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We investigated the climatic and ecohydrological controls of the monthly methane emission fluxes from freshwater wetlands across the globe. Fluxes of methane, photosynthetically active radiation (PAR), soil temperature (TS), atmospheric pressure, latent heat flux (LE), wind speed (WS), friction velocity, vapor pressure deficit (VPD), soil water content (SWC), water table depth, and precipitation were obtained from 32 FLUXNET wetland sites. Multivariate pattern recognition techniques of principal component and factor analyses were utilized to classify and group climatic and ecological variables based on their similarity as drivers, examining their interrelation patterns across the different sites. Partial least squares regression models were developed to estimate the relative linkages of methane emission fluxes with the climatic and ecohydrological drivers. When the wetlands were flooded (i.e., positive water table depth relative to the ground), PAR, LE, VPD, and TS had the strongest controls on the methane emission fluxes. However, in the absence of flooding (i.e., negative water table depth), the methane emission fluxes were mainly controlled by SWC and WS. For the wetland sites with unavailable water table depth data, PAR, TS, and WS had the strongest controls on the methane emissions and subsequent transport. Our findings provided important knowledge and insights for predicting and managing methane emissions in freshwater wetlands at a global scale. 

Abstract The mechanisms controlling transport and retention of microplastics (MPs) in riverine systems are not understood well. We investigated the impact of large roughness elements (LREs) on in-stream transport and retention of the ubiquitous polystyrene-microplastics (PS-MPs). Scaled experiments were conducted with and without LREs under various shear Reynolds numbers (Re*) in an ecohydraulics flume. Our results, for the first time, demonstrated a clear dependence of the MPs’ velocity onRe*in LREs-dominated channel. Two distinct regimes and thresholds were identified: lowerRe*(≤ 15,000) regime corresponding to higher velocities of MPs ($${U}_{MPs}^{*}$$ $U_{\mathrm{MPs}}^{\ast }$> 0.45), and higherRe*(> 15,000) to lower$${U}_{MPs}^{*} ($$ $U_{\mathrm{MPs}}^{\ast }($< 0.45). The presence and higher density of LREs increasedRe*, decreased$${U}_{MPs}^{*}$$ $U_{\mathrm{MPs}}^{\ast }$, and enhanced the PS-MPs capture. The LREs-generated turbulence kinetic energy (TKE) was found to be a good predictor of PS-MPs transport and retention rates, indicating the effectiveness of LREs in retaining PS-MPs in streams and rivers.