Molecular evidence for sediment nitrogen fixation in a temperate New England estuary

Primary production in coastal waters is generally nitrogen (N) limited with denitrification outpacing nitrogen fixation (N2-fixation). However, recent work suggests that we have potentially underestimated the importance of heterotrophic sediment N2-fixation in marine ecosystems. We used clone libraries to examine transcript diversity of nifH (a gene associated with N2-fixation) in sediments at three sites in a temperate New England estuary (Waquoit Bay, Massachusetts, USA) and compared our results to net sediment N2 fluxes previously measured at these sites. We observed nifH expression at all sites, including a site heavily impacted by anthropogenic N. At this N impacted site, we also observed mean net sediment N2-fixation, linking the geochemical rate measurement with nifH expression. This same site also had the lowest diversity (non-parametric Shannon = 2.75). At the two other sites, we also detected nifH transcripts, however, the mean N2 flux indicated net denitrification. These results suggest that N2-fixation and denitrification co-occur in these sediments. Of the unique sequences in this study, 67% were most closely related to uncultured bacteria from various marine environments, 17% to Cluster III, 15% to Cluster I, and only 1% to Cluster II. These data add to the growing body of literature that sediment heterotrophic N2-fixation, even under high inorganic nitrogen concentrations, may be an important yet overlooked source of N in coastal systems

Hurricane Disturbance Stimulated Nitrification and Altered Ammonia Oxidizer Community Structure in Lake Okeechobee and St. Lucie Estuary (Florida)

© Copyright © 2020 Hampel, McCarthy, Aalto and Newell. Nitrification is an important biological link between oxidized and reduced forms of nitrogen (N). The efficiency of nitrification plays a key role in mitigating excess N in eutrophic systems, including those with cyanobacterial harmful algal blooms (cyanoHABs), since it can be closely coupled with denitrification and removal of excess N. Recent work suggests that competition for ammonium (NH4+) between ammonia oxidizers and cyanoHABs can help determine microbial community structure. Nitrification rates and ammonia-oxidizing archaeal (AOA) and bacterial (AOB) community composition and gene abundances were quantified in Lake Okeechobee and St. Lucie Estuary in southern Florida (United States). We sampled during cyanobacterial (Microcystis) blooms in July 2016 and August 2017 (2 weeks before Hurricane Irma) and 10 days after Hurricane Irma made landfall. Nitrification rates were low during cyanobacterial blooms in Lake Okeechobee and St. Lucie Estuary, while low bloom conditions in St. Lucie Estuary coincided with greater nitrification rates. Nitrification rates in the lake were correlated (R2 = 0.94; p = 0.006) with AOA amoA abundance. Following the hurricane, nitrification rates increased by an order of magnitude, suggesting that nitrifiers outcompeted cyanobacteria for NH4+ under turbid, poor light conditions. After Irma, AOA and AOB abundances increased in St. Lucie Estuary, while only AOB increased in Lake Okeechobee. AOA sequences clustered into three major lineages: Nitrosopumilales (NP), Nitrososphaerales (NS), and Nitrosotaleales (NT). Many of the lake OTUs placed within the uncultured and uncharacterized NS δ and NT β clades, suggesting that these taxa are ecologically important along this eutrophic, lacustrine to estuarine continuum. After the hurricane, the AOA community shifted toward dominance by freshwater clades in St. Lucie Estuary and terrestrial genera in Lake Okeechobee, likely due to high rainfall and subsequent increased turbidity and freshwater loading from the lake into the estuary. AOB community structure was not affected by the disturbance. AOA communities were consistently more diverse than AOB, despite fewer sequences recovered, including new, unclassified, eutrophic ecotypes, suggesting a wider ecological biogeography than the oligotrophic niche originally posited. These results and other recent reports contradict the early hypothesis that AOB dominate ammonia oxidation in high-nutrient or terrestrial-influenced systems

Short Term Effects of Hurricane Irma and Cyanobacterial Blooms On Ammonium Cycling Along a Freshwater-Estuarine Continuum In South Florida

