Nitrogen Limitation of Intense and Toxic Cyanobacteria Blooms in Lakes within Two of the Most Visited Parks in the USA: The Lake in Central Park and Prospect Park Lake

The Lake in Central Park (LCP) and Prospect Park Lake (PPL) in New York City (NYC), USA, are lakes within two of the most visited parks in the USA. Five years of nearshore sampling of these systems revealed extremely elevated levels of cyanobacteria and the toxin, microcystin, with microcystin levels averaging 920 µg L−1 and chlorophyll a from cyanobacterial (cyano-chla) populations averaging 1.0 × 105 µg cyano-chla L−1. Both lakes displayed elevated levels of orthophosphate (DIP) relative to dissolved inorganic nitrogen (DIN) during summer months when DIN:DIP ratios were < 1. Nutrient addition and dilution experiments revealed that N consistently limited cyanobacterial populations but that green algae were rarely nutrient limited. Experimental additions of public drinking water that is rich in P and, to a lesser extent N, to lake water significantly enhanced cyanobacterial growth rates in experiments during which N additions also yielded growth enhancement. Collectively, this study demonstrates that the extreme microcystin levels during blooms in these highly trafficked lakes represent a potential human and animal health threat and that supplementation of these artificial lakes with public drinking water to maintain water levels during summer may promote the intensity and N limitation of blooms

Vitamin B1 and B12 uptake and cycling by plankton communities in coastal ecosystems

While vitamin B12 has recently been shown to co-limit the growth of coastal phytoplankton assemblages, the cycling of B-vitamins in coastal ecosystems is poorly understood as planktonic uptake rates of vitamins B1 and B12 have never been quantified in tandem in any aquatic ecosystem. The goal of this study was to establish the relationships between plankton community composition, carbon fixation, and B-vitamin assimilation in two contrasting estuarine systems. We show that, although B-vitamin concentrations were low (pM), vitamin concentrations and uptake rates were higher within a more eutrophic estuary and that vitamin B12 uptake rates were significantly correlated with rates of primary production. Eutrophic sites hosted larger bacterial and picoplankton abundances with larger carbon normalized vitamin uptake rates. Although the &gt;2 &#181;m phytoplankton biomass was often dominated by groups with a high incidence of vitamin auxotrophy (dinoflagellates and diatoms), picoplankton (&lt; 2 &#181;m) were always responsible for the majority of B12-vitamin uptake. Multiple lines of evidence suggest that heterotrophic bacteria were the primary users of vitamins among the picoplankton during this study. Nutrient/vitamin amendment experiments demonstrated that, in the Summer and Fall, vitamin B12 occasionally limited or co-limited the accumulation of phytoplankton biomass together with nitrogen. Combined with prior studies, these findings suggest that picoplankton are the primary producers and users of B-vitamins in coastal ecosystems and that rapid uptake of B-vitamins by heterotrophic bacteria may sometimes deprive larger phytoplankton of these micronutrients and thus influence phytoplankton species succession

Nitrogenous nutrients promote the growth and toxicity of Dinophysis acuminata during estuarine bloom events.

Diarrhetic Shellfish Poisoning (DSP) is a globally significant human health syndrome most commonly caused by dinoflagellates within the genus Dinophysis. While blooms of harmful algae have frequently been linked to excessive nutrient loading, Dinophysis is a mixotrophic alga whose growth is typically associated with prey availability. Consequently, field studies of Dinophysis and nutrients have been rare. Here, the temporal dynamics of Dinophysis acuminata blooms, DSP toxins, and nutrients (nitrate, ammonium, phosphate, silicate, organic compounds) were examined over four years within two New York estuaries (Meetinghouse Creek and Northport Bay). Further, changes in the abundance and toxicity of D. acuminata were assessed during a series of nutrient amendment experiments performed over a three year period. During the study, Dinophysis acuminata blooms exceeding one million cells L-1 were observed in both estuaries. Highly significant (p<0.001) forward stepwise multivariate regression models of ecosystem observations demonstrated that D. acuminata abundances were positively dependent on multiple environmental parameters including ammonium (p = 0.007) while cellular toxin content was positively dependent on ammonium (p = 0.002) but negatively dependent on nitrate (p<0.001). Nitrogen- (N) and phosphorus- (P) containing inorganic and organic nutrients significantly enhanced D. acuminata densities in nearly all (13 of 14) experiments performed. Ammonium significantly increased cell densities in 10 of 11 experiments, while glutamine significantly enhanced cellular DSP content in 4 of 5 experiments examining this compound. Nutrients may have directly or indirectly enhanced D. acuminata abundances as densities of this mixotroph during experiments were significantly correlated with multiple members of the planktonic community (phytoflagellates and Mesodinium). Collectively, this study demonstrates that nutrient loading and more specifically N-loading promotes the growth and toxicity of D. acuminata populations in coastal zones

The effects of elevated CO2 on the growth and toxicity of field populations and cultures of the saxitoxin-producing dinoflagellate, Alexandrium fundyense

