Hypolimnetic Conditions Research Articles

Habitat selection of a migratory freshwater fish in response to seasonal hypoxia as revealed by acoustic telemetry

Adaptive efforts to achieve water quality objectives by modifying nutrient loading can have attendant impacts on fish habitats and fisheries. Thus, coordinating fishery and water quality management depends on knowledge of fish behavioral responses to habitat change. This study combined acoustic telemetry of fish with water quality modelingto understand how water quality management might impact fishery management. We examined habitat use of a native demersal fish, lake whitefishCoregonus clupeaformis, in Lake Erie. We focused on the summer stratified period when habitat was expected to be most limiting and used a forecast model to predict temperature and oxygen in the hypolimnion when fish were detected. As hypothesized, lake whitefish occupied a subset of available conditions with occupied habitats characterized by a cool, normoxic, hypolimnion. On some occasions fish were detected when the hypolimnion was predicted to be hypoxic, suggesting that fish were either displaced vertically or horizontally into marginal habitats or uncertainty in model predictions was high. Still, when hypolimnetic conditions were hypoxic, fish tended to move toward normoxia as expected, but when initial conditions were cold with high dissolved oxygen, fish movements were toward lower oxygen (but still normoxic) conditions. We also observed a high affinity for fish to remain near the southern shore in eastern Ohio, Pennsylvania, and New York. If current nutrient reduction objectives are achieved and the extent and severity of hypoxia is reduced, an expansion of lake whitefish habitat and distribution may have significance to the spatial regulation of fishing effort in Lake Erie.

Human actions were responsible for both initiation and termination of varve preservation in Lake Vesij\xe4rvi, southern Finland

The influence of lake restoration efforts on lake bottom-water conditions and varve preservation is not well known. We studied varved sediments deposited during the last 80 years along a water-depth transect in the Enonsaari Deep, a deep-water area of the southernmost Enonselkä Basin, Lake Vesijärvi, southern Finland. For the last few decades, the Enonselkä Basin has been subject to ongoing restoration efforts. Varve, elemental, and diatom analyses were undertaken to explore how these actions and other human activities affected varve preservation in the Enonsaari Deep. In contrast to most varved Finnish lakes, whose water columns have a natural tendency to stratify, and possess varve records that span thousands of years, varve formation and preservation in Lake Vesijärvi was triggered by relatively recent anthropogenic stressors. The multi-core varve analysis revealed that sediment in the Enonsaari Deep was initially non-varved, but became fully varved in the late 1930s, a time of increasing anthropogenic influence on the lake. The largest spatial extent of varves occurred in the 1970s, which was followed by a period of less distinguishable varves, which coincided with diversion of sewage from the lake. Varve preservation weakened during subsequent decades and was terminated completely by lake aeration in the 2010s. Despite improvements in water quality, hypolimnetic oxygen depletion and varve preservation persisted beyond the reduction in sewage loading, initial aeration, and biomanipulation. These restoration efforts, however, along with other human actions such as harbor construction and dredging, did influence varve characteristics. Varves were also influenced by diatom responses to anthropogenic forcing, because diatoms form a substantial part of the varve structure. Of all the restoration efforts, a second episode of aeration seems to have had the single most dramatic impact on profundal conditions in the basin, resulting in replacement of a sediment accumulation zone by a transport or erosional zone in the Enonsaari Deep. We conclude that human activities in a lake and its catchment can alter lake hypolimnetic conditions, leading to shifts in lake bottom dynamics and changes in varve preservation.

The effects of hypolimnetic anoxia on the diel vertical migration of freshwater crustacean zooplankton

AbstractLakes and reservoirs worldwide are increasingly experiencing depletion of dissolved oxygen (anoxia) in their bottom waters (the hypolimnion) because of climate change and eutrophication, which is altering the dynamics of many freshwater ecological communities. Hypolimnetic anoxia may substantially alter the daily migration and distribution of zooplankton, the dominant grazers of phytoplankton in aquatic food webs. In waterbodies with oxic hypolimnia, zooplankton exhibit diel vertical migration (DVM), in which they migrate to the dark hypolimnion during the day to escape fish predation or ultraviolet (UV) radiation damage in the well‐lit surface waters (the epilimnion). However, due to the physiologically stressful conditions of anoxic hypolimnia, we hypothesized that zooplankton may be forced to remain in the epilimnion during daylight, trading oxic stress for increased predation risk or UV radiation damage. To examine how anoxia impacts zooplankton vertical migration, distribution, biomass, and community composition over day–night periods, we conducted multiple diel sampling campaigns on reservoirs that spanned oxic, hypoxic, and anoxic hypolimnetic conditions. In addition, we sampled the same reservoirs fortnightly during the daytime to examine the vertical position of zooplankton throughout the summer stratified season. Under anoxic conditions, most zooplankton taxa were predominantly found in the epilimnion during the day and night, did not exhibit DVM, and had lower seasonal biomass than in reservoirs with oxic hypolimnia. Only the phantom midge larva, Chaoborus spp., was consistently anoxia‐tolerant. Consequently, our results suggest that hypolimnetic anoxia may alter zooplankton migration, biomass, and behavior, which may in turn exacerbate water quality degradation due to the critical role zooplankton play in freshwater ecosystems.

