Spatio-Temporal Dynamics of Riverine Nitrogen and Phosphorus at Different Catchment Scales in Huixian Karst Wetland, Southwest China

Abstract

Spatio-temporal dynamics of riverine nitrogen (N) and phosphorus (P) in karst regions are closely linked to hydrological conditions, human activities and karst features in upstream catchments. From October 2017 to September 2019, we undertook 22 sampling campaigns in 11 nested catchments ranging from 21.00 to 373.37 km2 in Huixian karst wetland to quantify forms, concentrations, and fluxes of riverine total nitrogen (TN) and total phosphorus (TP), and to identify spatial and temporal variations of nutrients transfer from upstream to downstream, tributaries (Mudong River and Huixian River) to the main stem (Xiangsi River) in the dry and wet seasons. Considering the hydrological conditions, human activities and karst features within upstream catchments, the following three spatial and temporal variations of riverine nutrients were found over the monitoring period: (1) the dynamics of riverine nitrogen and phosphorus varied seasonally with hydrological conditions; (2) the spatial disparities of riverine nitrogen and phosphorus were induced by different human activities within catchment scales; (3) the dynamics of riverine nitrogen and phosphorus varied similarly at spatial scale restricted by karst features. The findings from this study may improve our understanding of the influence of hydrological conditions, human activities and karst features on nitrogen and phosphorus variations in river waters at different spatial and temporal scales in the Huixian karst wetland basin, and will help managers to protect and restore river water environments in karst basin from a catchment-scale perspective.

An Overall Perspective for the Study of Emerging Contaminants in Karst Aquifers

“…For this reason, one of the scientific research objectives is to understand the origins of nitrate transformations in the karst systems. High application doses of fertiliser have caused nitrate pollution of the karst aquifer for the cultivations of pineapples [47], rice, corn, rapeseed [48], soybeans [49], beans, tubers, cotton, apple, pear, melons [50], olive trees [51] and other vegetables [52]. These studies indicated that sustainable nitrogen fertilisation practices and rational irrigation are the keys to mitigating nitrate pollution in the karst environment.…”

“…Karst aquifers characterised by gullies, gaps and fracture networks within the karst architecture are mainly subjected to rapid transport of pollutants from surface to groundwater, affecting water quality [48]. Therefore, the water cycle is pollutant transfer's primary driver and carrier [141].…”

Influence of Environmental Factors on the Variability of Archaeal Communities in a Karst Wetland

“…The Huixian karst wetland is considered as the largest karst wetland in South China (Cai et al, 2009;Chen et al, 2020;Pan et al, 2020) and has been listed as a national wetland park since 2012. This wetland has crucial ecological functions with respect to the Li River, including flood control, water purification, and biodiversity support (Qin et al, 2020).…”

“…This wetland has crucial ecological functions with respect to the Li River, including flood control, water purification, and biodiversity support (Qin et al, 2020). Because of its significant social-ecological value to nearby regions, many recent studies have reported on the hydrology (Pan et al, 2020), soil properties (Li et al, 2017b), contamination (Chen et al, 2020;Huang et al, 2020), and microalgal and bacterial communities (Yan et al, 2020) of the Huixian karst wetland.…”