Passive samplers can be used to determine time-integrated patterns of water chemistry at one or many locations throughout a stream network while minimizing cost and sampling time. A passive flux meter (PFM) simultaneously estimates time-averaged water and solute mass fluxes in flowing water. PFMs have been used in groundwater to quantify contaminant flux but have been used only very recently in streams. In this study, PFMs were deployed in the surface and subsurface of headwater stream channels to examine the efficacy of the device to quantify mean concentrations of calcium, aluminum, and sulfur in streams of the Hubbard Brook Experimental Forest in New Hampshire, USA. In general, the PFM estimates of surface and subsurface stream chemistry were more accurate when flow rates were higher and more water passed through the PFM. During the lowest flows, PFMs overpredicted concentrations by 50 to 800%. In estimating calcium concentrations, 5 PFMs were within 10% of grab sample concentrations and 7 PFMs were within 30% of grab sample concentrations out of a total of 35 comparisons. Likewise, for sulfur concentrations, 4 PFMs were within 10% of grab sample concentrations and 7 PFMs were within 30% of grab sample concentrations out of 35 comparisons. Concentrations of aluminum were too low to be quantified above 90% confidence. PFMs calculated a lower cumulative discharge through the surface water PFMs than through the subsurface which may be explained by flow divergence around the sampler. Changes to PFM design and shorter deployment times are proposed to increase the efficacy of the PFM. / Master of Science / Passive sampling of headwater streams has advantages over traditional water sampling in quantifying stream water chemistry over time and space, while minimizing cost and sampling time. A passive flux meter (PFM) is a sampler that estimates local time-averaged discharge of water and time-averaged solute amount in flowing water without the need for constant monitoring, maintenance, or power sources. PFMs have been used in groundwater systems to quantify contaminant concentrations but have only been used very recently in streams or in the sediments below streams. In this study, PFMs were installed in headwater streams and the shallow sediments below the streams to examine the ability of the device to quantify the natural water chemistry. Concentrations of calcium, aluminum, and sulfate were evaluated in streams of the Hubbard Brook watershed in New Hampshire, USA. Concentrations of aluminum were too low to be quantified. In general, the PFM estimates of surface and subsurface stream chemistry were more accurate when flow rates were higher and more water passed through the PFM. During the lowest flows, PFMs overestimated stream concentrations. PFMs installed in small streams measured more total volume through the device than PFMs installed in sediments below the streams. PFM design may have had an impact on these results. Changes to PFM design and shorter deployment times are proposed to increase the efficacy of the PFM
| Identifer | oai:union.ndltd.org:VTETD/oai:vtechworks.lib.vt.edu:10919/83784 |
| Date | 26 June 2018 |
| Creators | Lee, David Parrish |
| Contributors | Forest Resources and Environmental Conservation, McGuire, Kevin J., Strahm, Brian D., McLaughlin, Daniel L. |
| Publisher | Virginia Tech |
| Source Sets | Virginia Tech Theses and Dissertation |
| Detected Language | English |
| Type | Thesis |
| Format | ETD, application/pdf |
| Rights | In Copyright, http://rightsstatements.org/vocab/InC/1.0/ |
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