As an essential component of proteins and genetic material for all organisms, nitrogen(N) is one of the major limiting factors that control the dynamics, biodiversity and functioning of lacustrine wetlands, in which intensified N biogeochemical activities take place. Reactive N loaded into wetland ecosystems has been doubled due to various human activities, including industrial, agricultural activities and urbanization. The main driving mechanisms of N transport and transformation in lacustrine wetlands are categorized to pushing forces and pulling forces in this study. Geomorphology, wetland age, N concentrations, and temperature are the main pushing forces(passive forces); whereas water table variation, oxygen concentration, other elements availability, oxidation-reduction potential(Eh) and p H, and microorganisms are the predominant pulling forces(active forces). The direction and kinetic energy of reactions are determined by pulling forces and then are stimulated by pushing forces. These two types of forces are analyzed and discussed separately. Based on the analysis of driving mechanisms, possible solutions to wetland N pollutions are proposed at individual, regional and global scales, respectively. Additional research needs are addressed to obtain a thorough understanding of N transport and transformations in wetlands and to reduce detrimental impacts of excessive N on such fragile ecosystems.
Nitrogen(N)is one of the most important components and ecological factors for natural wetland ecosystems.It is mainly derived from runoff input,atmospheric deposition,and biological N fixation.The transport and transformation of N in natural wetlands primarily occur in the hyporheic zone(HZ),a buffer area of intensified biogeochemical activity that is often regarded as the sink,source,and converter of N in wetlands.The main ways of N attenuation in the HZ are denitrification,anaerobic ammonia oxidation(anammox),and wetland plant adsorption.The effects of internal and human factors on the N cycle are illustrated in this article.The results indicate that N sources are influenced by human factors such as agricultural activities and fossil combustion,while N attenuation is affected by internal factors,including oxygen concentration,carbon and phosphorus availability,pH and Eh changes,and microorganism actions.Finally,some research trends are provided to get a better understanding of the N cycle in the HZ of natural wetlands.This study may provide a clear perspective of N cycle in the HZ and their interactions between various factors.
