Although nutrients are essential for the growth of an estuary's plants, an excess may trigger a string of events that depletes dissolved oxygen in the water. BOD is a measure of the quantity of organic material in the water and, therefore, the water's potential for becoming depleted in dissolved oxygen. Since bacteria decompose organic material, water with a high BOD level also generally has a high bacteria count. Although some waters are naturally organic rich, a high BOD often indicates pollution. Turbidity is a measure of the suspended particles in water.
Human activities can be the cause of turbidity as well.
Runoff from farm fields, storm water from construction sites and urban areas, shoreline erosion and heavy boat traffic all contribute to high levels of turbidity in natural waters. These high levels can greatly diminish the health and productivity of estuarine ecosystems. Turbid waters decrease light penetration, thereby reducing the ability of aquatic plants to grow. Particles may also accumulate on the gills of fish and inhibit breathing. Dissolved Oxygen - Dissolved oxygen is an essential indicator in assessing an estuary s health.