Clarity from Muddy Data: Approaches to Understanding Potential Impacts to Sediment Biota
Industries that extract raw materials from the ground, such as mining or oil and gas, can affect the surrounding ecosystems. To minimize the potential impacts on the natural environment from these activities, local and national regulatory entities have established requirements for defining the current baseline ecological conditions. During extraction activities, the operators are also required to monitor the biota in various ways to ensure that they remain healthy. Benthic organisms provide one of the most representative and cost-effective opportunities to evaluate the sediment and stream bed quality.
Benthic (or bottom-dwelling) communities are made up of species that live on or within the sediment. These organisms play a significant role in their environment by breaking down detritus, building ecosystems, serving as a food source for larger animals, and acting as indicators for ecological health. They also have a higher site fidelity and can provide an overall picture of temporal and spatial impacts. Organisms within these communities respond to all stressors that might not be otherwise captured in chemical analysis of the sediment.
Biological effects in sediments can be assessed either by (1) introducing organisms to sediment samples in a controlled laboratory environment and observing their response, or (2) collecting representative samples of the benthic community from a natural environment and identifying the organisms present to the lowest practical taxonomic level. Below are two recent examples of work that Spheros scientists have completed at EcoAnalysts that illustrate each of these approaches.
Ecotoxicology Assessments for Mining Operations
EcoAnalysts’ scientists helped a client complete ecotoxicological assessments required by regulations in Washington State at a remote, former mining site located adjacent to a creek that discharges into a lake 8 miles away. Remedial actions to prevent effects from mine-impacted groundwater were successfully completed in 2018. However, in 2020, an external laboratory’s biological assay tests (bioassays) conducted on sediments from the site indicated impacts were present and produced results that were inconsistent with other lines of evidence. Comparisons were also complicated by reference samples that failed to meet performance criteria for organism growth. EcoAnalysts’ scientists suspected environmental toxicity impacts were caused by low total organic content (TOC) in the sediments instead of chemically driven effects, and suggested adaptations to the bioassays that would produce results that control for site-specific challenges.
Following national standard test method updates, bioassay feeding regimens were increased in the 2024 assessment to support test organism growth, and additional coarse-grained, low TOC control treatments were added to each test to tease out potential effects due to low TOC alone. The client consulted with EcoAnalysts’ scientists to ensure reference sample locations were appropriate for the study and additional sites were added to produce robust comparisons with site samples. State regulators requested a third bioassay test for the 2024 program that had been deemed obsolete by national standard test methods. As such, EcoAnalysts worked with the regulators to adapt the test as much as possible to meet the State’s requirements while also following current method guidance.
Results from the 2024 assessment indicated sediment quality at the project site is protective of aquatic life and any observed toxicity was likely unrelated to contaminants from mining operations. Close collaboration between EcoAnalysts’ scientists, regulators, and the client ensured a robust, representative assessment was conducted that overcame challenges resulting from broadly standardized testing methods and complex site conditions.
Freshwater sediments undergo toxicity testing with organisms to evaluate biological effects, such as survival and growth.
Chironomus dilutus is a standard test species for freshwater sediments.
A benthic community sample waiting for processing in which organisms will be pulled out by hand under a microscope, sorted, and identified to the lowest practical level.
Ophiura sarsi is a common species of brittle star found in marine benthic communities of the Arctic.
Benthic Community Baseline Studies
Ecological baseline studies for oil and gas industries occur before operations at a site are established to determine potential environmental impacts. Benthic community assessments play a critical role in establishing these baselines. Samples are collected and sent to the taxonomy laboratory, which then processes them by removing and identifying the organisms present to the genus or species level, if possible. A detailed catalogue of the collected species identified can provide information about what organisms are present, their habitat, food preferences, and position within the trophic food web. Benthic community samples are then collected and analyzed repeatedly over time to evaluate whether there are measurable impacts on the benthos that could be attributed to drilling activities, the scope and spatial range of impacts on the community structure, and the recovery potential that could be expected at affected locations.
These assessments are often necessary to comply with regulations, such as those established by the U.S. Bureau of Ocean Energy Management (BOEM).
Key Takeaways
Analyzing benthic organisms presents a cost-effective and representative opportunity to assess potential anthropogenic impacts to the natural environment. Impacts can be evaluated either by introducing organisms to sediment samples from a site and evaluating their response within a controlled laboratory environment or by identifying the organisms that are present in these natural environments and monitoring how they respond over time. These assessments are required by a range of national and state-level regulations, and as methods evolve, comparing current results to past ones becomes more challenging and requires specialized scientific knowledge.
Meet our Sediment Experts
Michelle Knowlen is a Senior Project Manager of Toxicology and Ecology at the EcoAnalysts Port Gamble Environmental Lab, with a background in environmental science and marine ecology. As a toxicologist and ecologist, her focus is on management and execution of sediment characterization studies for potential biological impacts, including evaluation of dredged material and cleanup sites, implementing investigative bioassays, and performing benthic community risk assessments. Ms. Knowlen routinely assists in field operations for sediment projects as a Biological Lead and is skilled in sediment sample collection and processing. With more than 11 years of experience in both private and public sectors, she brings a multidisciplinary approach to a variety of ecological monitoring and aquatic toxicology projects. If you have a need related to sediment toxicology and ecological assessments, email Ms. Knowlen at mknowlen@ecoanalysts.com.
Megan Payne currently provides Technical Sales for EcoAnalysts’ Taxonomic Laboratory. Before joining EcoAnalysts, Ms. Payne worked at the Lake Superior Research Institute where she conducted sediment toxicology testing and water quality collections. Ms. Payne has a background in aquatic biology and has conducted fieldwork in wetlands, lakes, and rivers. At EcoAnalysts, she has served as primary analyst for any invasive mussel veliger projects, project coordinator, and laboratory manager. Ms. Payne has served as field lead for numerous projects throughout the Lake Superior, Columbia, and Missouri River Basins. If you have a need related to benthic community taxonomy and analysis, email Ms. Payne at mpayne@ecoanalysts.com.