Inflows of geothermal fluid chemicals to the Waikato River catchment, New Zealand

Abstract

Data collected from two monitoring programmes conducted by Environment Waikato, New Zealand, have been used to estimate the mass flows of Li, B, As, SO 4 , and Cl from geothermal fluids entering the Waikato River up stream of Lake Whakamaru. Chloride is the major anion in geothermal waters and is closely related to Li, B, and As. The total river water mass flow of Cl is 4600 g s -1 at the outlet of Lake Whakamaru and of this, 78% originates from geothermal fluids; 13% flows into Lake Taupo, and 65% enters the river down stream of Lake Taupo. The Wairakei field contributes the largest fraction of 45% and geothermal fluid flows which were not directly measured in the monitoring programmes contribute 23%. The remaining 10% derives from measured flows from 14 of the 16 known geothermal fields. The origins of Li, As, and B closely follow those of Cl. Geothermal SO 4 is produced from the oxidation of H 2 S carried by geothermal steam and the estimates made of the mass flows originating from geothermal fluids are less certain than those for Cl.

Geochemistry and Sources Apportionment of Major Ions and Dissolved Heavy Metals in a Small Watershed on the Tibetan Plateau

“…Thorsten et al [29] showed that concentrations of Mn, Zn, and Cu in Río Vacas Heladas (Chile) exceeded WHO guideline values for drinking water. Timperley et al [30] estimated that 78% of the Cl − in the Waikato River (New Zealand) comes from geothermal fluids. More and more studies are proving the impact of geothermal water on rivers related to river runoff.…”

Arsenic speciation of geothermal waters in New Zealand

“…17,18 As a consequence of this geothermal influence, elevated levels of arsenic have been identified along the Waikato River, in other waterways and biota across the TVZ. [18][19][20][21][22][23][24][25][26] For example, in a specific geothermally influenced area, the Reporoa Basin, 33% of the groundwater samples exceeded the New Zealand maximum acceptable value (MAV) for drinking water of 0.010 mg l À1 As, 27 with a maximum value of 0.556 mg l À1 As observed. 28 Several investigations have reported total and arsenic speciation in New Zealand geothermal waters and geothermally sourced rivers within the TVZ.…”

“…28 Several investigations have reported total and arsenic speciation in New Zealand geothermal waters and geothermally sourced rivers within the TVZ. However, many of the reported levels are direct measurements of total arsenic only, 17,[20][21][22]24 total arsenic and arsenite species with arsenate by difference between total arsenic and arsenite, 28 total arsenic and both inorganic species, 19,29 or total arsenic with inferred arsenic speciation. Approaches taken to date have included: (1) estimation of probable forms of inorganic arsenic in geothermal fluids (often deep fluids) by combination of solubility measurements with chemical speciation calculations.…”