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Nutrient Cycling + Prokaryotes > Hubbard Brook > Flashcards

Hubbard Brook Flashcards

1
Q

How can evapotranspiration be calculated from HB field data of forested watersheds?

A

P = S + ET

ET = P - S

where ET = evapotranspiration
P = precipitation (input)
S = streamflow (output)

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2
Q

What is considered nutrient input in a forested ecosystem like HB, according to Likens and Boorman?

A

precipitation (P) carrying chemicals

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3
Q

What is considered nutrient output in a forested ecosystem like HB, according to Likens and Boorman?

A

streamflow chemicals (S)

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4
Q

What is the mathematical relationship between precipitation and streamflow at HB?

A

P = ET + S

as P increases, S also increases (linear)

ET will not change over time because the buffer is maintained, the amount retained remains stable

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5
Q

What is the main source of silica at HB?

A

weathering of rocks

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6
Q

What is the fate of nitrate (NO3-) from precipitation during summer at HB?

A
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7
Q

Are nutrients lost evenly throughout the year in the streamflow at HB? explain

A

no

there’s a peak in the spring with the snowmelt (S > P) and a decline in the summer when there’s more water taken up by plants (S decreases)

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8
Q

What is the impact of clear cutting on mineral nitrogen?

A

huge loss of NO3- from leaching

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9
Q

How does Douglas-fir vary in nutrient budgets for Ca, Mg, K? explain

A
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10
Q

define mixotrophy

A

when organisms are both photosynthesizers and hetertrophs

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11
Q

Is mixotrophy important in Mirror Lake? where, why?

A

yes!! because they can photosynthesize and consume other organisms

common at surface in summer when lots of light
common throughout water column when less light

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12
Q

What kind(s) of cyanobacteria are found in Mirror Lake?

A

anabaena
chroococcus
merismopedia

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13
Q

Why are the cyanobacteria(s) found at Mirror Lake important?

A

because they are mixotrophs

Anabaena and Chroococcus can also fix N2

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14
Q

Who were the major authors from the HB models?

A

Likens and Bormann

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15
Q

What years did the HB study run?

A

1963-2013

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16
Q

What were the major papers published from the HB study?

A

Likens, G.E. (2013). Biogeochemistry of a Forested Ecosystem

Bormann, F.H., Likens, G.E. (1979). Pattern and process in a forested ecosystem

Likens, G.E. (1985). An ecosystem approach to aquatic ecology: Mirror Lake and its environment

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17
Q

What was the main lake involved in the HB model ecosystem study?

A

Mirror Lake

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18
Q

According to Likens and Bormann, what moves the inputs and outputs of ecosystems?

A

meteorlogic (atmospheric), geologic, and biologic drivers

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19
Q

in the conceptual model for HB, what are the inputs to an ecosystem?

A

meteorlogic (atmospheric) inputs

particulates in the air and gaseous particles

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20
Q

in the conceptual model for HB, what components are part of the intrasystem cycle of an ecosystem?

A

nutrients that have no prominent gaseous phase and cannot leave the boundaries of the ecosystem

organic compartment:
- living plant mass
- animal biomass (herbivore, carnivore, detritivore, omnivore)
- dead biomass (litter, dead animals)

available nutrients:
- on exchange sites
- in soil

primary and secondary minerals:
- mineral (rocks)
- precipitation

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21
Q

How are atmospheric inputs connected with the organic component of an ecosystem in the conceptual model?

A

atmospheric inputs are taken up by living organisms

and organisms release gases into the atmosphere

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22
Q

How are atmospheric inputs connected with the available nutrients of an ecosystem in the conceptual model?

A

atmospheric inputs are either wet or dry

wet: precipitation (snow, rain)
dry: ash, dust

are deposited onto plants or soil surfaces

organisms and soil release gases into the atmosphere

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23
Q

How are minerals connected with the available nutrients of an ecosystem in the conceptual model?

