Coastal wetlands are major global carbon sinks; however, they are heterogeneous and dynamic ecosystems. To characterize spatial and temporal variability in a New England salt marsh, greenhouse gas (GHG) fluxes were compared among major plant‐defined zones during growing seasons. Carbon dioxide (CO2) and methane (CH4) fluxes were compared in two mensurative experiments during summer months (2012–2014) that included low marsh (Spartina alterniflora), high marsh (Distichlis spicata and Juncus gerardii‐dominated), invasive Phragmites australis zones, and unvegetated ponds. Day‐ and nighttime fluxes were also contrasted in the native marsh zones. N2O fluxes were measured in parallel with CO2 and CH4 fluxes, but were not found to be significant. To test the relationships of CO2 and CH4 fluxes with several native plant metrics, a multivariate nonlinear model was used. Invasive P. australis zones (−7 to −15 μmol CO2·m−2·s−1) and S. alterniflora low marsh zones (up to −14 μmol CO2·m−2·s−1) displayed highest average CO2 uptake rates, while those in the native high marsh zone (less than −2 μmol CO2·m−2·s−1) were much lower. Unvegetated ponds were typically small sources of CO2 to the atmosphere (<0.5 μmol CO2·m−2·s−1). Nighttime emissions of CO2 averaged only 35% of daytime uptake in the low marsh zone, but they exceeded daytime CO2 uptake by up to threefold in the native high marsh zone. Based on modeling, belowground biomass was the plant metric most strongly correlated with CO2 fluxes in native marsh zones, while none of the plant variables correlated significantly with CH4 fluxes. Methane fluxes did not vary between day and night and did not significantly offset CO2 uptake in any vegetated marsh zones based on sustained global warming potential calculations. These findings suggest that attention to spatial zonation as well as expanded measurements and modeling of GHG emissions across greater temporal scales will help to improve accuracy of carbon accounting in coastal marshes.

Precise and rapid analyses of greenhouse gases (GHGs) will advance understanding of the net climatic forcing of coastal marsh ecosystems. We examined the ability of a cavity ring down spectroscopy (CRDS) analyzer (Model G2508, Picarro) to measure carbon dioxide (CO 2 ), methane (CH 4

Advanced N‐removal onsite wastewater treatment systems (OWTS) rely on nitrification and denitrification to remove N from wastewater. Despite their use to reduce N contamination, we know little about microbial communities controlling N removal in these systems. We used quantitative polymerase chain reaction and high‐throughput sequencing targeting nitrous oxide reductase (nosZ) and bacterial ammonia monooxygenase (amoA) to determine the size, structure, and composition of communities containing these genes. We analyzed water samples from three advanced N‐removal technologies in 38 systems in five towns in Rhode Island in August 2016, and in nine systems from one town in June, August, and October 2016. Abundance of nosZ ranged from 9.1 × 103 to 9 × 108 copies L−1 and differed among technologies and over time, whereas bacterial amoA abundance ranged from 0 to 1.9 × 107 copies L−1 and was not different among technologies or over time. Richness and diversity of nosZ—but not amoA—differed over time, with median Shannon diversity indices ranging from 2.61 in October to 4.53 in August. We observed weak community similarity patterns driven by geography and technology in nosZ. The most abundant nosZ‐ and amoA‐containing bacteria were associated with water distribution and municipal wastewater treatment plants, such as Nitrosomonas and Thauera species. Our results show that nosZ communities in N‐removal OWTS technologies differ slightly in terms of size and diversity as a function of time, but not geography, whereas amoA communities are similar across time, technology, and geography. Furthermore, community composition appears to be stable across technologies, geography, and time for amoA. Core Ideas We describe N‐cycling bacterial communities in advanced N‐removal septic systems. Geographic factors are weak drivers of community composition in nosZ. Technology design is a weak driver of community composition in nosZ. Community composition of amoA is similar across time, space, and among technologies Time drives differences in nosZ—but not amoA—diversity and abundance.

