Indian estuaries are hypothesized to export a significant amount of nitrogen nutrients to the coastal waters due to the high use of fertilizers. To examine the possible sources of nitrogen nutrients and their modifications within the estuary, a study was conducted by collecting samples at monthly intervals for a period of a year. The river Godavari is the largest monsoonal estuary in India and is fed by monsoon rainfall. Hence the entire estuary is filled with fresh water from July to September (the wet period) whereas saline water is dominant during the dry period. An order of magnitude increase in nitrate concentrations was observed during the wet due to a peak in discharge compared to the dry period. The isotopic composition of nitrogen in nitrate (δ¹⁵N_NO3) was lower during the wet than the dry period and displayed a significant linear relationship with Chlorophyll-a (Chl-a), particulate organic nitrogen (PON) and carbon (POC) indicating that biological process modified their composition. The lower δ¹⁵N_NO3 and higher δ¹⁸O_NO3 values were noticed during the wet than during the dry period. The δ¹⁵N_NO3 versus δ¹⁸O_NO3 plot suggests a possible source of nitrate through the nitrification of soil/sewage-borne nitrogen. The higher δ¹⁸O_NO3/δ¹⁵N_NO3 ratios (>1) were observed during August and September than in other months indicating the occurrence of denitrification during the former months. In contrast, an insignificant change in δ¹⁵N_NO3 and δ¹⁸O_NO3 within the estuary suggested that denitrification occurred upstream and not within the estuarine zone. River discharge brought residual nitrate to the estuary leading to less input of nitrate to the coastal Bay of Bengal than hitherto hypothesized.

由于化肥的大量使用，印度河口被假设向沿海水域输出大量的氮养分。为了检查河口内氮营养素的可能来源及其变化，进行了一项研究，在一年的时间里每月收集一次样本。戈达瓦里河是印度最大的季风河口，由季风降雨补给。因此，从 7 月到 9 月（湿润期），整个河口充满淡水，而在旱季，咸水占主导地位。与干燥期相比，由于排放峰值，在潮湿期间观察到硝酸盐浓度增加了一个数量级。硝酸盐中氮的同位素组成 (δ ¹⁵ N _NO3) 在湿润期低于干燥期，并且与叶绿素-a (Chl-a)、颗粒有机氮 (PON) 和碳 (POC) 呈显着线性关系，表明生物过程改变了它们的组成。与干旱时期相比，潮湿时期的δ ¹⁵ N _NO3值较低，δ ¹⁸ O _{NO3值较高。}δ ¹⁵ N _NO3与 δ ¹⁸ O _NO3图表明可能通过土壤/污水中氮的硝化作用产生硝酸盐。较高的δ ¹⁸ O _NO3 /δ ¹⁵ N _NO3在 8 月和 9 月观察到比值 (>1) 高于其他月份，表明前几个月发生了反硝化作用。相比之下，河口内δ ¹⁵ N _NO3和 δ ¹⁸ O _{NO3的微小变化表明反硝化作用发生在上游而不是河口区内。}河流排放将残留​​的硝酸盐带到河口，导致流入孟加拉湾的硝酸盐比迄今假设的要少。