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.
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