Bryan R. Davies

Cahora Bassa retrospective, 1974-1997: effects of flow regulation on the Lower Zambezi River

it has a catchment area of 1,570,000 km 2 , drains the southern borders of the Democratic Republic of Congo (DRC) and traverses Botswana, Zambia, Zimbabwe, Tanzania, Malawi and Mocambique (WELCOMME 1972). The lower river enters the sea through a mosaic of alluvial grassland and swamp forest (the Marromeu Complex) some 100 km inland from the coast, and a mangrove‐deltaic system with a sea frontage of about 290 km (e.g. TINLEY & SOUSA D IAS 1973). An extensive review of the basin can be found in DAVIES (1986). The river comprises three segments: Upper (1,078 km), from

A preliminary assessment of the effects of a small south african inter-basin water transfer on discharge and invertebrate community structure

This preliminary study (March–October, 1994) describes the effects of an inter-basin water transfer (IBT) on discharge and benthic macro-invertebrate community structure. The IBT from Theewaterskloof, an impoundment on the Riviersonderend system, to the Berg River in the Western Cape, South Africa is part of the water supply system for Greater Cape Town. Transfers occur during summer for irrigation and rainbow trout (Oncorhyncus mykiss) farming in the Berg catchment and lead to greatly elevated summer discharges in the recipient river: 4500% in late summer (March) and 830% in autumn (May). During winter and spring, when the transfer ceases, discharges revert to normal winter volumes below the outlet. A decrease in taxon richness of the invertebrate communities was observed below the transfer outlet, compared to the river above the transfer. Sensitive families such as the heptageniid Ephemeroptera and leptocerid Trichoptera were not recorded below the outlet during transfer months (March and May). On the other hand, collector-predators such as the hydropsychid trichopterans showed large increases in numbers during the same transfer months, when compared against above-outlet samples: 240 and 80 individuals m−2, in March and May, from above the IBT, versus 46 994 and 5600 individuals m−2 below the IBT. This change was probably due to the introduction of live zooplankton to the receiving river from the source reservoir. Dendrograms and MDS-ordination diagrams showed that, in summer, invertebrate communities sampled at the two sites above and below the IBT were between 52 and 56% similar, while in winter and spring, in the absence of water releases similarities were higher (>70%) in July and October. There were also seasonal differences between invertebrate communities sampled in different months, but, during water release months, MDS-ordination diagrams showed clear grouping of communities according to position above or below the IBT, rather than month. Results to hand indicate a ‘reset’ of the entire benthic invertebrate community during winter and spring when no transfers occur. Of concern is the potential for the transfer of cyanophyte blooms (commonly of the genus Anabaena) from the source reservoir to the Berg River: transfers of non-toxic, malodorous geosmin, a cyanophyte exudate which has affected the flesh of rainbow trout farmed in the Berg catchment, have already been reported.

Thermal acclimation and tolerance to lethal high temperature in the mountain stream amphipod Paramelita nigroculus (Barnard)

1. 1. Rates of upward and reverse acclimation were studied in Paramelita nigroculus (Barnard) from a mountain stream using a modification of the Critical Thermal Maximum (CTM) method. The upper lethal temperatures were measured using the LT50 method. 2. 2. Acclimation rates were found to be typical of most crustaceans, with a gain of resistance to high temperature, following transfer from 8.5 to 20°C, being completed in 1–2 days. Loss of heat resistance took slightly longer (3 days). 3. 3. The species is strongly sexually dimorphic, males being significantly smaller than females. Neither sex, body length nor feeding status was found to affect tolerance levels. 4. 4. The LT50 (min) for animals acclimated to 13.5°C ranged from approximately 300 min at 27°C to 4 min at 31°C. 5. 5. LT50 values for 20°C-acclimated individuals were significantly higher than those acclimated at 13.5°C at corresponding test temperatures.

Evaluating Existing Strategies to Limit Video Game Playing Time

Public concern surrounding the effects video games have on players has inspired a large body of research, and policy makers in China and South Korea have even mandated systems that limit the amount of time players spend in game. The authors present an experiment that evaluates the effectiveness of such policies. They show that forcibly removing players from the game environment causes distress, potentially removing some of the benefits that games provide and producing a desire for more game time. They also show that, with an understanding of player psychology, playtime can be manipulated without significantly changing the user experience or negating the positive effects of video games.