Toxicokinetics of pyrene in the freshwater alga Chara rudis

Chara has been suggested a good model to study uptake of xenobiotics into cytoplasm due to their large internode cells surrounded by a layer of cortex cells. We studied the uptake and elimination of pyrene (nominal concentration of 5 μg L−1) in the freshwater alga Chara rudis during 22 days in two treatments mimicking epilimnetic (warm and light) and hypolimnetic (cold and dark) conditions. The growth of Chara during the exposure was higher in epilimnetic conditions (40%) compared to both hypolimnetic pyrene exposed Chara and controls (epilimnetic and hypolimnetic, no pyrene). In the water, a more rapid dissipation of pyrene was observed in epilimnetic conditions, possibly as a result of the increased algal growth. In the cortex, pyrene, 1-OH-pyrene (minor metabolite) and an unknown hydrophobic major metabolite was measured. Pyrene amounts decreased over time, while amounts of the unknown metabolite increased. In internode cytoplasm, pyrene and 1-OH-pyrene showed initially increasing followed by decreasing trends, while the unknown metabolite was not detected. The total mass balance showed that we were able to account for the applied pyrene until 4 days of exposure. However, after this time, there was a significant decrease in amounts accounted for by fluorescence, suggesting that the metabolism of pyrene involves degradation of the ring structure. The degradation was larger in epilimnetic than hypolimnetic conditions.

Substrate limitation of sediment methane flux, methane oxidation and use of stable isotopes for assessing methanogenesis pathways in a small arctic lake

Among predicted impacts of climate change in the Arctic are greater thaw depth and shifts in vegetation patterns and hydrology that are likely to increase organic carbon and nutrient loading to lakes. We measured substrate limitation of sediment methane (CH4) flux, examined pathways of methanogenesis, and potential CH4 oxidation using stable isotope labeled acetate in intact sediment cores from arctic lake GTH 112 (68°40′20″N, 149°14′57″W). We hypothesized that the acetoclastic pathway would dominate methanogenesis, reflecting dissolved organic carbon supply from the surrounding landscape, and that sediment CH4 flux would be stimulated by addition of acetate. Experiments demonstrated acetate limitation of sediment CH4 flux with short-term CH4 flux response to availability of acetate, high rates of CH4 oxidation, and strong dominance of the acetoclastic over the hydrogenotrophic methanogenic pathway. The experiments also indicated that isotopic fractionation effects during isotope enrichment experiments are large during methanogenesis and can alter the methanogenic pathways being investigated. Under oxic conditions, CH4 oxidation at the sediment–water interface or in the water column is likely to account for much of diffusive CH4 flux, but under anoxic hypolimnetic conditions and increased substrate availability, conditions that are likely to occur with climate change, sediment CH4 flux will likely increase, with oxidation utilizing a smaller portion of sediment CH4 production.

Water and sediment chemistry of Lake Pumayum Co, South Tibet, China: implications for interpreting sediment carbonate

A combination of water and sediment chemistry was used to investigate carbonate produc- tion and preservation in Lake Pumayum Co (altitude 5,030 m a.s.l.), south Tibet, China. We compared the chemical composition of lake water in various parts of the lake with that of input rivers and found that the loss of Ca 2? results from calcite sedimentation induced by evaporation and biogenic precipitation. This is sup- ported by evaporation data from the catchment and d 18 O measurements on water. Results suggest that CaCO3 is the predominant carbonate in this lake. There is a positive correlation in the sediments among concentrations of total inorganic carbon (TIC), Ca, total organic carbon (TOC), and total nitrogen, con- firming that most carbonates in sediment are endogenic. The Jiaqu River is the largest inflow to Lake Pumayum Co and has a strong influence on both lake water chemistry and sediment composition. The river and lake bathymetry influence carbonate sedi- mentation by affecting water flow velocity and grow- ing conditions for macrophytes. Different carbon contents and relationships between TIC and TOC in the two long cores from different depths in the lake reveal that hypolimnetic conditions also influence carbonate precipitation and preservation.

