Enrichment and Bioavailability of Phosphate in a Highly Urbanized Zone of Cochin Estuary, South India

ABSTRACT

Sequential extraction (SEDEX method) was employed to explore the distribution of sediment-bound phosphorus (P) fractions and the bioavailability of P in Cochin estuary. Concentration of P fractions in surface sediments of the study area ranged as follows: Detrital P > Organic P > Authigenic P > Exchangeable P > Iron-bound P. Generally increasing trend was displayed by all the phosphate fractions toward the downstream sites due to effluent discharges from industrial, domestic, municipal, agricultural sectors and destruction of mangrove forests. The elevated levels of inorganic phosphorus (133.55–918.73 mg/kg) reflected the large-scale delivery of sediment loads associated with great floods during 2018 & 2019. Significant correlations of fine-grained sediment particles with all phosphate fractions indicated surface adsorption as a dominant distribution mechanism. Concentration of iron-bound phosphorus was controlled by adsorption on iron oxy-hydroxides. The buildup of bioavailable phosphate (range: 23.76 to 49.97%) indicate the fact that the estuarine sediments function as a sink for the nutrient. The upper and middle part of the study area recorded more severe contamination and eutrophication risk as indicated by phosphorous pollution index (range: 0.31 to 2.56).

KEYWORDS:

• Bioavailability
• Cochin estuary
• eutrophication
• phosphorus pollution index
• sequential extraction

Acknowledgment

The authors gratefully acknowledge the laboratory and instrumental facilities as well as the support provided by the Director, School of Environmental Studies and the Dean, Faculty of Environmental Studies, Cochin University of Science and Technology. We gratefully acknowledge the service rendered by Dr. Karung Phaisonreng Kom in the preparation of a digitized map of the study area. We extend our sincere thanks to the editor and anonymous reviewers for giving valuable comments to improve the manuscript.

Disclosure statement

The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.

Credit authorship contribution statement

Sreejisha U: Conceptualization, designed the experiment, sampling, performed the experiments, results, interpretation, and planned the statistical analysis. Vidya P V: Assisted sampling, instrumental methods, correction of the draft, and planned the statistical analysis. Roshni Mohan: Assistance for sampling and chemical analysis. Nazia Nazeer: Assistance for sample collection and chemical analysis. Sudha A: Assistance for sampling and chemical analysis. Ratheesh Kumar C S: Supervision, validation of the interpretation of the results, and was primarily responsible for drafting the manuscript with critical insights and editing.

Ethical approval

Not applicable, this article does not contain any studies involving human participants and/or animals performed by any of the authors.

Consent to participate

Not applicable, no human participants were involved in this study.

Consent to publish

Not applicable, no human participants were involved in this study.