A

minerals can be released and become available through weathering of rocks

available nutrients can form secondary minerals and add to the mineral component

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24
Q

How are the organic components connected with the available nutrients of an ecosystem in the conceptual model?

A

living organisms can immobilize (uptake) forms of nutrients

living organisms can mineralize nutrients in the soil, leaching of nutrients, throughfall, streamflow, exudation of nutrients to enter soil

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25
Q

In the conceptual model, what represents P in a watershed ecosystem?

A

P = precipitation (inputs)

the atmospheric (wet and dry deposition/precipitation), geologic, and biologic inputs

majorly precipitation

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26
Q

In the conceptual model, what represents S in a watershed ecosystem?

A

S = streamflow (outputs)

the atmospheric, geologic, and biologic outputs

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27
Q

In the conceptual model, what represents ET in a watershed ecosystem?

A

ET = evapotranspiration

the biological release of gases

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28
Q

Where is the HB watershed?

A

New Hampshire, USA

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29
Q

How many watersheds are in the HB?

A

6

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30
Q

Describe the geographic region surrounding the HB watershed experiment

A

In New Hampshire, USA

the watershed is proximal to Mt Cushman (977m) and Mt Kineo (1015m) all with rivers/streams running down to Mirror Lake (213m)

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31
Q

Which watershed at HB was clearcut? when?

A

in 1966-67, watershed 2 was clearcut

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32
Q

Which watershed at HB was the control?

A

watershed 6

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33
Q

What was the unit of study for the HB?

A

watersheds

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34
Q

What was the scientific approach to studying the hydrology of HB?

A

small watershed approach

devices (buckets, funnels) in multiple locations used to measure the inputs (precipitation in mm/yr) and concentrations of chemicals sampled

and weirs at independent streams were used to measure the outputs (streamflow in mm/yr) and concentrations of chemicals sampled

ET = P - S

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35
Q

Generally, how will the volume of water delivered through streamflow vary?

A

daily, seasonally, annually

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36
Q

describe the average hydrologic budget (water volume for P, S, ET) for watershed 6 measured from 1963-2009

A

P was highest at 1400 mm/yr

S was mid btw 800-1000 mm/yr

ET was lowest ~500 mm/yr

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37
Q

P was measured at 1400 mm/yr in watershed 6, how does this compare to volume of input in Victoria? Kamloops? Tofino?

A

pretty high

Victoria ~

Kamloops very low

Tofino very high ~3000 mm/yr

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38
Q

What part of Vancouver Island does watershed 6’s P compare to?

A

Campbell River

~1400 mm/yr

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39
Q

Which two components of measuring hydrology in HB are correlated when looking annually?

A

P and S

with increased P, S increased

but P always higher than S

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40
Q

When looking annually, how does ET compare to P and S in watershed 6? is it correlated/related?

A

ET is not correlated with P and S and does not follow the same trend

ET remains fairly constant because P - S = ET

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41
Q

when looking monthly, how do P and S trend in watershed 6?

A

P remains fairly constant with little seasonal variation

S increases in winter months because uptake of water by plants slows down during these months

S significantly increases and surpasses P in the spring because snowmelt

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42
Q

Why is precipitation higher than streamflow in watershed 6 in most months?

A

most of the year, plants are taking up water and photosynthesis is

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43
Q

Which variables, when annual ppt is plotted against annual streamflow or ET has significant correlation? what does this mean for the ecosystem?

A

precipitation and streamflow are significantly positively correlated

this means that the ecosystem is limited by precipitation

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44
Q

Based on the standard errors of the mean for the 4 watersheds’ P, S, and ET values, is the small watershed method accurate?

A

yes, the standard errors were between 0.45-1.30

high confidence in the values

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45
Q

Why is streamflow higher than P in the Spring?

A

snowmelt increases with warming weather = huge output of water flow in the streams

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46
Q

Why is there a peak in streamflow in the Fall months?

