Final Exam Potential Questions

8/19/2019 Final Exam Potential Questions

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Note: Read questions from top to bottom – if a question is repeated a second time (or more) I will not have

checked over the answer as thoroughly as earlier versions of the question !orrections or additions are in redtype" #nother disclaimer: although I have looked over these questions and corrected any glaring errors$ the

answers contained are not necessarily the very best answers possible" If you come up with other answers$ they

could be right too % &aren

Possible Aquatic Biology Final Exam Questions

'" efine a wetland and describe two of the maor types of wetland"#ccording to the *+ ,ish and -ildlife +ervice$ wetlands are transitional .ones between terrestrial and aquatic

systems where the water table is at or near the surface or the land is covered by shallow water" -etland mustsupport predominately hydophytes$ contain substrate predominated by hydric soil$ and/or contain substrate that

is nonsoil and saturated or covered with shallow water for part of the growing season each year" 0wo of the

maor types of wetland are bogs and swamps" 1ogs display no significant outflow or inflow$ accumulate

partially decomposed plant material known as peat$ contain acidic water$ and are dominated by +phagnum2oss" +wamps are wetlands dominated by water tolerant trees or shrubs such as cypress"

3" iscuss the distribution of nitrogen species in eutrophic and oligotrophic lakes and how it relates to thenitrogen cycle"

In eutrophic lakes the concentration of N456 is high in the epilimnion due to high rates of e7ternal loadingand high rates of nitrification (N89 ;3 N45

6 )" 0he concentration of N89 is low in eutrophic epilimnions

due to high rates of nitrification and high biological uptake (assimulation)" In the hypolimnion of eutrophic

lakes the concentration of N456 is low due to high rates of denitrification which occurs under ano7ic conditions

(N456 N3 (g) )" Nitrification does not occur due to absence of o7ygen" In addition$ biological demand is low"

0herefore$ concentration of N89 is high" 8igh rates of ammonification$ in which organic matter is converted to

N89$ also contributes to high N89 concentrations"

In the epilimnion of oligotrophic lakes the concentration of both N456 and N89 are low" -hat process produces it>


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0he dead .one occurs on the bottom of lakes around the depth of the thermocline" No benthic life persists in the

dead .one" 0he dead .one e7ists due to thermal seiches" uring a thermocline seiche the thermocline tilts fromside to side of a lake" 4n the side of the lake that the thermocline tilts up$ hypolimnetic water is abnormally

high" 4n the other side of the lake epilimnetic water is abnormally low" #s the thermocline tilts back and forth

organisms on the adacent lake bottom would e7perience changes in temperature as cold hypolimnetic water andwarm epilimnetic water alternately passed over them" ,luctuations in o7ygen concentration might also be

encountered$ since the hypolimnion of eutrophic lakes is generally ano7ic" 1enthic organisms are adapted to

specific o7ygen and temperature conditions" 0hus$ benthic life cannot survive in the dead .one where

thermocline seiches cause frequent changes in temperature and dissolved o7ygen concentration"

'" Name some adaptations that macrophytes have made to living in aquatic environments2acrophytes have buoyant stems and leaves to take advantage of the water as a structural support" 0hey also

have the ability to change height and form depending on the depth of the water" ,or instance$ they can be short

and bushy in shallow waters and long and sparse in deep waters" 2acrophytes? submersed leaves have no

cuticle$ ma7imi.ing !43 uptake across the entire leaf surface" ,inally heterophylly$ the differing of leaf shapedepending on whether the leaf is underwater or above the surface$ facilitates gas uptake underwater where most

leaves are long and thin$ big and broad$ or highly dissected"

3" escribe three predator avoidance tactics employed by .ooplankton"

@ooplankton e7hibit cyclomorphosis$ or changes in shape in response to seasonal cues or predators"


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5" -hy might the river continuum concept describe a river running through a deforested watershed poorly>

8ow might macroinvertibrates (shredders$ gra.ers$ collectors$ predators) change with the length of thisstrange river>

a" 0he rcc assumes that tree cover and leaf fall will mediate light availability and nutrient input in

low6order streams" -ithout tree cover there would be full light availability along the entirelength of the river allowing high primary production throughout" *pon the periphyton gra.ers

would thrive and predators might begin to dominate$ downstream" +hredders and collecters

would sadly have little to shred or collect"

9" 8ow do reservoirs differ from lakes>

a" 8igh sedimentation rates (this is true in lakes too$ but rivers entering reservoirs usually carrymore sediments than sources entering natural lakes" 0his statement is good relative to riversE)

b" -ater level change

c" !urrents/density flows

d" =ow water retention rates

Question 1 (1+2+1+1 points). -ould you e7pect there to be a high or low 43 level in the hypolimnion of anoligotrophic dimictic lake during summer stratification> escribe two factors that may have influenced this 43

level" o you e7pect there to be a high or low concentration of Fhosphorus in the hypolimnion water column>escribe one specific mechanism that can cause this kind of F concentration in the water column"

Answe 1. I e7pect there to be a high level of o7ygen in the hypolimnion because the low decomposition in this

oligotrophic lake has allowed o7ygen to remain available in the water" #lso$ more o7ygen can dissolve in the

cold water of the hypolimnion than in warm water" I e7pect a low concentration of F in the water column of the

hypolimnion" F can be accumulating in the sediments as insoluble ,eF49 precipitates"

Question 2 (2+1+2+1 points). -hat geologic and hydrologic factors affect the amount of suspended solids

