Conservation value of variable connectivity: aquatic invertebrate assemblages of channel and floodplain habitats of a central Australian arid-zone river, Cooper Creek

Rapidly expanding water resource development in arid and semi-arid zones of Australia threatens the flow regime and ecological integrity of the few large dryland rivers and their immense floodplains. Efforts to manage and conserve the surface waters of these rivers are hampered by limited scientific data on the ecology of their flora and fauna and on their responses to the high natural variability of flow regime that typifies dryland rivers. Irregular floods connect channel and floodplain wetlands to differing degrees and for varying periods of time but the ecological significance of this connectivity is poorly understood. On Cooper Creek, a large dryland river in central Australia, we explored the degree to which assemblage composition varied with connectivity and hydrological regime. Shortly after protracted regional flooding, we sampled aquatic macroinvertebrate assemblages from the principal microhabitats in 12 channel and floodplain wetlands. Ephemeral and temporary lakes tended to have fewer taxa than semi-permanent channel or terminal lake habitats. Although hydrological connection had only recently been lost for some wetlands, there was already evidence of divergence in aquatic macroinvertebrate assemblage composition. Disruption of the natural variability in connectivity and hydrological regime by excessive water abstraction or river-flow regulation threatens the ecological integrity and aquatic macroinvertebrate biodiversity of dryland rivers. Preservation of the irregular flow regime and sporadic connectivity underpins conservation of the mosaic of floodplain wetlands that play such a crucial role in the ecosystem functioning of rivers such as Cooper Creek.     

Sedimentation-induced eutrophication in large river floodplains – An obstacle to restoration?

Conservation and restoration of floodplain ecosystems and their specific functions often suffer from a deficient knowledge on basic processes and dynamics such as sedimentation and related nutrient inputs. In this study, we present the results of a joint analysis of site conditions and vegetation of alluvial meadows along a gradient of increasing distance to the main channel of the river Rhine. In particular we scrutinized whether the flooding frequency mediated by the ground elevation or the distance to the river channel determines the degree of eutrophication by river water and sediments.We found a remarkably strong transversal gradient in the functional floodplain. Extremely high concentrations of CAL-soluble phosphorous (more than 150 mg kg⁻¹) were measured in close proximity to the main channel. These sites were characterized by low vascular plant species richness and a significantly higher proportion of species with high nutrient demands. At a distance of 300 m from the main channel P concentrations in the soil dropped to a quarter of this figure, whereas the average species richness per plot strongly increased. Contrary to our expectations, the influence of the flooding duration was of minor importance for the nutrient status. We can specify that strong eutrophication effects induced by sediment deposits are confined to the close proximity to the main channel within a distance of 200–300 m. At more distant sites, target vegetation of flood meadows was obviously not affected by recent nutrient input in the course of flooding. Concerns by conservationists that the restoration of active floodplains by the removal of dykes will generally lead to unwanted eutrophication by river water and sediments require revision and thorough specification.     

Dispersal of Contaminant Metals in the Mining-Affected Danube and Maritsa Drainage Basins, Bulgaria, Eastern Europe

Metal dispersal in the Danube and Maritsa drainage basins resulting from metal mining activities in Bulgaria has been assessed through the collection of 611 samples of river water, river channel and floodplain sediment, and mine waste from over 218 sites. Concentrations of Cd, Cu, Pb, and Zn in river water were found to be highest in close proximity to locations of Cu and Pb–Zn mining regions in the Maritsa catchment. Downstream dispersal of solute metals in these catchments, and into the River Danube, was found to be limited by physical dilution and a well-buffered pH environment. Dispersal of contaminant metals in channel and floodplain sediment was found to be extensive. Contamination was particularly severe in the Rivers Timok and Iskar (Danube catchment) and the Topolnitsa, Chepelarska, and Arda Rivers (Maritsa catchment) and creates the potential of transboundary dispersal of contaminant metals.     

