No nitrification in lakes below pH 3

Multi-omics insights into biogeochemical responses to organic matter addition in an acidic pit lake: Implications for bioremediation

Acidic pit lakes (APLs) emerge as reservoirs of acid mine drainage in flooded open-pit mines, representing extreme ecosystems and environmental challenges worldwide. The bioremediation of these oligotrophic waters necessitates the addition of organic matter, but the biogeochemical response of APLs to exogenous organic matter remains inadequately comprehended. This study delves into the biogeochemical impacts and remediation effects of digestate-derived organic matter within an APL, employing a multi-omics approach encompassing geochemical analyses, amplicon and metagenome sequencing, and ultra-high resolution mass spectrometry. The results indicated that digestate addition first stimulated fungal proliferation, particularly Ascomycetes and Basidiomycetes, which generated organic acids through lignocellulosic hydrolysis and fermentation. These simple compounds further supported heterotrophic growth, including Acidiphilium, Acidithrix, and Clostridium, thereby facilitating nitrate, iron, and sulfate reduction linked with acidity consumption. Nutrients derived from digestate also promoted the macroscopic development of acidophilic algae. Notably, the increased sulfate reduction-related genes primarily originated from assimilatory metabolism, thus connecting sulfate decrease to organosulfur increase. Assimilatory and dissimilatory sulfate reduction collectively contributed to sulfate removal and metal fixation. These findings yield multi-omics insights into APL biogeochemical responses to organic matter addition, enhancing the understanding of carbon-centered biogeochemical cycling in extreme ecosystems and guiding organic amendment-based bioremediation in oligotrophic polluted environments.

Metagenomic insight into the acidophilic functional communities driving elemental geochemical cycles in an acid mine drainage lake

Acidophiles play a key role in the generation, evolution and attenuation of acid mine drainage (AMD), which is characterized by strong acidity (pH<3.5) and high metal concentrations. In this study, the seasonal changes of acidophilic communities and their roles in elemental cycling in an AMD lake (pH∼3.0) in China were analyzed through metagenomics. The results showed eukaryotic algae thrived in the lake, and Coccomyxa was dominant in January (38.1%) and May (33.9%), while Chlorella in July (9.5%). The extensive growth of Chlamydomonas in December (22.7%) resulted in an ultrahigh chlorophyll a concentration (587 μg/L), providing abundant organic carbon for the ecosystem. In addition, the iron-oxidizing and nitrogen-fixing bacterium Ferrovum contributed to carbon fixation. Ammonia oxidation likely occurred in the acidic lake, as was revealed by archaea Ca. Nitrosotalea. To gain a competitive advantage in the nutrient-poor environment, some acidophiles exhibited facultative characteristics, e.g. the most abundant bacterium Acidiphilium utilized both organic and inorganic carbon, and obtained energy from organic matter, inorganic sulfur, and sunlight simultaneously. It was suggested that sunlight, rather than chemical energy of reduced iron-sulfur was the major driver of elemental cycling in the AMD lake. The results are beneficial to the development of bioremediation strategies for AMD.

Comammox Nitrospira and Ammonia-Oxidizing Archaea Are Dominant Ammonia Oxidizers in Sediments of an Acid Mine Lake Containing High Ammonium Concentrations

