Loss of habitat through inundation and the conservation status of two endemic Tasmanian Syncarid crustaceans: Allanaspides hickmani and A. helonomus

Extant representatives of the ancient crustacean family Anaspididae are restricted to the island State of Tasmania, Australia. Allanaspides hickmani and Allanaspides helonomus were first described in the early 1970s from surface pools in buttongrass moorland in two adjacent watersheds in south-west Tasmania. Both of these catchments have since been inundated for hydroelectric power generation (Lake Gordon and Serpentine Impoundments). Surveys indicate that both species persist in a small number of highly fragmented populations on the margins of the two impoundments. A. hickmani and A. helonomus have extant Areas of Occupancy of c. 21 and 54 km2, respectively. We estimate that inundation resulted in the loss of 85–94% of the original range of A. hickmani and c. 78% of the original range of A. helonomus. Under IUCN Red List guidelines and National threatened species legislation A. hickmani but not A. helonomus may qualify for listing as Vulnerable (Area of Occupancy <20 km2). At the present time only A. hickmani is listed as Rare under Tasmanian (State) threatened species legislation but A. helonomus merits the same listing under State legislation. Global warming appears to pose the most significant potential threat to Allanaspides species.

Anomalous stratification behaviour of Lake Gorden, headwater reservoir of the lower Gorden River, Tasmania

Lake Gordon, a large hydro-electric reservoir in south-west Tasmania, holds water of low pH, high colour and low dissolved solids content. It stratifies each year, with consequent anoxia below the thermocline. The nett effect of the inflow pattern, combined with the deep-V morphometry of the reservoir, is to prevent holomixis. For 6 months of the year, the cold inflow of the upper Gordon River follows its old course and rolls down to the dam, intruding first as an underflow, then rising slightly to become an interflow as it warms and finds its density level. This inflow displaces older water upwards, sandwiching the former hypolimnion between the inflow and the epilimnion. The anoxic, sulfuretted water of the sandwiched stratum gradually mixes with water above and below it, leading to its ventilation and dispersion. Meanwhile; the inflowing water stagnates and anoxia develops afresh in bottom waters. This occurs at a time when the upper strata are restratifying, leading to a multiple sandwich of several strata of discrete lineage. The early history of the reservoir indicates that it was predisposed for partial meromixis of the Lake Barrington type, preconditioned by its morphometry and by a mass of flooded vegetation. That a lasting monimolimnetic pool did not form, as expected, is attributable to the annual inflow of dense, oxygenated water. The hypolimnion of Lake Gordon is now the effective headwater of, and greatest contributor to, the lower Gordon River. Because of the stratification pattern, the discharge stratum may be oxygenated or anoxic and laden with hydrogen sulfide, iron and manganese. Any undesirable effects of the latter are rapidly dissipated in a short stretch below the dam, but the relatively invariable nature of the temperature and major ion chemistry of this stratum impose an unwonted uniformity on the river, to its mouth.

Fabrics and Deformation of Archean Metasedimentary Rocks, Ross Lake – Gordon Lake Area, Slave Province, Northwest Territories

Metagreywackes, which lie stratigraphically above metavolcanics fringing a granitic complex (part basement), exhibit late Archean multiphase fold structures. F1 folds are large linear depressions and anticlinal culminations trending partly concordant with margins of the granitic complex. Open to isoclinal F2 folds vary and curve in trend. Though usually near upright, some F2 folds are overturned away from the complex and others towards F1 depressions. F3 folds are small-scale structures not present in most outcrops, but throughout a large region they are accompanied by a steep S3 axial-plane schistosity striking NW to N.Original orientations of an S2 schistosity, axial planar to F2 folds, are preserved as inclusion trails in biotite porphyroblasts. Angular deflections from the trails show that regional horizontal flattening across the S3 schistosity formed the F3 folds and tightened curved trends of F2 folds. Estimates of strain from the fabrics indicate no increase near the complex.As for folds in other Archean terrains, F1 and F2 folds could have developed mainly as gravity structures during diapiric uprise of a granitic basement. In contrast, the F3 structures may reflect horizontal movements of early crustal plates.

A method for computing the deformation of the crust caused by the filling of large lakes

abstract The load placed on the Earth's surface by the filling of large lakes is sufficient to cause deformation of the Earth's crust. The extent of such deformation is investigated. The analysis of the model presented is extened to allow for changes in the elastic parameters with depth. For Lake Gordon, a large man-made lake to be constructed in the Southwest of Tasmania, the maximum displacement that will be caused in the Earth's surface by the filling of the lake (a load of 1.5 × 1010 tons) is calculated to be about 7 cm.