Holomictic Conditions Research Articles

Dynamics of organic matter in the changing environment of a stratified marine lake over two decades

The marine lake (Rogoznica Lake), which fluctuates between stratified and holomictic conditions, is a unique environment on the eastern Adriatic coast affected by environmental changes. These changes are reflected in the warming of the water column, the apparent deoxygenation of the epilimnion, and the accumulation of organic matter (OM), toxic sulfide, and ammonium in the anoxic hypolimnion. Since the early 1990s, the volume of anoxic water has increased as the chemocline has moved to the surface water layer. A trend toward enrichment of refractory dissolved organic carbon (DOC) was observed in the anoxic hypolimnion, while a decreasing trend was observed in the oxic epilimnion in the spring DOC. At the same time, the most reactive surface-active fraction of DOC showed the opposite trend. In addition, there is evidence of accumulation of particulate organic carbon (POC) in the water column, followed by an increase in the fraction of POC in total organic carbon (TOC).On a multi-year scale (1996–2020), this work presents a unique time series of the dynamics of OM in the stratified marine system, showing a significant change in its quantity and quality due to climate and environmental variability. DOC-normalized surfactant activity is shown to be a good indicator of environmental change.

Pit Lakes Affected by a River Contaminated with Brines Originated from the Coal Mining Industry: Evolution of Water Chemistry in the Zakrzówek Horst Area (Krakow, Southern Poland)

Long-term coal mining activities in the Upper Silesia significantly affect the environment in southern Poland. Discharges of brines (with TDS reaching over 110 g/L) from mines are the main source of pollution of many rivers in Poland, including the Vistula River. The Zakrzówek horst is a small geological structure composed of the Upper Jurassic limestones. These limestones were exploited in several quarries. In the largest one (the “Zakrzówek” quarry), exploitation reached the depth of 36 m below the water table, i.e., about 32 m below the average water level in Vistula River which flows 700 m from the quarry. An important part of this inflow into quarries came from the contaminated Vistula River, with a chloride concentration over 2 g/L. The exploitation ceased in 1991, and dewatering ended in 1992. In the old quarry area, pit lakes appeared, which are unique because they present an example of a post-mining site affected by the riverine water contaminated with brines. Investigations of physicochemical parameters of water in the Zakrzówek area were carried out in the period of 1990–2020. Results showed that the largest pit lake was initially meromictic with a distinct stratification. After several years, holomictic conditions developed due to the surface layer freshening and convective mixing.

Impact of euxinic holomictic conditions on prokaryotic assemblages in a marine meromictic lake

The water column of marine Rogoznica Lake (Croatia) is stratified throughout the year. However, on rare occasions, the lake exhibits complete mixing, primarily driven by meteorological conditions. On such occasions, anoxic, sulfide-rich bottom water mixes with the oxic surface layer, triggering both the oxidation of sulfide predominantly to colloidal sulfur and the establishment of euxinic conditions throughout the water column. We investigated prokaryotic communities during euxinic holomictic conditions. High-throughput sequencing of the 16S rRNA gene showed that these sulfur-driven communities were dominated by Planctomycetales, chemolithotrophic Epsilonbactereota (mainly Arcobacteraceae) and Gammaproteobacteria (Thioglobaceae), followed by Alpha- (Rhodobacteraceae) and Deltaproteobacteria (Desulfobulbaceae and Desulfobacteraceae). The majority of archaeal sequences belonged to Nanoarchaeota, all of which were designated as Woesearchaeia. This class has not been recorded in other meromictic lakes. Both bacterial and archaeal 16S rRNA gene abundance did not vary significantly across the vertical profile of the lake, as shown by quantitative PCR. However, hierarchical clustering showed a significant difference between the microbial assemblage structure in stratified periods and during a holomictic event. Besides the structure, this stressful event had a manifold effect on bacterial and archaeal assemblages by decreasing their diversity and abundance when compared to the usual stratified conditions.