A

In the Fall, the uptake of water by plants is decreasing, so the amount of water leaving the watershed will be higher

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47
Q

In watershed 6, are the concentrations of Si, Ca, sulfate (SO4^2-) higher in P or S? why?

A

higher in S because Si, Ca, and Sulfate all have mineral inputs (sedimentary BGC cycles)

they do not enter the system from the precipitation, but from the rocks/minerals

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48
Q

In watershed 6, is nitrate (NO3-) higher in P or S? why?

A

higher in P

because Nitrogen has a gaseous BGC cycle and the major input of N is from the atmosphere

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49
Q

How do the minerals measured in watershed 6 (Ca, Sulfate, Nitrate, silica) compare to each other in their concentrations in P and S?

A

Ca, SO4^2-, and Si are in higher concentrations in the streamflow because their inputs are from sedimentary cycles - mineral/rock weathering

whereas,

nitrate (NO3-) is higher in P because its input is from the gaseous cycle - atmospheric input

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50
Q

What did the HB study of H+ ions in precipitation show? how is this related to acid rain?

A

because acid rain was a huge problem in the 1970s, and was addressed by decreasing/regulating use of sulfur in human activities,

[H+] ions in precipitation decreased over periods of years as precipitation became less acidic

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51
Q

How was the issue of acid rain addressed?

A

regulating the use of sulfur and NOx for human activities

H+ ions in P decreased over years and the HB study showed this

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52
Q

What was causing the problematic acid rain?

A

emissions of sulfur (SO2) and nitrogen based chemicals (NOx) from the US

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53
Q

How did HB show ecosystem recovery as sulfur and nitrogen-based chemicals were becoming more regulated in the US?

A

Watershed 6 showed recovery as the concentration of basic cations increased in the streamwater (S)

base cations have buffering capacities to neutralize acidic ions

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54
Q

How does acid rain harm watershed ecosystems? how can we chemically measure that this is happening?

A

as H+ ions increase in the P inputs, the watershed system loses it’s capacity to buffer acidic ions = less base ions in S

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55
Q

What did the HB study find about the affect of acid rain on cation concentrations in P and S in watershed 6?

A

Ca, Mg, K, Na were higher in the stream water than in precipitation, but were all decreasing in [] in the streamflow over years

this means that less cations are present in the streamflow, lowering the capacity of the system to buffer the acidity being inputted

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56
Q

Why are the units to measure concentration of Ca, K, Mg, Na different than for measuring P and S?

A

the units to measure the nutrients need to account for some nutrients have single charges or double charges

ex. Na+ vs. Ca2+

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57
Q

In watershed 6, why does the H+ ion decrease in P but not in S over time? why does H+ decrease over time in P? (over years)

A

As NOx and SO2 emissions are regulated and decreased, the amount of H+ ions in the P will decrease

H+ is constant in the streamflow, this means that more is being retained in the system than lost = H+ is buffered within the system

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58
Q

What is the difference between ammonium and nitrate in watershed 6 P and S? why is there a difference? (over years)

A

Ammonium in P is higher and is stable in S = ammonium is positively charged so it adheres tightly to clay particles within the system is harder to lose in the S

nitrate’s P and S overlap and follow the same decreasing trendline:
nitrate is negatively charged and is repelled by clay particles, so it’s easier to be lost in the S

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59
Q

How does sulfate compare to nitrate and ammonium in terms of P and S for watershed 6 (over years)?

A

Sulfate is much higher in the stream flow than in the precipitation

this is because S has both a sedimentary and gaseous cycle, whereas N (nitrate and ammonium) are both gaseous only

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60
Q

How can we tell that the system is acting as a buffer for acid rain in watershed 6?

A

looking monthly

the concentration of H+ is higher in precipitation than in the streamflow which has stable concentration

stable concentration of H+ in the stream flow means that more of the H+ coming in from P is being retained by the system (not lost in S) = the system is buffering the H+ ions

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61
Q

What is throughfall?

