Characterization of surface and ground water δ18O seasonal variation and its use for estimating groundwater residence times

Abstract

Abstract:18 O is an ideal tracer for characterizing hydrological processes because it can be reliably measured in several watershed hydrological compartments. Here, we present multiyear isotopic data, i.e.18 O variations (υ 18 O), for precipitation inputs, surface water and groundwater in the Shingobee River Headwaters Area (SRHA), a well-instrumented research catchment in north-central Minnesota. SRHA surface waters exhibit υ 18 O seasonal variations similar to those of groundwaters, and seasonal υ 18 O variations plotted versus time fit seasonal sine functions. These seasonal υ 18 O variations were interpreted to estimate surface water and groundwater mean residence times (MRTs) at sampling locations near topographically closed-basin lakes. MRT variations of about 1 to 16 years have been estimated over an area covering about 9 km 2 from the basin boundary to the most downgradient well. Estimated MRT error (š0Ð3 to š0Ð7 years) is small for short MRTs and is much larger (š10 years) for a well with an MRT (16 years) near the limit of the method. Groundwater transit time estimates based on Darcy's law, tritium content, and the seasonal υ 18 O amplitude approach appear to be consistent within the limits of each method. The results from this study suggest that use of the υ 18 O seasonal variation method to determine MRTs can help assess groundwater recharge areas in small headwaters catchments.

Role of a groundwater–lake interface in controlling seepage of water and nitrate

“…The sampler was installed 3.4 m from the lake shore in December, 2007 (close to two seepage meters) and left to equilibrate with pore water for one month. Upon retrieval, water in the chambers was extracted using a syringe, sampled in glass bottles with tight-fitting rubber sealed caps (Herczeg et al, 1992;Reddy et al, 2006), and stored at 5°C. The samples were analyzed with a dual-inlet mass spectrometer.…”

Time series of tritium, stable isotopes and chloride reveal short-term variations in groundwater contribution to a stream

“…Attempts have been made to correlate the TTs to catchment characteristics such as topography (McGuire et al, 2005;Mueller et al, 2013;Seeger and Weiler, 2014), geology (Katsuyama et al, 2010) or soil type (Tetzlaff et al, 2009(Tetzlaff et al, , 2011Timbe et al, 2014). Assessment of the relationship between groundwater RT and catchment TT has also been undertaken occasionally (Matsutani et al, 1993;Herrmann et al, 1999;Reddy et al, 2006). Because catchment storage is highly non-stationary, catchment TTs are known to vary over time ), yet the importance of temporal dynamics in TT distributions has been overlooked until recently.…”

Reply to comment on ‘Characterization of surface and ground water δ18O seasonal variation and its use for estimating groundwater residence times’ by R. E. Criss and W. E. Winston

“…The goal of the Reddy et al (2006) paper was to test the applicability of the υ 18 O amplitude-attenuation approach for estimating MRTs in a well-characterized catchment with significant surface-water-ground water interactions, and to evaluate the limitations of this approach by comparison of model predictions and other…”

“…Hence, in our report (Reddy et al, 2006) the isotopic analysis data used were for a specific group of samples analysed at the same time, in the same laboratory. In hindsight, it would have been beneficial to have updated our analysis with a more complete precipitation υ 18 O dataset when it became available.…”