The Diurnal Variation of the Gaseous Constituents of River Waters

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Abstract
Continuous variation is recorded throughout the 24 hrs. in the pH and dissolved O and ammonia-cal N of the waters of the Itchen (Hampshire) and the Lark (Suffolk) rivers. O, which is produced by photosynthesis, rises shortly after sunrise to a maximum soon after mid-day and then falls to a minimum which lasts through the night. The quantity and class of plants present in the river also influences the value of the maxima and minima. The highest values are attained during the heavy growth of diatoms in spring and to a less extent in autumn. Maximum values just exceeding saturation occur during the other spring and summer mo. In winter a maximum value near saturation is attained on bright days in the Itchen where Phanerogams occur in nearly as great quantities in winter as in summer. The brighter the day the longer the O remains near a maximum. The mean temp. chiefly affects the minimum values, which vary inversely as the temp. Greater variations are recorded for the Lark, which is slow-flowing and has a bed consisting of quantities of organic mud, than for the Itchen which is fast-flowing and has a bed of stones and plants. The Lark is also heavily polluted Sept.-Jan., and this interferes with the continuity of the results. The pH value varies in a similar way to O owing to the absorption of CO2 in photosynthesis. Ammoniacal N variation is significant only in the Lark, where it rises very rapidly when O content is low and falls with equal suddenness when the O is rising.

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