Abstract
Karst topography covers more than 1/3 of the People's Republic of China in area. The porous, fissured, and soluble nature of the underlying karst bedrock (primarily dolomite and limestone) leads to the formation of underground drainage systems. Karst conduit networks dominate this system, and rainfall takes a crucial role on water cycle at China karst area. Nitrogen loss from the karst system is of particular concern, with regard to nutrient use efficiency as well as water quality, as much of the karst system, including steeply sloping terrain, is used for intensive agriculture. We use simulated rainfall experiments to determine the relationship between rainfall and nitrogen loss at typical karst slope land and then estimate nitrogen loss from the karst soil. The results show that both surface runoff and subsurface runoff have a significant linear correlation with rainfall at all studied sites. Subsurface runoff is larger than surface runoff at two karst sites, while the opposite is true at the non‐karst site. Exponential function satisfactorily described the correlation between rainfall and nitrogen concentrations in runoff. Nitrates accounted for 60%–95% of the dissolved nitrogen loss (DN, an index of N‐loss in this research). The estimated annual N‐loss load varies between 1.05 and 1.67 Tg N/year in the whole karst regions of China from 1961 to 2014. Approximately, 90% of the N‐loss load occurred during the wet season, and 90% of that passed through the subsurface. Understanding the processes and estimating N‐loss is highly valuable in determining long‐term soil security and sustainability in karst regions.
Highlights
Karst topography is formed by the dissolution of soluble rock, usually carbonate rocks such as dolomite, limestone, and gypsum, and carbonate rocks outcrop across ~11% of the world’s ice-free land area (Badman, 2010; Dürr, Meybeck, & Dürr, 2005)
Rainfall-runoff conversion process at karst area takes a vital role on sustainable development of healthy ecosystem function
Soil water conservation capacity is important as rainfall is dominating source of water at karst system
Summary
Karst topography is formed by the dissolution of soluble rock, usually carbonate rocks such as dolomite, limestone, and gypsum, and carbonate rocks outcrop across ~11% of the world’s ice-free land area (Badman, 2010; Dürr, Meybeck, & Dürr, 2005). Rainfall simulations are often used to investigate both surface and subsurface runoffs, hydraulic conductivity, soil erosion, and nutrient loss under controlled conditions (e.g., Fu et al, 2015, 2016; Gao et al, 2009, 2010; Taucer et al, 2008). Li et al (2013) assessed that water and nutrient loss were seriously hindering natural vegetation growth in southwestern China Both ecosystem research for macroscopic scale and cellular functions study for microcosmic scale found N limitation at karst area in China (Kang et al, 2015; Zhang et al, 2015). During heavy rainfall events (i.e., during monsoonal wet season), there is significant runoff and an increased potential for soil nutrient loss This has profound implications for soil and water quantity and quality and ecosystem service provision, including water provision and food production. For further synthesis of above factors, we estimated the annual and monthly variations in dissolved nitrogen (DN) loss (N-loss) from karst regions in China between 1961 and 2014 according to monthly mean precipitation data
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