Carrie C. Wright

Archaeologists worldwide use strontium isotope analysis to determine provenance of both inorganic and organic materials. Mesopotamianists use strontium isotope ratios (87Sr/86Sr) to investigate top...

The results from a four-year study of a freshwater pond on Long Island, NY, USA, do not point to a single source of boron (and by proxy other elements including nutrients) in this system. However, boron data from samples associated with this pond can be explained by mixing between average precipitation (weighted average δ¹¹B = 22.7) in the area and the local sources of boron, both natural and anthropogenic. This multiyear study provided the opportunity to see both yearly and seasonal differences. One algae sample from the pond showed significant fractionation and enrichment in light boron relative to the water and suggests algae may act as a boron sink. This type of biological fractionation could explain an observed down-gradient trend to heavier boron isotope values in pond water, which corresponds to the slight reduction in boron concentration seen in 2021. However, the trend was subdued in the following year, likely due to differences in the water flow rates and/or rate of algal growth. An opposite trend was seen with depth in the water, where δ¹¹B showed a positive correlation to boron concentration, which increased with depth from the surface of the pond. This gradient may be explained by the stratification of the pond with a heavy source concentrating in the bottom waters. The bottom water composition was consistent with goose feces (δ¹¹B = 25.8) or the addition of chemicals from the application of rock salt to local roads in winter. Surprisingly, boron from seawater (average δ¹¹B = 39.8) did not appear to have a direct impact on Setauket Pond, other than its influence on precipitation, providing heavy δ¹¹B and very low boron concentrations.

The role of boron in terrestrial plant physiology is diverse and increasingly well understood, but its role in marine aquatic eukaryotes is less clear. Our research reveals a distinctive and large offset in boron isotopes from seawater, irrespective of seaweed type or season. We show that the offset is consistent with the incorporation of borate from seawater. Boron is a known micronutrient in plants but very few studies have used boron isotopes to investigate boron’s role in plant physiology. Seaweed, as the most primitive multicellular plant, has an important role in investigating wider plant adaptations that use boron to meet functional needs. Furthermore, seaweed and other plants are a key base nutrient provider in food webs, supplying boron to consumers and playing a critical role in boron environmental cycling.