ABSTRACT1. Detailed research into the ecological impacts of inter-basin water transfers (IBTs) is virtually nonexistent on a global scale. However, a growing awareness of the serious nature of such impacts-for example, the loss of biogeographical integrity, the loss of endemic biotas, the frequent introduction of alien and often invasive aquatic and terrestrial plants and animals, the genetic intermixing of once separated populations, the implications for water quality, the frequently drastic alteration of hydrological regimes, the implications for marine and estuarine processes, climatic effects, and the spread of disease vectors, amongst many others-demands a most urgent and world-wide appraisal of all current planning and research strategies.2. This paper first defines the types of extant IBTs, and details some case studies for three widely separated regions of the world, namely: south-eastern Australia, southern Africa, and the central and south-western parts of the United States of America. In doing so, it highlights the chronic paucity of ecological data on their impacts, while simultaneously emphasising their extreme complexities.3. Finally, we call for an international meeting on such schemes, as a matter of priority and extreme urgency, in order to assess the extent of IBTs, their geographical distribution, and their ecological and sociological impacts and implications.

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The quality and quantity of allochthonous inputs and of benthic organic matter were investigated in a secondorder, perennial mountain stream in the south-west Cape, South Africa, between April 1983 and January 1986. Although the endemic, riparian vegetation is sclerophyllous, low and evergreen, inputs of allochthonous detritus to the stream (434 to 500 g m-2y-1) were similar to those recorded for riparian communities worldwide, as were calorific values of these inputs (9548 to 10 032 KJ mm2y-'). Leaf fall of the riparian vegetation is seasonal, occurring in spring (November) as discharge decreases, resulting in retention of benthic organic matter (BOM) on the stream bed during summer and early autumn (maximum 224 g me2). Early winter rains (May) scoured the stream almost clean of benthic detritus (winter minimum 8 g mm2). Therefore, BOM was predictably plentiful for about half of each year and predictably scarce for the other half. Coarse BOM (CBOM) and fine BOM (FBOM) constituted 46 -64% of BOM standing stock, ultra-fine BOM (UBOM) 16 -33 070 and leaf packs 13 -24%. The mean annual calorific value of total BOM standing stock was 1709 KJ me2. Both standing stocks and total calorific values of BOM were lower than those reported for streams in other biogeographical regions. Values of C:N ratios decreased with decrease in BOM particle size with no seasonal trends. The stream is erosive with a poor ability to retain organic detritus. Its character appears to be dictated by abiotic factors, the most important of which is winter spates.

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Allochthonousinput and benthic coarse particulate organic matter (CPOM) standing stocks were investigated in a first-order stream in South Africa between May 1984 and April 1985. Monthly falls into the stream of all litter types (total) ranged from 11 (September) to 79 g rnM2 (March). Total annual litter fall was 426 g dry weight, which corresponds to 1.2 g m -2 d -'. Flowers, fruits and seeds contributed 37 g me2, woody debris, 122 g rnp2, and leaves 267 g me2 to this total. Leaf fall from native trees, which accounted for approximately 57 y0 of total litter input (244 g m-2 a-' ), was significantly higher in summer than in winter. The summer peak in leaf fall recorded is far smaller and more protracted than the autumnal peak recorded for many Northern Hemisphere streams.Monthly total standing stocks of CPOM ranged from 14 g dry weight me2 in January to 69 g m-2 in August, and a mean total CPOM standing stock of 41 g rnp2 mth-' was estimated. This comprised 18 g m -2 mth -r soft litter, and 23 g m -2 mth -' hard litter. CPOM standing stocks showed no seasonal trends, and with the exception of two species, standing stocks of endemic leaf species reflected their contributions to the total litter fall. Contrary to earlier reports for streams in the Fynbos Biome, Window Stream has CPOM standing stocks well within the ranges reported for low-order streams worldwide.

Decomposition o^ Potamogeton pectinatus in Swartvlei, a southern African coastal lake, followed an exponential pattefn of decay. The rate constant was 0.0205 day'' and decay was virtually complete after 158 days. The original stock of ash, phosphorus and potassium was lost more rapidly than dry matter in the initial stages of decomposition due to leaching. Almost the entire stock of potassium and 6

1. The occurrence, composition and invertebrate fauna of naturaUy-occurring leaf packs were studied over 24 months in Langrivier, a second-order mountain stream in the south-western Cape, South Africa. Langrivier is shallow and fast-tlowing and stores very low levels of allochthonous detritus, although natural leaf packs form an obvious part of the energy base in the stream throughout the year.2. The occurrence and size of the packs were influenced mainly by stream discharge and by the timing and character of leaf fall froin riparian trees. Packs were smallest (minimum dry mass 17 g, minimum volume 1.7xU)-^ m-) in winter when discharge was high, and largest (maximum dry mass lyi g, maximum volume 4.2x 10"' m') in spring w^hen discharge decreased and leaf fall from the evergreen riparian trees began. Through the year the packs covered a mean 0.41 % ofthe stream bed and had a mean abundance of 0.46 packs m-of stream bed. They were ephemeral, lasting on average < 1.7 months and yet accounted for 29% of the stored detritus in the system. Wood was the dominant component of packs, and leaves at ali stages of decomposition were present throughout the year.3. The ratio of numbers of invertebrates in packs: numbers of individuals in the benthos was very low (0.002-0.030). presumably because of the rarity and small size of the packs. Nevertheless, the density of invertebrates per unit area covered by leaf packs was consistently much higher than the density in an equivalent area of the benthos, except during peak leaf fall (October to December).4. Experiments were undertaken with artificial leaf packs in order to determine the extent to which these simulated natural packs. Although both natural and artificial leaf packs contained a high proportion of Plecoptera (46% and 29% respectively), the natural packs contained high numbers of simuliid larvae (33% of total), whereas artificial packs had a high percentage of chironomid larvae (62%), Several other taxa regularly occurred in both types of pack but in very low numbers. In addition,