Interactions between period of exposure,grazing and crop growth rate of Cynodon dactylon (L.) Pers. in seasonally flooded areas of the Pongolo River floodplain

Cynodon dactylon (L.) Pers. forms extensive meadows on seasonally inundated areas of the Pongolo river floodplain. As floodwaters receded during winter, the shoots of C. dactylon which had not decomposed during submergence sprouted. Crop growth rate was high (up to 23 kg/ha/d dry mass) and the meadows were heavily grazed by domestic stock which removed up to 15 kg/ha/d. The high crop growth rate was not maintained because as exposure period increased, soils became dry and water stress conditions developed. This caused the C. dactylon to become less palatable and brought about a shift in grazing which allowed a build-up of the grazeable and ungrazeable fraction standing crop. Maximum standing crop occurred at the onset of the next flood. Grazing is shown to have a net negative effect on production, although at different times during exposure defoliation had either a depressing or stimulating effect on growth. It is postulated that the duration of the inundation period is more significant than the duration of the exposure period in maintaining the C. dactylon meadows.     

Decomposition of Cynodon dactylon (L.) Pers. in the seasonally flooded areas of the Pongolo river floodplain: pattern and significance of dry matter and nutrient loss

Cynodon dactylon meadows occupying seasonally inundated areas of the Pongolo river floodplain, South Africa, decompose during periods of submergence. The loss of dry matter and nutrients from both fresh and dried material enclosed in litter bags was studied. The pattern of loss of dry matter was diphasic. Loss was more rapid from dried than from fresh material, half the mass being lost in 18 and 28 days respectively. Nutrient loss followed an exponential pattern. Nitrogen, phosphorus and magnesium were lost more rapidly from dried than from fresh material whilst rates of loss of sodium, potassium and calcium were similar. The significance of Cynodon decomposition in the functioning of the floodplain is assessed from estimates of the above- and below-ground standing crop around one small lake before and after submergence. It is concluded that decomposition of plants growing in seasonally inundated areas of the floodplain may contribute significantly to the productivity of the system, but that the extent of the contribution can be greatly influenced by the flooding regime. The completion of the Pongolapoort dam upstream of the floodplain will alter the natural flooding pattern, effecting a reduction in floodplain productivity, unless a programme for flood release can be initiated.     

The filtration rate of the zebra mussel Dreissena polymorpha used for water quality assessment in Dutch rivers

The effects of contaminated river water on the filtration rate of zebra mussels from a clean reference site were studied. After a 48-h exposure period to filtered water from the rivers Rhine, Meuse and Amstel (The Netherlands), the filtration rate was measured. It was demonstrated that water from contaminated locations inhibited the filtration rate. Inhibition was higher during low water levels in the rivers Rhine and Meuse than during high water levels, suggesting that contaminants are diluted during high water levels. It is concluded that the shortterm filtration assay with D. polymorpha can be used for assessing water quality.     

Devasting effects of river flooding to the ground-nesting bee, <Emphasis Type="Italic">Andrena vaga</Emphasis> (Hymenoptera: Andrenidae), and its associated fauna

Large populations of non-social bees are rarely seen in today's cultural landscapes. One of the few exceptions is the fossorial bee Andrena vaga Panzer, (Andrenidae), a typical insect species of river flood plains, which forms sizeable nesting aggregations along the high water dams of the Upper Rhine, each containing up to several tens of thousands of bees. In May 1999, a record flood of the River Rhine led to extreme water levels at the high water dams of the Upper Rhine. Though natural flooding is often viewed as a management practice with considerable conservation perspectives for river flood plain management, we demonstrate a catastrophic effect of the 1999 inundation on the immature offspring of two affected populations of A. vaga. All immatures in brood cells located low on the landward side of a dam died, very likely because saturation of the soil restricted oxygen availability.The two affected aggregations sited on the high water dam declined in the following year to 23 and 56% of pre-flood size, but not at a neighbouring, non-flooded aggregation. Rare parasites associated with A. vaga also decreased in number following flooding. These results highlight a dilemma on the use of natural flooding of river plains for conservation purposes.     

