Jenny A. Day

Predicting runoff-induced pesticide input in agricultural sub-catchment surface waters: linking catchment variables and contamination

An urgent need exists for applicable methods to predict areas at risk of pesticide contamination within agricultural catchments. As such, an attempt was made to predict and validate contamination in nine separate sub-catchments of the Lourens River, South Africa, through use of a geographic information system (GIS)-based runoff model, which incorporates geographical catchment variables and physicochemical characteristics of applied pesticides. We compared the results of the prediction with measured contamination in water and suspended sediment samples collected during runoff conditions in tributaries discharging these sub-catchments. The most common insecticides applied and detected in the catchment over a 3-year sampling period were azinphos-methyl (AZP), chlorpyrifos (CPF) and endosulfan (END). AZP was predominantly found in water samples, while CPF and END were detected at higher levels in the suspended particle samples. We found positive (p < 0.002) correlations between the predicted average loss and the concentrations of the three insecticides both in water and suspended sediments (r between 0.87 and 0.94). Two sites in the sub-catchment were identified as posing the greatest risk to the Lourens River mainstream. It is assumed that lack of buffer strips, presence of erosion rills and high slopes are the main variables responsible for the high contamination at these sites. We conclude that this approach to predict runoff-related surface water contamination may serve as a powerful tool for risk assessment and management in South African orchard areas.

Particulate organic matter in a mountain stream in the south-western Cape, South Africa

The quality and quantity of allochthonous inputs and of benthic organic matter were investigated in a second-order, 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 m−2y−1). 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 m−2). Early winter rains (May) scoured the stream almost clean of benthic detritus (winter minimum 8 g m−2). 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% and leaf packs 13–24%. The mean annual calorific value of total BOM standing stock was 1709 KJ m−2. 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 (CBOM 27–100; FBOM 25–27; UBOM 13–19) 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.

The predatory impact of invasive alien smallmouth bass, Micropterus dolomieu (Teleostei: Centrarchidae), on indigenous fishes in a Cape Floristic Region mountain stream

Fish populations in the Rondegat River, a mountain stream in the Olifants-Doring system in the Cape Floristic Region, South Africa were surveyed to assess the impact of predatory alien invasive smallmouth bass Micropterus dolomieu (Lacepède) on the indigenous fishes. This was the first such attempt to quantify the predatory impacts of M. dolomieu within this region. The Rondegat River is home to five species of indigenous fish and is partially invaded by M. dolomieu, which has penetrated the lower river up to a waterfall barrier. Seasonal surveys were conducted at five sites above, and five below, the waterfall. Physical habitat was measured at each site. Four of the five indigenous fish species were absent at bass-invaded sites. Labeobarbus capensis (Smith), while still present below the waterfall, appeared to have suffered a near-total loss of post-spawning recruits. Analyses of physical habitat quality failed to explain the loss of indigenous fish below the waterfall, although sedimentation may have increased the vulnerability of the catfish Austroglanis gilli (Barnard) to M. dolomieu predation by obliterating benthic cover. Consequently, predation by M. dolomieu was presumed to be the critical mechanism explaining the loss of indigenous fishes in the lower Rondegat River.

The impact of invasive fish and invasive riparian plants on the invertebrate fauna of the Rondegat River, Cape Floristic Region, South Africa.

Invasive fish and plants are widespread in the rivers and riparian zones of the Cape Floristic Region of South Africa and represent potential threats to the highly endemic freshwater fauna. We investigated the impact of invasive smallmouth bass (Micropterus dolomieu) and black wattle (Acacia mearnsii) on assemblages of macroinvertebrates and fish in a cobble-bed foothill river, the Rondegat River, in the Cederberg mountains, by sampling from sites representing four invasion conditions: no invasion; invasive trees; invasive fish; invasive trees and fish. Invertebrate assemblages were sensitive to invasion from bass and/or wattle: in the presence of A. mearnsii the abundance of some cobble-dwelling taxa were reduced, while those of particle-feeding mayflies and chironomids increased, reflecting increased leaf litter and sediment produced by acacias. In the presence of bass the abundance of most invertebrate taxa, particularly Chironomidae and Baetidae, increased, whereas the algal-grazing Heptageniidae and Elmidae were moderately reduced. These changes in invertebrate assemblages, coupled with data on the biomass and diet of fishes, indicate that smallmouth bass, in contrast to indigenous fish, do not exert a strong influence on the abundance of their invertebrate prey. Bass remove indigenous insectivorous fish predators, thereby reducing predation on invertebrate prey, with consequent food-web effects that influence the invertebrate community assemblage.

