| Macrobenthic invertebrates play an important role in maintaining the sustainable stability of the estuarine ecosystem as vital primary consumers and secondary producers in the intertidal wetland ecosystem. Studies on the micro-scale spatial distribution patterns of macrobenthic invertebrates in the tidal wetlands have not been reported up to now at home and abroad. Most of studies on the toxic contaminants accumulated by marine invertebrates are presented only on the whole body level. Besides, there is no discussion on the ecological economic values of an animal as yet. Studies on the ecological economic values of wetland ecosystems must be based on the precondition of completely understanding the ecological economic values of macrobenthic invertebrate dominant species in tidal wetland. So, it is necessary to study the distribution, environmental benefit and related aspects of a dominant species in the tidal wetland at first before we began to work over assessments on the ecological economic value of the wetland ecosystem. Based on these research background, Bullacta exarata, which constitutes an ecological significant component as a dominant and representative resource species which distributes widely in the tidal flat ecosystem of the Yangtze Estuary was selected as the experimental animal in this paper which mainly focuses on the studies of the spatial distribution, accumulation characteristics of heavy metals and ecological economic values of B. exarata. The main results of this paper are provided as follows: 1. Spatial distribution of B. exarata population Based on the data(including gridding data of the densities) of the densities of the investigation on B. exarata population in the Yangtze Estuary, macro-and micro-scale spatial distribution pattern of B. exarata population were analyzed and discussed with classic statistics(Tayor's power law, Iwao's patch regression, Morisita index and congregation) and geostatistics. The densities of B. exarata population in summer are different significantly from each other at eight sample sites in the Yangtze Estuary(F=42.52>F0.01(7,32)=3.26,P<0.01). B. exarata population in the Yangtze Estuary mainly distribute with negative bionomial distribution which are influenced comprehensively by three main factors, which are land reclamation, environmental pollution and the difference of natural conditions between the tidal flats in Nanhui and islands. The densities of B. exarata population in four seasons in Nanhui tidal flat differ from each other with the highest densities in summer and the lowest in winter. The results by analysis with geostatistics showed that the spatial patterns of B. exarata population in four seasons(spring, summer, fall and winter)in Nanhui tidal flat could be simulated with linear, spherical, spherical and exponential semivariogram models. The models with various parameters given in the paper suggested that the spatial heterogeneity of B. exarata population was significant different between seasons. The spatial heterogeneity of B. exarata population aroused by spatial autorelated factors in summer, fall and winter are 81%, 75% and 72.1% respectively. Population characteristics, the relationship between species and natural environmental conditions are main factors which affect comprehensively the micro-scale spatial distribution patterns. Moreover, the other factors also strongly influence the micro-scale spatial distribution patterns of B. exarata population, such as human-catching, the differences of micro-landforms, size composition of sediments and nutrient distribution caused by hydrodynamic conditions, salinity, storm tides, temperature and benthic diatom, and so on. 2. Accumulation characteristics of heavy metals of B. exarata Based on the determinations and analysis of the concentrations of eight heavy metals(Zn, Cu, Cr, Fe, Mn, Cd, Pb and As) in B. exarata, surface water and sediments, food in the stomach , and Metallothionein(MT) in B. exarata (Combined with silver saturation) by ICP—AES, this paper mainly and systematically focuses on the accumulation characteristics of eight heavy metals. The results indicate that: On the conditions of the concentrations of surface water and sediments different from each other significantly (CV%33.0-124.2% for surface water, 18.3-109.6% for sediments), accumulation characteristics of eight heavy metals by B. exarata differ significantly from each other with element-and species-specific difference. B. exarata accumulated heavy metals(Zn,Cu,Fe and Mn) exceed other four metals by at least one order of magnitude or more. The order of the accumulation levels of eight heavy metals in B.exarata is Fe>Mn>Cu>Zn>As>Cr(Cd or Pb) which can be divided into three groups according to the order of magnitude of their mean concentrations as follows: 1(Cr, Cd, Pb and As) , 10(Zn and Cu) and 102-103μg/g DFW(Fe and Mn). The linear relationships of the concentrations between Zn and Cu, Zn and Cr, Cu and Cd, Mn and Fe, Mn and Cd, and Mn and Pb in B. exarata are positive autorelated significantly(r>0.55, P<0.05). However, the linear relationships of the concentrations between Zn and Pb, Cu and Pb, As and Cu, As and Mn, As and Cd , As and Pb, and Cr and Cd in B. exarata are negative autorelated(r <0) with insignificantly different. The relationship of the concentration between As and other metals in B. exarata is not significant different at all. It indicates that it has independent accumulation behavior B. exarata. In addition, the linear relationship between Cd concentrations in B. exarata and in sediments is very significant. The linear equation is [Cd]B=0.9492 + 0.6604*[Cd]S(r=0.6721, F(1,14)=11.53, P<0.01). The concentrations of heavy metals in the body parts of B. exarata is different significantly from each other (P<0.001). The highest macro-concentration body parts of heavy metals are interface parts of body exposed to environment (mantle and gill), and visceral mass(liver and hermaphrodite gland). In general, the concentrations in other body parts are lower than the above body parts, such as egg-winding gland, foot and shell. The concentrations in calcified body parts are lower than the non-calcified ones. Liver with highest Cd and MT concentrations is the most important body parts for Cd detoxification in B. exarata. The characteristics of hermaphrodite accumulating highest concentration of detoxificated Pb, shell acting as stable regulatory and removal organ of heavy metals (especially for Mn), foot with the highest percentage of Cu gross are different significantly from other marine gastropods and molluscans. B. exarata accumulates and regulates six of eight heavy metals(except Zn and Pb) by exponential functions with obvious size effects and element-specific difference. Of all metals analysed in this paper, the concentrations varied significantly(P<0.05) with the dry fresh weight(DFW) of B. exarata, decreasing for Cr,Fe,Mn,As, increasing for Cu and Cd. Meanwhile, the concentration of MT in B. exarata also increases with DFW increase by exponential function. It indicates that the regulatory and accumulation capacity of B. exarata varied significantly with the increase of DFW. The concentrations of six of eight heavy metals(Zn,Fe,Mn,Cd,Pb,As) in B. exarata in productive periods, which are mainly accumulated in...
|
PDF Full Text Request