Author(s): Beatriz Negreiros; Silke Wieprecht; Sebastian Schwindt

Linked Author(s): Beatriz Medeiros Fernandes Negreiros

Keywords: River analyst; Riverbed; Hydraulic conductivity; Connectivity; Morphological units

Abstract: The hyporheic zone of rivers hosts critical exchange processes between surface and subsurface water, governed by the sedimentary characteristics of the riverbed and the hydraulic conditions. In-situ measurements of riverbed characteristics are key to quantifying these ecologically relevant exchange processes, including interstitial dissolved oxygen and riverbed permeability. However, such analysis is challenging because these quantities change in space and time, have different units, and little data amounts. This is why we ran extended statistical analyses on a large database with years-long observations. Statistical significance of the hyporheic parameters served for testing two hypotheses. Notably, we hypothesize that (1) riverbed permeability governs the transport of oxygen-rich surface water into the hyporheic zone; and (2) interstitial dissolved oxygen saturation (IDOS) in the hyporheic zone varies with morphological units. The results based on measurements from 17 rivers and a nature-like fishway show that IDOS, a critical parameter for ecosystem health, is not normally distributed. This prohibits common analysis techniques such as ANOVA or Pearson correlation. To enable comparisons of non-normally distributed IDOS, we use Spearman rank correlation and Kruskal Wallis tests. These tests support the first hypothesis with a statistically significant confidence (p < 0.05) and a Spearman correlation of rs = 0.54 between IDOS and a novel, non-dimensional permeability proxy. To test the second hypothesis, we compute a non-dimensional halving depth, which expresses the sediment depth where IDOS values halves in relation to the nearest-surface value. The tests show that the distributions of the halving depths do not significantly differ between morphological units of glides, riffles, and pools. In addition, temporal dependence emerged as a critical parameter to explain the variance in IDOS measurements, which could be related to discharge variations, drought conditions. In conclusion, this study identifies a significant influence of sediment permeability on IDOS in the hyporheic zone, and suggests evidence for increased climatic extremes to severely affect the ecological integrity of fluvial ecosystems.

DOI: https://doi.org/10.64697/978-90-835589-7-4_41WC-P1649-cd

Year: 2025