Carbon dioxide emissions from mineral springs in Northland and the potential of these sites for studying the effects of elevated carbon dioxide on pastures

Sites in Northland with mineral springs were examined for their potential as experimental areas to study the effects of elevated carbon dioxide (CO2) on grassland. A suitable site was defined as having: (1) grassland species; (2) cold springs; (3) high levels of gas flow; and (4) high concentrations of CO2. Two sites were selected for detailed study-Hakanoa Springs near Kamo and Waiare Spring near Kaeo. At Hakanoa, the vegetation was scrubby but at least 10 grassland species were present. Two vents released large volumes of CO2 resulting in concentrations at 10 cm above ground level that ranged from 5000 mu l/litre near the vent to 400 mu l/litre 10 m downwind. At Waiare, the spring was situated in a grazed grass paddock that contained 10 grass species as well as Trifolium repens and Lotus spp. There was little enrichment of CO2 above the canopy but high concentrations were measured at mid-canopy height with a maximum value exceeding 2000 mu l/litre. Because of the nature of the enrichment within, but not above the canopy, it appeared that the enrichment was from the soil. This was confirmed by measurements of soil CO2 efflux that were consistently very high (greater than 9.9 g CO2/m(2) per h in some instances). The springs have existed for decades and the sites offer the potential to study plant material that has been exposed to elevated CO2 for very long periods.