A Review of Nitrogen Export and Its Eco-Environmental Significance in the Superficial Karst Desertification Zone

Abstract

Epikarst is connected with a “binary” geological structure, and the hydrogeochemical processes are complex. Nutrients play an important role in the restoration of the surface ecosystem in the desertification area, which is prone to loss and leakage, and the transport and transformation of nitrogen is crucial to the growth and development of plants in the ecosystem and the safety of drinking water for the residents. In this study, we reviewed nitrogen research in the past 20 years in the “Web of Science (WOS)” and “China National Knowledge Infrastructure (CNKI)”, and we reviewed nitrogen research in the following areas. From the results of the systematic review, (1) We found that nitrogen-related research literature has been growing over time, and the growth has been faster in the past five years, mainly in the fields of agriculture, public health, and environmental science; (2) In karst water systems, researchers are mostly concerned with the sources of nitrate, distribution characteristics, and pollution of karst water, and the dual isotope techniques of δ15N and δ18O are used to identify these; (3) In karst water systems, surface water bodies and underground rivers are the main objects of study, relatively few studies have been conducted on karst springs, and NO3−-N, NO2−-N, and NH4+-N are the main forms of nitrogen presence. The study of nitrogen in karst water systems ignores the unique subsurface leakage problem of karst areas, and the study of the relationship between nitrogen and nutrient leakage in karst water systems should be strengthened for karst desertification management and ecological restoration. This review may provide some insights for researchers working in related fields.

Effects of Soil–Rock Geomorphic Units on the Yield of Surface Runoff: A Case Study on Uncultivated Land of a Karst Area

“…In order to analyze the influence of environmental factors on surface runoff generated by the soil patches, we measured the soil bulk density (g cm −3 ), soil porosity (%), soil hydraulic conductivity (cm s −1 ), and root biomass (Kg m −2 ) for each runoff plot after the surface runoff measurements. Soil samples were randomly collected in three replications at depths of 0-30 cm with cutting cylinders (inner diameter 70.00 mm; height 52.00 mm; volume 200 cm 3 ). The soil core method was also used to measure the root biomass of plants within a soil depth of 0~20 cm in each runoff plot.…”

“…Water loss into underlying rocks is one of the important factors limiting ecological restoration in karst areas, and its impact on agriculture has seriously restricted the social and economic development of these regions [1][2][3][4]. Water resources in a karst area are so reduced that even essentials such as drinking water for people and livestock are difficult to find.…”