Evaluation of management scenarios for controlling eutrophication in a shallow tropical urban lake

Urban lakes are typically smaller, shallower, and more exposed to human activities than natural lakes. Although the effects of harmful algal blooms (HABs) associated with eutrophication in urban lakes has become a growing concern for water resources management and environmental protection, studies focussing on this topic in relation to urban lakes are rare and knowledge of the ecological dynamics and effective management strategies for controlling eutrophication in urban lakes is lacking. This study applied an integrated three-dimensional hydrodynamics-ecological model for a small shallow tropical urban lake in Singapore and evaluated various management scenarios to control eutrophication in the lake. It is found that in-lake treatment techniques including artificial destratification, sediment manipulation and algaecide addition are either ineffective or possess environmental concerns; while watershed management strategies including hydraulic flushing and inflow nutrients reduction are more effective and have posed less environmental concerns. In this study, inflow phosphorus reduction was found to be the best strategy after evaluating the advantages and drawbacks of the management strategies studied. Runoff from the watershed exerts significant influence on urban lakes and thus an integrated water resources management at the watershed level is critical for the control of eutrophication

Distribution and abundance of human-specific Bacteroides and relation to traditional indicators in an urban tropical catchment

The study goals were to determine the relationship between faecal indicator bacteria (FIB), the HF183 marker and land use, and the phylogenetic diversity of HF183 marker sequences in a tropical urban watershed

Urban stormwater inputs to an adapted coastal wetland : role in water treatment and impacts on wetland biota

The Lake Pertobe wetland system is a semi-natural wetland that has been modified primarily for recreational use. However, this lake system receives stormwater from much of the central business district of Warrnambool City (Victoria, Australia) and serves as a buffer zone between the stormwater system and the Merri River and Merri Marine Sanctuary. This work considers the impact of stormwater inputs on Lake Pertobe and the effectiveness of the lake in protecting the associated marine sanctuary. Sediment contaminants (including heavy metals and polycyclic aromatic hydrocarbons (PAHs)) and water quality parameters within the lake, groundwater and stormwater system were measured. Water quality parameters were highly variable between stormwater drains and rain events. Suspended solids rapidly settled along open drains and shortly after entering the lake. Groundwater inputs increased both salinity and dissolved nitrogen in some stormwater drains. Some evidence of bioaccumulation of metals in the food chain was identified and sediment concentrations of several PAHs were very high. The lake acted as a sink for PAHs and some metals and reductions in Escherichia coli, biological oxygen demand and total phosphorus were observed, affording some protection to the associated marine sanctuary. Nutrient retention was inadequate overall and it was identified that managing the lake primarily as a recreational facility impacted on the effectiveness of stormwater treatment in the system.

Hydrologic response of a tropical watershed to urbanization

 Urbanization has profound influence on the hydrologic response of landscapes. Urban transformation affects the storages and processes that determine the generation of hydrologic fluxes. It also changes the time-scales associated with hydrologic processes. Shifts in hydrologic response of the watershed unit due to urban transformation may be more complex than the simple linear mixing (weighted sum) of responses from the urbanized and non-urbanized fractions of the landscape. This may especially be the case for tropical watersheds where the precipitation forcing of the watershed is frequent and intense - interacting with the shifting time-scales and changing storages with increasing urbanization. In this study, a fully distributed hydrological model (MOBIDIC) that captures hydrologic dynamics during storms and interstorms is applied in order to characterize the potentially nonlinear response of a tropical watershed to urban transformation. Indices that quantify the departures from linear response are introduced and used to test the effects of urbanization on different hydrologic processes and fluxes in a mixed (urban and non-urban) watershed. The tropical Kranji watershed in Singapore is used in this study. Fortunately two sub-watersheds within Kranji that have streamflow gaging stations are well-suited for the calibration of the model. One sub-watershed is nearly fully urbanized and another is pristine (non-urban). As a result the contrasting components (urban and non-urban) can be calibrated in the model. The simulation system is then used to assess the hydrologic response due to changing levels of urbanization. For some fluxes and storages, the hydrologic response due to changing urban fraction cannot be simply predicted from a linear mixing model.

Demo abstract: wind measurements for water quality studies in urban reservoirs

Water quality monitoring and prediction are critical for ensuring the sustainability of water resources which are essential for social security, especially for countries with limited land like Singapore. For example, the Singapore government identified water as a new growth sector and committed in 2006 to invest S$ 330 million over the following five years for water research and development [1]. To investigate the water quality evolution numerically, some key water quality parameters at several discrete locations in the reservoir (e.g., dissolved oxygen, chlorophyll, and temperature) and some environmental parameters (e.g., the wind distribution above water surface, air temperature and precipitation) are used as inputs to a three-dimensional hydrodynamics-ecological model, Estuary Lake and Coastal Ocean Model - Computational Aquatic Ecosystem Dynamics Model (ELCOM-CAEDYM) [2]. Based on the calculation in the model, we can obtain the distribution of water quality in the whole reservoir. We can also study the effect of different environmental parameters on the water quality evolution, and finally predict the water quality of the reservoir with a time step of 30 seconds. In this demo, we introduce our data collection system which enables water quality studies with real-time sensor data.