Erler, Dirk V., Shepherd, Benjamin O., Linsley, Braddock K., Lough, Janice M., and Cantin, Neal E. (2018) Coral skeletons record increasing agriculture-related groundwater nitrogen inputs to a South Pacific reef over the past century. Geophysical Research Letters, 45 (16). pp. 8370-8378.

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Abstract

Anthropogenic activity on tropical islands has been linked with nitrogen (N) contamination of groundwater and subsequent coral reef health decline. However, identifying the temporal patterns of groundwater N contamination has proven difficult because of an absence of long-term records. Here we use delta N-15 in coral skeleton organic material (CS-delta N-15) to reconstruct historical patterns of groundwater N discharge to a coral reef system at Rarotonga in the Cook Islands in the South Pacific. Analysis of coral skeletal material dating back to 1880 CE clearly shows that the delta N-15 of N available in the reef environment around Rarotonga increased between 1980 and 2000. We propose that rapid agricultural development in the Cook Islands between 1960 and 1985 increased aquifer N concentrations leading to the elevated delta N-15 of groundwater NO3-. The discharge of this groundwater N appears to have continued for at least 15 years after the cessation of the agricultural boom. This has important implications for the management of groundwater contamination on low-lying tropical islands.

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