Atmospheric Ammonia Deposition: A Significant Source of Nitrogen to an Oligotrophic Lake and Its Watershed

Across Europe, total nitrogen deposition is increasing and, of this total, atmospheric ammonia can contribute up to 50-80%. Average deposition of ammonia in the UK is likely to be around 15-20 kg ha-1 yr-1 , while in The Netherlands, which has some of the highest rates of deposition, this value is likely to be between 40 and 50 kg ha-1 yr-1 . It is argued that because of the processes of assimilation and nitrification this ammonia is an acidifying pollutant. Ammonia taken up by plants is most likely to be directly assimilated and this uptake can have a strong effect on the nutrient imbalances of the plant. With root uptake in particular, anions are taken up in preference to cations. However, simple soil/plant nutrient measurements are unlikely to be a definitive means of monitoring ammonia pollution. This is because the processes of ammonia metabolism and acidification affect soil ion activity, mycorrhizas, plant uptake, and foliar leaching. These effects interact with acidity per se, and are compounded by the strong correlative co-deposition of ammonia with sulphur. Evidence for uptake of gaseous and wet deposited ammonia by leaves is presented. The exact mechanism of ammonia toxicity is still not really clear, but could be due to physiological perturbation, rather than to the direct toxicity of the ion. Assimilation of ammonia by leaves releases protons which can cause cellular acidosis, and has important implications for acid-base regulation in cells. This regulation depends on intrinsic features of the plant's metabolism, that is in turn dependent on the ecology of root versus leaf nitrogen nutrition under normal conditions. Certain species are more acidic in a leaf physiological sense and tend to be prone to damage by pollutants. Likewise, acidic habitats are particularly prone to damage through both eutrophication and the different capacities of plants both to utilize and to buffer against this nitrogen enrichment. The current evidence from The Netherlands suggests that the part this plays in perturbing the ecosystem should not be underestimated. Contents Summary 283 I. Introduction 284 II. Emission and deposition of ammonia 284 III. Is ammonia toxic? 288 IV. The eflfects of ammonia deposition 289 V. Throughfall versus foliar uptake 293 VI. Physiological effects on ahove-ground parts 296 VII. Conclusions 301 Acknowledgements 302 References 302.

Clear Lake is a large, natural eutrophic lake located in northern California, United States. Persistent, toxic cyanobacterial blooms have been reported in the lake since 2011. However, our understanding of the spatiotemporal distribution of toxin-producing genera and their interaction with the biotic and abiotic environment is limited. Moreover, few studies have addressed how the co-occurring microbial communities respond to these toxic cyanobacterial blooms. Using multi-domain 16S/18S rRNA gene amplicon sequencing, a strong seasonal succession within the cyanobacterial and co-occurring eukaryotic assemblage was identified, which was primarily explained by variation in total phosphorus (~30%, P < 0.001) and temperature (~15%, P < 0.01). Cyanobacterial seasonal succession was often initiated by proliferation of diazotrophs (Dolichospermum and Nodularia) with concomitant increases in total nitrogen, followed by blooms of non-diazotrophs, such as Microcystis, Limnothrix, and Planktothrix. The picocyanobacterium Cyanobium, previously undocumented in the lake, was a dominant summer taxon in the western part of Clear Lake, accounting for ~45%-80% relative abundance of the cyanobacterial reads. Seasonal succession within the eukaryotic assemblage was influenced by photosynthetic chlorophytes and diatoms, as well as mixotrophic ciliates and cryptophytes. Among all toxin-producing cyanobacterial genera, Microcystis abundance was most strongly correlated with microcystin concentrations (P < 0.001), both of which appeared to influence co-occurring eukaryotes. Finally, using putative relationships based on correlation of sequence abundance and environmental variables, several potential grazers of Microcystis were identified, including cyclopoid copepods and Cryptomonas. These correlations need further confirmation and experimental work to validate the nature of the relationships.IMPORTANCEClear Lake is an important habitat for fish and wildlife, which also provides a myriad of human benefits, such as recreation, irrigation, and drinking water. Moreover, the lake is vital for tribal tradition and cultural practices. However, since the last decade, the lake has experienced recurring harmful algal blooms with toxin levels that frequently exceed California voluntary guidance levels. These high toxin concentrations pose a substantial threat to the residents, visitors, and tribal sustenance fishing and beneficial uses. However, significant gaps remain in our understanding of these toxic algal bloom dynamics and their interaction with the abiotic and biotic environments. This study characterized the seasonal and spatial patterns in the distribution of bloom-causing cyanobacteria and identified Microcystis as the major toxin producer in Clear Lake. Additionally, the co-occurring bacterial and eukaryotic microbial communities were also characterized, and their potential interactions with the cyanobacterial assemblage were identified and discussed.