(wash load) in a river or stream> 8ow can wetlands influence these factors> -hat biological factors can affectthe amount of course particulate organic matter (!F42) and fine particulate organic matter (,F42) in a river

or stream> -hat happens to the !F42 and ,F42 at dams>

Answe 2. 0he form/si.e of substrates (can be large rocks$ sand$ etc") and the velocity of the water can affect

the wash load in a stream/river" +mall substrates and high velocity advocate a high wash load" -etlands can

slow the stream velocity by providing a large area for water flow and by providing aquatic plants that create a

resistance to water flow" 0he amount of !F42 in a stream/river depends largely on the amount of leaf litterthat falls into the water from trees above" 0he amount of ,F42 in the water depends on how actively

GshredderH invertebrates are eating !F42 upstream (this GshreddingH yields ,F42)" #t dams$ almost all

,F42 is deposited and most allocthonous !F42 settles out or is processed"

Question ! (!+2+1+2+1 points). escribe three aspects of a natural watershed that can influence the amount

or quality of runoff entering a water body" -hat are two ways that anthropogenic development in a watershed

affects the surface runoff> 8ow does it influence sub6surface runoff> 1esides runoff$ what are two possiblee7ternal drivers that determine the dynamics of a lake> If two adacent lakes are highly coherent$ do internal or

e7ternal drivers likely determine most of the lakes? dynamics>

Answe !. Degetation can intercept precipitation$ decreasing runoff" 0he type of soil can influence infiltration$

the soaking of water into the soil$ which decreases runoff into a water body" 0he nutrient levels in soil

influences the amount of nutrients that runoff brings into a water body" #lso$ the slope of the watershed

influences the velocity of runoff" #nthropogenic development in a watershed usually increases the flow ofrunoff and the amount of pollution entering a water body" 0his development also impedes much sub6surface

runoff and deep ground infiltration because the area of impervious surfaces is high"


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0wo other e7ternal drivers are the invasion of some biological species and the activity of humans in the water

(recreation)" 0he dynamics of the two coherent lakes are likely determined by e7ternal drivers because theywould have similar e7ternal conditions"

Question " (#+2+1 points). iscuss the patterns of stratification and mi7ing in a dimictic lake in the winter$spring$ summer$ and fall" 1e sure to mention the role of the thermocline and wind" -hat are surface and

thermocline seiches and when do they occur> 8ow do thermocline seiches affect benthic biota living around

the thermocline>

Answe ". In the winter$ a weak thermocline develops between warmer denser water (9!) at the bottom andcooler lighter water (J9!) at the surface" 0he thermocline is not broken by currents from wind action because

the water is covered by ice" In the spring$ ice melts because of increased solar energy" -ith the e7posure ofliquid to wind$ the lake begins to mi7" +ometime between spring and summer$ the solar energy penetrating the

lake increases the lake?s surface temperature enough to create a stratification of water by temperature that resists

mi7ing by the wind" 0his stratification$ with a strong difference in epilimnion and hypolimnion temperatures

and densities$ remains throughout the summer" In the fall$ less solar input and continued cooling viaevaporation lessens the difference in temperature between the stratification layers" #long with the lessened

temperature difference comes a lessened density difference" *ltimately$ the wind force is strong enough to

break the thermocline and cause the lake to mi7"# surface seiche is the piling of epilimnetic water on one end of a lake$ and a thermocline seiche is the tilting of

the thermocline due to a surface seiche" 0hese seiches occur when strong winds are sustained over a lake"0hermocline seiches can e7pose benthic organisms that need o7ygen to o7ygen6depleted waters (causing themto die)"

'" 8ow could the addition of a piscivorous fish to a turbid lake whose (simple$ top6down) food web had

previously been dominated by .ooplanktivorous fish affect macrophytes in the lake>#nswer: 0he addition of a level to the food web would reduce .ooplanktivorous fish populations$ which would

increase .ooplankton populations$ and decrease phytoplankton biomass" 0his reduction would decrease

turbidity in the lake" If this reduction were substantial enough$ a phytoplankton6dominated lake could switch toa macrophyte6dominated lake$ as positive6feedback loops kick in to maintain low turbidity" 0his occurs only if

the turbidity decreases enough to allow macrophyte growth"

3" escribe how wetland flooding can remove nitrate from a river system"

#nswer: ,looded wetlands give an opportunity for denitrification processes to take place" In this process$

nitrate is converted into nitrogen gas$ which is released into the atmosphere" enitrification requires ano7ic

conditions" ,looded wetlands associated with rivers have high water residence times and are frequently ano7ic(at least in the sediments)$ so denitrification rates are high" (I would add that the alternate flooding and drying

is also important)

5" ams often have the effect of GresettingH the rivers they are on$ that is$ making it appear like a lower order

stream than it would otherwise"


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land upstream is lost underwater under the resulting reservoir" =ess obviously$ because water levels in a

reservoir tend to change more than in a natural lake$ there is a dead .one along the shore where neither lake norterrestrial organisms can survive$ because it is neither habitat for any length of time" 0his results in a loss of

habitat type in the land directly up from the dam" 0here will be no more riparian area near the water as there

probably was before the dam"

1. Explain t$e %ea& 'one. $at it is $ow it is *ome& an& $ow &oes it elate to biology:

0he dead .one is the area of the benthos that is alternately e7posed to o7ygenated epilimnetic waters and

ano7ic (in a eutrophic lake) hypolimnetic waters when the thermocline moves up and down during athermocline seiche" It can lead to large differences in temperature and 47ygen saturation at a single point in the

lake" It is very difficult for organisms to tolerate these changes in conditions so there is generally no life in thedead .one" 0hese fluctuations in the thermocline also e7pose benthic invertebrates to o7ygenated waters by

bringing epilimnetic water lower in the lake"

