Elevated ammonium concentrations from wastewater discharge depress primary productivity in the Sacramento River and the Northern San Francisco Estuary

Abstract

a b s t r a c tPrimary production in the Northern San Francisco Estuary (SFE) has been declining despite heavy loading of anthropogenic nutrients. The inorganic nitrogen (N) loading comes primarily from municipal wastewater treatment plant (WTP) discharge as ammonium (NH 4 ). This study investigated the consequences for river and estuarine phytoplankton of the daily discharge of 15 metric tons NH 4 -N into the Sacramento River that feeds the SFE. Consistent patterns of nutrients and phytoplankton responses were observed during two 150-km transects made in spring 2009. Phytoplankton N productivity shifted from NO 3 use upstream of the WTP to productivity based entirely upon NH 4 downstream. Phytoplankton NH 4 uptake declined downstream of the WTP as NH 4 concentrations increased, suggesting NH 4 inhibition. The reduced total N uptake downstream of the WTP was accompanied by a 60% decline in primary production. These findings indicate that increased anthropogenic NH 4 may decrease estuarine primary production and increase export of NH 4 to the coastal ocean.

The effect of inorganic nitrogen speciation on primary production in the San Francisco Estuary

“…Yoshiyama and Sharp (2006) examined a 26-yr dataset form the Delaware estuary and observed a "striking decline in production at NH 4 levels above a low threshold (10 mmol L À1 ) suggesting a strongly negative influence of NH 4 itself, or something that accompanies high NH 4 concentrations, or both". Depression of primary production and phytoplankton NH 4 uptake was recently reported for the Sacramento River, immediately downstream of the Sacramento Regional Wastewater Treatment Plant (SRWTP) (Parker et al, 2012). Suisun Bay chronically experiences high ambient NH 4 concentrations with 90% of NH 4 in Suisun Bay originating at the SRWTP (Jassby, 2008).…”

“…10 mmol N L À1 ) conditions and relatively low rNH 4 (ca. 0.10 mmol N L À1 h À1 ) characteristic of the northern SFE Dugdale et al, 2007;Parker et al, 2012) all minimize the potential impact of NH 4 regeneration on isotope dilution. Assuming an initial 15 N isotopic enrichment of 10% and NH 4 regeneration equivalent to uptake (0.1 mmol N L À1 h À1 ) the isotope enrichment would be reduced to 9.80% after 4-h resulting in an understate of NH 4 uptake by 2% (Dugdale and Wilkerson, 1986).…”

Impact of atypical ammonium concentrations on phytoplankton abundance and composition in fresh versus estuarine waters

“…which can grow at a concentration of 3000 µmol NH 4 + l −1 in culture without experiencing growth inhibition (Pahl et al 2012). Most importantly, these thresholds are far above the concentrations of NH 4 + occurring in Suisun Bay that have been suggested to place diatoms at a disadvantage relative to dinoflagellates and cyanobacteria (Glibert 2010, Glibert et al 2011, and to reduce their growth (Dugdale et al 2007, Parker et al 2012, suggesting that the changes in phytoplankton composition and growth observed in those investigations were due to factors other than NH 4 + concentration. The present data also demonstrate that at nonlimiting concentrations, nutrient ratios are not good predictors of phytoplankton community composition.…”

“…The genus Cyclotella has also been reported to dominate algal blooms in high-nutrient freshwater systems (Muylaert & Sabbe 1996, Wehr & Descy 1998, Mitrovic et al 2008, Beaver et al 2013. While these species have been reported to grow uninhibited in eutrophic estuaries at NH 4 + and NO 3 − concentrations approaching several hundred µmol l −1 (Collos et al 2005, Collos & Harrison 2014, other investigators have questioned whether concentrations of NH 4 + as low as 30 µmol l −1 near wastewater discharges negatively impact phytoplankton production (Thomas et al 1974, MacIsaac et al 1979, Glibert et al 2011, Parker et al 2012. Whereas 30 µmol NH 4 + l −1 is high for a marine system, culture investigations demonstrate that negative impacts on phytoplankton growth and production by nutrients typically occur at much greater concentrations.…”

“…In addition to the aforementioned factors, it has recently been proposed that the concentration of ammonium (NH 4 + ) in the wastewater effluent that flows into Suisun Bay impairs phytoplankton growth (Dugdale et al 2007, Parker et al 2012. Moreover, , compared with 2.9 ± 1 µmol l −1 at a site further upstream, and 4.8 ± 1 µmol l −1 in Suisun Bay.…”