Natural disturbances influence wetland carbon cycling, and fire is a key driver of terrestrial carbon stocks. However, the influence of fire on wetland carbon cycling remains poorly understood. Here, we investigated how prescribed fire and wildfire impact soil carbon storage in a forested floodplain of south-eastern Australia. We sampled four areas within Murray Valley National Park, the world’s largest river red gum (Eucalyptus camaldulensis) stand, and compared soil carbon (C), nitrogen (N) and C:N ratios between control (unburnt in the 50 years prior to sampling), prescribed burn and wildfire-impacted floodplain areas. Mean soil C and N concentrations were 4.7% ± 0.32% and 0.36% ± 0.02%, respectively, and mean C:N ratios were 14.23 ± 0.33. Carbon concentrations and C:N were highest in control areas of the floodplain, while N concentrations were highest at wildfire-impacted areas. However, flood frequency was a stronger driver of soil C than fire disturbance. Soils at more frequently flooded areas had higher C concentrations compared to less frequently flooded areas, suggesting that resilience to C loss through fire could be enhanced through hydrological restoration. We believe this warrants further research as a potential nature-based climate measure. Mean C density data indicate soil C stocks of 9.4 Tg across Barmah-Millewa Forest, highlighting the significant carbon storage value of this ecosystem.

Fluvial and colluvial deposits of Late Holocene age in South-Central Ontario catchments have provided few 14C dates, most by conventional methods registering century-old ages. Other young deposits, dated by conventional and accelerator mass spectrometry radiocarbon (AMS 14C), have yielded bomb-affected post-1950 ages over variable time limits. Attempts to date the base of Ah and lower-in-section soil horizons, in Early to Late Holocene stream terrace deposits, have yielded atomic bomb effects. Comparing bomb contamination in Late Holocene fluvial deposits, using both conventional and AMS methods, identifies a mix of bomb-affected beds juxtaposed with dated beds, the latter yielding ages with narrow standard deviations. Colluvial deposits overlying key glacial sections in the Rouge Catchment, while rare, yield bracketed AMS ages for an Ahbk horizon that refines weathering times relative to previously obtained conventional 14C dates. Bomb-affected sediment appears variably distributed within floodplain soils and in the ground soil of a colluvial section. Mass wasted deposits, with AMS 14C ages spread over the last few centuries, appear related to Little Ice Age (LIA) changes in climate, corroborated by pollen records. Further, these AMS-14C dated beds calibrate weathering of secondary Fe-Al oxihydroxides over the first half a millennium of weathering time.

Variation in human activities has greatly impacted the processes and intensities of erosion, sediment transport and storage throughout the Late Holocene, and many lowland rivers around the world have responded to these variations. Although this long-term process–response relationship has been established before, the effects of short-term (c.200-year) changes in human impact on lowland rivers are less well studied. Here, we followed an integrated approach whereby observations of floodplain changes are evaluated against detailed data on human impact for three lowland rivers in the Belgian loess belt: Dijle, Mombeek and Gete rivers. Pollen data were used to reconstruct changes in local and regional vegetation and to calculate human impact scores. Corings along transects and a database of c.160 radiocarbon ages were used to reconstruct geomorphic changes in the river valleys. Our results show a decrease in human impact between 200 and 800 AD, which can be related to the decreased population density in Europe during the first millennium AD. During this period, forests in the studied catchments regenerated, soil erosion decreased, hillslope–floodplain connectivity decreased due to the regeneration of valley-side vegetation barriers, and sediment input in the floodplain decreased. A reaction to this decreased human impact can be observed in the river valleys during the first millennium AD, with a regrowth of the alder carr forest and an increase in the organic matter content of the alluvial deposits with a local reactivation of peat growth. The observed trajectories of Belgian river valleys during the first millennium AD provide more insight into the sensitivity of these river valleys to short-term variations in human impact. These results can in turn be used to better estimate the effects of future changes in the catchments on the fluvial system.

