Upgrading northern municipal lagoons: Total nitrogen removal and phosphorus assimilation at ultra-low temperatures

In this study, a municipal lagoon with high wintertime effluent total ammonia nitrogen (TAN) concentrations was upgraded with a pilot-scale NIT-NIT-DENIT moving bed biofilm reactor (MBBR) treatment train to characterize its effluent over wintertime operation, investigate the feasibility of upgrading lagoons to achieve substantial biological total nitrogen removal across ultra-low temperatures (0.6 – 3.0°C) and investigate nitrification inhibition pathways in facultative lagoon systems at ultra-low temperatures. Throughout the study, it was observed that the system substantially reduced total nitrogen (TN) and total phosphorus (TP) effluent concentrations by an average of 69.0 ± 24.5% and 74.7 ± 20.1%, respectively, with average TN and TP concentrations exiting the treatment train of 7.60 ± 5.60 mg-N/L and 0.05 ± 0.02 mg-P/L, respectively, indicating the feasibility of upgrading municipal lagoons to meet increasing stringent effluent standards to ensure the perenniality of water resources. Furthermore, it was observed that sulfide toxicity may play an important role in the inhibition of nitrifying organisms in lagoons.

Nutrient enrichment increases size of Zostera marina shoots and enriches for sulfur and nitrogen cycling bacteria in root-associated microbiomes

ABSTRACT Seagrasses are vital coastal ecosystem engineers, which are mutualistically associated with microbial communities that contribute to the ecosystem services provided by meadows. The seagrass microbiome and sediment microbiota play vital roles in belowground biogeochemical and carbon cycling. These activities are influenced by nutrient, carbon and oxygen availability, all of which are modulated by environmental factors and plant physiology. Seagrass meadows are increasingly threatened by nutrient pollution, and it is unknown how the seagrass microbiome will respond to this stressor. We investigated the effects of fertilization on the physiology, morphology and microbiome of eelgrass (Zostera marina) cultivated over 4 weeks in mesocosms. We analyzed the community structure associated with eelgrass leaf, root and rhizosphere microbiomes, and of communities from water column and bulk sediment using 16S rRNA amplicon sequencing. Fertilization led to a higher number of leaves compared with that of eelgrass kept under ambient conditions. Additionally, fertilization led to enrichment of sulfur and nitrogen bacteria in belowground communities. These results suggest nutrient enrichment can stimulate belowground biogeochemical cycling, potentially exacerbating sulfide toxicity in sediments and decreasing future carbon sequestration stocks.