Fact-checked by Grok 2 weeks ago

Profundal zone

The profundal zone is the deepest layer of a lake or pond, located below the limnetic zone and beyond the reach of sunlight, where it forms an aphotic environment characterized by cold temperatures, low dissolved oxygen levels, and high density compared to upper water layers.^[1]^[2] This zone typically begins at depths greater than 6 meters in deeper water bodies, receiving organic detritus such as dead plankton and plants that sink from the photic zones above, which fuels decomposition processes.^[3]^[1] Physically, the profundal zone experiences minimal light penetration, preventing photosynthesis and leading to cooler waters—often around 4°C in temperate lakes during summer stratification—and variable oxygen depletion driven by heterotrophic respiration.^[4]^[5] In productive (eutrophic) lakes, thermal stratification can create anoxic conditions in this layer during warmer months, forming "dead zones" where oxygen demand from microbial breakdown exceeds supply, while mixing events in fall and spring replenish oxygen.^[3]^[5] Ecologically, the profundal zone is dominated by heterotrophic organisms, including bacteria that decompose organic matter and release nutrients back into the water column through processes like internal loading, which influences overall lake productivity.^[3]^[2] Benthic invertebrates such as oligochaetes (worms), chironomid larvae, and microcrustaceans inhabit the sediments, serving as decomposers and food for higher trophic levels, while coldwater fish like trout may access it during periods of circulation but avoid it in anoxic conditions.^[3]^[4] In oligotrophic lakes with low nutrients, the zone supports sparse communities, whereas in eutrophic systems, it plays a critical role in nutrient cycling but can contribute to water quality issues like algal blooms from recycled phosphorus.^[3]^[6]

Definition and Location

Depth and Boundaries

The profundal zone represents the deepest aphotic region in lakes, commencing below the compensation depth where net photosynthesis ceases due to insufficient light availability, typically defined as the level receiving about 1% of surface irradiance.^[7]^[8] This zone is characterized by perpetual darkness, distinguishing it from overlying photic layers where primary production occurs.^[9] In lakes, the profundal zone generally begins at depths of 10-30 meters, though this varies with water clarity; clearer oligotrophic lakes may extend the upper photic boundary to 30 meters or more, while eutrophic systems with high turbidity limit it to under 10 meters.^[10] These ranges reflect the zone's role as the lowermost water column layer before the benthic interface. The upper boundary of the profundal zone is demarcated at the base of the limnetic zone, corresponding to the effective limit of light penetration beyond which photosynthetic activity is negligible.^[7] Its lower boundary occurs at the sediment-water interface, marking the transition to the benthic zone where bottom sediments dominate.^[9] In lakes, this delineation ensures the profundal encompasses the deepest open-water habitats unsupported by benthic-rooted vegetation or significant algal growth. Boundaries of the profundal zone are influenced by water clarity, which determines light attenuation; latitude, affecting solar angle and seasonal insolation; and seasonal mixing, which can temporarily alter stratification and oxygen distribution in temperate systems.^[7] For instance, in stratified lakes, the thermocline reinforces the upper limit during summer, while full mixing in winter may homogenize conditions across depths.^[11] In oceans, upwelling and currents similarly modulate effective light reach in coastal versus open waters.^[12]

Occurrence in Lakes and Oceans

The profundal zone occurs primarily in deep freshwater lakes spanning oligotrophic to eutrophic trophic states, where sufficient depth creates a distinct aphotic layer below the limnetic zone and effective light penetration, typically starting at depths greater than 10–30 meters depending on water clarity and turbidity. This zone is prevalent in large, stratified lakes formed by glacial, tectonic, or volcanic processes, but it is entirely absent in shallow ponds, wetlands, and other lentic systems where the water column remains fully illuminated and lacks vertical stratification.^[1]^[10] In the Laurentian Great Lakes, for instance, the profundal zone is well-developed in Lake Superior, the deepest of the system at a maximum depth of 406 meters, where it extends below approximately 30–50 meters and covers extensive offshore areas dominated by fine sediments.^[13] Similar profundal conditions appear in other deep lakes like ultra-oligotrophic Lake Tahoe, where the zone begins around 40–50 meters and influences nutrient dynamics across the hypolimnion.^[14] These examples highlight the zone's role in lakes with relative depths exceeding 1–2% of their surface area, enabling persistent thermal or chemical separation from surface layers. The profundal zone is more pronounced in meromictic lakes, which exhibit permanent stratification due to density gradients from salinity, temperature, or chemical differences, preventing full seasonal mixing and isolating the lower monimolimnion as a stable profundal layer. In such systems, like certain crater lakes or saline-endorsed basins, the zone often remains anoxic year-round, contrasting with dimictic lakes where it may experience temporary oxygenation during turnover. This variation underscores how hydrodynamic stability enhances the profundal zone's persistence in globally distributed meromictic environments, estimated at fewer than 2% of all lakes but critical for specialized benthic habitats.^[15]^[16] While the term "profundal zone" is specific to freshwater systems, analogous deep aphotic conditions occur in marine environments in the pelagic water column beyond the continental shelves. These include the mesopelagic zone (200–1,000 meters) and bathypelagic zone (1,000–4,000 meters) in oceanic basins such as the Atlantic, where light extinction occurs above 1,000 meters. These areas, influenced by seafloor topography including mid-ocean ridges and trenches, form vast expanses, with the underlying abyssal plains (4,000–6,000 meters depth) covering over 50% of the global ocean floor and hosting sediment-dominated communities reliant on surface-derived organic inputs. The global distribution of such deep aphotic conditions thus spans deep lake bottoms—estimated to comprise 20–70% of the area in large lakes greater than 10 km²—and the expansive deep-sea water column and floor, shaped by tectonic features and basin morphology.^[17]^[18]