The increasing incidence of mass developments of Cyanobacteria in fresh- and brackish water is a matter of growing concern due to the production of toxins that threaten human and livestock health. The toxins that are produced by freshwater Cyanobacteria comprise hepatotoxins (cyclic peptides such as microcystins and nodularin, as well as alkaloids such as cylindrospermopsin) and neurotoxins (alkaloids such as anatoxin-a, anatoxin-a(S) and saxitoxins). The variation in toxicity between and within species of Cyanobacteria has been recognised for a long time. However, the toxic and non-toxic genotypes within a species cannot be discriminated under the microscope, which has been a major obstacle in identifying those factors that influence toxin production both in the laboratory and in the field. During the last decade, major advances were achieved due to the elucidation and functional characterisation of genes, such as the gene cluster encoding the synthesis of the hepatotoxic heptapeptide, microcystin. Genetic techniques, in particular, have been used to explore (i) the genetic basis, biosynthesis pathways, and physiological regulation of toxin (microcystin) production, (ii) gene loss processes resulting in a patchy distribution of the microcystin synthetase gene cluster among genera and species, as well as (iii) the distribution and abundance of the microcystin genes in the environment. In recent years, experience in detecting microcystin genes directly in the field has increased enormously and robust protocols for the extraction of DNA and the subsequent detection of genes by PCR (polymerase chain reaction)-based methods are now available. Due to the high sensitivity of PCR, it is possible to detect toxic genotypes long before a toxic cyanobacterial bloom may occur. Consequently, waterbodies that are at risk of toxic bloom formation can be identified early on in the growing season along with environmental factors that can potentially influence the abundance of toxin producing genotypes.

A study of atmospheric ammonia by means of modeling analysis in the Kanto region of Japan

Excess nitrogen deposition not only leads to environmental damage, but there are also serious political and societal consequences when reduction measures fail, as demonstrated by the Dutch nitrogen crisis. Deposition of atmospheric ammonia (NH 3 ) plays a key role, as it accounts for three-quarters of all nitrogen deposition in the Netherlands. Atmospheric NH 3 is governed by a wide range of processes and scales, spanning multiple disciplines, such as meteorology, biology and chemistry. The scales involved range from long-range transport driven by meteorological processes at the synoptic scale (1000 km) or the day and night cycle of the atmospheric boundary layer (1 -2 km), down to dry deposition at field scale (100 -1000 m) or the formation of aerosols (≈ 10 µm).