Community Shift from Phototrophic to Chemotrophic Sulfide Oxidation following Anoxic Holomixis in a Stratified Seawater Lake

Most stratified sulfidic holomictic lakes become oxygenated after annual turnover. In contrast, Lake Rogoznica, on the eastern Adriatic coast, has been observed to undergo a period of water column anoxia after water layer mixing and establishment of holomictic conditions. Although Lake Rogoznica's chemistry and hydrography have been studied extensively, it is unclear how the microbial communities typically inhabiting the oxic epilimnion and a sulfidic hypolimnion respond to such a drastic shift in redox conditions. We investigated the impact of anoxic holomixis on microbial diversity and microbially mediated sulfur cycling in Lake Rogoznica with an array of culture-independent microbiological methods. Our data suggest a tight coupling between the lake's chemistry and occurring microorganisms. During stratification, anoxygenic phototrophic sulfur bacteria were dominant at the chemocline and in the hypolimnion. After an anoxic mixing event, the anoxygenic phototrophic sulfur bacteria entirely disappeared, and the homogeneous, anoxic water column was dominated by a bloom of gammaproteobacterial sulfur oxidizers related to the GSO/SUP05 clade. This study is the first report of a community shift from phototrophic to chemotrophic sulfide oxidizers as a response to anoxic holomictic conditions in a seasonally stratified seawater lake.

Sensitivity analyses in pit lake prediction, Martha Mine, New Zealand 1: Relationship between turnover and input water density

Turnover events in pit lakes influence the water quality of pit lakes by homogenizing the chemistry of mixing layers and distributing dissolved oxygen, hence limnologic models that predict the depth of annual turnover are required for predictive studies of post-mining pit lake water quality. This study demonstrates a limnologic prediction of a proposed pit lake at the Martha Au–Ag Mine, New Zealand, created with the hydrodynamic program DYRESM. The model considered 5 years of lake-filling conditions where the pit will receive river water, groundwater, pit wall runoff, and direct rainwater followed by 1 year of steady-state conditions where the lake will receive only groundwater, runoff, and rainwater. Sensitivity analyses showed that input groundwater temperatures ≤ 17 °C produced meromictic conditions, whereas groundwater temperatures ≥ 17 °C produced holomictic conditions. Changes in the chemistry of runoff inputs had no effect on turnover because the quantity of runoff is significantly less than the quantity of other inputs. These results suggest that understanding the density of major lake inputs is critical toward predicting the limnologic evolution of a pit lake as small changes in the water chemistry or temperature between inputs may affect input density and the resulting turnover depth. Lakes filled with water from one principle source, such as groundwater, are more likely to be holomictic due to the relatively homogeneous character of the resulting lake water, whereas lakes filled with water from more than one source, such river water and groundwater, may develop meromictic conditions due to slight density differences between input waters. It may be possible for mine managers to engineer holomictic or meromictic conditions in future pit lakes to improve lake water quality.

Long Term Changes in the Limnology and Geochemistry of the Berkeley Pit Lake, Butte, Montana

The Berkeley pit lake in Butte, Montana is one of the largest accumulations of acid mine drainage in the world. The pit lake began filling in 1983, and continues to fill at a rate of roughly 10 million liters d-1. This paper details how changes in mining activities have led to changes in the rate of filling of the pit lake, as well as changes in its limnology and geochemistry. As of 2005, the Berkeley pit lake is meromictic, with lower conductivity water resting on top of higher conductivity water. This permanent stratification was set up by diversion of surface water—the so-called Horseshoe Bend Spring—into the pit during the period 2000 to 2003. However, the lake may have been holomictic prior to 2000, with seasonal top-to-bottom turnover events. The present mining company is pumping water from below the chemocline to a copper precipitation plant, after which time the Cu-depleted and Fe-enriched water is returned to the pit. Continued operation of this facility may eventually change the density gradient of the lake, with a return to holomictic conditions. A conceptual model illustrating some of the various physical, chemical, and microbial processes responsible for the unusually poor water quality of the Berkeley pit lake is presented.

