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Precipitation and River Water Chemistry of the Piracicaba River Basin, Southeast Brazil

Michael R. Williamsa, Solange Filosoa, Luiz A. Martinellib, Luciene B. Larab and Plínio B. Camargob

a The Ecosystems Center, Marine Biological Lab., Woods Hole, MA 02543
b Univ. of São Paulo, Centro de Energia Nuclear na Agricultura, Ave. Centenário 303, CEP 13416-000, Piracicaba, SP, Brazil



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  		Fig. 1. Map of the Piracicaba River basin indicating the locations of the stations used for the collection of precipitation and river water samples. Precipitation collection sites are (A) Bragança, (B) Campinas, and (C) Piracicaba. River sampling sites are Bairro da Ponte (1), Morungaba (2), Desembargador Furtado (3), Fazenda da Barra (4), Paulínia (5), Usina Ester (6), Carioba (7), Copersucar (8), Recreio (9), and Artemis (10). Subbasin boundaries are marked by dotted lines.

 


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  		Fig. 2. Monthly precipitation and runoff for Site 10 of the Piracicaba River basin. Long-term records indicate that precipitation and runoff are generally highest from October to March (wet season).

 


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  		Fig. 3. The relationship of storm size to the sum of major solutes (ionic sum) in the precipitation of the three sample collection sites (A, B, and C). Site A, located in a more rural setting than the other sampling sites, has the strongest relationship and commonly lower ionic sum values for equivalent storm sizes at the other sampling sites.

 


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  		Fig. 4. Relationships of river discharge to nitrate concentrations at the 10 river sampling sites of the Piracicaba River basin. Discharge–concentration relationships are generally inverse and logarithmic at upriver locations, and become less discernible at downriver locations. Numbers in parentheses are sampling site locations indicated in Fig. 1.

 



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  		Fig. 5. a. Comparison of inputs (precipitation), outputs (riverine), and the resulting mass balance (net export) of selected major solutes. Values are annual means in Mg yr-1 for the period of study. Numbers are ranked from upriver (1–4 and 9) to downriver (5–8 and 10) sampling sites to show possible trends in river chemistry.

b. Comparison of inputs (precipitation), outputs (riverine), and the resulting mass balance (net export) of selected major solutes. Values are annual means in Mg yr-1. Numbers are ranked from upriver (1–4 and 9) to downriver (5–8 and 10) sampling sites.

 



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  		Fig. 6. a. Residual export of solutes obtained by subtracting background concentrations from an upland catchment stream (Fazenda Bonfim). These values were divided by a silicate modification factor (described in text), which eliminates the effects of dilution, increasing basin area, and runoff on solute export. Values are in Mg yr-1.

b. Residual export of solutes obtained by subtracting background concentrations from an upland catchment stream. These values were divided by a silicate modification factor and are in units of Mg yr-1.

 


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  		Fig. 7. Spearman correlations of major solutes with SiO2 concentrations for six sampling stations along the main stem of the Piracicaba River. Numbers are ranked from upriver to downriver sampling sites to show possible trends in river chemistry. The designation of "Cat" refers to the mean correlation value for Na+, Ca2+, and Mg2+, whereas "An" refers to the mean correlation value for Cl- and SO2-4. SS is suspended sediments. Numbers 1, 3, and 5 are upstream sites, and 7, 8, and 10 are downstream sites.

 


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  		Fig. 8. Trajectories of the rising and falling limbs of the discharge hydrograph in 1995–1996 for selected solutes at Site 8. Rising limbs of the discharge hydrograph are designated by lines, whereas the falling limbs are designated by dashed lines with open circles. Most trajectories at Site 8 are inverse with clockwise hysteresis.

 




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