Dry River Research Articles

Consumer–resource coupling in wet–dry tropical rivers

1. Despite implications for top-down and bottom-up control and the stability of food webs, understanding the links between consumers and their diets remains difficult, particularly in remote tropical locations where food resources are usually abundant and variable and seasonal hydrology produces alternating patterns of connectivity and isolation. 2. We used a large scale survey of freshwater biota from 67 sites in three catchments (Daly River, Northern Territory; Fitzroy River, Western Australia; and the Mitchell River, Queensland) in Australia's wet-dry tropics and analysed stable isotopes of carbon (δ(13) C) to search for broad patterns in resource use by consumers in conjunction with known and measured indices of connectivity, the duration of floodplain inundation, and dietary choices (i.e. stomach contents of fish). 3. Regression analysis of biofilm δ(13) C against consumer δ(13) C, as an indicator of reliance on local food sources (periphyton and detritus), varied depending on taxa and catchment. 4. The carbon isotope ratios of benthic invertebrates were tightly coupled to those of biofilm in all three catchments, suggesting assimilation of local resources by these largely nonmobile taxa. 5. Stable C isotope ratios of fish, however, were less well-linked to those of biofilm and varied by catchment according to hydrological connectivity; the perennially flowing Daly River with a long duration of floodplain inundation showed the least degree of coupling, the seasonally flowing Fitzroy River with an extremely short flood period showed the strongest coupling, and the Mitchell River was intermediate in connectivity, flood duration and consumer-resource coupling. 6. These findings highlight the high mobility of the fish community in these rivers, and how hydrological connectivity between habitats drives patterns of consumer-resource coupling.

Methods for Successful Establishment of Cottonwood and Willow Along an Incised Stream in Semiarid Eastern Oregon, USA

Abstract Restoration of riparian plant communities in the dry interior Columbia River basin and other semiarid regions where channel incision has altered hydrological connections is a major challenge. Establishing riparian vegetation within incised systems has the potential to facilitate the aggradation of the stream bed by increasing bank stabilization and providing large woody debris inputs. We tested an alternative approach to irrigation in a heavily incised subwatershed of the dry interior Columbia River Basin by using motorized augers to penetrate lowered water tables. By planting dormant pole cuttings of black cottonwood (Populus trichocarpa) and willow (Salix spp.) in auger holes within terraces up to 2 m above the incised streambed elevation, we hypothesized that riparian vegetation could be established without the aid of irrigation. We also tested the efficacy of vented plastic tree shelters and circular fence cages with respect to survival, growth, and browsing after 15 months. Survival and average growth was significantly higher for pole plantings protected with vented plastic tree shelters and planted in auger holes where lowered water tables were penetrated (89% and 95 cm, respectively). Survival and average growth was significantly lower for unprotected pole cuttings planted in augur holes where lowered water tables were not penetrated (5% and 33 cm, respectively). Our results suggest that survival of willow and cottonwood pole plantings along incised streams can be greatly enhanced if they are: 1) placed in auger holes that reach the water table via deep-planting; and 2) protected with vented plastic tree shelters.

Influence of soil properties on trace element availability and plant accumulation in a Mediterranean salt marsh polluted by mining wastes: Implications for phytomanagement

