Other Types of Pollution
Dumping
In order to reduce the amount of waste kept in landfills, the amount of waste incinerators needed, or even simply reduce the cost of disposing of waste properly, a lot of waste ends up dumped into ocean. Some ends up in the ocean due to runoff rather than intentional dumping (especially in some developing nations), but the outcome is the same: solid waste in the ocean.
Dumping occurs in other aquatic ecosystems as well, but we will mainly focus on the ocean.
You've probably heard of the garbage patch in the ocean (of which there are multiple), seen the video of the turtle with the straw in its nose, or been told why you should cut the loops of those plastic bottle holders.
The waste that ends up in these aquatic ecosystems can be toxic to marine life, can be a choking hazard, create intestinal blockages, and can entangle organisms preventing their movement.
It is estimated that millions of tons of plastic enter the ocean each year, and many plastic breaks down into small particles known as microplastics. These microplastics have been found even in the bottom of ocean trenches, and studies estimate that humans consume tens of thousands of microplastics each year.
While some areas have worked to prevent the dumping of waste into the ocean, with the US passing the Ocean Dumping Ban Act in 1988, many nations have few environmental regulations or do not have a real means to enforce such bans.
Oil Spills
Most people have heard of an oil spill, and while they can happen on land, they are most damaging when they occur in aquatic ecosystems. Oil can stick to animals' fur or feathers, making it difficult to swim/fly while also reducing their ability to stay warm. The hydrocarbons within oil are highly toxic for organisms at every level of the food chain and kill organisms from simple contact, inhalation, or ingestion. As the oil spreads out, some sinks, smothering benthic organisms. It can block sunlight, disrupting photosynthesis from the autotrophs.
These are ignoring effects to humans as well, as there are numerous economic problems due to decreases in recreation and tourism, a loss of the oil, and decreased production of fisheries due to the killed marine life.
The oil can come from a variety of sources, such as oil tankers, pipelines, offshore drilling, and even some natural seepage from the bottom of the ocean. These spills can have immense effects, with the famous Exxon Valdez spill taking decades to clean up, affecting over 1,000 miles, and resulting in the death of so many organisms that some populations have not yet rebounded.
On the topic of cleaning up the spill - how does one clean up oil spilled in the ocean? There are a variety of methods that can be used. Boons (floating plastic barriers) can be used to contain the oil and prevent it from spreading further, after which oil near the surface can be sucked up with giant vacuums. Oil near the shore can be soaked up using absorbent materials. Dispersant chemicals can be used to break up the oil into smaller droplets that more readily mix with water, preventing damage to the coast, although they can be toxic to marine life. Oil can be burned, quickly reducing the amount of oil in the water, although this method releases a great number of air pollutants. Something that may end up being used more in the future is somewhat newly-discovered species of bacteria that actually consume and break down oil as part of their metabolism.
Nutrient Pollution and Eutrophication
Fertilizers, wastewater release, and animal waste can be carried into nearby bodies of water through runoff, which can lead to eutrophication. In eutrophication, excess nutrients (particularly nitrogen and phosphorus) will fuel algae growth. Algae blooms will form, covering the surface of the water, which blocks the sunlight and kills plants below the surface. The dead plants will be broken down by decomposers, which use oxygen to do so. Low oxygen levels (hypoxia) will result in the death of aquatic animals, which will then be decomposed, using more oxygen, resulting in more death, and so on... The areas without sufficient oxygen that cannot support aquatic animals are known as dead zones.
Oligotrophic vs Eutrophic
If eutrophic waterways are those with high nutrient levels, low dissolved oxygen, and lots of algae, oligotrophic waterways are the opposite.
Oligotrophic waterways have low nutrient levels, high dissolved oxygen, and stable populations of algae. Mesotrophic waterways are those in the middle of the two. Bodies of water naturally exist in these different forms and are able to transition from oligotrophic to eutrophic over time, but human activities are causing eutrophic events resulting in hypoxia and dead zones to last for longer periods of time and to be more severe.
Measuring Dead Zones
Something known as an oxygen sag curve can be used to show how oxygen levels change along with the distance from the source of pollution. As nutrient pollution is what causes eutrophication and dead zones, this source is usually something like a sewage pipe that brings excess nutrients and waste.
Sediment Pollution
Loose sand, clay, silt, and gravels/small rocks are one of the more common pollutants in rivers and streams. It can increase turbidity (making it difficult for animals to see and plants to photosynthesize), can clog gills of aquatic species, and can destroy benthic habitats, even burying benthic organisms.
Thermal Pollution
Another way that humans can pollute the environment without the addition of chemicals is by causing a significant change in the temperature of a body of water. We do this in two main ways: 1) removing vegetation that helped to moderate temperatures and 2) taking water from a source, using it to absorb heat (typically in energy generation or to cool machines for manufacturing), and then dumping the now warm water back into the original source.
Bringing species outside their range of tolerance for temperature can induce thermal shock, which can kill organisms. In addition, warm water cannot hold as much dissolved oxygen as cold water. As an increased temperature will cause ectotherms (cold-blooded organisms, like fish) to increase their metabolism and therefore their rates of respiration, but there is not enough oxygen, this could result in suffocation.
Steps have been being taken to reduce the effects of thermal regulation. For one example, cooling towers and holding ponds are being used to hold the warmed water and allow it to cool before it is returned. In the US, the EPA regulates the dumping of warm water into natural bodies of water.