Disruption of the Nitrogen Cycle in Acidified Lakes

Integrating resilience with functional ecosystem measures: A novel paradigm for management decisions under multiple-stressor interplay in freshwater ecosystems

Moving beyond monitoring the state of water quality to understanding how the sensitive ecosystems "respond" to complex interplay of climatic and anthropogenic perturbations, and eventually the mechanisms that underpin alterations leading to transitional shifts is crucial for managing freshwater resources. The multiple disturbance dynamics-a single disturbance as opposed to multiple disturbances for recovery and other atrocities-alter aquatic ecosystem in multiple ways, yet the global models lack representation of key processes and feedbacks, impeding potential management decisions. Here, the procedure we have embarked for what is known about the biogeochemical and ecological functions in freshwaters in context of ecosystem resilience, feedbacks, stressors synergies, and compensatory dynamics, is highly relevant for process-based ecosystem models and for developing a novel paradigm toward potential management decisions. This review advocates the need for a more aggressive approach with improved understanding of changes in key ecosystem processes and mechanistic links thereof, regulating resilience and compensatory dynamics concordant with climate and anthropogenic perturbations across a wide range of spatio-temporal scales. This has relevance contexting climate change and anthropogenic pressures for developing proactive and adaptive management strategies for safeguarding freshwater resources and services they provide.

Nitrifier Gene Abundance and Diversity in Sediments Impacted by Acid Mine Drainage

Extremely acidic and metal-rich acid mine drainage (AMD) waters can have severe toxicological effects on aquatic ecosystems. AMD has been shown to completely halt nitrification, which plays an important role in transferring nitrogen to higher organisms and in mitigating nitrogen pollution. We evaluated the gene abundance and diversity of nitrifying microbes in AMD-impacted sediments: ammonia-oxidizing archaea (AOA), ammonia-oxidizing bacteria (AOB), and nitrite-oxidizing bacteria (NOB). Samples were collected from the Iron Springs Mining District (Ophir, CO, United States) during early and late summer in 2013 and 2014. Many of the sites were characterized by low pH (<5) and high metal concentrations. Sequence analyses revealed AOA genes related to Nitrososphaera, Nitrosotalea, and Nitrosoarchaeum; AOB genes related to Nitrosomonas and Nitrosospira; and NOB genes related to Nitrospira. The overall abundance of AOA, AOB and NOB was examined using quantitative PCR (qPCR) amplification of the amoA and nxrB functional genes and 16S rRNA genes. Gene copy numbers ranged from 3.2 × 10⁴ – 4.9 × 10⁷ archaeal amoA copies ∗ μg DNA^-1, 1.5 × 10³ – 5.3 × 10⁵ AOB 16S rRNA copies ∗ μg DNA^-1, and 1.3 × 10⁶ – 7.7 × 10⁷Nitrospira nxrB copies ∗ μg DNA^-1. Overall, Nitrospira nxrB genes were found to be more abundant than AOB 16S rRNA and archaeal amoA genes in most of the sample sites across 2013 and 2014. AOB 16S rRNA and Nitrospira nxrB genes were quantified in sediments with pH as low as 3.2, and AOA amoA genes were quantified in sediments as low as 3.5. Though pH varied across all sites (pH 3.2–8.3), pH was not strongly correlated to the overall community structure or relative abundance of individual OTUs for any gene (based on CCA and Spearman correlations). pH was positivity correlated to the total abundance (qPCR) of AOB 16S rRNA genes, but not for any other genes. Metals were not correlated to the overall nitrifier community composition or abundance, but were correlated to the relative abundances of several individual OTUs. These findings extend our understanding of the distribution of nitrifying microbes in AMD-impacted systems and provide a platform for further research.

