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Murray-Darling Freshwater Research CentreMDFRC item.Sediment oxygen demands and water-atmosphere methane emissions of a highly productive, freshwater wetland on the floodplain of the River Murray in south-eastern Australia were quantified over a 14 month period in 1993–1994. Total sediment oxygen demands ranged from 1.3 to 3.3 mmol m−2 h−1, of which < 3 to 90% was due to chemical oxygen demand. Methane emissions ranged from < 0.01 mmol m−2 h−1 in winter to 2.75 mmol m−2 h−1 in summer. Methanogenesis accounted for at least 60% of the combined aerobic and methanogenic carbon flux in sediments from Eleocharis sphacelata beds, and at least 30% and 40% of the combined flux in sediments from Myriophyllum sp. beds and Vallisneria gigantea beds, respectively. In vitro incubations, using additions of sulfate and of molybdate, failed to indicate unequivocally competition for substrates between sulfate-reducing and methanogenic bacteria. However, in vitro methanogenesis was strongly inhibited by nitrate, suggesting an interaction between benthic methanogens and denitrifying or other nitrate-reducing bacteria. Fe3+ decreased in vitro methanogenesis by 16–49% during January, February and March 1994; oxidation of organic matter at the expense of the reduction of ferric ions could be a significant route for detritus processing in Eleocharis-bed sediments in the warmer months. Methanogenesis was increased consistently by additions of some low molecular weight substrates, such as acetate, but not by others, such as methanol, propionate and trimethylamine. Complex polymeric substrates, such as cellulose, starch and aquatic plant matter, increased in vitro methanogenesis rapidly and markedly. Despite this, no relationship between methane emissions and benthic cellulase activity was observed in the field. Methanogenesis was strongly temperature dependent, being maximal at 30 to 40°C and minimal at 5°C, thereby explaining the strong seasonality observed in methane emissions in situ.

Environmental monitoring is an essential feature of environmental assessment and natural resource management. Whilst the focus of monitoring programs is often on the response of chosen variables to a disturbance of particular concern, it is also important to consider the variability of disturbance pressures in relation to the variability of the ecosystem state. In this paper, we discuss the need to relate environmental variability to disturbance variability in small-scale monitoring programs designed to assess the impact of short-term pulses of visitors on the condition of aquatic ecosystems in protected areas. We use data from protected areas from six Koppen climate zones in Australia to highlight the fact that peaks in visitation do not always coincide with existing monitoring protocols or with optimal times for monitoring on the basis of environmental variability, particularly in relation to rainfall and temperature and, hence, likely biological activity. We highlight how recognising the inter...

Seasonality in tourism is a regular and predictable cycle of visitation across a year. Although seasonality in visitation is extremely common and is known, in principle, often to be driven by temporal changes in a range of natural and institutional factors, the relative importance of different individual pressures has yet to be quantified for any large-scale geographical areas. To assess the relative importance of natural versus institutional factors in driving tourism seasonality, data on visitation patterns were collated from 23 protected areas across six Koppen climate zones in eastern Australia. Analyses sought to determine the degree to which climatic variables (such as mean monthly rainfall and minimum and maximum temperatures) explained visitation patterns, and to understand how these relationships could assist in the prediction of tourism futures. Climate was the principal force driving seasonal patterns of visitation in equatorial, tropical, desert, grassland and temperate zones, whereas...

Although water regime modification and salinity are recognised as significant threats to wetland ecosystems worldwide, the effects of long-term saline flooding (decades) on woody tree persistence are poorly quantified. We compared the condition, growth, structure and reproduction (sexual and asexual) of mature individuals of the clonal tree, Melaleucaericifolia (Myrtaceae), that experienced continual (>30 years) flooding with trees that were only intermittently (approximately every 5 years) flooded. An index developed to assess the condition of multi-stemmed trees found that continually flooded trees were in significantly poorer condition than intermittently flooded trees, having lower crown cover, foliar cover and foliar density, and a higher incidence of dead stags and dieback. Annual stem growth correlated strongly with condition scores. Evidence for a trade-off between sexual and asexual reproductions was found; flooded trees were constrained in their vegetative lateral spread (

Aerial seed banks are potentially the main source of sexual recruitment for woody wetland plants. Whilst the importance of soil seed banks for the persistence and recruitment of wetland plants has been examined in many studies, the role of aerial seed banks has been largely neglected. We used seed traps and the seedling emergence technique to quantify the seed rain from aerial seed banks of the Swamp Paperbark Melaleuca ericifolia Sm. (Myrtaceae) in Dowd Morass, a Ramsar-listed, brackish-water wetland in south-eastern Australia. Nine plant species germinated from material collected in seed traps over 2004–2005, but emergents were dominated (80–97%) by M. ericifolia. The mean number of M. ericifolia emergents ranged from

