Nutrients. Plants love them – it helps them grow big and strong. You might think that an excess of nutrients in the waters of kelp forests would be a good thing for the kelp. Well, not necessarily….
In high nutrient conditions, algal turf is able to out-compete kelp. It quickly takes up any available space, and prevents new kelp growing. It’s becoming a particular issue in areas such as southern Australia, where the kelp forests are known to be areas of high biodiversity. Stressors on any ecosystem rarely act totally independently, and there is one big stressor to the global ocean that has scientists particularly worried – rising carbon dioxide levels.
Laura Falkenberg and colleagues at the University of Adelaide, Australia sought out to discover if rising carbon dioxide and nutrient input interact with each other to impact algal turf growth. Their experimental research revealed that increasing carbon dioxide and nutrient inputs together created faster growth in algal turf than either nutrient or carbon dioxide separately. That’s not good news, because our carbon dioxide emissions don’t look like they are going to reduced significantly any time soon.
There is one possible glimmer of hope though. The research indicated that if nutrient inputs are stopped, then the turf declines by some 75% – despite carbon dioxide levels remaining elevated. Excessive nutrient input doesn’t just affect kelp forests – check out my post on Google+ just a few days ago on agricultural pollution impacts on the Great Barrier Reef.
The question is, are we able to tackle nutrient pollution more successfully than carbon emissions?
Image: Gazing upward in a giant kelp forest. California, Channel Islands NMS. Credit NOAA Photo Library (CC BY 2.0)
Most life on Earth needs oxygen to survive – even those living in our oceans. So when oxygen levels in our coastal waters are severely reduced, (hypoxia), and worse still reduced to almost zero levels (anoxia), the impacts can be deadly.
These ‘dead zones’ (as they are commonly known) occur naturally, but there has been increasing concern that human activities – primarily our agricultural practices – are causing more, larger, and longer lasting dead zones in our coastal waters. Essentially, excess nutrients from the land run off (or are removed) either directly into coastal waters, or down rivers which end up in the coast. Algae loves these extra nutrients – so much so that they ‘bloom’ to extraordinarily numbers – forming algal blooms at the surface. Eventually they die off, sink down to the ocean floor where microbes get to work decomposing the remains. This is quite an oxygen-intensive process and eventually oxygen in these lower levels becomes fatally low for anything that cannot move away from the area.
The Gulf of Mexico is home to arguably the most famous of these man-made dead zones, and is subject to regular monitoring. In fact, researchers are even forecasting dead zones. And 2013, they said, would be a biggie. Researchers from Texas A&M University have been busy keeping an eye on the oxygen levels in the lower waters from the Gulf. Turns out, the predictions were right on target. And they are predicting as the summer temperatures warm up, it will get worse.
Want to explain the dead zone to your kids? Check out this interactive look at how dead zones in the Gulf of Mexico form, courtesy of the Science Museum of Minnesota.
Image: Red Tide caused by Dinoflagellates off the Scripps Institution of Oceanography Pier , La Jolla California. Credit – released into the Public Domain, August 2005. P. Alejandro Díaz and Ginny Velasque