Damming interacts with the flood pulse to alter zooplankton communities in an Amazonian river

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Fish Collections Taken from a Small Agricultural Water Withdrawal Site on the Groot River,Gamtoos River System,South Africa

Summary

Periodic water releases from Beervlei Dam on the Groot River of the Gamtoos River System were planned to flush the riverine pools of brack water and replace the pools with better quality water which was used to flood irrigate lucerne lands. Fish collections were made in a small irrigation canal situated on the banks of the Groot River. Three fish species were collected. Results indicated that up to a total of 131 smallscale redfin minnows, Pseudobarbus asper, are removed from the system every five minutes at this one small water withdrawal site. Larger minnow specimens and carp, Cyprinus carpio, were entrained during high river flows. When the river flow was reduced there were higher catches of young of the year fish. The fish are carried with the pumped water, which is flood irrigated onto lucerne fields, resulting in stranding and eventual mortality. It is recommended that the use of suitable screens, such as wedge-wire screens, could reduce the number of fish removed from the system during these irrigation periods.     

Influence of maternal stress on metal-induced pre- and postnatal effects in mammals

Studies in rodents have shown that, during pregnancy, maternal stress from restraint, noise, light, and heat among other factors may be associated with adverse effects on embryo/fetal and postnatal development. Moreover, it is also well known that exposure to certain metal levels during gestation can also cause maternal and developmental toxicity. Because potentially, pregnant women may be concurrently exposed to metals and various types of stress, the influence of maternal stress on the metal-induced adverse pre-and postnatal effects has been investigated for a number of elements. This influence is reviewed here. It is concluded that maternal stress enhances the metal-induced embryo/fetal and developmental toxicity only at doses of the metal which are also clearly toxic to the dam.     

Variations in stream water uptake by Eucalyptus camaldulensis with differing access to stream water

The stable isotopes ²H and ¹⁸O were used to determine the water sources of Eucalyptus camaldulensis at three sites with varying exposure to stream water, all underlain by moderately saline groundwater. Water uptake patterns were a function of the long-term availability of surface water. Trees with permanent access to a stream used some stream water at all times. However, water from soils or the water table commonly made up 50% of these trees' water. Trees beside an ephemeral stream had access to the stream 40–50% of the time (depending on the level of the stream). No more than 30% of the water they used was stream water when it was available. However, stream water use did not vary greatly whether the trees had access to the stream for 2 weeks or 10 months prior to sampling. Trees at the third site only had access to surface water during a flood. These trees did not change their uptake patterns during 2 months inundation compared with dry times, so were not utilising the low-salinity flood water. Pre-dawn leaf water potentials and leaf ¹³C measurements showed that the trees with permanent access to the stream experienced lower water stress and had lower water use efficiencies than trees at the least frequently flooded site. The trees beside the ephemeral stream appeared to change their water use efficiency in response to the availability of surface water; it was similar to the perennial-stream trees when stream water was available and higher at other times. Despite causing water stress, uptake of soil water and groundwater would be advantageous to E. camaldulensis in this semi-arid area, as it would provide the trees with a supply of nutrients and a reliable source of water. E. camaldulensis at the study site may not be as vulnerable to changes in stream flow and water quality as previously thought.     

Influence of maternal stress on metal-induced pre- and postnatal effects in mammals: a review

Studies in rodents have shown that, during pregnancy, maternal stress from restraint, noise, light, and heat among other factors may be associated with adverse effects on embryo/fetal and postnatal development. Moreover, it is also well known that exposure to certain metal levels during gestation can also cause maternal and developmental toxicity. Because potentially, pregnant women may be concurrently exposed to metals and various types of stress, the influence of maternal stress on the metal-induced adverse pre- and postnatal effects has been investigated for a number of elements. This influence is reviewed here. It is concluded that maternal stress enhances the metal-induced embryo/fetal and developmental toxicity only at doses of the metal which are also clearly toxic to the dam.     

First record of ostracods (Crustacea) in Baltic amber

Ostracods were found in two pieces of Baltic amber for the first time. The animals belong to the freshwater genus Cyclocypris. Since Baltic amber was formed during Eocene times in southern Scandinavia, the age of the specimens is estimated at 42–54 million years. As aquatic organisms, ostracods are seldom trapped in amber; it is considered that one specimen, already dead and dried, was either blown onto sticky resin on a plant stem, or washed there by a high flood level, while the other was probably splashed, alive, in a drop of water against the flowing resin, again probably during a flood. Associated faunal remains, including other crustaceans, suggest a coastal palaeoenvironment with some marine as well as freshwater influence.     

