Browsing by Author "Erwin, Elizabeth G."
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- Installation Matters: Implications for In Situ Water Quality MonitoringErwin, Elizabeth G.; McLaughlin, Daniel L.; Stewart, Ryan D. (American Geophysical Union, 2021-03-01)Novel in situ sensor technologies can measure water chemistry at high temporal frequencies, yet few studies have evaluated how installation affects measurements. In this study, we assessed the effects of commonly used protective housings on in situ sensor readings. Working in two mountain streams, we colocated specific conductance sensors in four different housing types that varied in openings for water exchange (mesh, screen, holes, and open). We compared measured conductance values through time and performed repeated salt tracer additions to evaluate the influence of housing type on calculated discharge. Sensors readings in mesh and, to a lesser extent, screen housings frequently diverged from housings with larger openings (i.e., holes and open), indicating reduced water exchange between stream water and housed sensors. Further, mesh and screen housings recorded more damped and delayed response to salt tracer additions compared to the other two housings, resulting in markedly different discharge values. From these findings, we recommend that water chemistry sensors should be deployed in a protective housing with large openings for sufficient water exchange.
- Measuring and Understanding Effects of Prescribed Fire in a Headwater CatchmentErwin, Elizabeth G. (Virginia Tech, 2019-07-11)Headwater catchments play a large role in the storage and release of water and chemical constituents, thereby influencing downstream flows and water quality. Recent advances in water quality monitoring technologies have created an opportunity to better assess water chemistry variation by using high temporal resolution, in situ sensors. However, despite these new technologies, there have been limited studies on installation approaches and their effects on sensor measurements. Accurate in situ monitoring is particularly important to capture catchment disturbance effects that may be highly dynamic over time (e.g., following storms) or limited in duration. For example, prescribed fire is a commonly applied forest management tool, but there remain questions regarding how this disturbance affects catchment soils and resultant stream water chemistry. Effective assessment of prescribed fire thus requires coupled monitoring of both soil properties and water chemistry. In this thesis, I addressed two linked objectives: i) assess the effects of commonly used protective housings on in situ sensor measurements (Chapter 2) and ii) evaluate prescribed burn effects in a southwestern Virginia, USA headwater catchment (Chapter 3). In Chapter 2, I compared four different housing types (mesh, screen, holes, and open) using in situ specific conductance measurements over time and from salt tracer injections for discharge estimates. This study demonstrated substantial effects from some of the housing types evaluated, where flow resistance reduced water exchange between stream water and water in contact with the sensor. From these findings, I suggest that in situ water quality sensors should be deployed in housing types with large openings perpendicular to flow. In Chapter 3, I assessed prescribed fire effects on soil properties (particle size, aggregate stability, and chemistry), stream discharge, and fine-scale water chemistry dynamics. Findings demonstrated some significant differences following fire in soil properties (e.g., overall decrease in aggregate stability, general decreases in total carbon and nitrogen of mineral soils), water quality (e.g., increased levels of DOC, turbidity, and nitrate) and discharge (increases in stage and flow). While these changes were statistically significant, differences in parameters before and after fire were generally small. Future work should examine if these effects persist through time, and whether the minor level of disturbance observed in this study results in any negative environmental impacts.