Abstract:Natural floodplains are spatially heterogeneous and dynamic ecosystems but at the same time, a highly endangered landscape feature due to climate change and human impacts such as water storage, flood control and hydropower production. Flow is considered a master variable that shapes channel morphology and the heterogeneity, distribution, and turnover of floodplain habitats. Despite their highly dynamic nature, the relative abundance of different habitat elements (islands, gravel bars) in natural floodplains seems to remain relatively constant over ecological periods and is referred to as the shifting mosaic steady state concept. In this conceptual context, we analysed spatiotemporal changes in relative habitat abundance and channel complexity of an alpine floodplain from its near natural state in 1940 before water abstraction and levee construction until 2007 using historical aerial images. Within the first decades of impairment, the relative abundance of floodplain habitats that depend on flood and flow pulses such as parafluvial channels and islands shifted toward a greater abundance of terrestrial forest and grassland habitats. After 1986, the duration and frequencies of high-precipitation events (>60 mm 24 h -1 ) triggering major, channel-reworking floods increased substantially and caused a restructuring of the floodplain and decrease in the abundance of more terrestrial habitat types. These results are contrary to expectations of the shifting mosaic steady state concept yet suggest its potential application as an indicator of landscape transformation and human impacts on floodplain ecosystems. Last, the results raise the applied question as to whether an increased frequency of high flow events induced by climate change can contribute to floodplain restoration.

The movement of bacterial and viral pathogens through soil and vadose zone and subsequently into groundwater is a major public health concern. There are relatively few studies on the transport and fate of microbes through variably saturated vadose zone media compared with their transport in the soil and saturated groundwater zones. In this study, we investigated the transport of Escherichia coli, F-RNA bacteriophage MS2, and a conservative solute tracer bromide through three intact vadose zone cores, under saturated (discharge rate ∼100 mm h −1 ) and unsaturated (discharge rate 10 and 0.5 mm h −1 ) flow conditions. The vadose zone media were sandy gravel overlying a sand lens in core 1, a heterogeneous SG mix in core 2, and SG with an open framework gravel lens through the middle of the core in core 3.The three flow regimes resulted in different transport characteristics through each of the cores. As expected, microbial transport through all cores was higher under saturated conditions, compared with unsaturated conditions. Overall, E. coli removal was consistently greater than that of MS2 phage irrespective of core media or flow conditions. There were relatively minor removals (factors of 1-2.5) of both microbes under saturated conditions, reductions of 2-3 orders of magnitude under the high flow unsaturated conditions, and almost complete removal (4 to >5 orders of magnitude) under the low flow unsaturated conditions. The much greater removal of microbes under unsaturated conditions has significant implications and potential benefits for land management decisions.