Lateral and longitudinal patterns within the stygoscape of New Zealand alluvial river - INRAE - Institut national de recherche pour l’agriculture, l’alimentation et l’environnement
Article Dans Une Revue Fundamental and Applied Limnology Année : 2008

Lateral and longitudinal patterns within the stygoscape of New Zealand alluvial river

Patterns écologiques latéraux et longitudinaux dans le stygoscape d'une rivière alluviale néozélandaise

Résumé

In landscape ecology, landscapes are viewed as hierarchically-organized groups of interacting components or zones. This perspective is applied in studies of riverscapes with increasing frequency, particularly in studies of channel habitats and channel-fl oodplain interactions. Stygoscapes, the subsurface portions of riverscapes, have received less attention. Stygoscapes are composed of three saturated zones beneath and lateral to river channels: the hyporheic, parafluvial and riparian zones. These zones are differentiated on the basis of hydrological, biological and chemical conditions, and the degree of interaction with the channel surface. In this paper, we describe lateral and longitudinal patterns in the shallow (30 cm 10 m depth) stygoscape of the alluvial Selwyn River, New Zealand. We used abutting hyporheic, parafl uvial and riparian zones in large-scale downwelling (losing) and upwelling (gaining) sections of the river mainstem to compare physico-chemical and biological conditions across a broad stygoscape. The stygoscape zones had the same arrangement in both sections: hyporheic zones within the wetted channel, riparian zones furthest from the channel, and parafl uvial zones between the hyporheic and riparian zones. Nitrate and dissolved reactive phosphorus concentrations and electrical conductivity were signifi cantly higher, and dissolved organic phosphorus concentrations and pH levels lower, in the gaining section than the losing section. In both sections, ammonium, dissolved reactive phosphorus, and dissolved organic carbon concentrations and pH were higher in the hyporheic zone than the riparian zone. Within the losing section, DON and DOP concentrations were higher in the hyporheic zone than the riparian zone. Physico-chemical conditions were intermediate in the parafl uvial zones of both river sections. These among-zone differences suggest that hyporheic zones are sinks for dissolved nutrients, and that effects of hyporheic sinks are greatest in losing river sections with unidirectional flow from the surface to the hyporheic zone. There were large differences among stygoscape zones in invertebrate assemblage composition, and smaller differences between the losing and gaining sections. Invertebrate densities, taxon richness and % insect taxa were higher in hyporheic zones than riparian zones. Invertebrate densities were intermediate in the parafl uvial zones, and taxon richness and % insect taxa were similar in parafl uvial and riparian zones. The spatial patterns we observed in the Selwyn River suggest that hydrological connectivity between zones, and permeability within zones, are among the most important determinants of chemical and biological dynamics in stygoscapes. Differences in large-scale upwelling and downwelling, and differences in water source (runoff and groundwater) appeared to be of secondary importance.
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Dates et versions

hal-02590748 , version 1 (15-05-2020)

Identifiants

Citer

T. Datry, M.R. Scarsbrook, S.T. Larned, G. Fenwick. Lateral and longitudinal patterns within the stygoscape of New Zealand alluvial river. Fundamental and Applied Limnology, 2008, 171 (4), pp.335-347. ⟨10.1127/1863-9135/2008/0171-0335⟩. ⟨hal-02590748⟩
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