ISSN:
1573-5117
Keywords:
Bangladesh
;
deepwater rice
;
Photosynthetically Active Radiation
;
water chemistry
;
oxygen
;
phosphate
;
sediments
Source:
Springer Online Journal Archives 1860-2000
Topics:
Biology
Notes:
Abstract This introduces a series of five papers describing physical, chemical and biological features of Bangladesh deepwater rice-fields. Flooding occurs typically from late June to early November. There were two distinct flood peaks (late July, mid-September) at the two main research sites during each of the years 1981–86, with maximum depths reaching about 1.5–2.0 m. Temperature showed a narrow range, with values for the upper part of the water column during July–October seldom outside the range 29–35 °C. Data for PAR (Photosynthetically Active Radiation) obtained with two types of sensor (4 π and cosine) are summarized, with examples of profiles and changes throughout the day. Water chemistries sampled from 13 different locations at various times during 1981–1983 are compared for: conductivity, pH, total alkalinity, O2, major metals (Na, K, Mg, Ca, Mn, Fe), minor metals (Co, Ni, Cu, Zn, Cd, Pb), NH4-N, NO2-N, NO3-N, filtrable reactive P, filtrable organic P, non-filtrable P, Cl, SO4-S, reactive-Si. Overall the concentrations of aqueous N and P may be regarded as providing a mesotrophic environment for algae, but with relatively low N : P. Filtrable organic P was at least as important as filtrable reactive P, with mean values at the various locations from 0.020 to 0.036 mg l−1 P for the former and 0.005 to 0.038 mg l−1 for the latter. Measurements of N and P in the water column at any one time typically gave values (expressed per unit area) slightly lower than totals for these elements deposited in sediments throughout the whole season. At least until the end of September, the upper part of the water column was almost always oxic during the daytime and occasionally supersaturated with O2 in the afternoon. However DWR fields in south Bangladesh (Phaltita) visited on a sunny day in late September had waters which were almost entirely anoxic even in the afternoon: channels were lacking here and rotting rice stems from an earlier crop were widespread.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1007/BF00007929
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