Spatial Variability of the Particle Size Composition of Overbank Floodplain Deposits

An important feature of overbank floodplain deposits is the spatial variability of their particle size composition. Analysis of such spatial variability can assist in developing an improved understanding of the transport and deposition of suspended sediment on river floodplains during overbank flood events, in investigating the fate of sediment-associated contaminants and in calibrating existing floodplain sediment deposition models. The study reported in this paper investigates the spatial variability of the grain size composition of overbank floodplain deposits at different spatial scales, through analysis of surface sediment samples collected from frequently inundated floodplain sites on the Rivers Cuhn, Stour and Severn in the UK. Significant lateral and downstream variations in the grain size composition of the sediment deposits have been documented at the study sites, and the results obtained have been interpreted in terms of the processes governing overbank floodplain flow and sediment transport and deposition, which are influenced by a number of factors including floodplain geometry and topography.     

Development and practical test of a weighable groundwater lysimeter for floodplain sites

Presently, the soil water balance of flood‐influenced soils in fluvial plains is insufficiently described. The new development of a weighable groundwater lysimeter is the basis for recording the water‐balance components precipitation, evapotranspiration, groundwater recharge, capillary rise, and interaction with the water course. Soil‐hydrologic measuring setups at two floodplain sites of the Elbe river serve for direct comparability of lysimeter measurements with data obtained on site. A groundwater control was designed for lysimeters that automatically adjusts the current groundwater level at the floodplain measuring setups and quantifies inflow into or outflow from the lysimeter. It turned out that the lysimeter developed is capable of identifying the individual water‐balance quantities at high accuracy. Contrary to previous assumptions, it was possible to prove groundwater recharge for the floodplain sites.     

Review of Ecological Engineering Solutions for Rural Non-Point Source Water Pollution Control in Hubei Province,China

Anthropogenic contamination by heavy metals in fluvial systems is mostly bound to fine-grained clay minerals and organic substances, which accumulate by vertical accretion in sediment traps along river courses (oxbow lakes, dams and floodplains). These environmental settings are considered as good archives of historical changes in contamination. Much less attention, however, is paid to deposits of river channels, which act as sourcing transport paths for these archives and/or build archives of their own. In order to provide a better insight into the spatio-temporal distribution of pollutants in channel deposits, we investigated contamination levels of Cu, Pb and Zn in a series of sediment cores along the River Morava, a left-hand tributary of the Danube River, Czech Republic. In particular, the relationships between metal concentrations, sediment lithology (facies), grain size, magnetic susceptibility and mineralogy and chemistry of fly-ash particles were investigated. Element chemistry and lithology of channel deposits were compared with those of the nearby floodplain deposits in the same catchment. Four river-channel facies were defined, ranging from sandy gravels to clayey silts, and confronted with the floodplain sediments. Al/Si ratios were found to be useful proxies of grain size, and Al was utilized as an excellent normalizing element for heavy metals, which filters out much of the grain size effects on contamination. The floodplain deposits are significantly less contaminated than their river-channel counterparts. Heavy-metal contamination of river bed sediments (expressed as enrichment factors, EFs) is not simply bound to fine-grained particles, and much of the contamination was found in coarse-grained, sandy facies. Elevated EFs of Zn, Cu and Pb in several sediment layers, which show high magnetic susceptibility (MS), high values of MS normalized to Fe and a high proportion of magnetic fly-ash spherules and their chemistry suggest that significant part of the heavy-metal contamination can be carried by magnetic fly-ash spherules. A part of this contamination is bound to coarse-grained fluvial facies, indicating that the magnetic spherules can be transported as bed load sediments. Magnetic pollution and heavy-metal pollution can therefore coincide in river bed deposits. It is suggested that most of this contamination can be related to local point sources of pollutants (fly-ash deposit spills).     

