Freshwater Biome Essay Test

Bottle ecosystem report. Abstract In this experiment, we developed a small experimental freshwater ecosystem and both abiotic and biotic factor within that freshwater ecosystem was monitored over the 5 weeks. Specifically this study investigated, how the changes in abiotic factors of ecosystem impact sustainability of biotic factors and the trophic relationship that exist within living species of that experimental ecosystem and how change in one trophic level effects the growth of aquatic animals. Our hypothesis was, all living organism within ecosystem will become self-sustained and survive throughout the 4 weeks period and all abiotic factors will be well balanced. Through this study, we found the stability of pH is significant to the aquatic animals and the certain amount of carbon oxide is required to neutralise alkaline water environment. Cumulative growth of floating plants such as duckweeds limits the growth and photosynthesis rate of submerged plants like Vallisneria by blocking sunlight and absorbing all the available nutrients. Introduction Freshwaters ecosystems defined as a subgroup of earth aquatic ecosystems. It consists of rivers, lakes and other small water bodies such as ponds, streams and wetlands. Freshwaters ecosystem differ from marines ecosystem, due to differences in its physical and chemicals compositions, for example salt concentration of freshwaters biomes vary with salt concentration of marine biomes as marine biomes contain high salt concentration (3%)than freshwater biomes (0.1%). (Clout et al .2015) The freshwater biomes such as lakes physical environment contain 3 types of zones. Top-most layer is known as a littoral zone, which is shallow, and it is capable of capturing more sunlight hence sustains abundant of floating aquatic plants. A wide range of aquatic animals such as fishes, waterbirds, amphibians, aquatic invertebrates such as insects grazes within littoral zone. Limnetic zone is surrounded by littoral zone and it is habitat for microorganisms like phytoplankton and zooplankton. Phytoplankton is responsible for providing oxygen and food source via photosynthesis for other aquatic animals. Zooplankton is responsible for decomposing all dead living organisms, which is essential for recycling of organic substances such as carbons, nitrogen and phosphorus based substances. Bottom part of lake is known as benthic zone and it is made of inorganic substances such as rocks, pebbles, sands, sediment and benthic zone is employed by other small microorganisms that decomposes dead living organic matters and by other macro-organisms such as vertebrates organism like fishes and invertebrates organisms like crabs and shrimps etc. A well-rooted submerged plant such as Vallisneria grows near benthic zone, where their roots are embedded with sediments, sands and pebbles. (The Aquatic biome, 2015) Freshwaters ecosystems such as lakes and rivers contains abundant and wide range of both heterotrophs and autotrophs organisms. Autotrophs include submerged and floating aquatic plants such as, duckweeds, lotus, and waterlily, vallisneria and bluegreen algae. Heterotrophs include, aquatic vertebrates, microbes, aquatic macroinvertebrates and amphibians. All biotic factors within aquatic ecosystem are closely connected with each other and their survival and reproduction rate depend on each others. The stability of those heterotrophs and autotrophs depends on abiotic factors such as dissolved oxygen, CO2 , pH, and sunlight energy, water, nutrients and salinity. The specific amount of sunlight, water and CO2 is required for aquatic plants to photosynthesise. For each different aquatic animals certain amount of pH, nutrients, salinity and oxygen is needed to maintain their optimum physiology, for example high salinity level cause imbalance in osmoregulation of freshwaters fishes as result it damage its physiological functions and lead to death. Change in one abiotic factor within ecosystem affect other abiotic factor for example, increase in dissolved CO2 in water cause pH of water to be low (makes water more acidic), this make harder for some living organisms to survive. The increment in water temperature lowers the concentration of dissolved