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The seasonal behavior of fluvial dissolved silica (DSi) concentrations, termed DSi regime, mediates the timing of DSi delivery to downstream waters and thus governs river biogeochemical function and aquatic community condition. Previous work identified five distinct DSi regimes across rivers spanning the Northern Hemisphere, with many rivers exhibiting multiple DSi regimes over time. Several potential drivers of DSi regime behavior have been identified at small scales, including climate, land cover, and lithology, and yet the large‐scale spatiotemporal controls on DSi regimes have not been identified. We evaluate the role of environmental variables on the behavior of DSi regimes in nearly 200 rivers across the Northern Hemisphere using random forest models. Our models aim to elucidate the controls that give rise to (a) average DSi regime behavior, (b) interannual variability in DSi regime behavior (i.e., Annual DSi regime), and (c) controls on DSi regime shape (i.e., minimum and maximum DSi concentrations). Average DSi regime behavior across the period of record was classified accurately 59% of the time, whereas Annual DSi regime behavior was classified accurately 80% of the time. Climate and primary productivity variables were important in predicting Average DSi regime behavior, whereas climate and hydrologic variables were important in predicting Annual DSi regime behavior. Median nitrogen and phosphorus concentrations were important drivers of minimum and maximum DSi concentrations, indicating that these macronutrients may be important for seasonal DSi drawdown and rebound. Our findings demonstrate that fluctuations in climate, hydrology, and nutrient availability of rivers shape the temporal availability of fluvial DSi. Plain Language Summary: The amount of dissolved silicon (DSi) in rivers is an important control on numerous ecological and biogeochemical processes, such as types of algae that bloom and rates of carbon sequestration. Compared to our knowledge of other nutrients, such as nitrogen and phosphorus, we have limited understanding of what controls the timing and concentration of DSi in rivers. Previous work identified five distinct seasonal patterns of DSi concentrations in rivers across the Northern Hemisphere; here we look at the environmental variables that control these seasonal patterns. We found that rivers often have one to five seasonal patterns over time due to interannual shifts in temperature, evapotranspiration, and streamflow. In addition, we found that the average shape of the seasonal pattern for a given river, specifically minimum and maximum DSi concentrations, was related to nitrogen (N) and phosphorus (P) concentrations, highlighting linkages between N, P, and DSi cycling in rivers. This work identifies why river DSi concentrations exhibit both within and between year variability, highlighting that temperature, streamflow, and nutrient availability control the timing of river DSi availability for biological uptake. Key Points: Seasonal variations in annual riverine dissolved silica concentrations (DSi regime) were correctly classified 80% of the timeClimate and primary productivity emerge as the most important drivers in differentiating among average DSi regimesMedian nitrogen and phosphorus concentrations strongly predicted minimum and maximum DSi concentration, regardless of regime type [ABSTRACT FROM AUTHOR]

Fluvial silicon (Si) plays a critical role in controlling primary production, water quality, and carbon sequestration through supporting freshwater and marine diatom communities. Geological, biogeochemical, and hydrological processes, as well as climate and land use, dictate the amount of Si exported by streams. Understanding Si regimes—the seasonal patterns of Si concentrations—can help identify processes driving Si export. We analyzed Si concentrations from over 200 stream sites across the Northern Hemisphere to establish distinct Si regimes and evaluated how often sites moved among regimes over their period of record. We observed five distinct regimes across diverse stream sites, with nearly 60% of sites exhibiting multiple regime types over time. Our results indicate greater spatial and interannual variability in Si seasonality than previously recognized and highlight the need to characterize the watershed and climate variables that affect Si cycling across diverse ecosystems. [ABSTRACT FROM AUTHOR]

City residents in the Global South commonly encounter the police. Yet, outside of established democracies, we know little about how ethnicity shapes everyday policing in diverse urban contexts. Existing approaches generate competing expectations, with some arguing that officers are more rather than less discriminatory towards coethnics. We test these theories through a survey experiment conducted in Karachi, Pakistan—one of the world's largest megacities. We find that civilians are only marginally less likely to expect procedural justice from non-coethnic officers, even in a context where ethnicity is highly salient. However, suggestive evidence indicates that this small effect is significantly magnified for respondents who perceive their group to be underrepresented in the police. Descriptive representation is therefore a powerful moderator of the relationship between ethnicity and expectations of police bias. These results have implications for the development of effective and legitimate police institutions in weakly institutionalized contexts. [ABSTRACT FROM AUTHOR]

Many socially conservative settings oppose pro-LGBT+ advocacy because of its perceived threat to "traditional values." Can messaging on these issues from sources considered to have similar values be more effective than messaging from sources considered to have different values? This research uses the move towards legal protection of certain LGBT+ rights in Angola, Botswana, Mozambique, and South Africa to understand whether signals of changing social norms from African sources are better able to shift perspectives of those elsewhere on the continent than primes from Western sources. Using a survey experiment conducted in Uganda, I show that neither one-off messaging from African sources nor one-off messaging from Western sources shifts beliefs or behavior on LGBT+ issues. Rather, these messages produce backlash to both African and Western sources. This work highlights the challenges of attempting to rapidly change perspectives on LGBT+ issues in the most socially conservative settings. [ABSTRACT FROM AUTHOR]