The effects of drying on sediment nitrogen content in a Mediterranean intermittent stream: a microcosms study
2012
Gómez, Rosa | Arce, M Isabel | Sánchez, J Javier | del Mar Sánchez-Montoya, M.
Mediterranean climates predispose aquatic systems to both flood and drought periods, therefore, stream sediments may be exposed to desiccation periods. Changes in oxygen concentrations and sediment water content influence the biotic processes implicated in nitrogen dynamics. The objectives of this study were to identify (1) the changes of inorganic nitrogen in stream sediments during the transition from wet to dry conditions, and (2) the underlying processes in N dynamics and its regulation. Extractable sediment NO3 −-N and NH4 +-N, organic matter and extractable organic carbon content were assessed during natural desiccation in microcosms with sediments from an intermittent Mediterranean stream. In agreement with our initial hypothesis, our results showed how the NO3 −-N content of the sediment was enhanced during the first 10Â days of sediment drying, whereas NH4 +-N was lost by 14Â days post-drying. During the first 10Â days, sediment desiccation seemed to stimulate the net N-mineralization and net nitrification from sediments. Afterwards, the extractable NO3 −-N concentration sharply dropped, which may be attributed to lower ammonium-oxidation rates as ammonium and organic matter are depleted, and to an increase in NO3 −-N consumption by microbial populations. Denitrification was inhibited, with a significant decrease as % water-filled pore space lowered. We hypothesize that the sediment inorganic N content enhanced during sediment desiccation could be released as part of the N pulse observed after sediment rewetting. However, the stream N availability after rewetting dried sediments would differ depending on desiccation period duration.
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