Practical Aquatic Ecology and Water Quality

Two characteristics of food webs

1) flow of energy (carbon is considered the currency) 2) circulation of materials (flux of energy or carbon is production)

Aquatic Ecological Research Methodology

1. Collection and recording of field data 2. correlation of gathered field data 3. mathematical modeling 4. controlled experiments

Oxygen

Above the compensation point there is lots of oxygen from photosynthesis, but below respiration dominates and there is low oxygen. In spring during circulation O2 is 100%. Supersaturation can occur when there is lots of productivity. In summer oligotrophic lakes there is *more O2 below (solubility increases with decreased temp and no one is respiring there)*, while in eutrophic lakes there is less the deeper you go. Fall/spring turnover is when the entire water becomes well mixed again

Flock and Lock

A flocculent causes flocculation of particles and a fixative ties up the P inorganically these two treatments together result in clear water (clearing of water). Combined flocculent and "lock" (ballast) is needed to precipitate all P (flocculant makes it clump and ballast sinks it down) and a fixative (lanthanum mondified clay which creates an insoluble mineral with phosphate) can lock up the sediment P for good. Makes it unavailable to biota.

Causes of extinction

Absorption is influenced by water, dissolved organic compounds (humic compounds) and particulate compounds. Absorbed light is transferred into low energy radiation (infared=heat). Suspended particles cause scattering and the degree to which something is scattered is expressed as turbidity. Direct radiation is mainly red and indirect is mainly blue (reflected off stuff). Red light is strongly absorbed by water, algae absorbs blue and red light, and humic acids absorb violet and ultraviolet light... therefore blue/green light penetrates the deepest. Light intensity and spectral composition vary with depth. Scattering causes light to have a longer path in water, making it more likely to be absorbed. Blue light is more strongly scattered therefore water looks blue from far away.

CO2 and CH4 gas fluxes linked with oxygen

CO2 and O2 dynamics are closely interlinked due to photosynthesis and respiration. In photosynthesis the release of 1 mole of O2 coincided with uptake of 1 mole of CO2. The O2:CO2 ratio "photosynthetic quotient" is not constant and depends on the species and environmental conditions. Different cellular compounds have different photosynthetic quotients as they each are composed of a different ratio of C-H-O. The inorganic nitrogen source also influences the quotient. The ratio between CO2 produced and O2 consumed depends on the compounds being respired. Phytoplankton can also use HCO3- w more energy. Therefore depending on the buffering capacity of the water photosynthesis may influence the pH. Depending on the pH the prevailing form of dissolved inorganic carbon might be carbon dioxide, bicarbonate, or carbonate. At low pH when only CO2 is present photosynthesis and respiration will have no effect on pH. At high pH, common ones, photosynthesis and respiration require the uptake and release of protons (6HCO3- + 6H+ instead of CO2 and H2O)

Physical Environment

Conditions: physiochemical features of the environment that are not consumed or used up by the activities of organisms, but affect survival, growth and/or reproduction Resources: Nutrients, water, substrate, energy etc. which may be consumed or used up by the activities of organisms and also affect survival, growth and/or reproduction sometimes environmental factors are always conditions (pH, temp, pressure etc), others can be conditions or resources depending on the organism (light)

Gross production

Change in biomass including all losses divided by the time interval. Losses are non-predatory: respiration, excretion, injury, death

hypertrophic

More than even eutrophic

Sediment Oxygen Demand

Degradation of OM in the sediment. Suspended organic substances can settle at the bottom of a water body as dead plant parts, feces, leaves, while bacteria are attached to fixed surfaces. Microbial oxidation in sediment uses oxygen from the water phase. Only a thin layer of the sediment is aerobic, under it anaerobic reduction takes place resulting in production of H2S, CH4, Fe2+ and Mn2+. Under anaerobic conditions FePO4 is more soluble and phosphate will be released. Therefore when oxygen is very depleted (in stratified summer lake bottoms) phosphorous will be released from the sediment due to anaerobic respiration of Fe.

