The Inter-annual Variation Of Water Quality And The Changing Trend Of Plume Area In The Yellow River

Since the1950s, the discharges in many rivers worldwide have met a remarkabledecrease due to climate change, as well as the water resources under intensedevelopment. The Yellow River basin mainly locates in the arid and semi-arid regionin the mid-latitude area, and the annual discharge in the Yellow River has droppedmore than70%during the last50years. As a result, the materials transport patternsand the fluxes from the land to the ocean have been greatly influenced. Especially inthe Yellow River estuary and its adjacent zone, the sharply shrinking plume area hasseriously deteriorated the estuarine eco-environment.In this study we basically focus on the control section in the Lijin station and theadjacent region in the Yellow River estuary. Firstly, the inter-annual variation ofwater quality in the Lijin station was discussed. Lijin hydrological station is the laststation in the Yellow River before it drainage into the sea, and its cross-section waterquality can represent the quality level discharge into the sea. Monthly monitored datawas collected in the Lijin station from August2010to July2011except for Januaryand February in2011, so that the seasonal variation of water quality and the fluxes ofcarbon and nutrients can be discussed, which may offer a better understanding of itsinfluence on the biogeochemical processes of the Bohai sea and even the wholePacific northwest area. Secondly, the relationship between the plume area and themonthly runoff was built. When this relationship is applied, we can further predict thesize of plume areas and its variety trend if discharge data is available, which is crucialin forecasting the size of plume area and reasonably allocate the water source. Themain conclusions are as follows:1、The concentration of the parameters relating to water quality and their fluxesto the sea was largely determined by the discharge. Basically, the lower of thedischarge would lead to the higher concentrations and the lower fluxes. There arenegative correlations between the concentration of dissolved inorganic carbon （DIC）and dissolved organic carbon （DOC） with the river discharge, and the concentrationof particulate organic carbon （POC） is positively correlated with TSS. The fluxes ofDIC, DOC and POC in the whole hydrological year （2010-2011） are5.80×10⁵tC, 3.97×10⁴tC,3.50×10⁵tC, respectively；All the nutrients showed a sensitive seasonallychange with higher values in flood season and lower ones in dry season. The fluxes ofnutrients in the whole hydrological year are as followed: NO₃^--N4.01×10⁹mol,NO2--N1.55×10⁷mol, NH₄⁺-N4.51×10⁷mol, PO43--P1.15×10⁷mol, SiO32--Si2.79×10⁹mol.2、The river discharge has decreased continuously during the last half century inthe Yellow River, accompanying with a downward trend of the river plume area. Theaverage plume area from1958to1968was1603.7km²; and it was780.8km²from1969to1985, a value nearly51%lower than the previous stage; then it decreased by74%to203.7km²between1986and2002; and it reverted to297.5km²in the periodfrom2003to2009. From the monthly variation of the plume area between2004and2009, we can conclude that the bigger plume areas mainly concentrated from June toOctober within a year in the Yellow River, which were larger than240km². Theaverage plume area was in serious shortage which was less than70km²in spring,when it is important for the breeding of all kinds of aquatic organisms in the YellowRiver mouth. Consequently, fresh water inflow is needed to maintain the health of theYellow River estuarine ecosystem, with about0.045×10⁸m³fresh water forincreasing one square kilometer of plume area.