Nitrate Loss for Denitrification during High Frequency Research in Floodplain Groundwater of the Tama River

This study aims to identify the possible roles of a floodplain inbiogeochemical nitrogen cycles, based on analysis of groundwaterdynamics of inorganic nitrogen species. Groundwater samples collected from boreholes made of poly vinyl chloride located onthe floodplain in the middle reach of the Tama River, Nagata district were analyzed for dissolved organic carbon, dissolved oxygen, inorganic nitrogen compounds, major anions and the stableisotope ratio of nitrate-nitrogen.Dissolved oxygen in groundwater samples collected from marked borehole (G-5) was low (50 ± 16 μM) and nitrate decreasedfrom 63 μM to < 10 μM during our research period. Concentrations of nitrate, nitrite and nitrous oxide decreased one after the other. These decreases in concentration, combinedwith ¹⁵N-enrichment of groundwater nitrate suggest denitrification as a significant nitrate sink, yielding an isotopic fractionation of nitrate-nitrogen with an enrichment factor (ε= –17.9‰) that is comparable tothose in various soil and groundwater systems. This study provesthat floodplains can perform as nitrogen sinks for groundwaterin river catchments.     

Morphological diagnostics of pedogenesis on the anthropogenically transformed floodplains in Moscow

At present, many parts of river valleys, including floodplains, are being actively used for urban construction. This leads to the disturbance of normal functioning of the valleys; alluvial deposits and soils become buried under the thickness of various anthropogenic materials. Four profiles of typical urban soils (urbanozems) developed on the floodplain of the Moskva River and its small tributaries have been studied. The macro- and micromorphological characteristics (including data of submicroscopic studies) and the chemical and physicochemical properties of these soils are analyzed. It is shown that the influence of ground-water on the anthropogenically transformed soils of floodplains and low terraces is preserved even upon the cessation of regular flooding. The substitution of urban pedosedimentogenesis for alluvial pedosedimentogenesis has a gradual character with a transitional stage of simultaneous occurrence of both processes. Clayey and clayey-calcareous infillings in the middle-profile horizons and newly formed phosphates of iron and calcium in the lower horizons affected by the groundwater can be considered typical diagnostic features of the urban-alluvial pedogenesis.     

Status Quo of Soil Contamination with Inorganic and Organic Pollutants of the River Oka Floodplains (Russia)

The contamination status of rivers and their floodplains with inorganic and organic pollutants in central Russia is poorly known. We investigated the concentrations of inorganic (As, Cd, Cu, Hg, Ni, Pb and Zn) and persistent organic pollutants (hexachlorocyclohexane, PCBs, cyclodienes, DDX and other pesticides) in floodplain soils of the Oka River catchment (Russia). The level of contamination was generally lower than in the Elbe River floodplain but in the same range as in other European river systems such as floodplains of the rivers Rhine, D?evnice and Yachroma. Only soil samples from the periphery of the city of Ryazan (200 km southeast of Moscow) had a higher anthropogenic enrichment of Cd, Cu and Zn which was comparable to the contaminated Elbe River floodplains. These soils also had the largest concentrations of persistent organic pollutants among all samples from the Oka River catchment. Therefore, the need for large-scale remediation seems to be less urgent than in Central European river catchments and mainly restricted to some “hot spot” areas.     

Influence of variable inundation regimes on soil collembola

Soil collembola in floodplain habitats are known to react dynamically to inundation, showing direct negative effects of inundation as well as rapid regeneration after flooding. Unknown, however, are how these communities react to variable inundation and the role that spatial and temporal habitat heterogeneity plays. Therefore, the small-scale spatio-temporal dynamics of soil collembolan communities after varying inundation were studied in floodplain habitats in the Upper Rhine Valley in Germany. After frequent flooding, significant differences in density and species richness were found between different floodplain levels of the same location. Due to different species’ responses, major differences occurred in community structure. After infrequent inundation the densities and species richness of the same sites and especially hygrophilous components decreased dramatically. Between neighbouring sites, species exchange occurred and community structures became more similar. The results show that at the same locality soil collembola react dynamically as well as differentially to changes in the hydrological regime. Small-scale landscape heterogeneity allows a mixture of differentially reacting species to occur within the same regional metacommunity. Long-term stability of collembolan communities despite the high spatio-temporal heterogeneity of floodplains is thus maintained by metacommunity dynamics.     

