Self‐purification of small freshwater streams: Phosphate, Nitrate, and Ammonia removal

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Abstract
Uptake of stream nutrients by organisms or sediments of the stream bed is affected by the nutrient loading to which the stream is accustomed. In a stream with nutrient‐poor waters, added phosphate and ammonia were removed rapidly and efficiently at water temperatures within the range 4.5–15.0°c on passing over a mat of filamentous algae and trapped sediment. Nitrate was removed less efficiently or not at all. In another stream where nutrients were abundant, phosphate and nitrate from a sewage outfall were not significantly removed by the stream bed flora up to 100 m downstream at summer temperatures. Sodium was used as an inert marker to measure the dilution of added nutrients or sewage effluent by the stream waters; electrical conductivity was rejected as a measure because it is influenced by photosynthesis. Studies of nutrient run‐off should take account of stream‐bed removal when the effects of run‐off on eutrophication of lakes are being considered.