No abstract

Understanding temporal trophic interactions in riverine food webs is essential for predicting river ecosystem function and improving management of these ecosystems. Temporal changes in energy flows through riverine food webs are readily assumed but are rarely tested. Temporal variability in food webs from two reaches of a lowland river (Ovens River, south‐eastern Australia) with differing levels of floodplain connectivity were examined over 12 months. We investigated how seasonal changes, flow variability and floodplain connectivity influence (i) stable isotope signatures of basal organic carbon sources (terrestrial sources: trees and grasses; aquatic sources: seston, biofilm and filamentous algae) and consumers (macroinvertebrates and fish) and (ii) the relative proportions of organic carbon sources contributing to consumer biomass using mixing models. We hypothesized (i) that during high flows, increased floodplain connectivity would increase the lateral exchange of terrestrial carbon subsidies to main channel consumers and (ii) that during low flow periods, main channel consumers would derive the majority of their carbon from aquatic benthic sources. Results indicated that isotope signatures for basal sources and for most of the consumers varied temporally and spatially. Mixing models indicated that increased floodplain connectivity did not increase terrestrial subsidies to consumers during high flows. Seston was the primary source during high flows whilst terrestrial vegetation increased in importance during low flows. Filamentous algae was also important during low flows for some consumers. These findings indicate that it is essential to include temporal variability in order to understand energy flows in lowland rivers, thus allowing for the dynamic nature of these ecosystems. Copyright © 2010 John Wiley & Sons, Ltd.

1. Seventeen sites were each sampled six times over 2 years for macroinvertebrates. A range of physicochemical variables was also measured to determine which factors were related to the distribution of species.2. Numerical classification of the faunal data indicated that four groups of sites or communities were distinguishable: lowland sites; sandy upland sites; cobble upland sites from the northern catchment; cobble upland sites from the southern catchment.3. Multiple discriminant analysis and multiple regression analysis demonstrated that particle size of the sediment, concentration of dissolved ions and altitude were the physicochemical features that were most strongly associated with changes in the faunal distribution.4. Abundances of shredders and predators did not vary between the site groups while those of scrapers, gatherers and filterers did: scrapers were most abundant at cobble sites while gatherers and filterers were least abundant on sand and increased in abundance downstream. The distribution of the feeding groups showed some similarity with that predicted by the River Continuum Concept, but the fact that the shredders did not decrease in abundance downstream was a notable difference.5. Abundance of the total fauna at a site was inversely related to the amount of benthic organic matter. This feature is contrary to the pattern usually reported from rivers in the northern hemisphere.

Chironomid larvae ( Chironomus spp., Oicrotendipes conjunctus and Procladius paludicola) collected from Cox Creek and Aldgate Creek, South Australia, showed morphological abnormalities similar to those reported in other studies elsewhere in the world. The sediment of Cox Creek contained high concentrations of pesticides and there was a significant correlation between the occurrence of mouthpart and antennal deformities in larvae and the concentration of DDT and the herbicide, Dacthal| Laboratory experiments were conducted using a culture of Chironomus sp. to determine whether or not a causal relationship existed between exposure to pesticides and the occurrence of deformities in larvae. Results showed a positive relationship between the concentration of DDT and the percentage of deformed mouthparts (menta). The results for the effect of DDT on antennae and those for the effect of Dacthal| were less clear, but generally showed a higher incidence of deformity for treatments compared with controls.

The life histories of the following species were studied over 2 years at various sites throughout the catchment of the La Trobe River: Tasmanocoenis tonnoiri and Tasmanocoenis sp. (Ephemeroptera : Caenidae), Atalophlebioides sp. and two Atalonella spp. (Ephemeroptera : Leptophlebiidae), two Baetis spp. (Ephemeroptera : Baetidae), Leptoperla primitiva and L. neboissi (Plecoptera : Gripopterygidae), Cyphon sp. (Coleoptera : Helodidae), Ecnomus sp. (Trichoptera : Ecnomidae). The life cycles of these species varied from univoltine (four taxa) to bivoltine (Leptophlebiidae, Baetidae, Ecnomus sp.) or trivoltine (T. tonnoiri). Although the species displayed various degrees of synchrony of growth, distinct changes in the size distribution of the larvae or nymphs occurred with time and thus cohorts were evident.

