Chemical Makeup

Like salinity and temperature, the chemical composition of the water helps determine where and how many plants and animals live within the Bay. The waters of the Bay contain organic and inorganic materials, including nutrients, dissolved gases, inorganic salts, trace elements, heavy metals and other potentially toxic chemicals.

Composition of Water

The composition of sea water is relatively constant from place to place; however, the composition of fresh water varies depending on the soil and rocks that the water has flown over.

Both fresh and salt water contain many natural dissolved materials from several sources.

• Bacteria and other microorganisms decompose dead organisms and release compounds into the water.
• Live organisms also release compounds directly into the water.
• Organic and inorganic material enters the Bay via its tributaries and the ocean.

Sea water also contains hundreds of trace elements important in many biological reactions.

• Metals such as lead and mercury naturally occur in low concentrations.
• As you move down the Bay, the composition of the water changes with the increasing salinity caused by more dissolved salts, including chlorides, sodium, calcium, potassium and magnesium.

Dissolved salts are important to the life cycles of many organisms. For example, anadromous fish spawn in fresh or brackish water and then move to more saline waters as they mature.

Dissolved Gases

Dissolved oxygen is essential for nearly all life in the Bay. The amount of oxygen in the water is affected by a number of factors, including temperature and salinity. Thus, oxygen concentrations vary, in part, with season and location.

Carbon dioxide, another dissolved gas, is important to underwater bay grasses because it provides carbon that plants use to produce new tissue during photosynthesis. It is also a byproduct of respiration. Like oxygen, carbon dioxide concentrations are affected by temperature and salinity.

Nitrogen and Phosphorus

Nitrogen and phosphorus are nutrients that occur naturally in air, water and soil and are vital to the growth of plants in the Bay. However, excess nutrients from stormwater runoff, agricultural lands, vehicle exhaust, wastewater treatment plants and other human-related sources are pollution. Nutrient pollution is the number one problem in the Bay ecosystem because it fuels the growth of algae, which can block sunlight from reaching underwater bay grasses and contribute to low levels of dissolved oxygen.

Nitrogen, used primarily by plants and animals to synthesize protein, is essential to the production of plant and animal tissue. Nitrogen enters the ecosystem in several chemical forms, some of which are taken up by algae. It also occurs in other dissolved or particulate forms, such as in the tissues of living and dead organisms.

Phosphorus is another key nutrient in the Bay's ecosystem, essential to cellular growth and reproduction in phytoplankton and bacteria. In the water, phosphorus occurs in dissolved organic and inorganic forms, often attached to particles of sediment.