Nitrous oxide emission from some English and Welsh rivers and estuaries

Abstract

Nutrient and N₂O concentrations in the water columns were measured seasonally over a full salinity range in the nutrified rivers Colne, Stour, Orwell, Deben, Trent, Ouse and Humber and their estuaries on the east coast of England between August 2001 and May 2002, and in the oligotrophic rivers Conwy, Dovey and Mawddach in North and West Wales between August 2002 and May 2003. Nutrient and N₂O concentrations in the nutrified English rivers and estuaries were much higher than those in the Welsh rivers. N₂O concentrations and % saturation in the estuaries were significantly correlated with nitrate, nitrite and ammonium concentrations in the water. The strongest correlation was with nitrite (r ² = 0.56, p < 0.01), suggesting that nitrite was the most significant factor among the different nutrients in regulating N₂O concentration in the estuaries. N₂O concentrations in the English rivers and estuaries were supersaturated throughout the year with annual averages from 186.9 to 992.9%, indicating that these rivers and estuaries were sources of atmospheric N₂O, whereas in the Welsh rivers N₂O concentrations were much lower with annual averages from 113.6 to 137.4% saturation. Although the estuarine area in the Colne was almost the same as that in the Conwy, the annual N₂O emission from the Colne was much higher (937498 mol N yr⁻¹) than in the Conwy (23020 mol N yr⁻¹). On the east coast, riverine emissions of N₂O were only 0.5–12.5% of the total emission from rivers and estuaries. Thus rivers were negligible, but estuaries were significant contributors to the UK N₂O inventory.