Nitrate levels modulate denitrification activity in tropical mangrove sediments (Goa, India)

摘要

A study to examine the short-term effect of nitrate and organic carbon addition on denitrification activity was carried out on sediments from a mangrove ecosystem prone to anthropogenic activities (Divar, Goa, India). Laboratory microcosms were prepared using sediment sectioned at every 2-cm-depth interval from the surface to 10 cm. The incubations were subjected to varying nitrate amendments at concentrations ranging from 0,5,10,20,40 to 60 μmol l~(-1) (up to three times more than measured in field). Nitrous oxide production rates increased significantly (n = 15; p < 0.001) on addition of the nutrient at all depths investigated indicating that denitrification in mangrove sediments was NO_3~-limited. Incubations amended with organic carbon were prepared using glucose as a substrate with concentrations ranging from 0%, 0.1%, 0.3%, 0.5%, 0.75% to 1%. No significant increase in N_2O production was observed on organic C addition. When both the substrates were in excess (1 mmol KNO_3 + 1 mmol glucose), potential denitrification rates decreased with depth and were up to 38 times higher than the in situ denitrification activity varying from 81.26 to 304.09 μmol N_2O-N m~(-2) h~(-1). These results reveal that mangrove sediments could act as a sink for nitrate and micro-bially mediated denitrification could effectively reduce N load controlling any adverse environmental impact in the adjoining estuarine system.