Photosynthesis

Different coloured algae represents chlorophyll with differing ability to absorb different wavelengths of light (colours). Pigments absorb energy. When a photon is absorbed it should possess a critical energy to excite a pigment molecule. Infrared is not energetic enough and ultraviolet is too energetic damaging chlorophyll. WHen it is absorbed a low energy electron is transferred to energy-rich state. Light harvesting antennae. Pigment protein complexes are located in specialized membrane called lamellae. These complexes are usually in chloroplasts but are dispersed in protoplasm in cyanbacteria. They are flattened sacks stacked like coins. The lamellae looks like a pair of membranes separating a narrow internal space (lumen) from the external stroma, which contains oxygen generating systems while the stroma contains CO2 fixing systems. The amount of light harvested by algal cells depends not only on the total amount of photosynthetic pigments but also on the size and shape of the algal cells or colonies. thin cylindrical filaments are more efficient per unit volume. Rate of photosynthesis depends on the rate by which proteons are absorbed, which depends on the pigment composition and irradiance intensity. Environmental conditions include quantity and quality of the light, temperature, concentrations of O2 Co2 and nutrients. Low light lowers rate, which increases proportional to increased light intensities reaching a plateau and decline. Three factors determine the shape of the photosynthesis irradiance curve: -dark respiration determines the y intercept -the initial slope (alpha) efficiency of photosynthesis -Pmax the light saturated growth rate primarily limited by carbon -x intercept is compensation point

Shallow lake organic carbon

Distributed evenly over the water column.

hypolimnion

During the summer months in a deep lake where stratification can occur. The cold water deep portion of the lake that has net respiration (more respiration than photosynthesis). There is more CO2 efflux than in the epilimnion.

Photosystem I

Electrons are carried to reduce NADP+ to NADH

Aquatic plants

Emergent macrophytes (upper infralittoral), floating-leafed macrophytes (middle infralittoral), submerged macrophytes (lower infralittoral, availability of light is important, grow 2-3mxsecchi depth), free-floating macrophytes.

Lotic

Flowing systems like rivers and streams

Organic Carbon

From autochtonous production and allochtonous input (from terrestrial plants). Dissolved organic carbon is smaller than particulate organic carbon. Dead OM is nonhumic substances (amino acids, carbohydrates, fats, protein, waxes), humic substances (most of OM, resistant to further degradation)

Temperature in Lakes

IN early spring the temperature at all depths is the same, causing wind to completely mix the water column. Later increased irradiance heats up the upper water layers with a lower density which does not mix with the deeper high density. It is stratified with 3 regions: 1) epilimnion upper stratum 2) metalimnion water stratum with a steep thermal gradient 3) hypolimnion lowest stratum of cold undisturbed water In fall the surface water cools and sinks and the stratification is lost. The water becomes well mixed by wind again. Water is at max density at 4C so cold water and ice can float on top.

Benthic organisms

Immature insects etc, abundant, diverse. Heterogenous due to environmental variables influencing organism's requirements. Food, substratum availability, and oxygen content are key factors. Some can survive in anoxic waters. Others might migrate daily into anoxic hypolimnion, during the day they are there to avoid fish predation and during the night they migrate upwards where they feed on zooplankton.

Oxygen Saturation

In clear water the oxygen concentration will be near or at saturation (flux in=flux out), but it can change due to the load of degradable organic compounds (stimulates decomposition processes which causes the purification processes of water to be over capacity), and oxygen production and consumption by excessive primary production (eutrophication). During the day oxygen is produced and in the night levels drop rapidly due to respiration/decomposition

Orthograde Curve

In oligotrophic lakes the relationship of oxygen over depth is called this because there is virtually no consumption of oxygen in the hypolimnion and oxygen concentrations are therefore higher in the hypolimnion bc the water is colder so it holds more oxygen

Inorganic Carbon

Increase in CO2 in atmosphere may affect the inorganic carbon concentration in fresh water and if nutrients are not limiting increase productivity. Whether air CO2 effects water CO2 is dependent on the rate of air-water exchange, and diffusion of gases is slow so water movement mainly determines the flux between air and water. (More movement= greater flux) Under most conditions CO2 is converted to carbonic acid (H2CO2) when it combines with water, which can donate protons (acid), and is a weak acid so it can dissociate into bicarbonate (HCO3-) depending on pH. this chemical dissociation is the carbon equilibrium [CO2+H2O<->H2CO3<-> H+ + HCO3- <-> 2H+ + CO3(2-)] while water is also in equilibrium [H2O<-> H+ + OH-] H2CO3 dominates at pH <6, at pH between 6 and 10 HCO3- dominates, and at pH>10 CO3(2-) dominates. (bc more H is available to combine with CO2 at low pH) Many aquatic plants have the ability to assimilate bicarbonate (needing carbonic anhydrase enzyme to do so). Dehydration of HCO3- to CO2 is coupled by the release of OH- from the cells. Uptake of CO2 and release of OH- increase with increasing pH (the more basic the more bicarbonate will dominate and the more basic the water will becomes from this reaction). Bicarbonate rich water will have considerable buffering preventing change in pH.

