Distribution And Change Characteristic Of Nitrogen And Phosphorus Forms In Water And Suspended Solids In The Daliao River Estuary

The Liaodong Bay of China has suffered serious water eutrophication and the Daliao River is one of the main rivers which input pollutants into the Bay.30surface water samples were collected in the tidal reach and nearshore estuary of the Daliao River, and they were analyzed to study the form component and spatial-temporal distribution of nutrient (nitrogen and phosphorus) in water and phosphorus forms in suspended solids. By combining the determined data in the wet/dry season with data in a tidal cycle, the mixing behavior of nitrogen and phosphorus and the main effects of environmental factor on them in the tidal reach and nearshore estuary of the Daliao River were studied. Finally, the water potential eutrophication of the nearshore estuary of the Daliao River were assessed by the method of potential eutrophication assessment, and the indicator of phosphate in the method were discussed and revised by the bioavailable phosphorus in suspended solids. The main results were as follows:(1) In the tidal reach and nearshore estuary of the Daliao River, the major form of total nitrogen was total dissolved nitrogen which accounted for over85%of total nitrogen, the percentage of dissolved inorganic nitrogen was more than80%in the total dissolved nitrogen, and the percentage of nitrate was over65%in the dissolved inorganic nitrogen. Particulate phosphorus accounted for over50%of total phosphorus and phosphate accounted for over55%of total dissolved phosphorus in the tidal reach and nearshore estuary of the Daliao River. In the dry season, the concentrations of nitrogen and phosphorus forms in water were higher than that in the wet season. From the tidal reach to nearshore estuary of the Daliao River, the concentrations of nitrogen and phosphorus forms in water reduced gradually because of the effect of seawater dilution.(2) In the tidal reach and nearshore estuary of the Daliao River, the major forms of total particulate phosphorus in suspended solids were extractable organic phosphorus and iron-bound phosphorus and they took up over50%of total particulate phosphorus, the bioavailable particulate phosphorus accounted for over62.60%of total particulate phosphorus. The concentrations of most phosphorus forms in suspended solids in the dry season were higher than that in the wet season in the tidal reach of the Daliao River, but the temporal distribution of them were contrary in the nearshore estuary of the Daliao River. From the tidal reach to the nearshore estuary of the Daliao River, the concentrations of phosphorus forms in suspended solids were gradually reduced, which was same as the spatial distribution of phosphate, total dissolved phosphorus and total phosphorus in water.(3) Over the course of a complete tidal cycle at Liaohe Park station, it showed that the concentrations of nitrogen and phosphorus in water were decreased with the increase of salinity during the flood tide and that were increased with the decrease of salinity during the ebb tide. But the concentration change of phosphorus forms in suspended solids was irregular during the tidal cycle. The concentrations of nitrogen and phosphorus in water and most phosphorus forms in suspended solids in the tidal reach and nearshore estuary of the Daliao River were negatively correlated with salinity. These indicated that the physical dilution of seawater played an important role in the distribution of nutrients and it largely covered the effects of other environmental factors.(4) In the nearshore estuary of Daliao River, the concentrations of dissolved inorganic nitrogen and phosphate in water were greater than0.30mg/L and0.045mg/L respectively, and the molar ratio of the dissolved inorganic nitrogen and phosphate was greater than60. The assessment result by the method of potential eutrophication assessment classified the water condition in the nearshore estuary of the Daliao River as a phosphate-limiting nutrient area. The content of bioavailable particulate phosphorus was considerable in the total phosphorus in water, and bioavailable particulate phosphorus tended to easily exchange with phosphate in water. Therefore, we revised the method of potential eutrophication assessment by using "the sum of phosphate in water and bioavailable particulate phosphorus" instead of "phosphate in water".