The weathering and oxidation of mine tailings has the potential to contaminate water and soil with toxic elements. To understand the mechanisms, extent and products of the long-term weathering of complex Bolivian tailings from the Cerro Rico de Potosí, and their effects on As, Pb, P and Sb cycling, three-year long laboratory column experiments were carried out to model 20 years of dry- and wet-season conditions in the Pilcomayo basin. Chemical analysis of the leachate and column solids, optical mineralogy, X-ray diffraction, scanning electron microscopy, electron probe microanalysis, microscale X-ray absorption near edge structure spectroscopy, Bureau Commun de Référence sequential extraction and water-soluble chemical extractions, and speciation modelling have shown that the weathering of As-bearing pyrite and arsenopyrite, resulted in a loss of 13–29% of the original mass of As. By contrast, Pb and Sb showed much lower mass losses (0.1–1.1% and 0.6–1.9%, respectively) due to the formation of insoluble Pb- and Sb(V)-rich phases, which were stable at the low pH (~2) conditions that prevailed by the end of the experiment. The experiment also demonstrated a link between the cycling of As, Sb, and the oxidation of Fe(II)-bearing sphalerite, which acted as a nucleation point for an Fe-As-Sb-O phase. Phosphorus was relatively immobile in the tailings columns (up to 0.3% mass loss) but was more mobile in the soil-bearing columns (up to 10% mass loss), due to the formation of soluble P-bearing minerals or mobilization by organic matter. These results demonstrate the influence of mine tailings on the mobility of P from soils and on the potential contamination of ecosystems with As, and strongly suggest that these materials should be isolated from fluvial environments.

During Lateglacial cold periods, permafrost developed throughout Scotland, sediment-mantled slopes were extensively modified by solifluction and other forms of periglacial mass movement, large-scale sorted patterned ground formed on plateaux, and enhanced rockfall resulted in talus accumulation below cliffs. Most rock-slope failures occurred within five millennia following ice-sheet deglaciation, with many probably triggered by uplift-induced earthquakes; numerous debris-free scarps represent sites where Lateglacial rockslide debris was excavated by glaciers during the Younger Dryas Stade (∼12.9–11.7 ka). Sandar and outwash fans deposited by glacial rivers during ice-sheet retreat were incised to form high-level terraces. Under the cool temperate but relatively stable climate of the Holocene, solifluction and patterned ground formation continued to operate on high ground, though accumulation of high-level aeolian deposits on most mountains was terminated by erosion during the Little Ice Age. Drift-mantled slopes and talus slopes have been extensively eroded by translational failures and debris flows, the latter depositing debris cones on upland valley floors. The incidence of Holocene rockslides has been much lower than during the Lateglacial period. Dating of alluvial deposits and low Holocene terraces suggests no consistent pattern of Holocene floodplain evolution: incision has apparently dominated in the Highlands, aggradation in the lowlands, and floodplains in the Southern Uplands have asynchronous histories of incision and aggradation. Studies of floodplain behaviour over the past 200–300 years suggest that though major floods rework the floodplains of braided and piedmont rivers, there is no tendency towards net floodplain aggradation or incision. Most valley-side alluvial fans accumulated episodically in the last 4000 years, many in response to lowering of hillslope stability by woodland clearance. For many postglacial landsystems, disentangling the effects of declining paraglacial sediment supply, climate change and local influences (extreme rainstorm events or anthropogenic impacts) remains challenging.

Field surveys and radiocarbon dating of buried logjams in the floodplain of an old-growth forest river demonstrate the formation of erosion-resistant “hard points” on the floodplain of the Queets River, Washington. These hard points provide refugia for development of old-growth forest patches in frequently disturbed riparian environments dominated by immature forest. Our surveys show that local bed aggradation associated with logjams not only influences channel patterns and profiles but leads to development of a patchwork of elevated landforms that can coalesce to form portions of the valley bottom with substantial (i.e., 1 to > 4 m) relief above the bankfull elevation. In addition, logjam-formed hard points promote channel avulsion, anastomosing morphology, and growth of mature patches of floodplain forest that, in turn, provide large logs needed to form more logjam-formed hard points. Hence, our findings substantiate the potential for a feedback mechanism through which hard points sustain complex channel morphology and a patchwork floodplain composed of variable-elevation surfaces. Conversely, such a feedback further implies that major changes in riparian forest characteristics associated with land use can lead to dramatic simplification in channel and floodplain morphology.