Multivariate statistical assessment of a polluted river under nitrification inhibition in the tropics

A large complex water quality data set of a polluted river, the Tay Ninh River, was evaluated to identify its water quality problems, to assess spatial variation, to determine the main pollution sources, and to detect relationships between parameters. This river is highly polluted with organic substances, nutrients, and total iron. An important problem of the river is the inhibition of the nitrification. For the evaluation, different statistical techniques including cluster analysis (CA), discriminant analysis (DA), and principal component analysis (PCA) were applied. CA clustered 10 water quality stations into three groups corresponding to extreme, high, and moderate pollution. DA used only seven parameters to differentiate the defined clusters. The PCA resulted in four principal components. The first PC is related to conductivity, NH4-N, PO4-P, and TP and determines nutrient pollution. The second PC represents the organic pollution. The iron pollution is illustrated in the third PC having strong positive loadings for TSS and total Fe. The fourth PC explains the dependence of DO on the nitrate production. The nitrification inhibition was further investigated by PCA. The results showed a clear negative correlation between DO and NH4-N and a positive correlation between DO and NO3-N. The influence of pH on the NH4-N oxidation could not be detected by PCA because of the very low nitrification rate due to the constantly low pH of the river and because of the effect of wastewater discharge with very high NH4-N concentrations. The results are deepening the understanding of the governing water quality processes and hence to manage the river basins sustainably.

High abundances of potentially active ammonia-oxidizing bacteria and archaea in oligotrophic, high-altitude lakes of the Sierra Nevada, California, USA

Nitrification plays a central role in the nitrogen cycle by determining the oxidation state of nitrogen and its subsequent bioavailability and cycling. However, relatively little is known about the underlying ecology of the microbial communities that carry out nitrification in freshwater ecosystems—and particularly within high-altitude oligotrophic lakes, where nitrogen is frequently a limiting nutrient. We quantified ammonia-oxidizing archaea (AOA) and bacteria (AOB) in 9 high-altitude lakes (2289–3160 m) in the Sierra Nevada, California, USA, in relation to spatial and biogeochemical data. Based on their ammonia monooxygenase (amoA) genes, AOB and AOA were frequently detected. AOB were present in 88% of samples and were more abundant than AOA in all samples. Both groups showed >100 fold variation in abundance between different lakes, and were also variable through time within individual lakes. Nutrient concentrations (ammonium, nitrite, nitrate, and phosphate) were generally low but also varied across and within lakes, suggestive of active internal nutrient cycling; AOB abundance was significantly correlated with phosphate (r² = 0.32, p<0.1), whereas AOA abundance was inversely correlated with lake elevation (r² = 0.43, p<0.05). We also measured low rates of ammonia oxidation—indicating that AOB, AOA, or both, may be biogeochemically active in these oligotrophic ecosystems. Our data indicate that dynamic populations of AOB and AOA are found in oligotrophic, high-altitude, freshwater lakes.

No nitrification in lakes below pH 3

Lakes affected by acid mine drainage (AMD) or acid rain often contain elevated concentrations of ammonium, which threatens water quality. It is commonly assumed that this is due to the inhibition of microbial nitrification in acidic water, but nitrification was never directly measured in mine pit lakes. For the first time, we measured nitrification by (15)NH4Cl isotope tracer addition in acidic as well as neutral mine pit lakes in Spain and Germany. Nitrification activity was only detected in neutral lakes. In acidic lakes no conversion of (15)NH4(+) to (15)NO3(-) was observed. This was true both for the water column as well as for biofilms on the surface of macrophytes or dead wood and the oxic surface layer of the sediment. Stable isotope analysis of nitrate showed (18)O values typical for nitrification only in neutral lakes. In a comparison of NH4(+) concentrations in 297 surface waters with different pH, ammonium concentrations higher 10 mg NH4-N L(-1) were only observed in lakes below pH 3. On the basis of the results from stable isotope investigations and the examination of a metadata set we conclude that the lower limit for nitrification in lakes is around pH 3.

Comparisons between experimentally- and atmospherically-acidified lakes during stress and recovery

In experiments lakes 223 (L223) and 302 South (L302S) in the Experimental Lakes Area in north-western Ontario, and Little Rock Lake (LRL) in northern Wisconsin, were progressively acidified with sulphuric acid from original pH values of 6.1–6.8 to 4.7–5.1. Although the lakes were at different locations with different physical settings and assemblages of plants and animals including fish, there were remarkable similarities in their responses, particularly in regard to biogeochemical processes and effects on biota at lower trophic levels.