2. ow &o &ams a**ect t$e biology o* steams,

1enthic algae levels increase because of the presence of more stable substrates like large boulders and the

increase in light from clearer water due to less suspended solids" Riparian vegetation like cottonwoods decline

because the floodplains disappear" 1enthic invertebrates decline if water levels fluctuate over the course of theday like in some hydroelectric dams" It is very hard for organisms to stay in place in the river with the abnorma

flows (or sudden dewatering strands them on dry river beds)" 2igratory fish like salmon are affected becausethe river is now barricaded by dams"

!. ow &oes $uman &e-elopment impact t$e $y&ologic cycle,

8umans take water out of the groundwater and don?t replace it$ thereby causing the water table to drop" *rban

environments characteri.ed by water6impermeable surfaces have very high water runoff rates after storms thatdrop off quickly" 0he resulting large discharge means sediment erosion$ loss of habitat$ and general difficulty

for biotic organisms" 0here are also no place for water to stop like wetlands or ponds that a natural setting

would have$ thereby increasing the influ7 of water into rivers and streams"

". %escibe t$e impotance o* timing in *is$ spawning.

,ish start out eating plankton$ then after having grown (not too much though)$ they switch to eating smaller fish0hus$ if fish spawn too late$ they will be eaten by fish that have already switched to eating smaller fish" #lso$ if

fish spawn at the same time as other fish$ there will be competition for food sources" If fish spawn too early in

the spring$ the cold water will kill their larvae or eggs" 0hus$ fish need to find the balance between spawning

after temperatures have become warm enough but before their competitors (and/or predators) have spawned"

'"

#nswer: Nitrogen in various forms is deposited on a floodplain during a flood" #s the water recedes

much of the silt and nitrogen forms that were brought on to the floodplain become ano7ic and provide a large

habitat for denitrifying bacteria which are able to convert N456

to N3" 0hus floodplains act as significant sinksof nitrate in a river system" -hen floodplains are removed or reduced$ as in the 2ississippi river$ sediments and

nitrates are not trapped and are instead dumped into the receiving body of water such as an ocean$ larger river$or lake" 0he water in such a body will have higher nitrate levels than before floodplain removal"

3" -hat are the two most important characteristics of lakes that are phosphate sources and those that are

phosphate sinks> -hy do these characteristics affect the phosphate levels>#nswer: =akes that are F sinks usually have a hypolimnion that remains o7ic and the characteristics that

go along with this: depth and colder" Increasing water residence time also increases F uptake" =akes that are

sources usually have a hypolimnion that goes ano7ic and a short -R0" -hether a lake goes ano7ic or not isvital to the source/sink status because a lake that remains o7ic will collect phosphate in its sediments and a lake


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that goes ano7ic will e7perience internal loading of F from the sediments" 0his is because phosphate

precipitation in iron comple7es occurs under o7ic conditions and bacteria and chemical processes that mediate phosphate release need an ano7ic environment" -R0 is important because it allows phosphate more time to be

processed within the lake" If the lake flushes water through quickly then it won?t have time to capture any

phosphate"

5" *se the River !ontinuum !oncept and the +erial iscontinuity 8ypothesis to describe the effects a large

dam might have on downstream sections of a large river"

#nswer: ams generally affect large rivers by reducing the stream order downstream" 0hey generallydo this by:

') ecreasing turbulence and nutrients to levels more likely to be found in a lower order medium si.edstream" 0his physical change will greatly affect the biotic dimension of the river downstream" ,or instance$ the

rockier stream bed and clearer water will act together to provide better habitat for periphytic algae" 0he algae in

turn will provide forage for a more diverse array of gra.ers and a more limited array of collectors" 2acrophytes

will also find the river bed more habitable as well"3) ecreasing in stream temperature to that more likely to be found in an upstream creek" 0his will

provide habitat for cold water fauna"

9"


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9" Name the characteristics of the organisms that can live in each layer of a stratified lake in summer

Epilimnion

• Need 43 (get from surface or have gills)

• !an use light

• Frobably not decomposers

• !an have mi7ing

• !an be rooted or floating

•-armer temperatures

$emocline

• Not much can live because varying conditionsKdead .one (only if confined to substrate)

• 8as to handle varying temp (only if confined to substrate)

• 8as to be able to deal with both o7ygen and not o7ygen (only if confined to substrate)

ypolimnion

• !an have no light

• =ittle to no o7ygen

• =ikes cold temp

• No mi7ing

•ecomposes possibly (bacteria>)

• ,ind prey without sight

• !an handle water pressure

1. Explain the hydrology of a forest in contrast to a developed piece ofland and one that has been clearcut.Forest- precipitation is intercepted by grass and trees. Depending on the substrate there is different amounts of infiltrationand surface runoff (infiltration is greater). As ater infiltrates the ground the groundater is recharged. !he groundater andthe surface ater flos into la"es streams or etlands ere it evaporates and restarts the cycle. Evapotranspiration fromtrees also accounts for the regeneration of precipitation.Developed- #n contrast to the forest there is no infiltration and surface runoff brings ith it pollution from the city to the la"es

and streams. $roundater regeneration is minimal.%lear cut- !here is a dramatic decrease in the evapotranspiration. there is increase in erosion and nutrient loading in thestreams and la"es. !he stream velocity is increased. &utrient upta"e is diminished alloing the nutrients to flo into thestreams and rivers (impact of ').