We employed X-ray diffraction methods to quantify clay mineral assemblages in the Indus Delta and flood plains since ~ 14 ka, spanning a period of strong climatic change. Assemblages are dominated by smectite and illite, with minor chlorite and kaolinite. Delta sediments integrate clays from across the basin and show increasing smectite input between 13 and 7.5 ka, indicating stronger chemical weathering as the summer monsoon intensified. Changes in clay mineralogy postdate changes in climate by 5–3 ka, reflecting the time needed for new clay minerals to form and be transported to the delta. Samples from the flood plains in Punjab show evidence for increased chemical weathering towards the top of the sections (6–≪ 4 ka), counter to the trend in the delta, at a time of monsoon weakening. Clay mineral assemblages within sandy flood-plain sediment have higher smectite/(illite + chlorite) values than interbedded mudstones, suggestive of either stronger weathering or more sediment reworking since the Mid Holocene. We show that marine records are not always good proxies for weathering across the entire flood plain. Nonetheless, the delta record likely represents the most reliable record of basin-wide weathering response to climate change.

Management of the Dutch embanked floodplains is of crucial interest in the light of a likely increase of extreme floods. One of the issues is a gradual decrease of floodwater accommodation space as a result of overbank deposition of mud and sand during floods. To address this issue, sediment deposits of an undisturbed embanked floodplain near Winssen along the river Waal were studied using ground-penetrating radar (GPR). A number of radar facies units were recognized. Boreholes were used to relate radar facies units to sedimentary facies and to determine radar velocity. The GPR groundwave is affected by differences in moisture and texture of the top layer and probably interferes with the first subsurface reflector. The architectural elements recognized in the GPR transects confirm earlier reported insights on human-influenced river behaviour. This is testified in the development of sand bars during flood regimes that are probably more widespread than previously established.

The Tonle Sap is the largest wetland in South-east Asia and the heart of the largest inland fishery in the world. Its unique flood pulse system and annual flow reversal is a hotspot for biodiversity and productivity, as well as an essential habitat for many endangered fishes and birds. Despite predicted changes to the wetland's hydrology due to climate change and hydropower development in the Mekong, the consequent impacts on the fauna of the lake are poorly understood. A spatial modelling framework was developed to simulate the impact of potential scenarios of change using relationships between fauna and biophysical characteristics. Potential impacts on 61 animal species with documented nutritional, conservation or ecological value were examined. A large number of species rely on gallery forest to provide important habitats for their life history, yet this area is likely to be highly impacted by permanent inundation. There is a strong synchronicity between life histories and the flood pulse; consequently continued hydrological disruptions will have a significant impact on ecosystem dynamics, imposing further challenges to conservation. Protecting areas that may become suitable for gallery forests and shrublands under a modified flood regime will be crucial to management planning and the maintenance of a diverse and healthy ecosystem.

In Amazonian fisheries, the silver arowana, Osteoglossum bicirrhosum (Cuvier 1829) is heavily exploited for human consumption as an adult, and for the aquarium trade as a small juvenile (yolk sac juvenile mainly). The periodicity of annuli formation on otoliths and growth variability of the silver arowana were studied in different river river-basins of the Peruvian Amazon between 2006 and 2009. Transverse stained sections of 606 individual otoliths were analysed from four different river-basins, the Amazonas, Ucayali, Napo and Putumayo, of which 554 could be interpreted. These belonged to 274 females ranging from 15 to 91 cm (standard length) and 280 males ranging from 30 to 91 cm. In addition, yolk sac juveniles of known age were collected to improve growth modelling. Monthly proportions of stained otolith edges validated the formation of a single annulus per year in two different river-basins with lagged hydrological cycles: the Amazonas-Ucayali and the Putumayo. Stained growth mark counts resulted in a longevity estimate of at least 16 years for the silver arowana in the Peruvian Amazon. This fish grew quickly during the first two years, and asymptotic growth was reached after four to five years, except in the Putumayo where it was reached slightly earlier. Results showed no significant growth dimorphism between sexes within basins, but indicated significant growth differences among river basins. Silver arowanas measured, on average, between 38 and 40 cm at the end of their first year. Length-at-age differences among river basins increased with age to reach over 14 cm (and >3 kg) after 7 years between the faster and slower growing populations (Amazonas and Putumayo, respectively). The growth differences observed emphasize the need for further investigation on the population structure of this species as, although these differences might merely be phenotypic responses to contrasted environmental conditions, they could alternatively reflect the existence of several populations with distinct genetic and life history characteristics. The consequences of such differences would be very important for the management and conservation of this fragile and extensively exploited species.

