31 October 2013 18:19 [Source: ICIS news]
HOUSTON (ICIS)--For the first time since 1980, nitrate levels in the Mississippi river basin are showing a substantial multi-year decrease as there has been a 21% drop in the amount of nutrients released into the Illinois river between 2000-2010, the US Geological Survey (USGS) announced on Thursday.
The Illinois river is one of the four major tributaries for the Mississippi river, with the critical US waterway playing the lead role in transporting nutrients that are washed out of agricultural fields and carried into the Gulf of Mexico. These run-offs eventually settle into the ocean and cause the seasonally hypoxic zone, frequently referred to as the ‘dead zone’.
When there is flooding events or excessive rains, it causes nitrogen-based fertilizer to leech out of the soil and be carried into the river system and eventually the ocean waters. The released nitrogen encourages the rapid growth of algal blooms, which eventually perish and sink to the ocean floor, where bacteria will decompose the organic matter.
At the same time, the bacteria consumes the oxygen levels and results in hypoxic, which is low-oxygen, or anoxic, oxygen-free, conditions. The dead zone typically appears in the summer as there is less mixing of currents.
While the research is showing improvements in the Illinois river, similar progress is not yet being realised in the other main tributary, the Missouri river or within the Mississippi river itself, which USGS said shows that there is still a great amount of work to be done in order to protect the environmental ecology of the basin and the Gulf of Mexico.
“These results show that solving the problem of the dead zone will not be easy or quick. We will need to work together with our federal and state partners to develop strategies to address nitrate concentrations in both groundwater and surface water,” said Lori Caramanian, Department of Interior Deputy Assistant Secretary for Water and Science.
USGS officials said the exact reason for an increase or decline in the annual nitrate levels has yet to be identified but that the primary contributing factors are believed to be related to fertilizer use, agricultural management practices, livestock waste and wastewater treatment applications. Currently the nitrate levels are being monitored at eight regional sites within the Mississippi river basin and four locations directly on the Mississippi.
The monitoring sites showed that in addition to the decline in the Illinois river, there was also a 10% drop in the amount present in the Iowa river. At the same time, there were consistent increases in nitrate concentrations in the 10-year period in the upper Mississippi, which is up by 29% as well as the Missouri river climbing by 43%.
The data showed that the Ohio river has the lowest levels of nitrate within the river basin system but that the Mississippi outlet to the ocean has seen its amounts increase by 12% from the period of 2000-2010.
In the report, the USGS said that groundwater is likely the dominant source of nitrate during periods of low flow and that it can take decades for nitrates to move from the land where it was applied into the groundwater and eventually releasing into the rivers. With this factor, the agency said it can take many years before water quality is impacted.
“Expanded research and monitoring is absolutely essential to tracking progress in reducing nutrient pollution in the Mississippi river basin,” said Nancy Stoner, Environmental Protection Agency, acting assistant administrator for water.
First documented in 1985, the dead zone has consistently covered about 6,000 square miles (15,000 square km) off the coast of Louisiana and impacts sea life as it forces the populations of fish and other shellfish to relocate or die. In 2013, the USGS has calculated the hypoxic zone encompassed 5,840 square miles.
Researchers have primarily placed the blame on farmland run-off, namely what they view as the overuse of fertilizers in the Corn Belt, as the main culprit with some fault attributed to weather conditions such as wind direction and water temperature.
Although farmers overall are using less fertilizer per acre than in previous decades, the amount of land being utilized for crops has increased and has added to the overall problem.
Some critics of fertilizer practices in the US have urged farmers to discontinue fall applications and instead wait until spring plantings. According to research data, the amount of nitrogen entering the Gulf has increased by about 300% since the 1960s with increase in agricultural operations suspected as well as the advancement and frequency of fertilizer applications.
A state and federal task force in 2008 released a goal to reduce the zone to less than 2,000 square miles by 2015, with the Environmental Protection Agency having set an objective of reducing these nutrient releases by 45% before the year 2045.
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