Jason P. Antenucci

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.

On internal waves near the high-frequency limit in an enclosed basin

Observations of the internal wave field using thermistor chains in Lake Kinneret (Israel) showed a substantial energy peak at frequencies just below the maximum buoyancy frequency. The waves were of the first vertical mode, occurred in groups, and resulted in isotherm displacements of up to 4 m in 22 m of water. The appearance of this high-frequency internal wave energy was closely related to the strength of the wind field. A weaker relationship was found with the phase of the basin-scale internal waves, with more energy observed under the same wind conditions when the metalimnion was closer to the surface. The relationship of the high-frequency waves to the wind and the basin-scale internal waves implies a generation mechanism associated with shear in the surface layer (observed to be approximately 0.08 s -1 ), similar to that responsible for generating high-frequency internal waves in the equatorial Pacific. A linear stability analysis of the mean state during periods of high-frequency wave activity revealed the existence of unstable modes, whose period and frequency bandwidth closely matched field observations.

A three dimensional model of Cryptosporidium dynamics in lakes and reservoirs: A new tool for risk management

Abstract A model of Cryptosporidium oocyst dynamics for lakes and reservoirs is presented. The model consists of a module that simulates oocyst inactivation, resuspension, settling and aggregation onto particles. This module was coupled to the three‐dimensional Estuary Lake and Coastal Ocean Model (ELCOM), which was used to simulate lake hydrodynamics in addition to oocyst advection and turbulent diffusion. A field experiment that tracked the passage of a flood inflow throughout Myponga Reservoir, South Australia, was used to validate the coupled model. The model accurately captured the thermal dynamics, and the spatial and temporal distribution of different inorganic particle size classes and oocysts. The model and data indicate that oocysts do not readily attach to inorganic particles as other researchers have suggested but settle as free‐floating oocysts according to Stokes sedimentation dynamics. The reduction in oocysts between the inflow and the offtake due to settling is therefore not as significant as previously thought. The potential for inactivation was also found to be small relative to the timescales for transport. The model is a useful tool to examine oocyst dynamics in lakes and reservoirs, to consider risk management assessments of different scenarios, and to assess the effectiveness of different sampling strategies.

Using Impellers to Distribute Local Nutrient Loadings in a Stratified Lake: Lake Como, Italy

The feasibility of using a vertically downward pointing impeller to remove polluted water from a coastal margin was investigated with a pilot experiment in Lake Como, Italy. The vertical jet induced by the impeller entrained surface water downward to depth, where upon reaching neutral buoyancy it intruded horizontally into the lake proper. A three-dimensional numerical hydrodynamic model was validated with results from an intensive (eight-day) field study during which rhodamine WT dye was introduced in the lee of the impeller and then tracked as it was transported into the lake. One of the major sources of pollution to the lake is the Cosia River underflow that drains a catchment adjacent to the City of Como. The numerical model, once validated, was used to show that six impellers, with the correct thrust, could be used to reduce the pollutants adjacent to the City of Como by half within two weeks; this was achieved by injecting the surface water to a depth that would intensify the Cosia River intrusion.

Modifying the Residence Time and Dilution Capacity of a Reservoir by Altering Internal Flow-Paths

Abstract Tracers were released into a small oligotrophic reservoir to determine the tracer dilution ratio (the ratio of inflow to outflow concentration) and two residence timescales (the arrival time and the cleansing time) as a function of lake geometry. The dominant transport mechanisms were inferred by assembling lake‐wide spatial and temporal fields of natural tracers such as temperature, pH, salinity, turbidity, and dissolved oxygen from a series of 37‐stations. These stations were monitored three times a day during an 8‐day field campaign and the field results were compared to numerical simulations of the system. The lakes hydrodynamic behaviour was successfully simulated with a hydrostatic three‐dimensional numerical model (ELCOM) that was used to investigate the deflection from existing flow‐paths by means of vertical impermeable curtains. Strategies were tested aimed at modifying the transport timescales and dilution capacity of the lake as may be required for the lake to act as a secure barrier against microbial contamination. Submerged curtains proved to improve the barrier capacity of the reservoir, described by the arrival time, the cleansing time, and the dilution ratio.