Mass mortality event in a small saline lake (Lake Rogoznica) caused by unusual holomictic conditions

The study of a small saline eutrophic lake was performed under meromictic and holomictic conditions. The meromictic period was characterised by anoxic conditions in the bottom layer with high sulphide and nutrient concentrations. The depth of the nutricline varied as affected by thermohaline conditions in the water column. In late summer 1997, holomictic conditions replaced ordinary meromitic conditions in the lake. This transformation caused anoxia to spread throughout the water column and mass mortality of almost all the organisms occured. Thereafter, oxic conditions were re-established slowly as the new phytoplankton population developed. As a consequence of the particulate organic matter decay, inorganic N and P concentrations increased and had doubled approximately six weeks after the mass mortality. The revitalisation of the phytoplankton population was initiated immediately after the mass mortality by the development of microflagellate species, which were favoured by the high ammonia concentrations. The larger phytoplankton species (diatoms and dinoflagellatae) developed at the expense of smaller ones when nitrate became the dominant nutrient in the water column. A year after the mass mortality the composition of the phytoplankton population was the same as before.

A hydrological tracer experiment with LiCl in a high mountain lake

AbstractThe water residence time of the high mountain seepage lake Gossenköllesee (2413 m, Tyrol, Austria) was determined by measuring the flushing rate of a tracer substance. During holomixis in July 1997, when circulation occurred throughout the entire water column, a dilute lithium chloride solution was injected into the lake causing the lithium concentration to rise from the background value of 0·06 to 3·1 μg L−1. The water residence time was derived from the exponential decline of the lithium mass in the lake between July and October holomixis. The water residence time was about 2 months, i.e. the lake volume was exchanged twice between the two periods of holomictic conditions. Copyright © 2002 John Wiley & Sons, Ltd.

Ion chromatographic determination of lithium at trace level concentrations: Application to a tracer experiment in a high-mountain lake

The water residence time of a high-mountain seepage lake in the Austrian Alps was derived from the flushing rate of a tracer substance. A diluted lithium chloride solution was injected into the lake during holomictic conditions in order to favour the homogeneous distribution of the tracer. The exponential decline of the mass of lithium in the lake revealed a water residence time of 1.5 to 3 months for summer and almost no lake water exchange during winter. Lithium concentrations ranged from background values of 0.06 μg l −1 to about 3 μg l −1 immediately after the tracer injection. Lake water samples were analyzed with ion-exchange chromatography using a Dionex device with a CS 12A separation column. The method detection limit determined according to the definition of the US Envirinmental Protection Agency amounted to 0.009 μg l −1.

A late glacial and holocene record of biological and environmental changes from the crater Lake Albano, Central Italy: An interdisciplinary european project (PALICLAS)

This paper reports the results of biological analyses (pigments, diatoms, chrysophyte cysts, cladocerans, chironomids and ostracods) of a ca. 14 m-long sediment core recovered from Lake Albano (Central Italy) in the course of the EU-funded project PALICLAS (PALaeoenvironmental analysis of Italian Crater Lake and Adriatic Sediments). A reconstruction of the environmental evolution and ecosystem response of Lake Albano during the last ca. 30 kyr was possible. Additional information on lake level oscillation is obtained from benthic and planktonic palaeocommunities. Several oscillations in the productivity and the level of the lake were detected in the oldest sediment layers (from ca. 30 kyr BP to ca. 17 kyr BP), followed by a long (ca. 5 kyr BP) period of low productivity in which cold, holomictic conditions prevailed. A period of high biological activity and, probably, meromictic conditions during the early-mid Holocene was detected. A clear impact of human activities in the catchment was found at ca. 4 kyr BP in the form of increased erosion, associated with a decline in the abundance of biological remains. Further signs of human impact on the lake ecosystem are recorded during the Roman period. Although large-scale environmental changes (e.g. regional climate changes) caused many of the observed biological changes, human activities were important during the mid-late Holocene.

