Lake Productivity Research Articles

Impacts of a century of land‐use change on the eutrophication of large, shallow, prairie Lake Manitoba in relation to adjacent Lake Winnipeg (Manitoba, Canada)

Abstract Evaluation of large lake response to centennial changes in land use and climate can be complicated by high spatial and hydrological complexity within their catchments, particularly in regions of low relief. Furthermore, large lakes can exhibit abrupt changes in structure and function that obscure causes of eutrophication. We provide the first quantification of historical trends in lake production, cyanobacterial abundance, sediment geochemistry and diatom composition since c. 1800 in Lake Manitoba, the 29th largest lake in the world, and compared them to Lake Winnipeg, a morphologically similar, adjacent basin with a 10‐fold larger catchment and an abrupt increase in production around 1990. Before 1900, Lake Manitoba was mesotrophic, with low sedimentary concentrations of carbon, phosphorus, nitrogen, cyanobacteria and algal pigments, as well as assemblages of low‐light‐adapted benthic diatoms. Analysis of pigment time‐series with hierarchical generalised additive models revealed that Lake Manitoba eutrophied during 1900–1930 as a consequence of the development of intensive agriculture within its local catchment, but thereafter exhibited stable cyanobacterial densities with limited expansion of N2‐fixing cyanobacteria despite persistent eutrophication. Lake Manitoba did not undergo an abrupt change as seen in Lake Winnipeg. These findings suggest that catchment size had little influence on water quality degradation and that nutrient influx from proximal agricultural sources was sufficient to initially degrade these large prairie lakes. The abrupt change in Lake Winnipeg around 1990 required additional intensification of local land use that did not occur in the Lake Manitoba catchment.

High stability of autochthonous organic matter in inland aquatic ecosystems

Recalcitrant dissolved organic matter (RDOM) is a key component of ocean carbon sinks and it can be preserved in seawater for thousands of years. However, the fate of RDOM derived from the primary production in inland lake is unclear. In this study of Erhai lake in China, used the combination of δ13C, carbon/nitrogen (C/N) ratio, and optical spectroscopy analyses to constrain the variation of organic matter in the vertical direction (i.e., lake water → trap sediments → surface sediments → core sediments), to trace the burial process of RDOM. Two autochthonous components (C1, C2) and two allochthonous components (C3, C4) were identified in the water. High concentrations of C2 in winter and spring indicate that these two seasons provide favourable burial conditions for autochthonous dissolved organic matter. Three autochthonous components (C1, C2, C5) and three allochthonous components (C3, C4, C6) were identified in the sediments. The contributions of autochthonous organic matter were ∼49.9 ± 5.84 % (based on PARAFAC analysis) and ∼56.7 ± 5.62 % (based on the C/N ratio) in the sediment trap samples; 43.4 ± 8.84 % (based on PARAFAC analysis) and 40.8 ± 14.26 % (based on the C/N ratio) in the surface sediments; and 44.5 ± 14.4 % (based on PARAFAC analysis) and 48.4 ± 6.04 % (based on the C/N ratio) in the core sediments. Additionally, C2, which is the autochthonous component after microbial mineralisation, was preserved as a significant part of the RDOM in the water. Our results suggest that the mineralisation of autochthonous organic matter (OM) in the core sediments did not promote bacterial mineralization, and that the burial of OM on long timescales dependents primarily on its concentration rather than on its origin. Our results provide a new perspective for studying the stability of autochthonous OM and highlight a new direction for the study of the carbon sink of inland lakes.

FROM ABUNDANCE TO ADVERSITY: UNDERSTANDING THE CHANGING DYNAMICS OF LAKE ALAU'S WATER QUALITY

Lake Alau, a critical water resource in the region, was subject to an extensive water quality assessment with the aim of assessing the impact of human activities on the physico-chemical parameters of Lake Alau, with a specific focus on water quality potentials of the Lake. The study spanned over a year, capturing variations in several physicochemical parameters using standard laboratory techniques. The data were computed and analysed using ANOVA. The findings reveal that the lake generally maintains water quality within permissible limits for aquatic ecosystems. The physical parameters of the lake, including Temperature, Total Solids (TS), Total Dissolved Solids (TDS), and Total Suspended Solids (TSS), were within the range of a productive lake, but higher concentrations of TDS (365.68g/L) and TSS (171.95g/L) might have altered the ecological balance of the lake. The chemical parameters, including pH, biochemical oxygen demand (BOD), Chemical Oxygen Demand (COD), Nitrite, Nitrate, and Phosphate, were within the permissible limit for a productive lake, supporting the biological parameters of the lake However, phosphate concentrations exceed 0.1mg/l which is the limit for drinking water. The observed variations underscore the lake's vulnerability to human activities and seasonal changes. Despite some concerns, Lake Alau remains suitable for aquatic life, with certain water quality management practices recommended to maintain its intergrity.

