Preliminary model of nitrogen loads from southern bluefin tuna aquaculture

Farming of wild tuna in coastal areas is a relatively new aquaculture industry and little is known about the magnitude of nutrient discharges to the environment. In this work we present a preliminary model of nitrogen loads from southern bluefin tuna (Thunnus maccoyii) aquaculture in lower Spencer Gulf, South Australia. The model was developed based on feed inputs, estimates of fish metabolism and environmental data. Two pens were monitored over a full grow-out season to determine nitrogen sedimentation fluxes, remineralization at the sediment-water interface and accumulation in the sediments. The model suggests that the high metabolic rates of tuna lead to low retention of nitrogen in fish tissues (7-12% of feed inputs) and high environmental losses (260-502kg Ntonne(-1) growth). Considering Australian annual production of 4380tonnes over initial stocked biomass, total loads can reach 1137tonnes N per year, 86-92% lost as dissolved wastes. The nature of wastes suggests low localized impacts at current stocking densities and holding periods.     

The contribution of agricultural and urban activities to inorganic carbon fluxes within temperate watersheds

The lateral transport of bicarbonate as dissolved inorganic carbon (DIC) to the oceans is an integral component of the global carbon budget and can represent the sequestration of CO₂ from the atmosphere. Recently studies have implicated land use change, in particular agricultural development, as an accelerator of bicarbonate export. However, due to the co-variation of land use, bedrock and surficial geologies, and the relationship between bicarbonate export and climate, the impact of anthropogenic activities on DIC export remains an important research question. In order to examine the land use controls on DIC export from small temperate watersheds we sampled 19 streams draining catchments of varying land uses with similar bedrock and surficial geologies. In addition to an agricultural effect, there was a strong correlation between the percent of watershed in urban development and DIC concentrations and DIC yields. Urban watersheds exported 7.8 times more DIC than their nearby forested counterparts and 2.0 times more DIC than nearby agricultural catchments. Isotopic data suggest that excess DIC export from altered systems results from increased chemical weathering, enhanced CO₂ production within urban green spaces, and as a result of organic matter loading from septic systems and leaky sewer lines. Furthermore, we found that nitrogen additions (e.g. fertilizers and manure) are aiding in the dissolution of lime, increasing the total export of DIC from agricultural watersheds. Calculated anthropogenic loading rates ranged from 0.43 to 0.86 mol C m^− 2 yr^− 1. These loading rates suggest that a significant portion of global DIC export might be attributable to human activities, although the impacts on CO₂ sequestration are difficult to determine.     

The application of GPR to barrier-lagoon sedimentation study in Boao of Hainan Island

Sedimentary successions and internal structure of the coastal barrier-lagoon system of Boao, eastern Hainan Island were studied through utilizing data from test holes and trenches and ground-penetrating-radar (GPR) profiles. During late Pleistocene, fluvial and delta plains developed over an unevenly eroded bedrock during low sea level stand, followed by the formation of littoral and lagoon facies and defined coastal barrier-lagoon-estuary system during the post-glacial uppermost Pleistocene-lower Holocene eustatic rise of the sea level, and the upper Holocene high stand. GPR results show that Yudaitan, a sandy coastal bar backed by a low-laying land (shoal) just east of the active lagoon, is a continuous, parallel and slightly-wavy reflectors indicating homogeneous sandy or sandy gravel sediments, and inclined reflectors partly caused by progradation and accumulation of beach sand and gravel. Quasi-continuous, hummocky and chaotic reflectors from the shoal of Nangang village correspond to mixed accumulation of sands and clay. This research indicates the GPR is a non-intrusive, rapid, and economical method for high-resolution profiling of subsurface sediments in sandy gravelly coast.     

