Lake ecosystem: Difference between revisions

<!-- Deleted image removed: [[Image:LSE pond.jpg|thumb|300px|rightupright=1.3|This small lake or mountain pool, together with its environment, can be regarded as forming a lake or lentic [[ecosystem]].]] -->

| page = 163 }}</ref> Lake ecosystems are a prime example of '''lentic ecosystems''' (''lentic'' refers to stationary or relatively still [[freshwater]], from the [[Latin]] ''lentus'', which means "sluggish"), which include [[pond]]s, [[lake]]s and [[wetland]]s, and much of this article applies to lentic ecosystems in general. Lentic ecosystems can be compared with [[lotic ecosystems]], which involve flowing terrestrial waters such as [[river]]s and [[stream]]s. Together, these two fieldsecosystems formare the more general study areaexamples of [[freshwater biology|freshwater]] or [[marine biology|aquatic ecologyecosystem]]s.

| publisher = Oxford University Press, Oxford

Two important subclasses of lakes are [[Pond|pondspond]]s, which typically are small lakes that intergrade with wetlands, and water [[Reservoir|reservoirsreservoir]]s. Over long periods of time, lakes, or bays within them, may gradually become enriched by nutrients and slowly fill in with organic sediments, a process called succession. When humans use the [[Drainagedrainage divide|watershedbasin]], the volumes of sediment entering the lake can accelerate this process. The addition of sediments and nutrients to a lake is known as [[eutrophication]].<ref name="Alexander">{{cite book|last=Alexander|first=David E.|title=Encyclopedia of Environmental Science|date=1 May 1999|publisher=[[Springer Science+Business Media|Springer]]|isbn=0-412-74050-8}}</ref>

{{refimprovemore citations needed|section|date=August 2021}}

Lake ecosystems can be divided into zones. One common system divides lakes into three zones. The first, the [[littoral zone]], is the shallow zone near the shore.<ref>{{Cite book |title=eLS |date=2001-05-30 |publisher=Wiley |isbn=978-0-470-01617-6 |editor-last=John Wiley & Sons, Ltd |edition=1 |language=en |doi=10.1038/npg.els.0003191}}</ref> This is where rooted wetland plants occur. The offshore is divided into two further zones, an open water zone and a deep water zone. In the open water zone (or photic zone) sunlight supports photosynthetic algae and the species that feed upon them. In the deep water zone, sunlight is not available and the food web is based on detritus entering from the littoral and photic zones. Some systems use other names. The off shore areas may be called the [[pelagic zone]], the [[photic zone]] may be called the [[limnetic zone]] and the [[aphotic zone]] may be called the [[profundal zone]]. Inland from the littoral zone, one can also frequently identify a [[riparian zone]] which has plants still affected by the presence of the lake—this can include effects from windfalls, spring flooding, and winter ice damage. The production of the lake as a whole is the result of production from plants growing in the littoral zone, combined with production from plankton growing in the open water.

[[Wetland|Wetlands]]s can be part of the lentic system, as they form naturally along most lake shores, the width of the wetland and littoral zone being dependent upon the slope of the shoreline and the amount of natural change in water levels, within and among years. Often dead trees accumulate in this zone, either from windfalls on the shore or logs transported to the site during floods. This woody debris provides important habitat for fish and nesting birds, as well as protecting shorelines from erosion.

[[Image:Foamlines.png|right|thumb|300pxupright=1.5|Illustration of Langmuir rotations; open circles=positively buoyant particles, closed circles=negatively buoyant particles]]

[[File:Nelumbo nucifera LOTUS bud.jpg|thumb|upright|''[[Nelumbo nucifera]]'', an aquatic plant.]]

