Unexpected shift from phytoplankton to periphyton in eutrophic streams due to wastewater influx

Pollution with nitrogen (N) and phosphorous (P) impairs streams by favoring suspended algae cyanobacteria over diatom-rich periphyton. Recently, wastewater treatment plants have been upgraded to biological nutrient removal eliminate both P N (mainly NH4+), although little is known of the effects this effluent on flowing waters. Here, we used high performance liquid chromatography quantify how abundance composition phytoplankton periphyton varied in response influx produced physico-chemical conditions small, turbid, P-rich northern Great Plains. At catchment scale, analysis generalized additive models (GAMs) explained 40.5–62.6% deviance total phototroph (as Chl a) 72.5–82.5% community biomarker carotenoids) planktonic benthic habitats when date- site-specific parameters were as predictors. In contrast, GAMs using input aqueous δ15N) a predictor up 50% a, ~60% composition, (51.6% 67.1% composition) attached communities (21.5% 58.8% composition). Phytoplankton was replaced within 60-km wastewater-impacted reach due dilution transparent addition urban NO3−, predominance re-established after confluence higher-order streams. Overall, shifted phytoplankton-rich clear ecosystems abundant epilithon improving water transparency providing NO3− favor diatoms chlorophytes.