Michael Doering

Spatial patterns in macroinvertebrate assemblages in surface-flowing waters of a glacially-influenced floodplain

We examined the spatial structure of macroinvertebrate assemblages in surface-flowing waters of a glacially-influenced floodplain. The floodplain main-channel responded longitudinally to changes in hydrology with evident coarse-scale zones of upwelling and downwelling; the lower floodplain main channel fell dry in late winter. Physico-chemical attributes differed among tributaries and the main channel. The main channel had lower values of conductivity, alkalinity and nitrate–N than tributaries, with right-side (east-facing) tributaries having the highest values. Left-side (west-facing) tributaries flowing over an exposed rock-face had warmer water temperatures than the main channel and right-side tributaries. The biomass of benthic organic matter and periphyton was highest in right-side tributaries, followed by main channel sites then left-side tributaries. Similarly, macroinvertebrate density and richness were higher in right-side tributaries, intermediate in main channel sites, and lowest in left-side tributaries. Macroinvertebrate assemblages clearly differed between main channel sites, right-side tributaries, and left side tributaries based on an NMDS analysis. Minor differences were observed among main channel sites, although most upstream sites showed some structural differences from downstream sites. Ephemeropterans and plecopterans were most common in main channel sites and right-side tributaries, whereas chironomids and trichopterans also were common in right-side tributaries. Although the main channel changed longitudinally in physico-chemical characteristics, no real patterns of zonation were evident in macroinvertebrate assemblages. Coarse spatial patterns in macroinvertebrate assemblages in the floodplain were reflected in the physico-chemical differences between the main channel and tributaries, and between left-side and right-side tributaries. We conclude that coarse-scale floodplain properties enhance the overall diversity of lotic macroinvertebrates. Consequently, floodplain alterations that reduce surface water heterogeneity/connectivity limits the potential macroinvertebrate diversity of floodplains.

Spatio-temporal relationships between habitat types and microbial function of an upland floodplain

Natural floodplains comprise a spatial mosaic of habitat types that vary in successional development. The physical–chemical properties of soils and sediments in these habitats vary spatio-temporally with changes in hydrology, thereby influencing microbial dynamics and general floodplain functioning. The major goals of this study were to characterize the spatio-temporal variation of different floodplain habitats and elucidate microbial function as a mechanistic basis underlying floodplain functioning. Microbial functional parameters (i.e. soil-sediment respiration, enzyme activity) as well as a microbial state variable (i.e. bacterial abundance, BA) were assessed in conjunction with abiotic properties of respective soils and sediments in different floodplain habitats over an annual cycle. BA and respiration differed significantly among habitat types, being lowest in early successional gravel and stream channel habitats and highest in older successional habitats of mature forest, islands, and riparian pasture/grassland. Coarse-scale floodplain hydrology influenced the spatial variation in microbial measures within specific habitats. A non-metric multidimensional scaling clearly separated habitat types based on the functional activities of eight tested enzymes and specific microbial variables could be linked to soil-sediment respiration. These results document a high functional heterogeneity of soil and sediment microbial variables that complements the shifting habitat mosaic found in most natural floodplains. Moreover, the use of functional measures such as respiration enhances the understanding of complex floodplain functioning.

Spatiotemporal heterogeneity of actual and potential respiration in two contrasting floodplains

Floodplains are vital components of river ecosystems and play an important role in carbon cycling and storage at catchment and global scales. For efficient river management and conservation, it is critical to understand the functional role of spatiotemporally complex and dynamic habitat mosaics of river floodplains. Unfortunately, the fundamental understanding of mineralization and carbon flux patterns across complex floodplains is still fragmentary. In this study, respiratory potential (i.e., electron transport system activity – ETSA) was quantified seasonally across different aquatic and terrestrial habitats (wetted channels, gravel bars, islands, riparian forests and grasslands) of two Alpine floodplains differing in climate, altitude, discharge, flow alteration intensity and land use (Soca – natural flow regime, 12% grassland area; Urbach – mean annual discharge reduction by 30% due to water abstraction, 69% grassland area). In situ respiration (R) was measured and ETSA/R ratios calculated to examine differences in exploitation intensity of the overall respiratory capacity among floodplain habitats and seasons. ETSA and R provided potential and actual estimates, respectively, of organic matter mineralization in the different floodplain habitats. Hierarchical linear regression across habitat types showed organic matter, grain sizes 8u2009mm were also highly important for the Soca floodplain. The combination of ETSA and R measurements conducted in contrasting floodplains increased our understanding of the relationships between floodplain habitat heterogeneity, organic matter mineralization and human impacts; i.e., structural-functional linkages in floodplains. These data are integral towards predicting changes in floodplain function in response to environmental alterations from increasing human pressures and environmental change.