oxygen within the freshwater ecosystem, which then effects respiration of all aquatic animals. Thus, all abiotic factors need to be balance in order to sustain all living organisms of ecosystems. Food webs play a vital role to maintain sustainable ecosystems. Food webs are the trophic relationship between the primary producer, primary, secondary and tertiary and quaternary consumer and detritivores. It is consist of all interconnected food chain that occur within the ecosystems. It mainly involves with transformation of food energy from its main sources (autotrophs) to consumer (heterotrophs) Thus, energy from food is crucial for every living organism to grow and functions optimally, to reproduce and to fight against predators and other diseases. (Foodweb,2015) Food webs always begin with a primary producer such as plants and other photosynthetic organisms and conclude with tertiary or quaternary consumer (carnivore). Detritivore such as fungi, bacteria and worms are responsible for decomposing the entire dead livings organism and recycling its nitrogen, carbon and phosphate based organics substances, ultimately primary producer can use those recycled organic substances as nutrients. In this experiment, we model experimental freshwater ecosystem in the 3-litre glass jar and we investigated its environment over the 5 weeks. The main aim of our experiment was, to observe how the change in abiotic factors influences the survival rates and sustainability of those biotic factors within that experimental ecosystem and to analyse food web and interrelationship that exist among organisms within ecosystems. Example of predicated food webs that exist within the experimental freshwater ecosystem Sun Green Algae Vallisneria Snail Duckweeds Corixidae (Water boatman) Dragonfly nymph Detritivore and decomposer such as ostracods, daphnia, ratifers and euglena. Decomposed elements such as N, C, and P are uptake by plants as nutrients. Materials and methods In this experiment, An freshwater ecosystem was constructed by transferring half kilogram of the mix of pebbles and sand (typical lakes/rivers sands and pebbles) into the bottom of 2 litre glass jar. Bottom sand and pebbles represent benthic zone. Then jar was filled with 1.5 litre of riverwater which was obtained from Karuah river .All those species (as mentioned below the table) were transferred into the glass jar and neck finish of glass jar was covered with flexible net, which was tied with rubber band Constructed freshwater ecosystem was kept in the rooftop with the average temperature of 23.6 ℃ for 4 weeks. Both biotic and abiotic factors within experimental ecosystem was monitored over the 4 weeks time period River water can contains certain amounts of nitrate, phosphate, microbes, blue-green algae spores and other elements such as sodium, potassium, calcium and sodium chloride. Some minerals and other ions can also be present in those sands and pebbles. Following species of aquatic plants and animals were used as living components of experimental freshwater ecosystem Species Vallisneria australis Wolffia lemnaceae (duckweeds) Trophic level Quantity Primary producer Produce its own energy to sustain itself by capturing energy from sun through photosynthesis. Considered as a submerged aquatic plant Primary producer Contain pale green coloured leaves, which contain pigment Chlorophyll that is essential for photosynthesis. 1 plant was planted on the top of sands and pebbles, as root was embedded into pebbles/ sands that act as supporting structure. Biomass: 13.63 gram Height from root to top or node: 57.4 cm 7.35 gram of duckweeds was scattered on the top layer (littoral zone) of freshwater ecosystems. Isidorella Planorbidae (Freshwater snail) Primary consumer: herbivore. Consume aquatic plants such as duckweeds, vallisneria and bluegreen algae. Obtain dissolved oxygen for respirations, metabolic and other physiological functions. CORIXIDAE (water boat man) Primary consumer: feed on bluegreen algae duckweeds and other aquatic plants. Single specie was added, usually habitat at littoral zone and benthic zone Dragonfly nymph (Fresh water macro invertebrate) Secondary consumer: considered as a carnivore. Consume other small aquatic insects such as water boat man and ostracods Single specie was added Detritivores: responsible for consumption of detritus and also consume aquatic plants such as duckweeds 2.69 gram of ostracods was added. Ratifers and daphnias (zooplankton) are heterotroph, consume algae and other aquatic plants ,phytoplankton and detritus . 