Rising Sea Levels and Saltwater Intrusion Poses a Growing Threat to Coastal Populations and Farms

November 28, 2017 – Increasing carbon dioxide (CO2) in the atmosphere from human activity has led to many unintended consequences: warmer mean atmospheric temperatures, warmer oceans and lakes with more carbon being absorbed by surface water, more active and extreme weather, more melting of continental and alpine ice fields, altered precipitation patterns, and changes in the distribution and size of animal and plant populations.

A warmer ocean causes its volume to expand. A warmer ocean alters the flow of coastal currents. A warmer ocean undermines ice shelves and surface ice in the polar regions of the planet. All of these consequences lead to saltwater and freshwater clashes with the fresh being undermined in coastal aquifers by salt intrusions.

Saltwater intrusion from oceans and seas is exacerbated by humans searching for underground and surface freshwater sources. Many cities and farms rely on subterranean freshwater. The Ogallala Aquifer in the U.S. Great Basin today is almost tapped dry. At the same time surface water sources are being overexploited with good examples in the Colorado and Rio Grande Rivers in the U.S. south. Both of these important surface water sources have lost significant volumes as farms and cities both within and also outside their watersheds draw more freshwater than natural processes can replace.

In China, the exploitation of surface sources has led to the development of engineered water diversion moving it from the Yangtze in the middle of the country to the Huang He (Yellow) in the drier north. The decreasing river volume in the former has caused significant damage downstream, impacting transportation, farms, and communities. It has also changed the fresh and saltwater interface where the Yangtze flows into the Yellow Sea.

In California, saltwater intrusion threatens farms within sight of the Pacific Ocean. The Yangtze, Nile, Indus, Ganges, Mississippi, Congo, Niger and Zambezi river deltas, significant farming areas are all threatened. Those in the business of conservation describe saltwater intrusion as the biggest untold water story on the planet today. According to the United Nations, more than half the world’s population lives within 60 kilometers (37 miles) of coastlines. And 75% of the largest cities on the planet also lie along coastlines.

Human reliance on coastal aquifers for freshwater is a big deal. Just how big? In Indonesia, Jakarta, a megacity of more than 10 million draws much of its freshwater from wells and recently has seen freshwater sources 11 kilometers (7 miles) inland become contaminated with saltwater. In India, the more than 7 million, who live in the city of Chennai, are seeing saltwater intrude into wells 15 kilometers (9 miles) from the coast.

From Florida to the Mexican border coastal communities and farms are witnessing Gulf of Mexico water pushing inland, spoiling freshwater aquifers. A similar phenomenon can be seen along the Atlantic Ocean coast from Cape Cod to the southern tip of Florida where saltwater is increasingly invading underground sources. In South Florida where 90% of drinking water comes from underground sources, the underlying limestone is highly porous allowing seawater to move inland and upward. A popular South Carolina resort, Hilton Head Island has had to shut down six of its freshwater wells in the last 10 years because the Atlantic Ocean is increasingly contaminating sources.

For farmers, saltwater intrusions endanger crops. Not many like salt. But having said that, the reality is that 20% of all irrigated farmland around the world is already salt contaminated contributing to poor yields. So agricultural scientists and geneticists have been working on trying to produce plants capable of thriving even as saltwater intrusions impact more farms.

Sea level rise is the new threat and its impact in low lying farm areas cannot be understated. States Tapas Paul, with the World Bank, “It’s hard to imagine how farmers will live” in reference to southern Tamil Nadu state in India. To deal with its growing population India needs every hectare of farmland to produce. Experts state categorically that India will need to produce 45% more food by 2050 or face potential famine and an increasingly malnourished population.

But the trend is to lost hectares with saltwater intrusions degrading close to 1.2 million (3 million acres) of coastal farmland once arable. “In the places subject to inundation and sea level rise, there are few options.”

Tweaking genes and selective breeding are the current methods of choice to find salt-tolerant alternatives to existing staple crops. Scientists are turning to naturally salt-tolerant plants, called halophytes, studying their genetic makeup to see if it can be applied through genetic modification to primary food staples. India’s neighbour, Bangladesh, is facing an even more urgent challenge with significant farmland losses. The same can be said about other Southeast Asian countries.

Today 62 million hectares (over 153 million acres) of arable land has become salt contaminated. And it is estimated that a rise of 50 centimeters (1.6 feet) in sea level by 2100 will add 1.9 million more hectares (almost 4.7 million acres) to the losses. So developing salt tolerance is really an important agricultural innovation.

In China, scientists are trying to create salt-tolerant rice with the hope they can match the yields of existing strains. This year they experimented with four types at the Qingdao Saline-Alkali Tolerant Rice Research and Development Center in eastern China’s Shandong Province. Diluted seawater, 0.6% salinity, was introduced into the soils. The four different rice strains produced between 6.5 and 9.3 tons per hectare compared to some salt-tolerant wild rices that yield between 1.125 and 2.25 tons per hectare.

In reporting these results the scientists noted that rice grown in the presence of salt changes the level of calcium in the crop. And the saline soil provides another benefit. It reduces the number of microbial pathogens that require herbicide and other pesticide treatment to maintain decent yields. Using less of these chemicals lowers costs and reduces exposure of the farmers to them.

It will be several more years before the scientists will be confident that they have an answer in the form of rice. Meanwhile, other staples like wheat, corn, potatoes, and cassava need similar solutions.

 


Len Rosen lives in Toronto, Ontario, Canada. He is a researcher and writer who has a fascination with science and technology. He is married with a daughter who works in radio, and a miniature red poodle who is his daily companion on walks of discovery.
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