Waterfowl of a subtropical African floodplain

Many water bodies in arid southern Africa are seasonal and waterfowl habitats become restricted during the dry winters. Nevertheless, some tropical species, such as the white-faced duck, are expanding their ranges into more temperate regions where summer habitats are available, thus increasing pressure on overwintering habitats. The subtropical Pongolo River floodplain is an important overwintering area for a diverse water-fowl community that includes 13 of the 16 species that breed in South Africa and one of the few regular migrants. Historical evidence suggests that numbers of white-faced duck, which represent over 70% of the floodplain community, have increased 10-fold over the last two decades. An abundant, nutritious food (Potamogeton crispus turions) attracts waterfowl to the Pongolo floodplain during winter and an increase in bird fat reserves suggests that they leave for summer breeding grounds in good condition. Unseasonal flood releases from an upstream reservoir may cause low food supplies in late spring before the onset of the summer rainy season when breeding habitats become available. This study emphasizes the need for a better understanding of the role of winter habitats in maintaining waterfowl populations.     

Increased drought tolerance of mycorrhizal onion plants caused by improved phosphorus nutrition

Onion plants (Allium cepa L, cv. Downing Yellow Globe) grown in pots and infected by the mycorrhizal fungusGlomus etunicatus Becker and Gerdemann were more drought tolerant than were non-mycorrhizal individials when exposed to several periods of soil water stress separated by periods of high water supply, as shown by greater fresh and dry weights and higher tissue phosphorus levels in the mycorrhizal plants. The tissues of stressed, non-mycorrhizal plants were deficient in P, despite the fact that only non-mycorrhizal plants were fertilized with high levels of P (26 mg P per 440 g soil). Differences in plant water relations (leaf water potentials or transpiration rates) and changes in soil P levels which may have affected plant growth were investigated, and discounted as factors important for the results. The P nutrition of plants has been implicated in the ability of plants to tolerate drought and it was concluded that the ability of the mycorrhizal fungus to maintain adequate P nutrition in the onions during soil water stress was a major factor in the improved drought tolerance. Infection of the root by the fungus was found not to be affected by water stress or P fertilization but fungal reproduction, as determined by spore numbers in the soil, was decreased by water stress and by P fertilization.Michigan Agricultural Experiment Station Article No. 10050     

Translocation and Spread of Piscivorous Fishes in the Burdekin River, North-eastern Australia

The distribution of the biogeographically distinctive fish fauna of the Burdekin River, north-eastern Australia, is largely determined by the presence of a large waterfall located at the lower quarter of the river’s length. Downstream of the falls, assemblages are characterised by the presence of piscivorous fishes whereas such species are largely absent from upstream reaches. Sleepy cod (Oxyeleotris lineolatus), a large piscivorous gudgeon, was first introduced into the upper reaches of the Burdekin River in 1980 and other releases, both official and unofficial, have occurred subsequently. The population remained small and restricted to the site of introduction for a decade, but expanded in size and distribution after the occurrence of a large flood and entry into a prolonged period of drought. This gudgeon is now present in every tributary system of the Burdekin Basin. Despite the occurrence of substantial temporal variation in fish abundance due to a highly variable flow regime, negative impacts on one species, a small gudgeon (Mogurnda adspersa), are evident. Both deliberate and accidental releases of other species into the upper Burdekin River have also occurred, often to satisfy recreational fishing demand. Such species are typified by large size and piscivorous habit, characteristics alien and inimical to the native fish fauna. It is hypothesised that these piscivorous species may have even greater impact than O. lineolatus in some tributary systems of the upper Burdekin River.     