2.65 gram was added Ostracods (Small microscopic invertebrate.) Mixed small organism such as daphnia, ratifers and euglena Euglena (Protista): are both heterotroph and autotroph. Euglena photosynthesise to obtain energy and it also consume detritus to obtain organics substances Such as nitrogen and phosphate Biomass: 2.65 gram. It was placed at bottom (benthic zone) of the ecosystem. Apparatus such as laboratory weighing scale was used to measured all biomass of all species, heights of plants was determined by the use of vernier caliper and detail physical structure of aquatic plants (Vallisneria and duckweeds ) was observed through the use of dissecting microscope . Light microscope, dissecting microscope and books on aquatic entomology and organisms, were used to identify the aquatic insects such as water boatman, dragon nymph fly and micro invertebrates like ostracods, daphnia, ratifers and euglena. Abiotic factors of an ecosystem including, pH, dissolved oxygen concentration salinity, and the water temperature was determined by pH meter, water temperature probe salinity sensor and dissolved oxygen sensor. Phosphate and nitrate concentration was tested, through the use API nitrate and phosphate test kit, written instruction in the package of kits, was used during the test. Biotic factors were monitored by observing physical characteristic of Vallisneria and duckweeds such as their leaves colour, their growths, reproduction and other physical activities of snail, waterboat man and dragonfly nymph were also examined. Both abiotic and biotic were inspected once a week over the 5 weeks period. Based on weekly inspection all the data’s and observation were recorded. Excel (computer software) was used to generate graphs and data's. Results Figure 1:pH differences within the experimental freshwater ecosytem over the five weeks study . 10 pHlevel 8 6 4 2 0 1 2 3 4 5 weeks Figure 1: Graph depicts the changes in the pH range of the water. Within the 2 week, there is an increment in the pH by a value of 1.3. There is a slight change in the pH over week 3 to 5. Average pH of an experimental freshwater ecosystem is 8.3. In a week 4, the pH was 8.9,which was the highest among other weeks. pH range from 6.5 to 8 is considered to be normal in fresh water ecosystem. (Lynda Radke, 2014) Though, the pH is slightly high than the normal range by the value of 0.3. oxygen per Mg/L Figure 2 :variation in dissolved oxygen concentration in a experimental freshwater ecosytem. 14 12 10 8 6 4 2 0 1 2 3 4 5 Weeks Figure 2:There is an increment and decrement of dissolved oxygen each week .in week 3, dissolved oxygen level increase by 2.33 mg/l however, in week 4 and 5, there is a reduction in oxygen level by 2.17 mg/L. the mean oxygen level is 10.94 mg /l. dissolved oxygen concentration of 10.94 mg/L is consider to be a normal for freshwater ecosystem. (Fondriest environmental, 2015) salinitylevel inμS/cm Figure 3: Difference in salinity in the experimental freshwater ecosytem over the five weeks study 350 300 250 200 150 100 50 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 weeks Figure 3: Each week, salinity level slightly different each week. In a week 2, salinity level suddenly increased by 98 μS/cm. during week 3, salinity reduced by 21 μS/cm. the average salinity concentration is 245.8 μS/cm. within week 4 to 5 there is little change. 245.8 μS/cm is an optimum salinity concentration for a freshwaters ecosystem (NSW environment, estuaryGuide, 2010) Figure 4:Nitrate level in the experimental freshwateecosystem over the five weeks 6 nitrate in ppm 5 4 3 2 1 0 0.5 1 1.5 2 2.5 3 weeks 3.5 4 4.5 5 5.5 Figure 4: During week 1, 3,4 and 5, there was no any presence of nitrate. But in week 2, a level of nitrate was 5 ppm. 5ppm falls within the normal range of nitrate concentration within the freshwater ecosystems. The presence of blue-green algae could be the main reasons, which caused the dramatic reduction in nitrate concentration of the ecosystem, from 5 to 0 ppm within week 3. figure 5:phopshate concentration in the experimental aquatic ecosystem over the five weeks phopshate conc ppm 0.6 0.4 0.2 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 weeks Figure 5: Each week, there is a slight change in the concentration of phosphate. 