Questions come from the Bluebook question bank.
Delta 15-N Values in Seagrass Samples from Four Sites on the Yucatan, 2016–2017Site February 2016 October 2016 February 2017 October 2017 Akumal Bay no data available 3.3 2.0 6.3 Mahahual 0.7 no data available 2.5 3.4 Tulum 6.1 5.9 2.3 5.5 Xahuayxol 0.9 0.3 −0.9 1.4
Because water from natural, uncontaminated sources is less enriched with the stable nitrogen isotope 15N than wastewater from human activities is, the presence of such wastewater in nature can be detected by examining delta 15-N values (a measure of the ratio of 15N to 14N) in plants. Karla A. Camacho-Cruz and colleagues assessed delta 15-N values in the seagrass Thalassia testudinum from sites on Mexico’s Yucatan peninsula with intermediate tourism development, including Akumal Bay and Tulum, and low tourism development, including Mahahual and Xahuayxol, throughout 2016 and 2017. The data suggest that the intermediate-tourism sites experienced influxes of human wastewater. However, the researchers concluded that this happened intermittently.
Which choice best describes data from the table that support the underlined conclusion?