Combining limnological and palaeolimnological approaches in assessing degradation of Lake Pskov

Historical spawning grounds for sea lampreys (Petromyzon marinus L.) in most Portuguese river basins are becoming inaccessible due to the construction of impassable dams and/or weirs. Studies like the one described in this paper are particularly important in areas like the Vouga river basin, where there is a considerable fishing effort from both professional fishermen and poachers. In fact, for management and conservation purposes, it is important to clarify several aspects of the sea lamprey spawning run in this particular watershed. Therefore, a total of 30 radio tagged, migrating sea lampreys were released in the River Vouga and some of its main tributaries during 2004 and 2005. Results from the tracking sessions were used to determine the effect of poaching on the spawners’ population and the characteristics of the resting sites used during the upstream movement. The rivers’ stretches were also characterized according to the type of substrate present in the riverbed and flow type, in order to determine its aptitude to constitute appropriate spawning habitats for sea lampreys. We have identified in the upstream stretches of River Vouga, and in the tributary River Caima, characteristics that are particularly suitable for the construction of nests by the spawners. Presence of larvae provided evidence that spawners migrated into the River Vouga’s upper reaches. However, abundance and age class diversity appeared to be higher downstream of Sernada and Carvoeiro weirs, corroborating the telemetry data which suggested difficulty in passing these obstacles during low precipitation years. In the River Caima, migration was most predictable, which might be related to daily water releases from a small hydropower dam at dusk, that stimulated the lampreys to resume migration. Poaching has had a considerable negative effect on the success of the tagged lampreys’ migration: 76% of the animals released during 2005 were captured. Electronic supplementary material  Supplementary material is available for this article at and accessible for authorized user     

Nitrate and Nitrite Reduction in Wheat Leaves as Affected by Different Types of Water Stress

The effect of different types of water stress on nitrate and nitrite reductases of wheat (Triticum vulgare L. cv. Mivhor) leaves was investigated. Water stress was applied either to leaf tissue by its incubation in mannitol or various salt solutions, or to intact plants by exposure of the root system to low temperatures or to salinity. Nitrite reductase was much less sensitive to water stress than nitrate reductase, and was not sensitive to salinity up to osmotic potentials of about — 13 bars. The decrease in nitrite reductase activity by water stress was attributed to a direct inhibition of the enzyme rather than to a repression of enzyme synthesis. This was based on the fast response of the enzyme after exposure of leaf tissue to reduced osmotic potential, on the lack of a continuous decrease in enzyme activity during a prolonged stress, and on the fact that light activation of reductase was unaffected by water stress. The inhibition of nitrate reductase under water stress was attributed to both a direct inhibition and a reduced rate in enzyme synthesis. This is concluded from the fact that a decrease in its activity was obtained already within 1 h after stress application and from the fact that light induction of the enzyme was inhibited by stress.     

The Rufiji River flood: plague or blessing?

The building of a large multipurpose dam is planned at Stiegler’s Gorge on the Rufiji River (Tanzania). Both national and local authorities have strongly emphasised the flood control aspect of the dam as they see the Rufiji floods as a major constraint to development. Though it is true that the Rufiji River has a high flow variability at various timescales, the flood perception in local communities differs from this view. The floods, essential for the sustenance of floodplain fertility, and therefore of the farming system, and vital to the productivity of most of the natural resources on which local communities depend, are perceived as a blessing, whilst droughts and the absence of regular flooding are perceived as the main threat. Historically, most of the food shortages in Rufiji District are associated with drought years and the myth of “the flood as a plague” emerged only in the late 1960s during the Ujamaa villagisation policy. The persistence of this myth is favoured by the inadequate assessment of the complexity of the local economies by the District technical staff. This difference in perception of the flood has major implications for development options. Under the current dam design, the alteration of the flooding pattern would have negative consequences for the downstream wetland and forest ecosystems and the flood-associated livelihoods of some 150,000 people. A cost-benefit analysis of flood control measures and a study of a dam design that would maintain the beneficial aspects of flooding should be accorded the highest priority.     

Floating vegetation mats on a floodplain billabong in the Northern Territory of Australia

The floristics and physical structure of a floating mat of vegetation in the Finniss River area of the Northern Territory are described. During the dry season floating mats contain green productive vegetation when the adjacent flood plains are dry and many of the plants are withered. At this time insects are more abundant on the mats than on the adjacent flood plain. Some flood plain vertebrates appear to concentrate their activity on floating mats during the dry season. During the period 1963 to 1978 the area of floating mat in the Finniss River study area was greatly reduced, probably as a result of high densities of feral water buffalo (Bubalis bubalus).(Present address: c/o 38 Hardy Terrace, East Ivanhoe, Victoria 3079).(Present address: c/o 38 Hardy Terrace, East Ivanhoe, Victoria 3079).     