The effects of coastal acidification on the growth and toxicity of the saxitoxin-producing dinoflagellate Alexandrium fundyense were examined in culture and ecosystem studies. In culture experiments, Alexandrium strains isolated from Northport Bay, New York, and the Bay of Fundy, Canada, grew significantly faster (16-190%; p < 0.05) when exposed to elevated levels of PCO2 ( 90-190 Pa=900-1900 µatm) compared to lower levels ( 40 Pa=400 µatm). Exposure to higher levels of PCO2 also resulted in significant increases (71-81%) in total cellular toxicity (fg saxitoxin equivalents/cell) in the Northport Bay strain, while no changes in toxicity were detected in the Bay of Fundy strain. The positive relationship between PCO2 enrichment and elevated growth was reproducible in natural populations from New York waters. Alexandrium densities were significantly and consistently enhanced when natural populations were incubated at 150 Pa PCO2 compared to 39 Pa. During natural Alexandrium blooms in Northport Bay, PCO2 concentrations increased over the course of a bloom to more than 170 Pa and were highest in regions with the greatest Alexandrium abundances, suggesting Alexandrium may further exacerbate acidification and/or be especially adapted to these acidi-fied conditions. The co-occurrence of Alexandrium blooms and elevated PCO2 represents a previously unrecognized, compounding environmental threat to coastal ecosystems. The ability of elevated PCO2 to enhance the growth and toxicity of Alexandrium indicates that acidification promoted by eutrophication or climate change can intensify these, and perhaps other, harmful algal blooms

Okadaic acid (OA), dinophysistoxins 1 (DTX1) and total pectenotoxins (total PTX) as fg cell^-1 for nutrient amendment experiments conducted using Northport Bay bloom water during 2011.

<p>Bars are means while error bars represent the SD of triplicate bottles. Asterisks indicate treatments that are significantly different from the unamended control. Abbreviations as in <a href="http://www.plosone.org/article/info:doi/10.1371/journal.pone.0124148#pone.0124148.g002" target="_blank">Fig 2</a>.</p

Nitrogen limitation, toxin synthesis potential, and toxicity of cyanobacterial populations in Lake Okeechobee and the St. Lucie River Estuary, Florida, during the 2016 state of emergency event

<div><p>Lake Okeechobee, FL, USA, has been subjected to intensifying cyanobacterial blooms that can spread to the adjacent St. Lucie River and Estuary via natural and anthropogenically-induced flooding events. In July 2016, a large, toxic cyanobacterial bloom occurred in Lake Okeechobee and throughout the St. Lucie River and Estuary, leading Florida to declare a state of emergency. This study reports on measurements and nutrient amendment experiments performed in this freshwater-estuarine ecosystem (salinity 0–25 PSU) during and after the bloom. In July, all sites along the bloom exhibited dissolved inorganic nitrogen-to-phosphorus ratios < 6, while <i>Microcystis</i> dominated (> 95%) phytoplankton inventories from the lake to the central part of the estuary. Chlorophyll <i>a</i> and microcystin concentrations peaked (100 and 34 μg L^-1, respectively) within Lake Okeechobee and decreased eastwards. Metagenomic analyses indicated that genes associated with the production of microcystin (<i>mcyE</i>) and the algal neurotoxin saxitoxin (<i>sxtA</i>) originated from <i>Microcystis</i> and multiple diazotrophic genera, respectively. There were highly significant correlations between levels of total nitrogen, microcystin, and microcystin synthesis gene abundance across all surveyed sites (<i>p</i> < 0.001), suggesting high levels of nitrogen supported the production of microcystin during this event. Consistent with this, experiments performed with low salinity water from the St. Lucie River during the event indicated that algal biomass was nitrogen-limited. In the fall, densities of <i>Microcystis</i> and concentrations of microcystin were significantly lower, green algae co-dominated with cyanobacteria, and multiple algal groups displayed nitrogen-limitation. These results indicate that monitoring and regulatory strategies in Lake Okeechobee and the St. Lucie River and Estuary should consider managing loads of nitrogen to control future algal and microcystin-producing cyanobacterial blooms.</p></div

September 2016 transect data of sites that represented a strong salinity gradient.

<p>Included are microcystin and salinity values (A), chlorophyll <i>a</i> concentrations (B), densities of the five most abundant phytoplankton (C), and total (D) and dissolved (E) inorganic nitrogen and phosphorus concentrations and ratios. Algal densities are represented on the log scale in C. Error bars denote standard deviations.</p

Diatom, cyanobacteria, and green algal pigment concentrations at 48 h from the September 2016 nutrient amendment experiment.

<p>Samples were collected from sites LO 1 (A), SLE 1 (B), and SLE 6.5 (C). Error bars represent standard deviations. Statistical significance (<i>p</i> < 0.05) of specific pigments among sites is denoted by different letter combinations. Letters are ordered relative to the order of parameters listed in the legend. For A, only cyanobacterial and green algal pigment concentrations exhibited statistical differences among treatments.</p

July 2016 transect data of sites that represented a strong salinity gradient.

<p>Included are microcystin and salinity values (A), chlorophyll <i>a</i> concentrations (B), densities of the five most abundant phytoplankton (C), and total (D) and dissolved (E) inorganic nitrogen and phosphorus concentrations and ratios. Algal densities are represented on the log scale in C. Error bars denote standard deviations.</p

Nitrogen limitation, toxin synthesis potential, and toxicity of cyanobacterial populations in Lake Okeechobee and the St. Lucie River Estuary, Florida, during the 2016 state of emergency event - Fig 1

<p><b>Sampling sites around Lake Okeechobee (A) and on the St. Lucie River Estuary (B) in Florida, USA.</b> Sites sampled in both July and September 2016 (●) and September 2016 only (×) are represented. Inserts denote the general region sites were located on the peninsula.</p