Radon and radium isotope assessment of submarine groundwater discharge in the Yellow River delta, China

Abstract

[1] Naturally occurring chemical tracers were used to assess the magnitude of submarine groundwater discharge (SGD) during two different sampling periods at a coastal site south of the Yellow River delta, China. We used salinity and pH as indicators of the terrestrial and recirculated seawater components of discharging groundwater and radium isotopes to quantify offshore transport rates. We then used an hourly time series of multiple radium isotopes ( 224 Ra, 223 Ra, and 226 Ra) to quantify SGD rates and also used 222 Rn and seepage meters to independently quantify SGD rates as a comparison to the radium results. Offshore transport rates were found to range from 3.3 to 4.7 cm s À1 . Modeled time series radium activities indicated average SGD rates ranging from 4.5 to 13.9 cm d À1 in September 2006 and from 5.2 to 11.8 cm d À1 in July 2007. Temporal trends associated with the radium approach agree with SGD patterns revealed by automated seepage meters deployed nearby, but the absolute fluxes are about 70% lower than those determined by the seepage meters. Modeled SGD rates based on 222 Rn (mean = 13.8 cm d À1 in 2006 and 8.4 cm d À1 in 2007) agree with those determined by the radium analysis. Differences in derived SGD rates between the different radium isotopes ( 226 Ra highest; 224 Ra lowest) are likely results of uncertainties in the background activities and our limited selection of appropriate groundwater/pore water end-member values. Scaling our results to the entire Yellow River delta, we find SGD fluxes (and corresponding nitrate fluxes) 2-3 times that of the Yellow River.

Dynamics of groundwater‐derived nitrate and nitrous oxide in a tidal estuary from radon mass balance modeling

“…In this section, the magnitude of SGD and its importance as source of NO spatial distribution of 222 Rn was typically mapped during one survey (Peterson et al 2008), the 222 Rn distribution was observed through 12 months of synoptic surveys. The sampling strategy was intended to account for the seasonal variation of 222 Rn concentration in the estuary.…”

The contribution of groundwater discharge to the overall water budget of two typical Boreal lakes in Alberta/Canada estimated from a radon mass balance

“…In areas where advective groundwater inflow could be verified by significantly higher excess radon concentrations, the influence of diffusive radon input was considered insignificant. The applied approach is common in other environments where advective groundwater discharge dominates other radon inputs (Cable et al, 1996;Peterson et al, 2008).…”

<sup>226</sup>Ra and <sup>228</sup>Ra in the stratified estuary of the Krka River (Adriatic Sea, Croatia): implications for submarine groundwater discharge and its derived nutrients

“…Following the approach of Peterson et al (2008), Eq. (12) was used to estimate the SGD flux as follows:…”

“…Similar to that of Ra activity, DIN and DSi variations had an opposite trend to salinity despite a small hysteresis effect observed (Figure 6c). There sources, such as SGD (e.g., Peterson et al, 2008;Moore, 2010 Ra balance as follows (Moore, 2003): 1.00 …”