The Spatialand Temporal Distribution Of Carbon,Nitrogen And Phosphorus In Sediments At The Estuarine Wetland Of Luoshijiang River

Estuarine wetland sediments are important reservoirs of pollutants,such as nitrogen,phosphorus and organic matter.When pollutants are effectively controlled,the pollutants in the sediments are released to the overlying water under certain environmental factors,causing secondary pollution.The wetland of Luoshijiang estuary is the first large-scale lake wetland in Erhai Lake,which is the natural barrier to reduce the pollutants of Erhai Lake.The pollution prevention and control of sediments has an important influence on the water quality protection of Erhai Lake.It is important premise for clarifying the pollution characteristics of wetland sediments to ensure the water quality of estuarine wetland and to restore the functions of wetland ecosystem effectively.At present,there are few studies on the temporal and spatial distribution of carbon,nitrogen and phosphorus in sediments of plateau estuary wetlands,there is very important significance of systematic research.The passage took the plateau estuarine wetland-the wetland of Luoshijiang estuary as the research object,the sediment samples were collected,and the temporal and spatial distribution characteristics of carbon,nitrogen and phosphorus were analyzed by the method of the pollution index,enrichment index,organic index and organic nitrogen index.The main results were as follows:(1)there is spatial difference of thickness of Sediment in Wetland of Luoshijiang River Estuary.The thickness of the sediment was between 10 cm and 100 cm,and the average thickness was 45 cm.In the south of the wetland and the surrounding islands,the mud is thick,but in the north and west side,the distribution of the sediment is thin.The amount of organic animal residue of the thick sediment was large,and the viscosity was good,the water content is high.On the contrary,the amount of organic animal residue was low and the water content was low.(2)The average contents of organic matter(OM),total nitrogen(TN),hydrolytic nitrogen(HN),total phosphorus(TP)and available phosphorus(AP)in the dry season were 76.29 g/kg,0.931 g/kg,0.303 g/kg,0.613 g/kg and 10.792 mg/kg respectively.The wet season were 53.193 g/kg,1.176 g/kg,0.244 g/kg,0.591 g/kg and 12.432 mg/kg,respectively.(3)There was difference of the spatial and temporal distribution of carbon,nitrogen and phosphorus in surface sediments.In the horizontal distribution,in the dry season,the content of OM,TP and HN were in the south> north,AP and TN content were the southern< northern;At the same time,two main channel surface sediment of TN,HN,TP and AP content expressed the waterway ?> waterway ?,except the OM.In the wet season,the contents of OM,TN and TP in the two main channels were in the south > north,and the contents of the two main channels were waterway ?<waterway ?.On the contrary,thecontent of HN and AP was the waterway ?> waterway ?.In the vertical distribution,the carbon and phosphorus in dry and wet season of the sediments were obviously enriched by the surface layer.The increasing of exogenous input and the geochemical effect of nutrients were the causes of the differences in the spatial and temporal distribution of carbon,nitrogen and phosphorus in sediments.(4)The ecological risk assessment of surface sediments carbon,nitrogen and phosphorus was carried out by using pollution index,enrichment index,organic index and organic nitrogen index,combining with environmental quality assessment standards developed by Ontario's Ministry of Environment and Energy.It is concluded that the pollution index of the other two indexes(OM,TP)was higher than that of wet season.Surface sediments in dry season and wet season of surface sediments TP were moderate enrichment,TN and OM were slightly enriched.The organic pollution of surface sediments in dry season was slightly larger than that in wet season.The results of organic nitrogen index evaluation and pollution index were consistent with that the pollution level of wet season nitrogen was more serious than that in dry season.(5)C/N and N/P values were valid indicators of sediment nutrient sources.There was differences on the spatial distribution of C/N and N/P values in surface sediments of Luoshijiang estuary wetland.In the dry season,the C/N value in the southern part was beween 1.236 and 4.908,and the northern part was between 1.669 and 69.803.The range of C/N in the wet season was 1.998~7.771 in the south and 1.590~15.960 in the north.There was a significant correlation between TN and OM in dry season,and there was a significant positive correlation with TN and OM in dry season.There was no correlation between TP and TN and OM in dry season sediments,and TP and TN,TP and OM had very significant positive correlation;TN and TP were mainly affected by exogenous,OM was mainly affected by endogenous,and the wet season was mainly influenced by the outside source,the dry season was mainly influenced by the inner source.