All three lakes generated an important part of their buffering capacity internally b\ the reduction of sulphate, and to a lesser extent by the reduction of nitrate. Alkalinity production increased as concentrations of biologically-active strong acid anions increased. Models relating the residence times of sulphate and nitrate to water renewal, or first-order kinetics, effectively predicted events.

Acidification disrupted nitrogen cycling in all three lakes. Nitrification was inhibited in L223 and L302S, while in LRL, nitrogen fixation was greatly decreased at low pH.

The phytoplankton communities of all three lakes were originally dominated by chrysophyceans and cryptophyceans. However acidification changed the dominant species and decreased diversity. Acidification tended to increase phytoplankton production and standing crop slightly, probably because light penetration was increased.

Littoral zones of all three lakes became increasingly dominated by a few species of filamentous green algae, which created nuisance blooms by pH 5.6. Mats or clouds of algae changed the entire character of the littoral zone.

Acidification of L223 and L302S caused the loss of several species of large benthic crustaceans as pH changed from 6 to 5.6. Large, acid-sensitive littoral crustaceans were absent from LRL before acidification, probably because the lake was already too acidic.

As acidity increased, the dominance of cladocerans within zooplankton communities increased. Daphnia catawba appeared at pH values near 5.6 and became more abundant at lower pHs as the lakes were acidified. Its appearance coincided with a decline in other Daphnia species: another cladoceran, Bosmina longirostris, increased in the experimentally-acidified lakes as did Keratella taurocephala: they became the dominant rotifers. Several sensitive zooplankton species declined or disappeared as the lakes were acidified, most notably Daphnia galeata mendotae, Epischura lacustris, Diaptomus sicilis and Keratella cochlearis.

The responses of different fish varied; they appeared to depend on the sensitivity of key organisms in the food chain. The ability of key fish species to reproduce was impaired as early as pH 5.8; their reproduction, except for yellow perch in LRL, had ceased at pH 5.0 in all the three lakes.

Acidification consistently reduced the diversity and richness of species in taxonomic groups studied, these effects resulting from losses of species and the increased dominance of a few acidophilic taxa.

Responses of experimentally-acidified lakes in north-western Ontario and atmospherically-acidified lakes in eastern Ontario were similar in most respects where records allowed comparisons to be made, notably in relation to biogeochemical processes and the disappearance of acid-sensitive biota.

When the acidification of L223 was reversed, several biotic components recovered quickly. Fish resumed reproduction at pHs similar to those at which it ceased when the lake was being acidified. The condition of lake trout improved as a result of greatly increased populations of small fish, their prey. Many species of insects and crustaceans that had been extirpated by acidification returned. Assemblages of phytoplankton and chironomids have retained an acidophilic character, although their diversity during recovery is similar to that at comparable pHs during progressive acidification. As their chemistry recovered, atmospherically-acidified lakes in the Sudbury area were able to sustain recruitment by species offish, including lake trout and white sucker, with rapid increases in the diversity of invertebrate taxa. Results from both L223 and lakes near Sudbury suggest a rapid partial recovery of lacustrine communities when acidification is reversed.

It is concluded that the experimental lakes responded similarly to acidification, and that experimental acidification can reliably indicate the effects of acidification attributable to acidic precipitation.

Global declines in oceanic nitrification rates as a consequence of ocean acidification

