A lot of discussion has been centering on Roxanne Conlin's historic bid to become Iowa's first female elected to the U.S. Senate. Iowa has never elected a woman to Congress and we share that distinction with just one other state – Mississippi.
Yet, this isn't the only connection between Iowa and our friends to the south in Mississippi. The other is water, and the issue that is beginning to get more attention as people focus on the Gulf oil spill is hypoxia.
Hypoxia or oxygen depletion is a phenomenon that occurs in aquatic environments as dissolved oxygen (DO; molecular oxygen dissolved in the water) becomes reduced in concentration to a point detrimental to aquatic organisms living in the system. Dissolved oxygen is typically expressed as a percentage of the oxygen that would dissolve in the water at the prevailing temperature and salinity (both of which affect the solubility of oxygen in water; see oxygen saturation and underwater). An aquatic system lacking dissolved oxygen (0% saturation) is termed anaerobic, reducing, or anoxic; a system with low concentration—in the range between 1 and 30% saturation—is called hypoxic or dysoxic. Most fish cannot live below 30% saturation. A “healthy” aquatic environment should seldom experience less than 80%. The exaerobic zone is found at the boundary of anoxic and hypoxic zones
Hypoxia is an issue that directly connects Iowa to the Gulf of Mexico.
“The hypoxia problem in the Gulf is considered to be due, at least in part, to too many nutrients flowing down the Mississippi River and into the Gulf of Mexico”
Hypoxia is often linked to inputs of Nitrate and Phosphorous from runoff in Midwestern farm states, including Iowa. The science tells us:
Oxygen depletion can be the result of a number of factors including natural ones, but is of most concern as a consequence of pollution and eutrophication in which plant nutrients enter a river, lake, or ocean, and phytoplankton blooms are encouraged. While phytoplankton, through photosynthesis, will raise DO saturation during daylight hours, the dense population of a bloom reduces DO saturation during the night by respiration. When phytoplankton cells die, they sink towards the bottom and are decomposed by bacteria, a process that further reduces DO in the water column. If oxygen depletion progresses to hypoxia, fish kills can occur and invertebrates like worms and clams on the bottom may be killed as well.
Hypoxia may also occur in the absence of pollutants. In estuaries, for example, because freshwater flowing from a river into the sea is less dense than salt water, stratification in the water column can result. Vertical mixing between the water bodies is therefore reduced, restricting the supply of oxygen from the surface waters to the more saline bottom waters. The oxygen concentration in the bottom layer may then become low enough for hypoxia to occur. Areas particularly prone to this include shallow waters of semi-enclosed water bodies such as the Waddenzee or the Gulf of Mexico, where land run-off is substantial. In these areas a so-called “dead zone” can be created. The World Resources Institute has identified 375 hypoxic coastal zones around the world, concentrated in coastal areas in Western Europe, the Eastern and Southern coasts of the US, and East Asia, particularly in Japan.
This is but one of the many reasons farmers, scientists, activists and organizations are working to find cooperative solutions to this growing problem. It is one of those issues where there are both natural and anthropocentric causes, but the conservation measures that can reduce human impacts are well known.