{"id":22453,"date":"2018-01-10T00:05:16","date_gmt":"2018-01-10T08:05:16","guid":{"rendered":"https:\/\/hakaimagazine.com\/?post_type=custom_news&p=22453"},"modified":"2018-01-09T21:08:19","modified_gmt":"2018-01-10T05:08:19","slug":"sea-level-rise-is-unlocking-decades-old-pollution","status":"publish","type":"custom_news","link":"https:\/\/hakaimagazine.com\/news\/sea-level-rise-is-unlocking-decades-old-pollution\/","title":{"rendered":"Sea Level Rise Is Unlocking Decades-Old Pollution"},"content":{"rendered":"

In 2015, Kate Tully visited farms near the eastern shore of the Chesapeake Bay. She was investigating whether sea level rise had caused brackish water to move upland, a process called saltwater intrusion\u2014evidence of which she found in the form of increased salinity in the fields and surrounding ditches. When the researchers viewed the sites on Google Earth, they could even see white rings around the farms where water had evaporated and left salt.<\/p>\n

\u201cIt\u2019s crazy,\u201d says Tully, an agroecologist at the University of Maryland, College Park. \u201cYou can taste it. You put your finger on the field, and it\u2019s salty.\u201d<\/p>\n

Saltwater intrusion was killing the area\u2019s soy, corn, and wheat, which couldn\u2019t tolerate the rising salinity.<\/p>\n

But as Tully and her team worked in the fields, they discovered an even more worrisome process that was well underway. Their studies suggest that the inundating seawater is triggering chemical reactions in the soil and releasing a long-dormant pollutant: phosphorus. The researchers worry that the phosphorus could reach the Chesapeake Bay and fuel oxygen-sucking algal blooms that kill fish and crabs.<\/p>\n

The phosphorus is from chicken manure fertilizer, which farmers have been laying on the fields ringing the Chesapeake Bay for decades. The region\u2014one of the oldest farming districts in the colonial United States\u2014is also part of the Broiler Belt, known for its intensive poultry industry. Phosphorus has accumulated in the soil, but now it may be released.<\/p>\n

Tully doesn\u2019t believe that the farmland nutrients will flood the bay all at once. But \u201cfirehose moments\u201d could occur, she says, when storms push seawater inland.<\/p>\n

The situation brings to mind other examples of how the long-term effects of climate change could trigger local events that amplify the environmental damage. For instance, warming of the Arctic permafrost and seafloor could cause the greenhouse gas methane to be released, driving further warming. Permafrost thawing, similarly, could release long-stored contaminants, such as mercury<\/a>. While nutrient pollution would not create a feedback loop that speeds up climate change\u2014as methane would\u2014Tully thinks the effects on the bay could be dramatic.<\/p>\n

\u201cIs there a possibility for us to tip the ecosystem into a different ecosystem?\u201d says Tully. \u201cYes, definitely.\u201d<\/p>\n

To come to their conclusion, Tully\u2019s team analyzed the soil at three farms in Maryland and found that phosphorus, bound up in the molecule phosphate, appeared to be moving from the fields toward ditches. From there, it could then flow into creeks connected to the bay.<\/p>\n

\"field<\/a>

Sea level rise is causing salt water to move toward farms in Maryland, killing crops and trees. Photo by Dani Weissman<\/p><\/div>\n

Salt water is likely unlocking phosphate from the soil through a series of chemical steps. In soil with plenty of oxygen, the phosphate in fertilizer can bind to iron. When the ground becomes waterlogged, soil pores containing oxygen fill with water instead. Under these conditions, iron releases the phosphate. Sulfate, an ion in seawater, then binds to iron\u2014leaving phosphate free to move around.<\/p>\n

Tully found that average phosphate levels in ditch water and nearby marshes are about an order of magnitude higher than the US Environmental Protection Agency\u2019s regional water quality guidelines for phosphorus. \u201cThey\u2019re screaming high,\u201d says John Kominoski, an ecologist at Florida International University in Miami.<\/p>\n

Levels of nitrogen, another fertilizer nutrient, in the study area were less worrisome, says Dani Weissman, an ecologist on Tully\u2019s team. Nitrogen has been the main nutrient polluter in the Chesapeake Bay, but phosphorus may become an increasing problem because it sticks around, says Chris Craft, a wetland ecologist at Indiana University Bloomington. Microbes can turn nitrogen-containing molecules, such as ammonium, into nitrate, which then gets converted into nitrogen gas that can be released into the atmosphere; phosphorus doesn\u2019t have a similar process. There\u2019s \u201cno way to take it out,\u201d Craft says.<\/p>\n

Tully\u2019s team doesn\u2019t yet have evidence that the nutrients have reached the Chesapeake Bay. Overall, the bay\u2019s phosphorus levels have declined over the past two decades, thanks to efforts to reduce fertilizer use on farms, Weissman says. But she is concerned that this legacy fertilizer could pollute the bay in the future.<\/p>\n

Ultimately, the amounts of nutrients released because of saltwater intrusion are probably small compared to runoff of recently applied fertilizer, Craft says. He compares the situation to giving another pack of cigarettes to a chain-smoker. \u201cThis is an added sort of insult,\u201d he says. Craft predicts that the damage will vary from year to year.<\/p>\n

But the problem goes beyond the Chesapeake Bay. Marcelo Ard\u00f3n, an ecologist at North Carolina State University, has studied a former farm that was converted to a wetland in North Carolina, where droughts increased the salinity of the wetland and appeared to have triggered the release of legacy nitrogen.<\/p>\n

Ard\u00f3n estimates that if the sea level in the region rises by one meter\u2014which could happen by 2100\u2014about 18,000 metric tonnes of ammonium could be released. That\u2019s roughly half the amount that the Mississippi River dumps into the Gulf of Mexico annually. Ard\u00f3n cautions that he doesn\u2019t know how quickly such a release would happen, but it could be \u201ca serious problem,\u201d he says.<\/p>\n

Legacy fertilizer releases could happen in other coastal agricultural areas as well, such as Texas, Alabama, Georgia, and California\u2019s Sacramento Valley, Kominoski says. Saltwater intrusion also is affecting Bangladesh and Vietnam, Tully notes. Farms there probably have less fertilizer stored in the soil than countries with a longer history of industrialized agriculture but will still suffer crop damage, she says.<\/p>\n

To stop the flood of nutrients, Tully\u2019s team is investigating the ability of salt-tolerant crops, such as rapeseed, and perennial grasses to grow well in the conditions observed at the Maryland farms. These plants could suck up phosphorus and nitrogen. Fields could later be converted to wetlands, which are better at retaining the nutrients. But most farmers in the area want to keep farming, Tully says.<\/p>\n

Scientists still lack critical numbers such as the amount of legacy fertilizer nationally and globally, Ard\u00f3n says. \u201cThis is an important risk that we haven\u2019t fully gotten a handle on.\u201d<\/p>\n","protected":false},"excerpt":{"rendered":"

In 2015, Kate Tully visited farms near the eastern shore of the Chesapeake Bay. She was investigating whether sea level rise had caused brackish water to move upland, a process called saltwater intrusion\u2014evidence of which she found in the form <\/p>\n

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