. Dra a bottom delling fish and a top feeder. hat are the ma*ordifferences+,a*or differences the bottom dellers coloration is generally located on its dorsal side to "eep it concealed from predatorsfrom above. !hey are characteri/ed by barbs that are used to search the ground for anything edible. !he mouth is found onthe bottom of the fish. !he top feeders coloration is also on its top to "eep it from being seen from above. 0elo it is alighter color to blend into the s"y from belo. !he mouth of a top feeder is pointed up so that it can eat from the surface.

(picture in slide sho)

'" iscuss seasonal changes in the temperature and o7ygen profiles in eutrophic$ dimictic lakes"

#t spring turnover the water temperature and dissolved o7ygen concentration are relatively constant from

the bottom to top of the lake" 2i7ing of the entire water column equali.es temperature and dissolved o7ygenlevels across the depth profile" #s temperatures warm$ heating of the top of the lake leads to lake stratification"

#n upper$ warm epilimnion and lower cold hypolimnion become established" 2i7ing between the layers does

not occur" (-hy not>) 0he epilimnion displays relatively constant temperature throughout because it is mi7ed

continually by the wind" 0he water temperature is also relatively homogenous in the hypolimnion$ thoughtemperatures drop slightly with depth" 0he hypolimnion and epilimnion are separated by a narrow .one of

ma7imum temperature change (definition>) called the metalimnion or thermocline" #t fall turnover the lake is


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again isothermic and displays constant o7ygen concentration" In the winter$ weak reverse stratification occurs$

with water colder than 9 degrees celcius at the lake surface and water around 9 degrees below" uring summer lake stratification o7ygen levels are high in the epilimnion due to high levels of

photosynthesis and atmospheric e7posure$ and low in the hypolimnion due to isolation from the atmosphere and

high rates of decomposition" 1eneath the thermocline o7ygen is eventually completely consumed and is notreplenished until fall turnover" *nder the ice o7ygen remains low near the lake bottom due to decomposition$

and higher at the lake surface (ice surface)" !older water temperature directly beneath the ice allows more

o7ygen to dissolve" In e7treme situations$ lakes may go completely ano7ic during the winter as decomposition

consumes o7ygen" =ack of photosynthesis and atmospheric isolation prevent o7ygen replenishment"

3" !ompare the distributions of alga biomass in an eutrophic lake with a surface bloom and in an oligotrophiclake"

In an eutrophic lake with a surface bloom alga biomass is greatest ust beneath the lake surface (often because

these are cyanobacteria that can maintain their depth with air vacuolesL other groups cannot do this and so do

not usually form surface blooms) and decreases with depth" #lgae at the surface shades out algae deeper in thewater column" #lgae that sink to the thermocline cannot survive because they are beneath the compensation

point" In oligotrophic lakes the maority of the alga biomass is concentrated at the theromocline" 0he algae sink

and accumulate at the thermocline since they cannot penetrate this density barrier (actually they can$ but it takesawhile$ resulting in a backup or accumulation of cells at the thermocline) " ue to nutrient limitation alga does

not accumulate rapidly at the lake surface and thus does not shade out alga at the thermocline"

5" 8ow can water discharge from reservoirs affect river biota downstream> 8ow does whether water is

released from the hypolimnion or epilimnion impact changes in river conditions>

-ater discharge from reservoirs causes rapid increases in river discharge during seasons when high discharge

would normally not occur" =otic biota have life cycles adapted to the natural hydrological cycles of rivers"0hus$ seasonal changes in flow patterns can prove detrimental to organisms" In addition$ due to water release

from reservoirs stream discharge can fluctuate greatly diurnally" 4rganisms may not be able to adust to these

frequent fluctuations" Releasing water from a reservoir can also change the normal thermal fluctuations of ariver" # natural river warms in the summer" 8owever$ releasing water from the reservoir?s hypolimnion keeps

the river at a constant cold temperature throughout the year" In coldwater rivers$ water released from the

epilimnion may be warmer than usual" !hanging the water temperature of a river effects biota since mostspecies are adapted to specific water temperatures" ,or e7ample$ trout can only survive in cold water with high

dissolved o7ygen content" 8ypolimneic water released from reservoirs may also have low o7ygen content and

high nutrient levels" =ow water o7ygen content can lead to mortality of species that cannot tolerate low o7ygen

conditions" Nutrient pulses may disrupt the natural competitive relationships between species and lead to alga blooms" 8ow might this affect phytoplankton productivity>

0he primary form of dissolved phosphorous in lakes is orthophosphate or F4936

" In the presence of o7ygenorthophosphate reacts with ,e3 and ,e(448) and precipitates out of the water column" 8owever$ under ano7ic

conditions the iron6phosphorous comple7es are soluble and phosphorus is released" Release of phosphorousfrom iron6phosphate comple7es in bottom sediments is known as internal loading" #naerobic bacteria may

mediate the release of phosphorous from iron comple7es under ano7ic conditions" If the hypolimnion of a lake

is o7ic internal loading does not occur$ and phosphorous in iron comple7es is perminently lost to the sediments"

4ne would e7pect the concentration of phosphorous in the water to be greater in lakes with ano7ic hypolimnion because internal loading prevents loss of phosphorous to the sediments" In addition$ ano7ic hypolimnetic

conditions suggest higher lake prodictivity$ indicating that phosphorous inputs may be high" Fhytoplankton

productivity should increase with phosphorous concentration$ and thus also be high in lakes with ano7ichypolimnion"


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'"


10/17

influx of excess nutrients into the lake causing an algal bloom after the sediments subside. (name a few of

these)

Question #2

What would be the likelihood that a piscivore population could survive if transplanted into a small, shallow,

high lake near the headwater?