Annual growth of brown trout in alpine lakes is highly influenced by spring snow depth and ice-out day

Growth of annular zones in otoliths of brown trout from the alpine lakes Litlosvatn and Kollsvatn on western part of the Hardangervidda mountain plateau have been studied during the period 2004–2021, concurrent with recordings of accumulated snow in spring and dates of ice-out. Unlike the conditions in lowland areas, years with much accumulated snow have not decreased during the last decades, and years with delayed ice break-up are still frequent, opposite the trend observed elsewhere in Europe and in North America. The annual growth of the brown trout otoliths is significantly reduced in years with much snow in April and late ice-out dates, irrespective of age of the fish, indicating that somatic growth of brown trout is considerably reduced in such years. Accumulated snow in spring and ice-out day may thus be useful parameters in predictions of fish production and potential yield in such alpine lakes.

Variability in lake bacterial growth and primary production under lake ice: Evidence from early winter to spring melt

AbstractClimate change is causing seasonally ice‐covered lakes of the boreal region to undergo changes in their winter regime by altering patterns of precipitation and temperature, often reflected as reduced snow and ice cover duration. The duration, extent and quality of ice, and snow cover have a pivotal role for production and carbon cycling in lakes in winter, with potentially cascading effects for the following open water period. We investigated under‐ice carbon cycling by assessing bacterial growth (including bacterial production, bacterial respiration, and bacterial growth efficiency) and primary production at five water depths during early winter, midwinter, late winter and melting season in a boreal lake, and report significantly different temporal patterns. Bacterial respiration was dominant in early and midwinter, whereas the late winter and melting season were dominated by bacterial production. Multiple linear regression models indicated that high early winter bacterial respiration was associated with senescing phytoplankton, whereas bacterial production was promoted by the onset of spring processes. Collectively, bacterial growth indices were inherently linked with bacterioplankton community composition and specific biomarker taxa. Primary production under ice increased in late winter when light‐blocking snow cover melted, and primary production measured from the lake ice exceeded that of the water column at the melting season. Ice samples hosted diverse eukaryotic communities including photoautotrophs, suggesting that the habitat potential of the understudied lake ice and the role of ice for ecological processes at ice melt should be further explored.

Seasonal variation of gross ecosystem productivity of periphyton in three post-mining lakes in the Czech Republic, Europe

We investigated the seasonal variation of gross ecosystem productivity (GEP) of periphyton biomass in three post-mining lakes in the Czech Republic. These lakes were established as part of recultivation efforts after coal mining activities and resulted in a unique series of anthropogenic oligotrophic lakes of gradual successional age. Periphyton is ubiquitous in aquatic habitats and performs numerous environmental functions such as nutrient cycling and self-purifying of aquatic ecosystems. Well-developed periphyton mat can be formed within a few weeks, so it can quickly become the dominant of littoral zone of newly established lakes. In studied post-mining lakes, the highly developed periphytic community covers the littoral zone of each lake to the depth of 2m (Bešta et al. 2022, Konopáčová et al. 2023) Fig. 1. We aimed to shed some new light on the processes controlling the dynamics of primary productivity in oligotrophic lakes. The accurate estimation of primary productivity is crucial for understanding the functioning of aquatic ecosystems, as primary productivity serves as the primary source of autochthonous carbon in these systems. In addition to phytoplankton, periphyton can significantly contribute to primary productivity in littoral zones, known for their high productivity and biodiversity. Conducting in situ measurements provides the most accurate means of inferring the metabolic activity of primary producers in littoral zones. We conducted detailed seasonal in-situ periphyton gross primary production (GPP) measurements in three post-mining lakes with different successional ages (Čapková et al. 2022). GPP and NPP of periphytic biomass were determined using direct in-situ measurement of O2 fluxes. O2 production and consumption were measured over 5 hours of in-situ light and dark gas-tight glass bottle incubation. Bottles were filled with the lake water from the corresponding depth, and a similar amount of periphytic biomass was enclosed Fig. 2. We used the Fibox3 fibre-optic oxygen meter coupled with a PSt3 oxygen sensor (PreSens, Regensburg, DE) to measure changes in O2 concentration. The O2 fluxes were normalized to periphytic biomass in each bottle (measured as total organic carbon). Data were corrected for O2 concentration changes in dark and light gas-tight bottles containing lake water without periphytic communities. This setup enabled us to monitor online oxygen flux, therefore, insights into metabolic activities. The primary productivity was measured in real-time, allowing us to capture the quantitative effect of various environmental drivers on periphyton productivity, i.e. phosphorus concentration and light intensity, as they are known to play significant roles in primary productivity. We showed that the primary production of periphyton mats exhibited seasonal variations, with higher productivity observed in spring compared to other seasons. This observation could be attributed to the occurrence of winter/spring upwelling events and vertical mixing, which resupply nutrients from the deeper strata. Furthermore, the physiological activity of periphyton was strongly influenced by the seasonal changes in light intensity, temperature, and nutrient concentration. We provided the first insight into the seasonal variation of primary productivity of the periphyton assemblage dominating the littoral zone of newly established post-mining lakes. We stress the importance of periphyton in aquatic ecosystems, particularly in anthropogenic oligotrophic lakes.

