Grant Award Year: 2017-2018
Principal Investigator:
David Boutt, Geosciences, University of Massachusetts Amherst
Research Description:
The resulting regional-scale monthly record of the stable isotopic composition of surface and ground water in Massachusetts will provide information on the sensitivity of stream baseflow to seasonal hydrologic variability and help to better inform water supply management.
Report
Basic Info
- Project Number: 2017MA465B
- Start Date: 3/1/2017
- End Date: 2/28/2018
- Funding Source: 104B
- Congressional
- District: MA-002
- Research Category: Climate and Hydrologic Processes
- Focus Categories: Hydrology, Drought, Groundwater
- Descriptors: None
- Principal Investigators: David Boutt
Publications
- Belaval, Marcel; Boutt, David; Schroeder, Timothy; Ryan, Peter; J. Kim, Jonathan, 2018, Characterizing the groundwater-surface water system in a PFOA-contaminated fractured rock aquifer using radon and stable isotopes, 53rd Annual GSA Northeastern Section Meeting - 2018, DOI: 10.1130/abs/2018NE-310939.
- Cole, A.; Boutt, D., 2017, Spatial and Temporal Mapping of Distributed Surface and Groundwater Stable Isotopes Enables New insights into Hydrologic Processes Operating at the Catchment Scale, American Geophysical Union, Fall Meeting 2017, abstract #H13G-1483
Problem and Research Objectives
Surface and ground water in the Northeast US are heavily impacted by intense land-use changes, urbanization (Weiskel et al., 2007), and climatic changes (Hodgkins et al., 2002; Hodgkins et al., 2003, Hunntington et al., 2004; Hayhoe et al., 2007). More emphasis is being placed on water suppliers, stakeholders, and environmental managers to assess water quantity and water quality with increasing confidence intervals for sustainable management (e.g. minimum streamflow regulations). However, an over-reliance on physical measures of hydrologic behavior (such as streamflow and water table elevation) that do not uniquely assess the connectedness, residence time, and age distribution of surface and ground waters (McDonnell et al., 2010) cloud decision-making and introduce significant uncertainty. Recently, advances in theory and instrumentation have allowed the use of geochemical tracers (such as H2O, D and 18O) in combination with physical data to resolve discrepancies in measurements and reduce uncertainty in system conceptualization (IAEA, 2000). These tools and techniques are not yet been widely available to water suppliers.
The interpretation of stable isotope data in isotope hydrology relies on accurate, high-precision measurements of H and O isotopes of water samples (Brand et al 2009; Wassenaar et al 2012). With the advent of low-cost and high-throughput liquid water isotope analyzers based on cavity ring-down spectroscopy (CRDS, Berden et al 2000), hydrologic scientists can fully utilize these tools for assessment and management decisions with greater certainty. The applicability of stable isotopic tracers rely on robust understanding of the seasonal behavior of precipitation and the characterization of the isotopic behavior of surface and ground water isotopes.
Methodology, Principal Findings, and Significance
Database and sample Collection: With support through the 104B program we have designed and built our isotope database. The current database consists of 1500 precipitation measurements across 15 stations, 2500 surface water measurements across 150 sites, and 2000 groundwater samples from 200 wells screened in overburden and bedrock wells. During the summer of 2016 alone we collected 800 new samples of surface water and groundwater. A map of new sample locations is presented in Figure 2. Significant effort was put into developing a network of collaborators at local watershed organizations. Through meetings with state entities –such as MA DCR – we are now having samples sent to us monthly from DCR and other cooperative water monitoring programs.
Results
Isotopic composition of the region varies significantly as a function of topography and season. Because of the coastal orientation of the region, there is a large variability in the mean 18O-H2O composition of precipitation due to locally dominant precipitation sources. Deuterium excess of precipitation in the range of 10 – 14 ‰ are typical. Five years of surface water samples across the region show a strong seasonal trend ranging from -10 to -3 ‰ δ18O-H2O. Surface waters depict seasonal evaporative enrichment in the heavy isotopes and demonstrate a similar magnitude of deuterium excess compared to the precipitation. During the winters of 2014 and 2015 typical seasonal trends are interrupted by distinctly depleted stream waters of the order of -12 to -11 ‰ δ18O-H2O. These excursions are consistent with a source of water vapor to the region from more northerly (colder) regions. Mean stream water δ18O- H2O isotopic compositions show a strong relationship to upgradient drainage area. Groundwater compositions range from -12 to -5 ‰ δ18O-H2O across all the sites. A correlation between groundwater well elevation and δ18O-H2O is observed with higher elevation sites depleted in heavy isotopes with variations of 2-3 ‰ δ18O-H2O at any given elevation. Groundwater isotopic composition is distinct between overburden aquifer types (till, glacial fluvial) and bedrock suggesting that these aquifers are experiencing unique mixtures of recharge water. The development of this database and the resulting science will enable local and regional water stakeholders to manage protect water resources while allowing hydrologists explore regional and globally relevant scientific questions.
The Database in Action
Through our partnership with MA DCR Quabbin watershed environmental quality team, we prototyped isotopic baseflow separation using data collected from the network during a precipitation event in June of 2016. Figure 3 summarizes the data collected during this event that plots total stream discharge (blue) and isotopic composition of the stream water during the event. A gray bar shows a composite analysis of the precipitation that fell during the storm (~ -4. δ18O-H2O ‰). Before the storm, streamflow isotopic composition was about -9 δ18O-H2O ‰. The isotopic composition of the stream water gradually increases to – 7.2 δ18O-H2O ‰ and then falls back towards the pre-event composition. Using a two endmember mixing model based on the isotopic composition of precipitation and that of the pre-event stream water we estimate that proportion of new water in the stream (the precipitation) is the red line on the hydrograph. Summing up the area of the curve it turns out that about 75% of the discharge during the event was old water stored in the catchment and hydraulically pushed out of the ground by infiltrating new water. This type of information is important to consider when interpreting run-off events from a water quality perspective.
Information Transfer Program Introduction
One of the Massachusetts Water Resources Research Center’s goals is the transfer of information on water resources. In FY2017 we proposed to hold two educational symposia: a water conference symposium focused on water supply challenges and the water-energy nexus, and the New England Graduate Student Water Symposium.
Progress results for each project are summarized for the reporting year in the following sections.