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

As part of an ongoing project to assess changes in ecosystem structure and function following wetland restoration, scientists from the United States Department of Agriculture’s Agricultural Research Service (USDA-ARS) have been measuring water chemistry, streamflow, water storage, and topography at a range of active cranberry farms and those that have been retired and converted into wetlands. As part of these assessments, post-restoration surveying has been conducted at two sites, Manomet Brook and Eel River.

The restored wetland complex in the Eel River preserve is one of the sites that were surveyed.

Surveying is conducted so scientists can map points of interest, such as restoration features like stream meanders and in-stream woody habitat structures. At each point surveyed, three measurements are collected: x and y coordinates, called a northing and easting, and an elevation. This allows for the land surface to be mapped in three dimensions. To obtain this information, one person operates a total station, which is an electronic instrument equipped with a movable telescope capable of measuring precise angles and storing information. A second person positions a survey rod containing a prism on each point of interest. A beam is sent out from the total station, hits the prism, and is reflected to its source to provide an accurate measurement of the distance. 

USDA-ARS physical science technician Joey Loffredo sets up the total station (left) and adjusts the survey rod height (right) to ensure the prism can be seen. 

At each site, a 125 m stream segment was selected for study. Cross-sectional surveys were conducted every 10 m along the reach, which provide information on floodplain topography, streambank slope, and stream depth.

Joey operates the total station (left) for cross-sectional stream surveys (right).

Survey data enable scientists to derive a variety of stream metrics, such as average width and depth, channel slope, and sinuosity (i.e., curvature of the stream). These factors can help us assess stream capacity for water retention and nutrient processing. Greater channel complexity, such as the presence of meanders, woody debris, and connectivity between the stream and the floodplain can reduce stream velocity, resulting in longer water retention times. These longer water residence times allow for more contact of nutrient-rich water with biologically active sediments and soils. Microbes on the streambed and in the floodplain can process and remove nutrients from the aquatic system. Since excess nutrients can lead to algal blooms and fish kills in downstream ponds and estuaries, removal of these nutrients by streams leads to better water quality.