April 16, 2013
California may be famous for its San Francisco counterculture or the Los Angeles entertainment industry, but one of the state’s most important contributions is agriculture. California is the most agriculturally productive state in the U.S. and contains 9 of the country’s 10 most productive counties. The San Joaquin Valley, located in the southern half of California’s Central Valley, is the world’s most productive agricultural region. However, the sustainability of productive agriculture in this region is threatened by salt build-up, known as salinization. Salt accumulates in groundwater and soils naturally due to evaporation and transpiration. However, if the water table is high and drainage is exceptionally poor, accumulating salts may persist in an area, threatening the ability of crops to take up water. Essentially, excess salt buildup as a result of over-irrigation, poor drainage, and high evaporation rates, all of which occur in the San Joaquin Valley, has deleterious effects on agricultural productivity and sustainability.
Schoups et al. devised a model to help understand historic changes in and predict future levels of groundwater and soil salinization, especially in the western part of the San Joaquin Valley. Irrigation in the valley began with gravity-driven diversions of surface water from the San Joaquin River in the early 19th century, and extensive groundwater pumping to meet higher irrigation demands began in the 1920s. The Central Valley Project of 1953 and the State Water Project of 1967 provided farmers greater access to surface water, so groundwater pumping declined. This decrease in groundwater pumping coupled with continued irrigation contributed to a relative rise in the water table which in turn encouraged salinization. The Corcoran clay layer in the western San Joaquin Valley posed and continues to pose particular problems with salinity in the area. The lack of permeability in the soil causes drainage problems and thus a buildup of salts as well as dangerous chemicals like selenium.
The ongoing soil salinization caused by agriculture and irrigation in arid lands like the Great Central Valley leads to a chain reaction of problems that are hard to fix. According to a 2006 report by the Central Valley Regional Water Quality Control Board, an estimated 700 thousand tons of salt are imported from the San Francisco Bay and San Joaquin River to a majority of the state’s water supply projects, water basins in the region receive at least 2 million tons of salt annually by state and federal water projects, 400 thousand tons of salt are added to the aquifer in the San Joaquin Basin, 113 thousand acres of retired land, and 400 thousand acres of saline-sodic soil in the region. The report lists several major issues caused by soil salinization that affect the Central Valley’s economy, agricultural production, land-use, and health risk for people. Although it may seem that the problem persists and may keep plaguing the region, there are efforts to mitigate and regulate salinization to avoid these issues.
The current solutions to the problem, as stated by Schoups et al., are to increase irrigation efficiency, grow salt-tolerant crops, drainage-water reuse, land retirement, and increase groundwater pumping. The Central Valley Regional Water Quality Control Board has developed a management plant to ensure that salts and other nutrients in irrigation water are kept to a minimum, and for every region to develop a salt management plan by the year 2014. There is also the Central Valley-Salinity Alternatives for Long-Term Sustainability (CV-SALTS) initiative managed by stakeholders “to develop sustainable salinity and nitrate management in the Central Valley.” There are also other resources, especially ones online, provided by Aquafornia that gives tips on what people at home can do to reduce salt contamination. Some of the tips include use less or low salt detergents, and conserving water that will not be contaminated by salts. The United States Department of Agriculture (USDA) also provides information on how to manage salinization problems. Techniques include maintaining a low water table, irrigation to maintain salts below the root zone, reducing deep tillage, installing artificial drainage systems, and eliminating seepage from canals, dugouts, and ponds. These tips and techniques are currently the best and most feasible approach to mitigate salts in agriculture from irrigation. There is really no way of preventing since salts are inevitable in irrigating in arid lands. But taking the effort to reduce water consumption and water use to reduce salts and increase efficient agricultural production will, at least, improve current conditions in the Central Valley for agricultural production and avoid further land degradation and risks to human health.
By Amanda Alvarez and Sergio Avelar