Intensive agriculture near the Mississippi has led to fertilizers leeching into the river, and ultimately the Gulf of Mexico, via soils and waterways. This has resulted in a huge oxygen-deprived dead zone in the Gulf that is now at its largest ever extent, covering an area greater than the state of New Jersey.
Rivers to the Sea
“Given their pervasive and persistent nature, microplastics have become a global environmental concern and a potential risk to human populations,” said Rachel Hurley from the University of Manchester and colleagues in their report, published in Nature Geoscience.
The equivalent of one garbage truck full of plastic waste is dumped into the world’s oceans every minute, equal to 8 million tons a year. New research suggests that 90 percent of that waste gets into the oceans through 10 major river systems.
Another reason global warming has not been too bad yet is because the ocean absorbs most of the earth’s excess heat. But oceans are warming due to greenhouse gas emissions. According to the National Oceanic and Atmospheric Administration, half of the increase in ocean heat content since 1865 has occurred over the past two decades. Warmer water holds less oxygen, but the respiration rate of animals (except for marine mammals) increases with temperature, so they need more oxygen at the same time that less is available. A warmer ocean has less turnover (vertical water movements), which normally brings nutrient-rich water up from deep water to the plankton that photosynthesize near the surface. With fewer nutrients, they photosynthesize less and animals can’t get enough food.
Since the beginning of April, Julia Parker has seen 216 sick pelagic birds come into the Santa Barbara Wildlife Care Network. There were only four in February, and three in March. Of those 216, mostly loons, grebes, and murres, only 65 survived long enough to be transferred to the International Bird Rescue center in San Pedro. Many more have been found dead on nearby beaches.
Researchers have more than once warned of “dead zones” and toxic algal blooms as a consequence of changing climatic conditions. Ocean temperatures are increasing, and this in turn encourages a new set of biochemical processes.
Professor Hollibaugh and a colleague report in the journal Environmental Science and Technology that over the course of eight summers they measured peaks of nitrite, alongside massive increases in the numbers of the microorganisms that produce it, in coastal waters off Georgia.
“Historically, at this time of year, we would see nice little bunches (of orcas) swimming back and forth in front of the house,” said Ken, who lives on the west side of San Juan Island. But this year, the whales have broken up into small family groups and are traveling around in seemingly random patterns, presumably in search of whatever salmon they can find.