Spartina Alterniflora Saltmarsh Sediment Stoichiometry And Its Ecological Effects As Responses To Artificial Landform

As ecotone between land and ocean ecosystem,coastal system suffers from the double influence from land and ocean environment,as well as huge burden from human activity.There is long history of coastal development and local landforms have been changed as result of human activity,however,the knowledge about potential impact on the balance of sediment composition and stability of intertidal ecosystem is rare.The presenting research clarifies the spatial-temporal heterogeneity of the sediment composition at the intertidal zone at the northern Jiangsu Province,China.Eutrophication level and heavy metal pollution risk are assessed using multiple geoindicator.Canonical correlation analysis was used to imply the shift of the vegetative growth traits such as height,basal diameter,leaf thickness,leaf number,biomass,and sexual reproduction process,as respondse to the spatial-temporal heterogeneity of sediment conposition at the microenvironment.Transition of the growth strategy of typical plant species Spartina alterniflora was revealed with the analysis on the traits such as population structure,allometry,calorific value and element contents.An analysis was done for content of biogenic elements(C,N,S and P)and heavy metal elements(Al,Fe,Mn,Pb,Cu,Zn,Cr,Ni,As and Cd)in surficial sediments under the impact of artificial landform.Artificial landform resulted in the enrichment of multiple biogenic elements and heavy metal elements in its surrounding sediments;sediment element composition at the tidewater scouring area in the front of S.alterniflora salt-marshes was not affected by artificial landform;there was no enrichment of elements in the area without plant establishment under the impact of artificial landform,indicating that the impact of artificial landform,plant establishment and phytocoenosium extension plays a key role during the process of enrichment of biogenic elements and heavy metal elements.Similarity and difference of sediment elements composition in spatial and temporal distribution were revealed through PCA analysis and clustering analysis,the distribution rule of sediment elements composition under artificial landform rested more on the pile-up process,leading to obvious differentiation between the clustering feature of sediment elements composition under artificial landform and that under natural condition,and influencing the correlativity among elements represented by P-N relationship.Distribution of biogenic elements and heavy metal elements in sediments may be depicted by two main components of pile-up process caused by water transporting and element deficiency caused by increasing soil organic carbon,indicating that generation of spatial heterogeneity of various elements under the impact of artificial landform is mainly originated from the accumulation of phytodetritus and separation of natural minerals with different grain diameters.Different elements in sediments were divided as follows by PCA based on the dependence on two main components:Al,Fe,Mn,S,Pb,Zn,Ni,etc.from enrichment of natural minerals;C,N,Cd and organic carbon due to enrichment of organic matters;Cu affected by the enrichment tendency of both organic carbon and natural minerals;P with deficiency due to enrichment of organic matters under the impact of artificial landform.It was shown via clustering analysis that the distribution of sediment elements composition under artificial landform was caused by pile-up of natural minerals,such as Al,Fe,Mn,Cr,Zn and Ni,accumulation of organic matters,such as C,Cu and N as well as the change of redox state,such as Cd,S and As.Multiple geological indicators were synthetically applied to estimate the eutrophication level and heavy metal exposure related risk.Geo-accumulation indexes,enrichment factor,Nemerow combined pollution index and other geological indicators are usually widely applied to assess the pollution risk of heavy metal elements,however,the applied range of these geological indicators were successfully extended in this research,and synchronously a comprehensive assessment was made on the eutrophication risk caused by accumulation of plant residues and the heavy metal accumulation risk caused by deposition of natural minerals under the impact of artificial landform.Geo-accumulation indexes show that artificial landform of the coastal zone for environmental contamination risk of sediment element composition was mainly placed on 2 biogenic elements(i.e.N and S)as well as multiple heavy metal elements(such as Cu,Zn,Cd,As,etc);enrichment factors were applied to depict the driving factor during the process of sediment elements enrichment,which proposed that Cu is a good indicator element concerning that the joint impact of plant residues accumulation and natural minerals deposition around artificial landform results in the heavy metal enrichment change;through comparison with the traditional Nemerow combined pollution index,it was found that the extended Nemerow combined pollution index may sensitively indicate the ecological risk brought by that sediment element composition is changed by artificial landform through combined consideration and estimation of biogenic elements.Effect of artificial landform on aquatic ecosystem was depicted from multiple perspectives such as individual growth characteristics,population structure and allometric growth characteristics related to spartina alterniflora loisel-the typical plant in the area.The element enrichment environment caused by artificial landform resulted in the improvement of such growth indexes as plant height,basal diameter,leaf number and aboveground biomass of Spartina alterniflora,thus promoting the vegetative growth of spartina alterniflora loisel.The acceleration of artificial landform on vegetative growth of spartina alterniflora loisel was induced by multiple elements like N,Cu and Fe enriched in sediment.Different nutrient elements have different effects on vegetative growth of spartina alterniflora loisel:in terms of positive effects on seasons,vegetative growth of Spartina alterniflora has an all-season response on the difference distribution of N,Cu and Fe have an accelerating effect on vegetative growth of S.alterniflora at the early stage of growing season;as to response indicators,the acceleration on vegetative growth of S.alterniflora from N is reflected on the improvement of plant height of ramet and biomass accumulation,and that from Fe and Cu on the improvement of plant height of ramet;regarding ramet preference,the improvement on vegetative growth of S.alterniflora from N is reflected on promotion of the overall growth of ramet,and the improvement on vegetative growth of ramet from Fe and Cu on release of nutrient limitation on dominant ramet.Tidewater impact triggered the response of contact morphogenesis of spartina alterniflora loisel,and led to the restriction on plant height,basal diameter,leaf thickness,leaf number and biomass accumulation of spartina alterniflora loisel during the early and middle stage of growing season,however,no evidence has proven that the existence of artificial dam has an influence on contact morphogenesis effect caused by tidewater at the front of S.alterniflora.Artificial landform remits the condition of nutrient deficiency in the surrounding spartina alterniflora population,but leads to more intense competition of ramet in the population for light and results in self-thinning of S.alterniflora population in summer,restricting the growth of young ramet in population,increasing the photosynthetic burden of leaves,hindering the normal withering process of leaves,raising the threshold value of ramet entering the process of generative propagation,and finally causing the degeneration of its generative propagation capacity at the end stage of growth season,which is reflected on the decline of seed setting rate in population.It indicated from the analysis result of element content and heat value of overground part of S.alterniflora that its variation difference in quadrats is relatively small,and also revealed that change of biomass is the main impact factor of element migration of overground part and energy distribution strategy of S.alterniflora.Emphasis was additionally done in this research on the importance of comprehensive consideration of scale and life history traits when assessing the influence of ecology of human activities.Sediment elements composition change caused by disturbed hydrodynamic process and its impact on life strategy of the typical plant spartina alterniflora loisel under the impact of artificial landform was first discussed in this research.The coastal zone areas are still crucially influencing the economic and cultural development of human society at present,but are also threatened by many aspects such as change of land utilization type and sea level rise.In this context,the harm on persistence of intertidal ecosystem around from disturbed hydrodynamic factors during the process of people exploitation at the coastal zone was revealed,and additionally,the necessity and urgency making the change of sediment stoichiometric ratio caused by hydrodynamic disturbance during the process of future exploitation as the long-term environmental effect for monitoring was emphasized in this research.