Oxygen and carbon isotope trends and sedimentological evolution of a meromictic and saline lacustrine system: the Holocene Medicine Lake basin, North American Great Plains, USA

Abstract The succession of sedimentary subfacies in the Medicine Lake basin (South Dakota, USA) documents numerous changes in total dissolved solids (TDS), lake level, and the nature and stability of meromixis during the Holocene. The lake formed about 10.6 ka B.P. when coarse clastics and massive fine-grained muds were deposited in a well-mixed freshwater system. Subsequently the lake became saline and meromictic, depositing a finely laminated unit composed of variegated and gray muds, organic facies, gypsum and aragonite laminae. Phototrophic bacterial plate communities (BPC) at the chemocline were significant producers of pelagic organic matter. Relatively high lake levels (at least 10 m higher than today) but saline and meromictic conditions predominated through the early to mid Holocene. At the end of this phase, lake level dropped and stable meromixis was disrupted. Sands and massive or banded muds were deposited in sublittoral areas and benthic microbial communities (BMC) spread over the lake, replacing BPCs as the predominant microbial producers. When lake level rose again, massive and laminated units were deposited under less saline conditions. Another pronounced episode of low lake level and high salinity followed. The most recent sediments are sapropels, massive or banded muds, and littoral sands. The δ18O record from authigenic aragonite shows more positive values during the arid mid-Holocene interval, with an abrupt increase at the end of this period, followed by generally more negative values during the cooler and wetter late Holocene. The small range of δ18O values (3%.) suggests that the lake was well buffered against high-frequency climatic cycles, probably as a result of groundwater modulation. We postulate that meromixis and the type of photosynthetic microbial communities dominating the basinal region of the lake system—either BPCs or BMCs—exerted major controls on the carbon cycle, and consequently, on the development of isotopic trends linking δ13C and δ18O values. More negative δ13C values during the early and mid Holocene are interpreted as a consequence of the predominance of 12C-enriched microbial carbon from BPCs. Examples of both covariant and inverse covariant isotope trends between δ13C and δ18O values occur in the Medicine Lake record. Inverse covariant trends characterize long periods of stable meromixis when BPCs predominate over BMCs. We hypothesize that well-developed water stratification caused by greater influx of relatively 18O-depleted freshwater induces higher productivity at the chemocline and, consequently, more positive δ13C values in the precipitated carbonates. Unstable phases of meromixis or holomictic conditions are characterized by a predominance of BMCs or other biogenic producers over BPCs, and a number of other factors combine to promote covariant trends. The Medicine Lake record is consistent with the paleoclimatic interpretation for the northern Great Plains of a more arid early and middle Holocene followed by an abrupt transition to a relatively cooler and wetter late Holocene. The sedimentary succesion in Medicine Lake documents a much more fluctuating and abrupt climate behavior than suggested by the vegetation paleorecord and suggest a late Holocene climate punctuated by arid episodes.

