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1.
The influence of contrasting suspended particulate matter transport regimes on the bias and precision of flux estimates 总被引:2,自引:0,他引:2
Moatar F Person G Meybeck M Coynel A Etcheber H Crouzet P 《The Science of the total environment》2006,370(2-3):515-531
A large database (507 station-years) of daily suspended particulate matter (SPM) concentration and discharge data from 36 stations on river basins ranging from 600 km(2) to 600,000 km(2) in size (USA and Europe) was collected to assess the effects of SPM transport regime on bias and imprecision of flux estimates when using infrequent surveys and the discharge-weighted mean concentration method. By extracting individual SPM concentrations and corresponding discharge values from the database, sampling frequencies from 12 to 200 per year were simulated using Monte Carlo techniques. The resulting estimates of yearly SPM fluxes were compared to reference fluxes derived from the complete database. For each station and given frequency, bias was measured by the median of relative errors between estimated and reference fluxes, and imprecision by the difference between the upper and lower deciles of relative errors. Results show that the SPM transport regime of rivers affects the bias and imprecision of fluxes estimated by the discharge-weighted mean concentration method for given sampling frequencies (e.g. weekly, bimonthly, monthly). The percentage of annual SPM flux discharged in 2% of time (Ms(2)) is a robust indicator of SPM transport regime directly related to bias and imprecision. These errors are linked to the Ms(2) indicator for various sampling frequencies within a specific nomograph. For instance, based on a deviation of simulated flux estimates from reference fluxes lower than +/-20% and a bias lower than 1% or 2%, the required sampling intervals are less than 3 days for rivers with Ms(2) greater than 40% (basin size<10,000 km(2)), between 3 and 5 days for rivers with Ms(2) between 30 and 40% (basin size between 10,000 and 50,000 km(2)), between 5 and 12 days for Ms(2) from 20% to 30% (basin size between 50,000 and 200,000 km(2)), 12-20 days for Ms(2) in the 15-20% range (basin size between 200,000 and 500,000 km(2)). 相似文献
2.
Hylander LD Meili M Oliveira LJ de Castro e Silva E Guimarães JR Araujo DM Neves RP Stachiw R Barros AJ Silva GD 《The Science of the total environment》2000,260(1-3):97-107
Sediments from nine floodplain lakes in Pantanal were analyzed for a large-scale (300 km) survey of mercury (Hg) load in sediments and soils of the Alto Pantanal and to study the relationship between Hg and reactive aluminum, iron, and manganese oxy-hydroxides. The results were compared with the Hg content in river and stream sediments from the Poconé gold mining area, where Hg has been extensively used and still is in use. The results indicate that the Hg concentrations were elevated in river sediment close to the mining area in Bento Gomes river basin (average in the < 74-microm fraction 88.9 ng Hg g(-1) dry wt.; interquartile range 50.3-119.5), but there was no clear indication that the local Hg emissions have contaminated the remote floodplain lakes, where concentrations were surprisingly low (average in the < 74-microm fraction 33.2 ng Hg g(-1) dry wt. sediment; interquartile range 18.4-46.8), in particular when considering geochemical characteristics of the sediment. The sediment from the floodplain lakes contained less Hg-tot and more reactive iron oxy-hydroxides than soils from the Tapajós area in the Amazon basin. This resulted in a mass ratio between Hg and amorphous oxy-hydroxides of only 5 x 10(-6) for Hg-tot/Fe-oxa (interquartile range 3-7 x 10(-6). 相似文献
3.
Multivariate analysis procedures have been used to trace possible correlations between changes in the composition of particulate organics and changes in the ratios of trace metal contents of suspended matter present in two major sedimentation basins of the river Rhine. In both basins, seaward gradients are observed in the organic characteristics as well as in the trace metal “patterns”. These two phenomena are well correlated. For both basins the changes in the two types of characteristics can be explained by simultaneously operating processes of sedimentation, autochthonous production and sediment resuspension. 相似文献
4.
Thi Ha Dang Alexandra Coynel Didier Orange Henri Etcheber 《The Science of the total environment》2010,408(20):4654-4664
The Red River (China/Vietnam, A = 155,000 km²) is a typical humid tropics river originating from the mountainous area of Yunnan Province in China. Based on information on daily discharge (Q) and suspended particulate matter (SPM) concentration between 1960-2008 for the SonTay gauging station (outlet of the River and entry to the Delta) provided by the National Institute IMHE-MONRE, the mean annual SPM flux was estimated at 90 Mt/yr, corresponding to a sediment yield of 600 t/km²/yr. The temporal variability of annual SPM fluxes (ranging from 24 to 200 Mt/yr) is strongly related to the interannual hydrological conditions. However, some years of high water flow were not associated with high sediment fluxes, especially after 1989 when the HoaBinh dam came into operation. Therefore, the median discharge pre- (3389 m3/s) and post 1989 (3495 m3/s) are similar indicating there was little or no change between both periods. Sediment rating curves (power law-type; SPM = aQb) were fitted for both periods (1960-1989; 1990-2008). The analysis of the pre- and post-1989 sediment rating parameters (a, b) suggests a downshift of b-parameter values after 1989, attributed to a decrease of the sediment supply due to the commissioning of the HoaBinh dam. A single sediment rating curve derived from 1960-1989 data was used to simulate the annual variability of former sediment delivery, generating excellent cumulative flux estimates (error ~ 1%). In contrast, applying the same rating curve to the 1990-2008 data resulted in systematic and substantial (up to 109%) overestimation. This suggests that the HoaBinh dam reduces annual SPM delivery to the delta by half, implying important metal/metalloid storage behind the HoaBinh dam. 相似文献
5.
