science projects, but also data providers, relatively early on. However, at the core and perhaps the most important factor contributing to the successful continuity of this project, is the dedication and engagement of the CLIC community scientists. We are incredibly fortunate that our community scientists are passionate and supportive of this work.To date, this project has collected over 52,500 lake ice phenology observations for 1008 lakes, and involved 935 monitors over the years (Fig. 3). As we work toward organizing these vast datasets, we look forward to exploring important questions on how climate change is affecting lake ice phenology across small and large lakes in the United States and identifying which lakes are most vulnerable to rapid ice loss.
AUTHOR CONTRIBUTIONSS conceived the idea and led the project. SS and LSL wrote the first draft. KB created figure 3. LSL, AB, KB, KS, DB, GB, and SS helped conceptualize the survey questions for the community scientists, contextualize the historical aspects of the project, and edited the manuscript.
ACKNOWLEDGMENTSFirst and foremost, the authors are indebted to the participants and citizen scientists from the Community Lake Ice Collaboration for their dedication and enthusiastic efforts to collect lake ice phenology data from their local lakes over the past 30 years.
In surface waters, the illumination of photoactive engineered nanomaterials (ENMs) with ultraviolet (UV) light triggers the formation of reactive intermediates, consequently altering the ecotoxicological potential of co-occurring organic micropollutants including pesticides due to catalytic degradation. Simultaneously, omnipresent natural organic matter (NOM) adsorbs onto ENM surfaces, altering the ENM surface properties. Also, NOM absorbs light, reducing the photo(cata) lytic transformation of pesticides. Interactions between these environmental factors impact 1) directly the ecotoxicity of photoactive ENMs, and 2) indirectly the degradation of pesticides. We assessed the impact of field-relevant UV radiation (up to 2.6 W UVA/m²), NOM (4 mg TOC/L), and photoactive ENM (nTiO 2 , 50 µg/L) on the acute toxicity of 6 pesticides in Daphnia magna. We selected azoxystrobin, dimethoate, malathion, parathion, permethrin, and pirimicarb because of their varying photo-and hydrolytic stabilities. Increasing UVA alone partially reduced pesticide toxicity, seemingly due to enhanced degradation. Even at 50 µg/L, nano-sized titanium dioxide (nTiO 2) reduced but also increased pesticide toxicity (depending on the applied pesticide), which is attributable to 1) more efficient degradation and potentially 2) photocatalytically induced formation of toxic by-products. Natural organic matter 1) partially reduced pesticide toxicity, not evidently accompanied by enhanced pesticide degradation, but also 2) inhibited pesticide degradation, effectively increasing the pesticide toxicity. Predicting the ecotoxicological potential of pesticides based on their interaction with UV light or interaction with NOM was hardly possible, which was even more difficult in the presence of nTiO 2 .
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