Climate-induced changes in the trophic status of a Central European lake

We present a case study of the development of Sacrower See, a stratified, eutrophic lake in northeastern Germany, over the past 13,000 years. Total epilimnetic phosphorus (TP) concentrations were reconstructed quantitatively using a diatom-TP transfer function. Fossil chironomid assemblages were used to support the trophic reconstruction and helped assessing past hypolimnetic oxygen availability. The results indicate eutrophic and anoxic conditions during the Younger Dryas cold period (~12,700-11,600 cal. BP) preceding the present interglacial. Throughout the early and mid-Holocene (~11,600-4000 cal. BP) stable oligo- to mesotrophic conditions with diatom-inferred TP values of ~20 μg L-1 prevailed. First evidence of increasing Holocene TP is recorded at ~3500 cal. BP associated with Bronze Age human impact and for the past 900 years diatoms indicate increasing TP values of 30-60 μg L-1. During the early Holocene and the past two millennia chironomids indicated anoxic hypolimnetic conditions. The chironomid fauna is considered typical of oligo- to mesotrophic lakes. As a consequence of strongly increased primary production the hypolimnion of Sacrower See became anoxic again during the past 140 years. Our results indicate that highly productive eutrophic conditions can exist prior to cultural eutrophication. At Sacrower See the shift from eutrophic conditions in the Lateglacial to oligo-mesotrophic conditions in the early and mid-Holocene was associated with the climatic warming at the Younger Dryas/Holocene transition. The high productive state during the cold Younger Dryas is associated with changes in seasonality: the prolonged winters caused longer ice cover, stronger stratification, anoxia in the hypolimnion, and consequent internal phosphorus loading. During the warm Holocene, however, hypolimnetic anoxia and internal phosphorus loading decreased significantly, resulting in a substantially lower productivity.

Daphnia galeata in the deep hypolimnion: spatial differentiation of a “typical epilimnetic” species

Daphnia galeata is traditionally regarded to be a non-migratory species, which lives in warm epilimnetic waters. Depth segregation or vertical migration is usually attributed to other Daphnia species such as D. hyalina or D. longispina. In a two-year study, we found that in a deep, dammed-valley reservoir (Řimov Reservoir, Czechia) the majority of the population of D. galeata lives in the warm epilimnetic waters during the summer months, but some specimens of this species could be always found in the deep strata as well. This hypolimnetic subpopulation stays in the cold hypolimnetic water and does not migrate. The abundance of hypolimnetic D.galeata does not exceed one specimen per litre and usually shows seasonal variation (minimal densities in early spring, maximal in late summer). Using allozyme electrophoresis, we found that the subpopulation from the deep hypolimnion was clearly genetically differentiated from the population in the epilimnion. We found significant differences in both allele and multilocus genotype frequencies; the FST values at most sampling dates exceeded 0.05. However, the spatial segregation between the epilimnetic and hypolimnetic subpopulations is not permanent. The reservoir is dimictic and hence, at least twice per year, all vertically segregated parts of the population are mixed together. Our results suggest that the deep hypolimnetic subpopulation is repeatedly re-established in spring by deepwater “colonists”, at least some of which seem to be ecologically specialised for the hypolimnetic conditions, and dominate the hypolimnion by the end of the season. The genetic differentiation is likely the result of both the different depth preferences of various D. galeata clones and different selective pressures in the epilimnion and hypolimnion.

Frequency of dividing cells and viability of Microcystis aeruginosa in sediment of a eutrophic reservoir

Blooms of Microcystis aeruginosa occurred in summer months for several years in the reservoir of Grangent (France). Disappearance of planktonic colonies in autumn does not necessarily mean the end of the life cycle for cyanobacteria, and part of them sink down to the sediment. Frequency of dividing cells (FDC) of benthic M. aeruginosa was measured under experimental hypolimnetic conditions in winter and in spring (darkness and temperature = 4 or 8°C) to show overwintering survival and difference between seasons. Enzymatic activity (viability) of benthic cyanobacteria was controlled in situ in winter and spring. Our study revealed that in winter (4°C), benthic colonies continued to divide, with low FDC (mean % = 13.49) and low enzymatic activity (mean ratio carboxyfluorescein diacetate (CFDA) fluorescence:autofluorescence = 1.27). In contrast, when temperature increased in spring (8°C), the viability values significantly increased (mean ratio = 3.78), and a rhythmic increase of FDC appeared every 8 h with maximum of ca. 27.5%. This corre- sponds to an ultradian rhythm of division, which provides strong evidence that benthic cells were under the control of an endogenous component synchronized by an internal clock. Our results suggest that hypolimnetic temperature plays an important role in the return of the active form of M. aeruginosa in spring.

