Quantifying potential nitrogen removal by denitrification in stream sediments at a regional scale

Abstract

Potential denitrification rates were measured using the acetylene block method, in sediments collected from streams in the sub-tropical, south-east Queensland region of Australia. Our aim was to estimate how much nitrogen could be removed from lotic systems by denitrification at the regional scale. Denitrification measured at 65 sites in August and September from a catchment of 22700 km2 was extrapolated to all streams and rivers in the region based on the sediment area available for denitrification. Denitrification rates ranged between 4 and 950 μmol N m-2 h-1, with most sites having rates below 150 μmol N m-2 h-1. Based on these results, the current study estimates that a total of 305 t of nitrogen could be denitrified per year from all streams and rivers in the region, representing 6% of the total annual nitrogen load from surrounding land use. During baseflow conditions, when nitrogen loads to streams are low, the proportion of nitrogen removed through denitrification would be substantially higher, in some cases removing 100% of the nitrogen load. It is proposed that denitrification is an important process maintaining low concentrations of dissolved inorganic nitrogen under baseflow conditions and is therefore likely to enhance nitrogen limitation of primary production in this region.