Influence of different controlled drainage strategies on the water and salt environment of ditch wetland: A model-based study

Ditch wetlands reduce agricultural nonpoint source pollution and protect the water environment in drainage areas. One effective management option is controlled drainage. However, for ditch wetlands receiving salt-laden drainage water in arid or semi-arid irrigation areas, controlled drainage may lead to eventual build up of salinity to critical levels that are detrimental to the ecological services and agricultural production of wetland systems. In order to evaluate the positive and negative impacts of agricultural practice of using controlled drainage to manage ditch wetlands water quality in arid or semi-arid irrigation area, based on the principle of water-salt balance we constructed an analysis model. A ditch wetland as a case example in semi-arid irrigation area was then used to display model predictions of salinity variations over time under different watertable control depths. The ditch wetland area to farmland area ratio is 0.091, and the input sources of water and salt are not unique. The results showed that the model established by considering various inflows and outflows has higher simulation accuracy. The water stored in the wetland is key to affecting the salt concentration of the wetland, and the amount of water can be regulated by controlled drainage. Controlled drainage changes the hydrological process of farmland and ditch wetlands, reduces drainage output and damage by high concentrations of salt. But this management measure also increases the risk of medium salt concentrations that may cause an increase in salt output. Considering agricultural production and environmental protection of ditch wetlands, the drainage water table controlled at 1.2 m is a suitable drainage management measure in this irrigation area. The results provide the underlying insights needed to guide the design of drainage management practices in ditch wetlands that receive drainage discharge in semi-arid regions that can be sustained to the maximum benefit of the agricultural system and the environment.