0.31 ppm is the average phosphate concentration of that experimental freshwater ecosystem. Less than 0.02mg/l is considered to be healthy within the freshwater ecosystems (Water Quality tests summary, 2007) .This suggested phosphate concentration of this experimental aquatic ecosystem is also in healthy range. Figure 7:variation in a water temperature within that experimental aquatic ecosytem over the five weeks 30 Temperatureindegreecelsius 25 20 15 10 5 0 0.5 1 1.5 2 2.5 3 3.5 4 4.5 5 5.5 weeks Figure 7: As the weeks pass, the water temperature of aquatic ecosystem increased. 23.8degree Celsius is an average temperature of an ecosystem, which is in a normal temperature range for the freshwater ecosystem. The temperature within the experimental ecosystem was directly affected by the location, as the bottle was located in the sunny area with an average temperature of 23.6-degree Celsius. It was also impacted by the weather, for example, in the hot and humid day (week 5), the temperature increased by 5-degree Celsius. Figure 8:change in biomass of biotics factor over five weeks 16 14 mass in grams 12 10 8 6 4 2 0 snail biomass duckweeds biomass vallsineria biomass blue column : week 1 red column : week 2 Figure 8: Snail biomass: over the five weeks period, snail biomass reduced by 0.78 gram. Duckweeds: increased its biomass by 1.48 gram. Vallisneria: there is a reduction in Vallisneria biomass by 6.37 gram Figure 9: height changes of vallisneria over five weeks 70 height in cm 60 50 40 30 20 10 0 1 5 weeks Figure 9: There is a reduction in height of Vallisneria plant by 8.3 cm. Discussion Analysis of this experiment results demonstrates variations in both biotic and abiotic factor within the experimental freshwater ecosystem. The pH of the water was quite alkaline, pH was above the normal range by the value of 0.3( Radke, 2015). Trace of calcium carbonate present in pebbles, rocks and sediments and presence of alkali metals such as sodium, potassium, and lithium in the river water may cause pH of the water to rise. During the second week, there was an appearance of blue-green algae in the water; algae also cause pH to increase. (Kemker et al, 2013) The photosynthetic plants such as duckweeds, green algae, Euglena and Vallisneria uses dissolved carbon oxide (produced by heterotrophs) as an essential material for photosynthesis. Dissolved carbon oxide makes water acidic by reducing pH, there could be inadequate amount of carbon oxide since there was less aquatic animals within that experimental ecosystem. Thus there is less concentration of certain amount of +¿¿ H ion in the water as +¿¿ H ion is needed to neutralise alkaline water environment, this could be the main reason, why the pH of water increase. (Craig S.Tucker et al 2008). Although, the freshwater organisms can survive within the pH range of 6.5 to 8.5. It is very likely that, slight increment in pH led to death of both dragonfly nymph and water boatman within week 4 weeks as pH above 8.5 during week 4. pH above 8.5 is lethal to freshwaters invertebrates. (Sharon Behar et al 1997) As the times pass, duckweeds and blue- green algae became greener and thicker, this indicate high photosynthesis rate among duckweeds and green algae species. As a result of higher photosynthesis, there is more energy available for cellular respirations, which allow effective growth and physiological function among those plants species and also caused biomass of duckweeds to elevate by 1.48 grams. Furthermore, through the photosynthesis process done by duckweeds and green algae, Each week oxygen concentration increased. Photosynthesis play significants role in food webs as it allow plants to produce energy enriched leaves, flower and fruits, which ultimately becomes great foods sources for aquatic animals and other small invertebrates like zooplanktons. This explained the reasons for why zooplanktons such