River floodplains and riparian areas are often considered efficient traps for sediment and sediment-associated nutrients such as nitrogen (N) and phosphorus (P). However, few studies have focused on the fate of sediment-bound N and P after deposition on floodplains. In this study, the leaching of N and P from sediment deposited on a Danish-restored floodplain was quantified by placing trapped sediment samples under a rainfall simulator and exposing them to in situ temperatures and precipitation for two months. The nitrate release was 2.72–1600 μg NO3-N.g−1 DW which corresponded to 0.06–6.42% of the total nitrogen contained in the sediment. Total dissolved phosphorus (TDP) release was 0.44–3.17 μg P.g−1 DW, corresponding to 0.021–0.065% of the TP content of the sediment. Our results indicate that N and P release from floodplain sediment subjected to rainfall events is very low, which should be considered when applying floodplain restoration to mitigate the load of N and P to rivers.

A comparative study was undertaken of Amazonian fish diversity and density (abundance and biomass) in nutrient poor (blackwater) and richer (whitewater – várzea) habitats in the vicinity of Tefé, Brazil. The whitewater sampling sites, in the floodplain of the Rios Solimōes and Japurá, had high turbidity (Secchi disc 0.03–0.7 m), a conductivity of 64–110 μS cm–1 at 25°C and a pH of 6.6–6.9. The blackwater sites Lagos Amanã, Iamã and Tefé had a low turbidity (Secchi disc 2.0–2.2 m), a conductivity of 7–11 μS cm–1 at 25°C and a pH of 5.3–6.0. The fish communities of open water, floating meadow and forest margin were sampled. Both whitewater and blackwater sites held high diversity fish communities with many species in common. Whitewater habitats were more diverse yielding 108 species, compared with only 68 from blackwater. Fish density within floating meadow was estimated during high water April and May 1994, and low water October 1994 and March 1995. During the high water season fish biomasses in blackwater lakes (31.1 gm–2) were significantly greater than those of either whitewater lakes (13.4 gm–2) or whitewater river channels (3.45 g m–2). At low water, in October, whitewater channels were generally found to hold the highest fish biomass (204 g m–2) although in March a blackwater site yielded the highest fish biomass recorded (285.9 g m–2). The amount of floating meadow habitat within Whitewaters is however much greater than that in blackwaters. It is suggested that blackwaters may offer a stable habitat resulting in a high standing crop. In comparison, variation in conditions such as dissolved oxygen concentration in the whitewater may limit standing crop, but still allow periods of high productivity. Evidence was found for migration of fish from várzea lakes during periods of low oxygen availability. The high diversity and biomass of fish caught in both whitewater and blackwater lakes indicates that water acidity and conductivity are poor predictors of fish diversity and density in tropical floodplain lakes.

Methods for mapping and determining the condition of archaeological resources while they are still underground have been in development for nearly half a century. The authors here offer an example from the frontiers of the art: the application of a package of remote sensing procedures not only designed to locate sites but to model the valley deposits which contain and cover them. The variation in success of different methods in different deposits offers a guide to the design of evaluation projects on sand and gravel terrain everywhere.

Among the hypotheses invoked to explain high species richness in tropical forests, the niche differentiation hypothesis has received observational and experimental support (Ashton 1969, Chesson 2000, Clark et al. 1999, Souza & Martins 2004, Svenning 2001, Terborgh & Mathews 1999). Habitat specialization with regard to edaphic factors and topography has been observed in several plant groups including trees, lianas, shrubs, ferns and palms (Clark et al. 1999, Ibarra-Manriquez & Martinez-Ramos 2002, Svenning 1999, Tuomisto & Ruokolainen 1993). Treefall gaps and light gradients have also been found to be important ecological factors affecting plant distribution and niche differentiation in the understory (Chazdon 1986, Poorter & Arets 2003, Terborgh & Mathews 1999). It is suggested that such habitat heterogeneity may not only maintain biodiversity but also may lead to the origin of new species through the process of parapatric speciation (Gentry 1989, Haffer 1997, Patton & Smith 1992).

Habitat use by the boto, or Amazon river dolphin Inia geoffrensis, was investigated in and around the Mamirauá Reserve, Brazil. Largely forested with numerous channels and lakes, Mamirauá comprises a variety of seasonal floodplain habitats known collectively as várzea. The annual cycle of flooding in this region (amplitude 11–15 m) dominates all life. Profound seasonal differences in dolphin density between habitats were consistent with known fish movements, in turn dictated by changes in water level and dissolved oxygen. An exodus of botos from floodplain to river at low water prevents dolphins being trapped in areas that become entirely dry. Densities of botos in floodplain channels were seasonally higher (up to 18 km−2) than reported for any cetacean worldwide. Adults were largely segregated by sex except at low water. Females and calves dominated in chavascal habitat–the areas most remote from rivers, which were preferred by males. Probable causes of this segregation are the energetic requirements of calves and the safety of females and/or calves from male harassment. Some 80% of botos occurring on rivers were within 150 m of the margins. The reliance of adult females and calves on várzea in a region with exceptional dolphin densities demonstrates the importance of floodplain habitats for the boto, and may be the key determinant of this species‘ distribution.

