| Seabirds,as outstanding ecosystem engineers between land and ocean,transport a large amount of nutrients to the habitat ecosystems through biological transportation,and also increase the risk of pollution associated with marine-sourced heavy metals and other pollutant.So far,there have been many studies on the biological transportation by seabirds,and most of them focused on the investigation at macro-scale,but lack of mechanism interpretation at micro-scale.For example,many studies have shown that the seabird-derived nitrogen and other nutrients have a significant impact on plant growth and community structure,while how seabird-derived nitrogen affect the plant nitrogen utilization was poorly understood.In addition,seabird guano contains a high level of phosphorus,which may have a significant impact on its cycling in surrounding lakes and other aquatic ecosystems,but most related studies focused on the total amount of phosphorus and lack of research on different phosphorus forms.In terms of heavy metal pollution caused by seabirds' biological transportation,many previous studies focused on the total amount of heavy metal elements in seabird tissues or bird droppings,while ignoring the heavy metal pollution in seabird food and the different forms of the heavy metals.Therefore,this study focused on the above issues,selected the seabird colonies of Antarctica and Xisha Islands that are far away from human activities as the research areas,collected different types of environmental samples such as soils,plants,ornithogenic sediments,fresh guano,seabird foods,including flyingfish and squid,lake water,lacustrine sediments in the field,and biological remains such as guano particles,fish bones and fish scales were obtained from the ornithogenic sediment.From the perspective of the combination of historical and modern times,and from the spatial contrast,focusing on the key topics of the impact of seabirds' biological transportation on the nitrogen and phosphorus cycling,and heavy metal pollution in the habitat ecosystem,conducting analyses of total amount and different forms of elements,and stable isotope analysis,including the application of compound-specific nitrogen isotope analyses,chemical sequential extraction and solution-state 31P nuclear magnetic resonance(31P-NMR)analysis,and the impact of biological transportation of seabirds on the habitat ecological environment in the Antarctica and Xisha Islands were studied by means of interdisciplinary research methods.The main findings were as follows:1.The impact of seabird biological transportation on terrestrial and aquatic nitrogencycles in the AntarcticaIn order to assess the spatial distribution of penguin-derived nitrogen and its impact on plant nitrogen utilization strategies,soil,moss,lake water,algae(microbial mat)and lacustrine sediments were collected inside and outside the penguin colony in Victoria Land,East Antarctica,and analyzed for concentrations and ?15N values of total and inorganic nitrogen(NH4+-N and NO3--N).Through comprehensive and comparative analysis,the dynamic cycle of nitrogen in the ecosystem of penguin activities areas was preliminarily constructed,and penguin-derived nitrogen was identified as a very important nitrogen source in the surrounding ecosystem.The input of penguin guano increased the soil nitrogen concentration,especially the ammonium concentration,and resulted in enrichment of 15N in the soil,moss and algae near the penguin colonies.Combined with the related previous studies,we inferred that penguin guano could cause a large impact area outside the penguin colonies,where the soil more than 1 km away from the penguin colony was still affected by ammonia volatilization from penguin guano.In addition,penguin activities significantly affected the nitrogen utilization strategies of moss.Inorganic nitrogen isotope analysis revealed that moss might prefer inorganic nitrogen in the absence of guano,while the dissolved organic nitrogen would become an important source for moss growing on ornithogenic soils.In addition to the significant impact on the terrestrial ecosystem function,penguin activities heavily influenced the aquatic ecosystem near the colonies.For example,the ?15N values of the aquatic algae vary in a gradient with the distance from the penguin colony.The ?15N values of the algae near the penguin colony is positive(10.4±1.7‰),and the ?15N values of the algae far away from the penguin colony is negative(-11.7±1.0‰),while the ?15N value of the algae at the intermediate sampling sites was about-0.5‰.Furthermore,the similar patterns were also observed in the nitrogen isotope values of lake water