National Research Council of Italy, Marine Science Institute-Venice, Castello 1364/a, Venice 30122, Italy.
J Environ Radioact. 2010 Jul;101(7):571-81. doi: 10.1016/j.jenvrad.2009.08.010. Epub 2009 Sep 4.
The four naturally-occurring isotopes of radium were coupled with a previously evaluated hydrodynamic model to determine the apparent age of surface waters and to quantify submarine groundwater discharge (SGD) into the Venice Lagoon, Italy. Mean apparent age of water in the Venice Lagoon was calculated using the ratio of 224Ra to 228Ra determined from 30 monitoring stations and a mean pore water end member. Average apparent age was calculated to be 6.0 d using Ra ratios. This calculated age was very similar to average residence time calculated for the same period using a hydrodynamic model (5.8 d). A mass balance of Ra was accomplished by quantifying each of the sources and sinks of Ra in the lagoon, with the unknown variable being attributed to SGD. Total SGD were calculated to be 4.1 +/- 1.5, 3.8 +/- 0.7, 3.0 +/- 1.3, and 3.5 +/- 1.0 x 10(10) L d(-1) for (223,224,226, 228)Ra, respectively, which are an order of magnitude larger than total mean fluvial discharge into the Venice Lagoon (3.1 x 10(9) L d(-1)). The SGD as a source of nutrients in the Venice Lagoon is also discussed and, though significant to the nutrient budget, is likely to be less important as the dominant control on SGD is recirculated seawater rather than freshwater.
镭的四个天然同位素与先前评估的水动力模型相结合，用于确定地表水的表观年龄，并量化意大利威尼斯泻湖的地下水排泄（SGD）。使用 30 个监测站和平均孔隙水端元确定的 224Ra 与 228Ra 的比值，计算了威尼斯泻湖的平均表观年龄。使用 Ra 比值计算的平均表观年龄为 6.0 d。该计算年龄与同一时期使用水动力模型计算的平均停留时间（5.8 d）非常相似。通过量化泻湖中 Ra 的每个源和汇来完成 Ra 的质量平衡，将未知变量归因于 SGD。总 SGD 分别计算为（223、224、226、228）Ra 的 4.1 +/- 1.5、3.8 +/- 0.7、3.0 +/- 1.3 和 3.5 +/- 1.0 x 10(10) L d(-1)，这是流入威尼斯泻湖的总平均河流径流量（3.1 x 10(9) L d(-1)）的一个数量级。还讨论了 SGD 作为威尼斯泻湖营养物的来源，尽管对营养物预算很重要，但由于 SGD 的主要控制因素是再循环海水而不是淡水，因此可能不太重要。
