1. This review is presented as a broad synthesis of riverine landscape diversity, beginning with an account of the variety of landscape elements contained within river corridors. Landscape dynamics within river corridors are then examined in the context of landscape evolution, ecological succession and turnover rates of landscape elements. This is followed by an overview of the role of connectivity and ends with a riverine landscape perspective of biodiversity.

2. River corridors in the natural state are characterised by a diverse array of landscape elements, including surface waters (a gradient of lotic and lentic waterbodies), the fluvial stygoscape (alluvial aquifers), riparian systems (alluvial forests, marshes, meadows) and geomorphic features (bars and islands, ridges and swales, levees and terraces, fans and deltas, fringing floodplains, wood debris deposits and channel networks).

3. Fluvial action (erosion, transport, deposition) is the predominant agent of landscape evolution and also constitutes the natural disturbance regime primarily responsible for sustaining a high level of landscape diversity in river corridors. Although individual landscape features may exhibit high turnover, largely as a function of the interactions between fluvial dynamics and successional phenomena, their relative abundance in the river corridor tends to remain constant over ecological time.

4. Hydrological connectivity, the exchange of matter, energy and biota via the aqueous medium, plays a major though poorly understood role in sustaining riverine landscape diversity. Rigorous investigations of connectivity in diverse river systems should provide considerable insight into landscape-level functional processes.

5. The species pool in riverine landscapes is derived from terrestrial and aquatic communities inhabiting diverse lotic, lentic, riparian and groundwater habitats arrayed across spatio-temporal gradients. Natural disturbance regimes are responsible for both expanding the resource gradient in riverine landscapes as well as for constraining competitive exclusion.

6. Riverine landscapes provide an ideal setting for investigating how complex interactions between disturbance and productivity structure species diversity patterns.

https://onlinelibrary.wiley.com/doi/pdf/10.1046/j.1365-2427.2002.00893.x

Riverine landscape diversity

/pdf/an-introduction-to-the-aquatic-insects-of-north-america-20i7stzjkw.pdf

An Introduction to the Aquatic Insects of North America

Species Diversity in Space and Time

SUMMARY 1. As rivers and streams are patchy and strongly hierarchical systems, a hierarchical patch dynamics perspective can be used as a framework for visualising interactions between structure and function in fluvial landscapes. The perspective is useful for addressing fundamental attributes of lotic ecosystems, such as heterogeneity, hierarchy, directionality and process feedback occurring across spatial scales and for illustrating spatio-temporal linkages between disparate concepts in lotic system ecology such as the River Continuum Concept, the Serial Discontinuity Concept, the Flood Pulse Concept and the Hyporheic Corridor Concept. 2. At coarse spatial scales, the hierarchical patch dynamics perspective describes each river network as a unique, patchy discontinuum from headwaters to mouth. The discontinuum is comprised of a longitudinal series of alternating stream segments with different geomorphological structures. Each confluence in the steam network further punctuates the discontinuum because the sudden change in stream characteristics can create a ‘gap’ in the expected pattern of downstream transitions. The discontinuum view recognises general trends in habitat characteristics along the longitudinal profile, but creates a framework for studying and understanding the ecological importance of each stream’s individual pattern of habitat transitions along longitudinal, lateral or vertical vectors at any scale. 3. Object-oriented modelling and programming techniques provide a means for developing robust, quantitative simulation models that describe the dynamic structure of patch hierarchies. Such models can simulate how the structure and function of lotic ecosystems are influenced by the landscape context of the system (the ecological conditions within which the system is set) and the metastructure (structural characteristics and juxtaposition) of finer-scale patches comprising the system. 4. A simple object-oriented, multiscale, discontinuum model of solute transformation and biological response along a stream channel illustrates how changing the branching pattern of a stream and the arrangement of its component patches along the downstream profile will result in substantial changes in predicted patterns of solute concentration and biotic community structure. 5. The importance of context, structure, and metastructure in determining lotic ecosystem function serves to underscore Hynes’ (1975) concept that ‘every stream is likely to be individual.’ Advancing the discipline of fluvial landscape ecology provides an excellent opportunity to develop general concepts and tools that address the individual character of each stream network and integrate the concept of ‘uniqueness within the river discontinuum’ into our ecological understanding of rivers and streams.

