Submarine groundwater discharge to a small estuary estimated from radon and salinity measurements and a box model

Abstract

Abstract. Submarine groundwater discharge was quantified by a variety of methods for a 4-day period during the early summer of 2004, in Salt Pond, adjacent to Nauset Marsh, on Cape Cod, USA. Discharge estimates based on radon and salinity took advantage of the presence of the narrow channel connecting Salt Pond to Nauset Marsh, which allowed constructing whole-pond mass balances as water flowed in and out due to tidal fluctuations. The data suggest that less than one quarter of the discharge in the vicinity of Salt Pond happened within the pond itself, while three quarters or more of the discharge occurred immediately seaward of the pond, either in the channel or in adjacent regions of Nauset Marsh. Much of this discharge, which maintains high radon activities and low salinity, is carried into the pond during each incoming tide. A box model was used as an aid to understand both the rates and the locations of discharge in the vicinity of Salt Pond. The model achieves a reasonable fit to both the salinity and radon data assuming submarine groundwater discharge is fresh and that most of it occurs either in the channel or in adjacent regions of Nauset Marsh. Salinity and radon data, together with seepage meter results, do not rule out discharge of saline groundwater, but suggest either that the saline discharge is at most comparable in volume to the fresh discharge or that it is depleted in radon. The estimated rate of fresh groundwater discharge in the vicinity of Salt Pond is 3000-7000 m 3 d −1 . This groundwater flux estimated from the radon and salinity data is comparable to a value of 3200-4500 m 3 d −1 predicted by a recent hydrologic model (Masterson, 2004; Colman and Masterson, 2004), although the model predicts this rate of discharge to the pond whereas our data suggest most of the groundwater bypasses the pond Correspondence to: J. Crusius (jcrusius@usgs.gov) prior to discharge. Additional work is needed to determine if the measured rate of discharge is representative of the longterm average, and to better constrain the rate of groundwater discharge seaward of Salt Pond.

Groundwater discharge to wetlands driven by storm and flood events: Quantification using continuous Radon-222 and electrical conductivity measurements and dynamic mass-balance modelling

“…Crusius et al, 2005;Santos et al, 2009;Taniguchi, 2002). Similarly, rapid variations in groundwater fluxes have been observed in lakes in response to factors such as seiching and precipitation (Rosenberry et al, 2013).…”

Inferring coastal processes from regional-scale mapping of 222Radon and salinity: examples from the Great Barrier Reef, Australia

“…A preliminary study in the Great Barrier Reef indicated that continuously measured radon along a coastline can be used as an indicator for the presence of SGD (Stieglitz, 2005). Burnett et al (2008) mapped radon in a coastal embayment along the Ubatuba coastline in Brazil, and Crusius et al (2005) estimated SGD discharge rates based on concurrently measured radon and salinity. Here a multi-detector field setup is evaluated for the spatial mapping of radon on a still larger spatial scale, and it is discussed how continuous mapping of this tracer, in combination with ocean water salinity, can be used to efficiently infer and interpret locations of radon input to the ocean.…”

Estimation of Groundwater and Nutrient Fluxes to the Neuse River Estuary, North Carolina

“…These include integrated marine seismic and marine electrical resistivity surveys to establish submarine groundwater salinity distribution in a hydrogeologic framework Manheim et al 2004); coring and sampling in offshore wells to analyze nutrients, stable isotopes, and groundwater age tracers, including tritium, tritium/helium, sulfur hexafluoride, and chlorofluorocarbons ); and natural groundwater tracer studies using radon gas emanation to evaluate groundwater discharge locations, rates of discharge, and time variability over tidal cycles (Crusius et al 2005). These and many other useful techniques for measuring and understanding groundwater in coastal regions, some of which were incorporated in our study of the NRE, are presented in Burnett et al (2006).…”