Patchiness of River–Groundwater Interactions within Two Floodplain Landscapes and Diversity of Aquatic Invertebrate Communities

Abstract

In fluvial systems, the interactions between rivers and groundwater significantly affect various ecological structures (for example, riparian vegetation) and functions. To examine the effects of hydrological exchange between groundwater and surface water on the distribution of aquatic invertebrates within a riverine landscape, we investigated the main stem, tributaries, and various surface and subsurface waters of two floodplains of a southern Alpine river (Brenno, Switzerland) in terms of their physicochemical, hydraulic, substratum, and faunal characteristics. The origins of the water were investigated by analyzing geomorphic settings and physicochemical variables. The two floodplains had different hydrological regimes. The middle floodplain was dominated by lateral inputs and exfiltration of hillslope groundwater from two different subcatchments. Bank filtration of river water sustained subsurface water only close to the channel. The aquatic habitats of the middle floodplain formed a rather homogeneous group with high taxon richness and intrahabitat diversities. These aquatic habitats resembled mountain springbrooks in their physicochemical characteristics and faunal compositions. In the lower floodplain, the exchange between river water and groundwater was more extensive. The aquatic floodplain habitats of the lower floodplain were fed mainly by deep and shallow alluvial groundwater, hyporheic exfiltration, and partly by surface water. In contrast to aquatic habitats of the middle floodplain, habitats of the lower floodplain showed a low intrahabitat and a high interhabitat diversity in terms of both substrate characteristics and faunal compositions. For both floodplains, ordination analyses showed a high concordance between the structure of the invertebrate community and the characteristics of the environmental habitat, including chemical, geomorphic, and hydraulic variables. Ordinations grouped aquatic habitats according to the origins of the waters. Taxon richness was related to local structural diversity, but species turnover was related to differential vertical and lateral connectivity. Exfiltration of groundwaters provided aquatic floodplain habitats for several specialized species. The results of this study show the significance of the river-groundwater connectivity for the creation of the habitat mosaic that sustains biodiversity in floodplains and thus have important implications for managing the ecological integrity of floodplains.

River flood plains are model ecosystems to test general hydrogeomorphic and ecological concepts

“…Differential patterns of surface-and groundwater exchanges produce a mosaic of 'shifting subsurface flow paths'. The importance of differential hydrologic exchange for biodiversity distributions has been demonstrated by Brunke et al (2003) by comparing different intermountain floodplains in southern Switzerland. Harner and Stanford (2003) found that cottonwood trees grew faster and had lower C:N in their leaves in zones of groundwater upwelling than downwelling zones on the same flood plain and suggested that the observed differences in riparian canopy trees could influence distribution and abundance of leaf herbivores.…”

Spatio‐temporal variations of hyporheic flow in a riffle‐step‐pool sequence

“…Since the formulation of the patch dynamics concept (Townsend, 1989), lotic ecologists and biogeochemists have developed an increased interest in these dynamics and the heterogeneity of hyporheic flows (Hendricks, 1993;Stanley et al, 1997;Lake, 2000;Brunke et al, 2003). Whereas patchiness makes hyporheic research difficult (Palmer, 1993), ecologists mostly identify such complexity as an enhancer of biogeochemical processes, e.g.…”

A conceptual framework for ecological responses to groundwater regime alteration (FERGRA)

“…The rapidly developing interest in using traits to understand ecological responses to disturbances (Schmera, Podani, Heino, Erős, & Poff, ) could be extended to GDEs. In more hydrologically dynamic GDEs, species with traits such as sensitivity to desiccation or poor dispersal ability may be vulnerable to groundwater regime alteration and therefore make especially effective ecological indicators (Brunke, Hoehn, & Gonser, ; de Szoeke, Crisman, & Thurman, ; Stumpp & Hose, ). Poor dispersers may lack the mobility to track favourable hydrological conditions and be restricted to hydrologically stable streams with groundwater regimes that buffer against precipitation variability (Kath et al, ).…”

“…The third step in FERGRA is to determine GDE–groundwater connectivity to assess the hydrogeological association of altered groundwater regimes with ecological responses by multiple GDEs in the landscape. The importance of groundwater connectivity for the persistence and functioning of the different classes of GDEs (Table , Figure ) is demonstrated by changes in the habitat and condition of riparian vegetation (Eamus et al, ), fish (Falke et al, ), macroinvertebrate (Brunke et al, ), and stygofauna (Stumpp & Hose, ) communities when groundwater connectivity is altered. Within FERGRA, we hypothesize that alterations to GDE–groundwater connectivity are the primary ecohydrological mechanism by which groundwater regime alterations elicit ecological responses in all classes of GDEs.…”