The current taxonomic understanding of the genus Riekoperla McLellan, 1971 (Gripopterygidae) is poor, with 15 of the 28 species and subspecies having unknown or uncertain larval associations. Sequences of a 657 bp fragment from the mitochondrial gene cytochrome c oxidase subunit 1 (CO1) were obtained from 122 specimens of 13 species collected throughout the alpine areas of New South Wales and Victoria, Australia. Of these, sequence data associated adults and larvae for the following 10 species: R. alpina McLellan, 1971, R. cf. intermedia, R. compressa Theischinger, 1985, R. hynesorum Theischinger, 1985, R. karki McLellan, 1971, R. montana Theischinger, 1985, R. reticulata (Kimmins, 1951), R. rugosa (Kimmins, 1951), R. trapeza Theischinger, 1985, and R. tuberculata McLellan, 1971. Adults of R. intermedia Theischinger, 1985, R. triloba triloba McLellan, 1971 and R. williamsi McLellan, 1971 were sequenced but no larvae were associated with them. The 13 species were reciprocally monophyletic and had minimum interspecific sequence divergences ranging from 7.2–19.5%, higher than the maximum intraspecific sequence divergences (0.6–5.8%). The combination of morphology and molecular data enabled rapid life stage association for alpine Riekoperla species and this method should be used more frequently for other environmentally significant aquatic insects.

Anthropogenic pressures such as river infrastructure, agriculture and power generation are rapidly increasing in Southeast Asia, aimed at providing food security within the region. However, this will lead to unintended river health consequences, and, currently, most Southeast Asian countries have no country-specific tools for monitoring river health. In Myanmar, one of Southeast Asia’s poorest and most rapidly developing countries, no country-specific tools exist, and there is an urgent need to provide tools that can inform better management and trade-off decision making. This research evaluated three rapid macroinvertebrate bioassessment methods under Myanmar conditions. The objective of the research was to assess the applicability of existing internationally accepted indexing methods for use in Myanmar. Through taxa identification in the laboratory and statistical analysis, it was concluded that the method with the best fit for Myanmar taxa is The Asia Foundation index method, although differences were small. This Asia Foundation method is comparable to the Australian Waterwatch method but includes a family present in our samples that is not included in the Waterwatch method. We then modified this method to include Myanmar taxa not recorded in The Asia Foundation method. The modified index method could be further developed into a Myanmar specific tool for widespread use potentially in combination with the also tested miniSASS, a much easier order-based method better suitable for non-professionals. We recommend additional testing using sites on other rivers across the country to establish a professional indexing method for Myanmar.

Microinvertebrates play a critical role in riverine food webs, and recent studies have hypothesized that slackwaters, non-flowing regions associated with the main channel, are important for their reproduction and recruitment. However, little is known regarding the population and community dynamics of microinvertebrate communities in slackwater regions, or how they compare with those in mid-channel regions. This study examined microinvertebrate communities in the epibenthic and pelagic zones of slackwater and mid-channel regions (i.e. four habitats) of an Australian floodplain river in relation to physico-chemical parameters and food availability (as estimated by chlorophyll-a concentration) between September 2005 and November 2006. Results from this study indicate that microinvertebrate abundance and diversity were greater in slackwater habitats than midchannel habitats overall, corresponding with the slower current velocities associated with the former. Nevertheless, communities in all four habitats were most abundant and diverse in late spring (coinciding with an increase in water temperature), and followed similar seasonal trajectories in terms of density, taxon richness and community structure. These findings support the view that slackwaters are important for in-channel microinvertebrate production, and suggest that animals frequently disperse (either actively or passively) among slackwater and other main channel regions year round. Given the critical importance of microinvertebrates in riverine food webs, rivers should be managed with a view to maintaining a natural variety of accessible slackwater regions in order to support the production and survival of microinvertebrate communities.