The aims of this study were to determine the factors which control metal and As phytoavailability in the different microenvironments (Sand Dunes, Salt Flat, Dry River and Shrubs) present at a Mediterranean salt marsh polluted by mining wastes. We performed a field study following a plot sampling survey. The analyses of soil parameters (pH, electrical conductivity (EC), organic carbon contents, etc.), total metal and As concentrations and their phytoavailability assessed with EDTA were related to each microenvironment and the corresponding plant species uptake. The averages of pH and EC were slightly alkaline (pH ≈ 7.5) and saline (≈ 2.2 to 17.1 dS m −1) respectively. The soil samples from the Salt Flat subzone showed the highest metal concentrations (e.g. 51 mg kg −1 Cd, 11,600 mg kg −1 Pb) while for As, the highest concentrations occurred in the Dry River (380 mg kg −1 As). The total metal and EDTA-extractable concentrations occurred as it follows: Salt Flat > Dry River > Degraded Dunes > Shrubs. In relation to plant metal and As accumulation, the highest root concentrations were obtained in the species from the Salt Flat subzone: ~ 17 mg kg −1 As, ~ 620 mg kg −1 Pb, for both, Juncus maritimus and Arthrocnemum macrostachyum. However the highest metal and As shoot concentrations occurred in species from the Sand Dunes: ~ 23 mg kg −1 As ~ 270 mg kg −1 Pb for Dittrichia viscosa; ~ 23 mg kg −1 As, ~ 390 mg kg −1 Zn for Crucianella maritima. The occurrence of edaphic gradients including salinity and texture determined the vegetation distribution. However, it cannot be concluded that there was a disturbance due to metal(loid)s soil concentrations in terms of vegetation composition except in the Degraded Dunes and Dry River. The higher EDTA-extractable concentrations were coincidental with the most saline soils but this did not result in higher metal(loid)s plant accumulation.

Hydrological changes and settlement migrations in the Keriya River delta in central Tarim Basin ca. 2.7–1.6 ka BP: Inferred from 14C and OSL chronology

Over one hundred artifacts, including shards, chopped wood, bronze and iron ware debris as well as footprints, have been discovered during archaeological investigations at and around the central Taklamakan Desert Yuansha Site (38°52′N, 81°35′E). Dating (14C and OSL) and landform study show that the present-day dry Keriya River once sustained an oasis human settlement in 2.6 ka BP, historically falling into the Spring and Autumn Period (716–475 BCE) of Chinese history. The chronology and archaeological interpretations also show that some 400 years later, the local Keriya River channel had shifted 40 km southeast to sustain a Western Han (206 BCE-25 CE) Wumi settlement at the Karadun site. In the meantime, river-channel migration had allowed reoccupation of a site west of Yuansha City around 1.9 ka BP (abandoned again by 1.6 ka BP). The remains’ chronology shows that this site was affiliated to Wumi culture and Eastern Han (24–220 CE) dynasty rule. Palaeoclimatic records indicate that the migrations of the river and oasis settlers between 2.7 and 1.6 ka BP were coeval with Central Asian climate changes. Yuansha City was built just after the end of 2.8 ka BP glacier advances in western China, suggesting that release of more water during the subsequent glacier recession may have facilitated oasis development such that Iron Age European peoples could settle in the Tarim Basin. As shown from analysis of archeological remains, not only at Yuansha but also in other ancient cities in the Tarim such as Loulan and Jingjue (Niya), conditions around 1.6 ka BP were dry enough to cause oasis decline. Thus, the results reported here enhance our knowledge about environmental changes and their effects on human activities and cultural evolution in western China and will stimulate further interdisciplinary studies of landscape and oasis history in the Tarim Basin.

Using satellite imagery to reveal the course of an extinct river below the Thar Desert in the Indo-Pak region

Digitally processed satellite images have unearthed the hidden course of a major lost river below the sands of the Thar Desert, in the India–Pakistan (Indo-Pak) region. The great Himalayan river of the Vedic period (10 000–8000 BP) is mentioned in ancient Indian literature. It was called the ‘Saraswati’ in India and the ‘Hakra’ in Pakistan and it dried up during 4000–3500 BP. Large numbers of archaeological sites from the Harappan civilization occur along the dry river bed. The mapped course of the river is 4–10 km wide and conforms to the size described in the Rigveda. The newly described course is validated through the drilling of tube wells in the channels and through archaeological, hydrogeological and sedimentary data. An enormous quantity of potable water has been found along these channels. The path of the (main) river course, the likelihood of the river shift and the reasons for its disappearance are discussed.

