A focal discussion point when talking about climate issues is water. Water is a critical resource so it’s no wonder there is so much concern over how climate change is altering our access to water. In fact, quality is as important as quantity, making concerns even more nuanced. Water, therefore, is a global issue that we must pay attention to.
Bodies of water play a huge role in the health of our environment. After all, the ocean is the world’s largest ecosystem. Water is necessary to sustain life. The services we gain from water, like the water cycle and shaping the climate, are critical. Plus, many people rely on the fishing industry for food and money. Climate change intensifying water issues doesn’t help ease concerns about water availability. The larger role water plays is being threatened by many factors but one major issue is dead zones.
What is a dead zone?
Dead zones are one of the most significant anthropogenic, that is human-induced, threats to aquatic ecosystems worldwide. Currently, dead zones are increasing exponentially and climate change only makes things worse. There are over 400 documented dead zones worldwide.
Dead zones happen as an ecosystem response to eutrophication, or the process of excessive nutrients polluting bodies of water. Algae, or phytoplankton, are primed to grow when these excessive nutrients, namely nitrogen and phosphorous, progressively leech into bodies of water. So, you get a nutrient-induced increase in phytoplankton activity which is called an algal bloom. These blooms can occur naturally and tend to happen in areas where the water warms up periodically, facilitating this growth. But due to climate change, seasonality is changing and weather is becoming more severe, explaining the exponential growth of dead zones worldwide.
Unfortunately, dead zones have immense consequences for biodiversity and ecosystem functioning. As the name implies, the algal bloom creates areas that cannot sustain life. As algae activity grows, the oxygen content of the water declines. This makes life amongst these blooms hard or not at all possible.
When dissolved oxygen in the water falls below 2 milliliters of oxygen per liter of water something called hypoxia occurs. Hypoxia is the term for when oxygen is not present in sufficient amounts. When the water falls below 0.5 milliliters of oxygen per liter of water massive die-offs occur. Hypoxic conditions lead to animal deaths due to lack of oxygen.
How do dead zones happen?
Although having a productive ecosystem can build a resilient environment, there are times when too much productivity can be harmful. Like when organic matter accumulates or when water warms, it encourages exorbitant microbe and phytoplankton activity. So, excess nutrients can feed algal blooms but warm temperatures can also speed up the growth of bacteria and phytoplankton. The dissolved oxygen gets used up as a result of the increased activity.
Organic matter can accumulate due to agricultural runoff after heavy rains, improper waste management, or pollution. Although the cause can be bacterial, viral, or chemical contamination, increased eutrophication is predominantly due to anthropogenic influences.
Although excessive nutrients play a huge role, temperature is also a driving force behind the patterns of hypoxia. Warm temperatures speed up growth, as stated before, but warmer water inherently holds less oxygen. Gas solubility decreases with temperature so as the water heats up, the less dissolved oxygen it can hold. The net effect of changing temperatures is that warming is predicted to expand dead zones.
Dead zones are a serious issue.
With dead zones expected to increase as temperatures continue to change, this makes the issues facing us due to climate change even more serious. Although changes seen in an ecosystem are due to a summation of factors, the role dead zones play in decreasing aquatic populations is clearly seen.
Unless able to cope with low-no oxygen environments, nothing can live in these areas. This leads to the restriction of habitat. Species are left to choose between warm shallow water that may exceed their thermal tolerance, aka the amount of heat stress the organism can withstand, or hypoxia in deeper waters. Ultimately, this limits access to crucial habitats like spawning grounds and nurseries, or leads to increased species death.
Furthermore, warmer temperatures associated with climate change will further promote hypoxia by preventing oxygenated surface waters from mixing with bottom waters. The lack of water mixing is called water stratification. Water stratification sets the stage for hypoxic bottom water. Sea level rise associated with climate change is also increasing the volume of bays, estuaries, and continental shelf areas. Increasing the volume of shallow coastal water only feeds more into this problem.
Warmer water also leads to increases in metabolic rates for animals like crabs and bivalves (think clams, oysters, and scallops). They need more oxygen in warmer temperatures to keep internal processes constant. A decreased oxygen availability and an increase in oxygen demand lead to stress, mortality, and ecosystem collapse.
Eutrophication sets off a chain reaction. You gain an overabundance of algae, the algae create a lack of oxygen, and animals suffocate. The algae then eventually decompose and produce a large amount of carbon dioxide which lowers the pH of the water. Climate change makes these issues even worse and, in the end, you’re left with lifeless bodies of water and an acidified ocean.
For us, this means limits to drinking water, limits to water used domestically, decreases in food production, and environmental harm. More than $4 billion are lost each year in the US alone due to algal blooms. We can’t afford to ignore this issue.
We must be mindful.
Climate change alters weather patterns and variability, so severe water impairments will likely become more frequent and worrisome. There are various direct and indirect effects caused by climate change but dead zones are one of the most alarming.
We need to address the climate crisis and our agricultural practices. Reducing meat consumption, buying organic products, and planting more trees can all decrease eutrophication. We must be mindful of the issues concerning our water and help reduce pollution to lessen the growing problem of dead zones.