Unveiling the ecological significance of algal mats and meadows: Insights into phosphorus cycling and primary production of benthic algae in post-mining lakes

Post-mining lakes are anthropogenic water bodies increasing globally due to mining suppression and recultivation. These lakes have ecological and socioeconomic significance, providing freshwater sources, wildlife habitats, and recreation potential. However, research on primary producers in these lakes is limited, with most studies focusing on phytoplankton while neglecting algal mats and meadows. If developed in high biomass, algal mats and macroalgal meadows play a crucial role in aquatic ecosystems. They contribute to the trophic structure, nutrient fluxes, primary production and to the purification of entire waterbodies. Yet, there is a lack of knowledge regarding the nutrient acquisition and the contribution of algal mats and meadows to total primary production and phosphorus (P) cycling, especially in oligotrophic lakes, including post-mining lakes. Our team investigates the benthic algal primary producers - algal mats and meadows in the littoral zone of tree newly established post-mining lakes located in the Czech Republic (Europe). Our main objectives are to describe the quality and quantity of primary producers, quantify the contribution of algal mats and meadows to the primary production and phosphorus cycling in the oligotrophic post-mining lakes. We have studied them throughout all seasons with a special focus on the generally neglected winter/spring season. Our sampling strategy encompasses three gradients of variability along which the composition and ecological role of benthic algae change: spatial variability along the depth gradient within each lake, itemporal variability throughout the seasons within each lake and successional variability between the lakes of different age. spatial variability along the depth gradient within each lake, itemporal variability throughout the seasons within each lake and successional variability between the lakes of different age. The methodological approach consists of measuring the limnological and chemical parameters of lakes, taxonomic determination, biomass estimation and C:N:P stoichiometry of algal biomass along the whole gradient of the euphotic zone (0-15m). The in situ measurement of primary production of benthic algae from various depths using the oxygen meter Fibox 3 (PreSens, Germany) with a combination of laboratory experiments was employed too (Čapková 2022). We measure the kinetic parameters of P uptake of algal mats and meadows using 33P-labelled orthophosphates under controlled conditions similar to the nature (Konopáčová 2021). According to our survey, algal mats and meadows exhibited high productivity in the entire littoral zone. Algal mats dominate the depth up to 3m Fig. 1 and are highly diverse, with more than 400 identified taxa (Bešta 2022). Macroalgal meadows formed by the genus Chara together with the genus Vaucheria, are key taxa occupying the deeper zone (3-15m) Fig. 2. The distribution of benthic algae in lakes is influenced by depth gradients, substrate quality, seasonality and age of lakes foundation, resulting in complex spatio-temporal patterns. Specific emphasis is placed on the fate of P, which is the limiting nutrient in investigated lakes. High C:P molar ratios in microalgal mats indicate strong P deficiency in studied lakes. Over the vegetation season, microalgal biomass doubled, while the P content in biomass dropped to 60% of the values from the start of the vegetation season. The maximum uptake velocity and specific P uptake affinity decreased by an order of magnitude from April to October, and P uptake affinity was measured for comparison in plankton too. Based on our results, we proposed a possible mechanism underlying a stable coexistence of planktonic and benthic primary producers, with plankton prospering primarily in summer and autumn and algal mats and meadows in winter and spring seasons. By integrating data collected during five years of investigation, our study aims to provide a comprehensive understanding of the ecological roles of primary producers in post-mining lakes.

