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A drinking water distribution system (DWDS) is the final and essential step to supply safe and high-quality drinking water to customers. Biological processes, such as biofilm formation and detachment, microbial growth in bulk water, and the formation of loose deposits, may occur. These processes will lead to deterioration of the water quality during distribution. In extreme conditions, pathogens and opportunistic pathogens may proliferate and pose a health risk to consumers. It is, therefore, necessary to understand the bacteriology of DWDSs to develop effective strategies that can ensure the water quality at consumers' taps. The bacteriology of DWDSs, both the quantitative growth and the qualitative bacterial community, has attracted considerable research attention. However, the researchers have focused mainly on the pipe wall biofilm. In this review, DWDS bacteriology has been reviewed multidimensionally, including both the bacterial quantification and identification. For the first time, the available literature was reviewed with an emphasis on the subdivision of DWDS into four phases: bulk water, suspended solids, loose deposits, and pipe wall biofilm. Special concentration has been given to potential contribution of particulate matter: suspended particles and loose deposits. Two highlighted questions were reviewed and discussed: (1) where does most of the growth occur? And (2) what is the contribution of particle-associated bacteria to DWDS bacteriology and ecology? At the end of this review, recommendations were given based on the conclusion of this review to better understand the integral DWDS bacteriology.

Biochar application to croplands has been proposed as a potential strategy to decrease losses of soil-reactive nitrogen (N) to the air and water. However, the extent and spatial variability of biochar function at the global level are still unclear. Using Random Forest regression modelling of machine learning based on data compiled from the literature, we mapped the impacts of different biochar types (derived from wood, straw, or manure), and their interactions with biochar application rates, soil properties, and environmental factors, on soil N losses (NH 3 volatilization, N 2 O emissions, and N leaching) and crop productivity. The results show that a suitable distribution of biochar across global croplands (i.e., one application of <40 t ha −1 wood biochar for poorly buffered soils, such as those characterized by soil pH<5, organic carbon<1%, or clay>30%; and one application of <80 t ha −1 wood biochar, <40 t ha −1 straw biochar, or <10 t ha −1 manure biochar for other soils) could achieve an increase in global crop yields by 222~766 Tg yr −1 (4%~16% increase), a mitigation of cropland N 2 O emissions by 0.19~0.88 Tg N yr −1 (6%~30% decrease), a decline of cropland N leaching by 3.9~9.2 Tg N yr −1 (12%~29% decrease), but with a fluctuation of cropland NH 3 volatilization by −1.9~4.7 Tg N yr −1 (−12%~31% change). The decreased sum of the three major reactive N losses amount to 1.7~9.4 Tg N yr −1 , which corresponds to 3%~14% of the global cropland total N loss. Biochar generally has a larger potential for decreasing soil N losses but with less benefits to crop production in temperate regions than in tropical regions. K E Y W O R D S biochar, machine learning, N leaching, N 2 O, NH 3 , spatial variability S U PP O RTI N G I N FO R M ATI O N Additional supporting information may be found online in the Supporting Information section at the end of the article. How to cite this article: Liu Q, Liu B, Zhang Y, et al. Biochar application as a tool to decrease soil nitrogen losses (NH 3 volatilization, N 2 O emissions, and N leaching) from croplands: Options and mitigation strength in a global perspective. Glob

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