Modern depositional processes in a confined, flood-prone setting: benches on the Shoalhaven River, NSW, Australia

Past research has suggested that in-channel alluvial landforms, often termed benches, are associated with flow events with specific return periods and that such landforms are inset within terraces, floodplains, or higher bench surfaces. Chronostratigraphic analysis and hydraulic modelling in a bedrock-confined reach of the lower Shoalhaven River show that they have been extensively eroded and at least partially reformed during the historical period. Lower benches are inundated by flood events with average recurrence intervals (ARI) of 2 or less years, middle benches by events ca. 5 years ARI, and upper benches by events ca. 10 years ARI. The lower benches commonly share over- or onlapping stratigraphic units, demonstrating that deposition can occur on multiple bench surfaces simultaneously. This is in contrast to earlier suggestions of discrete bench surfaces being associated with, and formed by, events that have a specific return period. In the Shoalhaven River, Pleistocene and Holocene terraces determine the large alluvial channel geometry for a wide range of discharges up to the 50-year return interval with benches forming temporary sediment storages within this larger channel. The large channel dimensions and associated hydraulics and high annual flood variability (flash flood magnitude index of 0.53) for the Shoalhaven River facilitate the construction of multiple bench surfaces across a range of elevations. Benches are formed of a wide range of facies from decimetre-thick massive sand units through interbedded sands and silts

Alluvium of antiquity: Polycyclic terraces in a confined bedrock valley

Confined river valleys are not the localities where long term preservation of alluvium would be expected. The 25 km long low gradient (0.0014 m.m- 1) confined valley setting of the Shoalhaven River has archived alluvium of middle Pleistocene age to maintain a relatively uniform channel as an efficient conduit for a wide range of flows in a confined bedrock valley of variable morphology. Single-grain optically stimulated luminescence (OSL) dating has identified polycyclic terraces up to 193 ka in age (marine isotope stage [MISI7) with lower terrace remnants dating from 173-140 ka (MIS 6) and 106 ka (MIS 5). Holocene alluvium 2-3.5 ka in age caps these old Pleistocene units and a well-constrained combination of one-dimensional and two-dimensional hydraulic modelling demonstrates that these polycyclic terraces are clearly within reach of the modem hydrological regime. The 106 ka terrace at 17 m above low flow is inundated by floods recurring on average every -20 years, and the 140-193 ka terraces at 20-22 m are overtopped every 50-100 years. These ancient diachronous landforms exhibit complex depositional histories and are on-lapped by longitudinal benches of modern sand and gravel. Their polycyclic nature appears to be a response to flow reduction, using alluvium to adjust the boundary of the otherwise inflexible morphology of a bedrock gorge

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

Infrared pre-excitation grants isotopomer-specific photochemistry

Species-selective photochemistry is often hampered by overlapping UV-Vis spectra. We overcome this long-standing problem by combined vibrational and electronic excitation as demonstrated by isotopomer selection. The influence of various factors on selectivity is discussed

Infrared pre-excitation grants isotopomer-specific photochemistry

Species-selective photochemistry is often hampered by overlapping UV-Vis spectra. We overcome this long-standing problem by combined vibrational and electronic excitation as demonstrated by isotopomer selection. The influence of various factors on selectivity is discussed

Infrared pre-excitation grants isotopomer-specific photochemistry

Species-selective photochemistry is often hampered by overlapping UV-Vis spectra. We overcome this long-standing problem by combined vibrational and electronic excitation as demonstrated by isotopomer selection. The influence of various factors on selectivity is discussed