Physical and Chemical Characteristics

Light and Temperature Profiles

The profundal zone is characterized by complete light exclusion, rendering it part of the aphotic environment where no measurable photosynthetically active radiation (PAR) penetrates below its upper boundary, typically defined as depths exceeding the euphotic zone where PAR falls below 1% of surface levels.^[19] This absence of sunlight stems from exponential attenuation by overlying water, particles, and dissolved substances, ensuring that less than 1% of incident solar radiation reaches these depths, with bioluminescent emissions from organisms often exceeding ambient daylight in intensity.^[20] As a result, photosynthesis is impossible, and the zone relies entirely on allochthonous organic inputs from shallower layers. Temperature profiles in the profundal zone exhibit near-constant cold conditions with minimal seasonal variation, attributed to water's high thermal inertia and limited mixing. In freshwater systems, the hypolimnion maintains temperatures around 4°C year-round during stratification, as this is the point of maximum water density, preventing significant heat exchange with surface layers.^[3] In deep ocean environments, temperatures range from 1-4°C in abyssal and hadal regions, similarly stable due to isolation from atmospheric influences. Heat transfer from overlying waters is restricted by the thermocline barrier in temperate and tropical settings, while in polar regions, profundal temperatures approach 0°C throughout the year owing to pervasive cold surface conditions and ice cover.^[21] These profiles are assessed using established limnological and oceanographic methods, including Secchi disks to estimate light penetration by measuring the depth at which an 8-inch alternating black-and-white disk vanishes from view, providing an indirect gauge of water clarity and the onset of aphotic conditions.^[22] For precise temperature mapping, conductivity-temperature-depth (CTD) profilers are deployed, which simultaneously record thermal gradients, salinity, and pressure across vertical profiles to delineate the profundal's stable cold layer.^[21]

Oxygen and Nutrient Dynamics

In the profundal zone of lakes, hypoxia or anoxia commonly develops due to the isolation of the hypolimnion by thermal stratification, where bacterial respiration of settling organic matter consumes dissolved oxygen faster than it can be replenished by diffusion from overlying waters.^[23] This oxygen depletion is exacerbated in eutrophic systems with high organic inputs, leading to hypolimnetic oxygen concentrations often falling below 2 mg/L during summer stratification.^[24] In oceanic profundal equivalents, such as the bathypelagic zone, oxygen minimum zones (OMZs) form at intermediate depths of 200–1000 m, driven by similar imbalances between aerobic respiration and limited vertical mixing, resulting in dissolved oxygen levels as low as <0.5 mL/L in intense regions like the Arabian Sea.^[25] Lower temperatures in these deep layers enhance oxygen solubility, partially mitigating depletion compared to warmer surface waters.^[24] Nutrient dynamics in the profundal zone feature enrichment of phosphorus and nitrogen compounds, primarily from the remineralization of sinking particulate organic matter that accumulates in the hypolimnion or on sediments.^[26] Soluble reactive phosphorus concentrations can reach 50–100 µg/L in anoxic hypolimnia of temperate lakes, far exceeding epilimnetic levels, while ammonium nitrogen builds up to several hundred µg/L due to ammonification under low-oxygen conditions. In ocean OMZs, denitrification and anammox processes further concentrate bioavailable nitrogen, with nitrite maxima often exceeding 5 µM, potentially fueling productivity during upwelling events that bring these nutrients to the surface.^[27] Near profundal sediments, pH typically decreases to 6.5–7.0 and redox potentials drop below -100 mV, creating acidic, reducing environments from anaerobic microbial metabolism, including sulfate reduction and organic acid production.^[28] These conditions mobilize iron-bound phosphorus and promote methanogenesis, with dissolved methane concentrations rising to >1 mM in anoxic lake bottoms. Seasonal variations in oxygen levels differ markedly between lake types: in holomictic lakes, fall and spring turnover events replenish hypolimnetic oxygen to near-saturation (8–10 mg/L), temporarily alleviating hypoxia.^[29] Conversely, in meromictic lakes with persistent stratification, the monimolimnion remains chronically anoxic year-round, with oxygen levels <1 mg/L and minimal replenishment.^[30]