Exploring nitrifiers in extreme environments is vital to expanding our understanding of nitrogen cycle and microbial diversity. This study presents that complete ammonia oxidation (comammox) Nitrospira, together with acidophilic ammonia-oxidizing archaea (AOA), dominate in the nitrifying guild in sediments of an acid mine lake (AML). The lake water was characterized by acidic pH below 5 with a high ammonium concentration of 175 mg-N/liter, which is rare on the earth. Nitrification was active in sediments with a maximum nitrate production potential of 70.5 μg-N/(g-dry weight [dw] day) for mixed sediments. Quantitative PCR assays determined that in AML sediments, comammox Nitrospira and AOA amoA genes had relative abundances of 52% and 41%, respectively, among the total amoA genes. Further assays with 16S rRNA and amoA gene amplicon sequencing and metagenomics confirmed their dominance and revealed that the comammox Nitrospira found in sediments belonged to comammox Nitrospira clade A.2. Metagenomic binning retrieved a metagenome-assembled genome (MAG) of the comammox Nitrospira from sediments (completeness = 96.76%), and phylogenomic analysis suggested that it was a novel comammox Nitrospira. Comparative genomic investigation revealed that this comammox Nitrospira contained diverse metal resistance genes and an acidophile-affiliated F-type ATPase. Moreover, it had a more diverse genomic characteristic on nitrogen metabolism than the AOA in sediments and canonical AOB did. The results suggest that comammox Nitrospira is a versatile nitrifier that can adapt to acidic environments even with high ammonium concentrations. IMPORTANCE Ammonia-oxidizing archaea (AOA) was previously considered the sole dominant ammonia oxidizer in acidic environments. This study, however, found that complete ammonia oxidation (comammox) Nitrospira was also a dominant ammonia oxidizer in the sediments of an acidic mine lake, which had an acidic pH < 5 and a high ammonium concentration of 175 mg-N/liter. In combination with average nucleotide identity analysis, phylogenomic analysis suggested it is a novel strain of comammox Nitrospira. Moreover, the adaption of comammox Nitrospira to the acidic lake had been comprehensively investigated based on genome-centric metagenomic approaches. The outcomes of this study significantly expand our understanding of the diversity and adaptability of ammonia oxidizers in the acidic environments.

Reactive and microbial inhibitory mechanisms depicting the panoramic view of pH stress effect on common biological nitrification

pH is a crucial factor of microbial nitrification, which often combines with high-strength ammonium to influence nitrogen removal pathway in wastewater treatment. However, the detailed inhibitory mechanisms of pH stress are not sufficiently disclosed yet. In this study, the pH stress effect on nitrification was comprehensively studied by a set of experiments which identified the reactivity of nitrification processes and activity of nitrifiers, the time dependence of inhibition effect and the hybrid pH stress effect with ammonium. The results revealed two distinct inhibitory mechanisms dominating in alkaline and acid ranges. In alkaline range (pH > 8), pH stress causes physiological damages on microorganisms which is named as microbial inhibition. It has the features of less recoverability of nitrifiers, time-dependent inhibition effect and low pH-tolerance of nitrite oxidation bacteria. Free ammonia enhanced microbial inhibition and greatly promoted nitrite accumulation. A novel reactive inhibition mechanism dominated in acid range (pH < 7) was disclosed. It only impedes ammonia oxidation process (AOP) but not impair microbial activity obviously and the effect is time-independent. The mechanism was clarified from H⁺ transport because AOP involved H⁺ production. The H⁺ transport was impeded under acid stress owing to the decrease of pH gradient across cell membrane. The two mechanisms formed a panoramic view of pH stress effect on nitrification advancing the understanding of nitrifier adaptability and nitritation regulation in wastewater treatment processes.

Facile ammonium oxidation to nitrogen gas in acid wastewater by in situ photogenerated chlorine radicals

The treatment of low-concentration ammonium (e.g., <50 mg L^-1) in highly acidic wastewaters through traditional biological nitrification, physical separation, or chemical stripping remains a huge challenge. Herein, we report that photocatalytic ammonium oxidation using bismuth oxychloride (BiOCl) can successfully occur in Cl^--laden solutions within a pH range of 1.0-6.0. All reactions follow pseudo-zero-order kinetics (with rate constants of 0.27-0.32 mg L^-1 min^-1 at pH 2.0-6.0 and 0.14 mg L^-1 min^-1 at pH 1.0), indicating the saturation of reactive species by the reactants. The interlayer is self-oxidized by the valence band holes (VB h⁺), resulting in the formation of Cl^• and subsequently HClO, which is excited upon UV irradiation to provoke consecutive photoreactions for chlorine radical generation. Compared to the free chlorine, HO^•, Cl^•, and Cl₂^•-, the ClO^• produced using the UV/BiOCl system plays a predominant role in oxidizing ammonium under acidic conditions. BiOCl exhibits good stability because of the compensation of Cl^- from solution and maintains high activity under different conditions (i.e., different cations and co-existing anions, temperatures, and initial substrate concentrations). The successful removal of ammonium from real wastewater using the UV/BiOCl system suggests that this is a promising method for treating diluted ammonium under highly acidic conditions.

