Role of synthetic fertilizers on stable isotope ratios of particulate organic matter in the Godavari River

In this study, we examined the major sources of particulate organic matter (POM) in the Godavari River during high flow and low flow periods, to understand the impact of excess nitrogen (N)-fertilizers used in agricultural fields. δ¹³C of particulate organic carbon (POC) and δ¹⁵N of particulate nitrogen (PN), elemental carbon (C) to N ratio and POC:Chl-a ratios indicated that in-situ sources predominantly contributed (~ 60%) during low flow period, whereas, terrestrial sources largely contributed during high flow period (75-80%). This is attributed to prevailing conducive conditions such as low flow, better light availability due to low suspended matter and availability of nutrients for phytoplankton growth during former period, whereas increased transport of particulate and dissolved materials from land to river during the latter period. δ¹⁵N_PN during low flow (7.4 ± 2.9‰) and high flow (9.4 ± 2.1‰) periods demonstrate that contribution of POM produced from N-fertilizers (δ¹⁵N_PN: 0 ± 1‰) is not significant, rather than hitherto hypothesized. It could be due to seepage of excess N-fertilizers used in agricultural fields into groundwaters rather than transporting to rivers and/or transformation to another from through nitrification/denitrification processes within soils.