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.

Read the following passage and answer the following questions accordingly. Before British colonisation in the late 18th Century, village tank cascade systems were owned by farmers who collectively managed and maintained them under the customary laws of the village. Under this process, it was mandatory for the community to take part voluntarily in maintaining the tank system. But the British regarded this system to be forced labour, abolishing it in 1832 and centralising responsibility for maintenance. This was followed by decades of local government neglect. After independence from the British in 1948, new government institutions like the Department of Agrarian Development and farmer organisations took control of tank system management. These institutional changes meant that tank systems today have no clear ownership and in many places are no longer managed and maintained by village communities. For those tank systems that do remain, more recent urban sprawl and expanding agriculture have also had various negative effects on their capacity to support local ecosystems and tackle drought. Aquatic invasive plants like water hyacinth and salvinia have blocked canals and streams in the irrigation network. Tree cover has been reduced and heavy reliance on chemical fertiliser has impacted the soil and biodiversity that the tank systems rely on. But restoration efforts are now underway. In 2017, UNESCO and FAO recognised Tank Cascades as a Globally Important Agricultural Heritage System. Following this, restoration of small tank systems and cascade management programs have been included in the country's National Adaptation Plan for Climate Change Impacts in Sri Lanka. Geekiyanage says that restoration of tank cascades – although a big challenge – has been a top agenda of development and conservation practitioners for several years now. One climate resilience project has restored 325 tanks in 30 cascades, and according to Dharmsena, another has addressed 1700 tanks in 280 cascade systems. Such efforts have already had positive impacts. According to a 2013 study, rehabilitation of the Thumbulla tank system in northwestern Sri Lanka improved yields and allowed villagers to cultivate 30 acres of non-rice crops, such as corn and vegetables, during the rainless period from May to September. Another study in 2016 explained that restoration of the Kapiriggama cascade system in north central Sri Lanka – which contains 22 tanks and supplies water to 800 acres of rice fields – has helped farmers in 11 villages to cultivate rice during the drought months.  There are some limits, however, to what restoration alone can achieve. Both Geekiyange and Dharmasena stress the need for proper coordination between different government and non-government entities involved in preservation, such as the irrigation and forestry departments _______ (7) the management of the surrounding tree cover. Plus, Geekiyanage notes that many villages' tank systems "cannot sustain" the larger cultivation areas needed to meet the demands of a growing population.