Biological Components

Adapted Organisms

The profundal zone, characterized by perpetual darkness, low temperatures, and often limited oxygen, supports a specialized assemblage of organisms primarily composed of benthic invertebrates, microbial communities, and occasional fish species. In lacustrine profundal zones, dominant groups include oligochaete worms, chironomid larvae, and amphipods such as Diporeia spp., which historically formed the bulk of the macroinvertebrate biomass in many Great Lakes profundal zones but have declined significantly due to invasive dreissenid mussels since the early 2000s.^[31]^[32]^[33] These invertebrates are complemented by dense microbial mats of bacteria and archaea in the sediments. In oceanic profundal equivalents, such as the bathyal and abyssal benthos, polychaete worms and holothurians (sea cucumbers) prevail among the macrofauna, alongside microbial communities adapted to extreme pressures. Fish are rare across both environments but include deepwater specialists like ciscoes and sculpins in lakes, and anglerfishes in oceanic depths.^[34]^[35] Key adaptations enable survival in these harsh conditions, including reduced metabolic rates to conserve energy in nutrient-scarce, cold waters. For instance, chironomid larvae in lake profundal zones exhibit extremely low metabolic activity during dormancy, relying on anaerobic respiration and ethanol production to endure anoxia for periods up to 205 days, facilitated by high-affinity extracellular hemoglobin that stores oxygen for extended low-oxygen periods.^[36]^[37] Similarly, amphipods like Diporeia in Great Lakes profundal habitats are stenothermic, thriving in near-bottom temperatures below 6°C with physiological adjustments such as lipid accumulation to support slow growth and reproduction in cold, hypoxic conditions.^[31] Oligochaetes tolerate low oxygen through pigments like erythrocruorin for efficient transport and, in some cases, symbiosis with chemoautotrophic bacteria in sulfidic sediments.^[32] In oceanic settings, pressure tolerance is achieved via osmoregulation, where body fluids match ambient hydrostatic pressure to prevent cellular damage, as seen in polychaetes and holothurians lacking rigid structures.^[38] Bioluminescence serves as a morphological adaptation for predation and mate attraction in deep-sea fish like anglerfishes, which deploy bacterial or intrinsic light organs as lures in the absence of sunlight.^[35] Organisms in the profundal zone predominantly occupy detritivore and scavenger trophic levels, feeding on settling organic particles from upper layers or decomposing remains. Benthic invertebrates such as Diporeia and chironomid larvae act as surface detritivores, ingesting sediment-bound organic matter and microalgae, while holothurians in oceanic benthos filter and process detritus through tentacle feeding, reworking vast quantities of seafloor sediment.^[31]^[39] Some polychaetes scavenge carrion or employ chemosensory adaptations to locate rare food pulses. Microbial communities rely on detrital decomposition via anaerobic pathways or localized chemosynthesis in anoxic sediments, where sulfate-reducing bacteria and methanogens process organic inputs, supporting higher trophic levels indirectly.^[40] Filter-feeding is common among settling-particle consumers, with structures like mucus nets in polychaetes capturing fine particulates.^[41] Representative examples highlight these traits in lacustrine and oceanic contexts. In lakes, chironomid larvae (Chironomus spp.) burrow into profundal sediments, ventilating tubes to access oxygenated water overlays while hemoglobin enables persistence in hypoxic zones below 3 mg/L oxygen.^[36] Oligochaetes like Tubifex tubifex dominate anoxic profundal muds, migrating vertically to exploit oxygen gradients. In oceanic profundal zones, polychaetes such as orbiniids regulate oxygen uptake down to partial pressures of 870 Pa, adapting respiration to sparse, detritus-based food. Holothurians, including species like Psychropotes spp., exhibit slow locomotion and tentacle retraction to process abyssal detritus efficiently, contributing to carbon flux with minimal energy expenditure.^[39] Rare fish, such as deepwater sculpins in lakes, show visual adaptations like rod-dominated retinas for detecting faint bioluminescent or residual light, underscoring the zone's selective pressures.^[34]