as Ratifers, daphnias and Ostracods survived through out the five weeks. (cogdel et al 2013 ). Within the freshwater ecosystem, there was the excessive growth of duckweeds colony, which indicate there was sufficient amount of nutrient and normal pH in the ecosystem that supported this excessive growth of duckweeds colony. Despite having positive ecological positive impact, excessive amount of duckweeds limits survival rate of others submerged aquatic plants like vallisneria and animals, since duckweeds grows effectively at littoral zone of freshwater ecosystem and rapidly its increase its colony which means it can potentially block sunlight and obtain all important elements such phosphorus, nitrogen, carbon oxide and others ions. (Aboutduckweed, 2009) The Same issue raised within that experimental ecosystem, as Vallisneria leaves became yellowish over times, this is caused by the lacks of sunlight, carbon oxide and other essential nutrients such as phosphorus, nitrogen, oxygen and ions thus Vallisneria could not efficiently produces chlorophyll in leaves which limits its ability to photosynthesis at optimum levels hence less energy is produced which means less cellular respiration and metabolic rate which lead both biomass and height of Vallisneria to reduced . (Mason,2015 ) . Vallisneria inability to effectively photosynthesis has affected snail food chain. The freshwater snails mostly consume Vallisneria as their main food source. As snail lives in the benthic zone and Vallisneria is submerged aquatic plants that grows near benthic zone. Snail eats more submerged plants like Vallisneria than the floating plants like duckweeds, as submerged vegetation’s is more accessible from snails habitat. (Nordsieck and Neudorf 2015) Lacks of photosynthesis prevent Vallisneria to produces energy and nutrient enriched leaves and oxygen’s. This showed that snail did not receive sufficient amount of oxygen’s and nutrients from Vallisneria leaves. Nutrients and oxygen’s deficiency is main reasons which cause a reduction in the biomass of snail. Oxygen’s, food energy (carbohydrate) and other nutrients play a significant role in snail cellular respirations, other metabolic function, growth and reproduction. Increased water temperature significantly reduces the dissolved oxygen concentration in the water. During the week, 5 temperatures were high in comparison with other weeks. Thus, on that particular day the oxygen level was also low, in comparison to other weeks. This can be particularly harmful to aquatic animals. In the five-week period, Salinity and phosphate level was within the normal range. The presence of phosphate and nitrate in the ecosystem gives the indication of the decomposing process of dead leaves and dead water boatman and dragon fly nymph which is carried out by small invertebrate and microbes. Aquatic organisms such as Vallisneria, duckweeds, snails and invertebrates are capable of surviving within that range of phosphate and salinity. However, nitrate concentration was quite high during week 2, this could be the main reasons, there was an appearance of blue-algae during that week as a high level of nitrate lead to blue-green algae spores to bloom. In the week 3 nitrate level declined to 0 ppm from 5 ppm and stayed 0 ppm through the remaining weeks, this may occur, due to presence of blue-green algae as it uptake nitrate as part of nutrient, which also help to reduce excessive nitrates content of freshwater. The Certain amount of blue-green algae is beneficial for the freshwater ecosystem, as it reduce nitrate content. Excessive amount of nitrate is harmful to the freshwater animals, as it depletes dissolved oxygen. (W.R.ullrich et al, 2015 ) and (water quality test,2007 ) Through the outcomes of this freshwater ecosystem experiment we analysed our main aim .it gave some understanding on how abiotic factor affect survival rate and sustainability of biotic factor within freshwater ecosystem and how changes in food web affects animals. As, dragon fly nymph and water boatman died as a result of high pH of water .Due to lack of nutrients, Vallisneria leaves became yellowish thus low photosynthesis rate, which also limits snail from obtaining all those nutrients and energy from its