Quantifying Nutrient Transport and Transformation in Stream Channels Associated with Active, Retired, and Restored Cranberry Farms

Last week, United States Department of Agriculture – Agricultural Research Service (USDA-ARS) research hydrologist Casey, postdoctoral research associate Molly, and physical science field technician Julian collected data at Manomet Brook as part of a project to evaluate the ability of restored streams and wetlands to improve water quality. Excess nutrients (e.g., nitrogen and phosphorus) from fertilizers and septic systems can lead to aquatic ecosystem impairment, including nuisance algal blooms and low oxygen. Therefore, scientists are investigating the efficacy of cranberry farm restoration, including stream channel re-meandering and addition of woody debris, in removing nutrients.

The restored stream-wetland complex in Foothills Preserve. Photo credit: Glorianna Davenport, The Living Observatory

Early in the week, water samples were collected from Manomet Brook and analyzed to determine nutrient concentrations. The researchers also installed sensors in the stream to measure temperature, conductivity, and dissolved oxygen. A small amount of salt solution was released in the stream and sensors recorded the passage of this solution at a downstream location to allow for calculation of streamflow. 

Molly collects a water sample (left) while Casey installs sensors (right). Photo credits: Molly Welsh, USDA-ARS

Later in the week, an experiment called a constant-rate injection was conducted. This entailed using a pump to drip water amended with salt and nutrients into the stream to measure uptake of nitrogen and phosphorus by microbes and vegetation on the streambed. The scientists reviewed sensor data in real-time during the experiment to evaluate when the solution being pumped into the stream was well-mixed at each sampling location along a 125-m reach.

Setting up the constant-rate injection (left) and monitoring the sensor data in real-time (right). Photo credits: Glorianna Davenport, The Living Observatory

After the solution was detected at the end of the reach, stream water was collected at fifteen locations. These samples will be analyzed for different forms of nitrogen and phosphorus, including nitrate and orthophosphate. A decline in nutrient concentrations from upstream to downstream will indicate nutrient uptake occurred in the stream. Data from Manomet Brook will be compared to data collected from other streams associated with active, retired, and restored cranberry farms to assess differences in nutrient processing. Stay tuned for future results!