Pathways for algal recolonisation in ephemeral streams

Our prior research showed that stream algae regrow rapidly from dry biofilm and suggested that ephemeral streams that lacked any permanent surface water showed much lower algal regrowth once streams recommenced flow. To determine whether the latter was true in a broader range of streams, we: sampled and cultured algae from a range of drought refuges in 9 streams, sampled algae from 18 streams in the week after flow recommenced and conducted a transplant experiment to identify the source of algal colonists. We found little specificity amongst algal taxa for different drought refuges and that the dry biofilm and leaf litter combined accounted for all taxa that regrew after flows recommenced. Regulation of streams with some permanent surface water is associated with increased algal regrowth from dry biofilm, not the presence of permanent surface water alone. Sources of algal recolonization may be dependent on the dominant algal composition within the stream, at a coarse taxonomic level.

Comparison of permanent and temporary streams of calcareous Provence [Translation from: Annales de Limnologie 9(3) 273-292, 1973]

The rainfall regime and the karstic nature of the subsoil determines the alternation of a period of flow and a period of drought for a large number of Mediterranean streams. Amongst this type of stream it is possible to distinguish temporary streams, characterised by a period of flow for several months permitting the establishment of the principal groups of aquatic insects; and ephemeral streams whose very brief period of flow permits the establishment of a community reduced to a few species of Diptera. This paper aims to study the structure of the communities which colonise this particular type of stream and the ecology of the principal species which constitute these communities. Four French temporary streams were examined and temperature regimes, dissolved oxygen, calcium and magnesium measured. Samples of fauna were taken regularly and the biotic composition established. The analysis of similarities between the three permanent streams are discussed and compared with permanent streams.

Is water extraction a threat to insect populations in intermittently-flowing streams?

Stream insects use a variety of refuges to survive drought that vary in their vulnerability to water extraction. We surveyed drought refuges in 16 ephemeral streams with different flow regimes. Perennial sections were the most important drought refuge, but are the most likely to disappear when water is extracted.

Investigations of six intermittent streams : (Solomon Creek, Otter Creek, Blue Creek, Kaskaskia Ditch, Steward Creek, and Brushy Creek) : April-September 1980.

"February, 1981."

Impacts of atrazine in aquatic ecosystems

A portion of all herbicides applied to forests, croplands, road sides, and gardens are inevitably lost to water bodies either directly through runoff or indirectly by leaching through groundwater into ephemeral streams and lakes. Once in the aquatic environment, herbicides may cause stress within aquatic communities and radically alter community structure. Atrazine is one of the most effective and inexpensive herbicides in the world and is consequently used more frequently than any other herbicide. Atrazine is frequently detected in aquatic waters, and has been known to affect reproduction of aquatic flora and fauna, which in turn impacts on the community structure as a whole. This paper presents a summary of the reported direct and indirect impacts of atrazine on aquatic organisms and community structure. The information can be used for developing improved management guidelines and legislation. It is concluded that a single universal maximum limit on the atrazine application in catchments, as suggested by many regulatory authorities, does not provide adequate protection of the aquatic environment. Rather, it is advocated that flexible limits on the application of atrazine be developed in line with the potential risk of contamination to surface and subsurface water and fragility of the aquatic environment.

Late Quaternary paleosols and their paleoenvironmental significance along the Andean piedmont, Eastern Bolivia

The Andean piedmont of eastern Bolivia is situated at the southern margin of Amazonia characterized by an overall humid climate regime with a marked contrast between the rainy and dry seasons. The nearby Subandean foothills deliver abundant sandy sediments to the piedmont, leading to a complex array of sediments and paleosol horizons. Within this setting, the presented study analyzes four profiles of paleosol-sediment-sequences along incised ephemeral streams near Santa Cruz de la Sierra with a focus on past pedogenic variability in the context of the regional late Quaternary geomorphic and environmental evolution. Based on field observations, micromorphological analysis, geochemical and clay mineralogical data five classes of paleosol horizons could be distinguished. The individual paleosol horizons as well as the sediments, in which they developed, were interpreted regarding their paleoenvironmental significance, taking into consideration the various controls on soil formation with particular focus on changes of local environmental conditions through time. Thus, three different pathways of soil formation were established. On the late Quaternary timescale, the results suggest a strong relation between paleoenvironmental conditions (climate, vegetation etc.), soil environment (soil water flow, micro-environment) and the type of paleosol horizons developed in the study area. The formation of “red beds” (Bw horizons) implies very dry soil environments under dominantly dry conditions, which seem to have prevailed in the study area some time before ∼ 18 cal ka BP. Moderately dry but markedly seasonal environmental conditions with a long dry season and strong seasonal contrasts in soil water flow could explain the formation of moderately developed Bwt horizons around ∼ 18 cal ka BP and much of the mid-Holocene. The formation of Bt horizons and/or clay lamellae in relation to intense neoformation of clay and dominant clay illuviation by soil water points to wet conditions similar to today, which have probably prevailed in the study area before ∼ 8 cal ka BP and since ∼ 5 cal ka BP.