-- Low in nutrients and high above the other lakes, the headwater lakes tend to support a few macroinvertabrates

and algae. If the lake somehow got stocked with a piscivore, it would be unlikely that there would be a

sufficient planktivore population to support it (energy transfer making smaller prey unlikely to support a large

fish). (However, under these circumstances, piscivore often do resort to alternative prey types like

invertebrates, and then grow very very slowly) There would be a small breeding population and a dismal

outlook and these fish would likely just travel back downstream to more suitable climates.

Question #3

Two stable eutrophic lakes experience a one-time massive infusion of nutrients. One lake is dominated by a

piscivore and the other by a planktivore and both lakes have a stable trophic cascade. What does each lake look

like right after the nutrient inflow?

-- The lake with the piscivore is most likely to be clear and have a rise in zooplankton population and piscivore

population. The lake with the planktivore is more likely to be turbid and have higher algae and planktivorepopulations. This is assuming that the nutrient influx would lead to an algal bloom.

Question #4

What kinds of organisms could be living in the hypolimnion of a hypereutrohic lake after a long productive

summer?

-- Any organism that could withstand anoxic conditions or could move from the hypolimnion to the epilimnion

on its own power.

1. Explain the changes in seasonal distribution of different types of phytoplan"ton and ho it relates to the seasonaldistribution of different types of /ooplan"ton in a dimictic la"e.

#n Dec. and 2an. numbers of /ooplan"ton and phytoplan"ton are both very lo due to cold temp. and light forphotosynthesis being bloc"ed by sno and ice cover hich limit groth. #n the early spring hen mixing occurs diatomspredominate because 3i becomes present throughout the ater column and they can use it in the photic /one (here thereis no more light) to gro. At this point /ooplan"ton populations rise because there is more phytoplan"ton to feed on. Asthe la"e becomes stratified at the beginning of the summer and the diatoms sin" belo the photic /one (because theirfrustrules are heavy and they need mixing to stay in the photic /one). 0y early summer the /ooplan"ton communities havebecome more substantial so there is a short clearater stage (because the /ooplan"ton are no depleting thephytoplan"ton). After the clearater period nutrients are lo and cyanobacteria are the dominant phytoplan"ton for a short hile because they have the advantage of being able to fix &. hen fall mixing occurs again diatoms are again able toutili/e 3i in the photic /one and become dominant before inter sets in again and all plan"ton decline.

. Explain the theory of trophic cascades and briefly explain ho this principle is the basis for the biomanipulation that asconducted ith piscivorous fish in 4a"e ,endota.!he theory of trophic cascades is that nutrient supply limits algae biomass and production affecting the entire food chainbut other variability in biomass throughout the food chain can be explained by the effects of predation. !his or"s becausepredators ith high enough consumption can control the biomass of their prey ith lo enough production of the prey. !hepurpose of the manipulation in 4a"e ,endota (adding piscivorous fish) as to increase ater clarity. According to thetrophic cascade hypothesis since piscivorous fish consume plan"tivorous fish they ould be able to deplete the populationof plan"tivorous fish. !he result ould be that since plan"tivorous fish consume /ooplan"ton the /ooplan"ton community ould then flourish. Finally since /ooplan"ton eat phytoplan"ton the phytoplan"ton community ould diminish thusdecreasing algal blooms and increasing ater clarity.


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5. Explain hy human impact on rivers has caused many la"es to become hypereutrophic.6ivers around the orld have to a large extent been dammed hich causes floodplains to rapidly disappear. Floodplainshave also been removed for agricultural and aesthetic purposes. Floodplains are very important in maintaining the balanceof nutrients in ater bodies because &-fixation and denitrification can only occur in anoxic conditions. hen ater ithhigh levels of nitrogen (hich is increasingly common no due the presence of & in fertili/ers and it running off ofagricultural fields into surrounding rivers and la"es) moves into a floodplain area the conditions can become anoxic andexcess & can be released into the atmosphere. #f this doesn+t occur then excess & ill remain in ater and because itcan be a limiting nutrient for algae can cause big algal blooms and eutrophication.

7. Explain some of the effects that landscape position and the terrestrial environment can have on hydrology and ater8uality in la"es.4a"es in surrounding areas ith good amounts of vegetation generally ill have feer nutrients than la"es in areas ith littlevegetation because plants use up nutrients in runoff and groundater that ould otherise reach the la"es. !he presenceof impervious surfaces allos pollutants or excess nutrients to runoff directly into la"es hereas areas ith only natural soil(pervious to ater) allo infiltration of ater and rather than contaminating la"es much runoff can become groundaterand be filtered. #n general la"es ith higher landscape position ill have loer conductivity than la"es ith loer landscapeposition because as ater runs don the landscape it collects more and more ions. 4a"es ith higher landscape positionalso usually experience loer A&% (acid neutrali/ing capacity) and therefore loer p9 because their main ater source israin hich is often acidifying and there are feer buffers present. As landscape position decreases la"es get more ater

input from other la"es and rivers A&% increases and p9 increases because more buffers are present.

