Grant Douglas

The provenance of sediments in Moreton Bay, Australia: a synthesis of major, trace element and Sr-Nd-Pb isotopic geochemistry, modelling and landscape analysis

Moreton Bay (MB) is a large semi-enclosed coastal embayment, located on the east coast of Australia adjacent to the Queensland capital city of Brisbane. The MB catchment is ca. 22 000 km2 while the bay itself is ca. 1500 km2. This represents a catchment:bay ratio of ca. 15:1. Within the MB catchment there are over 85 rocktypes with the most abundant, the Marburg Formation, constituting only ca. 12% of the catchment area. Detailed landscape analysis and a reconnaissance soil sampling program in combination with major and trace element and Sr, Nd and Pb isotope geochemistry were used to identify the major sources of sediment delivered to MB. A Bayesian linear mixing model allowed the proportion of sediment sources to be estimated. Model estimates suggest that there are substantial differences in the proportions of sediment being delivered into MB by the two major tributaries, the Brisbane and Logan Rivers despite both rivers containing a similar suite of major rocktypes. Over 50% of the sediment delivered to MB is derived from soils developed on the Marburg Formation. This equates to a catchment area/bay sediment deposition ratio of ca. 5. Basaltic soils of the Main Range Volcanics (Brisbane River catchment) and Lamington Group (Logan River catchment) and sediments from the Walloon Subgroup (present in both catchments) are on average also enriched in MB relative to the catchment by a factor of ca. 2.

Eutrophication management in surface waters using lanthanum modified bentonite: a review

This paper reviews the scientific knowledge on the use of a lanthanum modified bentonite (LMB) to manage eutrophication in surface water. The LMB has been applied in around 200 environments worldwide and it has undergone extensive testing at laboratory, mesocosm, and whole lake scales. The available data underline a high efficiency for phosphorus binding. This efficiency can be limited by the presence of humic substances and competing oxyanions. Lanthanum concentrations detected during a LMB application are generally below acute toxicological threshold of different organisms, except in low alkalinity waters. To date there are no indications for long-term negative effects on LMB treated ecosystems, but issues related to La accumulation, increase of suspended solids and drastic resources depletion still need to be explored, in particular for sediment dwelling organisms. Application of LMB in saline waters need a careful risk evaluation due to potential lanthanum release.

Towards effective phosphorus recycling from wastewater: Quantity and quality

Precipitation in the Mg-Ca-NH3-PO4 system has been explored to improve understanding of likely phases recoverable from complex wastewaters. Over a range of Mg/Ca combinations (0-100%) and pH 5-11, at least seven identifiable crystalline phases could be precipitated from artificial wastewater including: struvite, hydroxylapatite, newberyite, brushite, merrilite/whitlockite, octocalcium phosphate, and monetite. This experimental study has outlined the physicochemical conditions required to produce various phosphate products from synthetic wastewater, and found that large differences exist between experimentally formed phases and thermodynamical predictions. Struvite formation is the most desirable precipitate for the recovery of phosphate based upon purity, growth characteristics, dewatering properties, phosphate removal efficiency, and its ability to simultaneously remove ammonia. This study has also demonstrated that in specific cases the preliminary precipitation of brushite is a possible means of decreasing calcium content such that subsequent struvite formation could achieve higher-purity. Utilising experimental results and information on current commodity prices, discussion on the choice of Mg and Ca sources for phosphorus recovery provides guidance on appropriate means to optimise the formation and yield of high quality cost-optimised products.

Response of cultured Microcystis aeruginosa from the Swan River, Australia, to elevated salt concentration and consequences for bloom and toxin management in estuaries

A mixed bloom of Microcystis aeruginosa forma aeruginosa and forma flos-aquae from the Swan River, Western Australia, was confirmed toxic by HPLC analysis. At least four, and possibly 11, microcystins were detected in cell-free extracts. Live bloom material was cultured at salt concentrations up to 21.2 g L–1 (total salts). The cultures were salt tolerant up to 9.8 g L–1. Reduction in the total cell concentration in the first 23 h was only observed in the highest salt treatment and first-order rate constants for cell lysis were higher than the rates for reduction of the intracellular microcystin pool size for that treatment. This suggests preferential lysis of genotypes with lower salinity tolerance and toxigenicity. This increased the toxicity of the mixed bloom population and the apparent microcystin cell quota without any change to the intracellular microcystin pool size. Therefore, the toxicity of bloom material may change through preferential lysis of cells with lower tolerances to changing environmental conditions, including salinity. Managers should be aware that the World Health Organization alert levels of 105 cells mL–1 for human contact exposure to cyanobacteria may not be a suitable prima facie test during these periods.