Rate and historical change of direct recharge from precipitation constrained by unsaturated zone profiles of chloride and oxygen‐18 in dry river bed of North China Plain

AbstractQuantifying of direct recharge derived from precipitation is crucial for assessing sustainability of well‐irrigated agriculture. In the North China Plain, the land use is dominated by groundwater‐irrigated farmland where the direct recharge derived from precipitation and irrigation. To characterize the mean rate and historical variance of direct recharge derived from precipitation, unsaturated zone profiles of chloride and δ18O in the dry river bed of the Beiyishui River were employed. The results show that archival time scale of the profile covers the duration from 1980 to 2002 (corresponding to depths from 5 to 2 m) which is indicated by matching the δ18O peaks in the isotope profile with the aridity indexes gained by instrumental records of annual precipitation and annual potential evaporation. Using the chloride mass balance method, the mean rate of the direct recharge corresponding to the archival time scale is estimated to be 3·8 ± 0·8 mm year−1, which accounts for about 0·7% of the long‐term average annual precipitation. Further, the direct recharge rates vary from 2·1 to 6·8 mm year−1 since 1980. Despite the subhumid climate, the estimate of recharge rates is in line with other findings in semiarid regions. The low rate of direct recharge is considered as a result of the relative dry climate in recent decades. In dry river bed, unsaturated zone profiles of chloride and δ18O combined with instrumental records could offer valuable information about the direct recharge derived from precipitation during droughts. Copyright © 2011 John Wiley & Sons, Ltd.

Longitudinal river ecohydrology: flow variation down the lengths of alluvial rivers

AbstractLongitudinal flow variation is an emerging field of study in river ecohydrology. Longitudinal changes in the frequencies, magnitudes, durations and timing of floods, low‐flows and intermittence create a dynamic environment for flow‐dependent species and ecological processes. Analyses of flow variation and flow–ecosystem relationships in the longitudinal dimension require synoptic flow time‐series at multiple sites along a river. Complex channel geomorphology and a scarcity of rivers equipped with multiple flow gauges have slowed progress in longitudinal ecohydrology. The empirical longitudinal flow model (ELFMOD) is a new statistical tool for estimating flows at multiple points along rivers; which circumvents the requirement for multiple gauges. In this study, we used ELFMOD to explore longitudinal flow variation in four alluvial rivers from different geological terrains and climate zones: the Albarine (France), Methow (USA) and Selwyn and Orari (New Zealand). Differences among rivers in longitudinal and temporal flow variation were evident on date × location flow matrices and longitudinal profiles. There were notable differences among longitudinal gradients in flow magnitude and flow percentiles, and in the recurrence, extent, and rate of expansion and contraction of dry river reaches. There were also large differences in longitudinal flow‐permanence patterns. Temporal variation in the lengths of dry channel and numbers of dry reaches was predominately seasonal in the Albarine and Methow, and interannual in the Orari and Selwyn. Broad differences among the rivers in longitudinal flow patterns correspond to differences in the configuration of hydrogeomorphic discontinuities such as tributary confluences, channel divergences and convergences, and lithological contacts. Copyright © 2010 John Wiley & Sons, Ltd.

Natural variation in immersion and emersion affects breakdown and invertebrate colonization of leaf litter in a temporary river

Flow pulses that alternately immerse and expose benthic habitats are widely recognized as key determinants of biodiversity and ecosystem functioning in rivers. Terrestrial leaf litter input, colonization, and breakdown are also key processes in river ecosystems, but little is known about the effects of alternating immersion and emersion on these processes. We used litterbags to examine breakdown, microbial activity, and colonization of Populus sp. leaves by invertebrates along a natural gradient in immersion and emersion (i.e., submergence and exposure to air) in a temporary river. Rates of leaf litter mass loss, microbial activity and colonization by invertebrates differed among litterbags that were permanently immersed, intermittently immersed and permanently emersed, and breakdown rate coefficients (k) decreased with increasing cumulative emersed duration (the total number of day of emersion during the experiment). In contrast, the frequency of emersed periods had no detectable effects on these variables. k was positively correlated with the density of invertebrate shredders in immersed litterbags, with microbial activity and shredder density in intermittent litterbags, and with microbial activity in emersed litterbags. These correlations suggest that the relative importance of microbial activity on k increases with emersed duration, due to the periodic elimination of aquatic shredders and the scarcity of terrestrial detritivores. The fact that leaf litter breakdown was detectable under permanently emersed conditions indicates that mechanisms other than shredding by invertebrates, such as leaching and photodegradation, are dominant in dry river habitats.

