Nearby Lake Research Articles

Wind‐driven hydrodynamic and depositional patterns in shallow lakes: An exploratory modelling approach based on an archetypal case of Lake Hulun

ABSTRACTLake Hulun, the fifth‐largest lake in China, is a shallow lake (water depth <10 m) with typical wave‐dominated landforms developed around the shoreline, with a semi‐enclosed bay located in its southern corner. This novel study aims to understand wind‐driven hydrodynamics and its related depositional patterns in the data‐sparse Lake Hulun. To achieve this, a series of numerical simulations were conducted with a hydrodynamic and sediment transport model. The simulated hydrodynamic patterns are greatly influenced by wind direction shifts but are subject to little impact from wind speed changes which act mainly to accelerate flow. By varying the location and depth of the deepest part of the lake, this study reveals that the location of the depth centre has little impact on the overall hydrodynamic pattern of wind‐driven waterbodies. When the wind direction is perpendicular to the long‐axis shore, currents around the short‐axis shore flow in a direction that follows the wind direction. This study considers the wind‐induced longshore currents that are oblique to the long‐axis shore as the main driving force in transporting sediments along the shore and erosion of the shoreline. The formation of semi‐closed bays in both Lake Hulun, together with its nearby sister lake – Lake Buir – are attributed to the north‐west prevailing wind direction. Further exploratory simulations confirmed that prevailing winds tend to induce parallel distributed submerged sediment accumulations in the nearshore zone, challenging the notion of sediment accumulation solely in deep water zones. This study provides valuable insights into the hydro‐sedimentary dynamics in wind‐driven waterbodies, offering a process‐based perspective and contributing to current understanding of the palaeogeography of ancient lake systems.

Midlatitude mesosphere and lower thermosphere variations during the extreme gannon geomagnetic storm in May 2024

Recent studies based upon both observations and numerical simulations have indicated the impacts of the intense geomagnetic storms induced by Coronal Mass Ejections (CMEs) on the neutral dynamics in the mesosphere and lower thermosphere (MLT). Even in the midlatitude MLT, far equatorward of subauroral zone, significant variations were reported. Aurora is one of the major dynamic drivers in the MLT in high latitudes, but observations of the neutral dynamic variations under the aurora in the storm time MLT are sparse. The lack of such MLT observations during the presence of aurora leads to a critical gap in the understanding of upper atmospheric dynamics. In this paper, we present the unprecedented observations under the aurora during the Gannon Geomagnetic Storm in May 2024 by the Na Doppler lidar at Utah State University (42°N, 112°W) and the Advanced Mesospheric Temperature mapper (AMTM) at the nearby Bear Lake observatory (BLO). Significant warming (as much as ∼50 K) accompanied by fast equatorward flow in the lower thermosphere (up to ∼100 m/s changes in the meridional wind above 100 km altitude) were observed. The temperature enhancement (∼10 K) of the hydroxyl layer during the same period is also captured by the AMTM. Intriguingly, significant storm time depletion of sodium (Na) abundance on the topside of the mesospheric Na layer above 105 km, as much as more than 80%, was also observed. These observations provide insight for future investigations on the MLT responses to the intense geomagnetic storms, especially the role of aurora in these events.

U-Pb ages and Hf isotope data from detrital zircons in the metasedimentary rocks of the Mongolian Altai Group, Mongolian part of the Altai-Mongolian Terrane: implications on the provenance and tectonic setting

