The dynamic aspect of coarse particulate organic matter (CPOM) on the sediment surface of a second order stream free of debris dams (RITRODAT-LUNZ study area)

The importance of allochthonous organic matter for low order streams is described. Oberer Seebach is a second order stream, draining an uninhabitated and densly forrested catchment. Because of flood control the channel is free of debris dams since more than a century. The study site is characterized. Main emphasis is laid on the riparian vegetation and the distribution of dry and overflown channel areas in space and time. Amounts of leaf material, deposited on the sediment surface of the channel are significantly larger during defoliation (20 days) and shortly afterwards (accumulation period, 6.64 (110 days) and 29.42 g m² DW (133 days, mean of five years) for wet and dry areas, respectively) than during the rest of the year (intermediate period, 0.98 and 3.94 g m² (mean of five years) for wet and dry areas, respectively). Woody debris is too scarce to increase the retention capacity. Deposition of leaf material depends on the interaction of input (wind-drift and bank run off, 124 and 85 g m² for the accumulation- and intermediate period, respectively), discharge regime and the relationship between dry and wet channel areas. Periodically inundated areas increase the retention capacity of the stream channel and are comparable with the interrelationship between stream and floodplain.     

Particulate organic matter inputs to a glacial stream ecosystem in the Swiss Alps

1. Traps for litterfall and for lateral transport of organic matter were sampled over a 1-year period along longitudinal and lateral transects in a glacial stream system (Val Roseg, Swiss Alps), which is characterized by single-thread reaches and a large subalpine floodplain.
2. Allochthonous inputs to the glacier stream were low close to the glacier terminus but increased as woody riparian vegetation and forests develop. Annual inputs varied from 0.4 g ash free dry matter (AFDM) m^–2 year^–1 (direct input) and 0.7 g AFDM m^–2 year^–1 (lateral input) in the proglacial area to 23.0 g AFDM m^–2 year^–1 (direct input) and 10.7 g AFDM m^–2 year^–1 (lateral input) in the lowest reach with adjacent subalpine forests.
3. Direct inputs of organic matter decreased exponentially from forests at the floodplain edge to the floodplain centre, while lateral inputs of organic matter correlated linearly with distance to trees. Direct litterfall dominated litter input close to the forest, while lateral transport was the major pathway for channels more than 20 m away from the forest.
4. A conceptual framework is developed illustrating the influence of terrestrial vegetation and fluvial morphology on organic matter input along the continuum of glacial streams.     

The metabolism of organic matter in the hyporheic zone of a mountain stream, and its spatial distribution

Community respiration in hyporheic sediments (HCR) was studied in a characteristic riffle-pool-sequence of a mountain stream. HCR activity at the riffle site strongly exceeded that at the corresponding pool site with a mean ratio of 5.3. The vertical distribution of HCR activity was homogeneous in the pool, while there was a distinct maximum in the uppermost layer in the riffle. Similarly, the spatial distribution of certain fractions of particulate organic matter (POM), and their turnover, was largely determined by stream morphology. Mean annual HCR per unit area of stream bed was estimated as 1.71 g O₂ m⁻² d⁻¹. Hence, HCR contributes significantly to total heterotrophic activity in streams, thus enhancing the relative importance of heterotrophic processes in running waters containing hyporheic zones.     

Seed storage and germination in Kumara plicatilis,a tree aloe endemic to mountain fynbos in the Boland,south-western Cape,South Africa

Seed storage under appropriate conditions is a relatively inexpensive means of safeguarding plant genetic material for ex situ conservation. Post-storage germination trials are used to determine the viability of stored seeds, and hence the efficacy of the particular storage treatment. Kumara plicatilis (= Aloe plicatilis) is a tree aloe endemic to mountain fynbos in the Boland, south-western Cape. The viability and germination behaviour of K. plicatilis seeds were assessed for seeds stored for four and nine months at − 80 °C, 4 °C, 25 °C and under ambient conditions in a laboratory. Seeds were germinated under controlled conditions and germination rates and percentages determined. Ungerminated seeds were tested for viability using tetrazolium salt. Seed viability was not significantly reduced during storage. Seeds stored at − 80 °C for four and nine months exhibited the fastest germination rate overall (both 5.9 ± 0.3 weeks, mean ± S.E.), and slowest was for seeds stored under ambient conditions for four and nine months (both 7.8 ± 0.4 weeks). All seed lots showed similar percentage germination after four months of storage (78.0–90.4%). The highest percentage germination overall was for seeds stored at − 80 °C for four months (90.4%) and the lowest was for seeds kept at 4 °C and − 80 °C for nine months (39.2 and 39.6%, respectively). Respective percentage viability for ungerminated seeds in these two treatments was 82% and 87%, respectively, indicating the induction of secondary dormancy. Induced dormancy triggered by protracted cold temperatures may be an adaptation that enables seeds to survive prolonged extreme conditions that are unfavourable for germination. Further research on the long-term storage of aloe seeds would be beneficial for developing long-term seed storage and germination testing protocols for ex situ conservation.     

