Partitioning and behaviour of different forms of phosphorus in the TanshuiEstuary and one of its tributaries, northern Taiwan

Dissolved inorganic phosphorus (DIP), dissolved organic phosphorus (DOP), p articulate phosphorus (PP) and sedimentary phosphorus (SP), were determined in northern Taiwan's Tanshui Estuary and one of its tributaries. Concentra tions of DIP and PP (w/v) in the upper estuary were 15-20 times higher than those in the freshwater of the upper reaches in its tributaries, suggestin g that the Tanshui Estuary is a seriously phosphorus-polluted environment. The fraction of DIP generally accounted for more than 85% of the total diss olved phosphorus (TDF, DIP plus DOP) within the salinity <30 region, and th is decreased to c. 70% in the lower estuary (salinity >30). The fraction of PP accounted for about 60% of total phosphorus (TDP plus PP) in the salini ty <5 region but fell to 40-50% in the lower estuary (salinity >30). The lo garithm of distribution coefficient, log (K-D), ranged from 4.36 to 5.61 wi thin the whole estuary and was independent of the salinity. The total conce ntration of sedimentary phosphorus (TSP) ranged from 328 mg kg(-1) to 1240 mg kg(-1) within the estuary, and the inorganic form of phosphorus accounte d for 87-97% of TSP. The distribution of DIP in the Tanshui Estuary showed slight addition in th e upper estuary, removal in the mid-estuary and conservation in the lower e stuary. The addition and removal of P appeared to be related to desorption from and adsorption onto PP. The concentrations of PP(w/w) and TSP exhibite d addition in the salinity 5-10 region, strongly suggesting the removal of DIP onto the sediment. This removal of DIP probably resulted from co-precip itation or adsorption by Fe oxides/hydroxides. The upstream input of total P in the Tanshui River system was generally les s than 0.3 tP day(-1) and the phosphorus flux from the discharge of domesti c sewages input to the upper estuary was approximately 6.0 tP day(-1) durin g the study periods. A 2-D steady-state multi-box model was employed to cal culate the phosphorus sedimentary and estuarine export fluxes. The calculat ed results showed that approximately 4.0 tP day(-1) deposited in the upper estuary, and that the estuary also exported about 2.0 tP day(-1) to the coa st.