Influencing Factor Of Nutrient Transport In The Lower Reach Of Yellow River

Rivers carrying suspended and dissolved material from the land to the ocean arethe principal link in the transfer of nutrients between these systems. As the secondriver in China, Yellow River plays an important role in the transport of nutrients.Dissolved nutrient concentrations in the Yellow River were measured monthly anddaily during the period of water-sediment regulation in the downstream region at Lijinstation from2005to2009. Combined with historic hydrographic and water-qualitydata (1980~2009), the concentrations and compositions of nutrients, and theirtemporal change were discussed in the study, especially during the period ofwater-sediment regulation. The results are concluded as following：(1) Dissolved nutrient concentrations in the Yellow River were measuredsystemically during2005~2009. The concentrations of nitrate and nitrite ranged from144.6to363.6μmol/L and from0.06to22.4μmol/L, while the concentration ofammonia varied from0.97to48.9μmol/L. The concentration of phosphate and silicateranged from0.02to1.19μmol/L and from46.07to142.9μmol/L, respectively. Theconcentration of nitrate and silicate decreased in2005~2009, while the concentrationof phosphate decreased before2007and then increased. The ratio of DIN/DIP rangedfrom206to15567, and it suggests that the waters of the Yellow River at Lijin arestrongly P-limited.(2) The fluxes of nitrate, DIN, phosphate and silicate decreased during2005~2009.Nutrient fluxes also exhibited substantial seasonal fluctuations. Discharge was themain factor that controlled the fluxes of nitrate, phosphate and silicate. And for nitriteand ammonia, concentration of nutrient was also the main factor.(3) The changes of water and sediment were observed during the period ofwater-sediment regulation in2005~2009. The relationship between discharge andsediment were clockwise expecting the anaphase of2008. And sediment peak was infront. It means that sediment in the water-sediment regulation mainly come from the riverbed. But the relationship between discharge and sediment were anticlockwiseduring the rain period in2005and the anaphase of water-sediment regulation in2008.And water peak was in front. It means that sediment was soil mainly come from theYellow river basin.(4) The concentrations and fluxes of nutrients were analyzed during the period ofwater-sediment regulation in2005~2009. The relationships of nutrients and dischargeand sediment were complicated. The concentrations of nitrate, phosphate and silicateincreased with the increase of discharge when the discharge was low, and they weredecreased with the increase of discharge when the discharge was high. They wereinfluenced by the erosion of riverbed and beach, dilution effect of river-water and theamount of suspended particulate matter. The water flux was accounted about20%ofthe whole year during the period of water-sediment regulation. The fluxes of nitrateand silicate were accounted for20%～30%, while the fluxes of phosphate wasaccounted for about20%. The fluxes of nitrite and ammonia were just accounted forless than10%in most years. Fluxes of nitrate, phosphate and silicate were mainlycontrolled by water discharge.(5) The series data of nutrients at the downstream of Yellow River for about30years were reviewed. The concentrations of dissolved inorganic nitrogen and nitrateincreased from1980s to2000. No obviously changes of phosphate and silicate werefound from1980s to2000. The concentrations of dissolved inorganic nitrogen, nitrateand silicate decreased after2000, while the concentration of phosphate increased from2001to2007and then decreased after2007.(6) The specific fluxes of nitrate, phosphate and silicate of Yellow river werecalculated and compared with world rivers. The specific fluxes of nitrate, phosphateand silicate of Yellow river were lower than that of the same latitude rivers, becausethe actual discharge was much lower than the “natural” discharge due to thelarge-scale water take-off. The concentration of nitrate and silicate of Yellow riverwere higher than that of the same latitude rivers, while the specific fluxes ofphosphate was lower due to the low concentration and the large-scale water take-off.