Ecology, Conservation, and Restoration of Chilika Lagoon, India by C. Max Finlayson & Gurdeep Rastogi & Deepak R. Mishra & Ajit K. Pattnaik

Author:C. Max Finlayson & Gurdeep Rastogi & Deepak R. Mishra & Ajit K. Pattnaik
Language: eng
Format: epub
ISBN: 9783030334246
Publisher: Springer International Publishing

9.6.1.2 Variation of Nitrate

NO3 is the final oxidation product of N compounds in fresh as well as marine water. It is an important nutrient apart from NH3 and urea for the photosynthesis and growth of plankton community in the presence of light (Ganguly et al. 2015). The concentration of NO3 varies in the ecosystem with respect to space and time and is mostly controlled by the rate of uptake by primary producers and also an influx of the same through riverine discharge (Zepp 1997). NO3 concentration in the Chilika lagoon varied in the range of 0.12–19.88, with an average of 6.86 ± 5.14 μM. Like NO2 it also showed a major variation among sectors: NS; 7.77 ± 5.13 μM > CS; 6.99 ± 5.22 μM > OC; 6.44 ± 4.6 μM > SS; 6.17 ± 5.19 μM. However, the trend indicated the region with sea water influence (SS, OC) maintained lower concentration which could be due to dilution with seawater containing lower nutrient concentration. During the monsoon season (2008–09) the rate of NO3 flux into the lagoon recorded 4465 mol d−1 (Patra et al. 2016) which is closer to the recent observation during 2014 (3112 mol d−1). The regions with the influence of riverine discharge (NS) contain higher nutrient concentration (Fig. 9.3b). On a seasonal basis, the variation is also highly significant (Ganguly et al. 2015; Patra et al. 2016). As compared to other seasons, the summer (high residence time, Muduli et al. 2013) records the highest nutrient concentration which could be due to the mineralisation process (Panigrahi 2006). This observation is also in corroboration with findings of Muduli et al. (2012) and Gupta et al. (2008) who revealed the active mineralisation process in the NS of the lagoon. Some tropical estuaries also record high NO3 concentration during monsoon (Patil and Anil 2008; Pednekar et al. 2014) and the difference may be due to lesser residence time in Chilika (Muduli et al. 2013) which helps the nutrient to flush out. Many studies report a significant negative relationship of NO3 with salinity, indicates the major source of NO3 was from freshwater discharge. However, the present observation from the regression equation indicated there were mixed responses i.e. the source was from in situ process as well as from riverine discharge (negative relationship with salinity) (Fig. 9.5). As per Barik et al. (2017a), the relationship of NO3 with salinity not only varies in spatial scale but also in the temporal scale. The mixed response (Fig. 9.5) could be attributed to different seasons during which several factors influenced the NO3 concentration (as discussed above).

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