Effects of nutrient enrichment and leaf quality on the breakdown of leaves in a hardwater stream

1. The breakdown of leaf litter in streams is influenced strongly by leaf quality and the concentration of dissolved nutrients, primarily inorganic nitrogen (N) and phosphorus (P) in the water. We examined the effect of nutrient enrichment on the breakdown of three species of leaves in a hardwater, nutrient‐rich stream. The rate of microbial respiration was also measured on the decomposing leaves. 2. The breakdown rates of dogwood (Cornus stolonifera), aspen (Populus tremuloides) and birch (Betula occidentalis), k‐values of 0.0461, 0.0307 and 0.0186 day^–1, respectively, were unaffected by nutrient enrichment and generally faster than reported previously. Microbial respiration on the leaves was greater than reported previously for leaves of congeneric species. It appears that leaf breakdown in the study stream was not nutrient limited. 3. Nitrogen‐based measures of leaf quality, such as percentage N and carbon (C)/nitrogen ratio, did not correspond to measured breakdown rates among the three leaf types. The best predictors of relative breakdown rates were percentage lignin and the percentage of the total carbon that occurred as lignin. We suggest that, when leaf breakdown is not nutrient limited, measures of carbon quality (i.e. lignin‐based measures) are a better assessment of overall leaf quality than are N‐based measures. 4. Previous studies have indicated that the enzymes produced by aquatic hyphomycetes (microfungi) operate most efficiently at a basic pH and in the presence of calcium ions. The hardwater conditions (pH=8.6, total hardness > 300 mg CaCO₃ L^–1) and abundance of dissolved NO₃ and soluble reactive phosphorous (SRP) (approximately 50 μg L^–1, each) in the study stream appear to have provided conditions that resulted in a high respiration rate and rapid breakdown of leaf litter.     

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.     

Exploring patterns of population subdivision in the net-winged midge, Elporia barnardi (Diptera: Blephariceridae), in mountain streams of the south-western Cape, South Africa

1. The net-winged midges (Diptera: Blephariceridae) are a highly specialized group whose morphological characteristics and specific habitat requirements suggest a limited potential for dispersal. Levels of genetic variation were examined within streams, between streams in the same range and between mountain ranges in larval populations of Elporia barnardi in the south-western Cape of South Africa. The aim was to examine the hypothesis that population structure would reflect the poor potential for dispersal.
2. Significant deviations from Hardy–Weinberg equilibrium in 17 of the 57 individual comparisons indicate a non-random mating population. Given the swarming behaviour and life history traits, larvae sampled may reflect the product of limited matings.
3. Analysis of population substructuring revealed significant levels of differentiation among geographically proximate populations. Large differences between streams within Table Mountain, similar in magnitude to those between mountain ranges, suggest that movement of individuals out of the stream catchment is rare. Observed F _ST values are more similar to those of fully aquatic species than other lotic insects with winged adult stages.
4. Results suggest that mountain ridges provided effective physical barriers to the dispersal of E. barnardi , with the catchment representing the effective population unit.     

Cape mountain zebra in the Baviaanskloof Nature Reserve,South Africa: resource use reveals limitations to zebra performance in a dystrophic mountainous ecosystem

Resource use of Cape mountain zebra was studied in the Baviaanskloof Nature Reserve (BNR) over concerns of the poor performance in population growth. We assessed the seasonal diet, habitat suitability and forage quality of the Bergplaas area in BNR for mountain zebra. Grasses contributed 95.2% to the annual diet of mountain zebra, Tristachya leucothrix contributing the most (39.4%), followed by Themeda triandra (27.6%). Seasonally, T. triandra contributed most to the diet in winter, while T. leucothrix became more important in the summer and also was the only species preferred in all seasons. Mountain zebra concentrated their feeding in Kouga Grassy Fynbos and from our assessment this was the only habitat suitable for mountain zebra. Our analysis of mountain zebra dung indicated that the seasonal nitrogen and phosphorus content was below the threshold values prescribed for grazers, and our study suggests that mountain zebra at Bergplaas are severely resource limited. We emphasize the importance of fire and access to nutrient‐rich lowlands in influencing the nutritional ecology of mountain zebra and provide conservation management recommendations.     

Natural variation in macroinvertebrate assemblages and the development of a biological banding system for interpreting bioassessment data—a preliminary evaluation using data from upland sites in the south-western Cape,South Africa

The variability of macroinvertebrate assemblages was investigated at 27 upland reference sites in the south-western Cape, South Africa. Multivariate analyses showed that sites did not group on the basis of geomorphological zonation, i.e. mountain stream and foothill-cobble bed. When separate analyses were undertaken for mountain stream (n = 21) and foothill-cobble bed sites (n = 6), assemblages formed three and two groups, respectively. Similarity amongst groups ranged from 47% to 52%, while within-group similarity was between 54% and 67%. Environmental variables shown to contribute to this variability included distance from source, cation ratio ([Na⁺]+[K⁺]/([Na⁺]+[K⁺]+[Ca²⁺]+[Mg²⁺]), pH, longitude and stream width. Whilst overall variability in the metrics of the biotic index, SASS (South African Scoring System), is high at reference sites, the interpretation of monitoring-site data using biological bands derived from a range of reference sites, ensured that variability was taken into account and that detection of disturbance at a monitoring site was not impeded. A biological banding system has been developed for upland sites in the south-western Cape, together with a list of reference or expected SASS-taxa. This list includes details pertaining to seasonality and biotope preferences. The ability to define reference conditions that take intrinsic variability amongst reference sites into account is important for the accurate interpretation of bioassessment data. Handling editor: D. Dudgeon