A delay in the onset of the diatom bloom, together with lower values of the volume concentration, was found in 1999 compared to the results in 2000 and was attributed to the different stratification of the reservoir as a result of meteorological conditions. The diatom population sank from the epilimnion by sedimentation and formed aggregates that accumulated at the bottom of the epilimnion. Sedimentation to the hypolimnion occurred at the end of the bloom, where peaks of Chlorophyll a were found.

Interactions between Fragmented Seagrass Canopies and the Local Hydrodynamics.

The systematic creation of gaps within canopies results in fragmentation and the architecture of fragmented canopies differs substantially from non-fragmented canopies. Canopy fragmentation leads to spatial heterogeneity in hydrodynamics and therefore heterogeneity in the sheltering of canopy communities. Identifying the level of instability due to canopy fragmentation is important for canopies in coastal areas impacted by human activities and indeed, climate change. The gap orientation relative to the wave direction is expected to play an important role in determining wave attenuation and sheltering. Initially we investigated the effect of a single transversal gap within a canopy (i.e. a gap oriented perpendicular to the wave direction) on hydrodynamics, which was compared to fully vegetated canopies (i.e. no gaps) and also to bare sediment. The wave velocity increased with gap width for the two canopy densities studied (2.5% and 10% solid plant fraction) reaching wave velocities found over bare sediments. The turbulent kinetic energy (TKE) within the gap also increased, but was more attenuated by the adjacent vegetation than the wave velocity. As expected, denser canopies produced a greater attenuation of both the wave velocity and the turbulent kinetic energy within an adjacent gap, compared to sparse canopies. Using non-dimensional analysis and our experimental data, a parameterization for predicting TKE in a canopy gap was formulated, as a function of easily measured variables. Based on the experimental results, a fragmented canopy model was then developed to determine the overall mixing level in such canopies. The model revealed that canopies with large gaps present more mixing than canopies with small gaps despite having the same total gap area in the canopy. Furthermore, for the same total gap area, dense fragmented canopies provide more shelter than sparse fragmented canopies.