/pdf/fluvial-landscape-ecology-addressing-uniqueness-within-the-3cl2yytnpy.pdf

Fluvial landscape ecology: addressing uniqueness within the river discontinuum

https://cfpub.epa.gov/ncer_abstracts/index.cfm/fuseaction/display.files/fileID/13223

A Bayesian network of eutrophication models for synthesis, prediction, and uncertainty analysis

Aquatic habitat change caused by flooding was quantified along the Fiume Tagliamento, a morphologically intact gravel-bed river ecosystem in northeast Italy. Five different geomorphic reaches (each around 1.5 km), ranging from near the headwaters at 800 m above sea level (a.s.l.) to near the mouth at 5 m a.s.l., were studied over a 1-year period. All floodplain water bodies in each reach were delineated in August 1999 using a differential global positioning system. Each reach was remapped twice (in December 1999 and August 2000) to investigate the impact of autumn and spring flood seasons on aquatic habitat composition and configuration. A high degree (nearly 62%) of aquatic habitat turnover was documented in a braided headwater floodplain. The degree of aquatic habitat turnover decreased with decreasing elevation to approximately 20% turnover in a meandering reach at 5 m a.s.l. In contrast to turnover, braiding, sinuosity, and aquatic habitat composition changed little in response to flooding in all reaches. Location of aquatic habitats in floodplains changed considerably (turnover), whereas habitat configuration and composition remained relatively stable. These results support the applicability of the shifting mosaic steady-state model to riverine floodplain environments.

/pdf/aquatic-habitat-dynamics-along-a-braided-alpine-river-3nui1m4kpt.pdf

Aquatic Habitat Dynamics along a Braided Alpine River Ecosystem (Tagliamento River, Northeast Italy)

Although spatial scale, upstream–downstream gradients, environmental variability, and floodplain connectivity and complexity have been recognized as integral components of our understanding of riverine pattern and process, aquatic invertebrate community structure across lateral gradients from headwaters to the lowland of a river has received little empirical documentation. Aquatic invertebrate density, distribution, and richness were investigated at 29 study sites distributed laterally (main channel–floodplain) among 6 geomorphologically distinct river reaches from the headwaters to near the mouth of one of the last seminatural river corridors draining the European Alps, the Tagliamento River in northeastern Italy. Community relationships were examined using multivariate and diversity analyses to investigate patterns of taxonomic richness. Diversity parameters were scaled at the site, reach, and catchment levels to better understand local and regional patterns. Mean invertebrate density increased ...

https://www.jstor.org/stable/10.1899/05-037.1

Lateral organization of aquatic invertebrates along the corridor of a braided floodplain river

Habitat structure and diversity were investigated at multiple scales along the Tagliamento River (NE Italy) to analyze the spatial and temporal configuration of the aquatic habitat templet in a complex alluvial river corridor in the European Alps. A geomorphic approach was employed to determine floodplain structure and channel configuration using aerial photographs and digitized maps. Structural, thermal, and chemical variables were sampled monthly for one year in 3-km long study sections within six distinct geomorphic reaches along the longitudinal continuum. Aquatic habitat heterogeneity and complexity was quantified along the longitudinal dimension (corridor scale), within geomorphic reaches (floodplain scale) and within floodplain water bodies (within-habitat scale). Four major types of aquatic habitats were distinguished: surface-connected channels (SC), alluvial channels (AC), tributary channels (TC), and isolated standing water bodies (ISO). The first 3 types included primary, secondary, and tertiary branches plus backwaters. Active floodplain width was greatest in the island-braided lower floodplain (reach IV), which also exhibited the highest values for aquatic habitat area per river km, aquatic-terrestrial ecotone length per river km, within-floodplain thermal heterogeneity, and aquatic habitat diversity. Principal component analysis (PCA) clearly distinguished lotic from standing waters along the primary axis and substrate gradients (both longitudinally between floodplains and laterally within floodplains) on the secondary axis. PCA applied to 21 chemical variables illustrated a downstream increase in floodplain-scale spatio-temporal heterogeneity along the river corridor. Total environmental variance is considerably enhanced by the superimposition of longitudinal changes (corridor scale) on lateral changes within geomorphic reaches (floodplain scale). This study clearly demonstrated the high levels of structural complexity and habitat diversity that are possible in Alpine rivers, with implications for the important role of environmental heterogeneity in sustaining functional integrity.