Ocean acidification produced by dissolution of anthropogenic carbon dioxide (CO(2)) emissions in seawater has profound consequences for marine ecology and biogeochemistry. The oceans have absorbed one-third of CO(2) emissions over the past two centuries, altering ocean chemistry, reducing seawater pH, and affecting marine animals and phytoplankton in multiple ways. Microbially mediated ocean biogeochemical processes will be pivotal in determining how the earth system responds to global environmental change; however, how they may be altered by ocean acidification is largely unknown. We show here that microbial nitrification rates decreased in every instance when pH was experimentally reduced (by 0.05-0.14) at multiple locations in the Atlantic and Pacific Oceans. Nitrification is a central process in the nitrogen cycle that produces both the greenhouse gas nitrous oxide and oxidized forms of nitrogen used by phytoplankton and other microorganisms in the sea; at the Bermuda Atlantic Time Series and Hawaii Ocean Time-series sites, experimental acidification decreased ammonia oxidation rates by 38% and 36%. Ammonia oxidation rates were also strongly and inversely correlated with pH along a gradient produced in the oligotrophic Sargasso Sea (r(2) = 0.87, P < 0.05). Across all experiments, rates declined by 8-38% in low pH treatments, and the greatest absolute decrease occurred where rates were highest off the California coast. Collectively our results suggest that ocean acidification could reduce nitrification rates by 3-44% within the next few decades, affecting oceanic nitrous oxide production, reducing supplies of oxidized nitrogen in the upper layers of the ocean, and fundamentally altering nitrogen cycling in the sea.

Ecological and toxicological effects of inorganic nitrogen pollution in aquatic ecosystems: A global assessment

We provide a global assessment, with detailed multi-scale data, of the ecological and toxicological effects generated by inorganic nitrogen pollution in aquatic ecosystems. Our synthesis of the published scientific literature shows three major environmental problems: (1) it can increase the concentration of hydrogen ions in freshwater ecosystems without much acid-neutralizing capacity, resulting in acidification of those systems; (2) it can stimulate or enhance the development, maintenance and proliferation of primary producers, resulting in eutrophication of aquatic ecosystems; (3) it can reach toxic levels that impair the ability of aquatic animals to survive, grow and reproduce. Inorganic nitrogen pollution of ground and surface waters can also induce adverse effects on human health and economy. Because reductions in SO2 emissions have reduced the atmospheric deposition of H2SO4 across large portions of North America and Europe, while emissions of NOx have gone unchecked, HNO3 is now playing an increasing role in the acidification of freshwater ecosystems. This acidification process has caused several adverse effects on primary and secondary producers, with significant biotic impoverishments, particularly concerning invertebrates and fishes, in many atmospherically acidified lakes and streams. The cultural eutrophication of freshwater, estuarine, and coastal marine ecosystems can cause ecological and toxicological effects that are either directly or indirectly related to the proliferation of primary producers. Extensive kills of both invertebrates and fishes are probably the most dramatic manifestation of hypoxia (or anoxia) in eutrophic and hypereutrophic aquatic ecosystems with low water turnover rates. The decline in dissolved oxygen concentrations can also promote the formation of reduced compounds, such as hydrogen sulphide, resulting in higher adverse (toxic) effects on aquatic animals. Additionally, the occurrence of toxic algae can significantly contribute to the extensive kills of aquatic animals. Cyanobacteria, dinoflagellates and diatoms appear to be major responsible that may be stimulated by inorganic nitrogen pollution. Among the different inorganic nitrogenous compounds (NH4+, NH3, NO2-, HNO2NO3-) that aquatic animals can take up directly from the ambient water, unionized ammonia is the most toxic, while ammonium and nitrate ions are the least toxic. In general, seawater animals seem to be more tolerant to the toxicity of inorganic nitrogenous compounds than freshwater animals, probably because of the ameliorating effect of water salinity (sodium, chloride, calcium and other ions) on the tolerance of aquatic animals. Ingested nitrites and nitrates from polluted drinking waters can induce methemoglobinemia in humans, particularly in young infants, by blocking the oxygen-carrying capacity of hemoglobin. Ingested nitrites and nitrates also have a potential role in developing cancers of the digestive tract through their contribution to the formation of nitrosamines. In addition, some scientific evidences suggest that ingested nitrites and nitrates might result in mutagenicity, teratogenicity and birth defects, contribute to the risks of non-Hodgkin's lymphoma and bladder and ovarian cancers, play a role in the etiology of insulin-dependent diabetes mellitus and in the development of thyroid hypertrophy, or cause spontaneous abortions and respiratory tract infections. Indirect health hazards can occur as a consequence of algal toxins, causing nausea, vomiting, diarrhoea, pneumonia, gastroenteritis, hepatoenteritis, muscular cramps, and several poisoning syndromes (paralytic shellfish poisoning, neurotoxic shellfish poisoning, amnesic shellfish poisoning). Other indirect health hazards can also come from the potential relationship between inorganic nitrogen pollution and human infectious diseases (malaria, cholera). Human sickness and death, extensive kills of aquatic animals, and other negative effects, can have elevated costs on human economy, with the recreation and tourism industry suffering the most important economic impacts, at least locally. It is concluded that levels of total nitrogen lower than 0.5-1.0 mg TN/L could prevent aquatic ecosystems (excluding those ecosystems with naturally high N levels) from developing acidification and eutrophication, at least by inorganic nitrogen pollution. Those relatively low TN levels could also protect aquatic animals against the toxicity of inorganic nitrogenous compounds since, in the absence of eutrophication, surface waters usually present relatively high concentrations of dissolved oxygen, most inorganic reactive nitrogen being in the form of nitrate. Additionally, human health and economy would be safer from the adverse effects of inorganic nitrogen pollution.

