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Residual Nutrient Discharge in Streamwaters Influenced by Sewage Effluent Spraying

Perkins, Michael A., Goldman, Charls R., Leonard, Robert L.
Ecology 1975 v.56 no.2 pp. 453-460
absorbance, algae, basins, forest litter, lakes, long term effects, nitrates, photosynthesis, primary productivity, sewage effluent, spraying, streams, watersheds
The disposal of secondary sewage effluent on a subalpine forest floor was investigated in terms of its relationship to nutrient discharge in a Tahoe basin watershed. Heavenly Valley Creek showed significant increases in NO₃ — ¹—N and ultraviolet absorbance downstream form a site that had been used for land disposal 5 yr prior to this study. These increases were traceable to subsurface discharge from the sprayed area. Evidence indicated that substances present in the spray area discharge and the streamwater are inhibitory to algal photosynthesis at in situ concentrations. This effect may be due in part to NO₃ — ¹—N which undoubtedly becomes stimulatory through dilution in the lake. Discharge from the spray area can be traced into Lake Tahoe by following patterns of UV absorbance which correlate closely with patterns of primary productivity. This correlation, combined with estimates of continuing heavy NO₃ — ¹—N loading of Lake Tahoe by Heavenly Valley Creek, reveals the long—term impact of land disposal of effluent on the ultra—oligotrophic lake.