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Habitat change in braided flood plains (Tagliamento, NE-Italy) (2003)

Van Der Nat, Dimitry ; Tockner, Klement ; Edwards, Peter J. ; [et al.]

Oxford, UK : Blackwell Science Ltd

Freshwater biology 48 (2003), S. 0

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ISSN: 1365-2427

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Biology

Notes: 1. Relative changes and age distribution of habitats were investigated in the active channel of a bar-braided and an island-braided reach of the Tagliamento River (NE-Italy). Between September 1999 and January 2002, six habitat types were delineated with a differential Global Positioning System on five dates following floods of different magnitude. Overlay maps were employed to calculate age and relative change of habitats. We established exponential decay rates (k-values) for islands and major aquatic habitats.2. Relative changes of all aquatic habitats combined were up to 82% between survey dates in the bar-braided flood plain, with a cumulative rate of 85% over the 2.5-year period. Relative habitat changes in the island-braided flood plain were lower with a cumulative change of almost 60% during the study period. In the bar-braided flood plain significant exponential decay relationships were established for channels, alluvial channels, backwaters, and ponds.3. Half-lives were particularly short for backwaters and ponds. In the island-braided reach, significant relationships existed for channels and alluvial channels. The half-lives of channels and alluvial channels increased with the presence of vegetated islands. Relative habitat composition within the active corridor remained almost constant, supporting the applicability of the shifting mosaic steady state model to braided floodplain ecosystems.4. Our results indicate that under natural conditions aquatic floodplain habitats can be highly dynamic over short time-scales. Even small water level fluctuations (‘flow pulses’) can lead to major habitat changes with important consequences for the fauna and flora.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1046/j.1365-2427.2003.01126.x

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Invertebrates in Freshwater Wetlands of North America (2000)

Tockner, Klement

Oxford, UK : Blackwell Science Ltd

Freshwater biology 45 (2000), S. 0

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ISSN: 1365-2427

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Biology

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1046/j.1365-2427.2000.00645.x

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Hydrological connectivity, and the exchange of organic matter and nutrients in a dynamic river–floodplain system (Danube, Austria) (1999)

Tockner, Klement ; Pennetzdorfer, Doris ; Reiner, Niko ; [et al.]

Oxford, UK : Blackwell Science, Ltd

Freshwater biology 41 (1999), S. 0

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ISSN: 1365-2427

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Biology

Notes: 1. The relationship between hydrological connectivity, and the exchange processes of suspended sediments, organic matter and nutrients (NO3-N) was investigated in a dynamically connected river–floodplain segment of the Danube over a 15-month period in 1995 and 1996 in the Alluvial Zone National Park, Austria.2. Based on water level dynamics and water retention times, three phases of river–floodplain connectivity were identified: disconnection (phase I), seepage inflow (phase II) and upstream surface connection (phase III). The frequency of occurrence of these phases was 67.5%, 29.3% and 3.2%, respectively, during the study period.3. A conceptual model is presented linking hydrological connectivity with ecological processes. Generally, the floodplain shifts from a closed and mainly biologically controlled ecosystem during phase I to an increasingly open and more hydrologically controlled system during phases II and III. Phase I, with internal processes dominating, is designated the ‘biotic interaction phase’.4. Phase II, with massive nutrient inputs to the floodplain yet relatively high residence times, and therefore, high algal biomass, is classified as the ‘primary production phase’. This demonstrates that water level fluctuations well below bankfull may considerably enhance floodplain productivity.5. Finally, since transport of particulate matter is mainly restricted to short flood pulses above bankfull level, phase III has been defined as the ‘transport phase’.6. The floodplain served as a major sink for suspended sediments (250 mt ha−−1 year−−1), FPOM (96 mt ha−−1 year−−1), particulate organic carbon (POC; 2.9 mt ha−−1 year−−1) and nitrate-nitrogen (0.96 mt ha−−1 year−−1), but was a source for dissolved organic carbon (DOC; 240 kg ha−−1 year−−1), algal biomass (chlorophyll-a; 0.5 kg ha−−1 year−−1) and CPOM (21 kgha−−1 year−−1). Considerable quantities of DOC and algal biomass were exported to the river channel during phase II, whereas particulate matter transport was largely restricted to the short floods of phase III.7. The Danube Restoration Project will create a more gradual change between the individual phases by increasing hydrological connectivity between the river channel and the floodplain, and is predicted to enhance productivity by maintaining a balance between retention and export of nutrients and organic matter.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1046/j.1365-2427.1999.00399.x

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A landscape perspective of surface–subsurface hydrological exchanges in river corridors (2002)

MALARD, FLORIAN ; TOCKNER, KLEMENT ; DOLE-OLIVIER, MARIE-JOSÉ ; [et al.]

