Potential contribution to the nutrient pool due to the decomposition of Eichhornia crassipes under different salinity in an aquatic ecosystem—A laboratory study

Abstract

The opening of Thannermukkom saltwater barriers during monsoon causes an Eichhornia crassipes infestation in Cochin backwater, Kerala-India; an annual occurrence. During the process, the plants are exposed to varying salinity due to tidal action. Keeping this in mind, an experiment was conducted to study the nutrient released post-decomposition to saltwater exposure. The effect of salinity on the decomposition was varied. In contrast to low nitrite concentration (ca. 6 μM), ammonium concentration (∼70μM) was very high in the whole plant decomposition. Low nitrite concentration was correlated with the increase in ammonium. Nitrate concentration was 17 μM in 5 psu salinity. However, the increase in nitrate was negatively correlated with nitrite concentration. Phosphate concentration was ∼23μM in 25 psu salinity and silicate was in the range of ∼45μM. The decomposition of the cut pieces of E. crassipes leaf and petiole under dark conditions showed very high concentration of ammonium, and low concentration of nitrite and nitrate. The concentration of phosphate and silicate was higher in leaf decomposition. The study showed that the rate of decomposition was faster in cut leaf and petiole under dark condition. This indicates that the prevailing condition could influence the degree of decomposition and the eventual release of the nutrients. The study also illustrates the complexity of E. crassipes plant decomposition in varying salinity which is found in the backwater system. The estimated nutrients from this study suggested that the potential contribution from the decomposition of E. crassipes to the nutrient pool could be considerably high. The probable role of decomposing E. crassipes plant in the nutrient dynamics of the Cochin backwater system has been proposed for the first time.