Bren School of Environmental Science & Management, University of California, Santa Barbara , Santa Barbara, California 93106, United States.
Environ Sci Technol. 2014 Dec 16;48(24):14211-8. doi: 10.1021/es504017j. Epub 2014 Nov 26.
We coupled measurements of beach pore water residence time, determined using the radioisotopic tracer (222)Rn, with dissolved carbon and nitrogen chemistry to identify the temporal evolution and variability of dissolved inorganic nitrogen (DIN) concentrations in beach pore water along the Santa Barbara, California coastline. Pore water dissolved organic carbon (DOC) and total dissolved nitrogen (TDN) ratios (DOC:TDN) were negative exponentially correlated with residence time. Mean pore water residence times were positively correlated with tidal amplitudes, and ranged from 4.4 to 6.4 days. We used this range in mean residence times to model radon residence time distributions (RTDs), and integrated them with modeled DIN vs residence time relationships (DIN-temporal evolution, or DIN-te curves) to derive volume-weighted mean (VWM) DIN concentrations. We observed 1.2-fold and 5.2-fold differences (20% and 420% increases) in VWM DIN concentrations over the range in modeled RTDs and DIN-te curves, respectively, and a maximum 6.4-fold difference (540% increase) in VWM DIN concentrations for an interactive shift in the RTD and the DIN-te curve. Our study suggests that accounting for temporal variability in the RTD and DIN concentration of pore water is necessary to obtain more accurate estimates of DIN delivery to coastal oceans.
我们将海滩孔隙水停留时间的放射性同位素示踪剂（222）Rn 测量结果与溶解碳和氮化学相结合，以确定加利福尼亚州圣巴巴拉沿岸海滩孔隙水中溶解无机氮（DIN）浓度的时间演变和可变性。孔隙水溶解有机碳（DOC）和总溶解氮（TDN）的比值（DOC:TDN）与停留时间呈负指数相关。平均孔隙水停留时间与潮汐幅度呈正相关，范围为 4.4 至 6.4 天。我们使用此平均停留时间范围来模拟氡停留时间分布（RTD），并将其与模拟的 DIN 与停留时间关系（DIN-时间演变或 DIN-te 曲线）集成，以得出体积加权平均值（VWM）DIN 浓度。我们观察到，在模拟 RTD 和 DIN-te 曲线的范围内，VWM DIN 浓度分别相差 1.2 倍和 5.2 倍（分别增加 20%和 420%），而在 RTD 和 DIN-te 曲线的交互变化中，VWM DIN 浓度的最大差异为 6.4 倍（增加 540%）。我们的研究表明，考虑到 RTD 和孔隙水中 DIN 浓度的时间变异性，对于更准确地估计 DIN 向沿海海洋的输送是必要的。