Biodiversity Patterns

The profundal zone exhibits notably low biomass and species richness compared to shallower zones such as the littoral or limnetic areas. In oligotrophic tropical Lake Alchichica, for instance, the profundal benthic community consists of only two species with a biomass of approximately 16 mg C m⁻², in stark contrast to the littoral zone's 50 taxa and biomass exceeding 1,700 mg C m⁻². Similarly, in large temperate lakes like Tahoe, Crater, and Hövsgöl, profundal chironomid genera number 12–35, significantly fewer than in nearshore habitats, reflecting reduced productivity and habitat suitability at greater depths.^[42]^[43] Endemism is particularly high in the profundal zones of isolated deep lakes, where long-term stability fosters unique speciation. In ancient rift lakes like Baikal, approximately 85% of the roughly 200 oligochaete species are endemic, with many restricted to profundal sediments due to specialized adaptations to aphotic conditions. This pattern holds in other tectonic basins, such as Lake Ohrid, where endemic profundal oligochaetes contribute to elevated local diversity despite overall low richness.^[44]^[18] Key factors shaping these patterns include food scarcity, which constrains overall abundance, and extreme conditions like high hydrostatic pressure and near-freezing temperatures, which favor specialist taxa and promote community evenness over high richness. Organic matter sinking from upper layers provides limited energy, supporting sparse populations dominated by detritivores, while physiological tolerances to hypoxia and pressure filter generalists, yielding balanced but depauperate assemblages. In the deep ocean's analogous profundal-equivalent abyssal and hadal zones, similar constraints result in evenness among surviving polychaetes and isopods, though richness remains low relative to continental shelves.^[42]^[45] Biodiversity displays clear zonation patterns, with higher diversity near the profundal's upper boundaries transitioning from the limnetic zone and declining sharply with increasing depth due to diminishing oxygen and food availability. In studied lakes, Shannon-Wiener diversity indices generally decline with depth, ranging from 0.93–2.07 nearshore to 0.53–1.27 in deep profundal sediments. Hotspots occur in areas of localized upwelling, such as around lakemounts or oceanic seamounts, where nutrient fluxes enhance benthic productivity and support elevated densities of amphipods and nematodes.^[42]^[46] Species-area relationships in profundal basins underscore how larger habitat patches sustain greater richness, though overall metrics remain subdued compared to littoral zones. Recent surveys as of 2025 indicate ongoing challenges to profundal biodiversity from invasive species and warming-induced hypoxia, though new technologies are uncovering previously unknown microbial and meiofaunal diversity.^[47]

Ecological Processes

Nutrient Cycling Mechanisms

In the profundal zone, anoxic conditions prevalent in deep lake and ocean sediments facilitate denitrification, a microbial process where nitrate (NO₃⁻) is reduced to dinitrogen gas (N₂), thereby removing fixed nitrogen from the ecosystem. This anaerobic respiration is primarily mediated by denitrifying bacteria, such as those in the NC10 phylum, including Candidatus Methylomirabilis oxyfera, which couple denitrification to methane oxidation in profundal sediments. The key reaction can be represented as:

\text{NO}_3^- + \text{organic C} \rightarrow \text{N}_2 + \text{CO}_2

In Lake Constance, for instance, nitrate-dependent anaerobic methane oxidation serves as the dominant methane sink in profundal sediments, with potential rates reaching 660–4,890 µmol CH₄ m⁻² d⁻¹ in anoxic layers.^[48] Methanogenesis, another critical process under anoxic conditions, involves the production of methane (CH₄) from organic substrates by methanogenic archaea, often competing with denitrification for electron donors. The primary pathways include acetoclastic methanogenesis (CH₃COOH → CH₄ + CO₂) and hydrogenotrophic methanogenesis (CO₂ + 4H₂ → CH₄ + 2H₂O), occurring in deeper sediment layers where sulfate is depleted. However, nitrogen additions can inhibit methanogenesis by favoring denitrifying microbes, reducing CH₄ production rates. Sulfate-reducing bacteria, such as those in the Desulfobacterota phylum, further drive nutrient cycles by reducing sulfate (SO₄²⁻) to hydrogen sulfide (H₂S) via the reaction SO₄²⁻ + 2CH₂O → H₂S + 2HCO₃⁻, which influences sulfur and carbon dynamics in profundal environments. Under highly reduced conditions, these bacteria become active, accumulating H₂S in bottom waters and exacerbating toxicity to aquatic life.^[49]^[50] Phosphorus cycling in the profundal zone is dominated by sediment release mechanisms triggered by redox shifts, particularly the mobilization of iron-bound phosphorus under anoxic conditions. In oxygenated waters, phosphorus adsorbs to iron oxyhydroxides, but anoxia dissolves these minerals, liberating phosphate (PO₄³⁻) into porewaters and overlying water. For example, in ultra-oligotrophic Lake Tahoe, the upper 5 cm of profundal sediments hold 710 metric tons of redox-sensitive phosphorus, with release rates of 0.13–0.29 mg P m⁻² d⁻¹ under anoxia, potentially doubling water column concentrations after prolonged mixing events. This internal loading contributes to nutrient accumulation in hypolimnetic waters, linking profundal processes to surface productivity.^[51]^[52] Microbial communities, including sulfate-reducing and denitrifying bacteria, mediate these transformations, while physical mixing events transport nutrients vertically toward surface layers, sustaining upper water column productivity. Nutrient cycling rates in the profundal zone are notably slower than in the warmer epilimnion due to low temperatures (typically 4–10°C), which reduce microbial metabolic activity, limiting overall flux efficiency.^[50]

