Nitrogen uptakes dynamics with environmental variables in the southwest Bay of Bengal

Nitrate uptake is an essential nutrient for primary production. A study focused on the surface waters of the Bay of Bengal (BoB), new, regenerated, and total production were estimated from nitrate, ammonia, and urea (nitrogen uptakes). Understanding nitrogen uptake rates in coastal waters, where nutrient limitations can disturb environmental biological productivity, is essential. A detailed study of these uptake rates and metabolic processes is required to develop effective mitigation strategies to prevent further degradation of these ecosystems. Total production ranged between 1.39 and 7.43 mmol N m² d⁻¹, new production ranged between 0.58 and 2.83 mmol N m² d⁻¹ and regenerated production ranged between 0.83 and 4.59 mmol N m² d⁻¹. The study observed a significant negative correlation nitrogen uptake along with pH, sea surface salinity (SSS), and sea surface temperature (SST) was observed in the study. The R² values for SST were 0.605, 0.619, 0.503, 0.601, and 0.627; for SSS they were 0.688, 0.511, 0.498, 0.579, and 0.644 with nitrogen (Na¹⁵NO₃), ammonium (¹⁵NH₄Cl), urea (CO(¹⁵NH₂)²), regenerated, and total production uptake, respectively. pH was highly correlated with nitrate uptake (R² = 0.525), had a low correlation with ammonium uptake (R² = 0.439) and a moderate correlated with urea uptake (R² = 0.526). A positive relationship of nitrogen uptakes with chlorophyll-a, dissolved oxygen, and dissolved inorganic nitrogen (DIN) were observed. Chlorophyll-a had R² value of 0.608, 0.126, 0.524, 0.526, 0.578, with Na¹⁵NO₃, ¹⁵NH₄Cl, CO(¹⁵NH₂)², regenerated and total production uptake respectively. Dissolved oxygen (DO) related to ammonium uptake showed a very poor correlation (R² = 0.079) but a better correlation with urea (R² = 0.534). New production uptake rate showed a high positive correlation with DO (R² = 0.645), whereas regenerative production uptake rates showed a relatively low correlation (R² = 0.519). The positive relationship between DIN and nitrogen uptake had corresponding R² value of 0.642, 0.591, 0.558, 0.652 and 0.675 for nitrite, ammonium, urea, regenerated and total production uptakes respectively. Total nitrogen: Total phosphate (TN:TP) showed a positive correlation with ammonium. The TN:TP relationship fit nicely with R² = 0.576 (nitrate uptake), 0.524 (ammonium uptake), and 0.503 (urea uptake) in the coastal BoB. Hence, by applying statistical analysis, principal component analysis and pearson correlation, the interdependency of the environmental parameters enhancing the new production has been confirmed.