Feasibility of geoelectrical monitoring and multiphase modeling for process understanding of gaseous CO2 injection into a shallow aquifer

Potential pathways in the subsurface may allow upwardly migrating gaseous CO₂ from deep geological storage formations to be released into near surface aquifers. Consequently, the availability of adequate methods for monitoring potential CO₂ releases in both deep geological formations and the shallow subsurface is a prerequisite for the deployment of Carbon Capture and Storage technology. Geoelectrical surveys are carried out for monitoring a small-scale and temporally limited CO₂ injection experiment in a pristine shallow aquifer system. Additionally, the feasibility of multiphase modeling was tested in order to describe both complex non-linear multiphase flow processes and the electrical behavior of partially saturated heterogeneous porous media. The suitability of geoelectrical methods for monitoring injected CO₂ and geochemically altered groundwater was proven. At the test site, geoelectrical measurements reveal significant variations in electrical conductivity in the order of 15?C30?%. However, site-specific conditions (e.g., geological settings, groundwater composition) significantly influence variations in subsurface electrical conductivity and consequently, the feasibility of geoelectrical monitoring. The monitoring results provided initial information concerning gaseous CO₂ migration and accumulation processes. Geoelectrical monitoring, in combination with multiphase modeling, was identified as a useful tool for understanding gas phase migration and mass transfer processes that occur due to CO₂ intrusions in shallow aquifer systems.     

Deformation of a young salt giant: regional topography of the Red Sea Miocene evaporites

The deformational behaviour of ‘salt giants’ during and shortly after their deposition is difficult to decipher in ocean margin settings where the original evaporites have been deeply buried and strongly mobilized. Here, we examine seismic reflection data from the Red Sea, where evaporites deposited until the end of the Miocene (~5.3 Ma), are generally covered by only 200–300 m of low‐density sediments and where the presence of an axial spreading centre allows us to observe how they have responded to a varied configuration of underlying basement. The regional morphology of the S‐reflection, representing the evaporite surface, is mapped out from seismic data from 13 cruises. The S‐reflection is locally rugged and commonly angular. It is either underlain by layered reflectivity, suggestive of layered evaporite beds, or by more transparent seismic character, suggestive of massive halite. On average, the depth of the reflection on the flanks of the axial rift systematically declines from 700 to 1100 m below sea level (mbsl) going northwards from 16 to 23°N. In the central Red Sea, the S‐reflection has 100‐ to 200‐m‐deep depressions, extending towards the coasts in places. In the southern Red Sea, the S‐reflection forms a surface at 300–800 mbsl that appears less disrupted. We suggest that the evaporites originally had a flat, horizontal surface at the end of the Miocene and have subsequently been distorted by isostatic effects and axial rifting, which in turn promoted evaporite flowage. Off‐axis evaporite depressions correspond with flows identified with multibeam sonar. Furthermore, across‐rift lows in Bouguer gravity anomalies represent valleys in the underlying basement. The off‐axis evaporite depressions overlie those valleys, as would be expected if halokinetic movements were greatest where the evaporites are locally thick, leading to deflation of the evaporite surface. The thickness of post‐Miocene sediment, also mapped out as part of this procedure, confirms the generally pelagic nature of this interval and increases on average from ~250 to 300 m from the central to the southern Red Sea, mimicking the variation in pelagic productivity observed in the present water column.     

On empirical models of the upper atmosphere in the polar regions

The expression for the exospheric temperature in Jacchia's static diffusion models of the upper atmosphere has a discontinuous gradient at the poles. Therefore it cannot describe the true state of the upper atmosphere in the polar regions. Furthermore, it cannot be used to calculate quantities that depend on the derivative of the exospheric temperature, or the density, like pressure gradients, horizontal forces or horizontal heat fluxes. A modified expression for the exospheric temperature is suggested. This modification yields variables of state of the upper atmosphere that deviate little from Jacchia's values, but it has continuous gradient at the poles and is therefore more suitable for treating dynamical problems like the global wind pattern.     

Agents of landscape change in southern New Zealand, 1896–1920

The records of two large stock and station agents, Loan & Mercantile Agency in Dunedin and Wright Stephenson in Invercargill, allowed us to track the timing, nature, magnitude and rate of landscape change in southern New Zealand between 1896 and 1920. This period extends from the final years of subdivision of large estates, and includes closer settlement, the shift from pastoral farming to intensive agriculture, growth of dairying, and increasing mechanisation of agriculture. These changes are reflected in clients’ annual expenditures on capital items such as fencing and building materials, tools and implements, materials for drains.