A comparison of rapid bioassessment protocols used in 2 regions with Mediterranean climates, the Iberian Peninsula and South Africa

Abstract The ability of 2 Rapid Bioassessment Protocols (RBPs) to assess stream water quality was compared in 2 Mediterranean-climate regions. The most commonly used RBPs in South Africa (SA-protocol) and the Iberian Peninsula (IB-protocol) are both multihabitat, field-based methods that use macroinvertebrates. Both methods use preassigned sensitivity weightings to calculate metrics and biotic indices. The SA- and IB-protocols differ with respect to sampling equipment (mesh size: 1000 μm vs 250–300 μm, respectively), segregation of habitats (substrate vs flow-type), and sampling and sorting procedures (variable time and intensity). Sampling was undertaken at 6 sites in South Africa and 5 sites in the Iberian Peninsula. Forty-four and 51 macroinvertebrate families were recorded in South Africa and the Iberian Peninsula, respectively; 77.3% of South African families and 74.5% of Iberian Peninsula families were found using both protocols. Estimates of community similarity compared between the 2 protocols were >60% similar among sites in South Africa and >54% similar among sites in the Iberian Peninsula (Bray–Curtis similarity), and no significant differences were found between protocols (Multiresponse Permutation Procedure). Ordination based on Non-metric Multidimensional Scaling grouped macroinvertebrate samples on the basis of site rather than protocol. Biotic indices generated with the 2 protocols at each site did not differ. Thus, both RBPs produced equivalent results, and both were able to distinguish between biotic communities (mountain streams vs foothills) and detect water-quality impairment, regardless of differences in sampling equipment, segregation of habitats, and sampling and sorting procedures. Our results indicate that sampling a single habitat may be sufficient for assessing water quality, but a multihabitat approach to sampling is recommended where intrinsic variability of macroinvertebrate assemblages is high (e.g., in undisturbed sites in regions with Mediterranean climates). The RBP of choice should depend on whether the objective is routine biomonitoring of water quality or autecological or faunistic studies.

Conservation status of large branchiopods in the western Cape, South Africa

Temporary wetlands are an ecologically and economically important habitat in South Africa. They harbor large branchiopods, known to be flagship species of nonpermanent aquatic habitats, and sensitive to land use changes. In this study we review the current status of large branchiopods in the Western Cape, a South African province subject to increasing agriculture and urbanization. We studied the species diversity and distribution of large branchiopods by sampling 58 temporary wetlands in an area covering about 30% of the Western Cape. Information obtained from field samples was supplemented by incubating resting egg banks from the sampled wetlands. Our data were compared with all known distribution records for large branchiopods in the target region. Based on this combined information, the International Union for the Conservation of Nature and Natural Resources (IUCN) Red List category was assessed for each species. Four of the eight large branchiopod species known to occur in the sampling area were collected. Of all wetlands sampled, 40% harbored large branchiopods. Most anostracan populations were small, and species co-occurred in only one wetland. From the entire Western Cape, 14 species have been recorded in the past. Two of these are already included in the IUCN Red List. Insufficient data are available to determine the IUCN Red Data Category of six other species. A large variation in the telsonic appendages of S. dendyi was found across the studied area. In view of possible ongoing speciation and subsequent radiation, individual populations need protection. Since little information is available, it is difficult to evaluate recent changes in the conservation status of large branchiopods. Their populations are currently very low and have probably diminished in the last few decades. More knowledge about the functioning of temporary systems is needed to manage these vulnerable habitats and conserve their threatened species.