Quantitative inferences of past hypolimnetic anoxia and nutrient levels from a Canadan Precambrian Shield lake

Paleolimnological analyses were used to infer limnological changes during the past ~ 300 yrs in the west basin of Peninsula Lake, a small (853 ha) Precambrian Shield lake in Ontario, Canada, that has been subjected to moderate cultural disturbances (forest clearance, cottage and resort development). This study represents a pioneering attempt to use sedimentary chironomid assemblages and weighted-averaging models to quantify past hypolimnetic anoxia (expressed as the anoxic factor, AF). Impacts of forest clearance and human land-use on deepwater oxygen availability and surface water quality were assessed by comparing chironomid-inferred AF and diatom-inferred total phosphorus concentration ([TP]) to changes in terrestrial pollen and historical data. This study also discusses the ability of chironomids to quantitatively infer changes in AF.Pre-disturbance chironomid assemblages were stable and dominated by taxa indicative of oxygen-rich hypolimnetic conditions (e.g., Protanypus, Heterotrissocladius, Micropsectra type), while diatoms indicated oligotrophic lake status (diatom inferred [TP] = 5-7 μg·l-1). Chironomids characteristic of lower oxygen availability (e.g., Chironomus, Procladius) increased following land-clearance, road construction, establishment of a grist mill and lakeshore development beginning ca. 1870. Increased abundances of Tanytarsus s. lat., a multigeneric group of mainly littoral chironomids, since 1900, indicated that littoral chironomids may have comprised a greater proportion of fossil assemblages during periods of eutrophication and prolonged anoxia. Abundances of meso-eutrophic diatom taxa (e.g., Fragilaria crotonensis, Asterionella formosa, Aulacoseira ambigua, A. subarctica) increased concurrent with European settlement (ca. 1870) and diatom-inferred [TP] doubled (~ 6-12 μg·l-1), further indicating that naturally-oligotrophic Precambrian Shield lakes were extremely sensitive to initial land-clearance activities.Recent increases in oligotrophic diatom taxa (e.g., Cyclotella stelligera) indicate a shift to more oligotrophic conditions since ca. mid-1960s, with greatest changes since ca. 1980. The chironomids Heterotrissocladius and Micropsectra type also increased at this time suggesting greater deepwater oxygen availability. These recent water-quality improvements, possibly in response to enhanced nutrient removal from detergents and sewage, climate-related reductions in external phosphorus loads, and catchment (but not lake) acidification and reforestation, suggest that habitat for commercially-valuable cold-water fishes has improved in recent decades despite greater recreational lake-use.Paleolimnological assessment of trophic status changes in Peninsula Lake using fossil diatom and chironomid assemblages were in good agreement. Diatom inferences of [TP] and chironomid inferences of AF both suggest that Peninsula Lake was historically oligotrophic, became oligo-mesotrophic after European settlement, and returned to oligotrophy in recent yrs. Chironomid inferences of [TP] consistently underestimated the trophic status of Peninsula Lake, possibly due to its relatively large hypolimnion. These results suggest that AF represents a useful tool for quantitatively reconstructing the past trophic status of deeper, stratified lakes.

The environmental state of freshwater resources in Greece (rivers and lakes)

The dominant factor regulating Greek riverine dissolved inorganic solid concentrations is chemical weathering, which depends on catchment climate and petrography. The majority of Greek rivers are moderately polluted and only a few of them show significant human impact and an increase in pollutant concentrations over time. Due to droughts in recent years and anthropogenic influence, the mean annual riverine dissolved solid concentrations exhibit a general interannual increase and significant long-term variations in their intra-annual hydrochemical fluctuations. The shallow Greek lakes are eutrophic, while the deep ones are oligo-mesotrophic. The majority of the lakes are monomictic and show summer thermal stratification, while the shallow ones are characterized by anoxic hypolimnetic conditions. Catchment petrography is not a dominant factor in the composition of lake waters since biochemical processes prevail. The majority of Greek lakes are also moderately polluted and are characterized by phosphorous-limited photosynthesis.