Contrasting seasonal variations of geochemistry and microbial community in two adjacent acid mine drainage lakes in Anhui Province, China

Acid mine drainage (AMD) is generated by the bio-oxidation of sulfide minerals. To understand the AMD formation and evolution, it is necessary to determine the composition and variation of acidophilic community, and their role in AMD ecosystem. In this study, we compared seasonal variations of geochemistry and microbial composition of two adjacent AMD lakes with different formation histories in Anhui Province, China. Lake Paitu (PT) formed in 1970s near a mine dump and the pH was in the range of 3.01-3.16, with the lowest in spring and summer while the highest in winter. The main ions in PT were Al and SO₄^2-, whereas Fe concentration was relatively low. The concentrations of these ions were the lowest in summer and the highest in winter. Lake Tafang (TF) formed in around 2013 in a pit was more acidic (pH 2.43-2.75), but the seasonal variation of pH was the same as PT. Compared with Lake PT, TF had higher Fe, lower Al and SO₄^2- concentrations, and showed no significant seasonal changes. Despite salient seasonal variations of prokaryotic composition in Lake PT, Ferrovum was the major iron-oxidizing bacterium in most seasons. Furthermore, Lake PT was also rich in heterotrophic bacteria (48.6 ± 15.9%). Both prokaryotic diversity and evenness of Lake TF were lower than PT, and chemolithotrophic iron-oxidizing bacteria (71.7 ± 25.4%) were dominant in almost all samples. Besides Ferrovum, more acid tolerant iron-oxidizer Leptospirillum and Acidithiobacillus were also abundant in Lake TF. Chlamydomonas was the major eukaryote in Lake PT and it flourished repeatedly at the end of December, causing an extremely high chlorophyll a concentration (587 μg/L) at one sampling site in 2016, which provided rich nutrients for heterotrophic bacteria. The main alga in Lake TF was Chrysonebula, but its concentration was low, apparently because of the strong acidity and dark red color of lake water.

Adaptation of Coccomyxa sp. to Extremely Low Light Conditions Causes Deep Chlorophyll and Oxygen Maxima in Acidic Pit Lakes

Deep chlorophyll maxima (DCM) and metalimnetic oxygen maxima (MOM) are outstanding biogeochemical features of acidic pit lakes (APL). However, knowledge of the eukaryotic phototrophs responsible for their formation is limited. We aimed at linking the dynamics of phototrophic communities inhabiting meromictic APL in Spain with the formation of these characteristic layers. Firstly, the dynamics of DCM and MOM and their relation to physico-chemical parameters (photosynthetically active radiation (PAR), pH, dissolved ferric iron concentration, temperature), pigments and nutrient distribution is described; secondly, the phototrophic community composition is studied through a combination of microscopy, biomolecular and "omics" tools. Phototrophic communities of the studied APL show a low diversity dominated by green microalgae, specifically Coccomyxa sp., which have been successfully adapted to the chemically harsh conditions. DCM and MOM are usually non-coincident. DCM correspond to layers where phototrophs have higher chlorophyll content per cell to cope with extremely low PAR (<1 µmol m-2 s-1), but where photosynthetic oxygen production is limited. MOM correspond to shallower waters with more light, higher phytoplankton biomass and intense photosynthetic activity, which affects both oxygen concentration and water temperature. The main drivers of DCM formation in these APL are likely the need for nutrient uptake and photo-acclimation.

Optimization of the nitrification process of wastewater resulting from cassava starch production

The present study has the objective of optimizing operational conditions of an aerated reactor applied to the removal of ammoniacal nitrogen from wastewater resulting from the production of cassava starch. An aerated reactor with a usable volume of 4 L and aeration control by rotameter was used. The airflow and cycle time parameters were controlled and their effects on the removal of ammoniacal nitrogen and the conversion to nitrate were evaluated. The highest ammoniacal nitrogen removal, of 96.62%, occurred under conditions of 24 h and 0.15 L min^-1 L_reactor^-1. The highest nitrate conversion, of 24.81%, occurred under conditions of 40.92 h and 0.15 L min^-1 L_reactor^-1. The remaining value of ammoniacal nitrogen was converted primarily into nitrite, energy, hydrogen and water. The optimal operational values of the aerated reactor are 29.25 h and 0.22 L min^-1 L_reactor^-1. The mathematical models representative of the process satisfactorily describe ammoniacal nitrogen removal efficiency and nitrate conversion, presenting errors of 2.87% and 3.70%, respectively.