Salinization, a widespread threat to the structure and ecological functioning of inland and coastal wetlands, is currently occurring at an unprecedented rate and geographic scale. The causes of salinization are diverse and include alterations to freshwater flows, land-clearance, irrigation, disposal of wastewater effluent, sea level rise, storm surges, and applications of de-icing salts. Climate change and anthropogenic modifications to the hydrologic cycle are expected to further increase the extent and severity of wetland salinization. Salinization alters the fundamental physicochemical nature of the soil-water environment, increasing ionic concentrations and altering chemical equilibria and mineral solubility. Increased concentrations of solutes, especially sulfate, alter the biogeochemical cycling of major elements including carbon, nitrogen, phosphorus, sulfur, iron, and silica. The effects of salinization on wetland biogeochemistry typically include decreased inorganic nitrogen removal (with implica...

The utility of shallow water bodies in urban environments is frequently compromised either by dense beds of submerged plants or cyanobacterial blooms associated with nutrient enrichment. Although submerged plants are often harvested to facilitate recreational uses, this activity may alter the phytoplankton community, which in turn, also may restrict the use of the lake. We tested whether (i) plant harvesting reduced the abundance of flagellate algae and increased the abundance of cyanobacteria, and (ii) whether increasing levels of nutrient enrichment caused shifts in the dominance of heterocytous cyanobacteria, non-heterocytous cyanobacteria and Chlorophyta, in a shallow urban lake in Southern Australia as has been observed for shallow Danish lakes in previous studies. These predictions were tested with large (3000 l), replicated mesocosms in a warm, highly productive, shallow lake densely colonised by the submerged angiosperm, Vallisnaria americana Michaux. The heterokont algae, Chlorophyta, Cyanobacteria and Cryptophyta were the most numerous algal divisions in the lake. The Euglenophyta, although uncommon in early summer, became more abundant towards the end of summer. The Dinophyta and Charophyta were rare. The abundance of the heterokont algae and Euglenophyta was significantly reduced by plant harvesting even after plants had partially re-established 18 weeks after initial harvesting. The decline in the Euglenophyta in response to plant harvesting is consistent with earlier findings, that the relative abundance of flagellate algae tends to be greater in the presence of submerged plants. Contrary to our prediction, we found that the Cyanobacteria did not increase in response to plant harvesting, however the response may be altered under higher nutrient levels. Algal responses to nutrient enrichment in the presence of dense V. americana plants generally followed the patterns observed in shallow Danish lakes despite the large differences in climatic conditions. Both studies found that the abundance of heterocytous cyanobacteria declined at higher levels of nutrient enrichment, whereas non-heterocytous cyanobacteria and chlorophytes increased.

Taphonomic processes that may bias plant-fossil assemblages are important in explaining many aspects of the Cenozoic plant fossil record. Two tree genera, Eucalyptus and Nothofagus, are especially important for understanding the evolution of Australia's forests, because the former currently dominates the continent, whereas the latter is dominant in Cenozoic microfloras. Nothofagus also is prominent in temperate forests of South America and New Zealand, and in the Cenozoic history of these land-masses and Antarctica. This study measures standing biomass and leaf-litter production in contiguous cool temperate rainforest dominated by nanophyllous Nothofagus cunninghamii and wet sclerophyll forest dominated by macrophyllous Eucalyptus regnans in southeastern Australia. It tests an a priori hypothesis that the under-representation of Eucalyptus in the Australian Cenozoic record may reflect differential organ production by Eucalyptus and Nothofagus, respectively. A taphonomic bias was observed between ...

Temperature, dissolved oxygen and dissolved methane profiles were measured during autumn and summer, in a shallow floodplain lake in south-eastern Australia to determine the effects of water-column stability on methane and oxygen dynamics. The water column was well mixed in autumn. Strong thermal stratification developed in the late afternoon in summer, with top-to-bottom temperature differences of up to ∼6 °C. Methane concentrations in surface waters varied over a daily cycle by an 18-fold range in summer, but only by a 2-fold range in autumn. The implication of short-term temporal variation is that static chambers deployed on the water surface for short times (less than a day) in summer will significantly underestimate the diffusive component of methane emissions across the water–atmosphere interface. There was a marked diel variation in dissolved oxygen concentrations in summer, with the highest oxygen values (commonly 5–8 mg l−1) occurring in the surface waters in late afternoon; the bottom waters were then devoid of oxygen (< 0.2 mg l−1). Because of high respiratory demands, even the surface water layers could be nearly anoxic by morning in summer. The concentration of dissolved oxygen in the surface waters was always less than the equilibrium value. When the water column became thermally stratified in summer, the dissolved oxygen and methane maxima were spatially separated, and planktonic methanotrophy would be limited to a moving zone, at variable depth, in the water column. In summer the whole-wetland rates of oxygen production and respiration, calculated from long-term (∼5 h) shifts in dissolved oxygen concentrations over a diel period, were approximately 6–10 and 3–6 mmol m−3 h−1, respectively. These values correspond to net and gross primary production rates of ∼0.7–1.2 and ∼1.0–1.9 g C m−3 day−1, respectively.

