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

Abstract

Pollution with nitrogen (N) and phosphorous (P) impairs streams by favoring suspended algae and cyanobacteria over diatom-rich periphyton. Recently, wastewater treatment plants have been upgraded to biological nutrient removal to eliminate both P and N (mainly NH 4 +), although little is known of the effects of this effluent on flowing waters. Here, we used high performance liquid chromatography to quantify how the abundance and composition of phytoplankton and periphyton varied in response to both influx of effluent produced by biological nutrient removal and physico-chemical conditions in small, turbid, P-rich streams of the northern Great Plains. At the catchment scale, analysis with generalized additive models (GAMs) explained 40.5-62.6% of deviance in total phototroph abundance (as Chl a) and 72.5-82.5% of deviance in community composition (as biomarker carotenoids) in both planktonic and benthic habitats when date-and site-specific physico-chemical parameters were used as predictors. In contrast, GAMs using wastewater input (as aqueous δ 15 N) as a predictor explained up to 50% of deviance in Chl a, and~60% of deviance in community composition, in both suspended (51.6% of Chl a, 67.1% of composition) and attached communities (21.5% of Chl a, 58.8% of composition). Phytoplankton was replaced by periphyton within a 60-km wastewater-impacted reach due to dilution of streams by transparent effluent and addition of urban NO 3 À , although predominance of phytoplankton was re-established after confluence with higher-order streams. Overall, influx of effluent shifted turbid, phytoplankton-rich streams to clear ecosystems with abundant epilithon by improving water transparency and providing NO 3 À to favor benthic diatoms and chlorophytes.

Improvement of field fluorometry estimates of chlorophyll a concentration in a cyanobacteria‐rich eutrophic lake

“…Although turbidity occasionally enters predictive models elsewhere (Rome et al 2021), to the best of our knowledge, ours is the first model with turbidity as the main parameter that exhibits performance comparable to that of fluorescence‐based models. This finding is consistent with the observation that phytoplankton abundance controls turbidity measures in regional lakes and streams (Dröscher et al 2009; Bergbusch et al 2021), although we recognize that this finding may not apply when nonalgal turbidity is considerable. As turbidity probes are inexpensive, robust, and easy to calibrate relative to fluorometric sensors (Rome et al 2021), the strong performance of the MLR model should be compared to other locations to evaluate the suitability in monitoring phytoplankton blooms.…”

Differential Controls of Greenhouse Gas (CO2, CH4, and N2O) Concentrations in Natural and Constructed Agricultural Waterbodies on the Northern Great Plains

“…This contrasts our previous findings that primary production was not a significant driver of seasonal CO 2 concentrations in constructed reservoirs (Jensen et al., 2022), and may reflect difference in the relative control of autotrophic and heterotrophic control on temporal (Jensen et al., 2022) and spatial scales (this paper). The coupling of near‐surface CO 2 in reservoirs with DOC:NO x ratios, suggests that higher autotrophic activity depletes NO x content in this N‐limited region (Bergbusch et al., 2021; Glibert et al., 2016; Swarbrick et al., 2019; Waiser et al., 2011).…”

Predicting Daily River Chlorophyll Concentrations at a Continental Scale

“…Not only can the benthic algae contribute to productivity, but they can also produce cyanotoxins in rivers (Bouma‐Gregson et al., 2018). Recent research has demonstrated that effluent can shift systems from phytoplankton to periphyton communities (Bergbusch et al., 2021) and not accounting for benthic algae could miss important periods of algal activity in some systems. Adding information on benthic algae would help capture more spatial and temporal variability in stream productivity, water quality, and ecosystem health across streams and rivers.…”