Terrestrial invertebrates of dry river beds are not simply subsets of riparian assemblages

Dry river beds are common worldwide and are rapidly increasing in extent due to the effects of water management and prolonged drought periods due to climate change. While attention has been given to the responses of aquatic invertebrates to drying rivers, few studies exist on the terrestrial invertebrates colonizing dry river beds. Dry river beds are physically harsh and they often differ substantially in substrate, topography, microclimate and inundation frequency from adjacent riparian zones. Given these differences, we predicted that dry river beds provide a unique habitat for terrestrial invertebrates, and that their assemblage composition differs from that in adjacent riparian zones. Dry river beds and riparian zones in Australia and Italy were sampled for terrestrial invertebrates with pitfall traps. Sites differed in substrate type, climate and flow regime. Dry river beds contained diverse invertebrate assemblages and their composition was consistently different from adjacent riparian zones, irrespective of substrate, climate or hydrology. Although some taxa were shared between dry river beds and riparian zones, 66 of 320 taxa occurred only in dry river beds. Differences were due to species turnover, rather than shifts in abundance, indicating that dry river bed assemblages are not simply subsets of riparian assemblages. Some spatial patterns in invertebrate assemblages were associated with environmental variables (irrespective of habitat type), but these associations were statistically weak. We suggest that dry river beds are unique habitats in their own right. We discuss potential human stressors and management issues regarding dry river beds and provide recommendations for future research.

FIELD OBSERVATIONS OF WINDBLOWN SAND AND DUST IN THE TAKIMAKAN DESERT, NW CHINA, AND INSIGHTS INTO MODERN DUST SOURCES

ABSTRACTDespite the importance of desert dust at global and regional scales, its exact provenance is often unclear. The Taklimakan Desert in northwest China is a common source of high‐frequency regional dust storms and is also a large source of global dust production. On the basis of field observations and the determination of the fraction of aeolian dust in surface samples, we characterized the relative intensity of windblown sand/dust processes in the Taklimakan and the volume of dust emitted (PM10) during these processes. Major dust sources were degraded lands on the eastern desert margin, the Gobi and alluvial, fluvial and aeolian sediments occurring on the desert margin. These areas have high PM10 emission capacity due to high‐surface PM10 concentrations and intensive windblown sand/dust activity. Despite having intensive windblown sand activity, the central desert had lower PM10 dust emission capacity (<1·6 kg day−1 m−2 in spring, <0·08 kg day−1 m−2 in other seasons) due to lower surface PM10 fraction. The dry Taitema Lake bed was a source of potentially high dust emissions (at least 4·4–17 kg day−1 m−2 for the monitoring period) due to the intensity windblown sand/dust activities, despite low PM10 concentrations. The dry river beds on the southeastern desert margin had lower dust emission potential due to low PM10 concentrations and windblown sand/dust activity. Most dust emission sources lie in the paths of prevailing winds, leading to aeolian dust transported to and deposited in the desert hinterland or Hotan, Yutian and Minfeng areas, where wind stream convergence leads to high‐frequency dust storms. Copyright © 2011 John Wiley & Sons, Ltd.

남북공유하천 북한강의 물이용 문제점 및 수리권 추정 (II) -하류유역 수리권 추정

There are not many practical measures to solve a water conflict, when a hydromorphologically asymmetric situation in international rivers exists whereby downstream users may not affect upstream users but upstream users do cause downstream impacts. In taking advantage of this merit, North Korea has built Imnam Dam in upstream of North Han River and uses water for trans-basin hydropower generation. As an impact of this dam South Korean' area as a downstream user has been suffered from water deficit and dry river. It is very critical for South Korea to solve a key problem such as water allocation for water supply and river maintenance. Therefore, this study is aim to suggest alternatives for equitable water allocation in consideration of special circumstances between the South and the North. For this, reviewing the allocation methods of water rights is carried using lessons obtained from international river cases. The results show that the minimum desired streamflow is calculated at 7.3 ; water budget analysis by the equitable distribution of streamflows at the border line of the North Han River, the difference in water supply deficiency is at 3.7 before and after Imnam Dam; in the determined distribution method, the difference in water deficiency is at 11.38 . These results show that South Korea should be secured 11.38 from North Korean's Imnam Dam in respective of water use right and sound river maintenance.