Geoengineering in lakes: welcome attraction or fatal distraction?

Abstract The use of geoengineering techniques for phosphorus management offers the promise of greater and quicker chemical and ecological recovery. It can be attractive when used with other restoration measures but should not be considered a panacea. The range of materials being proposed for use as well as the in-lake processes targeted for manipulation continues to grow. With increasing political imperatives to meet regulatory goals for water quality, we recommend a coordinated approach to the scientific understanding, costs, and integration of geoengineering with other approaches to lake management.

Diagenetic cycling of trace elements in the bottom sediments of the Swan River Estuary, Western Australia

Abstract Teflon strips were used in-situ in the bottom sediments at two sites in the Swan River Estuary to collect diagenetic Fe–Mn oxyhydroxides and monitor monthly changes in their morphology and trace element geochemistry. This study demonstrates that substantial concentrations of trace elements accumulate at the redox front during the formation of diagenetic Fe–Mn oxyhydroxides. It is likely that the Fe–Mn oxyhydroxides initially nucleate and grow on the Teflon strips via bacterial activity. Trace element geochemistry of the diagenetic Fe–Mn oxyhydroxides is influenced by changes in the supply of trace elements from either the bottom sediments and/or water column or changes in the physico-chemical status of bottom and porewaters. If sufficient diagenetic Fe–Mn oxyhydroxides are preserved in the upper layer(s) of the bottom sediment it is possible that diagenetic (secondary) trace element enrichment profiles may be produced which modify the historical input of natural or anthropogenic trace element sources. Alternatively, partial or complete dissolution of the diagenetic Fe–Mn oxyhydroxides in response to temporal changes in the redox status of the bottom sediment may lead to a substantial underestimate of trace element fluxes in historical bottom sediment profiles. This study highlights that considerable care must be taken when interpreting short- to long-term geochemical profiles in bottom sediments due to the possible occurrence of rapid, seasonally mediated diagenetic processes.

Geo-Engineering in Lakes: A Crisis of Confidence?

The effective management of lakes suffering from eutrophication is confounded by a mosaic of interactions and feedbacks that are difficult to manipulate. For example, in lake processes can delay the relinquishment of legacy phosphorus (P) manifested within bed sediments for decades, even after effective catchment management. This recovery time is often deemed unacceptable and researchers have explored many in-lake management measures designed to “speed-up” recovery. The manipulation of biogeochemical processes (commonly targeting P) using materials to achieve a desired chemical and/or ecological response has been termed geo-engineering in lakes, and is becoming a commonly considered eutrophication management tool (Figure 1). Although this approach has been employed for many years it remains contentious largely due to variable results reported in the literature. This uncertainty risks ineffective management based on poorly designed or inappropriate applications. To address this, it is important that current levels of confidence in the approach be effectively communicated and that methods of increasing confidence are clearly demonstrated. We draw here on experiences of researchers and water managers at a global scale to demonstrate recent advances and consensus on recommendations (numbered below) for best practice. This information, although vital to underpinning successful management, has not been available in the peer reviewed literature.