'" Muestion: -hat could you do toincrease the #N! (acid neutrali.ing capacity)>

#nswer: Inputs: natural: input of organic acids from catchment (which might be>)" #nthropogenic inputs would

be acid rain (due to increased use of coal and oil)" 0o increase #N! one could add carbonate or bicarbonate

mechanically$ or do so by re6routing the input stream to run over bedrock that releases these molecules" Fossiblemake more inputs coming into it$ so it is not ust affected by acid rain"

9" Muestion: -hat would happen to a food web if the presence of .ooplankton were severely reduced (how

would it affect the trophic cascade)>

#nswer: 1ecause the alternate trophic levels are controlled by predation$ a problem would come when.ooplankton were supposed to be in lager concentration" If .ooplankton are reduced the secondary consumer

would also be reduced$ although it would normally be abundant" Fhytoplankton biomass (but not rooted plants)

would increase in abundance$ increasing turbidity"+econdary consumer primary consumer O.ooplanktonP phytoplankton


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'" escribe the biological differences you might see between a high seepage lake versus a low drainagelake in this area> !hemical differences> -hy>

=ow drainage lake: you would generally see more diversity in the lake (more fish species$ more

macrophyte species$ etc)" !hemically$ the lake will have a higher conductivity$ calcium concentrations$#N!$ and p8"

8igh seepage lake: biologically$ you would generally see less diversity" !hemically$ the lake would

have a lower conductivity$ calcium concentrations$ #N!$ and p8"

0he reasons for these differences have to do with the water connections in and out of the lakes" 8igh seepagelakes only get their water from the rain$ so they do not get much input of calcium or ions" In addition$ because

the lake is isolated$ it is hard for plant and animal species to reach the lake$ so there will be fewer species(although in some cases these lakes might serve as refugia for rare species because its less likely that invasive

species will reach them)" 4n the other hand$ the low drainage lake has rivers coming in and out as well as

groundwater from lakes higher in the land" 0his will increase the amount of ions as well as calcium" 0he rivers

will provide a conduit for plants and animals to e7pand their territory into the lake"

3" # fair si.ed wetland was situated to a yet undeveloped lake in Northern 2innesota" *nfortunately$ a

group of investors bought up the land and decided to develop the shoreline" 0o increase the amount ofavailable shoreline$ and their profit$ they decided to drain the wetland" -hat effects will the loss of the

wetland have on the water quality and biota of the lake (this is ignoring the effects of construction andshoreline development)>

-etlands act as storm6flow modification and decrease erosion" !onsequently$ the lake will now have an

easier time of eroding its shoreline as well as e7perience more flooding" #long with the storm6flow

modification$ the wetland also was a sink for heavy metals and sulfur$ which will now find their way

into the lake as well as the animals" =ess nitrogen will find its way into the lake (>) (ignoringanthropogenic sources) although more phosphorous and ammonia will find its way" 0his will increase

phosphorous levels and decrease nitrogen levels$ making nitrogen the limiting chemical$ hurting many

animals that depend on N for respiration" 0he wetland was also a source for 42 and F42$ makinglife harder for invertebrates and bacteria that depend on these levels" =astly$ the wetland removed many

suspended solidsL now those solids are going to be in the water column of the lake$ decreasing light

penetration into the water column$ causing problems for plants depending on that light for photosynthesis" (#lternatively$ the lack of 4! from the wetland may make the water less stainedE)

5" -e discussed in class and on the take home test how the R!! (River !ontinuum !oncept) e7plains the

placement of invertebrates along a river" 8owever$ when the river is dammed$ then the flow of nutrients andorganic matter is stalled at the dam" -hat effects does the dam have on the R!!>

1ecause of the dam$ much of the ,F42 and !F42 are dropped out of the water column$ so there is

significantly less organic matter getting below the dam" It could be that the phytoplankton and.ooplankton may replace some of the ,F42 and !F42$ but the water has to be released from the right

area in the reservoir for this to help (i"e" somewhere in the thermocline where there is hopefully still

o7ygen$ but there are dead plankton and .ooplankton they don?t have to be dead to be !F42 or

,F42)" !onsequently$ if there is little ,F42 and !F42$ the R!! is essentially going to be restartedat the head of the dam$ as the organic matter has to be brought back into the water column by scrappers$

and then consumed by gra.ers and collectors" 8owever$ this will also depend on the rate that water isreleased from the dam$ which can have its own daily effect on the invertebrates"

9" -e know that clear6cutting a forest should have lots of effects on a stream at the bottom of the watershed"


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the sedimentation will also decrease light availability$ making life harder for photosynthetic

organisms" +edimentation can also smother gravel beds critical for fish spawning"6 during storms$ there will be little interception and water will simply come rushing

through the watershed and cause more flooding than was observed under normal conditions" 0his

could have a large impact on the biota as they are simply swept downstream when they normallywould not have been"

1.) #f the secchi depth of a la"e is fairly small hat does that tell us about its trophic state+ hat can be say about the

amount of oxygen dissolved in the hypolimnion+e do not have enough information to anser this 8uestion because small secchi depths could be caused by staining (highD:%) lots of suspended inorganic solids or lots of suspended organic matter li"e phytoplan"ton. #f turbidity is caused byhigh concentrations of phytoplan"ton then e can infer that the la"e is eutrophic and the hypolimnion li"ely in anoxic for atleast some of the summer. 9igh D:% concentrations or lots of suspended inorganic solids do not necessarily correspond toa particular trophic state.

.) A larval fish is transparent hen lives in the epilimnion but moves to a ell-lit hypolimnion as it matures. ould it bemore adventageous for this fish to develop into a blue or red fish as it becomes older+ hy+#t ould be more adventageous for the adult fish to be of the color red since the hypolimnion is ell-lit and red light doesnot penetrate as far a blue light does.

5.) hat is the ma*or form of non-living carbon in higher order rivers and streams+ Explain its origin in terms of landscapeposition and predominant insect types in the loer order streams.F':, is the ma*or form of carbon in higher order streams. #t comes from loer order rivers upstream hich havesignificant amounts of allochthonous leaf litter input. !hese leaves are converted from %':, to F':, by shredders.