Death in a Dry River: Black Life, White Property, Parched Justice

This essay deals with the sentence handed down in April 2010 on the death of the 33 year-old Kumantaye Ryder in the dry creek bed of the Todd River in Alice Springs, Central Australia. The riverbed, we argue, is a racially marked and politically charged location that plays an historical and continuing role in defining relations between settler and colonized. We situate our analysis of this site in a context where autonomy over and access to land, and the significance of remote townships and town camps, are bitterly contested as part of a wider clash over Aboriginal subjectivities, citizenships and futures. Drawing on Cheryl Harris's critical insights (1993) into how in the United States ‘rights in property are contingent on, intertwined with, and conflated with race’, we examine the sentencing of the accused in the death of Kumantaye Ryder against the multiple meanings of property. We conclude our analysis by underscoring the manner in which racialised formations of law and property work to secure, entitle and affirm the very possibility of life and future itself.

Other Lives

30 LESLIE JOHNSON OTHER LIVES T he guest book sits on a pedestal in the funeral home lobby. Dean signs it, then flips the pages backward to see who else has come before him. He recognizes no one. He has an urge to scribble out his own name and escape, but an usher in a black suit materializes, handing him a prayer card, thanking him for coming, and directing him toward the viewing room. Dean follows on the spongy carpet, but stops to linger at a photo collage set up on an easel by the doorway. There in the center of the foam display board is an eight-by-ten photograph of Mrs. Zarembinski from her days as a fourth-grade teacher at Dry River Elementary School. Dean recognizes the mottled blue background that the photographer taped up every year on the back wall of the cafeteria for portrait day; briefly Dean thinks of the cheap plastic combs, pea green, given as rewards after the kids bared their teeth and smiled into the blinding flash of white light. Why after? Why didn’t they get the combs first, when they could use them? Dean, now forty-three, stares into Mrs. Zarembinski’s eyes, narrow slits above her fat, fake-smiling cheeks spotted with rouge. The shade of Mrs. Zarembinski’s stiff red curls, Dean decided as a boy, was what you’d get mixing orange and cherry cough syrup in a rusty bucket. When she used to lean over him and say, “Look at me when I’m speaking, Dean,” he could see where the dye soaked into her white scalp. When she used to walk up to the chalkboard, Dean remembers, she’d puff through her nose with each step, her double chin jiggling, and you could hear something squeaking underneath her clothes. Christ, how Dean had hated Mrs. Zarembinski! He stares hard at the photo collage, picking out a few grainy snapshots of the old neighborhood in Dry River. The development was brand new in 1972 when Dean’s stepfather moved them from Chicago to Arizona. The Zarembinskis lived two doors down. Mr. Zarembinski was old and let his yard fill with 31 Johnson brown weeds and spoke in a heavy accent that Dean’s stepdad said was Polack. The Zarembinskis’ only son was George, blubbery like his mother, smelling like powdered sugar and sweat, quick to cry and quit during neighborhood games, then bribing his way back in with his mother’s pastries. Dean’s own mother couldn’t wait to get out of Dry River. She thought the houses were cheap, the whole subdivision beneath her. She set her sights on Scottsdale, and within three years, by the time Dean was eleven, they were gone. He never went back to Dry River, and he hasn’t seen the Zarembinskis or anyone else from the old neighborhood for thirty years. He lives in Chandler now, less than an hour away, but there’s never any reason for him to drive that way. Why is he here, about to look at Mrs. Zarembinski’s dead body? He isn’t sure. Sunday morning, sitting at the kitchen table in his boxers after Karen took Cole to Sunday school, flipping through the Phoenix Gazette, the name Zarembinski jumped out at him from the obits. There was no picture, but Dean squinted and read. Retired teacher. Devoted chairwoman of St. Theresa’s holiday craft fair. Survived by her loving son, George Artur Zarembinski. Georgie the crybaby! He’d never known Mrs. Zarembinski’s first name, and he said it out loud: Paulette . The strange thing was, he had been talking about her only a few days earlier. His son Cole had come home upset about his new “behavior modification” plan at school. Something to do with colored cards on his desk that changed from green, to yellow , to red, to blue, depending on how many times Cole blurted out inappropriate comments or stood on his chair or pestered the kids sitting next to him. A blue card meant he had to stay inside at recess and pound clay instead of going outside to the playground. “You think you have it tough...