Temporal variation of bacterial population and response to physical and chemical parameters along a petrochemical industry wastewater treatment plant

The petrochemical industry has played a considerable role in generation and release of waste in the environment. Activated sludge and facultative lagoons are commonly used for domestic and industrial wastewater treatment due to their low-cost and minimal need for operational requirements. Microorganisms present in wastewater treatment plant (WWTP) are responsible for most nutrient removal. In this study, microbiological and physicochemical parameters were used to estimate changes in bacterial community in a petrochemical industrial WWTP. The activated sludge was the place with higher heterotrophic bacterial quantification. Denitrifying bacteria was reduced at least 5.3 times throughout all collections samples. We observe a decrease in the total Kjeldahl nitrogen, oxygen demand and phosphate throughout the WWTP. In this work, we also use Matrix-Assisted Laser Desorption Ionisation-Time-of-Flight Mass Spectrometry (MALDI-TOF MS) for bacteria isolates identification comparing with 16S rDNA sequencing. The MALDI-TOF MS allowed the identification of 93% of the isolates and only 5% show different results from 16S rDNA sequencing showing that the MALDI-TOF MS can be a tool for identifying environmental bacteria. The observation of microbial community dynamics in the WWTP is important in order to understand the functioning of the ecological structure formed in a specific environment.

Nitrate or ammonium: Influences of nitrogen source on the physiology of a green alga

In freshwaters, algal species are exposed to different inorganic nitrogen (Ni) sources whose incorporation varies in biochemical energy demand. We hypothesized that due to the lesser energy requirement of ammonium ( NH 4 + )-use, in contrast to nitrate ( NO 3 - )-use, more energy remains for other metabolic processes, especially under CO2- and phosphorus (Pi) limiting conditions. Therefore, we tested differences in cell characteristics of the green alga Chlamydomonas acidophila grown on NH 4 + or NO 3 - under covariation of CO2 and Pi-supply in order to determine limitations, in a full-factorial design. As expected, results revealed higher carbon fixation rates for NH 4 + -grown cells compared to growth with NO 3 - under low CO2 conditions. NO 3 - -grown cells accumulated more of the nine analyzed amino acids, especially under Pi-limited conditions, compared to cells provided with NH 4 + . This is probably due to a slower protein synthesis in cells provided with NO 3 - . In contrast to our expectations, compared to NH 4 + -grown cells NO 3 - -grown cells had higher photosynthetic efficiency under Pi-limitation. In conclusion, growth on the Ni-source NH 4 + did not result in a clearly enhanced Ci-assimilation, as it was highly dependent on Pi and CO2 conditions (replete or limited). Results are potentially connected to the fact that C. acidophila is able to use only CO2 as its inorganic carbon (Ci) source.

The cycle of nitrogen in river systems: sources, transformation, and flux

Nitrogen is a requisite and highly demanded element for living organisms on Earth. However, increasing human activities have greatly altered the global nitrogen cycle, especially in rivers and streams, resulting in eutrophication, formation of hypoxic zones, and increased production of N2O, a powerful greenhouse gas. This review focuses on three aspects of the nitrogen cycle in streams and rivers. We firstly introduce the distributions and concentrations of nitrogen compounds in streams and rivers as well as the techniques for tracing the sources of nitrogen pollution. Secondly, the overall picture of nitrogen transformations in rivers and streams conducted by organisms is described, especially focusing on the roles of suspended particle-water surfaces in overlying water, sediment-water interfaces, and riparian zones in the nitrogen cycle of streams and rivers. The coupling of nitrogen and other element (C, S, and Fe) cycles in streams and rivers is also briefly covered. Finally, we analyze the nitrogen budget of river systems as well as nitrogen loss as N2O and N2 through the fluvial network and give a summary of the effects and consequences of human activities and climate change on the riverine nitrogen cycle. In addition, future directions for the research on the nitrogen cycle in river systems are outlined.