Decomposition and Carbon Flux

In the profundal zone, organic matter that sinks from upper water layers undergoes decomposition primarily by benthic bacteria, with limited contributions from fungi due to the harsh, low-oxygen conditions. Aerobic decomposition occurs in oxygen-penetrated surface sediments, where bacteria oxidize labile organic compounds to carbon dioxide (CO₂), while anaerobic processes dominate deeper layers, involving sulfate-reducing and methanogenic bacteria that produce methane (CH₄) and dissolved organic carbon (DOC). These microbial activities convert particulate organic matter into gaseous and dissolved forms, with respiratory carbon loss in profundal sediments of oligotrophic lakes estimated at 4.6–15.6 mg C m⁻² h⁻¹, predominantly through bacterial respiration. In deep lake sediments like Lake Constance, acetoclastic methanogenesis prevails under permanently cold, anoxic conditions, yielding CH₄ as a key product alongside CO₂ from fermentation and other anaerobic pathways.^[53] Refractory organic matter, resistant to further microbial breakdown, accumulates in profundal sediments, contributing to long-term carbon burial. Globally, this process sequesters approximately 0.1–0.2 Gt C per year in deep ocean sediments, representing a significant portion of marine organic carbon burial and acting as a net sink for atmospheric CO₂. Burial efficiency is enhanced in low-oxygen profundal environments, where slow decomposition preserves ~1–10% of sinking organic carbon in refractory forms. Carbon flux in the profundal zone is governed by models of particulate organic carbon (POC) sinking and benthopelagic coupling, which links pelagic production to benthic processing. POC sinking rates typically range from 10 to 100 m day⁻¹, influenced by particle size and density, allowing organic matter to reach profundal depths within weeks to months. Benthopelagic coupling facilitates the downward flux of POC and upward release of remineralized products like DOC, sustaining nutrient and carbon exchange between water column and sediments. Decomposition rates in the cold profundal zone follow the Arrhenius equation:

k = A e^{-\frac{E_a}{RT}}

where k is the rate constant, A is the pre-exponential factor, E_a is the activation energy, R is the gas constant, and T is temperature in Kelvin. In these low-temperature environments (typically 2–4°C), the exponential term results in minimally varying k values, slowing degradation and promoting carbon preservation compared to warmer surface layers.

Ecological Significance

Role in Food Webs

The profundal zone functions as a critical bottom-up energy source in aquatic food webs, primarily through the sedimentation of detritus from overlying epilimnetic and metalimnetic layers, which serves as the main fuel for benthic consumers such as chironomid larvae and oligochaetes. In deep oligotrophic lakes, this detrital input supports profundal secondary production that can constitute 10-30% of the whole-lake total secondary production, depending on system morphometry and organic matter flux; for instance, in Lake Thingvallavatn, Iceland, zoobenthic production, including the profundal component, accounted for 32% of total secondary production.^[54]^[55] Trophic linkages between the profundal zone and upper water layers facilitate bidirectional biomass and nutrient exchange, with export to the surface occurring via ascending chironomid pupae that serve as prey for pelagic fish like perch, linking benthic production to higher trophic levels. Additionally, vertically migrating zooplankton and deep-diving fish species, such as lake whitefish, transport profundal-derived biomass upward by feeding on benthic organisms during diel or seasonal migrations. The microbial loop in profundal sediments recycles a substantial portion of this carbon, with heterotrophic bacteria converting allochthonous and autochthonous organic matter into biomass that supports protozoans and metazoans, thereby retaining energy within the system before potential export.^[56]^[57]^[58] Profundal benthic organisms play keystone roles as primary prey for deep-diving species, including amphipods like Diporeia that underpin populations of coregonids in large lakes such as Lake Superior, thereby influencing predator demographics and overall trophic structure. These communities also modulate whole-lake metabolism by driving sediment oxygen demand through respiration and decomposition, which can affect hypolimnetic oxygenation and nutrient availability for surface productivity. Energy transfer efficiency from profundal primary detritus to higher trophic levels remains low, typically 1-10%, owing to substantial losses from microbial respiration and incomplete assimilation, as quantified through stable isotope analysis of carbon pathways in subalpine lakes.^[57]^[59]^[55]

Impacts of Environmental Change

Eutrophication, driven by excessive nutrient inputs from agricultural and urban runoff, has profoundly impacted the profundal zone by increasing organic matter deposition, which intensifies oxygen depletion and anoxia. This process leads to hypoxic conditions that reduce habitat suitability for benthic organisms, resulting in decreased biodiversity and shifts toward tolerant species such as certain oligochaetes and chironomids. In Lake Erie, for instance, phosphorus loading during the 1960s and 1970s caused severe hypolimnetic oxygen declines, eliminating deepwater fish populations like whitefish and burbot and altering the benthic community structure.^[60] Climate warming exacerbates profundal oxygen deficits through the formation of deeper thermoclines and diminished vertical mixing, which limit oxygen replenishment from surface waters. In lakes, this stratification intensifies hypolimnetic deoxygenation, while in oceans, it contributes to the expansion of oxygen minimum zones (OMZs), with low-oxygen areas at intermediate depths increasing by approximately 4.5 million km² since the 1960s. These changes, observed globally, reduce aerobic respiration in profundal sediments and disrupt microbial processes, potentially releasing stored nutrients and amplifying eutrophication.^[61]^[62] Ocean acidification, resulting from elevated atmospheric CO₂ absorption, is projected to lower surface and deep-sea pH to around 7.8 by 2100 under high-emission scenarios, affecting profundal calcifying organisms such as benthic foraminifera and pteropods whose shells dissolve more readily in undersaturated waters. Concurrently, pollution from heavy metals like mercury and cadmium accumulates in profundal sediments, where low oxygen facilitates their remobilization and bioaccumulation in benthic invertebrates, posing risks to higher trophic levels through biomagnification.^[63]^[64] Restoration efforts, such as hypolimnetic aeration, have been implemented to counteract these impacts by artificially introducing oxygen to profundal waters while preserving thermal stratification. In Swiss lakes like Sempach, Baldegg, and Hallwil, oxygenation systems installed since the early 1980s have successfully mitigated hypoxia, reduced internal phosphorus loading, and supported benthic community recovery in eutrophic conditions.^[65]

