Timmons, Jeffrey Scott, MS MAY 2021
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Timmons, Jeffrey Scott, M.S. MAY 2021 GEOLOGY Identifying the Isotopic Signature of Lake Effect Precipitation on the Northeast Ohio Isoscape (126 pp.) Thesis Advisor: Anne J. Jefferson Lake effect precipitation occurs when cold air moves across an open body of warm water and water vapor from the lake rises through the air column, causing instability, which leads to precipitation predominantly downwind. The isotopes of hydrogen in water are less sensitive than oxygen isotopes to the kinetic fractionation that occurs during lake evaporation, resulting in a greater than normal excess of deuterium in lake effect or recycled precipitation. A water isoscape shows the spatial distribution of stable water isotopes and, in this study, I studied the isoscape of northeast Ohio to discern where lake effect precipitation affects groundwater and lake hydrology. I investigated a 10,000 km2 area in northeastern Ohio, where mean annual precipitation ranges from 900-1100 mm and winter snowfall varies from 800 to 2500 mm. Relief in the study area is <200 m. Higher elevation areas near Lake Erie form the primary snowbelt, and the surrounding areas make up the secondary snowbelt. The study area is underlain by glacial deposits and sedimentary rocks. From 13 December 2017 to 22 December 2018, precipitation was collected at 2 locations 50 km apart. One precipitation collector was in the primary snowbelt at Holden Arboretum in Kirtland, while the other precipitation collector was in the secondary snowbelt in Kent. Lake samples were collected from 30 lakes across the study area in May, July and September 2018. Groundwater samples were collected from 47 private wells during 2 sampling events in January and July 2018. River samples were collected from 7 rivers during May, July and September 2018. Twelve groundwater and surface water locations were sampled biweekly along a transect from Kent to Kirtland. All water samples were analyzed for δ18O and δ2H with a Picarro L2130-i. Precipitation in the primary and secondary snowbelts are isotopically similar, but during the winter there is clear indication of storms reaching one area but not both. Precipitation has marked inter- storm isotopic variability, particularly in the winter. Two-week weighted averages reflect this variability, somewhat masking the typical sinusoidal seasonal signal. The average annual precipitation for Holden has δ18O of -9.3‰ and δ2H of -60.6‰. The Kent, average annual precipitation has δ18O of -9.3‰ and δ2H of -59.9‰. The 2-week isotopic values for δ18O ranged from -19.5‰ to -3.4‰ and the δ2H ranged from - 140.9‰ to -15.0‰. The local meteoric water line (LMWL) was calculated from the precipitation samples δ2H =7.79 δ18O +11.42. The LMWL slope is similar to the global meteoric water line, but the d-excess is greater, indicating that precipitation is recycled. Groundwater δ18O varies by more than 6‰ across the study area (-10.45 to -3.21‰), with the most depleted ground waters occurring in the high elevation, primary snowbelt. D-excess ranged from -6.0‰ to 15.7‰, with 72% of wells (34) having a d-excess value greater than 10.0‰ and 26% of wells (12) having an evaporative signature in January. Lake water isotopes reflect an evaporative signature that does not provide clear evidence for precipitation recycling. The range of d-excess values for lakes 13.0‰ to -12.1‰, with 6 of 30 lakes showing a recycled isotopic signature in May and only 3 in September. Only four of the lakes showed a progressive evaporative enrichment over the summer. Evaporation to inflow ratios ranged from -0.206 to 0.083. IDENTIFYING THE ISOTOPIC SIGNATURE OF LAKE EFFECT PRECIPITATION ON THE NORTHEAST OHIO ISOSCAPE A thesis submitted to the faculty of Kent State University in partial fulfillment of requirements for the degree of Master of Science in Geology May 2021 BY Jeffrey S. Timmons © Copyright All rights reserved Except for previously published materials Thesis written by Jeffrey S. Timmons B.S., Kent State University, 2017 M.S., Kent State University, 2021 Approved by __________________________________________, Advisor Anne Jefferson __________________________________________, Chair, Department of Geology Daniel Holm __________________________________________, Interim Dean, College of Arts and Sciences Mandy Munro-Stasiuk Table of Contents TABLE OF CONTENTS --------------------------------------------------------------------------------------------------- v LIST OF FIGURES --------------------------------------------------------------------------------------------------------- vii LIST OF TABLES ----------------------------------------------------------------------------------------------------------- x ACKNOWLEDGMENTS ---------------------------------------------------------------------------------------------------xi CHAPTERS Introduction -----------------------------------------------------------------------------------------------------------------------1 Methods --------------------------------------------------------------------------------------------------------------------------10 Sample collection ----------------------------------------------------------------------------------------------------10 Precipitation ------------------------------------------------------------------------------------------------10 Groundwater -----------------------------------------------------------------------------------------------12 Lakes ----------------------------------------------------------------------------------------------------------12 Transect water samples ----------------------------------------------------------------------------------13 Rivers ---------------------------------------------------------------------------------------------------------14 Stable Isotope analyses ---------------------------------------------------------------------------------------------14 Evaporation to inflow ratios for lakes ---------------------------------------------------------------------------15 Results -----------------------------------------------------------------------------------------------------------------------------18 Distribution of sampling locations and northeast Ohio sub-regions ------------------------------------18 Precipitation -----------------------------------------------------------------------------------------------------------18 Precipitation and snowfall ------------------------------------------------------------------------------18 Precipitation Isotopes ----------------------------------------------------------------------------------- 22 Groundwater ----------------------------------------------------------------------------------------------------------28 Lithology, surface elevation and well depths -------------------------------------------------------28 Groundwater Isotopes ---------------------------------------------------------------------------------- 30 Groundwater d-excess ---------------------------------------------------------------------------------- 37 Lake --------------------------------------------------------------------------------------------------------------------- 43 Seasonal variability --------------------------------------------------------------------------------------- 43 v Lake Characteristics -------------------------------------------------------------------------------------- 46 Lake Isotopes ---------------------------------------------------------------------------------------------- 47 Lake d-excess and relationship with groundwater ----------------------------------------------- 54 Trends over time within regions ---------------------------------------------------------------------- 58 Evaporation to inflow ratios --------------------------------------------------------------------------- 67 Discussion ------------------------------------------------------------------------------------------------------------------------ 73 Identifying the lake effect signature on the precipitation isoscape ------------------------------------- 73 Identifying the lake effect signature on the groundwater isoscape ------------------------------------ 74 Identifying the lake effect signature in the lake samples -------------------------------------------------- 77 Testing the hypotheses ------------------------------------------------------------------------------------------- 79 Conclusion ------------------------------------------------------------------------------------------------------------------------81 Directions for future research ------------------------------------------------------------------------------------ 82 REFERENCES ----------------------------------------------------------------------------------------------------------------------83 APPENDICES A. [River data, graphs and maps] -------------------------------------------------------------------------86 B. [Transect data]---------------------------------------------------------------------------------------------96 C. [All isotope data with sampling location]-----------------------------------------------------------105 vi LIST OF FIGURES Figure 1. shows the locations of precipitation, groundwater, and lake sampling locations, with respect to county boundaries and identified sub-regions. ---------------------------------------------------------------18 Figure 2. Daily precipitation amount (mm) from the closest NOAA observer stations to each collection location: the Chardon NOAA observer station for Holden and Twin Lake Kent NOAA observer station for Kent comparison.---------------------------------------------------------------------------------------20