Response of Lower Sacramento River phytoplankton to high-ammonium wastewater effluent

Abstract

Since the 1980s, the San Francisco Bay Delta ecosystem has experienced large declines in primary production. Hypothesized reasons for this decline include (1) suppression of nitrate (NO3−) uptake, and thus phytoplankton growth, due to high concentrations of ammonium (NH4+), and (2) wastewater NH4+-induced changes in phytoplankton community composition away from large-celled diatoms. These twin hypotheses implicate NH4+ loading from the Sacramento Regional Wastewater Treatment Plant effluent outfall in explaining declines in primary production in the region. They have been controversial within the water resources management community and have stimulated a lengthy public scientific and regulatory debate. Here, in an effort to resolve this debate, we present results from a 48-h incubation experiment with surface water from both upstream and downstream of the Sacramento Regional Wastewater Treatment Plant effluent outfall, a major source of NH4+ loading to the ecosystem. We amended this water with either NH4+, NO3−, or full wastewater effluent. All assays were incubated under high light (52% of incident irradiance) or low light (6% of incident irradiance). NO3− uptake rates were suppressed to near zero in all treatments with either added NH4+, added wastewater effluent, or high in situ NH4+ concentrations. Yet, phytoplankton uniformly grew well on all dissolved inorganic nitrogen sources, including effluent and NH4+. Diatom species were the most abundant taxa at all stations, and diatom cell abundances increased at greater rates than all other taxa over the course of the experiment. Among all treatments, the light treatment had the greatest effects on chlorophyll a accumulation and phytoplankton growth rates. Our results suggest that high NH4+ loading is not a driver of the lower productivity in the San Francisco Bay Delta. Although phytoplankton preferred NH4+ to NO3− when both were available in our experiment, the form of dissolved inorganic nitrogen had no effect on growth rates or species composition.

Genome-Resolved Metagenomic Insights into Massive Seasonal Ammonia-Oxidizing Archaea Blooms in San Francisco Bay

“…High ammonia concentrations can lead to eutrophication in estuaries ( 4 ), though currently, phytoplankton dynamics in SFB are strongly influenced by light limitation ( 5 – 7 ) and grazing ( 8 , 9 ), leading to a high-nutrient, low-chlorophyll state in parts of SFB. However, the form of DIN could also be one of several factors influencing phytoplankton dynamics and composition in SFB ( 10 – 16 ), potentially linking rates of nitrification to phytoplankton community composition. Nitrate produced by nitrification can also be denitrified in suboxic/anoxic sediments of the bay ( 17 , 18 ) and lost from the system as N gases (e.g., N 2 and N 2 O).…”

Investigating eukaryotic and prokaryotic diversity and functional potential in the cold and alkaline ikaite columns in Greenland

“…Amplicon sequencing of 16S rRNA genes in DNA isolated directly from the ikaite columns showed that the dominating phyla were Pseudomonadota (Gamma and Alpha), Bacteroidota, Bacillota, Actinomycetota, and Cyanobacteriota. Especially Pseudomonadota and Bacteroidota are often dominating in cold environments like sea ice ( de Sousa et al, 2019 ; Strong et al, 2021 ; Winder et al, 2023 ), permafrost ( Frey et al, 2016 ; Hu et al, 2016 ), and freshwater ecosystems ( Cameron et al, 2012 ; Cavaco et al, 2019 ). Cyanobacteriota are abundant in sea ice, but can also be found in, e.g., permafrost samples ( Frey et al, 2016 ; Hu et al, 2016 ) and cryoconite holes, where they are the main primary producers ( Anesio and Laybourn-Parry, 2012 ).…”

Investigating Factors Contributing to Phytoplankton Biomass Declines in the Lower Sacramento River

“…The conditions leading to this decline in Chl-a have been the subject of many recent investigations. For example, light limitation is a widely recognized factor for regulating intrinsic phytoplankton growth in the estuary and in the Delta Cloern 1984, 1987;Alpine and Cloern 1988) and was recently demonstrated to be an important factor for regulating phytoplankton growth in the Sacramento River (Strong et al 2021). Another potentially important factor is rapid water velocities leading to short residence times (Jassby 2008;Hammock et al 2019), which prevents accumulation of phytoplankton biomass in a given area or region.…”