Net production

Increase in organic matter (accepting that there have been losses but not adjusting for this) divided by the timer interval

Mass transfer velocity

Increase it and compress the amplitude, decrease it and increase the amplitude

Lentic

Isolated bodies of water (pond, lake) no flow in or out

Lake Rauwbraken

Isolated man-made sand excavation, with an official bathing site. Two parts: deep area called buffer and shallow leisure pool, separated by a dike. When groundwater level drops water in shallow pool is replenished by pumping from the deeper pool. The pump is turned off in september and the shallow area dries out. The system is isolated apart from a drainage ditch along the railway that prevents the dike from flooding, but may also due to precipitation cause the sewer system to overflow into the drainage ditch. Fish are dominated by perch. Has experience blooms causing high turbidity, anoxia, fish kills, bad smell, and serious environmental and human health problems. Nutrients enter through groundwater enriched from agriculture, bank erosion, leaf litter and macrophyte decomposition. The lake is a sink so impaired conditions can be maintained.

In a shallow pond SOD and reaeration will be

Larger in effect. More mixing and more surface area per volume in contact with air (reaeration) and more respiration in the sediment due to more light and more oxygen.

Photosynthesis vs. Irradience

Light limitation occurs at low irradiance levels where photosynthesis rates are low because there is not enough light. Saturation is the point at which higher irradiance neither increases or decreases photosynthetic rate. Light inhibition occurs when irradiance is so high that light is damaging chlorophyll and photosynthetic rate decreases again.

Sediments and Internal Loading

Lots of P accumulates in the sediment, therefore there is internal loading of nutrients that can't be helped by preventing further inputs. Deep lakes have net sedimentation and therefore will become shallower over time. Depending on morphological conditions sediment can be resuspended, when shear stress at the bottom is high. In shallow lakes wind often causes resuspension and mixing. Scuba divers can also cause resuspension. P sediments in the water is from sedimentation of P minerals, allochtonous organic material, and autochthonous organic material. Resuspension can also happen in non-stratisfied deep lakes (not in the summer). Particulate P becomes interstitial (in betwen grains) due to oxidation (with Fe) reactions and then ends up in the water column above, when conditions become anoxic P is released from Fe. Sediments contain more P than standing water.

Oxygen Production and Consumption by Macrophytes

Macrophytes use energy of sunlight biomass by sequestering carbon and producing oxygen. During night they consume O2 for respiration/maintenance. We model this separately from algae consumption/production bc growth rates of algae is higher, macrophyte biomass increases gradually stabilizing in summer and decreasing in fall. In addition macrophytes are not transported in water systems unlike algae. -in short: modeled seperately bc the growth rate of algae is higher and it is transported over distance in water

Secchi disc

Method to obtain an estimate of water transparency. Weighed and the transparency is the mean of the depths at which the secchi disc disappears when viewed from the shaded side of a boat and at which it reappears upon raising done around midday. Sd=1.44/kd kd=extinction coefficient

Humic acids absorb

More blue part than in the red part. Humic acids do not scatter, only particles scatter

Nitrogen and Phosphorus in Lake Rauwbraken

N: many forms in water, organic (amino acids) to inorganic (ammonia, nitrate, N2) highly variable P: highly variable, especially with depth depending on algal uptake, productivity of lake, littoral zone loading, historical loading, thermal stratification. In anoxic hypolimnion of eutrophic lakes substantial release of P from sediment might occur during stratification (bc anoxic so Fe is oxidized).

Oligotrophic vs. Eutrophic CO2 emission

Oligotrophic lakes have more CO2 emission because there is more respiration than photosynthesis, because nutrients limit photosynthesis. Eutrophic lakes have lots of plant growth therefore there is less CO2 emission because it is all being used up in photosynthesis. Eventually the eutrophic lake will become oligotrophic because of this plant growth.