Paleoenvironmental changes on the central Tibetan Plateau over the last two millennia inferred from sedimentological proxies and brGDGTs in Bamu Co

Understanding multi-centennial climate variations and their impact on lake catchment productivity over the last 2000 years (the Common Era), is crucial for assessing the role of natural climatic factors in driving productivity changes, and for predicting productivity changes under recent global warming scenarios. However, the climate patterns on the Tibetan Plateau (TP), including temperature and hydrological variations, during the Common Era, and their possible links with productivity, are poorly understood. We present a quantitative reconstruction of mean annual air temperature (MAAT), together with grain size and other sedimentary records, from a non-glacial lake sediment archive on the central TP, with the objective of tracking changes in climate and lake catchment productivity over the past two millennia. Our results reveal an overall cooling trend in temperature reconstructed from branched glycerol dialkyl glycerol tetraethers (brGDGTs), with multi-centennial-scale fluctuations superimposed. These fluctuations include relatively warm periods during 200 BCE–400 CE and the Medieval Climate Anomaly (1050–1400 CE), and cold periods centered on ∼500–1000 CE and the Little Ice Age (∼1500–1900 CE). A rapid warming trend since 1900 CE corresponds to the Current Warm Period. The variations in sedimentary grain size reflect lake level changes associated with changes in the summer monsoon. Paleoproductivity inferred from total organic carbon (TOC) shows a similar pattern to the paleoclimate records, suggesting that millennial-scale productivity was influenced by both temperature and the catchment hydrology. In recent decades, human activities exerted a more substantial influence on lake productivity. Additionally, we suggest that the use of brGDGTs for temperature reconstruction necessitates the investigation of the temperature relationship of various fractions of brGDGTs, specifically tetramethyl-brGDGTs; and that careful selection of the temperature calibration equation is needed to minimize inaccuracies in paleotemperature reconstruction.

Lipid Biosignatures From SO4‐Rich Hypersaline Lakes of the Cariboo Plateau

AbstractModern and ancient hypersaline brines have been identified across the solar system, but the habitability of these environments remains unknown. Here, we evaluate organic matter (OM) production in MgSO4 and Na2CO3 rich hypersaline lakes whose chemistries resemble deposits on Mars such as those identified in Jezero crater. We focus our analysis on lipid biomarkers including fatty acids, alkanes, and ether‐bound lipids in modern brines, salt deposits, and surface sediments. We also report total organic carbon (TOC), carbon/nitrogen (C/N) ratios, and bulk OC (δ13C and δ15N) isotopes to contextualize the lipid biomarker data. In all lakes, the predominant biosignatures include midchain (12 < C < 23) fatty acids and alkanes suggesting microbial origin. Sediments also incorporate a greater diversity of lipids. Ether‐bound lipids derived from archaea and bacteria constitute a minor but measurable fraction of the lipids. This result contrasts with typical findings from other studies with NaCl brines which contain significant archeal biomass. TOC concentrations in all sediments are high, ranging from 0.7% to 12% with sulfate‐rich sediments having the highest concentrations. The isotopic and elemental compositions of TOC corroborate the biomarker results, showing δ13C values and C/N values indicative of aquatic microbial origin. This richness of organic matter and in situ microbial biosignatures differ from previously studied Cl‐dominated Mars‐analog sites which have shown limited OM production and preservation and acidic SO4‐rich hypersaline environments which were dominated by terrestrial inputs. Overall, our results suggest that MgSO4‐rich hypersaline environments are conducive for life and harbor a rich microbial biomarker landscape.

The effects of terrestrial dissolved organic matter on phytoplankton biomass and productivity in boreal lakes