Lacustrine and coastal systems are vulnerable to the increasing number and intensity of tropical storms driven by climate change. Strong winds associated with tropical storms can mobilize nutrients in sediments and alter nitrogen and phosphorus cycling, leading to amplification of preexisting conditions, such as eutrophication and cyanobacterial blooms (cyanoHABs). In 2016, Florida declared a State of Emergency within and downstream of Lake Okeechobee (LO) due to toxic cyanobacterial blooms (primarily Microcystis). The blooms originated in LO, but flood control measures released water from LO to the brackish St. Lucie Estuary (SLE). In September 2017, Hurricane Irma traversed the Florida peninsula with sustained winds exceeding 160 km h–1, generating torrential rains over the watershed. We quantified ammonium (NH4+) regeneration and potential uptake rates, and Microcystis toxin gene (mcyD) abundance in LO and SLE during the massive bloom in July 2016, the bloom in August 2017 (2 weeks before Irma), and 10 days after Hurricane Irma landfall. In 2016, cyanoHABs were present in both LO and SLE, and potential NH4+ uptake rates were high in both systems. In 2017, the bloom was constrained to LO, potential NH4+ uptake rates in LO exceeded those in SLE, and mcyD gene abundance was greater in LO than SLE. Post Hurricane Irma, potential NH4+ uptake rates decreased significantly in LO and SLE, while mcyD gene abundance decreased in LO and increased slightly in SLE. Average NH4+ regeneration rates could support 25–40% of water column potential NH4+ demand in the lake and, when extrapolated to the entire LO water column, exceeded external nitrogen loading. These results emphasize the importance of internal NH4+ recycling for bloom expansion and toxicity in the lake and downstream estuaries. In 2018, the cyanobacterial bloom in the Okeechobee region was one of the largest recorded and is presumed to be driven by the aftermath of Hurricane Irma. Large-scale blooms have also been observed in SLE, likely due to LO flushing and decreased salinity post-hurricane. Thus, results from this study support predictions that increased frequency and strength of tropical storms will lead to more intense blooms in aquatic systems

Catchment land cover and soil as predictors of organic carbon, nitrogen, and phosphorus levels in temperate lakes : [presentation]

The presentation took place at the 10th International Conference on Shallow Lakes in 2021.This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 951963. This study was funded by the Estonian Research Council grants PUTJD954, PRG705, and PRG709, and by the European Regional Development Fund through Estonian University of Life Sciences ASTRA project “Value-chain based bio-economy”. The Estonian Ministry of Environment and the Estonian Environment Agency supported data collection in the national monitoring program.This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 951963. This study was funded by the Estonian Research Council grants PUTJD954, PRG705, and PRG709, and by the European Regional Development Fund through Estonian University of Life Sciences ASTRA project “Value-chain based bio-economy”. The Estonian Ministry of Environment and the Estonian Environment Agency supported data collection in the national monitoring program

Ammonium recycling supports toxic Planktothrix blooms in Sandusky Bay, Lake Erie: Evidence from stable isotope and metatranscriptome data

Sandusky Bay, Lake Erie, receives high nutrient loadings (nitrogen and phosphorus) from the Sandusky River, which drains an agricultural watershed. Eutrophication and cyanobacterial harmful algal blooms (cyanoHABs) persist throughout summer. Planktothrix agardhii is the dominant bloom-forming species and the main producer of microcystins in Sandusky Bay. Non-N2 fixing cyanobacteria, such as Planktothrix and Microcystis, thrive on chemically reduced forms of nitrogen, such as ammonium (NH4+) and urea. Ammonium regeneration and potential uptake rates and total microbial community demand for NH4+ were quantified in Sandusky Bay. Potential NH4+ uptake rates in the light increased from June to August at all stations. Dark uptake rates also increased seasonally and, by the end of August, were on par with light uptake rates. Regeneration rates followed a similar pattern and were significantly higher in August than June. Ammonium uptake kinetics during a Planktothrix-dominated bloom in Sandusky Bay and a Microcystis-dominated bloom in Maumee Bay were also compared. The highest half saturation constant (Km) in Sandusky Bay was measured in June and decreased throughout the season. In contrast, Km values in Maumee Bay were lowest at the beginning of summer and increased in October. A significant increase in Vmax in Sandusky Bay was observed between July and the end of August, reflective of intense competition for depleted NH4+. Metatranscriptome results from Sandusky Bay show a shift from cyanophycin synthetase (luxury NH4+ uptake; cphA1) expression in early summer to cyanophycinase (intracellular N mobilization; cphB/cphA2) expression in August, supporting the interpretation that the microbial community is nitrogen-starved in late summer. Combined, our results show that, in late summer, when nitrogen concentrations are low, cyanoHABs in Sandusky Bay rely on regenerated NH4+ to support growth and toxin production. Increased dark NH4+ uptake late in summer suggests an important heterotrophic contribution to NH4+ depletion in the phycosphere. Kinetic experiments in the two bays suggest a competitive advantage for Planktothrix over Microcystis in Sandusky Bay due to its higher affinity for NH4+ at low concentrations

A Future Tale of Two Winters? Sediment-water interface nitrogen dynamics in Lake Võrtsjärv (Estonia) during the ice-free winter 2019/2020 : [presentation]

The presentation took place at the Lahti Lakes 2021 Symposium.This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 95196. Estonian University of Life Sciences ASTRA project “Value-chain based bio-economy”.This project has received funding from the European Union’s Horizon 2020 research and innovation programme under grant agreement No 95196. Estonian University of Life Sciences ASTRA project “Value-chain based bio-economy”

Adrenocortical incidentalomas and bone: from molecular insights to clinical perspectives.