Hanna-Kaïsa Saari Patrice Castaing Benoît Sautour J. Kirk Cochran 《The Science of the total environment》2010,408(20):4784-4794
The short-lived natural radionuclides 7Be (T1/2 = 53 days), 234Thxs (T1/2 = 24.1 days) and 210Pbxs (T1/2 = 22.3 years), i.e. 234Th and 210Pb in excesses of that supported within particles by the decay of their parent isotopes, were analysed in suspended particulate matter (SPM) to study the particle dynamics in the Gironde fluvial estuarine system (France), strongly impacted by heavy metal pollution. From surveys of this land-ocean interface in 2006 and 2007, we established a times series of these radioisotopes and of their activity ratios (7Be/210Pbxs and 234Th/210Pbxs ARs) in particles sampled under different hydrological conditions.The particulate 7Be/210Pbxs AR varies along the fluvial estuarine system mainly due to variations in 7Be activities, controlled by riverine, oceanic and atmospheric inputs and by resuspension of old 7Be-deficient sediments. These processes vary with river discharge, tidal cycle and season. Therefore, seasonal particle transport processes can be described using variations of the SPM 7Be/210Pbxs ARs.During high river discharge, the SPM 7Be/210Pbx ARs decrease from river to the ocean. The turbidity maximum zone (TMZ) is dispersed and the particles, and the associated contaminants, are rapidly transported from river to coastal waters, without significant retention within the TMZ. During low river discharge, the TMZ intrudes into the fluvial estuary, and the lowest 7Be/210Pbx ARs are observed there due to resuspension of 7Be-deficient sediments. Away from the TMZ, from the middle to lower estuary, SPM 7Be/210Pbx ARs increase, indicating that the particles have been recently tagged with 7Be. We explain this trend as being caused by marine input of dissolved radionuclides, as traced by SPM 234Th/210Pbxs ARs, followed by scavenging in the estuary. This result indicates that particle transport models based on 7Be and trace-metal budgets must consider oceanic dissolved inputs as an additional source of 7Be and, possibly, of contaminants to estuaries. 相似文献
6.
Daily measurements of water discharges and suspended particulate matter (SPM) concentrations and monthly analyses for arsenic were conducted from 1999 to 2005 on the Garonne, Dordogne and Isle Rivers, the three main tributaries of the Gironde Estuary, France. Despite the known historical polymetallic pollution affecting the Lot-Garonne River system, the highest As concentration level was observed in the Isle River. This was explained by the geological context and various Au/As deposits in this watershed. In the three studied rivers, dissolved As concentrations showed important seasonal variations with maximum values in summer. The dissolved As concentrations were closely related to water temperature and their increase in spring/summer appeared to be induced by water temperatures above approximately 15 degrees C, independently from discharge. The reduction of As(V) to more soluble As(III) and/or destruction of solid As carrier phases by micro-organisms could explain this observation, suggesting that temperature-dependent biogeochemical processes play an important role in controlling As partition and speciation in fluvial systems. Water and SPM fluxes in the Garonne River mainly control arsenic inputs into the Gironde Estuary and the downstream coastal zones. Based on the present data, we propose an empirical model to roughly estimate the annual dissolved and particulate As fluxes in the Garonne, Dordogne and Isle Rivers from annual water and SPM fluxes. The comparison of observed As fluxes and those estimated from the empirical model suggests that resuspension of historical, polluted reservoir sediments during a major flood accounted for approximately 50% of the annual As fluxes in 2003. 相似文献
7.
The overflow frequencies of combined sewer systems (CSSs) along Suzhou Creek in Shanghai are definitely lower compared with low interception ratio and design expectation. This noteworthy phenomenon was analysed and the results indicate that large sewer storage capacity due to a dense interconnection between sewer systems, flat pipe slope and pump drainage pattern, as well as the spatial–temporal difference of rainfall on a large catchment that is integrated by the connected network, lead to the overflow frequencies of combined sewer overflows (CSOs) along Suzhou Creek that are much less than those of designed and of Japanese counterparts. The drainage hydraulic model was used to simulate the performance of typical CSSs in Shanghai centre area to further explain the phenomenon. Meanwhile, as separate systems have serious illicit connections and are subject to heavy wet weather pollution in Shanghai, separate systems did not show the expected advantage in nonpoint pollution control. Thus, keeping old CSSs in the Shanghai downtown area seems to be of great value with respect to the control of urban non-point pollution. 相似文献
8.
Arne Marian Leitte Cristina Petrescu Matthias Richter Romanita Ionovici Uwe Schlink 《The Science of the total environment》2009,407(13):4004-4011