Abstract In this paper, we present the new results of the U–Pb age dating and Lu-Hf isotopic analysis of detrital zircons of the four representative metasedimentary rock samples from the Mongol Altai Group, Mongolian part of the Altai-Mongolian terrane. Our new results indicate that the metasedimentary rocks of the Mongol Altai Group were formed after ∼497 Ma, Late Cambrian and deposited during the Early-Middle Ordovician. The detrital zircons of four samples yield a two major age peaks at 503–517 Ma, and 775–843 Ma, respectively, with minor involvement of older zircons. The nearby Lake Zone of Ikh-Mongol Arc most likely provided plenty of Early Paleozoic materials, the subdominant Neoproterozoic detrital zircons could be supplied by the felsic intrusions along the western margin of the Tuva-Mongol microcontinent, and the sparse older zircons may be derived from its basement. With combination of previous studies in the Chinese Altai, Russian Altai and Hovd terrane, our data suggest that the Altai–Mongolian terrane possibly represents a coherent continental arc-accretionary prism system built upon the active margin of the western Mongolia during the Cambrian to Ordovician. Moreover, the dominant Neoproterozoic to Early Paleozoic detrital zircons from the Mongol Altai sequence yield largely varied εHf(t) values from −17.4 to +12.0, indicating that input juvenile material and reworking of crustal components are both important in the accretionary orogenesis. A compilation of U–Pb and Hf isotope data of detrital zircons shows that the source area underwent two most extensive magmatic activities at ca. 470–574 Ma and 687–967 Ma, respectively.

Distribution and in situ bioaccumulation test of radioecologically relevant metals in boreal freshwater sediments

Sediments act as important sinks for metals and their radionuclides in aquatic environments and play a crucial role in their transfer and uptake to aquatic organisms. Traditional radioecological models use radionuclide concentrations in water to predict concentrations in aquatic organisms. In this study, we investigated the distribution of radioecologically important metals (Ba, Co, Ni, Sr, U) among sediment, porewater and hypolimnion over seasons. We also studied the uptake of these metals to benthic organisms and importance of sediment as an uptake source by conducting a 28-day in situ bioaccumulation experiment with oligochaete worms (Lumbriculus variegatus). The studied metals were chosen based on common occurrence of their radioactive isotopes in nuclear fuel cycle. Measurements of total elemental concentration were used as proxies to study the behavior of specific radionuclides. Sediment and water samples were collected from two small lakes connected to a former uranium mine in Eastern Finland, and from a nearby reference lake connected to a different drainage area. Environmental characteristics and concentrations measured from sediment, porewater and overlying water indicated only minor changes between seasons. Measured metals were highly associated with sediment particles, rather than porewater or hypolimnion. Both the distribution of metals and in situ experiment indicated the importance of sediment as the main source of bioaccumulation. Significant differences in Ba, Ni and U concentrations between treatments containing contaminated sediment and reference sediment were noted, regardless of water concentrations. Additionally, as U contaminated lakes lacked seasonal overturn during our monitoring period, metal distribution and environmental conditions remained unchanged in deeper parts of those lakes. Lastly, the results of this in situ bioaccumulation experiment are in line with the findings of our previous laboratory study using sediments from these same lakes.

The Cultivation of Halophilic Microalgae Shapes the Structure of Their Prokaryotic Assemblages.

The influence of microalgae on the formation of associated prokaryotic assemblages in halophilic microbial communities is currently underestimated. The aim of this study was to characterize shifts in prokaryotic assemblages of halophilic microalgae upon their transition to laboratory cultivation. Monoalgal cultures belonging to the classes Chlorodendrophyceae, Bacillariophyceae, Trebouxiophyceae, and Chlorophyceae were isolated from habitats with intermediate salinity, about 100 g/L, nearby Elton Lake (Russia). Significant changes were revealed in the structure of algae-associated prokaryotic assemblages, indicating that microalgae supported sufficiently diverse and even communities of prokaryotes. Despite some similarities in their prokaryotic assemblages, taxon-specific complexes of dominant genera were identified for each microalga species. These complexes were most different among Alphaproteobacteria, likely due to their close association with microalgae. Other taxon-specific bacteria included members of phylum Verrucomicrobiota (Coraliomargarita in assemblages of Navicula sp.) and class Gammaproteobacteria (Salinispirillum in microbiomes of A. gracilis). After numerous washings of algal cells, only alphaproteobacteria Marivibrio remained in all assemblages of T. indica, likely due to a firm attachment to the microalgae cells. Our results may be useful for further efforts to develop technologies applied for industrial cultivation of halophilic microalgae and for developing approaches to obtain new prokaryotes with a microalgae-associated lifestyle.

