Chapter 6 – Aquatic Environments - Objectives Be able to describe the four types of aquatic habitats for microbes Be able to describe the microbial loop Understand 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 biofilms Be able to define the different regions of a water body: neuston, limnetic, littoral, and profundal zones Be able to define the thermocline, epilimnion, and hypolimnion Understand the ranges of numbers of microbes in oligotrophic and eutrophic water bodies Understand the driving force behind the vertical stratification of primary producers in the water column Understand how microbes adapt to extreme temperatures Be able to describe geothermal vents and their associated community

Aquatic environments Cover 70% of the earth’s surface Important zone of primary production Provides potable water Provides water for agriculture and industry Provides unique and extreme habitats Includes: Freshwater (rivers, lakes, streams, aquifers Marine (oceans, estuaries)

Habitats Planktonic – microbes suspended in the water column Benthic Mats Biofilms Grazing food chain: Primary producers zooplankton filter feeders/fish In coastal zones it take 1.5 to 3.5 steps to produce fish because plants are responsible for some primary production In the open ocean it takes approximately 5 steps to produce exploitable fish.

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 production 50% of fixed carbon is released as DOM Microbial Loop secondary production

2. Benthic habitat The 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.

Carbon CO O Aerobic respiration Surface (mineralization) CH oxidation Anaerobic respiration CH oxidation 4 CH CO 2 Fermentation and methanogenesis O Inner (core region) Surface C a r b o n

Nitrogen

The width of the mat ranges from several mm to cm A microbial mat 3. Mats Sand layer Microbial 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 cm Mats are vertically stratified with an aerobic zone on the top which is separated from the bottom anaerobic zone by a layer of oxidized iron. Cyanobacteria Oxidized iron Purple sulfur bacteria Precipitated iron sulfide

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.

4. Biofilms Biofilms 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.

Biofilm development proceeds in three phases: the surface is modified by attachment of organic molecules 2) reversible attachment of microbes to the organic layer and colonization 3) 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

Aquatic environments Freshwater Lentic (standing) vs. lotic (running) Springs Lakes oligotrophic – deep, low biomass eutrophic – shallow, high biomass Groundwater Marine Estuaries Oceans

Freshwater - A typical lake has several regions of interest. Neuston layer

The neuston layer occurs at the air-water interface. Nutrients and microbes aggregate at the neuston.

The limnetic zone which is the surface layer of open water where light can penetrate

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 > 4oC Summer Hypolimnion < 4oC 0 2 4 6 8 10 O2 mg/l Water surface Depth (m) Epilimnion 0 – 4oC -4 Thermocline Winter -8 Temperature -12 Hypolimnion > 4oC Sediment zone -16 0 5 10 15 20 25 Temp oC

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

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.

Eutrophic Lake Oligotrophic Lake

Stratification of primary producers