A New Trophic State Index for Lagoons

Mukesh Gupta

doi:10.1155/2014/152473

Abstract

This paper proposes a new nitrogen-based trophic state index (TSI) for the estimation of status of eutrophication in a lagoon system. Nitrite-nitrogen (NO2-N) is preferable because of its greater abundance in Chilika lagoon and its relation to other criteria of trophic state, for example, chlorophyll-a (Chl-a) and Secchi disk depth (SDD). Nitrite is preferable over nitrate because the former decreases the fluorescence and affects photosynthesis, thereby controlling primary production. This paper also computes TSI using Chl-a and SDD. The three parameters account for the biological, chemical, and physical characteristics of the lagoon. It will be possible to estimate the TSI of freshwater and brackish water lagoons and other water bodies using the new expressions taking into consideration the spatial and temporal variability in the dataset. Depending on the data availability, alternative TSI (Chl-a) and TSI (SDD) can account for the biological and physical contributions to eutrophication. The estimated TSI can account for Chl-a and NO2-N up to 322.18 mg m−3 and 61.99 μg L−1, respectively. The TSI based on these three parameters can serve as a complimentary and predictive tool for lagoon management and field programs to monitor the health of a lagoon.

Highlights

It is much easier to convey to the public the status and nature of a lagoon through an index, which provides the scientific accord of eutrophication and character of the lagoon
This paper presents a new detailed model of trophic state index (TSI) based on NO2-N with intercomparison to TSI based on Chl-a, and Secchi disk transparency depth (SDD) for Chilika lagoon’s eutrophication status
Chl-a, NO2-N, and SDD have been chosen as the potential candidates for estimating a TSI which can cover a substantial range of concentrations of each of the three parameters and is applicable to any brackish water lake, lagoon, inland water body, and reservoir

Summary

Introduction

It is much easier to convey to the public the status and nature of a lagoon through an index, which provides the scientific accord of eutrophication and character of the lagoon. Carlson [1] made early attempts to define an index, termed trophic state index (TSI), which could tell about the trophic status and nature of the lakes Based on this trophic index, further classification of eutrophication of a lake into oligotrophic, mesotrophic, and eutrophic was possible. Carlson [1] presented the trophic condition on a 0–100 scale; the author reported three different TSI values, that is, total phosphorus (TP), chlorophyll-a (Chl-a), and Secchi disk transparency depth (SDD) [2]. To eliminate this confusion, Osgood [3] suggested using differences in the indices to assess the water quality in lakes. There is no universally applicable trophic index reported which could adequately predict the productive character of a coastal lagoon

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Conclusion