Spatial distribution characteristics of organic matter and total nitrogen of marsh soils in river marginal wetlands

Contents of soil organic matter (SOM) and total nitrogen (TN) in the surface soils and subsurface soils were measured in five types of floodplains classified with different flood frequencies in river marginal wetlands of Erbaifangzi, China, in 1999. Contour maps and profile maps were constructed to describe the spatial distribution of SOM and TN in order to identify the influences of flood frequency on them. Results showed that spatial distributions of both SOM and TN were very similar in soil profiles (0–120 cm) of the five areas, decreasing gradually with depth except an accumulation peak in the flooded floodplain (B area). Also, the accumulation peak in the soil profile of B area was relevant to water table, nitrogen leaching, denitrification and mineralization. However, their horizontal distributions in surface soils (0–10 cm) were different in the five areas. Although the flood could bring the deposit of nutrients and sands, the highest content of SOM or TN did not appear in B area but in the floodplain with certain flood frequency. For example, SOM content (6.76%) in 5-year floodplain wetland was highest, and the highest content of TN (3666.4 mg/kg) appeared in 1-year floodplain wetland. However, SOM and TN contents in soils of B area were 4.08% and 2605.4 mg/kg, respectively. Soil clay content, wetland plant (Phragmites australis) litter inputs, soil moisture and water table greatly affected the spatial distribution of SOM and TN in floodplain wetlands. The ratios of carbon to nitrogen of wetland soils in this region were relatively lower than those in paddy soils. SOM and TN contents were significantly correlated with total phosphorus (TP) contents in floodplain wetlands except the 100-year floodplain wetland, but they were significantly influenced by soil pH values only in B area. Denitrification and ammonia volatilization were the main mechanisms resulting in nitrogen loss of surface soils in B area. Flood frequency significantly influenced the ecological functions such as nutrient retention and water quality maintenance of floodplains.     

英国Culm河河漫滩沉积物中磷素时空变化研究

河漫滩上沉积物的沉积伴随着与沉积物相结合的营养和污染物质的沉积。已有研究表明,河漫滩是与沉积物相结合的磷的沉积地。采用137Cs技术,并结合河漫滩沉积物中全磷(TP)含量的剖面信息,可以调查近年河漫滩沉积物中的TP含量,计算TP储量。本文根据英国Devon郡Culm河8个河漫滩采样环沉积物中的数据,重建了在过去40～50年内TP储量和含量的变化。结果表明,在Culm河河漫滩沉积物中,在1963～2000年间TP平均含量为0.60～1.96gkg-1,该值自河流上游向下游和自过去到现在有逐渐增加的趋势;在相同的河漫滩沉积物中,在相同的时期内TP储量为18.62～435.48gm-2,即0.49～11.46gm-2a-1,最大值出现在河流的中游。     

Hyporheic flow as a potential geomorphic agent in the evolution of channel morphology in a gravel-bed river

Morphologic and hydrologic properties of head-cut gullies formed in meandering bends of a gravel-bed river in northern Japan were examined to investigate their topographic development. head-cut gullies had incised to 2 m below the floodplain surface and had perennial seepage outflows. Because no surface runoff was observed across the meandering necks, we hypothesized that hyporheic flow erosion cutting into the down-river edge of the meandering necks is one factor for the development of head-cut gullies. Several topographic features caused by sapping and piping erosion were observed within the head-cut gullies. A tracer experiment and examination of the water table, water chemistry, and water table responses in wells on the floodplain and within the head-cut gully revealed that significant preferential hyporheic flow occurred between coarse cobble and fine sediment layers of the floodplain materials. During a storm event, water tables around the head-cut gully quickly responded to changes in the water table of the stream channel; this result also suggests that hyporheic flow occurred across the meandering bends. Hyporheic flow around the head-cut gullies had higher hydraulic conductivities and preferential flow paths that may relate to buried beds of paleochannels. An erosion model suggests that it is unlikely that hyporheic flow alone had enough energy to account for all the soil erosion. Thus, a combination of hyporheic flow (sapping erosion) and channel erosion (bank erosion) appeared to contribute to the formation of the head-cut gullies. Hyporheic flow is an important component in the geomorphic evolution of channels and the floodplain in a gravel-bed river.     

