What factors have had deleterious impacts on the ability of tank systems in Sri Lanka to sustain local ecosystems and combat drought?
I. Heightened dependence on chemical fertilizers
II. The intrusion of water hyacinth
III. The reduction of trees covering the area.

I. Heightened dependence on chemical fertilizers: This means that the increased use of chemical fertilizers has had a negative impact. Chemical fertilizers can harm the soil and biodiversity in the tank systems, affecting their ability to function effectively. II. The intrusion of water hyacinth: Water hyacinth is an invasive aquatic plant that has entered the tank systems. This plant can block canals and streams in the irrigation network, disrupting the flow of water and affecting the tank systems' functionality. III. The reduction of trees covering the area: This refers to a decrease in the number of trees in the region. The reduction of tree cover can have various negative effects on the tank systems, including the loss of shade and protection for the ecosystem, which can impact their capacity to support local ecosystems and combat drought. Trees play a vital role in maintaining the health of the tank systems. In summary, all three factors have contributed to the challenges faced by the tank systems in Sri Lanka.