'Mean residence times and sources of Christchurch springs'

摘要

The Stewart et al. (2018) paper reports the results of groundwater geochemical and age tracer analyses for five Christchurch springs post the Mw 6.2 Christchurch Earthquake (22 February 2011). The importance of the papers content and the application of the methodology cannot be overstated for ongoing Christchurch Artesian System (CAS) groundwater monitoring and input into the Environment Canterbury groundwater management plan. The provenances and tritium analyses of two of the Stewart et al. (2018) sampled springs are particularly important - WL wetland reserve, Woolston and SB Sandbar spring, McCormacks Bay located adjacent to and within the Avon-Heathcote Estuary, south-east Christchurch at the Canterbury Plains-Port Hills margin. Fringe Banks Peninsula springs at Ferrymead and Mount Pleasant, sourced from volcanic rock groundwater, have been known long-term (Brown and Weeber, 1994) but not CAS-sourced artesian springs. If WL and SB are artesian springs they are the first totally CAS coastal artesian springs to have been identified at Christchurch. To date for the Christchurch coastal plains sector all springs are derived from near surface Waimakariri River gravel channels, rain and drainage water. The mean residence times estimated from tritium (TU) were 150 years for WL and >180 years for SB, showing accordance of age with CAS-sourced groundwater. The paper lacks geological input as to Christchurch subsurface stratigraphy and site-specific hydrogeology descriptions for the springs. When these are considered for one of the sampled spring sites there is a distinct possibility that the sample was derived from a leaking abandoned well rather than an artesian spring. Photographs of the springs would have enhanced the paper.