Rainfall Mediated Partitioning of Heavy Metals in Surface Water, Sediments and Mesozooplankton Community of a Tropical Estuary

Parvathy, R and Padua, Shelton and Ratheesh Kumar, R and Vineetha, G and Lavanya, R and Raju, Aju K (2026) Rainfall Mediated Partitioning of Heavy Metals in Surface Water, Sediments and Mesozooplankton Community of a Tropical Estuary. International Journal of Environmental Research, 20. pp. 1-18. ISSN 2008-2304

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Abstract

This study examined how variable rainfall, characterised by four distinct rainfall regimes, low (LR), moderate (MR), high (HR) and peak rainfall (PR), influences the distribution of ten heavy metals (Fe, Ni, Cu, Mn, Co, Zn, Cr, Cd, Pb and As) in the surface water, sediments and mesozooplankton community of Cochin Estuary, a tropical monsoonal estuary along the south west coast of India. Iron exhibited highest concentration in all the components (surface water—15.26 to 94.70 µg L−1, sediment—7,275.37 to 23,094.60 mg kg−1 and mesozooplankton—157.80 to 6,905.40 mg kg−1). Metal concentration in mesozooplankton and estuarine sediments increased with rainfall, while surface water showed a noticeable decline. Rainfall increases the freshwater influx into the estuary transporting pollutants from industrial, agricultural and urban sources. Although intense flushing during such events reduces metal concentration in surface waters, sediments act as a sink for the incoming pollutants. Notably, mesozooplankton exhibited elevated concentration of heavy metals during PR period, particularly Fe, Zn, Co and Mn, despite low concentration in surface water. This suggests the presence of an alternate pathway for metal accumulation through sediment ingestion, indicating that metal uptake is not entirely dependent on the surface water concentration.

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