nitrogen intake through protein consumption and nitrogen loss through waste release on 15N enrichment in the body. When interpreting δ15N values of human remains, variations in nitrogen values within the same trophic level are also considered. Nitrogen variations in plants, for example, can be caused by plant-specific reliance on nitrogen gas which causes the plant to mirror atmospheric nitrogen isotopic values. Enriched or higher δ15N values can be achieved in plants that grew in soil fertilized by animal waste. Nitrogen isotopes have been used to estimate the relative contributions of legumes verses nonlegumes, as well as terrestrial versus marine resources to the diet. While other plants have δ15N values that range from 2 to 6‰, legumes have lower 14N/15N ratios (close to 0‰, i.e. atmospheric N2) because they can fix molecular nitrogen, rather than having to rely on nitrates and nitrites in the soil. Therefore, one potential explanation for lower δ15N values in human remains is an increased consumption of legumes or animals that eat them. 15N values increase with meat consumption, and decrease with legume consumption. The 14N/15N ratio could be used to gauge the contribution of meat and legumes to the diet. Oxygen The oxygen stable isotope system is based on the 18O/16O (δ18O) in a given material, which is either enriched or depleted relative to a standard. The field typically normalizes to both Vienna Standard Mean Ocean Water (VSMOW) and Standard Light Antarctic Precipitation (SLAP). This system is famous for its use in paleoclimatic studies but it also a prominent source of information in bioarchaeology. Variations in δ18O values in skeletal remains are directly related to the isotopic composition of the consumer's body water. The isotopic composition of mammalian body water is primarily controlled by consumed water. δ18O values of freshwater drinking sources vary due to mass fractionations related to mechanisms of the global water cycle. Evaporated water vapor will be more enriched in 16O (isotopically lighter; more negative delta value) compared to the body of water left behind which is now depleted in 16O (isotopically heavier; more positive delta value). An accepted first-order approximation for the isotopic composition of animal drinking water is local precipitation, though this is complicated to varying degrees by confounding water sources like natural springs or lakes. The baseline δ18O used in archaeological studies is modified depending on the relevant environmental and historical context of surrounding water sources. δ18O values of bioapatite