Nutrient Cycle in Aquaculture System

SA3323

DR HELENA KHATOONSchool of Fisheries & Aquaculture

Sciences

Universiti Malaysia Terengganu

What is nutrient cycle?

• Nutrient cycle (or ecological recycling) - movement &exchange of organic & inorganic matter back intoproduction of living matter

the

• Process is regulated by food web pathways thatdecompose matter into mineral nutrients

• Occur within ecosystems

• Begins with incorporation of substances into bodiesliving organisms from non-living reservoirs

of

What is nutrient cycle?

• Materials pass from organisms that first acquireinto bodies of organisms that eat them

them

• Until they complete cycle & return to non-living world,through decomposition

• Refers to biodiversity within community food websystems that loop organic nutrients or water suppliesback into production

Biogeochemical cycles

• continually through both biotic & abiotic componentsof ecosystems

• cyclic pathways involving biological, geological &chemical processes

• driven directly or indirectly by incoming solar radiationand gravity connect past, present, future forms of life

3 main categories of biogeochemical cycles

• Hydrologic

• hydrologic (water) cycle

Gaseous - involves exchanges& oceans

• among atmosphere, biosphere, soils

•

•

•

Carbon Cycle

Oxygen Cycle

Nitrogen Cycle

• Sedimentary - involvesback

• Phosphorous cycle

• Sulfur cycle

materials that move from land to oceans and

Carbon Cycling in Aquatic EcosystemsCarbon is an element that is the basis of all forms of life on Earth

•

• It moves through atmosphere, lithosphere, biospherehydrosphere

&

• Carbon cycle regulates Earth's global temperature &controls amount of carbon dioxide in atmosphere

• As carbon recycles, it is reused by numerousorganisms

Carbon Cycling in Aquatic Ecosystems

• Aquatic ecosystems are those that contain plants &animals dependent on water

• If toocool

much CO2 is removed from atmosphere, it will

• If tooit will

much CO2 is added (or remains in) atmosphere, warm

4 main reservoirs

• Lithosphere

• Biosphere

• Hydrosphere

• Atmosphere -

LithosphereLargest reservoir for earth’ carbon - rocks such as limestone(CaCO3) deposited as sediment on ocean floor & on continents

Enters

• death, burial, compaction over geologic time

• becoming sediment, marine sediments, sedimentary rock, fossil fuels

Leaves - very slowly

• weathering, uplifting over geologic time, volcanic activity

• exception: combustion of fossil fuels

•

•

•

Biosphere

• Biosphere is part of thesupports life of animals

Enters

• Photosynthesis

• consumption

Leaves

• cellular respiration

• death

earth & its atmosphere which& other living organisms

•

•

HydrosphereOceans - second largest reservoir of earth’s carbon which play role in regulating amount ofCO2 in atmosphere

CO2 is readily soluble in water - some stays dissolved in sea water, some removed by

•

•marine photosynthesizing producers & some reacts with sea water to form carbonate ions(CO32-) & bicarbonate

Enters

ions (HCO3-)

•

•

•

•

•

•

Weathering

Leaching

runoff

diffusion

cellular respiration• Leaves

•

•

•

Photosynthesis

Diffusion

incorporation into sediments

Atmosphere•

•

The gaseous envelope surrounding

Enters

the earth

•

•

•

•

•

cellular respiration

combustion of wood

combustion of fossil fuels

volcanic action

diffusion from ocean

• Leaves

• photosynthesis

• diffusion from the ocean

Flow of carbon in form of carbon• dioxide from atmosphere to biosphere(photosynthesis) and back to atmosphere (respiration)balance

- is approximately in

Carbon cycle

Types of ecosystem• Marine - largest ecosystems on Earth

• Most important subdivisions of marine ecosystems -oceanic, deep-water, estuarine, coral reefs, inter-tidalcoastal ecosystems

Living organisms range from bacteria, algae, corals, bivalves, fish & mammals

&

•

• Freshwater

• Major subdivisions - lakes & ponds, rivers & streams,reservoirs, wetlands & groundwater