7.) 3ay you ere to dump radioactive isotopes carbon 15 (in the form of %:) and oxygen 1; (in the form of :) on thesurface of a la"e and monitor their dispersal. hich one ould be more li"ely to disperse the fastest+ hy+%arbon 15 ould disperse the fastest because the radioactive %: ould be fixed into photosynthetic organisms hich ould be consumed by other organisms that can move around much faster than oxygen can (hich must rely on diffusion hich is much sloer). hmmmmm

'" 8ow does phosphorous e7it and enter a water body> escribe both theories"

< In dealing with the classical view$ phosphorous accumulates on the sediments under o7ic conditions"F4956 strongly absorbs to iron aggregate o7yhydro7ides (e"g"$ ,e448)L aggregates accumulate on

sediments$ in dead algae cells and other organic matter$ and insoluble ,eF49 precipitates (,e5)" In

ano7ic conditions$ ,e4486F49 and ,eF49 comple7es dissolve$ releasing F4956 and ,e3" 0he

ano7ic sediment F4956 concentration is Q63; times greater than water column" If water columnremains o7ic$ ,e5 precipitates and aggregates on the sediment surface prevent released F4956 from

diffusing upwards from ano7ic sediments and/or entering the water column" 2odern models suggest

that microbes play an active part in F6cycling"

3" escribe an isotherm diagram of a dimictic lake$ and tell what is going on in the water during eachseason"

6 In the spring the lake is turning over because of the equal temperature and densities" 0hus the

lake will mi7" In the summer the lake will stratify because of the different temperatures and the

different density" 0he top layer: epilimnion will be warmer and have a lower density$ and will beo7ic$ while the bottom layer$ the hypolimnion will be colder$ have a higher density$ and have low

o7ygen levels" In the spring the lake is turning over because of the equal temperature and

densities" 0hus the lake will mi7" In the winter$ the lake will again weakly stratify" 0his is due to

the ice cover and the cold temperatures of the water" It will also have an epilimnion and a


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hypolimnion$ although the density difference is minor and so there is not a strong separation

between the two layers"

5" -hy does -interkill occur and in what types of lakes do they occur in and what happens to the fish

populations in the lake>6 -interkill occurs in small$ shallow lakes with are ano7ic during ice6cover" 0he lakes go ano7ic

during ice6cover because of decomposition and because they have a small hypolimnion" ,ish

need to deal with the ano7ic conditions and some species of fish will leave the lake$ move

towards inlet$ move towards the ice/water interface$ and/or breathe bubbles" #lso smaller fish can be less tolerant of these conditions"

9" escribe what #N! and how you determine it"

6 #N! is a measure of the lakes water?s capacity to buffer ph change" #N! is determined be

titrating a water sample with a strong acid and monitoring the change in p8" -hen 8 is added$

it is first taken up by carbonate$ then by bicarbonate" #t this stage the p8 is appro7imately 9"Q"-hen more acid is added$ all the carbonate and bicarbonate is converted to carbonic acid and the

buffering capacity is e7hausted" 0hen the p8 is directly proportional to the amount of acid added

') 8ow do dam releases affect nutrients in the water downstream> 8ow would this affect the downstream

biota>0he answer to this question depends upon from where in the reservoir the water is released" If water is releasedfrom the hypolimnion$ downstream will be inundated with water with low amounts of dissolved o7ygen$ high

amounts of organic carbon in the form of dead and decomposing organisms$ high amounts of iron6phosphate

aggregates out of which phosphate would precipitate once it was released into the river where there are more

o7ic conditions$ ammonium$ which would undergo nitrification once it was released into the o7ic river" 0herelease of such nutrients would spur growth in the river$ causing algal blooms" 0his would allow less light to

come through the water column and negatively affect the growth of rooted plants and benthic invertebrates" If

water were released from the top of the reservoir$ it would be mostly nutrient6poor$ although high in o7ygen$e7cept in fall turnover$ which would result in pulses of water as described above" 0he mostly nutrient6poor

water the downstream river would be receiving for the maority of the year would eventually cause a shortage of

nutrients to be available to organisms growing downstream$ especially as it got to be later in the summer" 0hehigh amounts of o7ygen would be beneficial for animal growth$ but the low amounts of other nutrients for the

maority of the year would stunt plant growth"

3) 8ow does a fish such as a largemouth bass change its trophic position from hatching to adulthood>-hat are the energetic consequences of these trophic shifts>

-hen fish hatch they have a low trophic levelthey mostly eat .ooplankton$ which puts them about on level 5$

after phytoplankton and .ooplankton" #s they grow into uveniles$ they increase their trophic level and begineating insects or other fishes" 0his puts them another step up on the ladder" ,inally$ they become the piscivores

they remain throughout their lives$ putting them at the very highest trophic level$ e7cept for e7ternal predators

such as people" #s they rise in trophic level$ they gain more energy from their food"

5) 8ow could a cement channeli.ed storm sewer running into a small river affect its functional feeding

groups at the inflow point>0he storm sewer would bring with it a lot of course particulate organic matter$ like dead leaves and the like

these leaves represent a food source of the shredder feeding group" 0he shredder population would theoretically

increase at the inflow point$ which would cause the collector feeding group to increase$ as a result of the high

amounts of fine particulate organic matter being produced by the shredders" 0he increased numbers in thesetwo guilds would cause predators to flock to this area" 8owever$ with this great food source comes other factors

that would have negative effects on the biota at this point" ,or e7ample$ these e7tra dead leaves and such will

not all be able to be eatenthey will decompose$ leading to a possible shortage of o7ygen if the water is notturbulent enough to mi7 up the water at the inflow point" 0his could stress all of the functional feeding groups"