Abstract Allochthonous dissolved organic matter (DOM) structures many physical, chemical, and biological properties of lakes including key variables that control productivity at the base of freshwater food webs. A growing number of studies have documented increasing DOM concentrations within lakes across Europe and North America, including boreal lakes. Such increases are associated with the recovery of catchment soils from acid rain and rising precipitation linked to climate change. We examined phytoplankton biomass, productivity, and their drivers across eight pristine boreal lakes with DOM ranging from 3.5 to 9.5 mg dissolved organic carbon/L. Physical and chemical properties were assessed using standard limnological methods. Phytoplankton biomass was assessed using both chlorophyll a (Chl‐a) and via microscopy. Phytoplankton productivity was assessed using change in partial pressure of carbon dioxide within in vitro incubations. Increases in DOM were associated with significant increases in epilimnetic nitrogen, phosphorus and Chl‐a concentrations suggesting that nutrients associated with DOM stimulated phytoplankton biomass and productivity. Such results were misleading; there was no significant relationship between Chl‐a and phytoplankton biomass. Chl‐a:biomass and Chl‐a:carbon ratios indicated that increases in Chl‐a with DOM were driven by photo‐acclimation to declining light availability. Further, results presented as epilimnetic concentrations would not account for concurrent declines in thermocline depth or euphotic depth driven by DOM. Increases in DOM led to large declines in thermocline (c. 50%) and euphotic (c. 75%) depths, and depth‐integrated phytoplankton biomass (c. 70%) and primary production (c. 70%). Our results indicate that DOM plays a structuring role for key physical, chemical, and biological properties of lakes, including productivity, at a landscape level. Further, practitioners should be cautious when using Chl‐a as an indicator of phytoplankton biomass in studies using DOM or water clarity gradients, report results using depth integrated units due to changes in volumes of thermal layers induced by DOM, and incorporate estimates of sub‐epilimnetic productivity when evaluating DOM effects.

Spatiotemporal patterns and drivers of phytoplankton primary productivity in China's lakes and reservoirs at a national scale

Spatiotemporal patterns and drivers of phytoplankton primary productivity in China's lakes and reservoirs at a national scale

Paleohydrological changes during the Late Holocene recorded in the sediments of two mountain lakes in the Tatra Mountains (Central Europe)

Changes in local hydrological and climatic conditions over the last 5500 years have been reconstructed based on geochemical and paleobiological features recorded in the sediments of two mountain lakes. The lakes are located in the Tatra Mountains, in the highest mountain range of the Carpathians (Central Europe), which during the Holocene constituted an important climatic barrier. Because both studied lakes are relatively shallow, even relatively minor fluctuations in water level are clearly recorded both in the geochemical characteristics of the sediments and in the phyto- and zooplankton communities. The multiproxy records indicate several periods of high water stands: 5.4–5.2 ka, 3.5–2.7 ka, 1.4–1.0 ka and 0.5–0 ka, and prominent dry periods 2.7–2.1 ka and 1.7–1.5 ka. Comparison of the reconstructed water levels of the Tatra lakes with records from other European regions suggests that at the boundary of the Middle and the Late Holocene, the hydrological conditions in the Tatras were similar to those in Western and Central Europe. Later, beginning approximately 3500 years ago, records from the Tatras, the northern surroundings of the Pannonian Basin, and the southern part of the Carpathians were unified. In addition to changes in local and regional hydrology, the records from the studied lakes allowed us to reconstruct changes in lake productivity. Relatively high δ13C values, compared to the sedimentary organic matter of other lakes in the region, point to in-lake primary production as a major source of sedimentary organic matter in both lakes. The stable C:N ratio values suggest a constant proportion of organic matter coming from in-lake primary production and transported from the lake catchment. However, the amount of organic carbon and nitrogen and, most of all, differences in the composition of stable C and N isotopes indicate changes in the lake environment. These changes were correlated with some paleotemperature proxies from the region.

Methane and CO2 production in the wetland Lake Podpeč (Slovenia)

PurposeThis study deals with the identification of CH4 and CO2 sources in the high-carbonate wetland Lake Podpeč in the Ljubljana Marshes, Slovenia.Materials and methodsLake Podpeč is situated on the periphery of the Ljubljana Marshes in central Slovenia. A combination of chemical analysis and natural abundance analysis of stable carbon and hydrogen isotopes of CH4, along with analysis of dissolved inorganic carbon (DIC), was employed in an incubation experiment.Results and discussionThe isotopic composition of dissolved inorganic carbon (δ13CDIC) suggests three main processes occurring during incubation: oxic degradation of organic matter (OM), anoxic OM degradation, and methanogenesis. During oxic degradation of OM, the δ13CDIC values slightly decrease from − 13.2 to − 14.5‰. However, after 50 days, the δ13CDIC values started to increase, reaching − 12.2‰ by the end of the experiment. 13C enrichment coincided with the formation of CH4, which began to increase simultaneously. The CH4 produced had an average δ13CCH4 value of − 67 ± 1‰ and δ2HCH4 value of − 389 ± 3‰, suggesting that CH4 is formed through acetate fermentation. The contribution of calcite dissolution to DIC increased during the degradation of OM by 53%. However, during methanogenesis, there was no significant change in the concentrations of Ca, and the estimated contribution to DIC was only 3%.ConclusionsThis study enhances our understanding of methane production in wetland Lake Podpeč and its relevance in the context of other high-carbonate lakes. The findings offer insights into the complex interactions between OM degradation, methane production pathways, and carbonate dissolution, which has implications for the global carbon cycle and greenhouse gas emissions.