Rauwbraken Zonation

Open water area is called the pelagic zone, while the interface between land and water is the littoral zone. Profundal zone is the deeper part under the pelagic where the sediment is free of vegetation (benthic pelagic). The transition between the littoral and profundal zone is named the littoriprofundal. Littoral zone is: -Eulittoral (shoreline between highest and lowest water level) -Upper infralittoral (zone of emergent aka poking out root vegetation) -Middle infralittoral (zone of floating leaved rooted vegetation) -Lower infralittoral (zone of submerged rooted vegetatation)

internal loading

Phosphorous from the sediment is released causing increased nutrient loading

pH

Photosynthesis may influence the Ph of water depending on the buffering capacity of the water (aka abulity of water ro recived OH- and H+ ions without having an effect on pH due to carbon dioxide- bicarbonate -carbonate equilibrium). All low pH when only CO2 is there photosynthesis will not effect pH, while at common pH where HCO3- is utilized it requires the uptake and release of protons, and will lower the pH further.

Underwater Light

Solar radiation has profound effects on stratification and circulation of water, nutrient cycling, organism performance and distribution and food webs. Thermodynamically open systems with OM as the carrier of energy (allochthonous or autochthonous). Direct radiation from the sun has more red while indirect radiation (reflection from the sky) has more blue due to scattering by atmospheric particles. Radiation is ultraviolet which has damaging effects, visible which is photosynthetically active, and infrared which is mainly heat. When light hits the water surface it undergoes three processes: a) reflection which is higher in the winter b) absorption causing light to disappear and be converted to chemical energy (photosynthesis) or heat. water itself, dissolved components, suspended particles. Algae prefer blue while water prefers red, blue green light penetrates deep. c) scattering depends on size and concentration of particles causing light to diverge from its original path, which is strongest in the blue part which is why water looks blue from far away When solar radition has passed through the atmosphere it must first penetrate the air water interface, where solar photons becomes absorbed or are scattered prior which only increases the chance of absorption. This results in a decrease of a fixed portion at each depth. This decrease is called attenuation. Lower extinction coefficients indicate clearer values than higher values.

Salinity

Sum concentration of all ions dissolved in water. Conductance is measure of resistance of water to electrical flow, resistance increases with fewer ions in the water, so the fewer the ions the lower the conductance. Ionic composition of fresh water is determined by HCO3-, CO3(2-), SO4(2-), Cl-, Ca2+, Mg2+, Na2+, K+ and to some degree NO3-, PO4(3-), Fe. Dynamic ions concentration is influenced by biological activities while conservative ions are not. Dynamic may have marked seasonal and spatial heterogeneity. E.g. in the summer concentration of CaCO3 decreases in the epilimnion because of precipitation and photosynthesis. This increases conductivity in the summer.

Degradation of OM

Surface waters contain organic substances that can be mineralized by microorganisms mainly by aerobic oxidation. When the concentration of oxygen binding substances is not too high the supply and use of oxygen are in balance and no shortage of oxygen will appear. The self-cleaning capacity of water is in tact. Discharge of treated wastewater (still contains low amounts of OM), sewer overflow, accidental spills, decaying algae after explosive growth all increase OM load and deplete oxygen. Effluent is a mixture of many substances and not usually degraded entirely. Many substances are only partly oxidized at different speed of degradation. As a measure for the concentration of biologically degradable material the BOD (biological oxygen demand) value is used, aka the quantity oxygen necessary for the degradation of the substances. Kr is the reaction constant for degradation of BOD time-1

Turbidity

Suspended particles scatter light and this increases with higher loads of suspended matter, which quantifies the degree of light scattering in a sample. The degree to which a light beam traveling through water is being scattered is expressed as turbidity.

compensation level

The depth where oxygen production by photosynthesis and oxygen consumption by respiratory processes balance out, at about 1% light intensity. The water column above this point is the euphotic zone, water below it is the aphotic zone.

In a deep stratisfying lake photosynthesis occurs in

The euphotic zone (zone with light and nutrients) which can extend as deep as the hypolimnion, but also contains the littoral zone and the epilimnion.