Aquatic habitat diversityalong the corridor of an Alpine flood plain river (Fiume Tagliamento,Italy)n

Aquatic invertebrate community structure was quantified from six sites, each located in distinctly different geomorphic reaches along the Tagliamento River (N.E. Italy). Quantitative samples of benthic invertebrates were collected quarterly over one year from six sites (from 5- 1100m above sea level), while physico-chemical data were collected monthly. Total abundance of benthic invertebrates was highly vari- able in space and time with a minimum density of 433 ± 158 individuals m -2 (± 1 standard deviation; n = 3) occurring in the main channel of an island-braided flood plain midway along the continuum after the autumnal floods (November 1998). At most sites, maximum densities (111,226 ± 45,395ind.m -2 ) were observed during late summer (August 1998). In August, insects comprised more than 87% of all taxa in each reach, with Chironomidae (Diptera) and Baetidae (Ephemeroptera) being the most abundant insect families. Abundance of Insecta, Crustacea (primarily copepods and amphipods), Oligochaeta, Nematoda, and Hydrachnidia all increased with distance downstream. In general, dominant insect taxa were represented by highly mobile forms with potential for multivoltinism (Chironomidae, Baetidae, Simuliidae). Non-insect taxa were also well represented by high mobility (e.g., Echinogammarus spp.) and ability to rapidly reproduce (e.g., Oligochaeta, Nematoda, Copepoda), life-cycle strate- gies critical for persistence in a highly dynamic and physically harsh environment. Temperature, substrate size, nutrient concentrations, benthic organic matter, and bio- mass of epilithic algae all exhibited distinct changes along the continuum. Changes in benthic invertebrate community structure (abundance and diversity) also occurred along the longitudinal gradient and these changes were correlated with spatial and tem- poral shifts in various environmental factors. Longitudinal patterns revealed by Co- Inertia analysis, corroborated diversity and abundance patterns by illustrating the dis-

Spatio-temporal patterns of benthic invertebrates along the continuum of a braided Alpine river

Two headwater flood plains in tributaries of the Tagliamento catchment (N.E. Italy) were investigated to compare and contrast floodplain morphology, aquatic habitat structure, physico-chemical characteristics, and Trichoptera community relationships. The two flood plains (one stable and forested, the other dynamic and open) were similar with respect to position along the longitudinal continuum, elevation, stream order, and geological material. However, the two flood plains differed greatly in aquatic habitat structure, physico-chemical character, and Trichoptera abundance, distribution, and richness. The forested reach had lower slope, finer sediment, more standing waterbodies, significantly higher benthic organic matter standing stocks, and a closed canopy of predominantly Alnus incana. Trichoptera abundance in the forested flood plain was higher, as was taxa richness (27 taxa), than in the open flood plain (16 taxa). Differences in Trichoptera composition and richness were due to the presence of several species of Limnephilidae, which were correlated with benthic organic matter. These findings are discussed in the context of species-abundance relationships, environmental factors, and reach-specific morphological characters. Results illustrate the dependence of habitat type and invertebrate community response to reach scale factors (i.e., geomorphology and hydrology) that may be uncoupled from position along the longitudinal continuum.

Dave B. Arscott

Papers

Aquatic Habitat Dynamics along a Braided Alpine River Ecosystem (Tagliamento River, Northeast Italy)

Lateral organization of aquatic invertebrates along the corridor of a braided floodplain river

Aquatic habitat diversityalong the corridor of an Alpine flood plain river (Fiume Tagliamento,Italy)n

Spatio-temporal patterns of benthic invertebrates along the continuum of a braided Alpine river

Habitat Structure and Trichoptera Diversity in Two Headwater Flood Plains, N.E. Italy