Cannabis pollen sources and dispersal in the Iberian Pyrenees during the last century: Preliminary results and proposals for future studies

Meta-analyses of past pollen records have provided insights into the historical biogeography of Cannabis across the Iberian Peninsula (IP), with the southern Pyrenean flank being key to understanding cannabis cultivation and use during the Middle and Modern ages. However, studies on more recent times are rare. This paper offers a high-resolution comparison of the last century, particularly the significant Cannabis pollen peak observed in the mid-elevation Lake Montcortès between 1980 and 2000 CE, which was absent in the nearby highland Lake Sant Maurici. The Montcortès peak is linked to a phase of extensive hemp cultivation (1972–2006 CE) in the southeastern lowlands. The absence of a similar peak in Sant Maurici, despite the presence of other lowland pollen taxa, notably Olea and Quercus, suggests regional differences in pollen origin and dispersal likely influenced by wind patterns and rainfall. Studies on Cannabis pollen sources and dispersal are comparatively scarce and insufficient to provide a regional picture across the IP, similar to Olea or Quercus. However, the available data suggest that cannabis pollen is abundant mostly locally, in the vicinity of cannabis crops. The persistent presence of Cannabis pollen in Montcortès after 2000 CE likely reflects ongoing illegal cultivation. The study recommends combining paleoecological and aerobiological surveys to better understand pollen dynamics in the Iberian Pyrenees, with suggestions for future research based on these findings.

Lake-centred sedentary lifestyle of early Tibetan Plateau Indigenous populations at high elevation 4,400 years ago.

The onset of sedentism on the Tibetan Plateau is often presumed to be associated with the dispersal of agriculture or farmers from archaeological sites located in the low elevation margins of the plateau. Previous studies of the plateau assumed that all foragers were probably mobile, but few systematic excavations at forager sites have been conducted to inform us about their settlement patterns. Here we report the world's highest elevation sedentary way of living exhibited by the Mabu Co site at 4,446 metres above sea level, deep in the interior of the Tibetan Plateau 4,400-4,000 years ago. Our interdisciplinary study indicates that the site was occupied by Indigenous inhabitants of the plateau, representing the earliest known DNA evidence of foragers who predominantly harbour the southern plateau ancestry. The evidence shows that they had a sedentary lifestyle primarily supported by fishing at nearby lakes, supplemented by mammal and bird hunting, as well as small-scale exchanges of millet and rice crops.

Publisher Correction: Comparing long-term changes in cladoceran and diatom assemblages from a lake impacted by road salt seepage to a nearby reference lake near Toronto (Ontario, Canada)

Publisher Correction: Comparing long-term changes in cladoceran and diatom assemblages from a lake impacted by road salt seepage to a nearby reference lake near Toronto (Ontario, Canada)

An integrated probabilistic bipolar fermatean hesitant fuzzy transportation configuration for sustainable management of floral waste with risk assessment

This paper proposes the probabilistic bipolar fermatean hesitant fuzzy set (PBFHFS) and its triangular version as generalizations of bipolar fuzzy set (BFS) for delineating randomness and imprecision in a single framework. To enhance pragmatic applicability, the devised set has been examined based on its fundamental operations, basic properties, and defuzzification mechanism. Offerings made to temples are considered sacred, so they cannot be disposed of in landfills. Waste from temples is usually disposed of in nearby lakes, ponds, and rivers. Thus, management of the temple floral waste (TFW) is essential to enhance the sustainability of the environment. In this regard, a green 4-dimensional transportation system under PBFHF settings is developed for the effective and sustainable managements of floral waste that is dumped from places of worship. For the most cost-effective and environmentally friendly results, this transportation system optimises a number of metrics, transportation expenditure (TE), carbon emission (CE), transportation time (TT), and labour cost (LC). Three sub-models are further developed from the proposed model under PBFHF conditions by incorporating the theory of carbon policy and risk assessments. The suggested transportation system is addressed by employing a fuzzy methodology, fuzzy programming (FP) as well as two non-fuzzy approaches, weighted sum technique (WST) and goal programming technique (GP). At last, there is a numerical computation along with comparison analysis, management insights, a conclusion with limitations, and a scope for further study.

