The Influence Of Aquatic Plants On Travertine Deposition

The method combining hydrochemical automatic data logging, in-situ observation and sampling analysis is used to study the characteristics of aquatic plant diversity and its influence on travertine deposition. The influence of aquatic plants on the hydrochemistry in the travertine pools L1 to L4 with different type of aquatic organism included diurnal and seasonal variation in dry and rainy seasons. At the same time, organic glass substrates are placed in the inlet, midway and outlet of each travertine pool in order to obtain the calcium carbonate deposition, and to understand the controlling mechanism of carbon stable isotope of travertine.It was found that there was difference in bio-community and biomass between selected four travertine pools. The size of biomass was in the order L2>L3>L4>L1. These provide different biologic backgrounds for travertine deposition.The data showed different diurnal and seasonal variations in hydrochemistry among these travertine pools. It was found that water temperature changed remarkably from morning, midday to evening. Corresponding to this, the concentrations of H+, HCO3-, Ca2+, and specific conductivity changed also. In summer rainy season the photosynthesis of submerged aquatic plants enhanced this change, while the root respiration of emergent plants decreased this change.Compared to the pool L1, aquatic plants in the pools L2 to L4 have significant impact on the pH, specific conductivity,dissolved oxygen (DO), saturation index of calcite (SIc), and CO2 partial pressure (pCO2) of the water in these pools because of the increased biomass of aquatic plants in summer rainy season. In travertine pool L2, the root respiration of emerged plants showed effect on the variation of hydrochemistry in both daytime and nighttime. It is estimated that the influence of emerged aquatic plants on the CO2 partial pressure (pCO2) could be 17.28% in all. In the travertine pool L4, the photosynthesis of submerged aquatic plants at daytime produced O2, which reached the maximum (as DO) at 15:00, while respiratory activities at nighttime consumed O2, which reached the minimum during 21:00 to 7:00. It was estimated that the influence of submerged aquatic plants on CO2 partial pressure (pCO2) could be 27.44%. The influence of aquatic plants on hydrochemistry was not found in the pool L3 because of the interruption of the storm events during the field experiment.The field experiment of calcium carbonate deposition showed that the total rate of calcite precipitation is higher than the daytime calcite precipitation rate, the latter being higher than the nighttime calcite precipitation rate. Although the values of D (D= the daytime calcite precipitation rate/ the nighttime calcite precipitation rate) were almost the same for the four pools in winter dry season, they were in the order DL4> DL3> DL2> DL1 in rainy season, showing the influence of aquatic plants on calcite precipitation in summer rainy season, when aquatic plants grow well.It is found thatδ13C values of the calcite deposited on the substrates were lower in rainy season due to the dilution effect by rainwater and overland flow. It was estimated that the influence of aquatic plants onδ13C values of the calcite in the pools L2 to L4 at daytime was 12.88%, 15.59%, 15.93% respectively.In summary, the influence of aquatic plants on travertine deposition (including hydrochemical variation, calcite precipitation rate and carbon stable isotope of travertine) has been examined in this study. Obviously, aquatic plants have showed their important influence on the travertine deposition. However, there exists some difference between submerged plants and emerged ones. All these have implications for the research directions such as mechanisms of karstification, karst-related carbon cycle, formation of karst hydrochemistry, and paleoclimate reconstruction.