Visualisation modelling in 3D of an alluvial aquifer system at a valley-wide scale to understand groundwater status : Lockyer, QLD

Visualisation provides a method to efficiently convey and understand the complex nature and processes of groundwater systems. This technique has been applied to the Lockyer Valley to aid in comprehending the current condition of the system. The Lockyer Valley in southeast Queensland hosts intensive irrigated agriculture sourcing groundwater from alluvial aquifers. The valley is around 3000 km2 in area and the alluvial deposits are typically 1-3 km wide and to 20-35 m deep in the main channels, reducing in size in subcatchments. The configuration of the alluvium is of a series of elongate “fingers”. In this roughly circular valley recharge to the alluvial aquifers is largely from seasonal storm events, on the surrounding ranges. The ranges are overlain by basaltic aquifers of Tertiary age, which overall are quite transmissive. Both runoff from these ranges and infiltration into the basalts provided ephemeral flow to the streams of the valley. Throughout the valley there are over 5,000 bores extracting alluvial groundwater, plus lesser numbers extracting from underlying sandstone bedrock. Although there are approximately 2500 monitoring bores, the only regularly monitored area is the formally declared management zone in the lower one third. This zone has a calibrated Modflow model (Durick and Bleakly, 2000); a broader valley Modflow model was developed in 2002 (KBR), but did not have extensive extraction data for detailed calibration. Another Modflow model focused on a central area river confluence (Wilson, 2005) with some local production data and pumping test results. A recent subcatchment simulation model incorporates a network of bores with short-period automated hydrographic measurements (Dvoracek and Cox, 2008). The above simulation models were all based on conceptual hydrogeological models of differing scale and detail.

Phylogeography of Echinocladius martini Cranston (Diptera: Chironomidae) in closed forest streams of eastern Australia

The eastern Australian rainforests have experienced several cycles of range contraction and expansion since the late Miocene that are closely correlated with global glaciation events. Together with ongoing aridification of the continent, this has resulted in current distributions of native closed forest that are highly fragmented along the east coast. Several closed forest endemic taxa exhibit patterns of population genetic structure that are congruent with historical isolation of populations in discrete refugia and reflect evolutionary histories dramatically affected by vicariance. Currently, limited data are available regarding the impact of these past climatic fluctuations on freshwater invertebrate taxa. The non-biting midge species Echinocladius martini Cranston is distributed along the east coast and inhabits predominantly montane streams in closed forest habitat. Phylogeographic structure in E. martini was resolved here at a continental scale by incorporating data from a previous pilot study and expanding the sampling design to encompass populations in the Wet Tropics of north-eastern Queensland, south-east Queensland, New South Wales and Victoria. Patterns of phylogeographic structure revealed several deeply divergent mitochondrial lineages from central and south-eastern Australia that were previously unrecognised and were geographically endemic to closed forest refugia. Estimated divergence times were congruent with late Miocene onset of rainforest contractions across the east coast of Australia. This suggested that dispersal and gene flow among E. martini populations isolated in refugia has been highly restricted historically. Moreover, these data imply, in contrast to existing preconceptions about freshwater invertebrates, that this taxon may be acutely susceptible to habitat fragmentation.

Authenticating Multicast Streams in Lossy Channels Using Threshold Techniques

We first classify the state-of-the-art stream authentication problem in the multicast environment and group them into Signing and MAC approaches. A new approach for authenticating digital streams using Threshold Techniques is introduced. The new approach main advantages are in tolerating packet loss, up to a threshold number, and having a minimum space overhead. It is most suitable for multicast applications running over lossy, unreliable communication channels while, in same time, are pertain the security requirements. We use linear equations based on Lagrange polynomial interpolation and Combinatorial Design methods.