Estimates of Sediment Accumulation Rates and Bottom Core Ages in Northeast Lakes

The Northeast Lakes Sediment Diatom Collaborative (NLSDC) is committed to improving the management of northeastern U.S. lakes by assessing their current and past ecological integrity using sediment diatoms (i.e., microscopic siliceous algae). Through a Regional Applied Research Effort (RARE) Program grant, researchers from U.S. EPA Regions 1 and 2 compiled a dataset that includes sediment cores taken from 601 lakes between 1991 and 2018. All of the diatom samples in the RARE dataset were collected using the top-bottom approach to studying changes in diatom assemblages from sediment cores. The diatom assemblage collected from the top of the core (assumed to represent present-day lake conditions) is compared to the diatom assemblage at the bottom. A core bottom represents historical lake conditions which may represent natural, reference-quality conditions if the core was sufficiently deep to reach the pre-disturbance period sediments. However, the necessary depth depends on lake-specific sediment accumulation rates (SARs). Baud et al. (2021) developed a global relationship to determine SAR for lakes such as those included in the RARE study. The purpose of this project was to estimate the SAR of each RARE lake and determine the core depth corresponding to pre-industrial times by using and testing this model (Baud et al. 2021). Improved understanding of SARs for lakes in this dataset was an important component of the broader research and management objectives of the participants of the NLSDC to inform future sampling efforts and development of sediment diatom-based assessment tools for northeast lakes in a regionally consistent manner.

Impact/Purpose

This report resulted from a broader research project in collaboration with EPA and the Northeast Lakes Sediment Diatom Collaborative (NLSDC) to improve the management of northeastern U.S. lakes. The project focused on how to assess current and past ecological integrity of northeast lakes using sediment diatoms (i.e., microscopic siliceous algae) as biological indicators. Diatom samples from hundreds of lakes were previously collected using a top-bottom approach to sediment coring. The diatom assemblage collected from the top of the core (assumed to represent present-day lake conditions) can be compared to the diatom assemblage at the bottom of the sediment core. A core bottom represents historical lake conditions which may represent natural, reference-quality conditions if the core was sufficiently deep to reach the pre-disturbance period sediments. However, the necessary depth depends on lake-specific sediment accumulation rates (SARs). This report describes how to potentially estimate the SAR of each lake and back-calculate the core depth necessary to reach sediment diatoms before major human impacts using a global equation developed by Baud et al. (2021). The model was tested by comparing predicted SARs to observed SARs, from existing core chronology data from multiple depths along the sediment cores, in 106 lakes. The global equation overpredicted SARs for most lakes but the overprediction was not consistent enough to apply a correction factor; therefore, it is not recommend for estimating SARs in northeast lakes. However, the available core chronology data suggest that sediment core depths ≥50 cm would often represent sediments deposited earlier than 1800 CE, which would be before intensive agricultural and industrial land uses began in most places throughout the northeast. Upon obtaining accurate estimates of target ages and depths, the NLSDC can estimate whether the diatom assemblage from bottom core samples represents reference conditions. Such results will allow for continued efforts to develop biological models and potential biological criteria based on lake sediment diatoms. This report would be of interest to lake managers who are working on assessing long-term changes in biological condition using sediment cores and need to determine the appropriate depths of cores for the lake(s) in their study region.

Citation

Lee, S., B. Block, B. Jessup, K. Salk, AND B. Pickard. Estimates of Sediment Accumulation Rates and Bottom Core Ages in Northeast Lakes. U.S. Environmental Protection Agency, Washington, DC, EPA/600/R-23/015, 2024.

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