Clelia Luisa Marti

Near-Field Dilution Characteristics of a Negatively Buoyant Hypersaline Jet Generated by a Desalination Plant

Field experiments were conducted to investigate the near-field dilution characteristics of a hypersaline brine discharge into coastal waters via an offshore diffuser from a desalination plant. The aim was to determine the dilution of the negatively buoyant plume as it exited the diffuser under three different discharge Froude number regimes (one-third, two-thirds, and full-flow capacity) and to compare these measurements to scaling arguments derived from laboratory measurements. Equations based on the densimetric jet Froude number F , obtained from laboratory experiments, were found to adequately describe the dilution of the brine for cases when F>20 . For F<20 , no laboratory results exist and the dilution was found to be greater than that anticipated from an extrapolation of the laboratory results.

Dynamics of the benthic boundary layer in a strongly forced stratified lake

Field data and the three-dimensional (3D) Estuary and Lake Computer Model (ELCOM) were used to investigate the impact of periodic forcing on the structure and dynamics of the benthic boundary layer (BBL) in Lake Kinneret, Israel, a large lake that experiences strong thermal stratification and wind forcing events. Microstructure data were used to derive the thickness of the BBL and to describe the mean turbulent properties within the BBL. Time series temperature data from thermistor chains were used to characterize the thermal structure of the lake and the basin-scale internal wave field in the lake that was shown to force the turbulent field in the BBL. A clear connection between the dynamics of the BBL and the large-scale features of the flow is presented. The time history of the thickness of the BBL, the mixing in the BBL and the resulting cross-shore flux were shown to vary with the phase of the basin-scale internal wave field. Detailed comparison of simulation results with field data revealed that the model captured well the lake hydrodynamics and the spatial and temporal evolution of energetics of the BBL. Together, field data and numerical modelling provided a clear characterization of the dynamics of the turbulent BBL and its central role in setting up a boundary layer mass flux up the slope from the lake bottom to the height of the metalimnion. Both the turbulent environment in the BBL and the mass flux are of great importance for the ecological processessing of material in a lake.

Summer spatial variations in phytoplankton composition and biomass in surface waters of a warm-temperate, deep, oligo-holomictic lake: Lake Iseo, Italy

Abstract The spatial distribution of phytoplankton in the surface waters of a typical, deep subalpine lake was investigated by analysing water samples collected at 3 depth ranges (0–1, 9–13, and 15–19 m) at 7 sites (21 total samples) using a generalized linear model. The biovolume of different phytoplanktonic taxa significantly differed between depth ranges. Different algal taxa showed maximum population density at different depths as a result of different optima of light, physical conditions, and nutrients. The layer at 9–13 m depth showed the greatest abundance of phytoplankton, mainly represented by Bacillariophyceae and Cyanobacteria. Conversely, Chlorophyceae, which require few nutrients and are not inhibited by high light energy, were most abundant at the surface. The vertical heterogeneity in phytoplankton distribution closely paralleled that of nutrients, which in turn depend on the stable thermal stratification of the lake water column. Biovolume of phytoplankton taxa and chemical parameters did not differ significantly between sampling sites some kilometers apart due to large horizontal water movements in the lake that create relatively uniform conditions throughout the basin.

Disturbance, diversity and phytoplankton production in a reservoir affected by inter-basin water transfers

The effect of water transfers between two reservoirs on the phytoplankton community of the receiving reservoir was investigated over a 9-year period. Canonical correspondence analysis was used to demonstrate the significance of water transfers as an anthropogenic disturbance to the phytoplankton community and its diversity. A mass balance associated with a Granger causality test was applied to discriminate between the cell transport effect from the upstream reservoir and internal processes within the receiving reservoir, and to quantify the net phytoplankton growth in the receiving reservoir. Low and high disturbance regimes were identified and diversity was maximised during low disturbance conditions. The decrease of diversity during high disturbance conditions was explained by decreasing retention time, increasing silica loads and by the transport of specific phytoplankton genera, i.e. diatoms, from the upstream reservoir. Disturbance regimes significantly affected the relationship between phytoplankton production and diversity. Low disturbance regimes were described by phytoplankton dynamics likely influenced by complementarity effects, while high disturbance regimes were characterised by a phytoplankton community dominated by highly productive species and increased productivity, thus indicating an advantage of selection behaviour over complementarity effects. The phytoplankton diversity, expressed as evenness, was identified as a key variable explaining the relationship disturbance-diversity-phytoplankton production.

Using time scales to characterize phytoplankton assemblages in a deep subalpine lake during the thermal stratification period: Lake Iseo, Italy

A combination of field observations and 3-D hydrodynamic simulations were used to identify the phytoplankton species and to estimate the various time scales of the dominant physical and biological processes in Lake Iseo, a deep subalpine lake located in northern Italy, during a stratified period (July 2010). By ordering the rate processes time scales, we derive a phytoplankton patch categorization and growth interpretation that provides a general framework for the spatial distribution of phytoplankton concentration in Lake Iseo and illuminates the characteristics of their ecological niches. The results show that the diurnal surface layer was well mixed, received strong diurnal radiation, had low phosphorus concentrations and the phytoplankton biomass was sustained by the green alga Sphaerocystis schroeterii. The vertical mixing time scales were much shorter than horizontal mixing time scales causing a depth-uniform chlorophyll a concentration. The horizontal patch scale was determined by horizontal dispersion balancing the phytoplankton growth time scale, dictating the success of the observed green algae. The strongly stratified nutrient-rich metalimnion had mild light conditions and Diatoma elongatum and Planktothrix rubescens made up the largest proportions of the total phytoplankton biomass at the intermediate and deeper metalimnetic layers. The vertical transport time scales were much shorter than horizontal transport and vertical dispersion leading to growth niche for the observed phytoplankton. The study showed that time-scale hierarchy mandates the essential phytoplankton attributes or traits for success in a particular section of the water column and/or water body.

Horizontal transport, mixing and retention in a large, shallow estuary: Río de la Plata

We use field data and a high-resolution three-dimensional (3D) hydrodynamic numerical model to investigate the horizontal transport and dispersion characteristics in the upper reaches of the shallow Río de la Plata estuary, located between the Argentinean and Uruguayan coasts, with the objective of relating the mixing characteristics to the likelihood of algal bloom formation. The 3D hydrodynamic model was validated with an extensive field experiment including both, synoptic profiling and in situ data, and then used to quantify the geographic variability of the local residence time and rate of dispersion. We show that during a high inflow regime, the aquatic environment near the Uruguayan coast, stretching almost to the middle of the estuary, had short residence time and horizontal dispersion coefficient of around 77

The seasonal hydrodynamic habitat

\mathrm {m}^{2}\,\mathrm {s}^{-1}

Exchange between littoral and pelagic waters in a stratified lake due to wind-induced motions: Lake Kinneret, Israel

m2s-1, compared to the conditions along the Argentinean coastal regime where the residence time was much longer and the dispersion coefficient (40