Dominant role of ammonia-oxidizing bacteria in nitrification due to ammonia accumulation in sediments of Danjiangkou reservoir, China

Surface sediments are the inner source of contaminations in aquatic systems and usually maintain aerobic conditions. As the key participators of nitrification process, little is known about the activities and contributions of ammonia-oxidizing archaea (AOA) and bacteria (AOB) in the surface sediments. In this study, we determined the net and potential nitrification rates and used 1-octyne as an AOB specific inhibitor to detect the contributions of AOA and AOB to nitrification in surface sediments of Danjiangkou reservoir, which is the water source area of the middle route of South-to-North Water Diversion Project in China. Quantitative PCR and Illumina high-throughput sequencing were used to evaluate the abundance and diversity of the amoA gene. The net and potential nitrification rates ranged from 0.42 to 1.93 and 2.06 to 8.79 mg N kg^-1 dry sediments d^-1, respectively. AOB dominated in both net and potential nitrification, whose contribution accounted for 52.7-78.6% and 59.9-88.1%, respectively. The cell-specific ammonia oxidation rate calculation also revealed the cell-specific rates of AOB were higher than that of AOA. The Spearman's rank correlation analysis suggested that ammonia accumulation led to the AOB predominant role in net nitrification activity, and AOB abundance played the key role in potential nitrification activity. Furthermore, phylogenetic analysis suggested AOB were predominantly characterized by the Nitrosospira cluster, while AOA by the Nitrososphaera and Nitrososphaera sister clusters. This study will help us to better understand the contributions and characteristics of AOA and AOB in aquatic sediments and provide improved strategies for nitrogen control in large reservoirs.

An unexpected dual-response pH probe based on acridine

A new pH fluorescent probe 2,8-bis(acridin-9-ylethynyl)-6H,12H-5,11-methanodibenzo[b,f][1,5]diazocine (TBN), which has two acridine moieties attached to Tröger's base, is a useful fluorescent probe for monitoring extreme acidic and alkaline pH. TBN displays an excellent pH dependent behavior and responds linearly to extreme conditions in the pH ranges of 1.4–3.4 and 12.5–15.0. TBN can represent a novel type of fluorescent probe with perfect emission properties in extreme acidic and alkaline conditions by utilizing only one functional group.

A novel pH fluorescence probe for monitoring extreme acidic and alkaline pH which responds linearly to extreme conditions in the pH ranges of 1.4–3.4 and 12.5–15.0 by utilizing only the acridine moiety.

Quantifying Lake Water Quality Evolution: Coupled Geochemistry, Hydrodynamics, and Aquatic Ecology in an Acidic Pit Lake

Assessment of water quality evolution in the thousands of existing and future mine pit lakes worldwide requires new numerical tools that integrate geochemical, hydrological, and biological processes. A coupled model was used to test alternative hypothesized controls on water quality in a pit lake over ∼8 years. The evolution of pH, Al, and Fe were closely linked; field observations were reproduced with generic solubility equilibrium controls on Fe(III) and Al and a commonly reported acceleration of the abiotic Fe(II) oxidation rate by 2-3 orders of magnitude. Simulations indicated an ongoing acidity loading at the site, and the depletion of Al mineral buffering capacity after ∼5 years. Simulations also supported the existence of pH limitation on nitrification, and a limitation on phytoplankton growth other than the commonly postulated P and DIC limitations. Furthermore, the model reproduced the general patterns of salinity, pH, Al, and Fe during an uncontrolled river breach in 2011, however, incorporating sediment biogeochemical feedbacks is required to reproduce the observed postbreach internal alkalinity generation in the lake. The modeling approach is applicable to the study of hydrological, geochemical, and biological interactions for a range of lake and reservoir management challenges.

