Chesapeake Bay’s “forgotten” Anacostia River: eutrophication and nutrient reduction measures

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

“…) can exert taxon-specific effects on algae (Glibert et al 2016;Solomon et al 2019;Kim et al 2020). Although irradiance regimes affect both suspended and attached phototrophs in flowing waters (Munn et al 1989;Hutchins et al 2010), effects of photon flux vary seasonally with discharge and turbidity (Biggs 1995;Leland 2003), canopy cover (Rosemond et al 2000), nutrient content (Glibert et al 2016), and temperature (Baker and Baker 1979;Munn et al 2002;Wu et al 2011).…”

“…Following experimental evidence that pollution with P caused widespread eutrophication of freshwaters (Schindler 1977; Dodds and Smith 2017), many inland urban centers upgraded wastewater treatment plants in the 1970s to remove P by chemical precipitation, usually as insoluble ferric compounds (Tchobanoglous et al 2003). However, tertiary treatment does not eliminate inorganic N, and toxic levels (40 mg N–NH 4 + L −1 ) of ammonium (NH 4 + ) in effluent (Waiser et al 2011; others) can depress stream production (Waiser et al 2011), while also favoring toxic cyanobacteria (Donald et al 2011; Solomon et al 2019). To address this issue, biological nutrient removal technologies were developed that use sequential microbial nitrification, denitrification, and nutrient uptake to reduce total N by up to 95%, largely eliminate NH 4 + , and release only moderate levels of NO 3 − (<5 mg N‐NO 3 − L −1 ) and P (<1 mg P‐PO 4 3− L −1 ) to surface waters (Carey and Migliaccio 2009).…”

“…Excess nutrients promote phototroph blooms (Chambers et al 2012; Dodds and Smith 2017), as well as changes in community composition (Glibert et al 2016) and habitat of production (Roeder 1977; Wu et al 2011; Breuer et al 2017), with benthic diatoms giving way to chlorophytes and cyanobacteria in suspended (Mischke et al 2011) and benthic communities (Peterson and Grimm 1992; McCall et al 2017). However, nutrient effects should also depend on baseline production and stoichiometry of streams, as low N:P ratios may favor harmful cyanobacteria (Dodds and Smith 2017), while changes in individual chemical forms (e.g., NO 3 − vs. NH 4 + ) can exert taxon‐specific effects on algae (Glibert et al 2016; Solomon et al 2019; Kim et al 2020). Although irradiance regimes affect both suspended and attached phototrophs in flowing waters (Munn et al 1989; Hutchins et al 2010), effects of photon flux vary seasonally with discharge and turbidity (Biggs 1995; Leland 2003), canopy cover (Rosemond et al 2000), nutrient content (Glibert et al 2016), and temperature (Baker and Baker 1979; Munn et al 2002; Wu et al 2011).…”

“…Such seasonal changes also drive patterns of benthic and suspended community development (Andrus et al 2015), with enhanced production of diatoms in spring and fall and elevated densities of chlorophytes and cyanobacteria in summer (Breuer et al 2016; Moorhouse et al 2018). Overall, the degree to which natural phototrophic phenology interacts with effluent influx is poorly understood (del Giorgio et al 1991; Stevenson and White 1995; Solomon et al 2019), particularly for streams in nonboreal systems such as agricultural grasslands (Dodds et al 2004; Breuer et al 2017).…”

“…Phototrophic communities were quantified using taxonomically diagnostic pigment biomarkers (chlorophylls [Chl], carotenoids) to measure: (1) how regional variation in physico‐chemical conditions affected development of phototrophic biomass and community composition; (2) how modern effluent affected phytoplankton and periphyton; and (3) whether urban effluent had a differential effect on suspended or attached communities. We hypothesized that: (1) landscape patterns of abundance, composition and interaction of phytoplankton and periphyton would reflect spatial and temporal variation in regulation by physico‐chemical parameters (discharge, irradiance, temperature) in these eutrophic streams (Breuer et al 2016, 2017; Moorhouse et al 2018); (2) effluent influx would overwhelm natural landscape controls (discharge, irradiance, temperature) of periphyton (Murdock et al 2004; Hamdhani et al 2020) and phytoplankton development (del Giorgio et al 1991; Stevenson and White 1995; Solomon et al 2019); (3) modern urban effluent would favor phytoplankton over periphyton due to both changes in nutrient (Chambers et al 2012; Dodds and Smith 2017) and irradiance regimes (Munn et al 1989; Rosemond et al 2000); and (4) NO 3 − from effluent would favor siliceous algae and chlorophytes over cyanobacteria downstream of wastewater treatment plant outfall (Glibert et al 2016; Swarbrick et al 2019).…”