Temporal and spatial variation of N2O production from estuarine and marine shallow systems of Cadiz Bay (SW, Spain)

Macarena Burgos; Teodora Ortega; Jesús M Forja

doi:10.1016/j.scitotenv.2017.07.021

Temporal and spatial variation of N₂O production from estuarine and marine shallow systems of Cadiz Bay (SW, Spain)

Sci Total Environ. 2017 Dec 31:607-608:141-151. doi: 10.1016/j.scitotenv.2017.07.021. Epub 2017 Jul 27.

Authors

Macarena Burgos¹, Teodora Ortega², Jesús M Forja³

Affiliations

¹ Dpto. Química-Física, INMAR, Universidad de Cádiz, Campus Río San Pedro, s/n, Puerto Real, Cádiz, Spain. Electronic address: macarena.burgos@uca.es.
² Dpto. Química-Física, INMAR, Universidad de Cádiz, Campus Río San Pedro, s/n, Puerto Real, Cádiz, Spain. Electronic address: teodora.ortega@uca.es.
³ Dpto. Química-Física, INMAR, Universidad de Cádiz, Campus Río San Pedro, s/n, Puerto Real, Cádiz, Spain. Electronic address: jesus.forja@uca.es.

PMID: 28688256
DOI: 10.1016/j.scitotenv.2017.07.021

Abstract

There is still much uncertainty regarding the global oceanic emissions of N₂O, and particularly emissions from coastal regions, because spatio-temporal datasets have limited coverage. The concentration of dissolved N₂O in surface waters and the associated fluxes to the atmosphere have been studied in three coastal systems located near Cadiz Bay (southwestern coast of Spain) over different time scales. The three systems present different hydrodynamic characteristics (an estuary and two marine systems) that influence the distribution of N₂O in the water column. Nutrients, oxygen, and particulate organic nitrogen were also measured to investigate the processes responsible for N₂O production in the water column. Data on dissolved N₂O has been obtained in each system from i) two-year monitoring at fixed station; ii) four seasonal samplings along the longitudinal length of the system; and iii) daily sampling in summer. The concentration of N₂O ranges between 1.1 and 292.0nM indicating very high spatio-temporal variability. In general, the concentration of N₂O increased during the rainy season associated with the precipitation regime that, in turn, increases the lateral inputs of organic matter and nutrients from both natural sources (discharges into rivers and adjacent marshes) and anthropogenic activities (agriculture, urban effluents and fish farming). Dissolved N₂O also varied with the tides: the highest concentrations were measured during the ebb, which suggests that the systems export N₂O to the Bay and adjacent Atlantic Ocean. In addition nitrification seems to be an important process for N₂O formation in the water column, which also explains some of the variability in the dataset. The mean atmospheric flux of N₂O reveals that entire study area was a net source of N₂O to the atmosphere. The fluxes ranged between 0.5 and 313.2μmolm^-2day^-¹ in the estuarine system, and between -7.2 and 97.8μmolm^-2day^-¹ in the two marine systems.

Keywords: Air-water flux; Coastal systems; N(2)O; Nitrification; Spatio-temporal variability.