Indigenous systems of management for regulating extraction of non-timber forest products (NTFP) have not been well documented in arid zone grazing lands. Conservation projects have therefore lacked information on customary rights to trees, while they have enforced systems of tree resource management that often conflicted with the indigenous system. This study focused on the indigenous tree tenure system of the Turkana pastoralists called ekwar (plural ngikwarin). The indigenous tree management system in 15.4 km2 of the Turkwel River floodplain woodlands near Lodwar, Kenya was investigated. The study began in 1990 after impoundment of the Turkwel Gorge Dam. In 1990 and 1998, Turkana pastoralists were interviewed about the ekwar. In individual ngikwarin woody cover, wood volume and woody-plant density were measured, and wood extraction assessed in terms of stems and twigs removed by the pastoralists and the urban population of Lodwar. Intensity of charcoal burning was assessed in terms of the density of earthen kilns, and livestock impact in terms of browsing frequency on woody plants. Potential Acacia tortilis litter production was estimated and an ekwar quality index developed to describe woodland productivity conditions. Tree produce was shared with and leased to friends and relatives. Woody cover showed no significant changes, while woody-plant density and volume declined, over the 8-year period. The Turkana usually do not cut live trees, but use dead trees and dry tree-parts for making charcoal. Increased kiln density and increased extraction of tree-parts were considered to be indicative of increased pressure on the riverine woodlands. Livestock browsing did not seem to contribute to woodland degradation. However, decline in woody-plant density and volume might have contributed to the reduction of litter production of A. tortilis. Trends in woodlands in the floodplain might be associated with damming of the Turkwel River and local anthropogenic pressures. Also, the ekwar system of tree tenure seemed to be threatened by the official forestry policy that it be ignored. Incorporating the ekwar system into the forestry conservation policy may achieve sustainable use and improve conservation of the Turkwel River floodplain woodlands.

High cattle densities, expanding human settlements and the conversion of miombo woodland into farms and teak plantations are threatening wildlife populations in the Kilombero Valley, Tanzania, and conservation research on this internationally important wetland is required as part of an integrated approach to its future management. The effect of land-use change on antelopes (family Bovidae) was investigated by surveying tracks and dung during three seasons over 1999–2000 in an area of mixed land-use. Use of miombo woodland, grassland and farmland habitats by antelopes was highest during the wet season (April–May), probably representing the movements of animals away from the floodplain. Duiker, puku Kobus vardoni and reedbuck Redunca spp. predominantly used the farmland during the wet season, at which time buffalo Syncerus caffer were more common in the miombo woodland. The findings of this study have three main implications for the conservation of the valley. Firstly, the inadvertent provision of suitable wet season habitats for puku and other small-medium antelopes by rice farmers could lead to higher levels of illegal hunting, and may increase the potential for conflict between agriculture and wildlife. Secondly, the loss of miombo vegetation will most strongly affect the larger species of antelope (sable Hippotragus niger and waterbuck Kobus ellipsiprymnus), which favour open-woodland habitats; future work should therefore determine levels of habitat use by antelopes in and around maturing teak plantations. Thirdly, any management prescriptions to conserve the Kilombero Valley should include the land on the edge of the floodplain.

Temporal distribution and composition of ichthyoplankton and their relationships with some environmental variables of Leopoldo's Inlet (Ressaco do Leopoldo) on the upper Paraná River floodplain, southern Brazil, were analysed. Samples were taken from February 1991 to February 1992, and 3480 larvae were collected. The highest density of larvae was observed in November 1991 (36.79 larvae/10 m3) at night (night/day ratio 7: 1). Species composition showed a predominance of Characiformes (80%). There was a high density (4.28 larvae/10 m3) of Bryconamericus stramineus throughout almost the whole study period. The majority of the species were more frequently collected at night. Pearson's correlation indicated a relationship between larval density, temperature, and pluviometric index. Leopoldo's Inlet, whose ichthyofauna is mainly composed of grazing and resident species, shows favourable conditions for fish reproduction and development.