References

[1]
The freshwater biome
when they die, they fall into the deep-water part of the lake/pond, the profundal zone. This zone is much colder and denser ...
[2]
Pond Ecosystem - Kenilworth Park & Aquatic Gardens (U.S. National ...
Oct 10, 2025 · The deepest pond region is a profundal zone dominated by heterotrophs and has no light penetration.
[3]
[PDF] Lakes and Reservoirs: Guidelines for Study Design and Sampling
The profundal community receives nutrients and energy from organic matter loaded to or produced in the lake or res- ervoir (Cooke and others, 2005). Inorganic ...
[4]
Ecosystems: Aquatic Biomes - GMU
profundal zone · consists of deep, aphotic regions · too dark for photosynthesis · oxygen levels are low · inhabited by fish adapted to cool dark waters.
[5]
[PDF] ECOSYSTEM AND HABITAT - Ohio.gov
Between the lowest limit of the euphotic zone and the lake bottom is the profundal zone. This zone comprises the deeper and darker portions of the water ...
[6]
[PDF] 1 Ecological features and processes of lakes and wetlands Lakes ...
These types of lakes are typically oligotrophic and low in nutrients and productivity, and the profundal zone remains. Page 8. Conservation Guidelines for ...
[7]
Lentic Systems - an overview | ScienceDirect Topics
Areas below these depths are variously called the aphotic or profundal zone (the latter often in reference to benthos). The shallow, nearshore region of the ...
[8]
[PDF] Borders of Biodiversity: Life at the Edge of the World's Large Lakes ...
The unlit area of the lake that is deeper than the compensation depth is the profundal zone. Negligible photosynthesis occurs in the profundal zone. Finally, ...
[9]
Freshwater lakes | Research Starters - EBSCO
The profundal zone occurs in deep lakes and is the region below where light penetration occurs. The benthic zone is on the lake bottom and includes the region ...
[10]
[PDF] Lake Water Quality Module (1)
2). The waters directly below the Limnetic Zone are the cool dark waters referred to as the Profundal Zone. The bottom of the lake, whether below the Littoral ...
[11]
light in the ocean - Ocean Topic in Greater Depth
The compensation depth coincides with the depth in the ocean where the light level is 0.1% to 1% of the amount of the sunlight entering the surface of the ...Missing: lakes | Show results with:lakes
[12]
[PDF] Lake Monitoring Field Manual - State Water Resources Control Board
Light is scattered through the water column, and the depth at which the light is only 1% of the surface light is called the compensation depth. At this point, ...
[13]
The benthic community of Lake Superior: Analysis of spatial and ...
Jul 8, 2025 · Lake Superior is the deepest and one of the most oligotrophic lakes in the Laurentian Great Lakes system. ... deepest zone (>90 m).
[14]
Nutrient Fluxes From Profundal Sediment of Ultra‐Oligotrophic Lake ...
Feb 16, 2018 · Experimental results indicate that if deep water in Lake Tahoe goes anoxic, profundal sediment will release appreciable amounts of phosphate ( ...Missing: prevalence | Show results with:prevalence
[15]
Meromictic Lake Guide - New York Natural Heritage Program
Mar 26, 2024 · Meromictic lakes are relatively deep with small surface area ... lake may have oxygen deficiencies in deeper water (the profundal zone).
[16]
Permanent Thermal and Chemical Stratification in a Restored Urban ...
Meromictic lakes are unique aquatic ecosystems that occur extremely rarely. The phenomenon of meromixis can result from both natural and anthropogenic ...
[17]
Ocean Zones - Woods Hole Oceanographic Institution
The abyssal zone, or the abyss, is the seafloor and water column from 3,000 to 6,500 meters (9,842 to 21,325 feet) depth, where sunlight doesn't penetrate.Missing: profundal | Show results with:profundal
[18]
Borders of Biodiversity: Life at the Edge of the World's Large Lakes
Jul 1, 2011 · The unlit area of the lake that is deeper than the compensation depth is the profundal zone. Negligible photosynthesis occurs in the profundal ...
[19]
Reconciling Between Optical and Biological Determinants of the ...
Apr 14, 2021 · The “euphotic zone” depth based on 1% or 0.1% surface photosynthetically available radiation (PAR) is not an accurate measure of the ...
[20]
Adaptations | manoa.hawaii.edu/ExploringOurFluidEarth
In the disphotic zone light intensity allows vision but only low levels of photosynthesis. In the aphotic zone, sunlight is virtually absent, but there can be ...<|separator|>
[21]
https://www.fondriest.com/environmental-measurements/parameters/temperature/
[22]
Measuring lake health: Secchi disk how-to
