Name
Tracing phosphorus along the soil-freshwater continuum using stable isotopes of oxygen
Description
Many aquatic ecosystems in the world suffer from eutrophication and associated algal blooms due to the transfer of nutrients from agricultural fields to rivers and lakes. Phosphorus (P) is considered the ultimate element controlling these algal blooms in surface waters (Schindler et al. 2016). Other than carbon, nitrogen and sulfur, P only has one stable isotope (31P), which complicates tracing this element in the environment. However, at Earth’s surface phosphorus is usually associated with oxygen forming inorganic or organic phosphate [PO43-]. The stable oxygen isotope composition of phosphate can therefore be used as an indirect tracer for processes, sources and sinks in the environmental P cycle (Tamburini et al. 2014). Here, I will present recent advances in the use of this methodology and show a case study dealing with the transfer of P from an agricultural system to a first order stream. Soil phosphorus pools and the oxygen isotope composition of phosphate were analyzed along a transect through a vegetated riparian buffer strip of a first order stream located in a temperate grassland ecosystem which is primarily used for pasture. Our results do not show significant changes in the size of soil P pools along the transect but the 18O-PO4 values from topsoils and subsoils gradually increased towards the stream. This finding indicates enhanced biological cycling of P within vegetated riparian buffer strips which might alter the original oxygen isotopic composition of terrestrial P sources.