Holocene evolution of the crater lake at Malha, Northwest Sudan

A reconstruction of the hydrological and environmental evolution of the crater lake at Malha (Northern Darfur, Sudan) resulted from the mineralogical and biological study of a 9.21 m section of lake sediments, representing an uninterrupted sequence of lacustrine deposition since 8 290 14C years BP. Important changes in water supply and conditions of sedimentation are reflected in the nature of the sediments and the morphology and stratigraphical distribution of various salt minerals. Additional information on lake circulation patterns and salinity conditions are obtained from associated benthic paleocommunities, represented by ostracods and dipterid larvae. Combining both lines of evidence, the studied sequence can be divided in six distinct sections, which correspond to six successive periods in the lake's Holocene history. The first three periods, generally characterized by high lake levels, represent three generations of a meromictic lake, two of which have ended with a complete desiccation of the lake basin. Meromixis was stable during Period I, due to wind shelter and pronounced density stratification. In the course of Periods II and III stratification was repeatedly interrupted. During Period II, the disruptions were accompanied by important water budget fluctuations; a superimposed gradual decrease in net water supply eventually resulted in holomictic conditions terminating this period. Evidence of turbulence periodically affecting profundal waters is recorded in the sediments of Period III, suggesting that disruptions of stratification were now initiated by very strong winds. Between Period I and Period III, the littoral mixolimnion gradually evolved from near fresh to mesosaline. In Periods IV to VI, lake level was intermediate to low. The lake was holomictic for most of the time and meso- to hypersaline; during Period V, it repeatedly shrunk to a shallow brine pool. The Holocene evolution of Malha Crater Lake illustrates the progressive increase in aridity over most of North Africa following a well-established, early- to mid-Holocene major humid episode. The uninterrupted sedimentary sequence lends itself for detailed reconstruction of Holocene climatic evolution in arid Northeast Africa, a region where records of continuous lacustrine deposition are extremely scarce. As the chronology of critical events in the lake's history remains as yet unsupported by radiocarbon dates, correlation with other Holocene sequences in the eastern Sahara is highly tentative at this point.

Tertiary Lacustrine Sediments from Sentinel Butte, North Dakota and the Sedimentary Record of Ectogenic Meromixis

ABSTRACT About 10 meters of probable Oligocene or Miocene lacustrine sediments which crop out on top of Sentinel Butte in western North Dakota consist mostly of greenish-gray zeolitic mudstone interbedded with relatively thin layers of dolomite, limestone, and chalcedony. The dolomite layers are several centimeters thick and are mostly dolomicrite, with laminae or lenses of arkosic sand and pellets. They probably formed by deposition of protodolomite in shallow, closed, saline lakes. The limestone layers are up to 30 centimeters thick. Their basal portions contain varve couplets of micrite and organic matter. Graded bedding in micrite laminae and concentration of aeolian silt in organic laminae suggest that deposition of carbonate took place during a relatively brief portion of each year. Pres rvation of varves, fossil fish, and coprolites in the limestone imply deposition in a meromictic lake. In contrast, poor preservation of fish and bioturbation in the upper parts of two limestone beds record transition to holomictic conditions. Some variations in varve thickness appear rhythmic and possibly related to the sunspot cycle. Several asymmetric cycles of contrasting carbonate facies, ideally consisting of massive dolomite overlying clay and underlying laminated limestone, imply that the ancient lake in which the sequence was deposited underwent several episodes of shrinkage and closure during which its salinity increased, followed by expansion accompanied by abrupt development of ectogenic meromixis. Changes in authigenic mineralogy and upward increase in thickness of limestone beds relative to dolomite beds record a long-term trend toward freshening of basinal hydrology. Models involving ectogenic meromixis can explain intimate associations of evaporitic facies with varved sediments in other sedimentary sequences and may be applicable to some Precambrian iron formations.

Fossil pigments as a guide to the paleolimnology of Browns Lake, Ohio

Some aspects of the paleolimnology of Browns Lake, Ohio, have been ascertained by a study of preserved sedimentary plant pigments and conductivity of interstitial water. Temporal changes in the sedimentary environment, especially redox conditions, along with changes in the flora of the lake and the development of peat in the basin have brought about differential sedimentation and preservation of pigments. Measurement of changes in total and relative concentration and diversity of chlorophyll derivatives and carotenoids has provided important clues to late-glacial and postglacial evolution of the lake. Laminated sediments, rich in fossil remains, near the base of the core indicate eutrophic conditions and meromixis for several thousand years beginning shortly after lake inception. As meromixis broke down, the lake evolved gradually to holomictic conditions when sapropel was deposited. An advancing complex of reed swamp and fen forest began during midpostglacial time, providing ever-increasing amounts of highly organic, peaty sediments and continues to the present. The pond is now dystrophic, and increasing deposition of inorganic sediment is apparent at the top of the core, concomitant with land clearance and agriculture. In the same interval, an increase of water conductivity reflects recent agricultural practices and industrialization in the region.