Co-conception of integrated flood management solutions: riverscapes to facilitate dialog

When involved late in flood mitigation projects, biologists can suggest only minor changes. Conception should be multidisciplinary from the start. Riverscapes appear an excellent support to exchange information and share common conceptual views. Biologists thus summarize their expertise and local analyses, including a description of the potential biodiversity and processes. We built a riverscape typology for Polish mountain rivers and used it as a support to discuss compromises and adaptations for dry dams and river training. Translating the technical solutions into shift of types guide the choices. Serving a purpose, the typology is case-dependant and could be revised during a project. Riverscapes could also potentially be useful in multidisciplinary research.

Assessment of climate change impact on water resources in the Pungwe river basin

The Rossby Centre Regional Climate Model (RCA3) and the hydrological model HBV were linked to assess climate change impacts on water resources in the Pungwe basin until 2050. RCA3 was capable of simulating the most important aspects of the climate for a control period at the regional scale. At the subbasin scale, additional scalingwas needed. Three climate change experiments using ECHAM4-A2, B2 and CCSM3-B2 as input to RCA3 were carried out. According to the simulations annual rainfall in 2050 would be reduced by approximately 10% with increasing interannual variability of rainfall and dry season river flow and later onset of the rainy season. The ECHAM4-A2 driven experiment did also indicate a slight increase of high flows. If the results indeed reflect the future, they will worsen the already critical situation for water resources, regarding both floods and droughts. Uncertainties, however in the downscaled scenarios make it difficult to prioritize adaptation options. This calls for inclusion of more climate change experiments, in an ensemble of climate scenarios possibly by using a combination of dynamical and statistical downscaling of general circulation models, as well as extending the simulations to 2100 to further ensure robustness of the signal..

Long-term study of population dynamics and habitat selection of rodents in the Negev Desert

Population fluctuations of 13 rodent species in 5 habitats were monitored for 16 years in the central Negev Desert, Israel. Analysis of factors affecting population dynamics of 9 common and abundant species demonstrated that densities of most rodent species in the late summer, after the end of reproduction, were determined mainly by total precipitation during the previous rainy season. Rodent densities in the winter, before the reproductive season, were determined mainly by their densities in the previous (late summer) season. Rodent populations in dry river beds (wadi) demonstrated either no or negative correlations with total rainfall, suggesting episodes of population crash due to flash winter flooding. For all species occurring in more than 1 habitat, densities, at least in some habitats, were correlated with their contemporary densities in other habitats. For these species, processes of density-dependent habitat selection were indicated using isodars analysis. Generally, population dynamics of desert rodents were determined by the complex interactions of extrinsic (rainfall) and intrinsic mechanisms but were modified by density-dependent habitat selection. DOI: 10.1644/09-MAMM-S-162.1.

