Temperature is how hot or cold something is as measured on a definite scale. CBIBS buoys measure air temperature in degrees Celsius and also convert this measurement into degrees Fahrenheit. Technically, heat is an indicator of the kinetic energy, or energy of motion, of the gasses that make up the air. As gas molecules move more quickly, air temperature increases. CBIBS buoys report air temperature as a 10-minute average.
Barometric pressure--also referred to as air pressure--is the weight of the overlying air pressing down on the Earth. Barometric pressure is usually reported in inches mercury--inches Hg. Low barometric pressure means air is rising, while high pressure means the overlying air is sinking. Barometric pressure affects water chemistry and weather. Generally, high pressure (± 31 inches Hg) supports sunny, clear weather. Low pressure (~ 28 inches Hg) promotes rainy and cloudy weather conditions. Big changes in barometric pressure indicate big changes in weather. Barometric pressure can also affect the amount of a gas that can dissolve in water. When barometric pressure is high, more oxygen can be dissolved into the waters of the Bay; when the pressure is low, less oxygen can be dissolved into water. CBIBS buoys report barometric pressure as a 10-minute average.
Chlorophyll is the main chemical responsible for photosynthesis in plants, the process by which sunlight is converted into food energy. To track chlorophyll levels, the CBIBS buoys measure the amount of algae in the water in micrograms per liter (ug/l). This is reported as an hourly average. Algal blooms can be very damaging to Bay habitats because they can drive dissolved oxygen concentrations to very low levels. Excess algae, usually caused by an excess of nutrients which stimulate their growth, can also make the water cloudy, or increase turbidity, blocking the light needed by underwater grasses to survive. These damaging algae blooms, which can also produce toxins in some cases, are collectively known as harmful algal blooms. There are no hard and fast rules as to what constitutes a harmful concentration of chlorophyll, but as a general guide, above 50 ug/l represents a significant algal bloom, and above 100 ug/l represents a severe bloom. Some research suggests that harmful effects can occur at chlorophyll concentrations as low as 15 ug/l.
How can you help keep chlorophyll measurements in a healthy range?
Conductivity is the measurement of a substance's ability to conduct electricity. This is reported in S/m as an hourly average. Water conducts more electricity as chemicals such as salt are added to it. Like salinity, the conductivity of water influences the water’s chemistry and helps determine which living resources are adapted to exist there.
Current direction is the direction on a compass toward which water is moving. For example, a current direction reading of 90° indicates that the current is running toward the east. This is reported as an hourly average. Current direction is affected by tides, wind, and the shape of the water body.
Current is a movement of water; current speed is the speed of this movement. CBIBS buoys measure current speed in nautical miles per hour, also known as knots. This is reported as an hourly average.
The amount of oxygen dissolved in Bay waters is probably the single most important measure of habitat quality; without oxygen, living resources die. Dissolved oxygen (DO) is measured in milligrams per liter (mg/l). This is reported as an hourly average. When DO concentrations drop below 5 mg/l, the Bay's more sensitive organisms, such as fish, become stressed, especially if exposed to these conditions for prolonged periods. DO is affected by several factors. Temperature affects the concentration, because warmer water cannot dissolve as much oxygen as colder water. Salinity also affects the amount of dissolved oxygen; freshwater can hold more dissolved oxygen than can salt water. Photosynthesis by plants adds dissolved oxygen to the water. Because photosynthesis occurs during the day, dissolved oxygen is usually higher during the day and lower at night.
How can you help keep DO levels healthy?
Nitrate is one form of nitrogen found in Bay waters. It exists naturally in soil, plant materials, waste from wild animals, and the atmosphere, and is an important nutrient used by plants to fuel their growth. But human activities have greatly increased the amount of nitrates in the Chesapeake Bay ecosystem. Excessive levels of nitrates come from many sources, including wastewater treatment plants, runoff from farmland and urban and suburban areas, air pollution, including vehicle exhaust and power plants, and groundwater discharge. Like plants on land, algae need both nitrogen and phosphorous to grow. Algae fuel the food web, so they are fundamentally beneficial to the ecosystem. But when there are too many nutrients, algal blooms form. These can have harmful effects, and some are even toxic. Some blooms can block sunlight that native underwater grasses—which provide habitat for Bay species—need to grow. And when the algae die, the decomposition process starves the water of oxygen that living resources in the Bay need.
Relative humidity is the ratio, of the amount of moisture present in the air to the total amount of moisture that the air can hold at the same temperature. For example, if the relative humidity is 50%, then the air is only half saturated with moisture. This is reported as a 10-minute average. Without humidity, there would be no clouds and no precipitation. Warmer air can hold more moisture than colder air. Additionally, water vapor holds heat in the air--this is why humid air feels warmer.
Salinity is the concentration of salt in the water. CBIBS measures salinity in practical salinity units--PSUs. (Salinity is also available in parts per thousand--ppt.) Salinity levels are a function of the mixing of ocean waters, which contain approximately 32 ppt (parts per thousand) salinity with freshwater from the Bay’s tributaries (< 1 ppt salinity). This is reported as an hourly average. Salinity is an important factor in determining where the Bay’s plants and animals live and in some cases when the animals reproduce or migrate. In any given location, salinity can vary greatly depending upon river flow, being low during high flows and high during droughts. Most of the Bay’s living resources are adapted to these large swings in salinity, but extreme floods or droughts can lead to stressful conditions.
Turbidity describes how clear the water is. This is measured using a transmissometer, which records turbidity values in nephelometric turbidity units (NTUs). This is reported as an hourly average. Turbidity values over 15 NTUs are detrimental to Bay grass growth because the cloudy water blocks sunlight from reaching the grass. Increased turbidity can also lead to decreased fish health by increasing susceptibility to infectious diseases through increased stress and reducing the ability of fish gills to extract dissolved oxygen from the water. Areas of high turbidity can also cause the silting over--burying alive--of benthic organisms.
How can you support healthy turbidity levels in the Bay?
Wave Height (Mean)
The mean wave height is the average height of the waves--from crest to trough--that pass by the buoy. Measurements are based on data observed between 30 and 50 minutes past each hour as a representative sample of wave action. Mean wave height is the average wave height observed during this 20-minute time period.
Wave Height (Significant)
Significant wave height is the average height--from crest to trough--of the highest one-third of waves recorded in a given monitoring period at a buoy. Wave measurements are reported by CBIBS buoys every hour. Measurements are based on data observed between 30 and 50 minutes past each hour as a representative sample of wave action. Significant wave height is therefore the average height of the highest one-third of waves recorded during this 20-minute period.
Wave Period (Significant)
Significant wave period is the time that passes between two successive wave crests that move past a buoy. Wave measurements are reported by CBIBS buoys every hour. Measurements are based on data observed between 30 and 50 minutes past each hour as a representative sample of wave action. Significant wave period is the average wave period during this 20-minute time.
Wind direction describes the direction on a compass from which the wind comes. For example, a wind direction reading of 90° indicates that the wind is coming from the east. This is an average over the previous 10 minutes.
Wind gust describes the fastest wind speed recorded. At CBIBS buoys, this is the highest five-second running mean recorded during the previous 10-minute period. CBIBS measures wind gust in nautical miles per hour, or knots; wind gust is also available in miles per hour (mph) and meters per second (m/s).
Wind speed describes how fast the air is moving past a certain point at a certain time. CBIBS tracks this as a running mean over the previous 10 minutes. CBIBS measures wind speed in nautical miles per hour, or knots; it is also available in miles per hour (mph) and meters per second (m/s). Wind speed affects sea state (calm or wavy) as well as the mixing of water in the Bay.