One method involves using high-frequency sensors that measure the amount of light at different depths of a lake. An example is an instrument called a ...
[23]
Long-term development of hypolimnetic oxygen depletion rates in ...
Jan 30, 2017 · This study investigates over 30 years of dissolved oxygen dynamics in the deep interior of Lake Constance (max. depth: 250 m).
[24]
Climate-driven deoxygenation of northern lakes - Nature
Jul 1, 2024 · Climate warming has the potential to cause further oxygen loss via prolonged summer stratification and enhanced aerobic respiration rates.Missing: profundal | Show results with:profundal
[25]
Evolution and dynamics of the Arabian Sea oxygen minimum zone
Dec 1, 2023 · The Arabian Sea hosts a perennial and intense oxygen minimum zone (OMZ) at 150–1200 m depths with O2 concentrations <0.5 ml/l.
[26]
A biogeochemical approach to evaluate the optimization and ...
Feb 10, 2021 · Accumulation of nutrients in the hypolimnion is a typical phenomenon in eutrophic lakes, and it is linked to the thermal stratification of the ...
[27]
Dynamics of the Indian-Ocean oxygen minimum zones - ScienceDirect
In the Indian Ocean, mid-depth oxygen minimum zones (OMZs) occur in the Arabian Sea and the Bay of Bengal.
[28]
[PDF] Iron Reduction in Profundal Sediments of Ultraoligotrophic Lake ...
Jan 12, 2023 · Here, we study the elemental composition and redox state of the profundal sediment of Lake Tahoe as a function of sediment depth and combine ...
[29]
[PDF] Morphology and Water Quality in Three Abandoned Granite Quarries
An interesting difference between the quarries was that EQ was holomictic and WQ appeared to be meromictic. EQ circulated completely during the autumnal ...
[30]
Spatiotemporal analysis of microbial community dynamics during ...
May 11, 2017 · Such process is especially important in meromictic, and holomictic lakes, where the lack of upwelling results in greater accumulation of ...
[31]
[PDF] Transformation of the offshore benthic community in Lake Michigan
Diporeia are part of a fauna that inhabit cold, deep pro- glaciated lakes, brackish estuaries and coastal margins in the Holarctic region (Bousfield, 1989).
[32]
Annelids in Extreme Aquatic Environments: Diversity, Adaptations ...
Densities of oligochaete species living near the vent have been found higher than at similar water depths and approximately nearly half of these species are ...
[33]
Adaptive Evolution of Nearctic Deepwater Fish Vision
Feb 5, 2024 · We report evidence for molecular adaptation in vision in 2 lineages of Nearctic fishes that are deep lake specialists: ciscoes and deepwater sculpin.
[34]
Fishes of the Midnight Zone - NOAA Ocean Exploration
Jun 4, 2012 · One of the most striking adaptations of predatory fishes of the deep is the astounding variety of bioluminescent “lures” that fishes use to ...
[35]
Chapter 20: Least Oxygen Dependent | UF/IFAS
Discussion. Chironomids are often the only insects found in lake sediments of the profundal zone where hypoxic (oxygen concentrations less than 3 mg l-1) and ...
[36]
The adaptations to tube-dwelling life of Propsilocerus akamusi ...
Adequate body fuel accumulation during low temperature period of fast growth and extremely low metabolic rate during dormancy are allowing the larvae to survive ...Missing: profundal | Show results with:profundal
[37]
https://www.sciencedirect.com/science/article/pii/S007595111830118X
[38]
Ecology of Deposit-Feeding Animals in Marine Sediments
Deposit-feeding animals acquire food by swallowing large volumes of sediment. Possible food sources include organic debris and sediment-associated microbes.
[39]
Community structure of Archaea and Bacteria in a profundal lake ...
Our study gives a comprehensive insight into the structure of the bacterial and archaeal community of a profundal lake sediment, indicating that sulphate ...
[40]
The Pompeii Worm, Alvinella pompejana - SERC (Carleton)
The Pompeii worm, Alvinella pompejana, is a deep-sea polychaete found near hydrothermal vents. It can withstand high temperatures, and has a symbiotic ...
[41]
Patterns in Benthic Biodiversity Link Lake Trophic Status to Structure ...
Mean diversity varied between the depth zones of the three lakes, with the highest diversity in Lake Tahoe's nearshore community and the lowest in the Crater ...
[42]
https://pmc.ncbi.nlm.nih.gov/articles/PMC4296932/
[43]
Shedding Light on Deep-Sea Biodiversity—A Highly Vulnerable ...
In general, lower species diversity in the deep sea is found when conditions are suboptimal, such as low oxygen zones, strong currents, mudslides in deep sea ...Introduction · Methods to Assess Deep-Sea... · Threats to Biodiversity in the...
