Effects of revetment type on the spatial distribution of soil nitrification and denitrification in adjacent tidal urban riparian zones

摘要

Revetments between the river channels and riparian zones are important factors in the modification of urban riparian zones structure, particularly in zones adjacent to them. Although there have been many studies on the stability of revetments in tidal urban riparian zones, the quantitative effects of revetments on the nitrogen cycling in riparian zones adjacent to them remain unclear. Tidal riparian zones undergo more frequent river-soil exchanges than normal riparian areas, thus, revetments may have a greater impact on the nitrogen cycling. Nitrification and denitrification are two important biotransformation processes of nitrogen cycling. In this study, we used soil (depths of 0-20, 25-45, and 55-75 cm) nitrification and denitrification rates as indicators to study the effects of revetment type on the spatial distribution of soil nitrogen cycling in tidal urban riparian zones adjacent to three revetments (permeable concrete pile revetments (PR), impervious masonry stone revetments (IR), and no revetments (NR)) at three distances (0.3, 0.6, and 1.0 m). Our results indicated that compared with natural riparian zones (NR), PR significantly improved soil nitrification and denitrification rates, while IR significantly improved soil nitrification rates but decreased denitrification rates (P < 0.05), which were totally different from the general perception, particularly in impervious revetments. Revetment type mainly affected the temporary inundation zones (0-20 cm). For example, in the temporary inundation zones, the variation in soil denitrification rates was 14.49 mg kg(-1) h(-1), while in the frequent inundation zones (25-45 cm) and the permanent inundation zones (55-75 cm), the variations were 3.26 and 2.94 mg kg(-1) h(-1), respectively. Soil compaction was probably the main constraint factor for soil nitrification in natural riparian zones, soil organic carbon (SOC) and nitrogen availability were probably the main constraint factors for soil denitrification adjacent to impervious revetments. In order to take full advantage of the structural characteristics of impervious revetments and permeable revetments, the combination of impervious revetments in permanent inundation zones and permeable revetments in temporary inundation zones could be optimally designed to enhance soil nitrogen cycling function of tidal urban riparian zones during revetment construction.