Abstract. Deposition of atmospheric ammonia (NH3) to semi-natural ecosystems leads to serious adverse effects, such as acidification and eutrophication. A step in quantifying such effects is the measurement of NH3 fluxes over semi-natural and agricultural land. However, measurement of NH3 fluxes over vegetation in the vicinity of strong NH3 sources is challenging, since NH3 emissions are highly heterogeneous. Indeed, under such conditions, local advection errors may alter the measured fluxes. In this study, local advection errors (ΔFz,adv) were estimated over a 14 ha grassland field, which was successively cut and fertilised, as part of the GRAMINAE integrated Braunschweig experiment. The magnitude of ΔFz,adv was determined up to 810 m downwind from farm buildings emitting between 6.2 and 9.9 kg NH3 day−1. The GRAMINAE experiment provided a unique opportunity to compare two methods of estimating ΔFz,adv: one inference method based on measurements of horizontal concentration gradients, and one based on inverse dispersion modelling with a two-dimensional model. Two sources of local advection were clearly identified: the farm NH3 emissions leading to positive ΔFz,adv ("bias towards emissions") and field NH3 emissions, which led to a negative ΔFz,adv ("bias towards deposition"). The local advection flux from the farm was in the range 0 to 27 ng NH3 m−2 s−1 at 610 m from the farm, whereas ΔFz,adv due to field emission was proportional to the local flux, and ranged between −209 and 13 ng NH3 m−2 s−1. The local advection flux ΔFz,adv was either positive or negative depending on the magnitude of these two contributions. The modelled and inferred advection errors agreed well. The inferred advection errors, relative to the vertical flux at 1 m height, were 52% on average, before the field was cut, and less than 2.1% when the field was fertilised. The variability of the advection errors in response to changes in micrometeorological conditions is also studied. The limits of the 2-D modelling approach are discussed.

In the environmental problem of acidification, deposition of atmospheric ammonia is an important factor in NW Europe. Background concentrations are generally low but variations due to local sources may be large and rapid, so a sensitive measuring instrument with a high dynamic range and good time resolution is required. A photoacoustic ammonia measurement system with a detection limit for NH3 of about 1 ppbv and a time resolution of about 5 minutes is described. The results of 'a measurement campaign in the field during the spring of 1989, with the instrument installed in a caravan, will be reported. Concentrations were determined at a single position above the ground (2 m.). The instrument has since then been adapted to measurements at four different heights from which vertical fluxes can be derived. The encouraging first results will be presented.

World's largest oligotrophic Lake Baikal: Concerns about cyanobacterial blooms and potential microcystin producers along the littoral zone.

Lake sediment is an important reservoir for storage of phosphorus (P). Skaneateles Lake, a pristine oligotrophic, midsize lake in New York State, USA, is the primary unfiltered water source for the city of Syracuse and nearby communities. We conducted a lake‐wide survey of shallow sediments in Skaneateles Lake to inform understanding of the potential role of sediment in P storage and release into the water column. A total of 103 shallow samples of surface sediments were collected along 17 transects around the lake margin and analyzed for sediment and pore water elemental concentration, grain size, total organic carbon, nitrogen, carbonate content, stable isotopes of carbon, and mineral content. Reduction‐oxidation (redox) processes of Fe‐bound and Mn‐bound P appear to be a primary control of P storage and release. Sediment P concentrations are positively correlated with water depth and negatively correlated with Ca. Grain size and sediment P distributions around the lake are heterogeneous and patchy. Pore water concentrations reveal strong but variable partitioning of P, apparently controlled by sediment redox conditions. Pore water P concentrations (mean 90 μg L−1) are elevated compared with the oligotrophic water column (∼5 μg L−1) and may be an important source of nutrients to the water column of the lake.

The MODDAS-2D model (MOdel of Dispersion and Deposition of Ammonia over the Short-range in two dimensions) is presented. This stationary model couples a two-dimensional Lagrangian stochastic model for short-range dispersion, with a leaf-scale bi-directional exchange model for ammonia (NH3), which includes cuticular uptake and a stomatal compensation point. The coupling is obtained by splitting the upward and downward components of the flux, which can be generalized for any trace gas, and hence provides a way of simply incorporating bi-directional exchanges in existing deposition velocity models. The leaf boundary-layer resistance is parametrized to account for mixed convection in the canopy, and the model incorporates a stability correction for the Lagrangian time-scale for vertical velocity, which tends to increase the Lagrangian time-scale in very stable conditions compared with usual parametrizations. The model is validated against three datasets, where concentrations of atmospheric NH3 were measured at several distances from a line source. Two datasets are over grassland and one is over maize, giving a range of canopy structure. The model correctly simulates the concentration in one situation, but consistently overestimates it at further distances or underestimates it at small distances in the two other situations. It is argued that these discrepancies are mainly due to the lack of length of one of the line sources and non-aligned winds. Analysis shows that the surface exchange parameters and the turbulent mixing at the source level are the predominant factors controlling short-range deposition of NH3. Copyright © 2006 Royal Meteorological Society