Evolution and morphological diversity of the genus Diploneis (Bacillariophyta) in Lake Malawi, with description of six new species

ABSTRACT Lake Malawi, one of the world’s oldest and most important freshwater systems, harbours a remarkable biotic diversity partly due to variable fluctuations in climate and lake level. Over time, these fluctuations have contributed to the emergence and development of different ecological niches and microhabitats that have facilitated diversification within the lake. Despite our extensive knowledge of different animal groups, the evolutionary history of species-rich diatom groups in Africa and, particularly, in Lake Malawi has yet to be studied. Here, we used a combination of morphological, molecular, and paleontological data to assess the species richness and evolutionary processes of the diatom genus Diploneis in this lake. The comprehensive dataset revealed four putative new endemic species from modern and two apparently extinct Diploneis species from the fossil record of the lake, described here as new to science. Morphological analyses showed that all these new species exhibit remarkable differences and unique morphological patterns that were recently discovered in Diploneis species from nearby Lake Tanganyika. Molecular phylogenetic analyses revealed that the four new species now living in Lake Malawi are nested within a clade of Lake Tanganyika Diploneis species but do not form a monophyletic group. This suggests that the new Lake Malawi Diploneis species are derived from one or more Tanganyikan ancestors and that more than one colonization event probably occurred. However, further analyses are needed to elucidate their origin.

Female-biased sex ratios and delayed puberty in two fish species with different Ecologies in an Anthropogenically affected urban lake

In aquatic ecosystems, endocrine-disrupting compounds (EDCs) pose a growing concern for their potential adverse effects on fish reproduction and development. In lake Pyhäjärvi, located in the urban boreal region of Tampere, Finland, a significant number of sexually immature pikeperch (Sander lucioperca) individuals have been identified in size and age categories that are expected to be sexually mature. To explore if this phenomenon is attributed to estrogenic endocrine disruption, we conducted a comprehensive study comparing fish from lake Pyhäjärvi with those from a nearby reference lake, lake Näsijärvi. Roach (Rutilus rutilus), known for its susceptibility to EDCs, was also included for comparison. We examined various parameters in both pikeperch and roach, including size, condition factor, age, reproductive indicators, biometric indices and gonadal histology. We also assessed liver vitellogenin mRNA levels and genetic sex in roach, and measured estrogen levels in lake waters and wastewater treatment plant effluents. Results revealed that approximately one-third of fish in both species exhibited sexual immaturity in lake Pyhäjärvi, with a female-biased sex ratio. Surprisingly, we found no signs of estrogenic endocrine disruption, indicated by the absence of intersex fish in both species. Furthermore, vitellogenin levels in roach closely resembled those in the reference lake. Estrogens were undetectable in the lake waters, suggesting that factors other than estrogenic EDCs, including other potential endocrine disruptors such as PCBs or heavy metals, may be influencing delayed sexual maturity and skewed sex ratios. Further inquiry is needed to pinpoint these underlying causes. Our study provides essential baseline information on fish sexual development in lake Pyhäjärvi, emphasizing the need for ongoing monitoring and research to understand delayed sexual maturity and biased sex ratios. This is vital given the increasing concern about EDC impacts on aquatic ecosystems and the necessity for effective management strategies to protect these ecosystems' health and integrity.

Comparing long-term changes in cladoceran and diatom assemblages from a lake impacted by road salt seepage to a nearby reference lake near Toronto (Ontario, Canada)

Comparing long-term changes in cladoceran and diatom assemblages from a lake impacted by road salt seepage to a nearby reference lake near Toronto (Ontario, Canada)

Examining 22 Years of Ambient Seismic Wavefield at Mount St. Helens

Abstract An increase in seismic activity precedes most volcanic eruptions. Whereas event-based forecasting approaches have been successful, some eruptions remain unanticipated, resulting in casualties and damage. Our study leverages the recent advancements in ambient field seismology. We explore features extracted from continuous ambient fields using traditional methods, for example, peak ground velocity, peak ground acceleration, root mean square, root median square, real-time seismic amplitude measurement, and novel methods (displacement seismic amplitude ratio and spectral width). In addition, we explore unsupervised learning of higher order wavelet features using scattering networks. We find that combining all the methods was necessary to disentangle the effects of seismic sources from structural changes at Mount St. Helens. Although the ambient wavefield-based approach does not yield additional or more significant precursory signals than event-based methods at Mount St. Helens, our study demonstrates that the ambient wavefield provides supplementary information, mainly about structural changes and complements traditional methods. The ambient seismic wavefield offers additional insights into long-lasting processes. We find enhanced wave attenuation correlating with geochemical measurements. We interpret this as ongoing structural changes, such as dome growth or the evolution of the volcanic conduit system. On annual and decadal timescales, we interpret seasonal seismic attenuation in the shallow subsurface as groundwater fluctuations, corroborated by observations at the nearby Spirit Lake level. This multimethod approach at Mount St. Helens sheds light on a volcanic system’s underlying dynamics and structure.

