Major sources of particulate organic matter in the Godavari River, India: Role of synthetic fertilizers

Abstract In this study, we examined major sources of particulate organic matter (POM) in Godavari River during high flow and low flow periods, to understand the impact of excess N-fertilizers used in agricultural fields. δ13CPOC and δ15NPN, elemental C:N 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 for phytoplankton growth during former, and increased transport of particulate and dissolved materials from land during latter period. δ15NPN during low flow (7.4 ± 2.9‰) and high flow (9.4 ± 2.1‰) periods demonstrate that contribution of POM produced from N-fertilizers (δ15NPN: 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.