Algae, including both [[phytoplankton]] and [[periphyton]], are the principle photosynthesizers in ponds and lakes.<ref>{{Cite journal |last1=Cael |first1=B. B. |last2=Seekell |first2=David A. |date=2023 |title=How does lake primary production scale with lake size? |journal=Frontiers in Environmental Science |volume=11 |doi=10.3389/fenvs.2023.1103068 |issn=2296-665X |doi-access=free }}</ref> Phytoplankton are found drifting in the water column of the pelagic zone. Many species have a higher density than water, which should cause them to sink inadvertently down into the [[benthos]]. To combat this, phytoplankton have developed density-changing mechanisms, by forming [[Vacuole|vacuolesvacuole]]s and [[Gas vesicle|gas vesiclesvesicle]]s, or by changing their shapes to induce drag, thus slowing their descent.<ref>{{Cite web |last=Smriti |first=Saifun Nahar |date=2023-10-05 |title=Adaptation of Phytoplankton to Float in Water |url=https://greenleen.com/adaptation-of-phytoplankton-to-float-in-water/ |access-date=2023-10-05 |website=GreenLeen.Com |language=en-US}}</ref> A very sophisticated adaptation utilized by a small number of species is a tail-like [[flagellum]] that can adjust vertical position, and allow movement in any direction.<ref name="bronmark:2005"/> Phytoplankton can also maintain their presence in the water column by being circulated in [[Langmuir circulation|Langmuir rotations]].<ref name="kalff:2002"/> Periphytic algae, on the other hand, are attached to a substrate. In lakes and ponds, they can cover all benthic surfaces. Both types of plankton are important as food sources and as oxygen providers.<ref name="bronmark:2005"/>

[[Zooplankton]] are tiny animals suspended in the water column. Like phytoplankton, these species have developed mechanisms that keep them from sinking to deeper waters, including drag-inducing body forms, and the active flicking of appendages (such as antennae or spines).<ref name="brown:1987"/> Remaining in the water column may have its advantages in terms of feeding, but this zone's lack of refugia leaves zooplankton vulnerable to predation. In response, some species, especially [[Daphnia]] sp., make daily vertical migrations in the water column by passively sinking to the darker lower depths during the day, and actively moving towards the surface during the night. Also, because conditions in a lentic system can be quite variable across seasons, zooplankton have the ability to switch from laying regular eggs to resting eggs when there is a lack of food, temperatures fall below 2&nbsp;°C, or if predator abundance is high. These resting eggs have a [[diapause]], or dormancy period, that should allow the zooplankton to encounter conditions that are more favorable to survival when they finally hatch.<ref name="gliwicz:2004">Gliwicz, Z. M. "Zooplankton", pp. 461–516 in O'Sullivan (2005)</ref> The invertebrates that inhabit the benthic zone are numerically dominated by small species, and are species-rich compared to the zooplankton of the open water. They include: [[Crustacean|Crustaceans]]s (e.g. [[Crab|crabscrab]]s, [[crayfish]], and [[shrimp]]), [[Mollusca|molluscs]] (e.g. [[Clam|clamsclam]]s and [[Snail|snailssnail]]s), and numerous types of insects.<ref name="bronmark:2005"/> These organisms are mostly found in the areas of macrophyte growth, where the richest resources, highly-oxygenated water, and warmest portion of the ecosystem are found. The structurally diverse macrophyte beds are important sites for the accumulation of organic matter, and provide an ideal area for colonization. The sediments and plants also offer a great deal of protection from predatory fishes.<ref name="kalff:2002"/>

Other vertebrate taxa inhabit lentic systems as well. These include [[Amphibian|amphibiansamphibian]]s (e.g. [[Salamander|salamanderssalamander]]s and [[Frog|frogsfrog]]s), [[Reptile|reptilesreptile]]s (e.g. [[Snake|snakessnake]]s, [[Turtle|turtlesturtle]]s, and [[Alligator|alligatorsalligator]]s), and a large number of [[waterfowl]] species.<ref name="moss:1998"/> Most of these vertebrates spend part of their time in terrestrial habitats, and thus, are not directly affected by abiotic factors in the lake or pond. Many fish species are important both as consumers and as prey species to the larger vertebrates mentioned above.

