HR: 11:45h
AN: B52A-06    [Abstracts]
TI: Studying coupled hydrological and micro-biological processes by means of tracer injections and mathematical models
AU: * Worman, A
EM: anders.worman@bt.slu.se
AF: Dept. iof Biometry and Engineering /SLU, P.O. Box 70 32, Uppsala, S-750 07 Sweden
AU: Kjellin, J P
EM: johan.kjellin@bt.slu.se
AF: Dept. iof Biometry and Engineering /SLU, P.O. Box 70 32, Uppsala, S-750 07 Sweden
AU: Lindahl, A
EM:
AF: County Government of Vastra Gotaland, Sweden, Drottninggatan 2 , Vanersborg, S-462 82 Sweden
AU: Johansson, H
EM:
AF: SLU, Box 7032, Uppsala, S-750 07 Sweden
AB: To throw light on coupled hydrological, chemical and microbiological processes in treatment wetlands, this study uses both radioactive water and reactive tracers. A tracer mixture consisting of tritiated water, P-32 in the form of PO4- and N-15 in the form of N2O was injected to the 2.6 hectare large Ekeby wetland, Sweden. From the breakthrough curves of tritium, the mean residence time of water in pond 1 can be estimated to be about 3 to 3.5 days. The total injected activity of phosphorus was 17.98 GBq and about 13.73 GBq was recovered at the outlet during the investigation period ending 10 days and 16 hours after the start of the injection. This implies that 24% of the phosphate solution was removed in the November - December period in which the experiment was performed. The total injected amount of N-15 was 42.1 grams and 29.6 grams was retained at the effluent. This means that 30% of the nitrogen was either retained in the wetland or removed due to denitrification. An analysis of regular monitoring data shows that the annual removal rate in the entire wetland (each flow line passes two ponds in series) is about 50% for total phosphorus and 25% for total nitrogen. Probably, the most important mechanism for this removal is adsorption onto particulate matter and deposition. Analyses of vegetation material indicate that a certain (minor) fraction was adsorbed to submersed and emerging macrophytes, like Elodera Canadensis, Thypa sp. (Cattail) and Glyceria sp. (Manna grass). A 2D mathematical model for both water flow and solute transport could explain the N-transport through the wetland. The model accounts for the rate-limited exchange with bed sediments and denitrification in the water and bed sediment. Independent batch tests indicate a particularly high microbiological activity in the bed sediments. The rate-limited exchange with the bed limits also the denitrification capacity of the wetland.
DE: 1719 Hydrology
DE: 1871 Surface water quality
DE: 4840 Microbiology
SC: Biogeosciences [B]
MN: 2005 Joint Assembly