Atmospheric ammonia deposition and its role in a cool-temperate fragmented deciduous broad-leaved forest

Occurrence and air-water diffusive exchange legacy persistent organic pollutants in an oligotrophic north Patagonian lake.

Increasing toxic cyanobacterial blooms in freshwater demand environmentally friendly solutions to control their growth and toxicity, especially in arid countries, where most drinking water is produced from surface reservoirs. We tested the effects of macrophyte allelochemicals on Microcystis aeruginosa and on the fundamental role of bacteria in nutrient recycling. The effects of Ranunculus aquatilis aqueous extract, the most bioactive of four Moroccan macrophyte extracts, were tested in batch systems on M. aeruginosa growth, toxin production and oxidative stress response and on the ectoenzymatic activity associated with the bacterial community. M. aeruginosa density was reduced by 82.18%, and a significant increase in oxidative stress markers was evidenced in cyanobacterial cells. Microcystin concentration significantly decreased, and they were detected only intracellularly, an important aspect in managing toxic blooms. R. aquatilis extract had no negative effects on associated bacteria. These results confirm a promising use of macrophyte extracts, but they cannot be generalized. The use of the extract on other toxic strains, such as Planktothrix rubescens, Raphidiopsis raciborskii and Chrysosporum ovalisporum, caused a reduction in growth rate but not in cyanotoxin content, increasing toxicity. The need to assess species-specific cyanobacteria responses to verify the efficacy and safety of the extracts for human health and the environment is highlighted.

Toxic cyanobacterial blooms threaten freshwaters worldwide but have proven difficult to predict because the mechanisms of bloom formation and toxin production are unknown, especially on weekly time scales. Water quality management continues to focus on aggregated metrics, such as chlorophyll and total nutrients, which may not be sufficient to explain complex community changes and functions such as toxin production. For example, nitrogen (N) speciation and cycling play an important role, on daily time scales, in shaping cyanobacterial communities because declining N has been shown to select for N fixers. In addition, subsequent N pulses from N2 fixation may stimulate and sustain toxic cyanobacterial growth. Herein, we describe how rapid early summer declines in N followed by bursts of N fixation have shaped cyanobacterial communities in a eutrophic lake (Lake Mendota, Wisconsin, USA), possibly driving toxic Microcystis blooms throughout the growing season. On weekly time scales in 2010 and 2011, we monitored the cyanobacterial community in a eutrophic lake using the phycocyanin intergenic spacer (PC-IGS) region to determine population dynamics. In parallel, we measured microcystin concentrations, N2 fixation rates, and potential environmental drivers that contribute to structuring the community. In both years, cyanobacterial community change was strongly correlated with dissolved inorganic nitrogen (DIN) concentrations, and Aphanizomenon and Microcystis alternated dominance throughout the pre-toxic, toxic, and post-toxic phases of the lake. Microcystin concentrations increased a few days after the first significant N2 fixation rates were observed. Then, following large early summer N2 fixation events, Microcystis increased and became most abundant. Maximum microcystin concentrations coincided with Microcystis dominance. In both years, DIN concentrations dropped again in late summer, and N2 fixation rates and Aphanizomenon abundance increased before the lake mixed in the fall. Estimated N inputs from N2 fixation were large enough to supplement, or even support, the toxic Microcystis blooms.

Association between trophic state, watershed use, and blooms of cyanobacteria in south-central Chile