The major ion chemistry of some southern African saline systems

Africa south of about 23° S has few natural athalassic lakes, saline or freshwater. South Africa, however, is rich in temporary pans, many of which are saline, while permanent saline springs occur along the coastal strip of the Namib Desert in Namibia. This paper examines the chemistry of the major ions in 67 Namibian waters, 47 of which have not previously been reported in the literature, and compares them with 66 South African waters, five of which have not previously been reported, and with saline lakes in East Africa.The highest value for total dissolved solids in South African waters was 276 g l−1 (Koekiespan, south-western Cape) and the highest for Namibian waters were 160 g l−1 (Hosabes, a small spring on a gypsous crust) and 302 g l−1 (a salt pan at Oranjemund at the mouth of the Orange River). The dominant ions in fresh waters in the region are Ca2+ and HCOinf3−/COinf32−in the interior and in Namibia, and Na2+ and Cl+ on the south and east coasts. Regardless of the geochemistry of their substrata, the dominant ions in the saline waters throughout the region are Na+ and Cl−. Thus differential precipitation of CaCO3 and CaSO4, as a result of evaporative concentration at high salinities, appears to be the determinant of the proportions of the major ions in these systems.The permanent springs on gypsous crusts along the coast of Namibia, although dominated by Na+ and Cl− ions, contain considerable quantities of both Ca2+ and SO42−ions.

Aquatic biodiversity in the mediterranean region of South Africa

The Cape mediterranean region, part of South Africa’s Cape Floristic Realm (CFR), is recognised for its rich diversity and high degree of endemism of terrestrial vegetation. We review the biodiversity of the aquatic flora and fauna using literature sources and museum data. Geological, palaeohistorical and climate data are examined in relation to the formation of the winter-rainfall regime. Prehistoric humans had minimal impact on the aquatic biotas. Patterns and processes relating to the present-day climate, ecosystem status, distribution and diversity of plants, invertebrates and vertebrates in the CFR are reviewed. The proportion of endemic CFR species relative to the total number of species known from southern Africa is estimated. Observed distribution patterns are evaluated against temperate Gondwana vicariance, old African migrations, the role of the ancient Cape fold mountains and Pangaea. The lack of Pleistocene glaciations in Africa, the oligotrophic nature of the river systems and the palaeohistorical origin and distribution of taxa are considered when assessing reasons for disjunct distribution patterns. Impacts of anthropogenic interference with aquatic ecosystems are evaluated. Fragmented jurisdiction of nature conservation authorities is seen as a problem for attaining adequate conservation of CFR aquatic ecosystems. Systematic conservation planning is under way for the region.

Potential for Trichoptera communities as biological indicators of morphological degradation in riverine systems

Many rivers in southern Africa are increasingly threatened by accelerating geomorphological degradation due to unsustainable agricultural practices and deforestation. Thus, there is a critical need for biological indicators of morphological degradation in running waters. This study analysed the composition and abundance of Trichoptera taxa from 32 sites from rivers in eastern and northwestern Zimbabwe in relation to geomorphological and land use parameters. Redundancy analysis (RDA) and Spearman’s rank correlation analysis revealed that species in the genera Anisocentropus, Dyschimus, Lepidostoma, Leptocerina, Athripsodes, Parasetodes, Aethaloptera, Hydropsyche and Polymorphanisus were restricted to undisturbed forested sites, suggesting that these Trichoptera taxa may be used as indicators of structural degradation in watercourses. A species in the genus Hydroptila was the only Trichoptera taxon that showed a statistically significant numerical abundance at disturbed agricultural sites.

Influence of largemouth bass, Micropterus salmoides, on abundance and habitat selection of Cape galaxias, Galaxias zebratus, in a mountain stream in the Cape Floristic Region, South Africa

Predatory alien fishes have been widely introduced into streams in the Cape Floristic Region (CFR), South Africa, but little is known about their effect on native fishes. Results from this 2006 study suggest that the presence of alien predatory largemouth bass, Micropterus salmoides, may have influenced abundance and habitat selection of the native Galaxias zebratus at one location in a small CFR mountain stream. Numbers of adults, but not of juveniles, were significantly lower where M. salmoides was present, suggesting a size-specific influence on G. zebratus abundance. Because other studies have found the influence of a predator to be affected by prey size and the diel activity of predator and prey, we measured microhabitat use by adult and juvenile G. zebratus by day and by night. Galaxias zebratus selected deeper, faster-flowing microhabitats more strongly where M. salmoides was present than where it was absent. This suggests that G. zebratus adjusts its habitat use in the presence of M. salmoides, although differences in available habitat, or in interactions with other indigenous species, could be partly responsible for the observed differences. In-stream vegetation presence was strongly positively related to depth and strongly negatively related to velocity at positions where G. zebratus was observed, suggesting that the deeper, slower-flowing microhabitats occupied by G. zebratus were structurally more complex than the shallower, faster-flowing ones.