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Fig. 6. Seasonal changes in malodor indicator compounds in manure slurries of the two-stage phototrophic lagoon system. (A) p-Cresol (2-methyl phenol) (
,
) and 4-ethyl phenol (•,
). (B) Phenol (
,
) and indoles (indole + 3-methyl indole 
,
). Open symbols, two-stage first phototrophic lagoon (TS1PL); solid symbols, two-stage second phototrophic lagoon (TS2PL). Values are the averages of two samples for each lagoon, and the coefficient of variation over all sampling times was about 5%. A similar profile was observed for the single-stage phototrophic lagoon (SSPL) system (data not shown).
