A tracer to bridge the scales: on the value of diatoms for tracing fast flow path connectivity from headwaters to meso‐scale catchments

Abstract

Abstract:Connectivity between different landscape units and flow paths to the stream has gained much attention in hydrological science. Recent work has focused on the threshold sequencing of spatial sources in upland forested watersheds, connectivity and its spatial patterns in the hillslope-riparian-stream continuum. Fast flow path connectivity in the HRS continuum is still difficult to decipher because of the scale-limitations of hydrometric and tracer methods. Such connectivity may be strongly non-linear and controls streamflow response and chemistry. Recently, diatoms, one of the most common and diverse algal groups, were used to detect the onset and cessation of surface runoff to small headwater streams and constrain hydrograph separation methods. In this work, we investigate the potential for diatoms to determine fast flow path connectivity between their habitat and the stream over various scaled catchments. We used seven nested sub-catchments (0.45 to 247 km 2 ) with uniform and mixed geologies and land use types within the Attert River catchment (Luxembourg) for testing our hypothesis. We categorized the prevailing diatom communities based on their habitat in the hillslope-riparian-stream continuum of one headwater catchment and sampled a storm event for diatom communities in every catchment. We present the diatom dynamics during the event hydrograph. We also outline different occurring species of diatoms and present that combinations of species or individual species can be used as a tracer for source area connectivity. Further, we show that the occurrence of aerial diatom species decreases by a power law with scale, potentially limiting the scale of application. Finally, we discuss how diatoms could indicate temporal variability of contributions from different physiographic units.

Terrestrial diatoms as tracers in catchment hydrology: a review

“…Recent work by Klaus et al 46 has tested the potential for aerial diatoms to trace hydrological connectivity between their habitat and the stream network within a set of seven-nested catchments (0.45-247 km 2 ) in the Attert River basin. While the species richness was highly variable among catchments, it did not appear to be related to catchment size.…”

“…The substantial flushing of terrestrial diatoms during precipitation events confirmed saturation excess flow (as inferred from conventional tracer work) in riparian wetlands as the dominating runoff generating process during single-peaked events. 59 They concluded from their research that terrestrial diatoms were best-suited for determining rapid surface and subsurface hydrological connectivity between the riparian zone and the stream.Klaus et al 46 further documented that in the sandstone-dominated Huewelerbach, most runoff is fed by groundwater contributions. In the absence of riparian areas, rapid surface or subsurface flows play a minor role in runoff generation.…”

“…This suggests that the terrestrial diatom reservoir is not likely to be exhausted for a 1 in 10-year precipitation event. 46 found terrestrial diatom species bound to physiographic source areas to map across the complete set of nested catchments during a rainfall-runoff event-showing their potential for tracing hydrological connectivity (from multiple source areas) over a wide range of scales (up to 250 km 2 ).Regardless of how promising terrestrial diatom work may appear from exploratory work described above, it is important to note that many other interesting new artificial (particle) tracers have been tested in recent years. Sharma et al 60 have proposed polylactic acid microspheres with incorporated strands of synthetic DNA and paramagnetic iron nanoparticles as an almost unlimited source of labeled hydrological tracers-all exhibiting identical transport properties that remain perfectly distinguishable from each other.…”

Diel fluctuations of viscosity-driven riparian inflow affect streamflow DOC concentration

“…We valid index of higher terrestrial and SUVA-254 rapidly increased. (Glaser et al, 2016;Klaus et al, 2015). was induced by terrestrial DOC input that eventually led to a For the days with diel fluctuations we reject our first hypothesis that the instream processes.…”

“…For the combinations that included discharge, we generally observed weaker and more heterogeneous relationships (Figure 3 c,e,f and he Weierbach catchment, we are convinced that SUVAidentifying terrestrial DOC in diel DOC fluctuations. Several studies already demonstrated that SUVA (Catalán et al, 2013;Fasching et al, 2016;Lee et al, 2016;Weishaar et al catchment for rising SUVA-254 values serving as a valid index Immediately after rain events, discharge, DOC concentrations and SUVA surface or near-surface runoff processes (Glaser et al, 2016;Klaus et al, 2015) the increase in DOC concentrations was induced by terrestrial DOC input that s on processes controlling diel DOC fluctuations. For the days with diel fluctu generally observed both DOC and SUVA-254 maxima in the afternoon.…”