Chemical Waste

At times in this blog I have mentioned how marine pollution has not necessarily received the same attention that other global issues such as atmospheric pollution perhaps have. This is something nicely pointed out by Gelcich et al. (2014) in their paper on public perceptions of marine environments. This is not to say that ocean waste is more of a problem than our carbon emissions, but the focus on deforestation and fossil fuel burning has almost allowed the condition of our seas to slip under the radar a little bit. In fact, it is only relatively recently that marine pollution has become regarded as a problem in its own right that is in need of a solution. On occasion, it has managed to make front page news, but this is seldom the case and tends only to be in the instance of a catastrophic event. However, one good example of when this has been the case is the gulf of mexico oil spill in 2010, at Deepwater Horizon - described by then White House energy adviser, Carol Browner, as "the worst environmental disaster the US has faced".

Almost 100,000 birds died as a result of the Deepwater Horizon
oil spill (Source)

The spill at Deepwater Horizon was a truly devastating marine disaster, and acted as a perfect example of the damage that chemical pollution can do to the ocean. It therefore feels appropriate to have a brief look at a few of the many figures produced by the Natural Resources Defense Council (NRDC) in their 2015 report of the event. 68,000 square miles of surface water were contaminated by the spill, as well as over 1,000 miles of coastline. As many as 5,000 marine mammal deaths were estimated, with 1,000 of these being sea turtles. Economically, in excess of $11 billion has been paid in damages to businesses and individuals in the Gulf of Mexico who suffered the effects of the spill. However, whilst international disasters such as this make front page news worldwide, and rightly so, the ongoing chemical pollution of the ocean from other sources tends to go more unnoticed, despite the environmental threat they pose.

In my opening blog post I mentioned how increasing concentrations of nitrogen in the ocean can enhance microbial growth, thus leading to higher volumes of the greenhouse gas, nitrogen oxide, being produced. This in turn contributes to the warming of Earth's atmosphere, going to show that ocean pollution does not just effect marine life but can in fact influence climate on a global scale. That particular study pointed to increasing nitrogen emissions across northeastern Asia as being a cause for this, and further studies have suggested that nitrogen emissions in these areas are becoming greater. Two dominant sources of this ever-growing supply of nitrates to the ocean are the burning of fossil fuels, and agricultural fertilisers, with the latter becoming an increasingly large concern in coastal marine ecosystems.

Nitrates have been used in industrial fertilisers worldwide ever since the introduction of the Haber-Bosch process, which involves the manufacture of ammonia via nitrogen fixation. These nitrates end up in marine habitats via eutrophication - the result of surface water runoff from farms, as explained in my 'How does it get there' post. As discussed, this can increase microbial growth, increasing the production of the greenhouse gas nitrogen. However, this is not the only consequence of hiking up the microbial activity. Studies have shown that enhancing this activity can create 'dead zones', as the excessive amounts of organic matter, created by the nitrates, sinks and decomposes - using up oxygen in the process. Hence, dead zones are defined by a lack of dissolved oxygen in the water, and are a hostile environment for marine organisms. Worryingly, it has been suggested that the occurrence of these dead zones could be set to rise. Figure 1 below is a map of the world's dead zones as of 2005, and unsurprisingly they appear to be rather clustered around the countries which use the most fertiliser.

Figure 1: Dead zones and fertilisers (Source)

Unfortunately, there are yet more threats that eutrophication poses to coastal environments, one such threat being the production of Harmful Algal Blooms (HAB's). These are toxic algae created by chemicals from agriculture and industry that are capable of destroying coral reefs. One study in the Gulf of Oman showed how branching coral species were completely lost due to the HAB's, whilst further species experienced 'substantial reductions' in abundance and richness. Other studies have pointed to the impact that they can have on human health. This is most commonly through the consumption of poisoned shellfish, where the the shellfish concerned have been living in habitats affected by HAB's. One example of this is amnesic shellfish poisoning, which can cause intense gastrointestinal distress and even death, whilst survivors may experience severe memory loss. Due to the impacts of poisoned shellfish, the tourist and fishing industries in these areas can suffer.

In our day to day lives it is likely that we will use oil, whether it be through petrol in your car (or the bus if you take it), or perhaps it is used for your heating at home. Similarly, it is perhaps even more likely that the food you eat everyday has been grown on a farm somewhere, using chemical fertilisers. Oil and agricultural chemicals are thus two huge components of everyday life around the world, so as long as we are reliant on them it is important that we understand their impacts on the environment, to allow for mitigation. Now, as promised for the optimists out there, the remainder of this blog will focus more on what is hopefully going to be promising news on marine pollution, by looking at the progress being made to stop it.