| Hydrological connectivity as a key ecological process in tidal wetlands plays vital roles in the conservastion and restoration for the tidal wetlands.The macrobenthos is an important component of wetland ecosystems and a key link in the food chain.Due to its sensitive reaction to the environmental changes,the macrobenthos is often considered as a key indicator of wetland ecosystem health.The changes in its community can also directly reflect the stability and change of the ecosystem.In order to preserve the regional and local ecosystemss tability,it is crucial to understand how hydrological connectivity of wetlands affects habitats and biological communities.This understanding may also serve as a scientific foundation for the conservation and restoration of the tidal wetlands.In this study,three seasons of the field sampling and in-situ observations were conducted on three tidal gully with obviously hydrological connectivity gradient in tidal wetland of the Yellow River Delta.Biological,water and sediment samples were collected for further analysis.The chemical-hydrological connection of the wetlands was evaluated by using multi-element analysis.The spatial and temporal distribution characteristics of the macrobenthic community structure were analyzed.Stable isotope techniques was adopted to investigate the effects of different spatial and temporal hydrological connectivity on macrobenthic food webs.Our aim was to clarify the spatial and temporal changes in community characteristics and biological responses of macrobenthic communities under different hydrological connectivity.The main results showed that:1.Hydrological connectivity affected the environmental physicochemical properties of different tidal gully,forming the spatial and temporal heterogeneity of habitats.High connectivity habitats showed the characters of high water exchange frequency,rough substrate surface and high permeability,whereas,low connectivity habitats showed the characters of high nutrient level,fine substrate,higher water salinity,conductivity,temperature and sediment organic matter and nutrient content.The following environmental factors,dissolved oxygen,conductivity,salinity,temperature,sediment fine particle content,carbon,nitrogen and organic matter content,phosphate,silicate and ammonium content of interstitial water,all decreased along the hydrological connectivity gradient.During,the hydrological connectivity was low with high water salinity and conductivity during the dry season,but was high with high nutrient habitat.during thewet senson.In summer,the flushing effect was strong,and the salinity,conductivity and dissolved oxygen of the habitat water were low.In autumn,the dissolved oxygen was high,the flushing effect was weakened,and the substrate is fine.2.The distribution and variation of multi-element composition and concentration in sediments were analyzed by the multi-element analysis.Based on the results,chemical-hydrological connectivity was found to exist in study area.The sediment elements had similar migration and accumulation characteristics.The chemical-hydrological connectivity was influenced by the hydrological connectivity,presenting with spatially different feaures.The composition of sediment elements was closely similar in the connected areas.We also found the greater difference in hydrological connectivity,the lower the chemical connectivity.Hydrological connectivity affected elemental concentrations through habitat modification.The concentrations of Mn,Cu,Cd,Pb,V,Cr,Fe,Co,Ni,Zn,As and Ti decreased with increasing hydrological connectivity gradients.These results demonstrate that multi-element analysis can be used to assess the chemical-hydrological connectivity of tidal wetlands.3.The hydrological connectivity could impact both the macrobenthic community structure and the spatial and temporal distribution patterns of species.Different taxa groups had different response characteristics to the hydrological connectivity gradient.Maintaining a certain level of hydrological connectivity was conducive to the increase of speciesnumber,density,biomass and diversity of the macrobenthic community.Biodiversity was highest in the areas with moderate hydrological connectivity,whereas,both low and high hydrological connectivity had a negative impact on the macrobenthic community.Meanwhile,hydrological connectivity had seasonal differences.In spring and autumn,the hydrological connectivity was moderate.At this time,the total species number,density,biomass and richness index of the macrobenthic community increased along the hydrological connectivity gradient.The hydrological connectivity was greatest in summer along with reduced spatial heterogeneity,which was unfavorable to organisms by decrease the density of macrobenthic communities.The third tidal gully had a strong scouring effect with the lowest species number and richness index.Secondary tidal gully had medium hydrological connectivity and short migration distances with the highest species number and richness index.The primary tidal gully had a stable environment and the longest migration distance with the lowest diversity.4.Hydrological connectivity affected the macrobenthic food webs.The stable isotope values were different between species.If the acrobenthic food sources were abundant,and the trophic level differences were large.The better hydrological connectivity increased the biological trophic level and food web structure complexity,wheras,the low hydrological connectivity decreased the biological trophic level,leading to a simplification of the food web structure.Food web consumers can be divided into five trophic groups,including zooplankton,filter feeding bivalves,omnivorous crabs,omnivorous shrimps,omnivorous and sediment feeding polychaetes,and carnivorous fish in different hydrological connectivity areas.Seasonal variations in hydrological connectivity could influence the source of particulate organic matter in wetlands.During the dry season,the composition of particulate organic matter varies little between regions,whereas,it mainly came from.the marine sources during the wet season in the low hydrological connectivity area.In conclusion,based on field investigations and laboratory analyses,the present work assessed the chemical-hydrological connectivity of tidal wetlands in the Yellow River Delta and coupled with the macrobenthic community by using multi-element analysis and stable isotope techniques..The response of macrobenthic habitats,communities charactics and food webs to the seasonal hydrological connectivity gradient were summarized at different spatial and temporal scales.The aim is to enhance the understanding of the mechanism of hydrological connectivity of wetlands on ecological processes,then provide scientific basis for the maintenance of hydrological connectivity,protection of biodiversityas well as wetland conservation and restoration in the Yellow River Delta region. |
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