02540naa a2200253 a 450000100080000000500110000800800410001910000170006024501070007726000090018452018390019365000170203265000110204965000230206065000160208365000230209965300110212265300150213365300170214870000200216570000180218570000200220377300630222318024522017-03-10       1995    bl ---       0--  u    #d1 aDEVOL. A. H.  aSeasonal variation in chemical distributions in the Amazon (Solimões) riverba multiyear time series.  c1995  aThe results of a 10-year time series study of the chemistry of the Amazon River mainstem near Manaus, Brazil, are presented. All variable measured showed distinct seasonal patterns linked to the discharge hydrograph except respiration rate and PO³4 concentation. Stepwise multiple regression analysis showed that alkalinity, calcium, fine suspended sediment, and sulfate were correlated, primarily, with the percentage of the total water discharge that was derived from Andean drainages. Silicate, potassium, and the weight percentages of carbon and nitrogen in the coarse suspended sediment were correlated with the precentage of water attributable to local lowland drainages. These correlations suggest that seasonal cycles of these variables were particulate carbon, nitrongen, and phosphorus species were controlled by river surface slope, suggesting that the seasonal cycles of these variables were controlled by river turbulence. The biogeochemically active elements O2, CO2, NO3, and SO=4, along with pH, Na, and C1 were all highly correlated with river discharge. The shaoes of the seasonal cycles of O2 and CO2 and much of their amplitude could be reproduced by a quasi steady state model in which respiration was balanced by air-water gas exchange. In the model, increases in river depth during annual cycle result in increased depth-integrated respiration rates. This produces a drawdown of O2 concentration, which increases air-water gas exchange, until the two processes are in balance. Thus the model produces seasonal cycles in which minimum dissolved O2 and maximum dissolved CO2 coencide with high water and the converse at low water, in agreement with the observations. The remainder of the amplitude signal was probably either advected in from upstream or produced by lateral exchange with the fringing floodplain.  aAmazon River  aBrazil  aseasonal variation  aHidrografia  aVariação Sazonal  aBrasil  aHidrograph  aRio Amazonas1 aFORSBERG, B. R.1 aRICHEY, J, E.1 aPIMENTEL, T. P.  tGlobal Biogeochemical Cyclegv. 9, n. 3, p. 307-328, 1995.