Water Quality

The Impact of Human Activity on Marine Ecosystems

Ponds, bays, and estuaries are vital to the overall health of the Earth and the many species that live here, but these delicate ecosystems are under constant threat from human activity. Among these threats are eutrophication, recreational activities, and climate change. Chemicals and nutrients that enter the water from fertilizers and waste products can offset the delicate balance by causing excess algae growth. Climate change and increased carbon dioxide in the atmosphere are also extreme issues for the Earth’s waters. They put a strain on marine plants and animals and can disrupt migration patterns leading to the death of large numbers of wildlife. To protect these areas, scientists need to understand the threats facing every individual body of water. Water quality testing is extremely important in this regard because it allows for a comparison between waters with different levels of nutrients, oxygen, and pH, and allows them to see how these results translate into the health of the location and the wildlife that live there.
There are many indicators when it comes to determining water quality. There are a variety of Benthic organisms that live in these ecosystems and the type of creature in each location depends on the water quality. For example, aquatic worms, black flies, and Planarians are all species that can survive in all types of environments. Water pennies, gilled snails, and aquatic snipe flies, however, can only survive in locations where there are low levels of pollutants. Looking at the different organisms in a body of water can allow one to determine the levels of nutrients and pollutants. Testing kits are vital to getting a precise read of the different variables that impact water quality. The main things scientists test for are the levels of nitrate, phosphate, and dissolved oxygen, the wide-range pH, turbidity, and biochemical oxygen demand. Nitrate (NO3) and phosphate (PO4) are nutrients that increase plant growth and are often found in fertilizer. Phosphate is found naturally in the water, but human impact is contributing to much higher levels of it. More than half of the phosphates that are in the water are not natural and are there due to human activities. Low levels of phosphate help an ecosystem’s plant life thrive but such an excess of the nutrient poses many problems. Levels of phosphate that exceed .03ppm cause accelerated and amplified plant growth. Nitrate is also found naturally in soil and waterways but has become more prevalent due to farming and increased human populations, especially near coastlines. Waters that contain less than 4ppm of nitrates are considered unpolluted by nitrogen, but levels less than this still increase plant growth and can be harmful to estuarine ecosystems. It is important to look at the amount of these nutrients when determining the health of an ecosystem because they show how susceptible a location is to fertilizer runoff and other pollutants. pH is a measure of the amount of activity of H+ ions in a substance. The relationship between them is that the pH is equal to the logarithm of the reciprocal of the H+ ion’s activity level. Liquids with a higher concentration of H+ ions have a lower pH and are more acidic. pH is measured on a scale from 0 to 14 with 0 being extremely acidic and 14 being basic. Pure water is neutral with a pH of 7 while a pH between 6.5 and 8.2 is best suited for marine life. pH is also affected by the nutrients in the water. Increased amounts of algae cause more carbon dioxide to be filtered out, increasing the pH and negatively impacting aquatic life. Turbidity is another common test that shows how clear the water is. This can be impacted by sediment and algae. Water that contains higher levels of fertilizer runoff is often more turbid so it is a good indicator of the clarity and algae levels in a body of water. Dissolved oxygen comes from the air and is essential for ocean life. Levels of dissolved oxygen are increased by plants and algae. The optimal level of dissolved oxygen to support marine life is between 5 and 6ppm. Amounts lower than this can make the fish and animals less healthy and, if the dissolved oxygen reaches below 2ppm, often will kill them. Biochemical oxygen demand or BOD is how much oxygen is used by the bacteria that break down dead plant and animal matter. The higher this is, the less oxygen is available for other organisms.
Nitrate and phosphate are naturally occurring in soil and are essential for plant growth, but because some soil is not always optimal for plants due to overuse or erosion, artificial fertilizers are used to replenish the nutrients that the ground may be lacking. On farms where the primary goal is yield, fertilizer is often used in excess to make sure that the plants will grow. The nitrogen in fertilizers is very soluble and can easily get into the groundwater. This happens to fertilizer that isn’t used by the plants. Having excess nitrate and phosphate in the groundwater can be very dangerous for the humans who drink the water. The polluted water travels through the ground and over paved surfaces and ends up in bays, lakes, and the ocean. These nutrients upset the balance of these ecosystems in a few key ways. First, they accelerate the growth of algae in the water which leads to the occurrence of algal blooms. Algae is extremely important to all marine ecosystems because it provides an essential food source and produces large amounts of oxygen. When enough algae grow, however, it forms a kind of film over the surface of the water that makes it difficult for sunlight to reach the plants on the seafloor. Without sunlight, these plants are unable to photosynthesize, but they can store enough glucose to survive without sunlight, at least periodically. The real issue arises when the algae have used up the nutrients in the water and no longer have enough nitrate or phosphate to sustain themselves. The algae die and fall to the seafloor where it begins to decompose. In the process of decomposition, different species of bacteria eat the dead algae. This process uses a large amount of oxygen and increases the biochemical oxygen demand which poses a threat to the rest of the ecosystem. The main ways that nitrate and phosphate get into the water are through fertilizer runoff from farms and residential lawns, the waste from livestock facilities, and unsustainable sewage systems.
Despite the many threats they face, marine ecosystems are resilient and there is much humans can do to preserve them. Algae is a vital food source for shellfish. They take in water through their gills, then they push the clean water back out. One oyster can filter the algae out of more than 50 gallons of water in a single day. If humans invest in the farming of shellfish and water quality research, as well as reduce their use of fertilizers it will be possible to reverse the effects of harmful pollutants and even climate change.