High phytoplankton diversity in eutrophic states impedes lake recovery

AbstractAimThe widely observed positive response of productivity to biodiversity, known as the biodiversity‐productivity relationship (BPR), underpins nature‐based solutions for mitigating and adapting to global changes. Little is known of the role of such emergent processes in the restoration of damaged ecosystems. Here, we test for evidence of a BPR in degraded freshwater lakes, and its role in underpinning or undermining lake recovery from eutrophic states.LocationLower Yangtze and Huaihe river basins, China, East Asia.TaxaFreshwater phytoplankton; also macrophytes, fish, zooplankton and zoobenthos.MethodsA systematic review of biodiversity studies was conducted to enumerate freshwater biodiversity change during eutrophication, encompassing 572 samples from 155 lakes in East China. Empirical samples were then taken of 93 phytoplankton communities from 38 lakes in ecologically degraded states of eutrophication. Samples were analysed for niche overlap in relation to biodiversity and productivity, and metrics of network structure indicative of community stability.ResultsReviewed publications on eutrophication in East China lakes revealed losses in biodiversity of macrophytes, fishes, zooplankton and zoobenthos but not phytoplankton. Empirically sampled eutrophic lakes maintained high phytoplankton biodiversity through niche differentiation, and phytoplankton biodiversity correlated positively with biomass, in line with the expectations of BPR.ConclusionsThe positive effect of biodiversity on phytoplankton productivity in eutrophic lakes acts in opposition to the negative impacts on productivity induced by eutrophication‐management strategies of nutrient suppression. In degraded systems, the BPR contributes to sustaining productivity of lake phytoplankton communities, impeding recovery from a eutrophic state. This is a case of the BPR playing an undesirable role at the ecosystem level. Lake recovery programmes need to anticipate that the control of phytoplankton biomass will depend on reducing nutrients to a level sufficient to degrade the internal structure of the phytoplankton community.

Spatial and Seasonal Variations in Dissolved Methane Across a Large Lake

AbstractLakes process large volumes of organic carbon (OC), are important sources of methane (CH4), and contribute to climatic warming. However, there is a lack of data from large lakes >500 km2, which creates uncertainty in global budgets. In this data article, we present dissolved CH4, OC bioreactivity measurements, water chemistry, and algal biovolumes at 11 stations across Lake Mälaren, the third largest (1,074 km2) Swedish lake. Total phosphorus concentrations show that during the study period the lake was classed as mesotrophic/eutrophic. Overall mean CH4 concentration from all stations, sampled five times to cover seasonal variation, was 2.51 μg l−1 (0.98–5.39 μg l−1). There was no significant seasonal variation although ranges were greatest during summer. Concentrations of CH4 were greatest in shallow waters close to anthropogenic nutrient sources, whilst deeper, central basins had lower concentrations. Methane correlated positively with measures of lake productivity (chlorophyll a, total phosphorus), and negatively to water depth and oxygen concentration, with oxygen emerging as the sole significant driver in a linear mixed effects model. We collated data from other lakes >500 km2 (n = 21) and found a significant negative relationship between surface area and average CH4 concentration. Large lakes remain an understudied contributor to the global CH4 cycle and future research efforts should aim to quantify the spatial and temporal variation in their diffusive and ebullitive emissions, and associated drivers.

Investigating the impact of climate change on the lake ecosystem during the late Holocene using a sedimentary record from the southern Arabian Desert, Yemen