Lentic systems gain most of their energy from photosynthesis performed by aquatic plants and algae.<ref>{{cite journal |last1=Zhang |first1=Ke |last2=Yang |first2=Xiangdong |last3=Kattel |first3=Giri |last4=Lin |first4=Qi |last5=Shen |first5=Ji |title=Freshwater lake ecosystem shift caused by social-economic transitions in Yangtze River Basin over the past century |journal=Scientific Reports |date=21 November 2018 |volume=8 |issue=1 |pages=17146 |doi=10.1038/s41598-018-35482-5 |pmid=30464220 |url=https://www.nature.com/articles/s41598-018-35482-5 |access-date=13 January 2024 |language=en |issn=2045-2322|hdl=11343/219728 |hdl-access=free }}</ref> This [[Indigenous (ecology)wikt:autochthonous|autochthonous]] process involves the combination of carbon dioxide, water, and solar energy to produce carbohydrates and dissolved oxygen. Within a lake or pond, the potential rate of photosynthesis generally decreases with depth due to light attenuation.<ref>{{Cite journal |last=Pirc |first=Helmut |date=January 1986 |title=Seasonal aspects of photosynthesis in Posidonia oceanica: Influence of depth, temperature and light intensity |url=https://linkinghub.elsevier.com/retrieve/pii/0304377086900215 |journal=Aquatic Botany |language=en |volume=26 |pages=203–212 |doi=10.1016/0304-3770(86)90021-5}}</ref> Photosynthesis, however, is often low at the top few millimeters of the surface, likely due to inhibition by ultraviolet light. The exact depth and photosynthetic rate measurements of this curve are system -specific and depend upon: 1) the total biomass of photosynthesizing cells, 2) the amount of light attenuating materials, and 3) the abundance and frequency range of light absorbing pigments (i.e. [[chlorophylls]]) inside of photosynthesizing cells.<ref name="moss:1998"/> The energy created by these primary producers is important for the community because it is transferred to higher [[trophic level]]s via consumption.<ref>{{cite journal |last1=Shimoda |first1=Yuko |last2=Azim |first2=M. Ekram |last3=Perhar |first3=Gurbir |last4=Ramin |first4=Maryam |last5=Kenney |first5=Melissa A. |last6=Sadraddini |first6=Somayeh |last7=Gudimov |first7=Alex |last8=Arhonditsis |first8=George B. |title=Our current understanding of lake ecosystem response to climate change: What have we really learned from the north temperate deep lakes? |journal=Journal of Great Lakes Research |date=1 March 2011 |volume=37 |issue=1 |pages=173–193 |doi=10.1016/j.jglr.2010.10.004 |url=https://www.sciencedirect.com/science/article/abs/pii/S0380133010002091 |access-date=13 January 2024 |issn=0380-1330}}</ref>

The vast majority of bacteria in lakes and ponds obtain their energy by decomposing vegetation and animal matter. In the pelagic zone, dead fish and the occasional [[allochthonous]] input of litterfall are examples of coarse particulate organic matter (CPOM>1&nbsp;mm). Bacteria degrade these into fine particulate organic matter (FPOM<1&nbsp;mm) and then further into usable nutrients. Small organisms such as plankton are also characterized as FPOM. Very low concentrations of nutrients are released during decomposition because the bacteria are utilizing them to build their own biomass. Bacteria, however, are consumed by [[protozoa]], which are in turn consumed by zooplankton, and then further up the [[trophic level]]s. Nutrients,Elements includingother thosethan thatcarbon, containparticularly carbonphosphorus and phosphorusnitrogen, are reintroducedregenerated when protozoa feed on bacterial prey <ref>{{Cite journal|last=Pernthaler|first=Jakob|date=July 2005|title=Predation on prokaryotes intoin the water column atand anyits numberecological ofimplications|url=https://www.nature.com/articles/nrmicro1180|journal=Nature pointsReviews alongMicrobiology|language=en|volume=3|issue=7|pages=537–546|doi=10.1038/nrmicro1180|pmid=15953930 this|s2cid=336473 food|issn=1740-1534}}</ref> chainand viathis excretionway, ornutrients organism death,become makingonce themmore available again for bacteriause in the water column. This regeneration cycle is known as the [[microbial loop]]<ref>{{Cite journal|last1=Azam|first1=F|last2=Fenchel|first2=T|last3=Field|first3=Jg|last4=Gray|first4=Js|last5=Meyer-Reil|first5=La|last6=Thingstad|first6=F|date=1983|title=The Ecological Role of Water-Column Microbes in the Sea|url=http://www.int-res.com/articles/meps/10/m010p257.pdf|journal=Marine Ecology Progress Series|language=en|volume=10|pages=257–263|doi=10.3354/meps010257|bibcode=1983MEPS...10..257A|issn=0171-8630}}</ref> and is a key component of lentic food webs.<ref name="bronmark:2005"/>