英国Culm河河漫滩沉积物中磷素时空变化研究

河漫滩上沉积物的沉积伴随着与沉积物相结合的营养和污染物质的沉积.已有研究表明,河漫滩是与沉积物相结合的磷的沉积地.采用137Cs技术,并结合河漫滩沉积物中全磷(TP)含量的剖面信息,可以调查近年河漫滩沉积物中的TP含量,计算TP储量.本文根据英国Devon郡Culm河8个河漫滩采样环沉积物中的数据,重建了在过去40～50年内TP储量和含量的变化.结果表明,在Culm河河漫滩沉积物中,在1963～2000年间TP平均含量为0.60～1.96 g kg-1,该值自河流上游向下游和自过去到现在有逐渐增加的趋势;在相同的河漫滩沉积物中,在相同的时期内TP储量为18.62～435.48 g m-2,即0.49～11.46 g m-2 a-1, 最大值出现在河流的中游.     

Does reproductive plasticity in Lumbricus rubellus improve the recovery of populations in frequently inundated river floodplains?

Flooding events often eradicate all of the individuals of the earthworm species Lumbricus rubellus living in river floodplains, although earthworm cocoons usually survive immersion, permitting populations to recover after the flood waters recede. Yet, if the area is flooded again before earthworms hatching from cocoons or migrating from adjacent areas reach reproductive maturity, it is unlikely that their populations will recover. The objective of this study is to determine the importance of the length of the dry period for population recovery in L. rubellus. Earthworms were collected at three floodplain sites along the Rhine River that were frequently, moderately or seldom flooded. Reproductively mature L. rubellus from the frequent flooded site were half the weight and probably younger than those from the other sites. A mechanistic population model was used to estimate the time for earthworm development from hatching to reproductive maturity, and to calculate the probability of population recovery after flooding. The model results show that the probability of extinction increases when the dry period is not long enough for individuals to reach reproductive maturity. When this condition is met population extinction is virtually absent resulting from the high lifetime reproductive output of L. rubellus. Parameterization of the model with site-specific data indicate that population survival on the site with the shortest dry period drastically decreases if worms mature at the weight measured at the other sites. The results therefore strongly suggest that the dry period is critical for population recovery in river floodplains and that earthworm populations have adapted to local (site-specific) conditions.     

Genetic and ecological impacts of heavy metal and flooding stress on the earthworm Lumbricus rubellus in floodplains of the Rhine river

In the highly polluted river Rhine system, earthworms face environmental stress resulting from flooding and elevated heavy metal concentrations in the floodplain soil. Previous field studies have revealed adaptation to flooding for the earthworm species Lumbricus rubellus as this species matures at a lower weight in floodplain sites with a high frequency of flooding compared to less frequently flooded sites. Also heavy metals have effects on L. rubellus and heavy metals are influencing the genetic composition of this species. In this study, it was tested whether flooding and heavy metals had an impact on the genetic composition of L. rubellus living in floodplains along the river Rhine system. Earthworms were sampled at three sites previously studied along the river to assess earthworm diversity, biomass, density, and individual weight, and developmental status of L. rubellus. The genetic variation by means of isozymes was studied for 175 individuals. The results showed lowest density of L. rubellus adult and sub-adult life-stages and lowest individual weight of these life-stages at the frequent inundated site. The genetic composition, however, showed no effects of flooding on the genetic composition, but effects of heavy metals could not be ruled out.     