CADÊ A ÁGUA QUE ESTAVA AQUI? OS LEITOS SECOS NA MEMÓRIA E NA HISTÓRIA

This article refers to a case study, conducted in the city of Goias Hidrolândia. Such study discusses, from the perspective of environmental history and oral history, the possibilites of unraveling the historical realities built on landscapes that today are seen as abject due the current state of degradation. In other words, on the one hand, the historiography after the enlargement of its thematic approaches adopted the medium and large rivers as major sources of research, on the other, forgot a colossal hydraulic mesh represented by small streams that, largely are now extincts or dying in face of predation. From this, the restlessness that drives our research is to know for where are sent the dry rivers. Thus, we will show that these multiples spaces hydraulic, especially those whose beds have dried up, directly involved in the construction of memories, given the importance it had in the lives of people, once served by its water, is in the production of their socio-economic areas, is in the construction of maps of the world around them.

Widespread omnivory and low temporal and spatial variation in the diet of fishes in a hydrologically variable northern Australian river

This article examines the trophic ecology of freshwater fishes (22 species in 15 families) in a wet and dry tropical Australian river of high intra-annual and interannual hydrological variability. Seven major trophic groups were identified by cluster analysis; however, four food items (filamentous algae, chironomid larvae, Trichoptera larvae and Ephemeroptera nymphs) comprised almost half of the average diet of all species. The influence of species, fish size, spatial effects and temporal effects on food use was investigated using redundancy analysis. Size, time and space accounted for little of the perceived variation. Ontogenetic changes in diet were minor and limited to a few large species. Spatial variation in trophic composition of the fish assemblages reflected the effects of the Burdekin Falls and dam, a major geographic barrier, on species distributions. Little spatial variation in diet was detected after accounting for this biogeographical effect. Temporal variations in flow, although marked, had little effect on variations in fish diet composition due to the low temporal diversity of food resources in physically monotonous sand and gravel channels. Species identity accounted for<50% of the observed variation in food choice; omnivory and generalism were pronounced. The aquatic food web of the Burdekin River appears simple, supported largely by autochthonous production (filamentous and benthic microalgae, and to some extent, aquatic macrophytes). Allochthonous food resources appear to be unimportant. The generalist feeding strategies, widespread omnivory and absence of pronounced trophic segregation reported here for Burdekin River fishes may be common to variable and intermittent rivers of subtropical and tropical northern Australia with similar fish communities and may be a general feature of rivers of low habitat diversity and characterized by flow regimes that vary greatly both within and between years.

Development of vegetation patterns in early primary succession

Question: We investigated colonisation filters in early plant community development on a glacial outwash plain. We asked if these were related to seed limitation or to a lack of safe sites, if topographical heterogeneity affected species patchiness and how species life cycles influence successional trajectories. Location: An outwash plain (Skeiðarársandur) in southeast Iceland. Methods: We identified surface heterogeneity at two different scales, ca. 10–15 cm (larger stones and established plants) and ca. 50 m (shallow depressions representing dry river beds) at two study sites. We quantified species cover, flowering plant density, seed production, seed rain, seed bank density, seedling emergence and seedling survival from June 2005 to June 2007 for the whole plant community, and measured seed production for five species. Results: Mean vegetation cover was <2.5% at the sites. Low emergence rates and high seedling mortality were the two main recruitment filters. Only 1.4% of seedlings emerging in 2005 survived into the 2007 growing season. Topographical heterogeneity had little effect on plant colonisation. High annual variation was recorded, and the two study sites (ca. 2 km apart) differed in their colonisation success. Of the five species, establishment of Cerastium alpinum and Silene uniflora was most limited by lack of seeds, whereas establishment of Luzula spicata, Poa glauca and Rumex acetosella was most limited by safe sites. Conclusions: We conclude that colonisation processes and patterns in early primary succession on Skeiðarársandur were largely influenced by stochastic factors.

Self-action of a low-frequency acoustic wave and generation of the second harmonic in dry and water-saturated river sand

The amplitude-phase effects of self-action and generation of the second harmonic are observed for a low-frequency longitudinal acoustic wave propagating in dry and water-saturated (wet) river sand under a static load. On the basis of the measured dependences of the amplitude and phase delay of the fundamental frequency’s carrier wave and its second harmonic’s amplitude on the initial wave’s amplitude, equations of state are proposed for dry and water-saturated sand. The parameters of these equations are determined from the comparison of analytic calculations with experimental data.