===Benthic Invertebratesinvertebrates===

| title = Lakes as islands: biogeographic distribution, turnover rates, and species composition in the lakes of central New York

| volume = 8 1| pages = 75–83

| jstor = 2844594| doi =10.2307/2844594}}</ref> Additional factors, including temperature regime, pH, nutrient availability, habitat complexity, speciation rates, competition, and predation, have been linked to the number of species present within systems.<ref name="bronmark:2005"/><ref name=Keddy/>

| issue = 4 | doi = 10.1127/archiv-hydrobiol/106/1986/433 | s2cid = 84069604 }}</ref> described these patterns as part of the Plankton Ecology Group ([[Plankton Ecology Group model|PEG]]) model, with 24 statements constructed from the analysis of numerous systems. The following includes a subset of these statements, as explained by Brönmark and Hansson<ref name="bronmark:2005"/> illustrating succession through a single seasonal cycle:

| issue = 2| s2cid = 9886026
| url = http://oceanrep.geomar.de/4048/1/Hillebrand_2004_Amer_nat.pdf

[[Eutrophication|Eutrophic]] systems contain a high concentration of phosphorus (~30&nbsp;µgμg/L), nitrogen (~1500&nbsp;µgμg/L), or both.<ref name="bronmark:2005"/> Phosphorus enters lentic waters from [[sewage treatment]] effluents, discharge from raw sewage, or from runoff of farmland. Nitrogen mostly comes from [[Fertilizer|agricultural fertilizers]] from runoff or leaching and subsequent groundwater flow. This increase in nutrients required for primary producers results in a massive increase of phytoplankton growth, termed a "[[Algal bloom|plankton bloom]]." This bloom decreases water transparency, leading to the loss of submerged plants.<ref>{{Cite journal |last1=Birk |first1=Sapriya |last2=Miller |first2=J. David |last3=MacMullin |first3=Aidan |last4=Patterson |first4=R. Timothy |last5=Villeneuve |first5=Paul J. |date=February 2023 |title=Perceptions of Freshwater Algal Blooms, Causes and Health among New Brunswick Lakefront Property Owners |journal=Environmental Management |language=en |volume=71 |issue=2 |pages=249–259 |doi=10.1007/s00267-022-01736-2 |issn=0364-152X|doi-access=free |pmid=36318287 |pmc=9628596 }}</ref> The resultant reduction in habitat structure has negative impacts on the species that utilize it for spawning, maturation, and general survival. Additionally, the large number of short-lived phytoplankton result in a massive amount of dead biomass settling into the sediment.<ref name="moss:1998"/> Bacteria need large amounts of oxygen to decompose this material, thus reducing the oxygen concentration of the water. This is especially pronounced in [[Lake stratification|stratified lakes]], when the [[thermocline]] prevents oxygen-rich water from the surface to mix with lower levels. Low or anoxic conditions preclude the existence of many taxa that are not physiologically tolerant of these conditions.<ref name="bronmark:2005"/>

| publisher = Oxford University Press, Oxford