Community structure and photosynthetic activity of epilithon from a highly acidic (pH?2) mountain stream in Patagonia, Argentina

We explored a benthic community living on stones in an acidic (pH< or =2) stream of active volcanic origin from Patagonia, Argentina, by combining in situ measurements (temperature, pH, conductivity, dissolved oxygen), photosynthesis of intact biofilms (measured with microsensors by the light-dark shift method), pure-culture experiments on isolated algae, and confocal laser scanning microscopy on the biofilms. The epilithon of the Agrio River was dominated (99% of total biomass) by one species: Gloeochrysis (Chrysophyceae). This species was observed as brown, mucilaginous, 200-microm-thick films on stones, growing in clumps in a dense matrix of fungal hyphae, bacteria, and inorganic particles held together by extracellular polymeric substances. Gloeochrysis was isolated and cultivated. The photosynthetic rate measured at saturation irradiance was 120 micromol oxygen (mg chlorophyll a)(-1) h(-1) under laboratory conditions, and the saturation rate of photosynthesis by carbon dioxide was 90 micromol oxygen (mg chlorophyll a)(-1) h(-1) for oxygen evolution. Photosynthetic activity of the biofilm was light-dependent and saturated above 200 micromol photons m(-2) s(-1). In the dark, the stone surface became anoxic. Our data suggest that primary production in the Agrio River was not limited by light, carbon, or phosphorus but instead, nitrogen-limited.

Losses of biota from American aquatic communities due to acid rain

Models based on chemical survey data and geochemical assumptions were calibrated for areas where rates of acidification are known, then used to predict the declines in alkalinity and pH of lakes in the eastern and midwestern U.S.A. These results were combined with known acid tolerances of different taxonomic groups to estimate the extent of damage caused by acid rain to biological assemblages.An average of over 50% of the species in some taxonomic groups have probably been eliminated from lakes in the Adirondacks, Poconos-Catskills and southern New England. Moderate damage to biotic communities was predicted for lakes in central New England, and north-central Wisconsin. Damage predicted in Maine, upper Michigan, northeastern Minnesota and the remainder of the upper Great Lakes region was slight. Crustaceans, molluscs, leeches and insects were among the most severely affected groups. Among fishes, species of minnows (Cyprindae) were depleted in the most heavily acidified regions, with some declines in salmonid and centrarchid species.Predicted damage to individual lakes in all areas was highly variable. In areas receiving highly acidic deposition, 100% of the species in acid-sensitive taxonomic groups were eliminated in some lakes, while damage to other lakes was predicted to be slight.Estimated damage varied from lake to lake within each subregion, based on chemical characteristics. The most heavily damaged lakes in the Adirondacks and Pocono-Catskills have probably lost all species of molluscs, leeches and crustaceans. On the other hand, lakes of the Midwest showed either slight increases or decreases in the richness of predicted biotic communities.The possible ranges of original sulfate concentrations in lakes and the proportion of sulfuric acid in precipitation that liberated base cations from catchments were confined to relatively narrow limits by the model.