The prospects of poop: a review of past achievements and future possibilities in faecal isotope analysis

Abstract

What can the stable isotope values of human and animal faeces tell us? This often under‐appreciated waste product is gaining recognition across a variety of disciplines. Faecal isotopes provide a means of monitoring diet, resource partitioning, landscape use, tracking nutrient inputs and cycling, and reconstructing past climate and environment. Here, we review what faeces are composed of, their temporal resolution, and how these factors may be impacted by digestive physiology and efficiency. As faeces are often used to explore diet, we clarify how isotopic offsets between diet and faeces can be calculated, as well as some differences among commonly used calculations that can lead to confusion. Generally, faecal carbon isotope (δ13C) values are lower than those of the diet, while faecal nitrogen isotope values (δ15N) values are higher than in the diet. However, there is considerable variability both within and among species. We explore the role of study design and how limitations stemming from a variety of factors can affect both the reliability and interpretability of faecal isotope data sets. Finally, we summarise the various ways in which faecal isotopes have been applied to date and provide some suggestions for future research. Despite remaining challenges, faecal isotope data are poised to continue to contribute meaningfully to a variety of fields.

Nitrogen isotopes in herbaria document historical nitrogen sewage pollution in the Mersey Estuary, England

“…, not treated, and hence not denitrified 59 ) was the cause behind the 1821–1863 δ 15 N values recorded for the Mersey Estuary. Raw human sewage would have a similar δ 15 N value to the diet they were consuming 60 and based on a modern-day equivalent dietary value this would represent a range between +4‰ and +8‰. 61 Although raw sewage can explain the δ 15 N record, agricultural practices cannot be excluded.…”

Dogs in Lithuania from the 12th to 18th C AD: Diet and Health According to Stable Isotope, Zooarchaeological, and Historical Data

“…The cereal δ 13 C value was adjusted according to diet to tissue offsets from Fernandes and colleagues [45]. Fecal values were calculated according to Kuhnle and colleagues [48] and Reid and colleagues [49], on the basis of the bone collagen values of commoners living between the 16th and 18th C AD in Vilnius. The fecal values were δ 13 C −22 ± 0.4‰ and δ 15 N 8.5 ± 0.8‰.…”

“…Estimating fecal consumption is challenging, as fecal stable isotope values depend on a variety of factors, such as human diet (vegetarian, fish or meat based), exposure time in the open environment, etc. [12,48,49,74]. As there are no stable isotope studies of medieval and early modern coastal populations in Lithuania, the fecal values of Vilnius urban populations were included in the modelling of the Klaip ėda/Memelburg dog intakes.…”