The Effect Of Yellow River Delta Lobe Evolution On The Ecological Environment Variation Of Wetland System

The coastal wetland of the Yellow River delta is youngest and most unique wetland in the world. A wide variety of wetlands which has unstable site conditions, the natural oscillation frequency rivers, is a significant dynamic estuary. Moreover, the former Yellow River Delta wetland system affected by climate change, natural disasters, Yellow River cutoff, oilfield development, human activities such as building dams project, sea-level rise, coastal erosion, saltwater intrusion and so on, lead to a fragile ecosystem which is easy destroyed.In this paper, based on field survey in Yellow River Delta, according to the channel change of Yellow River in history, interpretation of remote sensing data, the distribution of channel and natural levee, the time of artificial construction, topographic map of time series, low-water line, coastline, rivers variation, observation of field section, we divide ten delta lobes of sediment exposed at the surface which were formed since 1855 into seven areas, and conduct a habitat classification in every area. Based on this work, we collected lots of water chemistry samples in each lobe outcrops, including the maintenance of wetland habitats, 205 shallow groundwater samples, 18 surface water samples, 12 sea water samples of the delta inshore (in 6m fathom lines), 4 water samples of the active Yellow River and so on. Shallow water sampling activities coverd the seven sedimentary areas which is mentioned above. Water chemistry tests include macro elements, minor elements, nutrients and trace metals. The main findings include:(1)According to time series of the lobe evolution divided into seven sedimentary areas, the district area were: 1062, 861.9, 318.8, 230.4, 889.9, 1068 and 251.6 km².(2)By analyzing and observing eight field cross sections, it shows that in the vertical profile, the geological body of this wetland system was formed crossbedding by sediments of different times and sedimentary facies. The successions of these sedimentary phases are more complicated, and there is not a unified aquitard in space. So wetland ecosystem here is very fragile.(3)Our research pointed out that the shallow water in the Yellow River Delta lobes originated in mix waters of the Yellow River water and sea water, formed during "surrounding rock" of the aquifer bed transformed by geological and biogeochemical processes. In shallow water, the macro components of K⁺, Na⁺, Mg²⁺, Cl^-, SO4^2-, and TDS, etc., nutrients as NO₃^-and NH₄⁺, and trace components of Fe, Mn, Sr, Br, etc. are controlled by vegetation zoning, and reflects the close relativity with vegetation distribution. In particular, Ca²⁺ and HCO₃^- in the different wetland ecological habitats were reflected very high, infer that these two elements have some relation with biological activity, which HCO₃^- has positive relativity with respiration of plant roots and we can find the evidence from its lower components in water sampling from inter-tidal zone in 4th depositional area. And Ca's biogeochemical behavior is more complicated, probably associated with animal remains in wetland.(4)The restrictions of artificial dams and Yellow river channel play a very important controlling role on the spatial distribution of macro components. The detail is: shallow water whether in reeds or in tamarisk all shows high macro elements originated from sea water in 2nd areas. The reason can be attributed to seawater recharge in the coastal part of the abandoned route Diaokou Route, combined with no fresh water supplies in northern wetlands, to make the ecological habitat here suffered by high salinity stress. If comparing reed habitats in each area, the sea water originated macro elements also seems unusually high in 6th area. In it, the north shore is fully open state, the shallow water salinity increased to reeds which need shallower water, while tamarix in the same area which need more deeper depth water, so its shallow water is less affected to sea water originated macro elements from such an open water shoreline.If comparing distribution of sea water originated macro elements in Suaeda habitats in each area. Only 2nd area has higher distribution of macro elements, in other areas the sea water originated macro elements increases from the young to old area. Suaeda glauca distributes in the inter-tidal zone and the abandoned lobes around the trap sea water. So older lobes experienced longer period of evaporation and resulting in high macro element originated from sea water.(5) micro-components Sr and Li and nitrite NO^2-and SiO₃^2- show the normal distribution from new to old in shallow water of every depositional area. While element I distributes as a concave curve, which reflects the biogeochemical. "mature" process in lobe.(6)The values of trace metals of shallow water in delta lobes has high content comparing with the Yellow River water and sea water. It is presumable that a variety of industry, agriculture and sewage discharge on delta results to these consequences. In shallow water of wetland ecosystem, trace metals Cu, Pb, Zn and As cause serious pollution, even some samples surpass the 1st type sea water in national standard. Wetland ecosystem has degradation action to trace metals Cr.