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Chemical evidence of water movements in the deepest part of Lake Leman (Lake Geneva) (1991)

Meybeck, M. ; Blanc, P. ; Moulherac, A. E. ; [et al.]

Springer

Aquatic sciences 53 (1991), S. 273-289

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ISSN: 1420-9055

Keywords: Bottom waters ; lake dynamics ; dissolved oxygen ; silica

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract Regular surveys of bottom water chemistry (SiO2, O2, Fe, Mn) have been carried from 1978 to 1986 in the deepest 30 m of Lake Léman (max. depth 309 m) including interface waters sampled with a Jenkins Mortimer corer. When compared to normal chemical gradients near bottom, i.e. O2 decrease and SiO2 increase, three types of anomalies (lens, interface, and behaviour) have been observed on O2 and SiO2, the most sensitive chemical species. These anomalies were found throughout the year, in several stations of the deepest part of the lake and even along the slope of the lake basin. Major anomalies (ΔO2 + 3 to 10 mg ·l−1; ΔSiO2 -1 to 2 mg·l−1) were generally found at the sediment water interface and may extend 10–20 m above the sediment and last 10 weeks. Others marked lens anomalies could be observed for 3 to 4 months. Several mechanisms are probably responsible for this injection of surface waters along the lake slope (accumulation of turbid water on lake banks after severe windstorms; river density currents due to temperature and/or turbidity difference with lake waters). These water-inputs do not represent important volumes (≤ 1% total lake volume) but, when occuring at the interface, they ensure a sufficient oxygen level to prevent diffusion of phosphate and ammonia from pore waters when winter lake overturns do not reach bottom layers (from 1972 to 1980). Complete overturns, as observed in 1980/81, are connected with major interface anomalies (bottom O2 moves up from 2 to 10 mg·l−1) occuring before surface mixing reaches the deepest layers.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1007/BF00877137

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Spatial and temporal variability of Total Suspended Solids in the Seine basin (1999)

Meybeck, M. ; Idlafkih, Z. ; Fauchon, N. ; [et al.]

Springer

Hydrobiologia 410 (1999), S. 295-306

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ISSN: 1573-5117

Keywords: Total Suspended Solids ; space variability ; statistical distribution ; Seine river

Source: Springer Online Journal Archives 1860-2000

Topics: Biology

Notes: Abstract We analyze the TSS distribution over the whole Seine basin (67 500 km2, stream order 8) from: 1. a set of 236 stations sampled quaterly to bimonthly from the french national water quality monitoring network over the 1971–1997 period, 2. four stations sampled daily over 3 and 4 years located on stream orders 1, 5, 6 and 8, 3. a weekly survey of the exceptional 1994/95 high water stage at 4 stations upstream and downstream of Greater Paris (10 M. people). Due to very low relief and even rainfall distribution over the year, the Seine and its river network from order 3 to 8, are characterized by very low TSS: 79% of medians (C50%) are between 8 and 32 mg l-1 and maximum TSS barely reach 300 mg l-1. Due to similar relief distributions, runoff patterns and geology in all sub-basins, major tributaries have near-identical long-term TSS regimes and seasonal variations during the 1994/95 flood stage. Second order TSS variations are linked to lithology: streams draining argillaceous and marl terrains are up to 3 and 4 times more turbid than those draining limestones and chalks. Basin size was also tested: the TSS range (quantiles C1% to C99%) decreases from order 1 to 8, and quantiles levels C10% to C75% double from order 3 to 8. Human impacts on TSS levels are quite limited: Greater Paris influence on longitudinal profiles is not observed; in periurban streams, where population density reach 1000 p km-2, TSS levels are twice those observed in rural conditions (40 p km-2): C75% are 32 ± 12 and 17.5 ± 9 mg l-1, respectively. In orders 6 to 8, the lower TSS quantiles (C10% and C25%) are higher than in orders 3 – 5, this can be attributed to eutrophication and/or to an important fluvial traffic. No significant trend was observed on the TSS distributions at the river mouth from 1971 to 1997. Comparison with a previous daily survey in 1863–1866 showed present marked decrease of average TSS and TSS yearly range attributed mostly to locks.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1023/A:1003712032230

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