Dissolved oxygen is essential to all aquatic life. When the algal blooms sink to bottom waters, oxygen is depleted as the algae decay. If the oxygen is reduced below 3 mg/ L, plants, fish and other sea life are harmed or killed or may leave the area if they are mobile. This often occurs during the summer months when nutrient pollution and algal blooms cause low dissolved oxygen levels, or hypoxia. At times, areas of our waterways may even be anoxic, which means the water is devoid of oxygen (0 mg/L). This can be characterized as the waters being "dead". When oxygen in deep water is depleted, fish and other species will die unless they move to other areas of suitable habitat.
Water clarity measures the ability of light to pass through the water. Should light not be able to penetrate the water, underwater grasses are not able to survive. Causes of poor water clarity can be excessive algal blooms or sediments from erosion. Algal blooms can become so dense that they reduce the amount of sunlight available to submerged aquatic vegetation (SAV). Without sufficient light, plants cannot photosynthesize and produce the food they need to survive. The loss of sunlight can kill the grasses. These grasses are a vital part of the aquatic ecosystem and many forms of marine life needs the aquatic vegetation for food and shelter from predators. The plants also produce oxygen. Water clarity can also be reduced by sediment entering the waters from runoffs from the land or soil erosion on the banks of the waterways. Suspended sediments make the water cloudy so less light is available for underwater grasses In addition to increasing the turbidity, sediments can also carry high concentrations of certain toxic materials that contaminate waterways and may also carry nutrients, particularly phosphorus, which increase nutrient pollution in the rivers.
pH levels are directly related to the health of fish and aquatic plant life in the water. In a healthy system, pH levels should be in a neutral range between 6.5 and 8.5. Levels of pH below 6.5 indicate that the water is in an acid state. The most common reason for acid water is storm water runoffs and air deposition of nitric and sulfuric acids and other toxic chemicals discharged by industries, power plants and automobiles. Toxicity depends on many factors such as concentration, chemical and physical form, and persistence of the chemical. Levels of pH greater than 8.5 usually indicate the presence of algal blooms because intense photosynthesis by algae removes CO2 from the water and increases the pH.
Nutrients, like nitrogen and phosphorus, occur naturally in water, soil and air. Just as the nitrogen and phosphorus in fertilizer aids the growth of agricultural crops, both nutrients are vital to the growth of plants within the Chesapeake Bay and our Talbot County rivers and creeks. However, the main causes of the pollution of our rivers are elevated levels of these two nutrients. In addition to the natural sources of nitrogen and phosphorous, sewage treatment plants, private in ground septic systems, industries, vehicle exhaust, acid rain, and runoff from agricultural, residential and urban areas contribute nutrients to the waterways. Although plants and animals in the rivers need nutrients to live and flourish, excess nutrients become pollutants. Excess nutrients in our waterways cause rapid growth of algal blooms. These algal blooms cloud the water and reduce the amount of sunlight reaching the Bay's underwater plants and fish.
Editors note: For more detailed information on the causes and effects of pollution of our waterways, access www.chesapeakebay.net or the Talbot County Creekwatchers 2001 - 2003 Water Quality Monitoring Report found on the Creekwatcher section of this website.
