Evaluation of Phosphorus Loadings to Lake Geneva from the Venoge and Other Rivers, Switzerland

Diplôme Thèse Evaluation of Phosphorus Loadings to Lake Geneva from the Venoge and Other Rivers, Switzerland eng 1988-12-19 author Zhang Li 540824 director Vernet Jean-Pierre 25061 director Thomas Richard Lynn 22008 97 10.13097/archive-ouverte/unige:174806 Sc. 2333 Le phosphore a une influence sur l'eutrophisation des lacs car il a la propriété de favoriser la croissance des plantes aquatiques et notamment des algues. Il est admis, depuis environ 20 ans, que les phénomènes d'eutrophisation sont accélérés par l'excès de charge et d'apport de phosphore et d'azote aux lacs. L'excès de phosphore induit non seulement une augmentation de la biomasse, mais aussi des variations dans la composition de la population phytoplanctonique. Il faut souligner que le phosphore a un effet particulièrement efficace dans les eaux douces. Le phosphore est ainsi un élément limitatif qui joue un rôle important en contrôlant à la fois la quantité et la qualité de la production primaire dans l'écosystème lacustre. Si la charge en phosphore du bassin versant est grande, la concentration en phosphore dans l'eau du lac augmente, ce qui entraîne l'accroissement de la production primaire du lac. (...) In order to monitor annual phosphorus loadings to Lake Geneva from its tributaries, during 1986 and 1987, routine samples were collected at the mouths of the Rhône, Venoge, Aubonne and Promenthouse Rivers, Switzerland. Complementary sampling was undertaken for several storm events during the same years on the Venoge River, a storm dependent system. Soluble reactive phosphorus (SRP), and total soluble phosphorus (TSP) were analysed using filtered or centrifuged waters. Total particulate phosphorus (TPP), organic phosphorus (OP), inorganic phosphorus (IP), apatite phosphorus (AP) and non-apatite inorganic phosphorus (NAIP), as well as other geochemical parameters of the samples were determined on the suspended sediment (SS) <63 μm recovered by centrifugation. The annual low and high flow loads of these phosphorus forms are estimated for each river. The total phosphorus (TP) loads, and in particular, the bio-available phosphorus (BAP) loads of these rivers are compared to assess their contributions to Lake Geneva. The results show that, although, the Rhône River annually transports TP about 29 times and TPP 47 times more than the three small rivers together, the BAP loading from the Rhône River is only 9 times higher than for the three small rivers. The phosphorus influence of these smaller rivers on the lake is important because it is the BAP load rather than the TP or TPP load that determines the response of the lake ecosystem to phosphorus inputs. A digital filter was developed to simulate SS transport behaviour during storm events as a fonction of discharge. The simulation curves of SS concentration for the five sampled events were tested and found to be similar in shape to the measured ones. SS loads estimated by the calculated SS concentrations for these events have a difference, as a whole, of about 11 % from the measured concentrations. Moreover, a progressive regression procedure was developed to relate the estimation of TPP concentration to the SRP and SS concentrations measured for the sampled storm events. This allows estimation of other forms of particulate phosphorus if the TPP concentration is known, based on the simple linear relationships between these phosphorus forms for the Venoge storm samples. The relative error of the calculated TPP from the measured TPP is generally no more than ±10%. These two models provide a means to approximate SS and phosphorus concentrations, and thereby their loadings using discharge and SRP and SS measured during storm events on the Venoge River. The SS and phosphorus loads derived from the models complement the sampling programme as well as resultant load estimates. For example, the 1987 TP load for the Venoge River, estimated using the filter model procedure (23.3 tonnes), is comparable to those assessed with the sampled data (26.8 tonnes) and by CIPEL (20.0 tonnes). Phosphore Léman (lac) Dewey 550 41 Département F.-A. Forel des sciences de l'environnement et de l'eau 153 false 0548ccc4-4388-41a5-90c7-5fe53f42c95f Thesis Public Zhang_these.pdf 44764436 application/pdf Restricted 2088-12-19 786f16a28fc0844821ddd5732be1d7f8f3d40313ef0d921f272d21482c21e595 3e67ccf7-1973-459c-ae97-bc202674d4a0 Imprimatur Public Zhang_imprimatur.pdf 165253 application/pdf fd7477034e7071ba0e3e4661b7e62e1acdc609f6a2feee71613f859060d312b4 embargoedAccess Faculté des sciences / Section des sciences de la Terre et de l'Environnement / Département F.-A. Forel des sciences de l'environnement et de l'eau

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Evaluation of Phosphorus Loadings to Lake Geneva from the Venoge and Other Rivers, Switzerland				1988	216	1

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Zhang, Li