The researchers studied how Pontederia cordata plants can clean heavily polluted river water in different seasons. They grew the plants in tanks with and without aeration to see how it affected their growth and ability to purify the water. They found that aeration affected the plants' size and the levels of certain substances in their leaves and roots. The plants in aerated tanks had shorter roots, stems, and leaves, but higher levels of certain enzymes in their roots. The water in aerated tanks had more nitrogen removed, but less phosphorus removed compared to non-aerated tanks. The effects of aeration on the plants were most noticeable in autumn, when the differences in water quality between the two types of tanks were smaller.