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Human-induced salinization caused by the use of road deicing salts, agricultural practices, mining operations, and climate change is a major threat to the biodiversity and functioning of freshwater ecosystems. Yet, it is unclear if freshwater ecosystems are protected from salinization by current water quality guidelines. Leveraging an experimental network of land-based and in-lake mesocosms across North America and Europe, we tested how salinization-indicated as elevated chloride (Cl-) concentration-will affect lake food webs and if two of the lowest Cl- thresholds found globally are sufficient to protect these food webs. Our results indicated that salinization will cause substantial zooplankton mortality at the lowest Cl- thresholds established in Canada (120 mg Cl-/L) and the United States (230 mg Cl-/L) and throughout Europe where Cl- thresholds are generally higher. For instance, at 73% of our study sites, Cl- concentrations that caused a ≥50% reduction in cladoceran abundance were at or below Cl- thresholds in Canada, in the United States, and throughout Europe. Similar trends occurred for copepod and rotifer zooplankton. The loss of zooplankton triggered a cascading effect causing an increase in phytoplankton biomass at 47% of study sites. Such changes in lake food webs could alter nutrient cycling and water clarity and trigger declines in fish production. Current Cl- thresholds across North America and Europe clearly do not adequately protect lake food webs. Water quality guidelines should be developed where they do not exist, and there is an urgent need to reassess existing guidelines to protect lake ecosystems from human-induced salinization.

Nitellopsis obtusa (Desv.) J. Groves (starry stonewort) is a macroalga in the Characeae family first documented in North America c. 1974. Since initial introduction, N obtusa clonal populations quickly established in inland lakes as early as 2005. Despite increased N obtusa monitoring over the last decade, only sterile or male specimens were documented in North America; however, during routine monitoring in Lake Simcoe and Lake Scugog in 2022, we discovered the presence of female gametangia on N obtusa. In addition, two other Characeae genera had prevalent antheridia and oogonia, co-occurring with oogonia-presenting N obtusa, which had not been observed previously despite intensive monitoring since 2008. Further studies in North America are required to confirm the proportion of female populations present within invaded regions, as well as to identify plausible causes shifting gametangia development across non-native and native Characeae, especially within the context of climate change. The presence of oogonia on N obtusa represents a major change to our understanding of this species and its reproductive ecology in North America. Key words: oogonia, sexual reproduction, Characeae, stoneworts, Introduction Nitellopsis obtusa (Desv.) J. Groves, 1919, is a macroscopic alga belonging to the Characeae family, and the species is considered invasive in North America. How N obtusa was introduced [...]

Nitellopsis obtusa was first reported in North America in 1974. The overall ecological threat that N. obtusa poses towards freshwater ecosystems in its non‐native range is thought to be similar to other invasive macrophyte species. However, few studies have evaluated the impacts to aquatic communities upon successful establishment of this species in North America. Despite N. obtusa being a non‐native invasive species in North America, it is considered a beneficial macrophyte within its native range in EurasiaWe evaluated the impacts associated with the non‐native invasive charophyte N. obtusa on the lower aquatic food web (LAFW) communities (phytoplankton, macroinvertebrates, and macrophytes) in a large, shallow lake in Ontario, Canada. To tease apart abiotic and biotic factors that influence LAFW species assemblages, a generalised linear latent variable model (GLLVM) was used.Over the course of the 4‐year study period, N. obtusa abundance significantly increased throughout the lake (pairwise comparison, p < 0.001) and notable shifts in community composition occurred across years (PERMANOVA, p < 0.001), especially for the phytoplankton and macrophyte communities.Nitellopsis obtusa was also found to be associated with a decline in diversity, where Simpson's diversity indices across all LAFW communities decreased as a function of increasing N. obtusa biomass. The GLLVM analysis revealed significant negative associations between N. obtusa and the majority of LAFW taxa. Most notably, there was a significant (p < 0.001) negative relationship between Myriophyllum spicatum, a previously established non‐native invasive macrophyte, and N. obtusa. The GLLVM model also demonstrated that N. obtusa had positive co‐occurrence relationships with other members of the macrophyte community including Utricularia vulgaris, Najas flexilis, Potamogeton crispus, and Stuckenia pectinata.These results show for the first‐time significant impacts to the LAFW in an invaded ecosystem, which raises major concerns for fish communities that depend on the LAFW for food and habitat. Further studies are necessary to confirm the extent of these impacts in other invaded lakes. [ABSTRACT FROM AUTHOR]

Smith ED, Balika D, Kirkwood AE. 2021. Community science-based monitoring reveals the role of land use scale in driving nearshore water quality in a large, shallow, Canadian lake. Lake Reserv Manage. 37:431–444. As shorelines and watersheds become increasingly developed, lake condition declines due to nutrient enrichment, excess algae growth, and contaminant loading. Lake Scugog, a large shallow lake in southern Ontario, Canada, is no exception, and has been experiencing increased urban development in its agriculture-dominated watershed over the last few decades. By applying a 3-pronged co-production model (stewardship group, watershed authority, and university laboratory), a nearshore water quality monitoring program was implemented using a community-science approach. Nearshore water samples were collected over 3 years (2017–2019) by trained community scientists. We found strong relationships between water quality parameters and land use, at the buffer and subcatchment scale. The strength of the land use relationships varied by parameter and scale, where chloride was significantly predicted by buffer land use, and phosphorus was explained by development at the subcatchment scale. Based on the high rate of participation compliance, the community science approach proved to be effective for capturing spatially explicit water quality data, which allowed us to establish current baseline conditions in Scugog's nearshore zone. Future watershed management should consider both scales of land use, but prioritize restoration efforts on the scale that corresponds to their specific water quality goals. [ABSTRACT FROM AUTHOR]