The original version of this article unfortunately contained a mistake in Figure 1. There is a typo in the word "osteoclastogenesis" and the word "activity" is missing in the same entity. It should be "osteoclastogenesis" instead of "osteoclestogenesis"

Reaction: Italian referendum and Matteo Renzi’s resignation

Italian Prime Minister, Matteo Renzi, has announced he will resign following defeat in the country’s constitutional referendum. We asked a number of EUROPP contributors for their immediate thoughts on the result, Renzi’s resignation, and where Italy is heading next. Alberto Alemanno: “The vote has killed the dream of once in a generation change” James Newell: “The result was not simply another anti-establishment revolt” Andrea Lorenzo Capussela: “Rationality imposed itself, and in large numbers” Silvia Merler: “Italy is now headed for a complex and delicate period of political and economic uncertainty” Lorenzo Piccoli: “Renzi did not have much choice but to resign” Jonas Bergan Draege: “Both the M5S and Lega Nord could emerge strengthened from the No vote” Angelo Martelli: “The determinant factor of Renzi’s defeat has been the sluggish pace of the Italian recovery” Davide Morisi: “The correlation is clear: Renzi’s personalisation strategy has backfired” Mattia Guidi: “Listening to the will of the people will be a hard task: several questions have no answer at present” James Dennison: “This was no Brexit-Trump moment: The package of reforms was complex and broad enough for citizens of all stripes to find cause for concern” Fabio Bordignon: “Renzi’s 41% – ironically, the same result he had obtained at the 2014 European election – became the symbol of his defeat

Mitigating cyanobacterial harmful algal blooms in aquatic ecosystems impacted by climate change and anthropogenic nutrients

Mitigating the global expansion of cyanobacterial harmful blooms (CyanoHABs) is a major challenge facing researchers and resource managers. A variety of traditional (e.g., nutrient load reduction) and experimental (e.g., artificial mixing and flushing, omnivorous fish removal) approaches have been used to reduce bloom occurrences. Managers now face the additional effects of climate change on watershed hydrologic and nutrient loading dynamics, lake and estuary temperature, mixing regime, internal nutrient dynamics, and other factors. Those changes favor CyanoHABs over other phytoplankton and could influence the efficacy of control measures. Virtually all mitigation strategies are influenced by climate changes, which may require setting new nutrient input reduction targets and establishing nutrient-bloom thresholds for impacted waters. Physical-forcing mitigation techniques, such as flushing and artificial mixing, will need adjustments to deal with the ramifications of climate change. Here, we examine the suite of current mitigation strategies and the potential options for adapting and optimizing them in a world facing increasing human population pressure and climate change

It Takes Two to Tango: When and Where Dual Nutrient (N & P) Reductions Are Needed to Protect Lakes and Downstream Ecosystems

Preventing harmful algal blooms (HABs) is needed to protect lakes and downstream ecosystems. Traditionally, reducing phosphorus (P) inputs was the prescribed solution for lakes, based on the assumption that P universally limits HAB formation. Reduction of P inputs has decreased HABs in many lakes, but was not successful in others. Thus, the "P-only" paradigm is overgeneralized. Whole-lake experiments indicate that HABs are often stimulated more by combined P and nitrogen (N) enrichment rather than N or P alone, indicating that the dynamics of both nutrients are important for HAB control. The changing paradigm from P-only to consideration of dual nutrient control is supported by studies indicating that (1) biological N fixation cannot always meet lake ecosystem N needs, and (2) that anthropogenic N and P loading has increased dramatically in recent decades. Sediment P accumulation supports long-term internal loading, while N may escape via denitrification, leading to perpetual N deficits. Hence, controlling both N and P inputs will help control HABs in some lakes and also reduce N export to downstream N-sensitive ecosystems. Managers should consider whether balanced control of N and P will most effectively reduce HABs along the freshwater-marine continuum