Four approaches were used to assess the effect ofinundation on methane emissions from floodplainwetlands in Victoria, Australia: (i) fieldobservations following natural rainfall events; (ii)experimental manipulation of water levels in smallfloodplain depressions; (iii) experimentalmanipulation of water levels in replicated mesocosms;and (iv) in vitro incubation of floodplainsediment under laboratory conditions. Raftery'sSwamp, a large (150 ha) wetland on the floodplain ofthe Goulburn River, became inundated in June 1993following autumn-winter rainfall. Methane emissionspeaked (1.7 ± 0.05 mmol m-2 h-1) somesix months later, and the methane content of sedimentgas bubbles reached 59% v/v, even though the positivesediment redox potentials (176 to 243 mV) indicatedthat sediments were only moderately reducing. Threesmall (< 1 ha) depressions on the floodplains of theRiver Murray and Kiewa River were inundated eithernaturally (by rain and/or overflow from nearby rivers)or artificially by flooding at specific times of year;emissions from these sites were usually negligibleafter flooding in autumn or winter. In contrast, theonset of methane emission was very rapid (within 3 to6 days) after the depressions had been flooded insummer, and the methane content of sediment gasbubbles could then reach 36% v/v. At their peak,emissions from the ephemeral wetlands were similar topeak emissions from permanent wetlands insouth-eastern Australia. Emissions from replicatedwetland mesocosms (4.5 m diameter, 0.9 m deep) werealways very small (

Murray-Darling Freshwater Research CentreMDFRC item.Biofilms were allowed to develop on wooden slides of the River Red Gum (Eucalyptus camaldulensis Dehnh., Myrtaceae) submerged in two billabongs of south-eastern Australia. The slides were placed in the photic zone and the aphotic zone, and the biofilms sampled after eight week''s growth over the summer of 1989–1990 and winter of 1990. Bacterial numbers, estimated with epifluorescence microscopy, ranged from 4–78 × 106 cells cm–2. Bacteria were more abundant in the photic zone than the aphotic zone, and more abundant in summer than winter. Fewer than 0.5% of the bacteria could be cultivated on nutrient agar plates. Concentrations of phospholipids ranged from 8–79 ng cm–2, which corresponded to bacterial abundances of 2–17 × 106 cells cm–2. Fifty five phospholipid fatty acids (PLFA) were identified, of which 16:0 (13–29% of total PFLA) was the most common. Other abundant PFLA included 16:17c (6–28%), 18:26 (3–16%), 18:33 (4–12%), 18:19c (3–5%), 18:l7c (5–11%) and 18:0 (2–8%). Minor PLFA included 14:0, i and a 15:0, 15:0, 16:l5c, 16:113c, 18:36, 18:43, 20:46 and 20:53. The PLFA profiles of the biofilms were quite different from those of the sediments and plankton. There was a clear distinction between the PLFA profiles of summer and winter biofilms, but less evidence for unequivocal site or light-regime effects.

Two approaches employing 16S rRNA oligonucleotide probes, in situ hybridization combined with 33P-autoradiography and 32P-labeled slot-blot hybridizations on nitrocellulose filters, were used to enumerate methylotrophic bacteria in the water column of Ryans 1 Billabong, a small floodplain lake in northeastern Victoria, Australia. Methylotrophic bacterioplankton numbered 0.6–1.2 × 109 cells liter−1 in the winter of 1994, and 0.8–5.5 × 109 cells liter−1 in the summer of 1994–95. This was equivalent to 10–46% of total bacterioplankton cell counts, determined via epifluorescence microscopy. Methylotrophic bacteria were not detected in the water column of the nearby Kiewa River, and a set of laboratory controls indicated that the high abundance of methylotrophs in the billabong samples was not a methodological artifact. There was no change, with water depth, in total bacterioplankton or methylotroph abundance in winter, a result consistent with the water column being well mixed at this time of year (dissolved O2 concentrations 5–7 mg liter−1; dissolved methane concentrations 45 cm; dissolved methane concentrations 500 μg liter−1 near the sediments) and there was a correspondingly marked increase in the abundance of total bacterioplankton and methylotrophs with depth. In situ hybridizations and slot-blot hybridizations both indicated that type II methylotrophs (detected with a probe specific for the 9-α subgroup of Proteobacteria) were markedly less abundant than were type I and X methylotrophs (detected with a probe specific for the 10-γ subgroup of Proteobacteria).

