Now available at the Susquehanna CBIBS buoy: nitrate levels. The first nitrate sensor in the CBIBS system was deployed on the Susquehanna buoy because the Susquehanna River provides roughly 40% of the freshwater flow into the Chesapeake Bay. Nitrates, a form of nitrogen, exist naturally and are an important nutrient used by plants to fuel their growth. They occur naturally in soil, plant materials, waste from wild animals, and the atmosphere.
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—nitrates are found in many residential and agricultural fertilizers, as well as discharges from septic systems and boats, and in animal manure
- Air pollution, including vehicle exhaust and power plants
- Groundwater discharge; nitrates may be stored in groundwater for decades
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.
Nitrogen in the water can be in several forms—one of these forms is nitrate. When the different forms of nitrogen are added together, that makes up “dissolved inorganic nitrogen.” Having different forms of nitrogen is important because different types of algae prefer different forms. Whether or not algal blooms form is not only a result of having the right kind and amount of nitrogen, but also the right proportion of phosphorous.
While no formal definitions of “how much is too much” for nitrate in the Bay have been set, the Chesapeake Bay Program’s Phytoplankton Index of Biotic Integrity (PIBI) notes that Chesapeake water with more than 0.07 mg/L of dissolved inorganic nitrogen is considered degraded. Remember, this measurement is for total nitrogen—not only nitrate. But if nitrate levels are greater than 0.07 mg/L, because DIN is the sum those three forms of nitrogen including nitrate, DIN levels must also be greater than 0.07 mg/L.
Other definitions regarding nitrate and nitrogen levels are still being developed and considered. Nitrate levels depend greatly on the amount of water flow; thus, they are generally higher in the spring when flow is higher. More information about nitrogen loads and river flow to the Bay is available, as is background on research under way on water column chemistry.
Data from the nitrate sensor are reported in milligrams per liter (mg/L) as part of the water-quality measurements, and are updated every hour.
Measurements from the nitrate sensor at the Susquehanna CBIBS buoy will allow scientists to see how nitrate levels change over time in response to changes in river flow at the Conowingo Dam, a short distance up the Susquehanna River. Data from the sensor will help track seasonal patterns and trends over the years, and will support research to determine if nitrate levels in the upper Bay correspond to nitrogen levels around the Bay. The U.S. Geological Survey plans to add real-time nitrate sensors similar to the one on the CBIBS buoy at the Conowingo Dam in the near future.
What can you do to reduce nitrate levels in the Bay? Minimize your use of fertilizers, and avoid using them before big rainstorms, which will simply wash the fertilizer away and on into the Bay. Fertilize your lawn only in the fall, which encourages the desirable cool season grasses and reduces the risk that the fertilizer that runs off will fuel algae blooms. Pump out septic tanks regularly, and pump boat waste to an onshore facility. To reduce nitrogen in the atmosphere, which will eventually fall into the Bay, reduce vehicle emissions. Can you combine errands into one trip, carpool, or use alternative or public transportation? If you are buying a new vehicle, can you buy a more fuel-efficient one? We can all do something to help.