Lake morphology

The maximum length of a lake represents the maximum fetch, max depth, mean depth= V/A volume/surface area, water volume (estimated by series of truncated cones summed)

Clinograde curve

The relationship of oxygen with depth in eutrophic lakes, which is a decrease with depth.

Aquatic Ecology

The scientific study of the interrelationships among aquatic organisms and between these organisms and all abiotic and biotic aspects of their environment.

Reaeration

The solubility of oxygen depends on the pressure, temperature, and concentration of dissolved minerals. Colder and less salty contains more oxygen. (Cs= saturation concentration, dependent on temp Kh, pressure Pt). When the water is undersaturated O2 will diffuse in, when water is oversaturated O2 will diffuse out. The magnitude of diffusion flux is proportional to the driving force: the deviation from saturation. Flux also depends on the diffusion coefficient and the thickness of the boundary layer which is controlled by turbulence at the water-atmosphere boundary layer. Gas transfer velocity=Kl (turbulence measured by depth and stream velocity in moving water and wind speed in stagnant water), flux depends on difference of Cs-[O2] and Kl and the height of the water column (bc flux needs to distribute over the water column). Ka the reaeration constant has units time-1 and is Kl/H. Oxygen flux will have more of an effect on the shallow than the deep water.

Chlorophyll A

The total amount is used to measure the phytoplankton biomass bc all photosynthetic organisms have it. Vertical distribution varies greatly by seasons. Oligotrophic lakes have lots in the deep water that can persist for months, while in eutrophic lakes it is the opposite (all in the epilimnion and live for a short time). Metalimnetic chlorophyll maxima do also occur, mainly cyanobacteria and cryptophytes which move between nutrient rich hypolimnetic water and warmer lighter epilimnetic waters to harvest light inaccessible to other organisms.

epilimnion

The upper portion of a deep lake (when stratified aka in the summer when the water is warmed differently leading to different densities) where there is net photosynthesis, aka photosynthesis dominates over respiration. There is lower CO2 efflux than in the hypolimnion due to this

Trophic Interactions

The vertical connections within a community. Typical pelagic food webs have 4. In reality, many interactions among organisms and their environment exist, where the communities are not only shaped by predation as the sole driving force.

Inorganic carbon distribution in a lake

Total inorganic carbon is distributed evenly over the water column in lakes without thermal stratification (aka shallow lakes and deep lakes during periods of complete mixing aka not summer). However, during thermal stratification in the summer there are large changes with depth. Oligotrophic lakes: Co2 in hypolimnion is higher than in the epilimnion (but not by much), pH is lower with depth (bc more CO2, more CO2 means more acidic, but again not much), and O2 increases with depth bc more is living and respiring in the top layer. Epilimnion has less CO2 because of decrease solubility Eutrophic lakes: High photosynthetic activity in the trophogenic zone causes strong reduction of CO2 (and therefore increase in pH). In the zone below (increased depth) decomposition of the upper water layers causes increase CO2 with depth and decrease in pH. Oxygen is depleted with depth. For any thermally stratified lake temp decreases with depth

Behavior of organic micro pollutants

Transport and bioavailability of persistent organic micro-pollutants generally depends on sorption to particles. Absorbed POPs are less available to organisms and adsorption determines fate (suspended, sediment etc) distribution. Through sedimentation POPs are removed and transported to the sediment, and the buried sediment layer no longer participates in transport/release to aquatic animals. POPs are non-polar so thermodynamics predicts polar water is unfavorable, leading to low solubility in water, high hydrophobicity and high volatilization. Kp, the partition coefficient, is ratio concentration adsorbed to concentration dissolved. This ratio is referred to as the adsorption isotherm. In sediments hydrophobic compounds are adsorbed almost completely to OM (dominated by soots, kerogen or coals, but in absence of condensed carbon Kp can be determined by fraction organic carbon and partition coefficient for organic carbon). Partition coefficient for organic carbon depends on the hydrophobicity of the substance. DOC (dissolved organic carbon) reduces adsorption to sediment and increases the mobility of POPs, however most DOC is composed of the most hydrophilic fraction of OM. *Generally there are three states for POPs: dissolved state, bound to particulate organic carbon (POC), bound to DOC.* Gas chromotograph can read the concentration of chlorobenzenes by reading the presence of chlorine in the water state, and the amount in the sediment is the difference between this concentration and the initial added concentration. The larger and more hydrophobic the molecule is the more room is required in between water molecules in the aqueous phase which takes more energy to break the hydrogen bonds than for a smaller molecule

