Concentrations Of Heavy Metals And Plant Nutrients In Aquatic Macrophytes Of Yangtse Estuary

Wetland ecosystem has the common ground like other ecosystem, but also has its own particularity since its special location. Aquatic macrophytes in wetland play a important role in element transferring, they always absorb all kinds of elements including plant nutrients and heavy metals from the sediment, water and air. These elements transport and circle in the roots, stems and leaves. With the development of industry, some of cities and factories along the Yangtse River drain the waste water into the river directly without any treatment. The pollution accumulates gradually in the wetland of estuary, and destroys the balance of wetland ecosystem, so the research in elements absorbing by macrophytes is very important to the sustained development.The dissertation was supported by science & technology project: "the nutrient transfer and circle in wetland ecosystem in Chongming Island. The research focus on the plant nutrients and heavy metals transferring and circling in four main macrophytes, and analyze the nutrients and heavy metals transplanting in different part of plant, try to find out the main factor which affect element absorbing most. According to the fieldwork and indoor experiment, the conclusion includes:1. The concentration of heavy metals in all parts of macrophytes is different (C_root> C_leaf > C_stalk), most of the heavy metals centralized in the roots of plants, and the percentage of total heavy metals in Phragmites australis (LW) and Spartina alterniflora Loisel (HHM) is above 50%, which is significant to transfer the heavy metals from the wetland through reaping the plants. Whilst heavy metals in Scirpus mariqueter (SB) and S. triqueter (B) transfer upward less, at last, it deposits and accumulates in the sediment.2. LW is partial to Ni, then Cr, Pb, and Cd, it proved that the capability of absorption to Ni is strongest; but the concentration in SB and B is diverse with the different sampling place, in south bank of Yangtse, the capability of absorption is: Pb>Ni>Cr>Cd, whilst in the bank of Chongming Island, it shows: Ni>Pb>Cr>Cd, which means Ni and Pb is the favorite heavy metals. HHM absorb and accumulate Ni most, then Cr, Pb and Cd.3. Different aquatic plants show different absorption profile, in the same period, the absorption of HHM to Cd, Pb, Ni and Cr is stronger than other plants, for example, in summer, the average accumulation of LW, B and HHM to Pb is 1.01mg/kg, 1.8mg/kg and 2.37mg/kg respectively. The transferring ability of HHM is strongest among four analyzed plant.4. The plant nutrients in macrophytes are different with the change of sampling periods and sites, generally, there are obvious rules in plant nutrients absorption: the concentration of three major nutrients (N, P and K) increase with the height of different parts: C_leaf>C_stalk>C_root, and these elements are easy to transport in aquatic plants. According to the average concentration of N, P and K, the correlation among them isn't obvious. In root, the difference of K is very little, but the change of concentration value is more resemble. The concentration of Ca and Mg is lower than that of N, P, K, whose rule is the same as heavy metal, the concentration is highest in the roots, and lowest in the leaves.5. Different aquatic plants have their own favorite element. For LW, the concentration of nutrients is: C_K>C_p>C_N>C_Ca>C_Mg; For HHM, which is more complicated, the range in roots is: C_K>C_ca >C_p>C_n >C_Mg, the range in stalk is C_k> C_p>> C_n C_Ca >C_Mg, the range in leaf is C_k >C_p>C_n>C_Mg>C_ca; the concentration range of B is also diverse in different parts. It proves B and HHM like Ca most, and P is the favorite of B as well.6. The interaction among the nutrients is weak, there is no obvious correlation among most of plant nutrients in roots according to the nutrients concentration in roots. But the Ca concentration of LW is positive correlated with P and Mg. In stalks, most of nutrients is positive correlated, but that is not significant in leaves.7. The correlation among heavy metals is obvious, especially between the necessary metals for the macrophytes. But the experiment indicates there is different correlation in the parts of all kinds of aquatic plants. In roots, the correlation of LW and B among heavy metals is stronger than that of stalks. But in leaves, that shows other trend, the correlation is not significant.8. The plant nutrients affect heavy metals absorption. In roots, K, Ca and heavy metals are correlated significantly. The experiment also indicates that K inhibits heavy metals absorption, they are negative correlated. But Ca is positive correlated with heavy metals. Otherwise, the correlation in stalks and leaves between nutrients and heavy metals is not significant.9. Fe, Ni and Cr are difficult to absorb by B and LW, otherwise, they can absorb Cd, Cu, Pb and Zn easily, especially to Cd. In autumn, the rate of transportation of LW is higher than other analyzed plants, most of them are above 1, which shows the transportation of LW to heavy metals is apparently stronger than others.