The impact of transfers on water quality and the disturbance regime in a reservoir.

The effect of water transfers between two reservoirs on the water quality of the receiving reservoir was investigated over a 9-year period (2000-2008). Different management strategies were implemented in term of the magnitude and timing of water transfers, i.e. the amount of transferred volume and the frequency at which transfers occurred. These different operational modes were analysed to determine changes in nutrient and metal concentrations, chlorophyll a, algal genera and biovolume. During high water transfers, chlorophyll a and total algal biovolume increased, with larger diatoms preferentially selected due to the high silica content of the pumped inflow and a significant shift in cyanobacteria genera occurring from Microcystis to nitrogen-fixing genera. The magnitude and timing of water transfers exerted a strong control on phytoplankton competition and disturbed the typical seasonal succession during low pumping years of a spring diatom bloom followed by summer cyanobacteria dominance: intensive and frequent water transfers resulted in dominance by diatoms for the whole year and effectively limited cyanobacteria summer growth. From this analysis, we identified iron concentration and diatom biovolume as the key water quality indicators to be included in any optimal management, able to control the transfer regime from both a water quantity and water quality prospective.

The importance of transport processes and spatial gradients on in situ estimates of lake metabolism

We measured spatial gradients of dissolved oxygen in a eutrophic reservoir from repeated transects over a 5-day period. The equation typically used to compute lake metabolism was extended to the full advection–diffusion–reaction equation, which includes transport terms. These transport terms were computed and found to be of similar magnitude to the rate of change of dissolved oxygen. We demonstrate that neglecting transport terms in this reservoir could lead to over-estimates in net ecosystem production calculations in the surface layer of up to 100%. We advocate the calculation of nondimensional Peclet and Damkohler numbers in future studies to assist in determining the importance of transport terms on lake metabolism estimates.

Sustainability assessment of the impact of the Marina Bay development on Singapore: application of the index of sustainable functionality

The index of sustainable functionality (ISF) was applied to assess the impact of the Marina Bay development project on the sustainability of Singapore. The development project has three aims: water supply, flood control and lifestyle attraction; construction for the various stages began in 2005, with scheduled completion end of 2009. The period of study was 2001–2007, before and during construction. The ISF increased from 2001 to 2004, then decreased slightly and stabilised from 2005 onwards, staying below the 2004 ISF value, showing that the development has not increased sustainability. A quick forecasting exercise, for the case that the three aims above were achieved and all other indicator values the same as those in 2007, increased the ISF value by 5.1%. Continued ISF construction would indicate if the functionality, and thus sustainability, of Singapore would increase after the Marina Bay development is completed and the benefits can be realised.

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.

The management of Lake Burragorang in a changing climate: The application of the Index of Sustainable Functionality

Abstract Lake Burragorang is the largest water supply source for the Sydney region, providing up to 80% of Sydneys water supply. The Index of Sustainable Functionality (ISF) was applied to the geographical domain of its catchment (Warragamba Catchment) for the 20 year period from 1989 to 2008 as a measure of its health and sustainability. The ISF values showed a slight negative trend over the study period, indicating decreasing functionality of the reservoir; however, climate variability, especially its effect in significantly decreasing the lake water level, played a dominant role. The effect of water level on the occurrence of an algal bloom event in 2007 was investigated using the Estuary, Lake and Coastal Ocean Model coupled with the Computational Aquatic Ecosystem Dynamics Model (ELCOM-CAEDYM) simulations. Results reinforced the dominant role played by water level, demonstrating that at a higher water level (an increase of 20 m) the bloom may not have occurred. Increased alertness and more rapid response to prevent events such as algal blooms could be achieved through the use of ELCOM-CAEDYM combined with the ISF.