Nutrient and dissolved organic carbon removal from water using mining and metallurgical by-products

Excess nutrient input to water bodies frequently results in algal blooms and development of oxygen deficient conditions. Mining or metallurgical by-products can potentially be utilised as filtration media within water treatment systems such as constructed wetlands, permeable reactive barriers, or drain liners. These materials may offer a cost-effective solution for the removal of nutrients and dissolved organic carbon (DOC) from natural waters. This study investigated steel-making, alumina refining (red mud and red sand) and heavy mineral processing by-products, as well as the low-cost mineral-based material calcined magnesia, in laboratory column trials. Influent water and column effluents were analysed for pH and flow rate, alkalinity, nutrient species and DOC, and a range of major cations and anions. In general, by-products with high Ca or Mg, and to a lesser extent those with high Fe content, were well-suited to nutrient and DOC removal from water. Of the individual materials examined, the heavy mineral processing residue neutralised used acid (NUA) exhibited the highest sorption capacity for P, and removed the greatest proportions of all N species and DOC from influent water. In general, NUA and mixtures containing NUA, particularly those with calcined magnesia or red mud/red sand were the most effective in removing nutrients and DOC from influent water. Post-treatment effluents from columns containing NUA and NUA/steel-making by-product, NUA/red sand and NUA/calcined magnesia mixtures exhibited large reductions in DOC, P and N concentrations and exhibited a shift in nutrient ratios away from potential N- and Si-limitation and towards potential P-limitation. If employed as part of a large-scale water treatment scheme, use of these mining and metallurgical by-products for nutrient removal could result in reduced algal biomass and improved water quality. Identification and effective implementation of mining by-products or blends thereof in constructed wetlands or other intervention structures to augment nutrient and DOC retention has considerable potential as an aquatic ecosystem management tool.

Identification of sediment sources to Lake Wivenhoe, south-east Queensland, Australia

Effective management of sediment fluxes in aquatic systems involves, in part, the identification of catchment sediment sources. Lake Wivenhoe (LW), the largest water storage in south-east Queensland, serves two important roles: it supplies 80% of the drinking water to the region and acts as a major flood mitigation feature for the city of Brisbane. Highly developed subcatchments in LW have resulted in declining waterway health, with sediment movement from the catchment to LW of major concern. Although there is considerable hydrological information, only limited data exist on sediment and nutrient fluxes. A detailed lake sediment (128 samples) and reconnaissance catchment soil sampling program (89 samples) was undertaken. Geochemical, Nd-Sr isotopic and statistical analyses were used to identify major sources of sediment to LW. A purpose-built Bayesian mixing model was then used to quantitatively estimate the proportion of sediment from major catchment sources. Approximately 36% of the LW catchment delivers the majority of sediment; enrichment factors for the three major sediment sources (dam to catchment ratio) range from ∼2 to 5. The Esk Formation is the major sediment source comprising ∼10% of catchment area but contributing 50% of the sediment and 33% of the total phosphorus delivered to LW.

Fitzroy River Basin, Queensland, Australia. I. Identification of Sediment Sources in Impoundments and Flood Events

Environmental Context. The Fitzroy River Basin is a major contributor to the loads of suspended sediment and nutrients reaching coastal areas in the southern Great Barrier Reef. Cost-effective investment in improved land, vegetation, and water management to lower these loads requires an understanding of the sources and movement of sediments within the basin. This multidisciplinary geochemical and modelling study provides for the first time a quantitative estimate of sediment sources and spatial and hydrology-related variation within the Fitzroy River Basin. Abstract. An integrated geochemical, modelling, and reconnaissance soil sampling approach has been used to identify the sources of sediment in the Fitzroy River Basin (FRB). The composition of sediment in weirs and dams within the FRB indicate that in the southern and central FRB the Dawson River contributes only a small basaltic component and the inputs are dominated by soils from the Surat and Bowen Basins. Rivers from the central FRB carry variable amounts of basaltic soils. In contrast, basaltic soils constitute the majority of sediment transported during flood events. Surat Basin soils form a minor component of flood events with little contribution from soils of the Bowen Basin despite it constituting the majority of the area of the central FRB. Soils from the Thomson Fold Belt constitute a substantial proportion of the sediment transported by, and retained in, impoundments in the central FRB and also dominate sediment delivered from the western FRB. This study will inform cost-effective investment by government to target remedial actions to reduce sediment and nutrient loads within the FRB that may be ultimately transported via the Fitzroy River Estuary to the southern Great Barrier Reef.