Growth of Nitrosococcus-Related Ammonia Oxidizing Bacteria Coincides with Extremely Low pH Values in Wastewater with High Ammonia Content

Ammonia oxidation decreases the pH in wastewaters where alkalinity is limited relative to total ammonia. The activity of ammonia oxidizing bacteria (AOB), however, typically decreases with pH and often ceases completely in slightly acidic wastewaters. Nevertheless, nitrification at low pH has been reported in reactors treating human urine, but it has been unclear which organisms are involved. In this study, we followed the population dynamics of ammonia oxidizing organisms and reactor performance in synthetic fully hydrolyzed urine as the pH decreased over time in response to a decrease in the loading rate. Populations of the β-proteobacterial Nitrosomonas europaea lineage were abundant at the initial pH close to 6, but the growth of a possibly novel Nitrosococcus-related AOB genus decreased the pH to the new level of 2.2, challenging the perception that nitrification is inhibited entirely at low pH values, or governed exclusively by β-proteobacterial AOB or archaea. With the pH shift, nitrite oxidizing bacteria were not further detected, but nitrous acid (HNO₂) was still removed through chemical decomposition to nitric oxide (NO) and nitrate. The growth of acid-tolerant γ-proteobacterial AOB should be prevented, by keeping the pH above 5.4, which is a typical pH limit for the N. europaea lineage. Otherwise, the microbial community responsible for high-rate nitrification can be lost, and strong emissions of hazardous volatile nitrogen compounds such as NO are likely.

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.

Significant seasonal variations of microbial community in an acid mine drainage lake in Anhui Province, China

Acid mine drainage (AMD),characterized by strong acidity and high metal concentrations, generates from the oxidative dissolution of metal sulfides, and acidophiles can accelerate the process significantly. Despite extensive research in microbial diversity and community composition, little is known about seasonal variations of microbial community structure (especially micro eukaryotes) in response to environmental conditions in AMD ecosystem. To this end, AMD samples were collected from Nanshan AMD lake, Anhui Province, China, over a full seasonal cycle from 2013 to 2014, and water chemistry and microbial composition were studied. pH of lake water was stable (∼3.0) across the sampling period, while the concentrations of ions varied dramatically. The highest metal concentrations in the lake were found for Mg and Al, not commonly found Fe. Unexpectedly, ultrahigh concentration of chlorophyll a was measured in the extremely acidic lake, reaching 226.43-280.95 μg/L in winter, even higher than those in most eutrophic freshwater lakes. Both prokaryotic and eukaryotic communities showed a strong seasonal variation. Among the prokaryotes, "Ferrovum", a chemolithotrophic iron-oxidizing bacterium was predominant in most sampling seasons, although it was a minor member prior to September, 2012. Fe²⁺ was the initial geochemical factor that drove the variation of the prokaryotic community. The eukaryotic community was simple but varied more drastically than the prokaryotic community. Photoautotrophic algae (primary producers) formed a food web with protozoa or flagellate (top consumers) across all four seasons, and temperature appeared to be responsible for the observed seasonal variation. Ochromonas and Chlamydomonas (responsible for high algal bloom in winter) occurred in autumn/summer and winter/spring seasons, respectively, because of their distinct growth temperatures. The closest phylogenetic relationship between Chlamydomonas species in the lake and those in Arctic and Alpine suggested that the native Chlamydomonas species may have been both acidophilic and psychrophilic after a long acclimation time in this extreme environment.

Cooling and eutrophication of southern Chilean lakes

Understanding the impacts of global warming and human-disturbances on lakes is required for implementing management strategies aimed at mitigating the decline of the quality and availability of water for humans. We assessed temporal trends in water parameters, and the contribution of land use to the eutrophication of the largest lakes of central-southern Chile. The mean values of water parameters varied seasonally, with lakes Chapo and Caburgua exhibiting lower pH, temperature, and N/P ratio values. Over the assessed period (19 years), we found a temporal reduction in water conductivity and temperature of the lakes. The concentration of NO3(-)-N, PO4(3-)-P and dissolved oxygen increased in all the lakes, but pH increased in eight out of the ten lakes. The negative temporal trend in temperature was more pronounced as the depth level increased. Lakes whose basins had a higher percentage of forest plantation and urban areas had larger values of Chlorophyll a and pH, as well as, smaller values of dissolved oxygen. Lakes whose basins included larger percentages of native forest had smaller nutrient (NO3(-)-N, PO4(3-)-P) concentrations. Our findings suggest that decreased rainfall in central-southern Chile due to climate change may cause a decrease of particulate material that is carried by tributaries into the lakes. The observed temporal decrease in temperature, especially at the deeper levels, may be explained by the rapid melting of glaciers. Although the studied lakes are classified as oligotrophic, deforestation and expansion of urban areas around the lakes have led to increased nutrient input, thus accelerating their eutrophication.