Barry T. Hart

A review of the salt sensitivity of the Australian freshwater biota

In Victoria, Australia, both dryland salinity and salinity in irrigation regions are serious agricultural problems. One option to control the latter is to pump groundwater to maintain it below the surface. However, this leaves a saline wastewater for disposal, probably into local streams or wetlands. This review of the salt sensitivity of the biota of Australian streams and wetlands gives information of interest to those responsible for developing controls on these discharges. The review addresses the lethal and sub-lethal effects of salinity on microbes (mainly bacteria), macrophytes and micro-algae, riparian vegetation, invertebrates, fish, amphibians, reptiles, mammals, and birds. Data suggest that direct adverse biological effects are likely to occur in Australian river, stream and wetland ecosystems if salinity is increased to around 1 000 mg L−1. The review highlights a general lack of data on the sensitivity of freshwater plants and animals to salinity increases.

Parameterisation and evaluation of a Bayesian network for use in an ecological risk assessment

Catchment managers face considerable challenges in managing ecological assets. This task is made difficult by the variable and complex nature of ecological assets, and the considerable uncertainty involved in quantifying how various threats and hazards impact upon them. Bayesian approaches have the potential to address the modelling needs of environmental management. However, to date many Bayesian networks (Bn) developed for environmental management have been parameterised using knowledge elicitation only. Not only are these models highly qualitative, but the time and effort involved in elicitation of a complex Bn can often be overwhelming. Unfortunately in environmental applications, data alone are often too limited for parameterising a Bn. Consequently, there is growing interest in how to parameterise Bns using both data and elicited information. At present, there is little formal guidance on how to combine what can be learned from the data with what can be elicited. In a previous publication we proposed a detailed methodology for this process, focussing on parameterising and evaluating a Bn. In this paper, we further develop this methodology using a risk assessment case study, with the focus being on native fish communities in the Goulburn Catchment (Victoria, Australia).

Uptake of trace metals by sediments and suspended particulates: a review

This review addresses three of the possible mechanisms by which trace metals can be concentrated by sediments and suspended particulate matter. These are physico-chemical adsorption from the water column, biological uptake particularly by bacteria and algae, and the sedimentation and physical entrapment of enriched particulate matter. The relative importance of these three mechanisms will be different, depending upon the aqueous system, but there have been insufficient studies to allow the establishment of even ‘rule-of-thumb’ guidelines, as yet, about their quantitative importance under different conditions.

Trace metal complexing capacity of natural waters: A review

Abstract The theoretical basis of trace metal complexing capacity of natural waters and the analytical methods used to measure it are reviewed. The current literature on this subject is also reviewed, in an attempt to draw out the most important features relating to the validity of the methods used and the nature of the metal‐binding ligands and complexes formed.

Effects of salinity on river, stream and wetland ecosystems in Victoria, Australia.

Salinity is a growing problem in many parts of the world. In Australia both dryland salinity and salinity in irrigation regions are serious problems. Options being considered to control the latter involve pumping the groundwater to lower the watertable; however, this leaves a saline wastewater to be disposed, probably into local streams or wetlands. A previous review by the authors covered the lethal and sub-lethal effects of salinity on individual species within the following groups of aquatic organisms: microbes (mainly bacteria), macrophytes and micro-algae, riparian vegetation, invertebrates, fish. amphibians, reptiles and mammals and water birds. That review concentrated on Australian information, information it is argued that will be more typical of the effects occurring over a large part of the world than data from the better watered areas of North America and Europe. This paper uses these data on individual species to determine the possible adverse effects of saline wastewater discharges on aquatic ecosystems, in particular lowland rivers and streams and wetlands. In these freshwater systems, the macroinvertebrates and plants (riparian vegetation, macrophytes and micro-algae) were assessed to be the most salt sensitive biological communities, with direct adverse biological effects likely to occur when salinity is increased to around 1000 mg 1-t. More subtle sublethal and indirect effects possibly occur at salinities below this, however the scientific data are not presently available to assess the extent that this might occur. A set of guidelines for assessing the possible biological effects in particular salt-affected rivers, streams or wetlands is developed.