Lake systems respond physically, chemically, and biologically to hydro-climatic change and variability, and these responses are documented in the sediments. Individual proxies and lacustrine environments may respond to climate variations in a nonlinear way, making it difficult to determine the direction and extent of a climatic shift. Here we investigate the response of lake ecosystem to climatic and environmental changes using a suite of paleo-proxies including ostracods, chironomids, and n-alkanes distribution from paleolake ‘Gayal el Bazal (Yemen)’. A previous study from this site has provided a continuous, and high-resolution dataset providing an understanding of precipitation during the last ca 1200 years, particularly during Medieval Climate Anomaly (MCA) and Little Ice Age (LIA). However, the response of the lake ecosystem to these changing hydro-climate conditions, including water-level, salinity, and productivity, remains unknown. The n-alkanes dataset shows that during pluvial interval such as the MCA, the lake experienced an increase in nutrient input resulting in enhanced aquatic productivity. Concurrently, ostracods assemblage displays an increased abundance of swimmer species (like Bradleytriebella lineata and Fabaeomiscandona cf. breuili), suggesting an indirect response between ostracods and climate shifts. The chironomid community during the MCA interval is dominated by taxa belonging to the subfamilies of Chironomini, suggesting a warm, shallow, productive environment with macrophyte vegetation. The LIA interval is marked by increased abundance of higher-chain length n-alkanes, suggesting increased contribution from higher plants. Furthermore, ostracod distribution revealed increased abundance of non-swimmer species like Vestalenula cylindrica., which thrive under saline conditions in the lake. Changes in abundances of Tanytarsini during the LIA interval, which are associated with higher oxygen levels, suggest changes in lake productivity. As a result, the overall patterns in biological indicators reveal that their individual abundance and species/tribe distribution fluctuates in response to changes in the climate and hydrological conditions.

Millennial hydrological variability in the continental northern Neotropics during Marine Isotope Stages (MISs) 3–2 (59–15 cal ka BP) inferred from sediments of Lake Petén Itzá, Guatemala

Abstract. Lake Petén Itzá (Guatemala) possesses one of the longest lacustrine sediment records in the northern Neotropics, which enabled study of paleoclimate variability in the region during the last ∼400 000 years. We used geochemical (Ti, Ca/(Ti+Fe) and Mn/Fe) and mineralogical (carbonates, gypsum, quartz, clay) data from sediment core PI-2 to infer past changes in runoff, lake evaporation, organic matter sources and redox conditions in the water column, caused by hydrological changes in the northern Neotropics during Marine Isotope Stages (MISs) 3–2. From 59 to 39 cal ka BP climate conditions were relatively wet, and the lake was marked by higher primary productivity and anoxic bottom waters. This wet environment was interrupted for two periods of possible low water level at 52 and 46 cal ka BP, when our data suggest higher evaporation, high terrestrial organic matter input and persistent oxic conditions. Between 39 and 23 cal ka BP, evaporation and input of terrestrial organic matter increased considerably, lake level declined, and lake bottom waters generally became oxic. These conditions reversed during the Last Glacial Maximum (23.5–18.0 cal ka BP), when runoff and lake productivity increased, and rising lake level caused bottom waters to again become anoxic. Comparison of our hydrologic proxy data with sea surface temperature anomalies between the eastern Pacific and the Caribbean suggests that changes in the intensity of the Caribbean Low-Level Jet (CLLJ) may have influenced long-term changes in runoff during MISs 3–2. Higher intensity of the CLLJ during the onset of MIS 3 and the LGM might have led to greater runoff into the lake, whereas the MIS 3–2 transition experienced a weaker CLLJ and consequently less runoff. A refined, high-resolution age–depth model for the PI-2 sediment core enabled us to identify millennial-scale Greenland interstadials (GIs) 14–2, Greenland stadials (GSs) 14–2 and Heinrich stadials (HSs) 5–1. In general, HSs and GSs were characterized by drier conditions. In contrast to GSs and HSs, GIs were characterized by greater runoff and overall wetter conditions, with the most pronounced GI peaks between 40 and 30 cal ka BP. Whereas GSs 9, 8, 7 and 6 began with abrupt increases in evaporation and ended with gradual increases in humidity, GSs 11 and 10 showed reversed patterns. The Lake Petén Itzá paleohydrology record, along with other regional paleoclimate records, led us to conclude that shifts in the position of the Intertropical Convergence Zone (ITCZ) altered moisture delivery to the lake on millennial timescales. During GSs and HSs, high evaporation from Petén Itzá (dry climate conditions) was associated with a more southerly position of the ITCZ, whereas wetter GIs prevailed during a more northerly ITCZ position. Although abrupt millennial-scale shifts in ITCZ and hydroclimate between GSs/HSs and GIs can be linked to instabilities in the Atlantic Meridional Overturning Circulation (AMOC), longer-term changes were additionally influenced by changes in atmospheric convection linked to modulations of the CLLJ in response to ΔSST between the equatorial Pacific and tropical Atlantic.