Eutrophication

Uncouples the aglae-grazer interface and causes a shift from submerged macrophytes to suspended algae. Turbid water has less habitat for visually hunting piscivorous fish which releases planktivorous fish from predation control, resulting in low zooplankton so even less herbivory control of algae. Not all phytoplankton is edible and a certain amount is toxic which limits zooplankton predation as well. P is usually the limiting nutrient. P has very little nutrients, while N can be lost by denitrification, so P tends to accumulate in the sediment, therefore simply stopping input will not be sufficient.

Oxygen Equilibirum

Water at normal temperature contains little oxygen compared to air, gas molecules diffuse from areas of high concentration (air) to low concentration (water). When the volume of oxygen diffusing in either direction is equal the water is at saturation. This is uncommon and there is usually less oxygen in the water. At higher temperatures oxygen content of water decreases (cold water holds more oxygen) while the demand of animals rises, but this can be compensated by water movements which keep the maximum possible supply of oxygen available in immediate vicinity of animals (done by animals themselves) Main inputs: reaeration, primary production Main outputs: degradation/decomposition, losses to the atmosphere, sediment oxygen demand

Water Quality

Water quality is usually defined as the condition of water in relation to its function or suitability to a particular purpose (drinking, irrigation, recreation etc)

Water plants as a nutrient pump

When there is a lot of plant growth the plants will eventually die. When they do they act as a nutrient pump because they release a lot of nutrients into the system. This can cause eutrophication and lead to toxic algal blooms.

Calcium and inorganic carbon

When water percolates through the soil it becomes enriched with CO2 from decomposition of OM, causing carbonic acid concentrations in the percolation water to rise. Hydrogen ions dissociate and are replaced on bicarbonate with cations in the soil matrix (mainly calcium and magnesium) resulting in calcium bicarbonate [Ca(HCO3)2 <-> CaCO3 + H2O + CO2 calcium carbonate equilibrium]. Therefore hydrogen ions from bicarbonate play a major role in weathering of soils (romoval of Mg and Ca from rock). Therefore a concentration of Ca allows CO3 to remain in solution after the carbonic acid equilibrium has been reached. When the concentration of free CO2 increases above the concentration needed for keeping Ca(HCO3)2 in solution additional CaCO3 will dissolve. When photosynthetic activity depletes the pool of free CO2 a large quantity of CaCO3 is precipitated by algae and macrophytes.

Zooplankton

Zooplankton forages on phytoplankton and herbivorous zooplankton. Many are omnivorous. Copepods are larger or Daphnia that are keystone species that occupy a central role in pelagic food webs of temperate and arctic lakes and ponds by controlling phytoplankton biomass and species composition, and serve as a link to the survival of many species that depend on invertebrate biomass. Daphnia have vertical migration every day, during the day they are in the deep cold waters avoiding predation from visually oriented fish and at dusk they move upward to the phytoplankton rich warm water going back in dark. In littoral zone there is horizontal migration where they migrate to macrophyte beds during the day and into open water during the night that provide refuge from predators but there is less food and invertebrate predators still.

photosystem II

complex where water is split

Modeling Oxygen and Dynamics

dO2/dt = production - respiration -SOD + reparation - BOD. The typical diurnal pattern of oxygen during the day and night is caused by primary production and respiration. The peaks and troughs of this graph are more pronounced in eutrophic lakes, and the amplitude is much lower in oligotrophic lakes. Respiration rate is constant while growth rate depends on nutrients, temperature and light. Growth rate decreases with increasing depth because light limitation increases. The extinction coefficient is a measurement of how turbid the water is. Km is the half saturation constant of light on macrophyte O2 production.

Carbon in aquatic systems

dissolved organic forms (dissolved organic carbon and particulate organic carbon), but as dissolved inorganic forms (mainly). Very little is in living biota. The concentration of each component of inorganic carbon is dependent on pH (CO2, CO3(2-), HCO3- and H2CO3)

Secondary production

formation of biomass by heterotrophic organisms

SOD

sediment oxygen demand must be lowered to increase the amount of oxygen in the peaks of the graph