Catchment-wide impacts on water quality: the use of ‘snapshot’ sampling during stable flow

Abstract Water quality is usually monitored on a regular basis at only a small number of locations in a catchment, generally focused at the catchment outlet. This integrates the effect of all the point and non-point source processes occurring throughout the catchment. However, effective catchment management requires data which identify major sources and processes. As part of a wider study aimed at providing technical information for the development of integrated catchment management plans for a 5000 km 2 catchment in south eastern Australia, a ‘snapshot’ of water quality was undertaken during stable summer flow conditions. These low flow conditions exist for long periods so water quality at these flow levels is an important constraint on the health of in-stream biological communities. Over a 4 day period, a study of the low flow water quality characteristics throughout the Latrobe River catchment was undertaken. Sixty-four sites were chosen to enable a longitudinal profile of water quality to be established. All tributary junctions and sites along major tributaries, as well as all major industrial inputs were included. Samples were analysed for a range of parameters including total suspended solids concentration, pH, dissolved oxygen, electrical conductivity, turbidity, flow rate and water temperature. Filtered and unfiltered samples were taken from 27 sites along the main stream and tributary confluences for analysis of total N, NH 4 , oxidised N, total P and dissolved reactive P concentrations. The data are used to illustrate the utility of this sampling methodology for establishing specific sources and estimating non-point source loads of phosphorous, total suspended solids and total dissolved solids. The methodology enabled several new insights into system behaviour including quantification of unknown point discharges, identification of key in-stream sources of suspended material and the extent to which biological activity (phytoplankton growth) affects water quality. The costs and benefits of the sampling exercise are reviewed.

Ecological risk to aquatic systems from salinity increases

Salinity is a major problem in many regions of Australia, and is predicted to get considerably worse over the next 30-50 years. Most effort has focused on the terrestrial environment, and specifically on the loss of productive agricultural land. Increased salinity can also result in unwanted changes to aquatic ecosystems in rivers, streams and particularly wetlands. This paper first reviews the importance of assessing risks from salinity increases in a catchment context, and then introduces a disturbance-response conceptual model to assist with the understanding of such situations. Two factors are shown to be particularly important in assessing which freshwater systems will be most susceptible to increases in salinity—the location of the systems in the landscape, and the current ecological condition of the system. The resilience of an ecosystem to salinity disturbances is shown to be a useful concept which with further knowledge may be incorporated into risk-assessment approaches. The development of a new ecological risk assessment approach for assessing risks to aquatic systems in the Goulburn-Broken catchment from increases in salinity over the medium (20 years) and long (100 years) term is reported. The risks to the biota in Hughes Creek, a tributary of the Goulburn River, are assessed by using a probabilistic approach. Current salinity levels in the creek present a low risk to the biota. Finally, the paper addresses the challenge of making the ecological risk assessment method more quantitative by discussing the following two key aspects: how to better quantify the linkages between the key stressors and the biotic components, and how to better handle uncertainties. BT02 Eco t om ty B. T. H

A strontium isotopic investigation of the origin of suspended particulate matter (SPM) in the Murray-Darling River system, Australia