Oxford UK : Blackwell Science Ltd.

Freshwater biology 47 (2002), S. 0

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ISSN: 1365-2427

Source: Blackwell Publishing Journal Backfiles 1879-2005

Topics: Biology

Notes: 1. River corridors can be visualised as a three-dimensional mosaic of surface–subsurface exchange patches over multiple spatial scales. Along major flow paths, surface water downwells into the sediment, travels for some distance beneath or along the stream, eventually mixes with ground water, and then returns to the stream.2. Spatial variations in bed topography and sediment permeability result in a mosaic of patch types (e.g. gravel versus sandy patches) that differ in their hydrological exchange rate with the surface stream. Biogeochemical processes and invertebrate assemblages vary among patch types as a function of the flux of advected channel water that determines the supply of organic matter and terminal electron acceptors.3. The overall effect of surface–subsurface hydrological exchanges on nutrient cycling and biodiversity in streams not only depends on the proportion of the different patch types, but also on the frequency distribution of patch size and shape.4. Because nutrients are essentially produced or depleted at the downwelling end of hyporheic flow paths, reach-scale processing rates of nutrients should be greater in stretches with many small patches (e.g. short compact gravel bars) than in stretches with only a few large patches (e.g. large gravel bars).5. Based on data from the Rhône River, we predict that a reach with many small bars should offer more hyporheic refugia for epigean fauna than a reach containing only a few large gravel bars because benthic organisms accumulate preferentially in sediments located at the upstream and downwelling edge of bars during floods. However, large bars are more stable and may provide the only refugia during severe flood events.6. In river floodplain systems exhibiting pronounced expansion/contraction cycles, hyporheic assemblages within newly created patches not only depend on the intrinsic characteristics of these patches but also on their life span, hydrological connection with neighbouring patches, and movement patterns of organisms.7. Empirical and theoretical evidence illustrate how the spatial arrangement of surface–subsurface exchange patches affects heterogeneity in stream nutrient concentration, surface water temperature, and colonisation of dry reaches by invertebrates.8. Interactions between fluvial action and geomorphic features, resulting from seasonal and episodic flow pulses, alter surface–subsurface exchange pathways and repeatedly modify the configuration of the mosaic, thereby altering the contribution of the hyporheic zone to nutrient transformation and biodiversity in river corridors.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1046/j.1365-2427.2002.00906.x

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Physico-chemical heterogeneity in a glacial riverscape (2000)

Malard, Florian ; Tockner, Klement ; Ward, J.V.

Springer

Landscape ecology 15 (2000), S. 679-695

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ISSN: 1572-9761

Keywords: flow path ; flood pulse ; glacial river ; hydrological connectivity ; riverscape heterogeneity ; water chemistry ; water source

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract Spatio-temporal heterogeneity in physico-chemical conditions associated with the annual expansion/contraction cycle in a complex glacial flood plain of the Swiss Alps was investigated employing a landscape approach. The diverse and dynamic aquatic habitats of the flood plain were visualized as an aquatic mosaic or riverscape. Based on samples collected at ca. monthly intervals for 1.5 yr along 17 floodplain transects, the 3 components of riverscape heterogeneity, extent, composition, and configuration, were quantified using categorical maps and indices of landscape patterns for turbidity and specific conductance. Changes in the spatial heterogeneity of 13 other physico-chemical parameters were further analyzed by means of a within-dates principal component analysis. Riverscape heterogeneity (RH), quantified by applying several indices of landscape pattern to turbidity and specific conductance data, was minimum during groundwater-dominated base flow in winter. Despite an increase in surface connectivity in the channel network with rising discharge, RH rose in spring and summer as additional chemically-distinct water sources (i.e., snowmelt runoff and glacial ablation) contributed to surface flow within the flood plain. Most other physico-chemical variables measured during this study exhibited the same spatio-temporal heterogeneity as turbidity and specific conductance. Overall, the glacial flood plain shifted from a monotonous physico-chemical riverscape in winter to a complex mosaic in summer, this seasonal pattern being clearly driven by hydrological factors operating at the catchment scale rather than by autogenic processes within individual water bodies. Although RH exhibited a predictable annual pattern in response to the seasonal flow regime, we expect the channel network to undergo future modifications from stochastic factors associated with flood events and long-term changes reflecting movements of the glaciers.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1023/A:1008147419478

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