Biological nitrogen removal (BNR) systems are increasingly used in the United States in both centralized wastewater treatment plants (WWTPs) and decentralized advanced onsite wastewater treatment systems (OWTS) to reduce N discharged in wastewater effluent. However, the potential for BNR systems to be sources of nitrous oxide (N 2 O), a potent greenhouse gas, needs to be evaluated to assess their environmental impact. We quantified and compared N 2 O emissions from BNR systems at a WWTP (Field's Point, Providence, RI) and three types of advanced OWTS (Orenco Advantex AX 20, SeptiTech Series D, and Bio-Microbics MicroFAST) in nine Rhode Island residences (n = 3 per type) using cavity ring-down spectroscopy. We also used quantitative polymerase chain reaction to determine the abundance of genes from nitrifying (amoA) and denitrifying (nosZ) microorganisms that may be producing N 2 O in these systems. Nitrous oxide fluxes ranged from −4 ´ 10 −3 to 3 ´ 10 −1 mmol N 2 O m −2 s −1 and in general followed the order: centralized WWTP > Advantex > SeptiTech > FAST. In contrast, when N 2 O emissions were normalized by population served and area of treatment tanks, all systems had overlapping ranges. In general, the emissions of N 2 O accounted for a small fraction (<1%) of N removed. There was no significant relationship between the abundance of nosZ or amoA genes and N 2 O emissions. This preliminary analysis highlights the need to evaluate N 2 O emissions from wastewater systems as a wider range of technologies are adopted. A better understanding of the mechanisms of N 2 O emissions will also allow us to better manage systems to minimize emissions. Comparison of N 2 O Emissions and Gene Abundances between Wastewater Nitrogen Removal SystemsElizabeth Quinn Brannon,* Serena M. Moseman-Valtierra, Brittany V. Lancellotti, Sara K. Wigginton, Jose A. Amador, James C. McCaughey, and George W. Loomis H umans substantially modify global nitrogen (N) cycles by industrially fixing N for fertilizer and ultimately releasing reactive N back to the environment through various mechanisms, including wastewater treatment. The continued growth of the human population will lead to further increases in excess reactive N, increasing the need for N remediation (Galloway et al., 2003). In recent years, remediation has focused on upgrading centralized wastewater treatment plants (WWTPs) to include biological nitrogen removal (BNR). Since one in five US homes are serviced by conventional onsite wastewater treatment systems (OWTS) (USEPA, 2013) they can also be large sources of N (Zhu et al., 2008;USEPA, 2015). The use of OWTS can be advantageous relative to centralized WWTPs, as they recharge groundwater supplies, require less infrastructure, and have lower energy costs (USEPA, 2013). To ameliorate N inputs to the environment, conventional OWTS are also being upgraded to advanced OWTS that include BNR.Although BNR systems at WWTPs and OWTS vary in design, all employ nitrifying (conversion of ammonium to nitrate) and denitrifying (convers...

Biological nitrogen removal (BNR) in centralized and decentralized wastewater treatment systems is assumed to be driven by the same microbial processes and to have communities with a similar composition and structure. There is, however, little information to support these assumptions, which may impact the effectiveness of decentralized systems. We used high-throughput sequencing to compare the structure and composition of the nitrifying and denitrifying bacterial communities of nine onsite wastewater treatment systems (OWTS) and one wastewater treatment plant (WTP) by targeting the genes coding for ammonia monooxygenase (amoA) and nitrous oxide reductase (nosZ). The amoA diversity was similar between the WTP and OWTS, but nosZ diversity was generally higher for the WTP. Beta diversity analyses showed the WTP and OWTS promoted distinct amoA and nosZ communities, although there is a core group of N-transforming bacteria common across scales of BNR treatment. Our results suggest that advanced N-removal OWTS have microbial communities that are sufficiently distinct from those of WTP with BNR, which may warrant different management approaches.