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On the morning of April 14, 2005, a catastrophic pollution event occurred at Bangs Lake, a tidal lake within the Grand Bay National Estuarine Research Reserve (NERR) in Mississippi. The spill occurred when the walls of retaining ponds filled with wastewater collapsed at a fertilizer manufacturing company located 1.1 km (0.7 mi) from the lake. Approximately 17.5 million gallons of polluted water flowed out of the retaining ponds and into the lake. The released wastewater had a pH of 2.2 to 2.4 and contained elevated levels of phosphorus 4000-5000 ppm (parts per million). Mississippi Phosphates, the company that operates the fertilizer manufacturing plants, says that walls of the retaining ponds may have collapsed because of unusually high rainfall (over 43 cm) from March 31 to April 11.
Water quality data from the spill was captured at a monitoring station 1.9 km (1.2 mi) from where the spill entered the lake. The spill caused an immediate drop in pH. A water quality monitoring station maintained by Grand Bay NERR at the center of the lake showed that on April 15, the pH dropped three entire units in one hour. That day, the water registered a pH low of 3.7 units. Eleven days later, phosphorous levels in the lake were about 5000 times greater than levels before the spill. Chlorophyll-alpha (or chlorophyll-a), a measure of primary productivity was nonexistent, suggesting that there was little or no phytoplankton or algae in the lake.
The contaminants of the spill were two sources of waste products that come from the creation of phosphates for fertilizer: calcium sulfate and wastewater (contaminated with phosphoric acid and other pollutants). In order to get useable phosphate for fertilizer, phosphate ore is reacted with sulfuric acid to produce phosphoric acid.
Much of the damage was not immediate, but resulted from a chain of causes and effects. For example, several weeks after the spill, large algal mats covered the surface of some of the shallow, enclosed areas of the lake. Scientists believe that the algae populations exploded because there were so many nutrients in the water. Phosphates are some of the nutrients necessary for algae growth. In some estuaries, phosphates may be the growth-limiting nutrient.
The extensive algal blooms occurred in the shallow, enclosed waters near the point where the polluted water entered Bangs Lake. As these algal mats decayed, oxygen was removed from the water, eventually contributing to lower levels of dissolved oxygen (DO) in the lake. These hypoxic conditions contribute to the stress and death of various forms of life. Low dissolved oxygen levels continued into the fall.
Despite the extent of the damage, the estuary recovered relatively quickly. The algal blooms cleared up within a couple of months. Also within 4-8 weeks, fish and blue crabs had moved back into the area. The marsh vegetation began to recover during the summer and appeared to be “normal”
by the time Hurricane Katrina hit the area in August of 2006. The upland vegetation has taken longer to recover; the grasses have come back but the shrubs and trees suffered high mortality.
The phosphate company where the gypsum stacks failed, Mississippi Phosphate, claims that the gypsum stack holding the wastewater failed because of heavy rainfall. Although the Mississippi Department of Environmental Quality (MDEQ) accepts this as a possibility, it also believes
that the company tried to increase the capacity of the ponds and built the retaining walls too big and too fast. The gypsum stacks are ringed by a moat-like system, which environmental permits say should be designed to capture such spills. MDEQ believed that the levees around the gypsum stacks were not sufficient to catch the pond spill before it poured into the marsh.
The company’s permits from MDEQ specify that the waste ponds must be designed to withstand a storm producing about 11 inches in a 24-hour period, according to the standard calculations produced by the National Oceanic and Atmospheric Administration for this part of the Gulf Coast.
Weather information from the Southern Climate Data Center indicates that there was no rainfall in Pascagoula on April 13 or 14, when the spill occurred. Weather service radar and Southern Climate Data Center reports indicate that on April 1, two weeks before the spill, an area along the
Mississippi/Alabama border may have received about 8 inches of rain, the largest rainfall the Climate Data Center reported for that month.
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