food sources (Vallisneria) and which affect its growths as it led to decrement in snail biomass. However, this experiment did not quite approve our prosed hypotheses. As some organisms like duckweeds, Ratifers, daphnias and Ostracods were able to sustain themselves and other organisms such as vallisneria,snails and water boatman did not remain sustainable, as water boatman and dragonfly nymph died out. We can improve this experiment, by extending experiment duration for longer times period, by increasing physical size of experimental freshwater ecosystem (for e.g. use fish tank that has area of 0.50 m × 0.50m),by adding more freshwaters plants and animals species to increase its biodiversity, by constantly measuring abiotic factors (once a day instead of once a week) and by doing thorough observations of ecosystem through the use of higher quality apparatus such as well calibrated advance probes and other chemical sensors . This would allow, us to produce more reliable results and experiment would also perfectly represent real world freshwaters ecosystems. References The aquatic biome (2015). University of California. Accessed 23/9/15.Available at http://www.ucmp.berkeley.edu/exhibits/biomes/aquatic.php. Clout, M (2015). Ecology. Campbell Biology (Reece, J.B.Meyers, N.Urry, L.A .et al.) pp.1187-1267. Food Web. National geography. (1996-2015). Accessed: 23/9/15. Available at http://education.nationalgeographic.com/encyclopedia/food-web/ Radke, L. (2014). pH of waterways. OZ coasts. Accessed: 25/9/2015. Available at http://www.ozcoasts.gov.au/indicators/ph_coastal_waterways.jsp Fundamental of environmental measurement. (2015). Fondriest environment. Accessed:25/9/15. Available at http://www.fondriest.com/environmentalmeasurements/parameters/water-quality/ph/ Waterwatch Estuary Guide. Environment NSW. Accessed: 25/9/2015. Available at: http://www.environment.nsw.gov.au/resources/waterwatch/estuaryGuide/201 00685EstuaryGuide.pdf Water Quality tests summary.(2007).Accessed : 25/9/2015. Available at: http://www.sasta.asn.au/v2/adc/datalogging/DataSinglePagePDFs/ADCBookDa talog13-23.pdf MUDGEL, C.R and Haller, W.T,(2009). Effect of pH on Submersed Aquatic Plant Response to Flumioxazin. J. Aquat. Plant Manage. 48: 30-34. Available at http://www.apms.org/japm/vol48/vol48p30.pdf Tucker, C .S and D’Abramo1,L.R.(2008). Managing High pH in Freshwater Ponds. SRAC Publication No. 460. Available at http://www.extension.org/mediawiki/files/1/10/ManagingHighpHinFreshwate rPonds.pdf Cogdell, R. (2013). Photosynthesis. Molecular aspects; PLANT evolution; BOTANICAL chemistry. EFFECT of carbon dioxide on plants. NEW scientist.vol.217.issues 2902.pp 8-18. Nitrates and their effects on water quality.(2015). Wheatley river improvement group. Accessed on 26/10/15. Available at http://www.wheatleyriver.ca/current-projects/wrig-pilot-nitratestudy/nitrates-and-their-effect-on-water-quality-a-quick-study/ Ullrich, WR. Lazarová, J. Ullrich, CI . (1998). Nitrate uptake and extracellular alkalinization by the green alga in blue and red light. Journal of Experimental Botany. , Vol. 49 Issue 324, p1157. 6p. Nordsieck, R and Neudorf,R. (2015) freshwater snails . Living world of molluscs. Available at http://www.molluscs.at/gastropoda/index.html?/gastropoda/freshwater.html. About duckweeds. Lakelawn and pound.(2009). Accessed on 27/9/15. Available at https://www.lakelawnandpond.com/DuckweedAbout.aspx Vegetative Growth of Duckweeds.(2014). Accessed on 5/10/15. Available at http://www.mobot.org/jwcross/duckweed/duckweed-rapid_growth.htm Behar, S. Testing the water. Chemical and physical vital signs of a river. River watch network. Available at :http://www.fosc.org/WQData/WQParameters.htm Mason, S. yellow leaves can indicate plant problems. University of Illinois Extension. Accessed on 5/6/15. Available at https://web.extension.illinois.edu/cfiv/homeowners/070828.html Freshwater invertebrate. Biodiversity snapshot. Museum victoria. Accessed on 3/10/15. Available at http://www.biodiversitysnapshots.net.au/bdrscore/public/speciesInfo.htm?spid=683 Dragonfly Nymph. University of Sydney. Accessed on 4/10/15. Available at http://bugs.bio.usyd.edu.au/learning/resources/Entomology/internalAnatomy/ imagePages/dragonflyNymph.html

