Comparative assessment of N2O emissions from a New Zealand hypereutrophic lake against an oligotrophic reservoir

Abstract

ABSTRACT To establish if highly eutrophic lakes generate higher N2O emissions than non-eutrophic aquatic environments in New Zealand, we monitored N2O emissions from hypereutrophic Lake Horowhenua, near Levin, and the oligotrophic Turitea dam reservoir, near Palmerston North, used as control. Based on more than 12 months of monitoring data, N2O emissions from Lake Horowhenua were estimated to −0.05–6.93 mg-N2O·m−2·d−1 (n = 66), with a median of 0.30 mg-N2O·m−2·d−1. At the Turitea reservoir, N2O emissions ranged from −0.02–1.51 mg-N2O·m−2·d−1 with a median of 0.15 mg-N2O·m−2·d−1 (n = 53). No correlation was found between N2O emissions and the water temperature, sunlight, dissolved oxygen, nutrient concentration or chlorophyll a. When extrapolating the emission data to NZ, we estimated NZ lakes could release 83 kt of N2O as CO2eq each year, which is low in comparison to other sectors such as agriculture. Following the Intergovernmental Panel on Climate Change methodology, the N2O emission factor for Lake Horowhenua was estimated at 0.0019 kg N2O-N per kg of N-NO3 − input into the lake.