2012 Annual Report
1a.Objectives (from AD-416):
This project seeks to develop novel sediment source tracking methods to evaluate the effectiveness of stream restoration in reducing watershed sedimentation. We will (1) develop a reach-scale method for tracking the fate of stream bank sediments during storms using rare earth elements, (2) determine sources of suspended sediments in stream water using the sediment fingerprinting approach, (3) test the ability of both methods to quantify sediment source reductions following stream restoration.
1b.Approach (from AD-416):
This collaborative project will involve scientists from USDA-ARS, Canaan Valley Institute, Virginia Tech, and West Virginia University. Research will be conducted at two watershed locations that represent the Appalachian Valley and Ridge region of the Chesapeake Bay basin. The first phase of research will involve the development of a reach-scale method for labeling stream bank sediments with rare earth elements and tracking their fate during successive storm events. This work will be carried out at Stroubles Creek, a 25 km2 mixed land-use watershed in Blacksburg, Virginia. Initial laboratory experiments will be conducted to understand rare earth element sorption to stream bank sediments and to determine the most appropriate method for labeling stream bank sediments with rare earth elements. A field study will then be conducted where stream bank sediments labeled with five different rare earth elements are artificially introduced into an experimental stream reach during selected storms. This study will enable mapping and characterization of stream bank sediment fate and transport in response to storm flows as well as test the ability of rare earth element tracers to quantify stream bank sediment contributions to suspended sediment loads in streams. The second phase of research will focus on evaluating sources of suspended sediment before and after stream restoration using the reach-scale sediment tracking methods developed and validated at Virginia Tech, as well as using established sediment fingerprinting techniques. This research will be conducted at select watershed locations in the Cacapon River watershed in West Virginia, where the combination of steep topography and anthropogenic disturbances, particularly those resulting from intensive agricultural and forest management activities, have led to problems with stream bank erosion and increased sediment yields. Three tributaries to the Cacapon River have been selected for study, each with steep, forested headwaters and mixtures of cropland and pasture land in the valley. Two of the tributaries will receive a battery of stream restoration practices to correct failing stream banks, whereas a third stream will not be restored and will serve as the control. Watershed-scale sediment fingerprinting techniques [inorganic elements, radionuclides, stable carbon (C) and nitrogen (N) isotopes, etc.] will be used to identify principal sources of suspended sediment before and after stream restoration on the treated watersheds as well as on the control. In addition, reach-scale studies using rare earth elements will be conducted on stream banks pre- and post restoration to evaluate the effectiveness of different practices. The project will yield a new methodology for tracking sources of sediment and will demonstrate a new application of sediment tracking technology for evaluating the effectiveness of stream restoration in mixed land-use watersheds of the Appalachian Highlands region of the Chesapeake Bay basin. In addition, results will help target stream restoration to maximize sediment reductions and improve water quality.
In 2011, we worked with collaborators at Virginia Tech University to carry out a study on Stroubles Creek that focused on developing a method for labeling stream bank sediments with rare earth elements and tracking their fate during successive storm events. The study was led by a Master’s student, who started his program in August 2010. Two lines of investigation were pursued. First, we conducted a laboratory study using two rare earth elements (Lanthanum and Ytterbium) to (1) estimate their adsorption to stream bank sediments and (2) determine their desorption potential in stream water. This study showed that rare earth elements sorb strongly to stream bank sediments, and that the potential for desorption to stream water is low. Thus, we concluded that rare earth elements hold great potential for use as sediment tracers in streams.
The second study was initiated during the summer and fall months of 2011. We labeled stream bank sediments with two rare earth elements (Lanthanum and Ytterbium) and injected them into Stroubles Creek during two different storm events. We collected integrated suspended sediment samples at regular intervals along an 875 m stream reach after each event. In addition, we also collected within-storm samples of suspended sediment at a location 250 m below the injection point to determine the arrival time and duration of the rare earth element pulse. The results of this study showed that rare earth elements could be easily detected in suspended sediments at distances of up to 875 m downstream of the injection point. We concluded that rare earth elements can successfully be used to track suspended sediments in streams, and that using these tracers is a novel approach for understanding the link between erosion (soil and stream bank) and sediment fate and transport.
The Master’s student successfully defended his thesis on April 23, 2012, and the results from his research are described in two publications that will be submitted to peer-reviewed journals this summer. Future work is planned to build upon the findings from the rare earth element research conducted at Stroubles Creek. We plan to conduct additional rare earth element injections this summer and fall (using different rare earth elements) to more completely understand the fate and transport of labeled sediments during storms. In addition, we plan to test different approaches for applying rare earth elements to stream bank sediments in situ (e.g., spraying rare earth elements versus injection). Finally, long-term plans include trialing the rare earth element sediment tracking method in the Cacapon River watershed to evaluate the ability of stream bank restoration to reduce suspended sediment transport during storms.