The oil leak on Mississippi Canyon seafloor of the Gulf of Mexico proceeds apace. It is not clear that recent actions have succeeded in plugging the leak. The widely dispersed petroleum is a great disaster, but I get the distinct impression that this oil is seen as despoiling a pristine environment. Nothing could be further from the truth. I get this impression because, to my knowledge, the sorry state of the Gulf of Mexico before the oil spill has not been discussed. Before the oil spill, the Gulf of Mexico was being ravaged by—
- coastal erosion
- hypoxia (very low oxygen)
- harmful algal blooms (red tides)
These ongoing, slower-acting environmental disasters have a common cause: human activity. Let’s start with coastal erosion.
The Louisiana coast depended for thousands of years on the routine overflow of the Mississippi River to deposit its sediment load and build land. But, beginning around the 1930s, in order to save lives and cities, the federal government built massive levees to constrain and control the river, effectively stopping it from doing what nature wants it to do.
As a result, for the past 70 years or so, the sinking of the delta coast has continued unabated. As salt water pushes inland from the gulf, it kills wetlands and marshes, habitat for wildlife and fish, and is increasingly threatening homes for many thousands of people.
Let’s move on to hypoxia and the Gulf of Mexico Dead Zone.
The Gulf of Mexico dead zone is an area of hypoxic (less than 2 ppm dissolved oxygen) waters at the mouth of the Mississippi River. Its area varies in size, but can cover up to 6,000-7,000 square miles. The zone occurs between the inner and mid-continental shelf in the northern Gulf of Mexico, beginning at the Mississippi River delta and extending westward to the upper Texas coast… Dead zones can be found worldwide. The Gulf of Mexico dead zone is one of the largest in the world.
The dead zone is caused by nutrient enrichment from the Mississippi River, particularly nitrogen and phosphorous. Watersheds within the Mississippi River Basin drain much of the United States, from Montana to Pennsylvania and extending southward along the Mississippi River. Most of the nitrogen input comes from major farming states in the Mississippi River Valley…
Nitrogen and phosphorous enter the river through upstream runoff of fertilizers, soil erosion, animal wastes, and sewage. In a natural system, these nutrients aren’t significant factors in algae growth because they are depleted in the soil by plants. However, with anthropogenically [human-caused] increased nitrogen and phosphorus input, algae growth is no longer limited. Consequently, algal blooms develop, the food chain is altered, and dissolved oxygen in the area is depleted. The size of the dead zone fluctuates seasonally, as it is exacerbated by farming practices. It is also affected by weather events such as flooding (more info) and hurricanes…Nutrient overloading and algal blooms lead to eutrophication, which has been shown to reduce benthic biomass and biodiversity. Hypoxic water supports fewer organisms and has been linked to massive fish kills in the Black Sea and Gulf of Mexico.
Satellite image of the northern Gulf of Mexico/Mississippi Delta showing hypoxic coastal water (light blue). This color change is due to excessive nutrients being washed into the sea.
Let’s finish up with harmful algal blooms (HABs), also called red tides.
- There are some 4,000 known species of microscopic algae, called microalgae or phytoplankton, in the global ocean. Approximately 300 of these have been identified with periodic explosions of growth, in what amounts to extensive monocultures of the particular species involved. Dense growths of microalgae are broadly termed “blooms.”
- While single species blooms can turn the water surface red, brown, yellow, green or white, they are often generically referred to as “red tides” and are often associated with harmful or toxic effects. When the blooming microalgae have properties that are deemed harmful to humans or other life, the blooms are called Harmful Algal Blooms, or HABs.
- In recent years, there has been growing alarm over what appears to he an “epidemic” of HABs worldwide… Although there are some scientists who believe the increase in reports of HABs is a function of increased awareness and monitoring, others have provided compelling evidence that, for some regions, human activities play an important role. The primary human contribution to HABs is thought to be nutrient pollution — from, amongst other things, agriculture, sewage outfalls and mining — creating a more favorable, nutrient-rich environment in coastal waters in which certain groups of phytoplankton can thrive.
- Climate change may also be making some coastal environments more hospitable to harmful phytoplankton species [via ocean warming[
- Many species of phytoplankton are also transported
around the world in ships’ ballast water and discharged in areas where they did not previously occur. Others are distributed accidentally through the transfer of shellfish for aquaculture.
Reading this text, perhaps you’ve gotten the impression that the Gulf of Mexico is just one big toxic waste dump. You would be correct. Although coastal erosion, deepwater hypoxia and algal blooms are natural processes, human interference has made such conditions much worse in each case.
So there you have it. Is this brief presentation meant to detract from the awfulness of the oil spill? Not at all. I merely wish to point out that the oil spill is a case of piling on. Many species in the Gulf were already under severe pressure before the blow-out. Now everything, including the wildlife, is covered with oil, which just accelerates the ongoing environmental deterioration & species die-off. See my How We Wrecked The Oceans to understand the full extent of our destruction of the world’s oceans.
As if all this weren’t bad enough, everybody is forecasting a very severe hurricane season. Let’s conclude with some pictures. (Thanks to my friend Sally for the photos.)