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Online exhibits : The world's biomes

The freshwater biome


A lake at Acadia National Park, Maine.
 

Freshwater is defined as having a low salt concentration — usually less than 1%. Plants and animals in freshwater regions are adjusted to the low salt content and would not be able to survive in areas of high salt concentration (i.e., ocean). There are different types of freshwater regions:

Ponds and lakes
These regions range in size from just a few square meters to thousands of square kilometers. Scattered throughout the earth, several are remnants from the Pleistocene glaciation. Many ponds are seasonal, lasting just a couple of months (such as sessile pools) while lakes may exist for hundreds of years or more. Ponds and lakes may have limited species diversity since they are often isolated from one another and from other water sources like rivers and oceans. Lakes and ponds are divided into three different “zones” which are usually determined by depth and distance from the shoreline.

The topmost zone near the shore of a lake or pond is the littoral zone. This zone is the warmest since it is shallow and can absorb more of the Sun's heat. It sustains a fairly diverse community, which can include several species of algae (like diatoms), rooted and floating aquatic plants, grazing snails, clams, insects, crustaceans, fishes, and amphibians. In the case of the insects, such as dragonflies and midges, only the egg and larvae stages are found in this zone. The vegetation and animals living in the littoral zone are food for other creatures such as turtles, snakes, and ducks.


From left: a view across Manzanita Lake toward Mt. Lassen, California; a forest pond near Donnelly, Idaho; a Great Blue Heron; Paranagat Lake, southeastern Nevada.

The near-surface open water surrounded by the littoral zone is the limnetic zone. The limnetic zone is well-lighted (like the littoral zone) and is dominated by plankton, both phytoplankton and zooplankton. Plankton are small organisms that play a crucial role in the food chain. Without aquatic plankton, there would be few living organisms in the world, and certainly no humans. A variety of freshwater fish also occupy this zone.

Plankton have short life spans — when they die, they fall into the deep-water part of the lake/pond, the profundal zone. This zone is much colder and denser than the other two. Little light penetrates all the way through the limnetic zone into the profundal zone. The fauna are heterotrophs, meaning that they eat dead organisms and use oxygen for cellular respiration.

Temperature varies in ponds and lakes seasonally. During the summer, the temperature can range from 4° C near the bottom to 22° C at the top. During the winter, the temperature at the bottom can be 4° C while the top is 0° C (ice). In between the two layers, there is a narrow zone called the thermocline where the temperature of the water changes rapidly. During the spring and fall seasons, there is a mixing of the top and bottom layers, usually due to winds, which results in a uniform water temperature of around 4° C. This mixing also circulates oxygen throughout the lake. Of course there are many lakes and ponds that do not freeze during the winter, thus the top layer would be a little warmer.

Streams and rivers
These are bodies of flowing water moving in one direction. Streams and rivers can be found everywhere — they get their starts at headwaters, which may be springs, snowmelt or even lakes, and then travel all the way to their mouths, usually another water channel or the ocean. The characteristics of a river or stream change during the journey from the source to the mouth. The temperature is cooler at the source than it is at the mouth. The water is also clearer, has higher oxygen levels, and freshwater fish such as trout and heterotrophs can be found there. Towards the middle part of the stream/river, the width increases, as does species diversity — numerous aquatic green plants and algae can be found. Toward the mouth of the river/stream, the water becomes murky from all the sediments that it has picked up upstream, decreasing the amount of light that can penetrate through the water. Since there is less light, there is less diversity of flora, and because of the lower oxygen levels, fish that require less oxygen, such as catfish and carp, can be found.


From left: McArthur-Burney Falls State Park, California; trout; Green River, Utah; Brooks River, Alaska.

Wetlands
Wetlands are areas of standing water that support aquatic plants. Marshes, swamps, and bogs are all considered wetlands. Plant species adapted to the very moist and humid conditions are called hydrophytes. These include pond lilies, cattails, sedges, tamarack, and black spruce. Marsh flora also include such species as cypress and gum. Wetlands have the highest species diversity of all ecosystems. Many species of amphibians, reptiles, birds (such as ducks and waders), and furbearers can be found in the wetlands. Wetlands are not considered freshwater ecosystems as there are some, such as salt marshes, that have high salt concentrations — these support different species of animals, such as shrimp, shellfish, and various grasses.


From left: Pescadero Marsh, California; coastal marsh at Umpqua Dunes, Oregon; trees and bogs on Esther Island, Alaska.

Visit our gallery of wetlands images, which illustrate the amazing diversity of wetland ecosystems.
 

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