Mercury and amino acid content relations in northern pike (Esox lucius) in subarctic lakes along a climate-productivity gradient

Mercury is a highly toxic element for consumers, but its relation to amino acids and physiology of wild fish is not well known. The main aim of this study was to evaluate how total mercury content (THg) of northern pike (Esox lucius) is related to amino acids and potentially important environmental and biological factors along a climate-productivity gradient of ten subarctic lakes. Linear regression between THg and sixteen amino acids content [nmol mg−1 dry weight] from white dorsal muscle of pike from these lakes were tested. Lastly, a general linear model (GLM) for age-corrected THg was used to test which factors are significantly related to mercury content of pike. There was a positive relationship between THg and proline. Seven out of sixteen analysed amino acids (histidine, threonine, arginine, serine, glutamic acid, glycine, and aspartic acid) were significantly negatively related to warmer and more productive lakes, while THg showed a positive relationship. GLM model indicated higher THg was found in higher trophic level pike with lower cysteine content and inhabiting warmer and more productive lakes with larger catchment containing substantial proportion of peatland area. In general, THg was not only related to the biological and environmental variables but also to amino acid content.

Excessive use of chemical fertilizers in catchment areas raises the seasonal pH in natural freshwater lakes of the subtropical monsoon climate region

In recent years, the pH of some oligotrophic natural freshwater lakes in the subtropical monsoon climate region has generally reached an extremely high level of approximately 9.0 during the summer and autumn. It has not been proven that the explanation for why carbon assimilation in productive lakes exceeds carbon supply and causes a rise in pH also applies to oligotrophic freshwater lakes. Regardless, this may have been caused by changes in the solute composition of inflowing rivers as a result of changes in land use in catchment areas. Beimiao Reservoir in Baoshan City, Yunnan Province, where pH has increased significantly in summer and fall over the past few years, was chosen for this research in order to verify this hypothesis. This paper evaluates the status quo of water quality and nutrition in this reservoir. In addition, this paper analyzes the effects of water temperature, the metabolism of aquatic organisms, and river input on the horizontal and vertical spatial differences, diurnal variations, seasonal changes, and annual changes in the pH of the reservoir. It was discovered that one of the primary causes of the pH increase in natural freshwater lakes in the subtropical monsoon climate region during summer and autumn can be summarized as follows: A large amount of nitric acid and sulfuric acid are produced in the soil when chemical fertilizers are overused in runoff areas, particularly during intensive horticultural crop cultivation. Therefore, the subtropical monsoon climate region's soil loses calcium and magnesium ions, whose combined equivalent concentrations significantly exceed those of bicarbonate ions. The combined equivalent concentrations of calcium ions and magnesium ions in the inflowing rivers in summer and autumn are also significantly higher than those in the lake, resulting in the depletion of free carbon dioxide caused by calcium carbonate precipitation and an increase in pH. The conclusion of this research casts new light on the preservation and treatment of the ecological environment of lake water with similar issues.

Paleoindian land use at pluvial Lake Mojave: A temporally and seasonally dynamic wetlands resource patch in California’s central Mojave Desert

This study creates and preliminarily tests a biotic resource structure and optimal foraging theory inspired land use model for Silver Lake, one of two playa lakes that once formed pluvial Lake Mojave in California’s central Mojave Desert. The land use model predicts that when Silver Lake was a high-rank resource patch, Paleoindians optimally decreased inter-basin mobility as part of a wetland stable strategy (WSS); conversely, when Silver Lake was a low-rank resource patch, Paleoindians optimally increased inter-basin mobility using a wetland transient strategy (WTS). Specific land use expectations are developed in 500-year timesteps for the period 14.0–9.0 ka based on yearly and seasonal variations in the productivity of Silver Lake’s wetland habitat. Data limitations with the fine-grained version of the model led us to test a simplified version that supports the hypothesis that Paleoindians selected the optimal land use solution, a WTS, when Silver Lake was a low-rank wetlands resource patch during the terminal Pleistocene/Early Holocene (TP/EH) and more recent groups a WSS when patch rank improved after the Early Holocene. Though the simplified model’s conclusion that Paleoindians employed a WTS during the TP/EH fits the available archaeological evidence at Silver Lake and broader Great Basin/Mojave Desert, it is a static interpretation that implies Paleoindians used a single land use strategy during the several thousand-year TP/EH. This is unrealistic because pluvial lakes were dynamic water bodies that fluctuated through time and directly influenced the extent of and caloric returns from the available wetland habitat. Despite the current inability to test the fine-grained model, which we think would reveal temporal and seasonal variations in Paleoindian land use, not considering or integrating such factors into land use models misses opportunities to better understand the myriad decisions Paleoindians made under ever changing resource structure conditions.