[44]
[PDF] Are lakemounts hotspots of productivity and biodiversity? - CEE LAB
Sep 30, 2024 · Lakemounts may serve similar roles as seamounts, with upwellings boosting productivity and biodiversity, similar to how seamounts bring ...
[45]
Borders of Biodiversity: Life at the Edge of the World's Large Lakes
Aug 6, 2025 · Beyond the littoral zone, the lakes are divided into the well-lit open- water zone (surface to compensation depth) and the profundal zone ( ...
[46]
Anaerobic methane oxidation coupled to denitrification is the ... - NIH
Although denitrifying methanotrophs obviously play a significant role at profundal sites, the ecological relevance of denitrifying methane oxidation might be ...
[47]
Combined effects of carbon, nitrogen and phosphorus on CH 4 ...
Changes in nutrient availability can affect major biogeochemical reactions (i.e., methanogenesis, denitrification) which impact greenhouse gas emissions and ...
[48]
Effects of aerobic and anaerobic conditions on P, N, Fe, Mn, and Hg ...
Under highly reduced conditions sulfate-reducing bacteria become active and sulfides can accumulate in bottom waters.
[49]
Nutrient fluxes from profundal sediment of ultra-oligotrophic Lake ...
Jul 20, 2022 · Experimental results indicate that if deep water in Lake Tahoe goes anoxic, profundal sediment will release appreciable amounts of phosphate ( ...Missing: prevalence | Show results with:prevalence
[50]
Spatial and seasonal changes of phosphorus internal loading in two ...
During summer time, phosphorus released from bottom sediments in the profundal zone is accumulated in the water layer near the bottom of the lake. In the ...
[51]
The role of zoobenthos in energy flow in deep, oligotrophic Lake ...
... 10–20 m, and (5) the profundal zone community from 20–114 m. Total mean lakewide production was 78 kJ m−2 yr−1. Herbivores, detritivores, and carnivores ...
[52]
Efficiencies of benthic and pelagic trophic pathways in a subalpine ...
This has led to the suggestion that energy may be more efficiently passed along benthic food chains relative to their pelagic counterparts. To test this idea, ...
[53]
Benthic–pelagic coupling in lake ecosystems: the key role of ...
Feb 14, 2012 · Chironomid larvae rarely served as prey for perch. While chironomid pupae from the littoral region were of minor importance as perch prey, we ...Missing: adaptations | Show results with:adaptations
[54]
Distribution of the Amphipod Diporeia in Lake Superior
Diporeia, formerly the dominant benthic macroinvertebrate in the Great Lakes, remains a keystone species in Lake Superior. Little is known, however, ...
[55]
Whole‐lake estimates of carbon flux through algae and bacteria in ...
Jul 1, 2009 · This study quantified new biomass production of algae and bacteria in both benthic and pelagic habitats of clear-water lakesMissing: profundal | Show results with:profundal
[56]
[PDF] what in the benthos have we learned about habitat linkages in lakes?
Mar 23, 2020 · No photosynthesis occurs in the profundal zone, but detrital fallout from the open-water and littoral zone fuels heterotrophic microbial ...
[57]
Assessing and addressing the re-eutrophication of Lake Erie
During the 1960s and 1970s, increased phosphorus inputs degraded water quality and reduced central basin hypolimnetic oxygen levels which, in turn, eliminated ...
[58]
Declining oxygen in the global ocean and coastal waters | Science
Jan 5, 2018 · Open-ocean oxygen-minimum zones (OMZs) have expanded by an area about the size of the European Union (4.5 million km2, based on water with <70 ...
[59]
FAQ: Ocean Deoxygenation - Scripps Institution of Oceanography |
Globally, about 2% of the oxygen content in the ocean has been lost since the 1960s. The area of low oxygen water in the open ocean has increased by 4.5 ...Missing: profundal | Show results with:profundal
[60]
Ocean Acidification - Smithsonian Ocean Portal
If we continue to add carbon dioxide at current rates, seawater pH may drop another 120 percent by the end of this century, to 7.8 or 7.7, creating an ocean ...
[61]
Heavy metal accumulation in deep sediment benthic invertebrates ...
Oct 8, 2025 · Associations with deep sediments appear to increase metal accumulation, which is understandable as heavy metals tend to precipitate out of the ...Missing: profundal zone
[62]
A Review of the Effects of Hypolimnetic Oxygenation on Lake and ...
Deep oxygen injection systems have been operating in Lakes Sempach, Baldegg, and Hallwil, Switzerland, since the early 1980s to ameliorate cultural ...