Thirty-one rivers of varying trophic status located in Ontario and Quebec, Canada, were sampled in order to determine the factors related to heterotrophic bacterial and flagellate abundance. Bacterial abundance ranged from 1.80 X 106 to 9.92 X 106 cells ml-' and flagellate abundance ranged from 1.18 X 103 to 17.4 X 103 cells ml-' There was a highly significant, positive relationship between bacterial abundance and both total phosphorus (R2 = 0.551 and chlorophyll a (R2 = 0.55). Bacterial abundance was not related to dissolved organic carbon concentration which ranged from 4.6 to 13.0 mg 1-' A significant positive relationship was observed between heterotrophic flagellate abundance and both heterotrophic bacterial abundance (R2 = 0.46) and total phosphorus (R2 = 0.52). Neither bacterial nor flagellate abundance was significantly related to water residence time. No relationship between zooplankton biomass and bacterial or flagellate abundance was observed, possibly because of the low biomass of zooplankton in the rivers (mean = 11.3 pg 1. ' dry mass). Results suggest that in rivers there is little transfer of energy from the microbial food web to the planktonic food web due to the scarcity of metazoan zooplankton.

Syndemics or synergies of cooccurring epidemics are widely studies across health and social sciences in recent years. We conducted a meta-knowledge analysis of articles published between 2001 to 2020 in this growing field of academic scholarship. We found a total of 830 articles authored by 3025 authors, mostly from high-income countries. Publications on syndemics are gradually increasing since 2003, with rapid development in 2013. Each article was cited more than 15 times on average, whereas most (n = 604) articles were original studies. Syndemics research focused on several areas, including HIV/AIDS, substance abuse, mental health, gender minority stressors, racism, violence, chronic physical and mental disorders, food insecurity, social determinants of health, and COVID-19. Moreover, biopsychosocial interactions between multiple health problems were studied across medical, anthropological, public health, and other disciplines of science. The limited yet rapidly evolving literature on syndemics informs transdisciplinary interests to understand complex coexisting health challenges in the context of systematic exclusion and structural violence in vulnerable populations. The findings also suggest applications of syndemic theory to evaluate clinical and public health problems, examine the socioecological dynamics of factors influencing health and wellbeing, and use the insights to alleviate health inequities in the intersections of synergistic epidemics and persistent contextual challenges for population health.

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