SOIL GENESIS IN RELATION TO GROUNDWATER AND SOIL MOISTURE REGIMES NEAR VEGREVILLE,ALBERTA1

The study was designed to obtain information on flow and salinity of the groundwater, and on moisture regimes above the water table at selected sites near Vegreville, Alberta, and to relate this information to features of soil genesis revealed by soil mapping and analysis. All soils on the lower slopes, unlike those at upper elevations, contained accumulations of salts and gypsum, but the depth of salt accumulation and therefore the kind of soil appeared to be related only partly to current groundwater flow directions and the depth of the water table. The sodium content of the discharging groundwater and past flow conditions also appeared to be important. Lateral flow above the water table is suggested as being of possible importance in desalinization of surface horizons.     

Comparative analysis of the soil cover diversity in floodplain areas of the Partizanskaya River valley (Sikhote-Alin Mountains)

The regularities of the soil cover formation and pattern in the Partizanskaya River valley (Sikhote-Alin Mountains) were revealed. The diversity of the soil cover was shown to depend on the landscape hydrological zone of the river basin, the structure of the floodplain, and the difference in flooding of the floodplain sections. The comparative assessment of the soil cover diversity using the Shannon index showed that, in the zone of accumulative landscapes, the soil cover diversity of the floodplain sections that were formed under the meandering of the river was higher than the diversity of the soil cover in the sections formed upon branching (furcation) of the channel. The maximum values of the Shannon index and the maximum supply with water characterize the floodplain in the mouth zone of the valley with the most stable conditions of soil formation. The determination of the diversity index for the soil cover and water supply of the floodplain sections is expedient in planning the economic activities in the valley.     

Water Exchange and Deposition of Sediment and Phosphorus during Inundation of Natural and Restored Lowland Floodplains

Water exchange, flow patterns and deposition of sediment and phosphorus were measured in cross-sections of a naturally functioning floodplain during one winter and in three restored floodplains following remeandering of formerly straightened and channelized rivers. Sediment and phosphorus depositional processes were studied, deploying artificial grass mats at different distances from the river channel. In addition, a mass-balance approach was applied on the experimental site. Our results show that the deposition of sediment and particulate phosphorus constituted 3,000–4,700 g DW m^?2 and 1.2–7.3 g P m^?2, respectively, on the four floodplains studied during a winter where flood duration lasted between 20 and 76 days. The storage efficiency for sediment ranged between 28–47 and 4.0–7.0% for phosphorus.     

Optimal farm management responses to emerging soil salinisation in a dryland catchment in eastern Australia

Secondary salinisation of soil and water resources is an acute management issue over large parts of Australia. This paper focusses on the situation in the Liverpool Plains, where secondary soil salinity is on the increase due to rising saline groundwater tables. The Liverpool Plains are famous for the vast alluvial floodplains where self-mulching black clays provide the production basis for an extensive dryland cropping industry. The farmers there are asking how best to manage their resources under the present hydrological conditions, and are concerned whether their businesses will remain viable in the future. A multi-period programming model is applied to a model farm situation. The objective function reflects the economic paradigm of farming. The model includes a simulation sub-routine which links land use, rainfall and lateral groundwater flow into a point water balance and estimates the salt-affected area. A feedback relationship applies between soil salinity and land productivity. The results of the model suggest that the prevailing cropping practices that rely on long fallowing for soil moisture retention are sub-optimal. Increased cropping frequency increases farm income and reduces on-farm recharge to groundwater. Diversification into lucerne is favourable for the same reasons. Unless trees have commercial value, tree planting is not a favoured option except on salt-affected land. The farm achieves complete on-farm recharge control. However, assuming that the groundwater table rises at a rate of 10 cm per year independent of on-farm recharge, salinisation continues despite these land management changes. The subsequent land productivity losses render the model farm financially unviable in the medium term. Sustaining the productivity of the Liverpool Plains is an issue of reducing recharge to the groundwater system by changing land-use practices throughout the entire catchment. © 1997 John Wiley & Sons, Ltd.