1 Chapter 6 – Aquatic Environments - Objectives Be able to describe the four types of aquatic habitats for microbesBe able to describe the microbial loopUnderstand why activity in the benthos is high and have a basic understanding of the biogeochemical cycling of carbon and nitrogen in the benthos.Be able to describe the makeup of a microbial mat including examples of microorganisms found in a mat.Understand how biofilms develop and the reasons why microbes form biofilmsBe able to define the different regions of a water body: neuston, limnetic, littoral, and profundal zonesBe able to define the thermocline, epilimnion, and hypolimnionUnderstand the ranges of numbers of microbes in oligotrophic and eutrophic water bodiesUnderstand the driving force behind the vertical stratification of primary producers in the water columnUnderstand how microbes adapt to extreme temperaturesBe able to describe geothermal vents and their associated community
2 Aquatic environmentsCover 70% of the earth’s surfaceImportant zone of primary productionProvides potable waterProvides water for agriculture and industryProvides unique and extreme habitatsIncludes:Freshwater (rivers, lakes, streams, aquifersMarine (oceans, estuaries)
3 Habitats Planktonic – microbes suspended in the water column Benthic MatsBiofilmsGrazing food chain:Primary producers zooplankton filter feeders/fishIn coastal zones it take 1.5 to 3.5 steps to produce fish because plants are responsible for some primary productionIn the open ocean it takes approximately 5 steps to produce exploitable fish.
4 1. Planktonic – Microbes suspended in the water column Phytoplankton are photosynthetic microbes (primarily cyanobacteria and algae).Responsible for most of the primary production in aquatic environments.Major food supply in aquatic environments.Support a complex food web.primary production50% of fixed carbon is released as DOMMicrobial Loopsecondary production
5 2. Benthic habitatThe benthos is a transition zone between the water column and the mineral subsurface.This interface is a diffuse and noncompacted mix of organic matter that has settled from the surface/mineral particles/water.Microbial numbers are up to 5 orders of magnitude higher than in the planktonic environment.Since activity is high, oxygen is utilized quickly and as a result, biogeochemical gradients develop that control the types of microbes and microbial activities found in this region.
9 The width of the mat ranges from several mm to cm A microbial mat3. MatsSand layerMicrobial mats are also an interface in the aquatic environment in which many microbial groups are laterally compressed into a thin mat.The width of the mat ranges from several mm to cmMats are vertically stratified with an aerobic zone on the top which is separated from the bottom anaerobic zone by a layer of oxidized iron.CyanobacteriaOxidized ironPurple sulfur bacteriaPrecipitated iron sulfide
10 Mats form in extreme environments. Stromatolites are fossilized mats that are 3.5 billion years old and are among the first indications of life on earth.Stromatolites were thought to be extinct but were discovered 40 years ago in Shark Bay, Australia in a hypersaline area. The hypersalinity prevents marine animals from thriving and grazing on the mat material.
11 4. BiofilmsBiofilms are a layer of organic matter with attached microbes.Biofilms form on submerged rock surfaces, plants, skin, ship hulls, pipes, teeth, catheters and implants, and basically any submerged surface.Biofilms can be beneficial (wastewater treatment, skin barrier) and can be harmful (pipeline corrosion, medical implants, tartar).Benefits (to the microbe) of biofilm growth: Microbes growing in a biofilm are more resistant to: antibiotics, predation, dessication, changes in environmental factors (pH, temperature). They also have better access to solution nutrients because the solution is constantly flowing over the biofilm.
12 Biofilm development proceeds in three phases: the surface is modified by attachment of organic molecules2) reversible attachment of microbes to the organic layer and colonization3) irreversible attachment and biofilm formation. In a mature biofilm, the cells are organized into columns surrounded by large void spaces that form channels to carry nutrients (O2) deep into the biofilm
13 Aquatic environments Freshwater Lentic (standing) vs. lotic (running) SpringsLakesoligotrophic – deep, low biomasseutrophic – shallow, high biomassGroundwaterMarineEstuariesOceans
14 Freshwater - A typical lake has several regions of interest. Neuston layer
15 The neuston layer occurs at the air-water interface. Nutrients and microbes aggregate at the neuston.
16 The limnetic zone which is the surface layer of open water where light can penetrate
17 The thermocline is a zone defined by a rapid change in temperature The thermocline is a zone defined by a rapid change in temperature. The zone above the thermocline is the epilimnion and the zone below is the hypolimnion. The thermocline prevents mixing of lake water through much of the year. Mixing can only occur in the fall and spring as the water either cools (fall) or warms (spring) so that the thermocline disappears.Epilimnion > 4oCSummerHypolimnion < 4oCO2 mg/lWater surfaceDepth (m)Epilimnion 0 – 4oC-4ThermoclineWinter-8Temperature-12Hypolimnion > 4oCSediment zone-16Temp oC
18 Estuaries are transition areas between freshwater and ocean environments. Salinities range from 1 to 3.2%. Estuaries harbor unique ecosystems such as the mangrove swamps and are subject to high levels of pollution from freshwaters carrying surface runoff that enter the estuary. Estuaries also serve as environments that can be used to treat polluted waters before they reach the open ocean.Oceans have a salinity of 3.5% compared to a salinity of 0.05% in freshwater environments. Oceans can reach depths of 11,000 m and are generally divided into two zones, the photic zone (where light penetrates) which ranges from 1 to 200 meters, and the aphotic zone.Marine water
19 Microbes in the aquatic environment Numbers vary so much with different water bodies that it is difficult to provide generalities. However, there are ranges and patterns of microbes in an oligotrophic and a eutrophic lake environment.Planktonic numbers are up to 5 orders of magnitude lower than benthic numbers.Heterotrophic numbers increase dramatically at the neuston, the thermocline, and the benthos.Primary producers arrange themselves in zones according to the wavelength of light that their chlorophyll-like molecules absorb and according to availability of H2S.