Geothermal arsenic (As) and its inorganic species transformation in river systems are of global concern, since As has a potential negative impact on human health and ecosystems. Periods of increased precipitation may change As concentrations and As partitioning in streams, due to elevated water tables, increased runoff generation, dilution, and interactions with sediment.In this study we investigate hydrological conditions of Jemez River, located along the Jemez fault in NM, USA, during the monsoon months June, July and August of 2015. We aim at determining how different hydrological conditions in the Jemez River during the monsoon months might affect the concentrations and riverine mass flows of geothermally derived (total) As and As III discharging in a travertine- and hot spring area called Soda Dam. Water and sediment from the river and hot springs sites, as well as streamflow measurements along a 22 km river reach were collected. The chemical composition of water and sediment was determined using Inductively Coupled Plasma-Optical Emission Spectrometry/Mass Spectrometry (ICP-OES/MS); and Ion Chromatography (IC) as well as a High Performance Liquid Chromatograph (HPLC) coupled to an ICP-MS for further water analysis. Discharge and mass flows as well as element inputs and outputs to/from Soda Dam was computed. The measurement months were characterized by a median discharge of 1642 L/s. During the measurement campaigns peak flows occurred with discharges of 2.5×104 to 6.1×104 L/s during the measurement campaigns. Arsenic concentrations were between 1.3 and 107 μg/L in river water, between 167.3 and 6707 μg/L in hot spring waters, and between 0.37 and 13.1 μg/kg in river bed sediment. Arsenic III was found in hot springs water and river water. Infiltration and subsurface flows induced by fault-associated fractures and permeability structures were found to be likely to divert water at Soda Dam, as reflected in large discharge differences along the reach (470 to 1305 L/s). These flows also had an impact on As concentrations in riverine and hot spring water since they mobilize As from bedrock and sediment. Changing mass flows of As can only in a few cases be explained by dilution processes by Jemez River, which has previously been assumed to be the main control on As mass flows along the stretch. Instead, our findings are likely to reflect changes in chemical composition of the mixed geothermal waters discharging at Soda Dam, due to changing mixing ratios of ground waters of different compositions. The present study hence provides a refined interpretation of the hydrological pathways in Soda Dam and Jemez River, and calls for more discharge and geochemical investigations during a longer study period, to properly investigate the driving forces behind the fate of the As from geothermal fluids.
| Identifer | oai:union.ndltd.org:UPSALLA1/oai:DiVA.org:su-127418 |
| Date | January 2016 |
| Creators | Hansson, Lina |
| Publisher | Stockholms universitet, Institutionen för naturgeografi |
| Source Sets | DiVA Archive at Upsalla University |
| Language | English |
| Detected Language | English |
| Type | Student thesis, info:eu-repo/semantics/bachelorThesis, text |
| Format | application/pdf |
| Rights | info:eu-repo/semantics/openAccess |
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