and lacustrine sediments near penguin colonies,indicating that the loss of nitrogen in ornithogenic soil through runoff,leaching,and denitrification processes caused a significant increase in the amount of nitrogen,especially ammonium,in surrounding lakes and sediments,and showed 15N-enriched signals.In order to have a comparative study of the biological transportation of penguins between East and West Antarctica,the moss and moss-growth soil,lichen and lichen-growth soil,and lake water samples were collected from King George Island(Fildes Peninsula,Adley Island,Barton Peninsula),West Antarctica.The concentrations of total nitrogen,ammonium and nitrate and their nitrogen isotopic compositions were then analyzed.The results showed that the nitrogen concentrations and nitrogen isotope values of moss and lichen affected by penguin activities were higher than those without penguin activities.Moreover,ammonium is the major form of inorganic nitrogen in the moss-growth soil and lichen-growth soil samples,which is consistent with the results of East Antarctica.The results of nitrogen isotopes of lichen and lichen-growth soil showed that,unlike moss,soil is not a potential nitrogen source for lichen,and lichen mainly take up nitrogen from atmospheric deposition.In addition,there is also a great difference in the nitrogen concentration of lake water affected by penguin activities between East Antarctica and West Antarctica.The nitrate concentration is higher than ammonium concentration in the lake water samples affected by penguin guano in Adley Island,West Antarctica,while on the contrary,the ammonium concentration in lake water affected by penguin guano is higher than that of nitrate in the Inexpressible Island,East Antarctica.This may be related to the significant differences in environmental factors,such as microorganisms and climate in the two regions,which need to be further studied in the future.2.Characteristics of nitrogen spatial distribution in Xisha IslandsTo illustrate the possible impacts of seabirds and human activities on nitrogen cycling in the soil-plant system of Xisha Islands,the nitrogen concentrations and stable nitrogen isotope values of soil and plant samples from Qilian Yu Islands,Dongdao Island and Yongxing Island was analyzed.The results showed that mean nitrate concentration(12.33±12.88 mg/kg,n=12)was higher than that of ammonium(3.02±2.86 mg/kg,n=12)in the soil of Xisha Islands,regardless of whether it is affected by seabirds or not,which is contrary to the Antarctica,where the mean ammonium concentration was higher than that of nitrate.On the one hand,it might be attributed to the climate,temperature,soil microorganisms and other conditions of Xisha Islands are very conducive to the occurrence of nitrification,resulting in the part of ammonium converted into nitrate,on the other hand,it might be related to a large amount of loss of ammonium in the soil.The guano input increased the nitrogen concentration of soil in Xisha Islands,and increased the nitrogen isotope values of soil and plant foliar,which was consistent with the results of the Antarctic study.For Yongxing Island,which is greatly affected by human activities,although there are few seabirds in modern times,the concentrations and nitrogen isotope values of ammonium in surface soil were very high,and the nitrogen isotope values in plant foliar were also very high,which may be related to human activities.Therefore,with the increasing of human activities on Xisha Islands,the influence of artificial nitrogen sources on the nitrogen cycle in Xisha Islands deserves more attention.3.The impact of seabird biological transportation on phosphorus cycling in the East Antarctic lakesThere are a large number of penguin colonies in the ice-free regions of Antarctica,and penguin guano is enriched in phosphorus and some other nutrients,which have significant impacts on the surrounding terrestrial and aquatic ecosystems.In this study,we reported the P fractions distribution characteristics and their influencing factors,the potential of P release,as well as dynamic process of P cycle in four lacustrine sediment cores from Inexpressible Island,Ross Sea region,East Antarctica.Using chemical sequential extraction and solution-state 31P NMR analysis,five P forms and specific organic P(OP)structure were identified.The results showed that inorganic P(IP)was the main form in these four lacustrine sediment cores and the proportion of OP was relatively low.Iron/aluminum-bound P(Fe/Al-P)was the predominant form of P in the ornithogenic sediments.Guano input significantly enhanced the amount of bioavailable P(BAP)in the sediment