Seasonal variability of sediment controls of nitrogen cycling in an agricultural stream

• Published in: Biogeochemistry 2020-03, Vol.148 (1), p.31-48
• Main Authors: Comer-Warner, Sophie A., Gooddy, Daren C., Ullah, Sami, Glover, Luke, Kettridge, Nicholas, Wexler, Sarah K., Kaiser, Jan, Krause, Stefan
• Format: Article
• Language: English
• Subjects: Agricultural watersheds; Ammonium; Ammonium compounds; Attenuation; Autumn; Biogeochemistry; Biogeosciences; Catchment area; Catchments; Denitrification; Earth and Environmental Science; Earth Sciences; Ecosystems; Environmental Chemistry; Gravel; Life Sciences; Mineral nutrients; Nitrates; Nitrogen cycle; Nitrogen dioxide; Nitrous oxide; Nutrient concentrations; Nutrients; ORIGINAL PAPERS; Rivers; Sand; Seasonal variation; Seasonal variations; Seasons; Sediment; Sediments; Streambeds; Streams; Water quality
• ISSN: 0168-2563; 1573-515X
• DOI: 10.1007/s10533-020-00644-z

Agricultural streams receive large inputs of nutrients, such as nitrate (NO₃⁻) and ammonium (NH₄⁺), which impact water quality and stream health. Streambed sediments are hotspots of biogeochemical reactivity, characterised by high rates of nutrient attenuation and denitrification. High concentrations of nitrous oxide (N₂O) previously observed in stream sediments point to incomplete denitrification, with sediments acting as a potentially significant source of global N₂O. We investigated the effect of sediment type and seasonal variation on denitrification and N₂O production in the streambed of an agricultural UK stream. Denitrification was strongly controlled by sediment type, with sand-dominated sediments exhibiting potential rates of denitrification almost 10 times higher than those observed in gravel-dominated sediments (0.026 ± 0.004 N₂O–N lg g⁻¹ h⁻¹ for sand-dominated and 0.003 ± 0.003 N₂O–N µg g⁻¹ h⁻¹ for gravel-dominated). In-situ measurements supported this finding, with higher concentrations of NO₃⁻, nitrite (NO₂⁻) and N₂O observed in the porewaters of gravel-dominated sediments. Denitrification varied substantially between seasons, with denitrification increasing from-winter to autumn. Our results indicate highest NO₃⁻ reduction occurred in sand-dominated sediments whilst highest N₂O concentrations occurred in gravel-dominated sediments. This suggests that finer-grained streambeds could play an important role in removing excess nitrogen from agricultural catchments without producing excess N₂O.