Carolyn Oldham

A preliminary model for predicting heavy metal contaminant loading from an urban catchment.

The toxicity of heavy metals to biota in urban catchments has been regarded as a very important non-point source pollution issue. Numerous studies on heavy metal pollution in urban receiving waters have found that metal transport by surface runoff is closely correlated to the partitioning of the metal forms between dissolved and particulate phases, where sediment plays an important role in the transport process. Sediment cycling on urban streets, metal binding form, and rainfall character in the catchment area are considered to be the key factors for metal transport. A preliminary model is developed based on these considerations. Starting from classical build-up and wash-off processes for the suspended sediment (SS) on the urban impervious surface, the model links the transport of suspended sediment to the transport of metal species. Monitoring data from a small highway catchment were used in the model development. A total of 47 rain events over 1 year were monitored intensively at short time intervals (5-10 min) for hydrological data, rainfall intensity, and stormwater quality. In developing the model, lead was used for the metal load prediction, as it has been a common fuel additive for urban transportation. Agreement between model results and monitoring data indicates that the model can be used in predicting metal load from impervious urban areas, such as streets and roadways, on a long-term basis.

Steady convective exchange flows down slopes

Abstract: Horizontal exchange flows driven by destabilising buoyancy fluxes through the surface waters of lakes and coastal regions of oceans are important in understanding the transport of nutrients, micro-organisms and pollutants from littoral to pelagic zones. Our interest here is in the discharge flow driven by cooling or destabilising forcing at the water surface in a water body with variable depth due to sloping bottom topography. Flow visualisation studies and measurements in a laboratory model enabled us to develop scaling arguments to predict the dependency of discharge upon surface forcing and the angle of bottom slope. The results were used to interpret both the laboratory measurements and field data from a small shallow lake with sloping sides and an essentially flat bottomed interior, as well as published results from the literature. The steady state horizontal exchange can be described by Q = 0.24 B1/3 (l tan θ/(1 + tan θ))4/3, where Q is the discharge rate per unit length of shoreline, θ is the angle of the bottom slope, B is the surface buoyancy flux and l is the horizontal length of the forcing region over the slope. The flushing timescale of the wedge shaped littoral region was given by τf∼l2/3 (1 + tan θ) 4/3/ (B tan θ1/3. While the buoyancy flux in the field is almost never constant in space or time and the slope from the shore is seldom uniform, we found that the exchange rate was relatively insensitive to buoyancy flux changes and only moderately sensitive to slope.

Exchange dynamics of a shallow contaminated wetland

Flux pathways are investigated for a wetland system comprised of a river flowing through two shallow forebays and then entering the main basin of a lake. The hydrodynamic exchanges between these three components influence the fate and transport of heavy metals in the system. During non-storm summer flows the river plume, comprised of river water and entrained forebay water, was cooler than the lake surface water and so plunged as it entered the main basin and inserted near the seasonal thermocline. Because the river plume plunged, only a fraction of its metals flux was available to the epilimnion. A return flow into the forebay was always observed immediately above the river inflow, ensuring a predominantly two-layer exchange system. However during days of negative heat flux (surface heating), an additional exchange mechanism existed when the surface waters from the forebay formed a buoyant plume, flowing out into the main basin. This heated outflow produced a significant, but short-lived, arsenic flux from the forebay into the surface waters of the lake.

Arsenic remobilization in a shallow lake: the role of sediment resuspension

Oxic resuspension occurs regularly in shallow lakes, yet its role as a mechanism for contaminant remobilization remains ill defined. This study investigated contaminant remobilization during sediment resuspension and determined whether changes in contaminant sediment partitioning reflected the mechanisms controlling remobilization. Arsenic-contaminated sediment from a shallow wetland was subjected to simulated resuspension under a range of differing initial pH conditions. The effect of resuspension on As partitioning was evaluated using a fractionation scheme targeting the dissolved, ion exchangeable, carbonate, organic, amorphous iron oxide, crystalline iron oxide, and apatite fractions. Rate investigations demonstrated that arsenic remobilization occurred on timescales similar to resuspension events, with concentrations reaching steady state within 24 h. The sediment also buffered slurry pH to 8.3 in experiments where the initial pH was between 4 and 10. This pH regulation was attributed to carbonate dissolution or acid-base equilibria of surface base functional groups, although iron oxide and organic matter dissolution did occur in experiments with an initial pH outside this range. Remobilization caused losses in arsenic associated with the ion exchangeable, organic, and amorphous iron fractions but changes in initial pH have a negligible effect on arsenic remobilization or partitioning within the well-buffered region. Resuspension released approximately 20% of the total sediment arsenic, although calculations indicated that a single resuspension event would not significantly change water column arsenic concentrations. While not conclusively proving the mechanisms of remobilization, fractionation gave valuable insight into the effect of sediment resuspension on contaminant remobilization.

Will it rise or will it fall? Managing the complex effects of urbanization on base flow

Sustaining natural levels of base flow is critical to maintaining ecological function as stream catchments are urbanized. Stream base flow responds variably to urbanization. Base flow or water tables rise in some locations, fall in others, or remain constant. This variable response is the result of the array of natural (e.g., physiographic setting and climate) and anthropogenic (e.g., urban development and infrastructure) factors that influence hydrology. Perhaps because of this complexity, few simple tools exist to assist managers to predict baseflow change in their local urban area. We address this management need by presenting a decision-support tool that can be used to predict the likelihood and direction of baseflow change based on the natural vulnerability of the landscape and aspects of urban development. When the tool indicates a likely increase or decrease, managers can use it for guidance toward strategies that can reduce or increase groundwater recharge, respectively. An equivocal result from application of the tool suggests the need for a detailed water balance. The tool is embedded in an adaptive-management framework that encourages managers to define their ecological objectives, assess the vulnerability of their ecological objectives to changes in water-table height, and monitor baseflow responses to urbanization. We tested our framework with 2 different case studies: Perth, Western Australia, Australia and Baltimore, Maryland, USA. Together, these studies show how predevelopment water-table height, climate, and geology together with aspects of urban infrastructure (e.g., stormwater practices, leaky pipes) interacted such that urbanization led to rising (Perth) and falling (Baltimore) base flow. Greater consideration of subsurface components of the water cycle will help to protect and restore the ecology of urban fresh waters.

