No impact--environment

A2: DEAD ZONES

Gulf of Mexico Dead Zone Anyone who's ever seen a cow pasture would likely recognize some of the most immediate environmental impacts of large-scale livestock farming--trampled ground, eroded stream banks, lots of manure. However, a less visible but equally worrisome effect appears thousands of miles from the Midwest's muddy cow pastures, in the tropical waters of the Gulf of Mexico. Amidst increasing concern for the growing 'dead zone' where the Mississippi River flows into the Gulf, livestock farming practices are increasingly coming under scrutiny. In fact, the FAO says, the livestock sector is the major driver of increasing water pollution in most geographical areas. The Mississippi's Loaded Waters The Mississippi River drains 41 percent of the contiguous United States into the Gulf, a drainage basin that includes almost all the country's industrial livestock farms and livestock feed production. Rainwater runoff, treated sewage, and other wastewater add to the river's nutrient load. When dumped into the Gulf, these nutrients are consumed in explosive algal blooms, driven largely by nitrogen and phosphorous. When the blooms die and sink to the bottom, they are decomposed by bacteria on the ocean floor. In the process, these bacteria drain the water of its dissolved oxygen, forcing fish, shrimp, and other marine life to relocate to survive. The dead zone in the Gulf of Mexico is the second biggest in the world, comprising thousands of square miles where the dissolved oxygen is so low that the water can support only the most minimal life.

The report also suggests that the demand for energy will increase eutrophic conditions worldwide. Total global energy consumption is expected to rise by 50 percent by 2030 and a majority of that will be in the developing world. “Though renewable energy sources are being developed, fossil fuels such as coal, oil and natural gas, are expected to continue meeting 86 percent of global energy needs,” said Selman. “When fossil fuels are burned, they release nitrogen oxides into the atmosphere, which are then deposited to land and water through rain and snow.” Some studies have found that atmospheric sources of nitrogen are a significant source of coastal pollution, particularly in industrialized countries with high NOx emissions. In the Chesapeake Bay, atmospheric deposition accounts for 30 percent of the nitrogen pollution found in the watershed. “Because there are so many pathways, sources, and drivers of nutrient pollution, the policies that address eutrophication cannot be limited to traditional environmental regulations,” said Selman. “Instead, policymakers must look more broadly at agricultural, energy, land use, and public health policies and find ways that these policies can be designed to mitigate nutrient pollution.”

The 2005 tropical storm season for the Gulf of Mexico is notorious for the devastating effect of hurricanes Katrina (in August) and Rita (in September) on the Louisiana coast. However, two additional earlier storms—hurricanes Cindy and Dennis— generated sufficiently high wave and windfields to disrupt hypoxia on the Louisiana shelf in July, before the scheduled cruise that maps the extent of midsummer hypoxia took place. The subsequent size of the hypoxic area was smaller (11 840 km2) than predicted by the nitrate–N load in May (16 083 km2) based on the Turner et al. (2006) model (Figure 5). However, hypoxia had re-established across a larger area by August (NNR, unpublished data), when Hurricane Katrina crossed the southeastern Louisiana coast. The variability in the changes of oxygen conditions near the bottom in a 20-m water column is illustrated by the 2003 hurricane season (Figure 6). The passage of several tropical storms and hurricanes in June–August 2003 disrupted stratification and hypoxia, but to varying degrees. The path of Tropical Storm Bill was very close to station C6C, but it passed rapidly north and the wave field was insufficient to re-aerate the bottom waters. Although it passed well to the south of station C6C, Hurricane Claudette generated a field of 30-knot winds at the site of the observing system, as it moved slowly towards the west. As with Hurricanes Cindy and Dennis in 2005, which resulted in a smaller area of hypoxia than predicted for the spring nitrate–N load, the effect of Hurricane Claudette in 2003 was sufficient to reduce the size of the bottomwater hypoxia to 8560 km2, which was 2.5% less than the predicted size of 20 000 km2. Tropical Storms Erika and Grace had opposite effects. The former had no effect on hypoxia former, whereas the latter caused an increase in bottom oxygen.