Biological control of three floating water weeds,<Emphasis Type="Italic">Eichhornia crassipes,Pistia stratiotes</Emphasis>, and <Emphasis Type="Italic">Salviniamolesta</Emphasis> in the Republic of Congo

Since 1999, four specific weevils (Coleoptera, Curculionidae) were released in the Republic of Congo against three exotic floating water weeds: Neochetina eichhorniae Warner and N. bruchi Hustache against water hyacinth, Neohydronomus affinis Hustache against water lettuce, and Cyrtobagous salviniae Calder and Sands against water fern. Recoveries of exotic weevils were made from all 24 release sites except one, and all four species have established and spread (up to 800 km for water hyacinth weevils). Within a few years of releases, control of water fern and water lettuce was such that fishing and navigation could be resumed, while reductions of water hyacinth populations were only beginning.     

Synchrony of Seed Dispersal, Hydrology and Local Climate in a Semi-arid River Reach in California

The temporal availability of propagules is a critical factor in sustaining pioneer riparian tree populations along snowmelt-driven rivers because seedling establishment is strongly linked to seasonal hydrology. River regulation in semi-arid regions threatens to decouple seed development and dispersal from the discharge regime to which they evolved. Using the lower Tuolumne River as a model system, we quantified and modeled propagule availability for Populus fremontii (POFR), Salix gooddingii (SAGO), and Salix exigua (SAEX), the tree and shrub species that dominate near-channel riparian stands in the San Joaquin Basin, CA. A degree-day model was fit to field data of seasonal seed density and local temperature from three sites in 2002–2004 to predict the onset of the peak dispersal period. To evaluate historical synchrony of seed dispersal and seasonal river hydrology, we compared peak spring runoff timing to modeled peak seed release periods for the last 75 years. The peak seed release period began on May 15 for POFR (range April 23–June 10), May 30 for SAGO (range May 19–June 11) and May 31 for SAEX (range May 8–June 30). Degree-day models for the onset of seed release reduced prediction error by 40–67% over day-of-year means; the models predicted best the interannual, versus site-to-site, variation in timing. The historical analysis suggests that POFR seed release coincided with peak runoff in almost all years, whereas SAGO and SAEX dispersal occurred during the spring flood recession. The degree-day modeling approach reduce uncertainty in dispersal timing and shows potential for guiding flow releases on regulated rivers to increase riparian tree recruitment at the lowest water cost.     

Transgenic Plants of Creeping Bent Grass Harboring the Stress Inducible Gene, 9-cis-epoxycarotenoid dioxygenase, are Highly Tolerant to Drought and NaCl Stress

Transgenic lines of creeping bent grass were generated by Agrobacterium-mediated transformation with the VuNCED1 which was cloned from cow pea has a homology to 9-cis-epoxycarotenoid dioxygenase, which is supposed to be involved in abscisic acid (ABA) biosynthesis. ABA, a cleavage product of carotenoids, is involved in stress responses in plants. The limiting step of ABA biosynthesis in plants is presumably the cleavage of 9-cis-epoxycarotenoids, the first committed step of ABA biosynthesis. Molecular analyses of transgenic lines as performed by Southern hybridization genomic DNA-PCR revealed integration of the VuNCED1. Challenge studies performed with transgenic plants by exposure to salt stress (up to 10 dS m⁻¹) and water stress (up to 75%) for 10 weeks, revealed that more than 50% of the transgenic plants could survive NaCl and drought stress whereas wild-type was not. ABA levels were measured under drought and normal conditions, endogenous ABA was dramatically increased by drought and NaCl stress in transgenic plants. These results indicate that it is possible to manipulate ABA levels in plants by over expressing the key regulatory gene in ABA biosynthesis and that stress tolerance can be improved by increasing ABA levels. Chenna Reddy Aswath and Sun Hyung Kim - First two authors contributed equally to this work