Artificial tracer testing is an effective technique to identify fluid flow pathways and characterize subsurface hydrological properties. Synthetic DNA tracers, available in virtually unlimited number of unique variations, enable multiwell tracer testing and have the potential to improve the characterization of groundwater flowpaths enormously. This study investigated the effect of DNA length (i.e., number of base pairs) and adsorption on DNA tracer transport via well‐controlled laboratory experiments. Nine unique synthetic double‐stranded DNA tracers were designed with varying lengths (90–200 base pairs) and flowed with reference solute tracers (bromide and lithium) through columns packed with glass beads or Ottawa sand. The peak arrivals of DNA tracers were earlier than bromide in the glass‐bead column test, yet significantly retarded in the sand column test. In a given porous medium, DNA length did not have noticeable effects on peak arrival or tracer dispersion. However, DNA tracer recovery increased with increasing DNA length in the glass‐bead column test but decreased with increasing DNA length in the sand column test, likely resulting from the corresponding trends in partition coefficients as revealed by tracer transport modeling. Such reversed trends in different porous media likely resulted from the different likelihoods for longer DNA to have multisegment attachment during transport. Our findings suggest that both DNA length and the surface properties of the porous medium have notable effects on DNA tracer transport and hence need to be considered carefully in future tracer test designs in terms of site selection, DNA sequence design and data interpretation.

中文翻译：

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DNA示踪剂通过多孔介质的运输-DNA长度和吸附的影响

人工示踪剂测试是一种有效的技术，可识别流体流动路径并表征地下水文特性。合成DNA示踪剂几乎可以无限数量地使用，可以进行多孔示踪剂测试，并有潜力极大地改善地下水流动路径的特性。这项研究通过良好控制的实验室实验研究了DNA长度（即碱基对数）和吸附对DNA示踪剂运输的影响。设计了九种独特的合成双链DNA示踪剂，它们具有不同的长度（90-200个碱基对），并与参考溶质示踪剂（溴化物和锂）一起流过装有玻璃珠或渥太华沙的色谱柱。在玻璃珠柱试验中，DNA示踪剂的峰值到达时间早于溴化物，但在砂柱测试中却明显滞后。在给定的多孔介质中，DNA长度对峰到达或示踪剂分散没有明显影响。但是，在玻璃珠柱试验中，DNA示踪剂回收率随DNA长度的增加而增加，而在砂柱试验中，DNA示踪剂回收率随DNA长度的增加而降低，这可能是由于示踪剂转运模型显示的分配系数的相应趋势所致。不同多孔介质中这种相反的趋势可能是由于较长的DNA在运输过程中具有多段连接的可能性不同。我们的发现表明，DNA长度和多孔介质的表面性质都对DNA示踪剂的运输有显着影响，因此，在未来的示踪剂测试设计中，从位点选择上需要仔细考虑，