Coupled capture and photocatalysis of g-C3N4 based magnetic composites: Mechanism and disinfection activity against Staphylococcus aureus

The disinfection ability of g-C3N4 by photocatalysis is restricted, owing to its small surface area and rapid combination of holes (h+) and electrons (e−). Moreover, recycling of g-C3N4-based photocatalysts from aqueous solution is difficult, which increases the cost of application. In the present study, g-C3N4 was combined with magnetic biochar (MBC) by high temperature calcination to fabricate g-C3N4/MBC composites. The as-prepared g-C3N4/MBC composites acquired larger specific surface area, narrow bandgap, and broad-range of visible absorption capability. The g-C3N4/MBC composites showed good killing efficiency towards Staphylococcus aureus (S. aureus) under visible light irradiation. Efficient photocatalysis was achieved by the effective separation of e−/h+ within the g-C3N4/MBC composites. Moreover, the capture effect of MBC for S. aureus reduced the distance and increased the contact area between the g-C3N4/MBC composite and S. aureus. The g-C3N4/MBC-10 % showed notable stability and reusability over a broad pH range of 4–8 and in presence of different inorganic ions (Cl− and SO42−) and humic acid. After 5 cycles, the g-C3N4/MBC-10 % could still eliminate about 95 % of S. aureus cells. The g-C3N4/MBC-10 % was also highly effective in reducing the bacterial population in water samples taken from a nearby lake, thus showing considerable promise for use in water sterilization. In addition, g-C3N4/MBC composites were highly effective in eliminating the biofilm and inhibiting the growth of the new biofilm of S. aureus. The main active species in photocatalytic disinfection were determined, to be •OH, h+, and •O2−. This study would help to understand the capture and photocatalysis of g-C3N4 based composites for environmental applications.

Contrasting sedimentary and long-lasting geochemical imprints of seismic shaking in a small, groundwater-fed lake basin (Klopeiner See, Eastern European Alps)

In slowly deforming tectonic settings (e.g., European Alps), large earthquakes occur too infrequently to be adequately represented in instrumental and historical records. This leads to uncertainties and inaccuracies of seismic hazard estimations. To extend the seismic record, lacustrine paleoseismologists usually resort to the sedimentary archive of large lakes where earthquakes can be recorded as mass-transport deposits and associated turbidites. The imprint of seismic shaking is generally more subtle and poorly understood in small lakes (<2 km2) with small catchments and therefore such sediment-starved basins are often neglected for paleoseismology. However, these basins might harbour additional information about past earthquakes, thus constituting a valuable supplement to other paleoseismic data. Here, we present the 18 ka-long paleoseismic record of Klopeiner See, a small and rather shallow groundwater-fed lake in the Eastern European Alps. Reflection seismic profiles and sediment cores reveal that several large earthquakes led to extensive mass-wasting in early Late-Glacial times when sedimentation rates were very high (~10 mm/yr). In the Early and Middle Holocene, low sedimentation rates (~0.2-0.5 mm/yr) may have decreased the lake´s sensitivity for recording seismic shaking and no imprints were found for paleo-earthquakes inferred from other records in the region. A short succession of turbidites at ca. 3160 cal BP suggests a burst of strong paleoseismic activity. This may have caused permanent modifications of inflowing ground water systems, archived as a permanent shift in the geochemical signal of the sediment. Such a period of enhanced paleoseismic activity was also inferred from the nearby Lake Wörthersee, but it remains unclear whether these represent the same earthquakes or migrating paleoseismicity. This study highlights the unexpected potential and peculiarities of paleoseismology on small ground-water fed lakes.