Abstract The strontium isotopic composition of suspended particulate matter (SPM) from the Murray-Darling River system (M-DRS) in eastern Australia varies significantly as a function of particle size. Colloidal matter ( 87 Sr 86 Sr vs. 1/Sr mixing and 87 Sr 86 Sr vs. 87 Rb 86 Sr isochron diagrams indicating simple two component mixing; isotopic ratios decrease as a function of particle size (e.g., Murray River-Merbein, 87 Sr 86 Sr = 0.7221−0.7160 ). This is the first time this type of mixing has been recognised in fluvial systems and highlights the influence of particle size on isotopic composition. The two components involved are detrital silicate grains (aggregates) and varying amounts of natural organic matter present as surface coatings. The proportion of natural organic matter increases from approximately 10–80% with decreasing particle size. The natural organic matter contains high concentrations of unradiogenic Sr which has been complexed from solution (e.g., Murray River-Merbein, 87 Sr 86 Sr = 0.7164 ). Particulate fractions (>1 μm) are dominated by the silicate component and are isotopically heterogeneous and displaced from the colloidal mixing lines, with distinctly more radiogenic Sr (e.g., Murray River-Merbein, 87 Sr 86 Sr = 0.7316−0.7354 ). The variation in the strontium isotopic composition is due to the differential weathering of minerals in the sediment source. Weathering of plagioclase produces unradiogenic Sr which dominates the colloidal and dissolved ( 0.003 μm) and dissolved ( 87 Sr 86 Sr and [Sr] concentration, but markedly lower [Rb] concentration and Rb/Sr.

Adsorption of natural organic matter onto goethite

The factors influencing the association of two natural organic matter (NOM) samples (from Redwater Creek in Australia and Suwannee River in USA) with goethite were studied. Sorption occurred very rapidly (minutes) and at very low NOM concentrations (about 0.5 mg C 1−1), implying that mineral surfaces in the natural aquatic environment would not remain uncoated by NOM for long. The sorption behaviour of the two NOM samples followed the Langmuir adsorption equation. The maximum sorption density for the unfractionated Redwater Creek NOM was 1.1 μmol C mg−1 of goethite. The hydrophobic fractions (both acidic and neutral) separated from the Redwater Creek sample had much greater sorption affinities for the goethite surface than did the hydrophilic fraction. Calculation of the surface crowding indicates that a monolayer of sorbed NOM exists over the goethite surface. Sorption was influenced by solution pH and calcium ion concentration. Maximum sorption density occurred at around pH 3–4, and decreased at higher pH. The sorption density of NOM also appears to be influenced by the presence of non-ionic hydrophobic solutes. This component could shield the electrostatic repulsive forces between neighbouring adsorbed anionic NOM molecules on the goethite surface, thus leading to an increase in the maximum amount of NOM adsorbed. Calcium ion concentration increased sorption of NOM up to calcium concentrations of around 1 mM but higher calcium concentrations resulted in reduced sorption. Sorption of the hydrophobic acid fraction was most affected by calcium concentration. The main effect of NOM sorption on the surface characteristics of goethite is alteration of the surface charge. The isoelectric point of the NOM-coated goethite is shifted markedly to lower pH, compared to that of uncoated goethite. Thus, at the normal pH of natural waters, NOM-coated goethite has a net negative charge which would significantly influence the types of interaction occurring at the surface of the NOM-coated particles in natural aquatic systems. The model advanced for suspended particulate matter (SPM) in aquatic systems, namely a mineral core with coatings of hydrous metal oxides and NOM, appears to explain adequately many aspects of the behaviour of natural SPM.

Luxury uptake of phosphorus by sediment bacteria

This note reports the results of experiments aimed at confirming the luxury uptake of phosphorus (P) by sediment bacteria as polyphosphate (Poly-P). Aerobic suspensions of sediments from two different sites were spiked with 1 mg P/L as orthophosphate and augmented with acetate (a fermentation product) or glucose. The orthophosphate was rapidly taken up over a period of a few hours. When these aerobic uptake experiments were made anaerobic and additional organic carbon added, only the acetate-amended sediment released a significant amount of the added phosphorus. It was hypothesised that during the aerobic stage, and with the addition of acetate, some of the phosphorus was accumulated as Poly-P by sediment microorganisms, which was released during the subsequent anaerobic stage (provided acetate was still present). Two lines of evidence--transmission electron microscope analysis of sediment bacteria and 31P-NMR analysis of sediment extracts--are presented to support the hypothesis that a portion of the phosphorus taken up during the aerobic experiments was stored as Poly-P.