• Living organisms include algae, fish, amphibians & plants

Carbon Source

• Main source of the Earth's carbon is carbon dioxidegas from submarine volcanic eruptions

• Some of this carbon dioxide dissolves in ocean

• Another part escapes into atmosphere throughevaporation of ocean

• A further part is absorbed by marine biomass suchas plankton, algae & bacteria

Photosynthesis

Plants & algae in freshwater & phytoplankton (marine organisms & algae) use sun's energy photosynthesis

•for

• They convert carbon dioxide & water they haveabsorbed into sugars & oxygen

• They store sugars as energy & release oxygen backinto water

Fish

Freshwater algae & marine phytoplanktonfish

• are food for

• Fish inhale dissolved oxygen from water withexhale carbon dioxide back into water

their gills &

• They store carbohydrates they have eaten as energy &excrete inorganic calcium carbonate & bicarbonate

• These compounds are carried by currents to deep oceanwhere they precipitate

Decomposition

• Dead organisms decompose on the river, lake orsea bottom and emit carbon dioxide

• The gas recycles into the freshwaterwhere other organisms absorb them evaporates into the atmosphere

and sea wateror the gas

Precipitation

• Rainfall dissolves carbon dioxide in the atmospherereturns it as a mild acid to ground & water systems

&

• On the ground, rain water exposed carbonate rockssuch as limestone

• Limestone remains of inorganic carbonates thatprecipitated as excreta from fish & the skeletons of dead fish, corals or other marine life

Run-Off

• Rainwater accumulates beneath the soil asgroundwater & runs off via rivers & lakes into seas

• Its carbon dioxide content is absorbed byfreshwater & marine organisms for photosynthesis& aquatic carbon cycle resumes

Carbon cycle in freshwater & marine

Nitrogen & Phosphorus Cycle

• N & P - essential nutrients for plant growth

• Accelerated input of these two nutrients intoaquatic ecosystems due to human activities, is the primary cause of most algal bloom problems

• Nutrient cycle - the ways in which these elementsare transported & transformed within theenvironment, is therefore essential tounderstanding & effectively managing algal blooms

• N & P cycles are fundamentally different to eachother

• N cyclingis mostly

- most common element in atmospheremediated by living organisms

-

• P cycling - is primarily a chemically mediatedprocess that originates with the weathering of rocks

Nitrogen cycle• Nitrates are produced & used in aquatic ecosystems through a

process called nitrogen cycle

• Plant & animal by products first break down to produce ammonia

• Bacteria within the water oxidize that ammonia to produce nitrites, and then other bacteria colonies oxidize the nitrites to produce nitrates

• Nitrates are then used as a fertilizer for blue-green algae & aquatic plants, which enables plants & blue green algae colonies to grow & perform photosynthesis

• Plants become food for aquatic animals, which produce ammonia-rich waste, & nitrogen cycle begins again

Major nitrogen & categories

Plant & animal by products produceammonia

Protein in dead organic matter, such as in dead aquatic plantsbreaks down into ammonia as organic matter decays

•

• Waste from living aquatic animals, as well as the waste ofterrestrial animals that streams into waterways, also containsammonia

• Ammonia is toxic to all aquatic animal life

• Meanwhile, as the proteins and waste break down into ammonia,the living plants within the aquatic ecosystem release oxygen intothe water as a by product of their photosynthesis

Bacteria oxidize ammonia to producenitrites

Nitrosomonas bacteria within the water bind ammonia in water with oxygen released by plants & oxygen that is mixed into water from air through movement at water's surface

•

• Oxidized ammonia that the nitrosomonas produce is called nitrite,also called NO2

• Like ammonia, NO2 also toxic to aquatic animal life

• Nitrosomonas bacteria oxidize ammonia in order to gain energythrough oxidation, which they use to fuel their metabolic

Bacteria colonies oxidize nitrite toproduce nitrates

• Colonies of aquatic nitrospira bacteria then bind anotheroxygen to the nitrite, to produce nitrate (NO3)

& ammonia, nitrate is also toxic tois relatively neutral when compared

• Though, like nitratesaquatic animal life, itthose chemicals

to

• It is also in the form of nitrogen that can be directly absorbedby plants & cyanobacteria

