John A. Izbicki Peter W. Swarzenski 2009 <p>This paper presents repeat field measurements of<span>&nbsp;</span>²²²Rn and<span>&nbsp;</span>^{223,224,226,228}<span>Ra,&nbsp;electromagnetic&nbsp;seepage&nbsp;meter-derived advective fluxes, and multi-electrode, stationary and continuous marine resistivity surveys collected between November 2005 and April 2007 to study coastal groundwater dynamics within a marine beach in Santa Barbara, California. The study provides insight into magnitude and dynamics of submarine groundwater discharge (SGD) and associated nutrient loadings into&nbsp;near-shore&nbsp;coastal waters, where the predominant SGD drivers can be both spatially and temporally separated.</span></p><p>Rn-222 and<span>&nbsp;</span>^{223,224,226,228}Ra were utilized to quantify the total and saline contribution, respectively, of SGD. The two short-lived<span>&nbsp;</span>^224,223<span>Ra isotopes provided an estimate of apparent near-shore water mass age, as well as an estimate of the Ra-derived&nbsp;eddy diffusion&nbsp;coefficient,&nbsp;</span><i>K</i>_h<span>&nbsp;</span>(²²⁴Ra&nbsp;=&nbsp;2.86&nbsp;±&nbsp;0.7&nbsp;m²<span>&nbsp;</span>s⁻¹;<span>&nbsp;</span>²²³Ra&nbsp;=&nbsp;1.32&nbsp;±&nbsp;0.5&nbsp;m²<span>&nbsp;</span>s⁻¹). Because<span>&nbsp;</span>²²²Rn (<i>t</i>_½&nbsp;=&nbsp;3.8&nbsp;day) and<span>&nbsp;</span>²²⁴Ra (<i>t</i>_½&nbsp;=&nbsp;3.66&nbsp;<span>day) have comparable half-lives and production terms, they were used in concert to examine respective water column removal rates. Electromagnetic seepage meters recorded the physical, bi-directional exchange across the&nbsp;sediment/water interface, which ranged from −6.7 to 14.5</span>&nbsp;cm day⁻¹, depending on the sampling period and position relative to the low tide line. Multi-day time-series<span>&nbsp;</span>²²²Rn measurements in the near-shore water column yielded total (saline&nbsp;+&nbsp;fresh) SGD rates that ranged from 3.1&nbsp;±&nbsp;2.6 to 9.2&nbsp;±&nbsp;0.8&nbsp;cm day⁻¹, depending on the sampling season. Offshore<span>&nbsp;</span>²²⁶Ra (<i>t</i>_½&nbsp;=&nbsp;1600&nbsp;year) and<span>&nbsp;</span>²²²Rn gradients were used with the calculated<span>&nbsp;</span><i>K</i>_h<span>&nbsp;values to determine&nbsp;seabed&nbsp;flux estimates (dpm m</span>⁻²<span>&nbsp;</span>day⁻¹), which were then converted into SGD rates (7.1 and 7.9&nbsp;cm day⁻¹, respectively). Lastly, SGD rates were used to calculate associated nutrient loads for the near-shore coastal waters off Santa Barbara. Depending on both the season and the SGD method utilized, the following SGD-derived nutrient inputs were computed (mol per day per meter of shoreline): NH₄⁺&nbsp;=&nbsp;0.06–0.29&nbsp;mol day⁻¹<span>&nbsp;</span>m⁻¹; SiO₄&nbsp;=&nbsp;0.22–0.29&nbsp;mol day⁻¹<span>&nbsp;</span>m⁻¹; PO₄³⁻=&nbsp;0.04–0.17&nbsp;mol day⁻¹<span>&nbsp;</span>m⁻¹; [NO₂⁻&nbsp;+&nbsp;NO₃⁻]&nbsp;=&nbsp;0–0.52&nbsp;mol day⁻¹<span>&nbsp;</span>m⁻¹<span>;&nbsp;dissolved inorganic nitrogen&nbsp;(DIN)</span>&nbsp;=&nbsp;0.01–0.17&nbsp;mol day⁻¹<span>&nbsp;</span>m⁻¹<span>, and&nbsp;dissolved organic nitrogen&nbsp;(DON)</span>&nbsp;=&nbsp;0.08–0.09&nbsp;mol day⁻¹<span>&nbsp;</span>m⁻¹. Compared to the ephemeral nature of fluvial and marine inputs into this region, such SGD-derived loadings can provide a sustained source of select nutrients to the coastal waters off Santa Barbara, California that should be accounted for in mass balance estimates.</p> application/pdf 10.1016/j.ecss.2009.03.027 en Elsevier Coastal groundwater dynamics off Santa Barbara, California: combining geochemical tracers, electromagnetic seepmeters, and electrical resistivity article