Terrestrial laser scanning technology for measuring streambank retreat along East Fork Poplar Creek and calculating the effect on mercury release.

Mercury (Hg) is a globally distributed inorganic pollutants of human concern. The high toxicity is mainly related to the capacity of Hg species to accumulate and biomagnify along aquatic food webs. Along East Fork Poplar Creek (EFPC), erosion represents the principal mercury input into the local waters, eventually reaching humans through the food chain. This research project aimed to monitor streambank erosion along a mercury-contaminated creek using Light Detention and Ranging (Lidar) technology and erosion pins. A Terrestrial Laser Scanner (TLS) was used to generate high-resolution point clouds from August 2020 to January 2021 across nine streambank locations to detect changes in soil volumes. These volumes were simultaneously monitored using erosion pins, and with the results, estimates of soil input into the creek from streambank erosion were obtained. For all the sites, the volumes of soil introduced into the EFPC for the erosion pins ranged between 0-6.29 m³ and 3.93-14.18m³ for the TLS. Using erosion estimates, bulk density measurements, and known concentrations of Hg in bank soils, estimates for the mass of Hg entering EFPC were obtained. Estimates of Hg released into the EFPC ranged between 0-11.84 kg and 0-0.4 kg for the erosion pins and TLS, respectively. Erosion pin estimates of Hg and soil introduced into EFPC were both on average of 64 times greater than those given by the TLS. Measurements obtained with the TLS can be considered more reliable than those given by the erosion pins since this new technique has more spatial coverage, higher resolution and can account for irregularities and changes within the whole streambank, compared to erosion pins which interrogate only a tiny fraction of the volume of a streambank. This assessment identified locations in EFPC where soil erosion and mercury release are highest, thereby targeting specific locations for possible future remediation actions to prevent mercury mobilization.