The utility of freshwater dinoflagellate cyst assemblages as a paleoecological proxy: An assessment from boreal lakes (northwest Ontario, Canada)

Aquatic palynomorphs have the potential to provide valuable insights into past environments but little has been done to assess the utility of freshwater dinoflagellate cysts as palaeoecological proxies of lacustrine environments. This study is the first to compare the distribution of freshwater dinoflagellate cysts found in surface sediments from 32 boreal lakes with varying physical and chemical characteristics. Cysts of Fusiperidinium wisconsinense, Parvodinium umbonatum, and Peridinium willei were nearly ubiquitous, but of the remaining cyst taxa, only Parvodinium inconspicuum, Peridinium limbatum, and Peridinium volzii were abundant but present in a smaller number of lakes. Assemblage composition broadly clustered into three groups: 1) an assemblage (primarily Peridinium spp.) associated with relatively shallow, mesotrophic lakes; 2) an assemblage dominated by F. wisconsinense in mesotrophic lakes with intermediate depth and relatively high pH and alkalinity; and 3) an assemblage dominated by P. umbonatum in deeper oligotrophic lakes. Moreover, changes in dinoflagellate cyst assemblage were assessed in a sediment core spanning the Holocene from nearby Gall Lake and interpreted alongside other previously published paleoecological proxies from this core. High abundances of many dinoflagellate cysts including P. limbatum, P. willei, F. wisconsinense, and P. inconspicuum were observed when lake production was high at a time when lake-levels were low and climate was more arid than today. This study suggests that dinoflagellate cysts in lacustrine sediments are, when abundant, promising both in modern and core samples, and the relationships between assemblages today and in the past can contribution additional information in understanding past ecological conditions.

Elastic Stress Coupling Between Supraglacial Lakes

AbstractSupraglacial lakes have been observed to drain within hours of each other, leading to the hypothesis that stress transmission following one drainage may be sufficient to induce hydro‐fracture‐driven drainages of other nearby lakes. However, available observations characterizing drainage‐induced stress perturbations have been insufficient to evaluate this hypothesis. Here, we use ice‐sheet surface‐displacement observations from a dense global positioning system array deployed in the Greenland Ice Sheet ablation zone to investigate elastic stress transmission between three neighboring supraglacial lake basins. We find that drainage of a central lake can place neighboring basins in either tensional or compressional stress relative to their hydro‐fracture scarp orientations, either promoting or inhibiting hydro‐fracture initiation beneath those lakes. For two lakes located within our array that drain close in time, we identify tensional surface stresses caused by ice‐sheet uplift due to basal‐cavity opening as the physical explanation for these lakes' temporally clustered hydro‐fracture‐driven drainages and frequent triggering behavior. However, lake‐drainage‐induced stresses in the up‐flowline direction remain low beyond the margins of the drained lakes. This short stress‐coupling length scale is consistent with idealized lake‐drainage scenarios for a range of lake volumes and ice‐sheet thicknesses. Thus, on elastic timescales, our observations and idealized‐model results support a stress‐transmission hypothesis for inducing hydro‐fracture‐driven drainage of lakes located within the region of basal cavity opening produced by the initial drainage, but refute this hypothesis for distal lakes.

A common multi-host parasite shows genetic structuring at the host species and population levels.

Although individual parasite species commonly infect many populations across physical space as well as multiple host species, the extent to which parasites traverse physical and phylogenetic distances is unclear. Population genetic analyses of parasite populations can reveal how parasites move across space or between host species, including helping assess whether a parasite is more likely to infect a different host species in the same location or the same host species in a different location. Identifying these transmission barriers could be exploited for effective disease control. Here, we analysed population genetic structuring of the parasite Pasteuria ramosa in daphniid host species from different lakes. Outbreaks occurred most often in the common host species Daphnia dentifera and Daphnia retrocurva. The genetic distance between parasite samples tended to be smaller when samples were collected from the same lake, the same host species and closer in time. Within lakes, the parasite showed structure by host species and sampling date; within a host species, the parasite showed structure by lake and sampling date. However, despite this structuring, we found the same parasite genotype infecting closely related host species, and we sometimes found the same genotype in nearby lakes. Thus, P. ramosa experiences challenges infecting different host species and moving between populations, but doing so is possible. In addition, the structuring by sampling date indicates potential adaptation to or coevolution with host populations and supports prior findings that parasite population structure is dynamic during outbreaks.