and water.The high input of algae(microbial mats)in the ponds obviously increased the amount of OP,resulting in the increase of P releasing potential in the sediments.All the results suggest that the predominant factor influencing P content and fractions distribution is the source of sedimentary organic matter.In addition,some environmental factors,such as grain size,pH,and TOC content,may also play an important role.31P NMR spectra revealed that orthophosphate was the main P form in all the sediment samples,and ortho-monoesters was the predominant OP form.However,the signal of ortho-monoesters detected in the sediment samples weakened rapidly with the increase of depth,and this might be related to the mineralization in the deep layer after deposition.4.Seabirds' biological transportation of heavy metals and pollution record on Xisha IslandsIn order to investigate the impact of seabirds' biological transportaion on the heavy metal pollution on Xisha Islands,in this study,the ornithogenic sediment,fish bone residues and modern fish muscle tissues were selected as the main environmental samples,and performed the analysis of heavy metal pollution in combination with the historical and modern processes.A 700-year-old ornithogenic sediment profile was collected from Nandao Island,South China Sea,and fish bone remains were extracted from the sediment,the concentrations of Cu,Zn,Cd,and Hg in the bulk sediments and subfossil fish bones were analyzed to examine the relationship between the seabirds' biological transportation and heavy metal pollution from a historical perspective.The results showed that changes in Cu,Zn,Cd,and Hg concentrations of bulk sediments over time were consistent with that of guano proportion in the ND1 profile,and the peak values of Cu,Zn,Cd,and Hg concentrations of bulk sediment correspond to a period with a large number of seabirds.It shows that the more seabirds there existed,the more heavy metals were transported.The preservation status of historical fish bone samples was analyzed by Fourier transform infrared spectroscopy,the results showed that fish bones from before?1850 CE experienced significant diagenesis due to the erosion of guano in sediment profile,and could not be used to reconstruct historical record of heavy metal pollution,indicating that the impact of guano rich in heavy metals on the environment cannot be ignored.However,the heavy metal concentrations of bulk sediments and well-preserved fish bone subfossil samples after 1850 CE indicated that since then,the heavy metal pollution from human sources has gradually increased on Naodao Island,South China Sea,especially the Zn pollution was more obvious.In addition,the Hg pollution of two main food source of Xisha Island seabirds,flyingfish(Exocoetus volitans)and squid(Uroteuthis chinensis)were analyzed under modern environmental conditions.The results showed that there were significant positive correlations between muscle tissue Hg concentrations and organism size(length and weight),as well as ?15N values,indicating that with the increase of the individual size and the trophic level of seabird food,the concentration of heavy metals in the seabirds body or in the guano may increased,and the habitat of seabirds may have the risk of heavy metal pollution through the biological transportation.5.Distribution characteristics of Cd fractions in ornithogenic soil from AntarcticaCd was selected as the target element,combined with the total amount and different Cd forms to compare the difference of Cd concentrations between the soil affected by penguin guano and the background soil in the East Antarctica.Meanwhile,the distribution characteristics of Cd fractions in the surrounding lacustrine sediments were investigated,and the environmental geochemical process of Cd was preliminarily analyzed.The results showed that the penguin guano input increased the soil Cd concentration,especially the Fe/Mn oxide bound and organic bound Cd,but eventually Cd was mainly preserved in the form of residual form in the ornithogenic soil for a long time.Fractionation analysis of Cd in lacustrine sediments from Inexpressible Island revealed that Cd mainly existed in the residual form in the ornithogenic sediment,indicating that the migration of Cd was inhibited with the increase input of guano.It is worth noting that due to the high concentration of total amount of Cd in the fresh penguin guano,and concentrations of Fe/Mn oxide bound Cd and exchangeable Cd were at high levels and easy to migrate,the Cd pollution associated with seabird transportation should not be ignored. |
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