Strong Precipitation and Human Activity Spur Rapid Nitrate Deposition in Estuarine Delta: Multi-Isotope and Auxiliary Data Evidence

Abstract

The intensive development of the Yellow River Delta has caused huge transportation of non-point pollutants into the Bohai Sea through source river estuaries and thus poses a considerable threat to eco-environmental security in the region. Long-term irrigation in the Yellow River basin, with occasional heavy rainfall and the related effects of ensuring hydrological processes and human activities in terms of nitrate N transport via surface water systems, is unclear. Using stable isotope (δ2H-H2O and δ18O-H2O, δ15N-NO3− and δ18O- NO3−) and auxiliary geographic data, the ISO source model was run to quantitatively analyze the supply relationship of river systems and the rapid change in the spatial pattern of nitrate N due to heavy rainfall in the estuarine delta. This analysis made clear the dominant contribution of agricultural activities and urbanization to NO3−-N emission, on which basis refined management measures were proposed to deal with NO3− in surface water from the “source-process”. The results of the study show that: (1) The relationship of surface water replenishment in the Yellow River Delta was affected not only by rainfall, irrigation, and other water conservancy measures but also the proportion of water from Yellow River flow declined from the source to estuary; (2) To a certain extent, rainfall diluted the concentration of nitrate N in the river and increased instantaneous flux of nitrate N into the sea, where nitrate N flux continuously increased from upstream to downstream; (3) The rapid deposition of nitrate in the estuary delta was driven by heavy rainfall and human activities such as excessive use of nitrogen fertilizers, rapid urbanization, and livestock waste discharge, and; (4) Scientific measures were needed to realize the interactive effect of the output of non-point source pollutants and the carrying and absorption capacity of coastal fragile ecosystems of the exogenous inputs.

The Nutrient and Heavy Metal Contents in Water of Tidal Creek of the Yellow River Delta, China: Spatial Variations, Pollution Statuses, and Ecological Risks

“…The concentration of NO3 --N in the water samples of the 7 sample sites ranged from 0.32 to 1.95 mg L −1 , with an average of 0.64 mg L −1 . Compared with other research results, the average concentration of NO3 − -N in the tidal creek water in this study was lower than that in the eight rivers of the YRD in Laizhou Bay (before rainfall, the average NO3 − -N content was 1.37 mg L −1 ; the average content after rainfall is 1.47 mg L −1 ) [11]. There were significant differences in the NO3 − -N concentration among different sample sites (F = 40.558, p < 0.001).…”

“…As the youngest estuary delta in the world, the YRD has a wide distribution of saline-alkali land due to its low precipitationevaporation ratio and seawater influence. Therefore, farmers in the YRD increased the use of fertilizer to improve crop yield in saline-alkali land and increased the amount of nitrogen and phosphorus fertilizer applied in the YRD, resulting in a large amount of land nitrogen and phosphorus into the water of the YRD [11]. The Yellow River Delta is an important mining area of Shengli Oilfield.…”

Changes in Surface Water Quality of the El Salvador River in La Joya de los Sachas, Ecuadorian Amazon Region

“…[21] located around the river (Figure 1), with transient crops being the most demanding in the use of synthetic fertilizers. In Guatemala and Honduras, a study showed that the leaching and runoff of fertilizers used in agriculture and human manure caused nitrogen contamination of 92% and 55.5%, respectively, in surface water and groundwater [40,41], causing the development of invasive macrophytes and the eutrophication of the river [42]. This statement is corroborated by Zaresefat et al [43], who point out that the concentration of nitrates in rivers is due to the widespread use of nitrogen fertilizers in high-yield crops; they also mention that high nitrogen inputs can negatively affect human health and aquatic ecosystems.…”