Estimates of flushing times, submarine groundwater discharge, and nutrient fluxes to Okatee Estuary, South Carolina

Abstract

[1] A physical model based on determining the fraction of the tidal prism that returns to the estuary on the next high tide is used to estimate the flushing time of the Okatee River estuary. Ra is used to determine the apparent age of water in the estuary. These ages range from 1.6 to 5 days, with an average of 3.4 days. These three independent estimates are in remarkably close agreement, certainly within the error of each estimate. We use these residence times to develop a mass balance model for the radium isotopes in the Okatee estuary. We consider decay, mixing, sedimentary input, river input, and submarine groundwater discharge (SGD). The major loss term for each isotope is mixing with water in Port Royal Sound; the major input for each isotope is SGD. At steady state these terms must balance. Knowing the water age and the radium isotope composition of groundwater entering the Okatee allows us to estimate an average SGD flux of 1 m 3 /s. The SGD flux is a factor of 3-4 greater during the summer relative to the winter. This SGD supplies a considerable quantity of nutrients and carbon into the Okatee system.

Unexpected source of Fukushima-derived radiocesium to the coastal ocean of Japan

“…1B). To quantify the magnitude of this 137 Cs source, we used parallel measurements of radium isotopes ( 223 Ra, 11.4 d; 224 Ra, 3.66 d), which are a well-established tool for providing regional scale estimates of submarine groundwater discharge (21,22). Radium isotopes are continuously produced in aquifer sediments by the decay of insoluble thorium parent isotopes.…”

“…A Ra isotope mass-balance model (21)(22)(23)(24) for the surf zone was used to estimate the volume of ocean water that exchanges with the beach aquifer on a daily basis. In the model, we assume that submarine groundwater discharge is the only source of Ra to the surf zone and that this source is balanced by Ra loss due to decay and mixing.…”

“…The model assumes (i) that the system is at steady state, which is a fair assumption due to the fast production rate of shortlived radium isotopes (40); (ii) that submarine groundwater discharge is the primary source of Ra to the surf zone (23,24), in other words, that diffusion from sediments is negligible, which we think is satisfied given the high-energy surf zone (41,42); and (iii) that this input is balanced by the loss of Ra due to decay and mixing (ref. 22 and Eq. 3).…”

<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

“…Generally, in a defined system with an assumed steady state, the Ra mass balance is equal to the sum of inputs, which are usually from river supply, sediments diffusion, SGD, and the loss, which includes open seawater mixing and Ra decay (e.g., Moore et al, 2006). Based on this, Ra mass balance model is another approach to quantify the magnitude of SGD.…”

Discovery and characterization of submarine groundwater discharge in the Siberian Arctic seas: a case study in the Buor-Khaya Gulf, Laptev Sea

“…Some authors suggest that it would take ∼ 5-7 millennia for subsea permafrost to reach thaw point (Romanovskii et al, 2005), meaning that the coastal subsea permafrost is still stable. Others believe that in the coastal areas of the shallow Siberian Arctic seas, where permafrost was submerged most recently, taliks (layers or columns of thawed sediments within permafrost) might form as a result of the combined effect of geothermal flux from fault zones, the warming effect of rivers and overlying seawater, and the already present thermokarst Shakhova et al, 2009Shakhova et al, , 2015Nicolsky and Shakhova, 2010; Figure 1. A view of the Arctic hydrological cycle showing key links between land, ocean, and atmosphere (modified from http://arcticchamp.…”