Fine scale diversity in the lava: genetic and phenotypic diversity in small populations of Arctic charr Salvelinus alpinus.

A major goal in evolutionary biology is to understand the processes underlying phenotypic variation in nature. Commonly, studies have focused on large interconnected populations or populations found along strong environmental gradients. However, studies on small fragmented populations can give strong insight into evolutionary processes in relation to discrete ecological factors. Evolution in small populations is believed to be dominated by stochastic processes, but recent work shows that small populations can also display adaptive phenotypic variation, through for example plasticity and rapid adaptive evolution. Such evolution takes place even though there are strong signs of historical bottlenecks and genetic drift. Here we studied 24 small populations of the freshwater fish Arctic charr (Salvelinus alpinus) found in groundwater filled lava caves. Those populations were found within a few km2-area with no apparent water connections between them. We studied the relative contribution of neutral versus non-neutral evolutionary processes in shaping phenotypic divergence, by contrasting patterns of phenotypic and neutral genetic divergence across populations in relation to environmental measurements. This allowed us to model the proportion of phenotypic variance explained by the environment, taking in to account the observed neutral genetic structure. These populations originated from the nearby Lake Mývatn, and showed small population sizes with low genetic diversity. Phenotypic variation was mostly correlated with neutral genetic diversity with only a small environmental effect. Phenotypic diversity in these cave populations appears to be largely the product of neutral processes, fitting the classical evolutionary expectations. However, the fact that neutral processes did not explain fully the phenotypic patterns suggests that further studies can increase our understanding on how neutral evolutionary processes can interact with other forces of selection at early stages of divergence. The accessibility of these populations has provided the opportunity for long-term monitoring of individual fish, allowing tracking how the environment can influence phenotypic and genetic divergence for shaping and maintaining diversity in small populations. Such studies are important, especially in freshwater, as habitat alteration is commonly breaking populations into smaller units, which may or may not be viable.

Small-holder Fish Farming in the Upper Kuttanad and Brackish Water Villages of Alappuzha District, Kerala, India

In Kerala, smallholder aquaculture emerges as an alluring and significant part of rural lives, improving livelihoods and ensuring a sustainable supply of inland fish. One hundred and four smallholder fish farms were surveyed from the upper Kuttanad and brackish water villages of Alappuzha, the state's leading district for inland fish production. Personal interviews and questionnaires were employed to get primary data on species farmed, culture method, feed, and the challenges smallholder farmers faced. The most common fish species cultured in smallholder fish farms is Oreochromis niloticus (GIFT) (34%), followed by Etroplus suratensis (31%), Pangasius pangasius (15%), Anabas testudineus (6%), Channa striata (6%), Labeo rohita (4%), and Heteropneustes fossilis (4%). In the brackish water villages, 60% of the fish cultured are Etroplus suratensis. Eighty-one per cent of the farmers used ponds, 11% used biofloc, and 8% used cages. Sixty-six percent of farmers used commercially manufactured pellet feed, 21% poultry waste, 12% used food waste, and 1% live Black soldier flies. Fish cultured using the bio floc method are the most affected by the fungal disease, gill rot. Anabas testudineus cultured at high stocking density in bio floc showed tail-biting behaviour followed by bacterial infection. Fifty-one percent of farmers reported a lack of appropriate technical and financial aid from the government, including the withdrawal of subsidies for feed purchases. Even though the 2018 flood seriously affected the fish farms, only 8% of farmers reported the flood as a problem affecting their farms. The major challenges brackish water farmers faced were the intrusion of saline water from the nearby lake and the poaching of juvenile and mature fish from natural ponds. Apart from the monetary assistance provided by the government for starting farms under the "Jankeeya Matsya Krishi" Project, smallholder farmers should need additional help with insurance and subsidies to promote sustainable aquaculture.