HIGH-RESOLUTION SPATIAL AND TEMPORAL MAPPING OF SURFACE AND GROUNDWATER STABLE ISOTOPES ENABLE INSIGHTS INTO HYDROLOGIC PROCESSES AT THE CATCHMENT SCALE

Isotopic analyses of d¹⁸O and d²H of water through the hydrologic cycle have allowed hydrologists to better understand the portioning of water between the different components. Isoscapes on a large spatial scale have been created to show isotopic variation in waters as a function of elevation, temperature, distance to coast and water vapor source. Though this has not been done on a 10,000 sq mi area, sub-regional scale or for that matter exhaustively sampling the important components of the terrestrial hydrologic cycle (groundwater, surface water and soil waters). We present the spatial and temporal isotopic results of precipitation, surface water, and groundwater of an ongoing study across Massachusetts, USA in order to establish an isotopic baseline and isoscape for the region. The isotopic signature of d¹⁸O and d²H of the samples are measured by a wavelength scanned cavity ring-down spectrometry on un-acidified water samples by a Picarro Cavity Ring Down Spectrometer (L2120-I) analyzer. Our current database consists of water samples from 14 precipitation sites, 409 ground water sites and 516 surface water sites from the three climate zones of Massachusetts as determined by the National Climate Division Center. Our results show that groundwater ranges from δ¹⁸O -11 to -1 ‰ surface water ranges from δ¹⁸O -13 to -3.84 ‰ and precipitation ranges from δ¹⁸O -17.88 to -2.89 ‰. On a first order, timing of groundwater recharge and surface water storage effects the isotopic composition of surface and groundwater. Though, on a second order, elevation and geographic location affect the isotopic composition of precipitation, groundwater and surface water. Our results indicate that for precipitation, surface water and groundwater the mean δ¹⁸O are more enriched in climate zone 3, which encompasses areas near the coast, than climate zone 1 and 2 which encompasses the western and central portion respectively. Within Massachusetts the isotopic composition of groundwater in till, glacial fluvial and bedrock aquifers are distinct which indicates the potential for surface and groundwater interaction. This dataset will become an important tool for water management and water resources.