Ivars Reinfelds

Longitudinal effects of a water supply reservoir (Tallowa Dam) on downstream water quality, substrate and riffle macroinvertebrate assemblages in the Shoalhaven River, Australia

Approximately 15% of the world’s total run-off is presently retained by more than 45 000 large dams. However, the extent of the downstream ecological impacts of those dams is rarely assessed. The longitudinal effects of a large reservoir on the substrate, water quality and riffle macroinvertebrate communities were examined between 0.5 and 18.3 km downstream of Tallowa Dam. The number of taxa and the Australian River Assessment Scheme observed v. expected score generally increased with increasing distance from the dam, average clast size decreased with increasing distance and water quality showed distinct longitudinal patterns. Classification of the macroinvertebrate assemblages identified two groups, one from riffles ~4 km downstream of the dam and one further downstream, suggesting the main impact occurs close to the dam. The difference between the two groups of riffles resulted mainly from the following macroinvertebrates, Edmundsiops (Baetidae), Hemigomphus (Gomphidae), Illiesoperla (Gripopterygidae), Physa (Physidae), Nannoplebia (Libellulidae) and Austrolimnius larvae (Elmidae), occurring less frequently in the near-dam riffles. Water quality was probably the main cause of the altered macroinvertebrate assemblage structure, not altered hydrology, a result attributable to the small operational capacity of Tallowa Dam relative to the annual inflow volumes.

Shock, stress or signal? Implications of freshwater flows for a top-level estuarine predator.

Physicochemical variability in estuarine systems plays an important role in estuarine processes and in the lifecycles of estuarine organisms. In particular, seasonality of freshwater inflow to estuaries may be important in various aspects of fish lifecycles. This study aimed to further understand these relationships by studying the movements of a top-level estuarine predator in response to physicochemical variability in a large, temperate south-east Australian estuary (Shoalhaven River). Mulloway (Argyrosomus japonicus, 47–89 cm total length) were surgically implanted with acoustic transmitters, and their movements and migrations monitored over two years via fixed-position VR2W acoustic receivers configured in a linear array along the length of the estuary. The study period included a high degree of abiotic variability, with multiple pulses (exponentially high flows over a short period of time) in fresh water to the estuary, as well as broader seasonal variation in flow, temperature and conductivity. The relative deviation of fish from their modal location in the estuary was affected primarily by changes in conductivity, and smaller fish (n = 4) tended to deviate much further downstream from their modal position in the estuary than larger fish (n = 8). High-flow events which coincided with warmer temperatures tended to drive mature fish down the estuary and potentially provided a spawning signal to stimulate aggregation of adults near the estuary mouth; however, this relationship requires further investigation. These findings indicate that pulse and press effects of freshwater inflow and associated physicochemical variability play a role in the movements of mulloway, and that seasonality of large freshwater flows may be important in spawning. The possible implications of river regulation and the extraction of freshwater for consumptive uses on estuarine fishes are discussed.

Environmental flow management using transparency and translucency rules

River flow regimes and their variability are considered by many authors to be the most important factor structuring their physical and ecological environment. In regulated rivers, environmental or instream flows are the main management technique used to ameliorate the ecological effects of flow alteration. We highlight two concepts that are not commonly used in a managed flow regime but help return natural flow variability to a managed river, namely, transparent and translucent flow rules. Transparency flows target lower flows up to a defined threshold so that all inflows are released from a dam or are protected from abstraction. Translucency flows form a percentage of inflows greater than the transparency threshold that are released to maintain a proportion of flow pulses in the river system. The main ecological concept underlying transparency and translucency flows is that riverine biota are adapted to the historical flow regime. Although the loss of small to moderate flood events may arise from implementation of translucency and/or transparency flow regimes, we advocate that these rule types would, nonetheless, be beneficial in many managed flow regimes and present two case studies where they have been defined and implemented.

Combining otolith chemistry and telemetry to assess diadromous migration in pinkeye mullet, Trachystoma petardi (Actinopterygii, Mugiliformes)

This study examines the complex diadromous movements in pinkeye mullet (Trachystoma petardi) of south-eastern Australia. The techniques used to study these movements included LA-ICP-MS single line ablation transects and microchemical imaging as well as preliminary acoustic telemetry results which were used to aid in interpretation of chemical signatures related to complex movement patterns across salinity gradients. Ba:Ca and Sr:Ca from single ablation transects and microchemical images revealed differences between the otolith core and outer regions. Otolith Ba:Ca and Sr:Ca patterns were more easily distinguished in images compared to transects and these revealed that T. petardi spend their early life in saline waters. Movement patterns for adults varied, with a range of movements identified between fresh and saline waters. Telemetry data assisted in explaining the likely cause of the ambiguity in otolith microchemistry data, including identification of multiple rapid movements across salinity gradients. However, many movements through salinity gradients appear too brief to result in any clear Sr:Ca or Ba:Ca saline or mesohaline signature within the chemistry of the otolith. The combination of otolith chemistry and telemetry proved useful in providing information on this poorly understood species suggesting that T. petardi display a catadromous life history.