Kinetic reaction modeling framework for identifying and quantifying reductant reactivity in heterogeneous aquifer sediments.

Water-sediment interactions triggered by the injection of oxidized aqueous solutions into anoxic groundwater systems usually modify both the aquifer matrix and control the final aqueous composition. The identification and quantification of these reactions in complex heterogeneous systems remains a challenge for the analysis and prediction of water quality changes. Driven by the proposed injection of large quantities of oxic water into a deep anoxic heterogeneous pyritic aquifer; this study was undertaken to quantify the reactivity of aquifer sediments with respect to oxidant consumption and to characterize the variability of the reaction rates across different lithological units. A total of 53 samples were incubated for periods of 14, 37, and 50 days, during which the gas-phase was continuously monitored and the aqueous composition analyzed. A geochemical modeling framework was developed that incorporated a mixed set of equilibrium and kinetic reactions and supported the interpretation and quantification of the geochemical controls. The good agreement between simulated and experimental results of O2 consumption, CO2 production, pH, major ions, and trace metals suggests that the framework was able to successfully quantify reaction rates of competing redox and buffering reactions for the different lithological aquifer material.

Structural and spectroscopic studies of some copper(I) halide tert-butyl isocyanide adducts.

Single-crystal structural characterizations confirm the existence of the unusual 1 : 4 copper(I) halide : unidentate ligand adducts [Cu(CNt-Bu)4]X for X = Cl, Br (two forms), I (the chloride and one form of the bromide being solvated) with crystal packing dominated by stacks of interleaving cations. Cu-C range between 1.941(2) and 1.972(4) A. The structure of the 1 : 2 chloride complex is also recorded, being [ClCu(CNt-Bu)2], with the copper(I) atom environment trigonal planar, while CuCN : (CNt-Bu) (1 : 1) is a single-stranded polymer which spirals about a crystallographic 3-axis (CN scrambled), the ligands being pendant from the ...CuCNCuCN... string. The (5Cu static broadline NMR spectra of [Cu(CNt-Bu)4]I and [Cu(CNt-Bu)4]Br.H2O in the solid state exhibit dominant, narrow -1/2 <--> +1/2 central transition resonances and associated +/-1/2 <--> +/-3/2 satellite transition resonances which are characteristic of first-order quadrupole broadened systems, while associated high-resolution 65Cu MAS NMR data provide accurate measurement of the 65Cu isotropic chemical shifts. Both approaches provide complete data on the quadrupole and chemical shift interactions which contribute to these spectra. Far-IR spectra of products of reactions involving a range of CuX : t-BuNC ratios reveal the existence of 1 : 1.5 adducts for X = Br, I. Metal-carbon and metal-halogen bands are assigned in the far-IR spectra, which indicate a binuclear double halogen-bridged structure for the 1 : 1.5 complexes.

The use of an ultrafiltration technique for measurement of orthophosphate in shallow wetlands

The overestimation of orthophosphate by filterable reactive phosphorus (FRP) measurement techniques has long been accepted. The aim of this study was to quantify that overestimation in 17 wetlands over time. Specifically an ultrafiltration technique was used prior to the application of the molybdenum blue phosphorus detection method to quantify orthophosphate concentrations. Samples were collected over a 6-month period and analysed for total filterable (< 0.50 microm) phosphorus (TFP), filterable reactive phosphorus (FRP < 0.50 microm) and ultrafiltered (< 10(3) Da) reactive phosphorus (PO4). FRP correlated well with PO4, however, FRP overestimated PO4 particularly with increasing colloidal phosphorus concentration. The ratio of DOC to TFP (C:P) influenced the fate of PO4 in the water, implying that DOC was forming complexes with phosphorus. The PO4 concentrations decreased with increasing C:P ratios in some of the wetlands over the 6-month monitoring period.

Extremophile microbiomes in acidic and hypersaline river sediments of Western Australia

We investigated the microbial community compositions in two sediment samples from the acidic (pH ∼3) and hypersaline (>4.5% NaCl) surface waters, which are widespread in Western Australia. In West Dalyup River, large amounts of NaCl, Fe(II) and sulfate are brought by the groundwater into the surface run-off. The presence of K-jarosite and schwertmannite minerals in the river sediments suggested the occurrence of microbial Fe(II) oxidation because chemical oxidation is greatly reduced at low pH. 16S rRNA gene diversity analyses revealed that sequences affiliated with an uncultured archaeal lineage named Aplasma, which has the genomic potential for Fe(II) oxidation, were dominant in both sediment samples. The acidophilic heterotrophs Acidiphilium and Acidocella were identified as the dominant bacterial groups. Acidiphilium strain AusYE3-1 obtained from the river sediment tolerated up to 6% NaCl at pH 3 under oxic conditions and cells of strain AusYE3-1 reduced the effects of high salt content by forming filamentous structure clumping as aggregates. Neither growth nor Fe(III) reduction by strain AusYE3-1 was observed in anoxic salt-containing medium. The detection of Aplasma group as potential Fe(II) oxidizers and the inhibited Fe(III)-reducing capacity of Acidiphilium contributes to our understanding of the microbial ecology of acidic hypersaline environments.

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.