Korosi JB, Adano RC, Do PHP, Hall RI, Jeyarajah J, Stewart EM, Wiklund JA, Thienpont JR. 2024. Ecosystem impacts of an invasive charophyte (Nitellopsis obtusa) interpreted in a multiple stressor context using paleolimnology. Lake Reserv Manage. 40:132–144. Proliferation of Nitellopsis obtusa (starry stonewort), an aquatic invasive macroalga, is an emerging water quality concern in North America, but disentangling its effects is complicated by multiple stressors and a lack of long-term data. In this study, we investigated the potential impacts of N. obtusa on benthic oxygen depletion and the lower food web of Lake Scugog (southern Ontario, Canada) in a multiple-stressor context through a paleolimnological assessment of ecosystem changes up to the invasion and proliferation of N. obtusa. Results reveal that myxoxanthophyll, a pigment produced by colonial cyanobacteria, was no longer detected in the sediments after the early 1990s despite being prevalent throughout the earlier history of Lake Scugog. This indicates that recently documented blooms of Microcystis, which have been hypothesized to be unprecedented and facilitated by N. obtusa, are not a new phenomenon but instead may represent a resurgence in cyanobacteria production following a period of water quality improvement. Sediment cores also documented increased relative abundance of Chironomidae taxa associated with low benthic oxygen availability after about 1920, while changes in subfossil diatom assemblage provided evidence of increased frequency and/or duration of thermal stratification indicative of climate warming effects. This suggests that N. obtusa may be acting synergistically with existing stressors on Lake Scugog to exacerbate challenges with benthic hypoxia.

Korosi JB, Adano RC, Do PHP, Hall RI, Jeyarajah J, Stewart EM, Wiklund JA, Thienpont JR. 2024. Ecosystem impacts of an invasive charophyte (Nitellopsis obtusa) interpreted in a multiple stressor context using paleolimnology. Lake Reserv Manage. 40:132–144. Proliferation of Nitellopsis obtusa (starry stonewort), an aquatic invasive macroalga, is an emerging water quality concern in North America, but disentangling its effects is complicated by multiple stressors and a lack of long-term data. In this study, we investigated the potential impacts of N. obtusa on benthic oxygen depletion and the lower food web of Lake Scugog (southern Ontario, Canada) in a multiple-stressor context through a paleolimnological assessment of ecosystem changes up to the invasion and proliferation of N. obtusa. Results reveal that myxoxanthophyll, a pigment produced by colonial cyanobacteria, was no longer detected in the sediments after the early 1990s despite being prevalent throughout the earlier history of Lake Scugog. This indicates that recently documented blooms of Microcystis, which have been hypothesized to be unprecedented and facilitated by N. obtusa, are not a new phenomenon but instead may represent a resurgence in cyanobacteria production following a period of water quality improvement. Sediment cores also documented increased relative abundance of Chironomidae taxa associated with low benthic oxygen availability after about 1920, while changes in subfossil diatom assemblage provided evidence of increased frequency and/or duration of thermal stratification indicative of climate warming effects. This suggests that N. obtusa may be acting synergistically with existing stressors on Lake Scugog to exacerbate challenges with benthic hypoxia.