The many sheltered embayments, riverine estuaries and drowned river valleys of temperate eastern Australia support a large area and a wide diversity of coastal wetlands. This region also supports over one-half of the country’s population and includes its major tourist and industrial centres. The story of Cinderella provides an excellent simile for the status of coastal wetlands in this region of Australia: coastal wetlands provide extremely valuable ecosystem services (indeed, of considerably greater value than those provided by an equivalent area of inland wetland), yet they are undervalued by the general community, by natural-resource managers and by funding agencies. The selective investment of ecological research (including rehabilitation studies) into inland wetlands – and in particular into floodplain wetlands of the Murray–Darling Basin – has left us inadequately equipped to understand how temperate coastal wetlands function, how they will respond to climate change, and how degraded sites can be rehabilitated. Not only is an increase in research funding required, but funding has to be coordinated and focussed. The problem, however, is not only a lack of research funding; at a more fundamental level, the widespread ignorance of the value of temperate coastal wetlands needs also to be addressed.

Murray-Darling Freshwater Research CentreMDFRC item.We used the stable isotopes of carbon and nitrogen to examine the food webs of three small flood-plain lakes (billabongs) in south-eastern Australia. With few exceptions, stable carbon isotope analysis could not be used to discriminate among the conspicuous potential sources of fringing, emergent or floating vegetation or benthic detritus. These primary sources showed little spatial or temporal variation in 13C values, with means ranging from-28.5 to-26.8 in spring and-29.1 to-25.4 in late summer. Submerged vegetation had similar 13C values to the above sources in spring but showed greater spatial variation and were less 13C-depleted, considerably so in some species, in late summer. Epiphytes and algae were 13C-depleted in spring compared with the other primary sources but became more 13C-enriched in late summer. Mean 13C values for primary and secondary consumers were not only far more variable (-37.4 to-22.7) but in general were more negative than the potential food sources, particularly in spring. Using the combined information from stable carbon and nitrogen isotope analysis, we could narrow down the list of potential primary sources driving food webs in these billabongs. The freshwater crayfish (Cherax) was one of the few taxa that appeared to obtain its biomass carbon from detrital material. Gastropods and leptocerid caddis larvae on emergent or submerged vegetation obtained a mixture of carbon from epiphytes and macrophytes; in both taxa, epiphytes contributed more to biomass carbon than did the macrophytes. However, other common grazers and collector/gatherers sampled from macrophytes, e.g. baetid mayflies, chironomid larvae and atyid shrimps, were often too 13C-depleted even to have derived their biomass carbon solely from epiphytes. Many other primary consumers, including zooplankton, and mussels (Velesunio), and most of the secondary consumers, including water mites (Hydracarina), phantom midge larvae (Chaoborus) and fish, were also 13C-depleted. The enormous biomass of littoral and fringing vegetation could contribute to metazoan food webs in these billabongs only if an additional highly 13C-depleted source was consumed simultaneously. Methane released from billabong sediments could provide such a 13C-depleted carbon source that is re-introduced into metazoan food webs via the consumption of methanotrophic bacteria. Alternatively, food webs in these water bodies are largely driven by an unknown and inconspicuous 13C-depleted primary producer, such as planktonic Chlorophyta.

Murray-Darling Freshwater Research CentreMDFRC item.Billabongs, lentic waterbodies common to the floodplain of Australian rivers, differ considerably from the lotic riverine environment in terms of hydrology, physiochemical characteristics, and biological assemblages present. As little is known regarding the bacterial ecology of billabong habitats, a comparison was made of the bacterial assemblages in the water column of seven paired river/billabong sites in the Murray-Darling Basin of southeastern Australia. Billabongs supported larger populations of bacteria (1-157 x 10(9) cells liter-1; 11-10,270-mu-g C liter-1) than did rivers (1-10 x 10(9) cells liter-1; 6-143-mu-g C liter-1). Phospholipid analyses confirmed that billabongs (14-111-mu-g phospholipid fatty acid liter-1) had larger bacterial populations than rivers (< 12-mu-g liter-1). Bacterial production, measured with H-3-leucine, was also greater in billabongs (0.28-3.05-mu-g C liter-1 hour-1) than rivers (0.05-0.62-mu-g C liter-1 hour-1). Production calculated from the frequency of dividing cells confirmed this conclusion, and suggested bacterial production in some billabongs could exceed 100-mu-g C liter-1 hour-1. An INT-formazan method indicated that usually < 25% of bacterial cells were active in either habitat, but this was probably an underestimate of the bona fide value. Turnover times of glucose were usually shorter in billabongs, and the cell-specific activity greater for billabong than river assemblages. The factors most likely to be responsible for the differences between the bacterial assemblages in rivers and billabongs relate to hydrological regime and the availability of organic carbon substrates.