Abstract
The rapid growth of the economy in China has caused dramatic growth in the industrial and agricultural development in the Yellow River (YR) watershed. The hydrology of the YR has changed dramatically due to the climate changes and water management practices, which have resulted in a great variation in the fluxes of riverine nutrients carried by the YR. To study these changes dissolved nutrients in the YR were measured monthly at Lijin station in the downstream region of the YR from 2002 to 2004. This study provides detailed information on the nutrient status for the relevant studies in the lower YR and the Bohai Sea. The YR was enriched in nitrate (average 314 μmol·L−1) with a lower concentration of dissolved silicate (average 131 μmol·L−1) and relatively low dissolved phosphate (average 0.35 μmol·L−1). Nutrient concentrations exhibited substantial seasonal and yearly variations. The annual fluxes of dissolved inorganic nitrogen, phosphate, and silicate in 2004 were 5.3, 2.5, and 4.2 times those in 2002, respectively, primarily due to the increase in river discharge. The relative contributions of nutrient inputs to nitrogen in the YR were: wastewater > fertilizer > atmospheric deposition > soil; while to phosphorus were: wastewater > fertilizer > soil > atmospheric deposition. The ratios of N, P and Si suggest that the YR at Lijin is strongly P-limited with respect to potential phytoplankton growth.
Highlights
Rivers carrying suspended and dissolved materials from the land to the ocean are the principal link in transferring nutrients between these systems [1,2] and this greatly influences the aquatic ecology, especially in estuaries [3,4,5,6]
The Lijin Hydrographic Station, located 100 km upstream from the Yellow River (YR) estuary, is the last station before the river debouches into the Bohai Sea, and the records at Lijin represent the standard figures of the contributions of the YR to the sea
Compared to other major world rivers, the YR was relatively enriched in NO3−-N but relatively poor in Dissolved inorganic phosphorus (DIP)
Summary
Rivers carrying suspended and dissolved materials from the land to the ocean are the principal link in transferring nutrients between these systems [1,2] and this greatly influences the aquatic ecology, especially in estuaries [3,4,5,6]. Anthropogenic perturbations (e.g., wastewater and fertilizer inputs) have caused significant increases in fluvial nutrient fluxes [7], and have substantially modified coastal ecosystems [8,9,10]. The construction of riverine impoundments such as dams and reservoirs can modify the hydrology and the fluvial transport of nutrients and sediments [11,12,13]. Previous studies have identified that the major sources of nitrogen and phosphate in the Yellow River (YR) were soil, fertilizer and wastewater inputs [14]. Owing to the substantial ongoing industrial and agricultural development in China, the nutrient fluxes in the YR have changed significantly over the last few decades. The DIN fluxes varied from 0.92 × 109 mol/a in the 1980s to about
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