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#nother stress on all feeding groups would be pollution brought in to the river" 8owever$ also brought in would

be nutrients such as phosphorus and nitrogen$ which would have been runoff from people?s lawn fertili.er" 0hiscould cause a bloom in algal populations$ which would be a boon to the scraper guild$ which could then be

eaten by predators" 1ut the storm sewer would also bring in a lot of sediments$ which would smother most

benthic invertebrates$ a maor component of the shredder$ collector$ and scraper guilds" 4verall$ it seems likethe storm sewer would have a total negative effect on the functional feeding groups at the influ7 point in the

stream"

9) Sour local lake is e7periencing chronic e7treme algal blooms" 8ow do you fi7 it>0he first thing to do is to look at nutrient levels in the lake" 0hey will probably be high" If they are$ look for

point sources of nutrient input to the lake$ such as construction sites$ a farm field$ or a sewage treatment plants"4nce identified$ legislation or other measures can be enacted to reduce the pollution from these specific points"

8owever$ there may not be point sources" If phosphorus loading is a component of the problem$ check and see

if there?s any internal loading from an ano7ic hypolimnion" If so there are several bandaid measures one could

take$ like dredging the sediments$ adding chemicals to precipitate out the phosphorus$ aerating the hypolimnion$and such things" 4ne could also take a more ecological approach by restoring wetlands around the edge of the

lake to act as a nutrient sink" 4ne could also manipulate the food web by adding a lot of predatory fisha

trophic cascade would then occurthe big fish would eat the small fish$ the absence of the small fish wouldallow the large .ooplankton to prosper$ which would then eat a lot of algae" #nother ecological approach one

could take would be to attempt to get rooted plants to growthese plants would then take up nutrients whichwould otherwise be used by algae"

'" -hy do managed marshes demonstrate e7tremely different hydroperiods than their natural counterparts>

Name some of the differences between managed and natural marshes observed throughout the course of the

year$ and possible reasons for such patterns"-ater levels for a marsh depend on the time of year$ the ratio of precipitation to evaporation$ and water

sources and drainages" In terms of differences between natural and managed marshes$ it?s been observed

that managed ones generally have a higher baseline water level throughout the year$ and while naturalsystems tend to peak around #pril$ managed systems have ma7imum water levels in #ugust" Fossible

e7planations for this behavior include man6made dams obstructing water flow$ different vegetation and

ecosystem life in managed systems selected for certain species$ or the manipulation of water levels forhuman needs – for e7ample$ draining more water during the hot periods of the summer to match demands"

3" 8ow does man6made channeli.ation of braided rivers affect the biotic communities> +pecifically address

benthic algae and invertebrates$ riparian vegetation$ and fish"1ecause the channeli.ation of rivers essentially changes the R!! numbers$ the various species groups in the

river are affected" 1enthic algae usually increase in abundance because there is clear flowing water coming

down the channel$ which means more light and potential for photosynthesis" If there is a change in waterflow$ some invertebrate species that are dependent on flow at specific times may become less abundant$

while others could change their drifting periods to the wrong time of the year" Riparian plants are likely to

decrease in abundance and diversity because of habitat loss$ and similar results may be seen in fish" ue to

changing habitat and temperature$ fish may be forced to adapt to new conditions or migrate"

5" 8ow do dams affect o7ygen levels downstream> -hat does that do to the organisms in the river$ and whatsort of adaptations may come in handy for such conditions>

If the dam is large enough to build a big reservoir with an ano7ic hypolimnion$ the water released

downstream could have very low o7ygen levels" In terms of the biota$ certain fish can live only with a

certain amount of o7ygen in the water" 4nce a level below 3 mg/= is reached$ essentially no fish can live"0herefore fish that are able to migrate or tolerate low o7ygen conditions may be the only ones to survive"

4ther species like macroinvertibrates would survive if they had other adaptations like siphons or hair to

catch surface air" =arge macrophyte beds would not be able to live right downstream of the dam$ becausethere would be little o7ygen to take up during photorespiration"


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9" Co through a possible scenario for a molecule of carbon working its way through an aquatic system$ startingin a terrestrial leaf that falls into a headwater stream and ending in a top6predator on the food chain"

!arbon starts out in the leaf and falls to the steam in autumn as part of allochthonous nutrient input"

2acroinvertebrates go to work shredding the leaf into smaller pieces$ or fine particulate organic matter "0his ,F42 can be digested outside of bacteria cells and broken down into dissolved organic carbon" ,rom

here$ the carbon may be utili.ed by bacteria and then filtered up to the macro6foodweb$ passing from

.ooplankton to primary predators to secondary predators such as piscivous fishes" #dmittedly$ the

probability of ! going from bacteria to the macroinvertebrates is kind of low (it is thought that cyclingwithin the microfood web is more likely) and the mechanisms are not fully known$ but there is a connection

with outside inputs eventually working up through the foodweb" #n alternative route would be for the,F42 to be consumed by a macroinvertebrate collector$ the macroinvertebrate eaten by a fish and so on up

the food chain"

'"


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0hen$ due to loss of breeding (or refuge) habitat Odecr in macrophytesP decr in .ooplankivores and small fishes decr in piscivores (this process might take many years because larger fishes are long6lived)

3" -hat will effect finishing the planned developments have on =ake -ilsonia and why>Favement (and roof6tops$ etc) is an impervious surface and leads to increased storm runoff which will carry

many pollutants from the factory$ parking lots$ roads and gas station" 0he concrete will keep surface water from

reaching the groundwater recharge points – leading to a drop in groundwater levels"

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