Blue-green algae & plants metabolize nitrates toproduce amino acids

• Cyanobacteria (blue-green algae) arephotosynthesis

aquatic bacteria that performs

• Though individual cyanobacteria are single-celled organisms, theygrow in colonies that can become so large they're visible to the naked eye

• A cyanobacterium also makes up the plant cell's chloroplast, whichis what allows the plant to perform photosynthesis

• Dead plant matter left over from feeding also releases ammonia intoaquatic ecosystem, fueling nitrogen cycle

Blue-green algae & plants metabolize nitrates toproduce amino acids

• Amino acids make up proteinbuilding block of life

molecules, & protein is an essential

• Nitrate acts as a fertilizer for the aquatic plants

• Plants then become foodammonia-rich waste

for aquatic animals, which produce

• Dead plant matter left over from feeding also releases ammonia intoaquatic ecosystem, fueling nitrogen cycle

Process of nitrogen cycle

• Assimilation – conversionNH4+) by phytoplankton &organic N

of inorganic N (mostly NO3 or other aquatic plants, into

• Ammonification – NH4+ (re)generation, resulting from decomposition of dead organisms & breakdown of animal wastes

• Nitrification – oxidation of NH4+ to NO2- & further oxidation of NO2- to NO3- by aerobic bacteria, which obtain energy through nitrification process

Process of nitrogen cycle

• Recycling – refers to repeated movement of N through differentorganisms within an estuary via assimilation, ammonification &nitrification

• Sedimentation/resuspension – organic N from dead organismsfalls to the ecosystems floor & is incorporated into sediments;disturbance of sediments can return it to water

• Sediment flux – release of NH4+ from the sediments into overlyingwater

Nitrogen cycle

Nitrogen cycle

Phosphorus cycle

• Phosphorus is found in soils, rock minerals,organisms & water

living

• but unlike nitrogen it is not present in atmospherefound by itself in nature

nor

• Pure phosphorus is highly reactive & rapidlycombines with oxygen when exposed to air

• In natural systems it usually exists as phosphate

Forms of phosphorus in water• Orthophosphate is the major form of biologically available

phosphorus found in water. It is usually present as acombination of HPO4 2- and H2PO4- depending on pH

• Sum of all forms of phosphorus in water is known as Total

Phosphorus (TP)

Process of phosphorus cycle• Adsorption – is process where PO4 binds to the surface of solid particles

Desorption – is reverse process where adsorbed PO4 is released into water

•

• Assimilation – uptake of PO4 & conversion to organic phosphorus, by phytoplankton & other organisms

• Mineralisation – release of PO4 from organic compounds by microbialbreakdown

• Sedimentation/resuspension – organic & particulate phosphorus falls toestuary floor & is buried in sediments; disturbance of sediments can return itto water

• Sediment flux – release of PO4 from sediments into overlying water

Phosphorus cycle

http://arnica.csustan.edu/carosella/Biol4050W03/figures/phosphorus_cycle.htm

Conclusion

Nitrogen & phosphorus contribute to problemin our coastal waterways

• of eutrophication

• These nutrients are present in several forms

• It is important to consider not just total nutrient conc. butof different forms of nutrient

conc.

• Dissolved inorganic nutrient conc. determine what plantscan access at any time

& algae

• But total conc. tell us a lot more about what may becomeavailable over time

• There are important differences between nitrogen &phosphorus cycles

• Nitrogen is found in several different bioavailable forms,can be lost to atmosphere though denitrification

&

• Phosphorus cycle is dominated by one main bioavailableform (PO4) but is complicated by its reversible movementthrough both living organisms (assimilation-mineralisation)& particulate phases (adsorption-desorption)

• Phosphorus does not exist as a gas & can only be physicallyremoved by being flushed from estuary or through permanent accumulation in sediments

• Both N & P can be released from sediments under anoxicconditions

• A coupled reduction in input of these two nutrients is onlyviable long-term approach to confronting problem ofeutrophication

• But direct intervention techniques provide additional optionsin the short term