Article Dans Une Revue Aquatic Sciences - Research Across Boundaries Année : 2026

Spatial variability in nutrient and organic matter concentrations during hydrological fragmentation of an intermittent temperate catchment

Résumé

Intermittent and ephemeral streams are watercourses that cease to flow and/or dry up during part of the year. Their seasonal drying is sometimes preceded by a stream fragmentation phase with formation of isolated pools where the biogeochemistry differs from that of perennial reaches. Our objective was to analyse how hydrological fragmentation alters the spatial variability in dissolved nutrient and organic matter concentrations in a temperate-oceanic and agriculture-impacted headwater stream, where nutrient loadings are high. We conducted repeated synoptic sampling campaigns at high spatial resolution (150–200 m) along the stream network of the Naizin catchment (7 km2) during the spring–summer-fall of 2023. We sampled 38 sites and analysed dissolved organic carbon (DOC) concentrations and fluorescence properties, dissolved inorganic nitrogen (DIN) and soluble reactive phosphorus (SRP) concentrations, during four sampling campaigns: stream recession, early and late fragmentation and reconnection. Our results showed an increase in the spatial variability of concentrations, with monotonic longitudinal gradients along the stream disappearing during hydrological fragmentation. Both DOC and SRP concentrations were higher in isolated pools than in flowing reaches, while DIN concentration was lower. The chemical composition of DIN and DOC also changed with stream fragmentation, with increasing proportions of nitrite and ammonium in DIN and humic-like organic matter in DOC. These results suggest that the main controlling processes in the isolated pools were streambed mobilisation of SRP and DOC, along with denitrification under anoxic conditions. We expect the observed spatio-temporal patterns in nutrient and DOC concentrations to become more widespread in the future as intermittent streams will become more frequent owing to climate change.

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Dates et versions

hal-05370583 , version 1 (18-11-2025)

Identifiants

Citer

Andrés Casanova, Rémi Dupas, Daniel von Schiller, Laurent Jeanneau, Anne Jaffrezic, et al.. Spatial variability in nutrient and organic matter concentrations during hydrological fragmentation of an intermittent temperate catchment. Aquatic Sciences - Research Across Boundaries, 2026, 88 (1), pp.12. ⟨10.1007/s00027-025-01247-2⟩. ⟨hal-05370583⟩
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