Boron Isotope as a Powerful Tool for Nutrient Source Tracking: A Multi-isotope Study of Surface-water in South FloridaEnvironmental Forensics
Oral Presentation
Prepared by A. Sharifi1, S. Ahearn2, Z. Cernada3, K. Reagan4, M. Garcia5, K. Swart1, S. Rubin Mason1
1 - SGS Isobar Science and SGS Beta Analytic, 4985 SW 74th Court, Miami, Florida, 33155, United States
2 - SGS Beta Analytic, Research and Development, Miami, FL, United States., 4985 SW 74th Court, Miami, FL, 33155, United States
3 - SGS Beta Analytic, Department of IRMS Mass-spectrometry, Miami, FL, United States., 4985 SW 74th Court, Miami, FL, 33155, United States
4 - SGS Beta Analytic, Research and Development, Miami, FL, United States, 4985 SW 74th Court, Miami, FL, 33155, United States
5 - SGS Beta Analytic, Department of IRMS Mass-spectrometry, Miami, FL, United States, 4985 SW 74th Court, Miami, FL, 33155, United States
Contact Information: [email protected]; 818-926-7929
ABSTRACT
With 260,000 Km2 expansion of the aquifer, Florida has abundant surface and ground-water resources providing fresh water for 11 million Floridians—these can easily be contaminated. Exposure to contaminated drinking and recreational waters threatens public health. Excessive urban development and rapid population growth in South Florida are straining the freshwater resources of the region and climate impacts on the water availability imposed another layer of stress on these vulnerable resources. Nutrient input, heavy metals, and organic enrichment as well as bacterial contamination represent the leading causes of degraded water quality in lakes, rivers, estuaries, and coastal waters of South Florida. Nutrient pollution, mainly nitrate, in surface water has become an environmental problem of both regional and national concern. In order to provide a successful management program for effective control of the nitrate pollution in surface water, it is essential to both identify the pollution sources and reduce the input of nitrate. This became even more important in a large aquifer system such as the one in Florida where contaminants from different point sources and non-point sources find their ways into the hydrological system. During the past decades, nitrogen and oxygen isotopes of nitrate (δ15NNO3 and δ18ONO3) has conventionally been utilized for identifying the source and fate of nitrate pollution in surface-water. However, owing to the complexity of nitrate pollution sources and the influence of isotopic fractionation, the application of this method is not straight forward. In this study, we paired the δ15NNO3 with δ11Bwater data on water samples from six selected sites to better confine the nitrogen sources. The conventional isotope pairs (δ15NNO3 and δ18ONO3) suggest that in the collected samples the nitrate contaminants may have sourced from manure, sewer, inorganic fertilizers, and even marine nitrate. By using δ15NNO3 - δ11Bwater pairs, all samples clustered in the region representing manure as a source of nutrients. We also took a multi-isotope approach to characterize the surface-waters of South Florida by analyzing an array of isotopes at selected sites. The local surface-water line was established by pairing the δ2Hwater and δ18Owater isotopic values. The δ18Owater for studied sites varies in a relatively narrow range from 0.94 to 2.41‰ and the δ2Hwater values ranged from 10.56 to 18.44‰. This δ18OPO4 values of dissolved phosphate also suggesting the animal faeces as source for contamination. The δ11Bwater, 87Sr/86Sr, and D14CDOC values all show distinctive variation between the sites suggesting different contributions from potential contamination sources and various mixing paths. By combining all isotopic measurement, we were able to provide an isotopic signature for each water sample, a key information for better understanding the contribution of different contamination sources and their flow paths to each site.