A

precipitation that falls through plant leaves

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62
Q

What is stemflow?

A

precipitation that falls along plant stems

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63
Q

how is the net change of solutes in precipitation calculated for watershed 6?

A

precipitation under canopy - precipitation over canopy = net change

64
Q

What does the net change of solutes in precipitation mean for the biology of watershed 6? Use calcium as an example

A

the net change for the method that included stemflow in the under canopy measurements was significantly larger than that for the method that only considered throughfall

so, stemflow is enriched with nutrients and acts as an important input of nutrients in the soil

ex. Calcium

Calcium was much higher under the canopy when both throughfall and stemflow were considered (0.67 v. 0.41) = higher net change in Calcium overall (0.45 v. 0.09)

so calcium increases from the stemflow P

65
Q

What are some examples of organisms on tree stems that can contribute to the nutrient input in stemflow?

A

moss and lichen have Ca, N, and some N2 fixing bacteria (lichen)

66
Q

What was n for watershed 6?

A

46 years

study ran from 2009-1963 = 46 years

67
Q

Which key nutrients had mean net losses from watershed 6 over 46 years?

A

sulfate
Dissolved organic carbon
dissolved silica

68
Q

Which key nutrients had mean net gains from watershed 6 over 46 years?

A

ammonium
nitrate
phosphate

69
Q

Are nutrients lost or gained from the system when P > S?

A

gained (less in streamflow)

70
Q

Are nutrients lost or gained from the system when P < S?

A

lost (more in streamflow)

71
Q

why are there peaks of losses of key nutrients from watershed 6 in the spring and fall?

A

this is driven by the hydrologic cycle

during spring there’s the snowmelt and during fall there’s more precipitation than plants are taking up

72
Q

Overall, there’s a monthly average loss or gain of cations in watershed 6 over the 46 years?

A

losses of Ca, Mg, Na, Al, and Si

= higher in S than P

73
Q

Overall, there’s a monthly average loss or gain of H+, ammonium, and phosphate in watershed 6 over the 46 years?

A

gain

higher in P than S

74
Q

Why are the average fluxes of ammonium, phosphate, and H+ higher in P than S?

A

these nutrients are being retained in the system

some of the differences are significant, but not all

75
Q

why did K, sulfate, chloride and dissolved organic carbon have seasonal variation in S but not P in watershed 6 when looking at monthly averages for 46 years?

A

they follow the hydrologic cycle as well, so the increase of water flowing out of a system in spring and fall due to snowmelt and lack of water intake by plants increases the loss of these nutrients

76
Q

what does the average flux of nitrate in watershed 6 (over 46 years, looking at monthly averages) tell us?

A

nitrate has seasonal variations in loss in streamflow with

peak in april with high water flow

dramatic dip in summer months to the fall = nitrate is tightly regulated because it is needed for photosynthesis

77
Q

How did the concentration of calcium change in the HB ecosystem from 1963-69 to 1987-92?

A

aboveground biomass increased

below ground biomass increased

throughfall and stemflow decreased

leaf litter remained the same

78
Q

why is stored calcium (in living biomass) higher in 1987-92 than in 1964-69?

A

stored calcium in living biomass increased because the system improved at retaining Ca from the stemflow and throughfall

stemflow and throughfall decreased over time - this calcium is being stored in biomass instead of lost in streamflow

78
Q

How did the concentration of sulfur change in the HB ecosystem from 1964-69 to 1993-98? what does this mean?

A

higher concentration in above and below ground biomass

decrease in stemflow/through fall and decreased P input

this means concentrations of S in the atmosphere decreased (emissions reduced) and more sulfur is being retained by the system than lost in streamflow outputs

78
Q

How can NPP be an indicator of ecosystem recovery from acid rain?

A

if nitrogen is being retained by a system, NPP will increase, and the ability to retain and uptake NO3- instead of it being leached in the streamflow means that there’s more plants photosynthesizing

78
Q

What did the second HB study look at?

A

how BGC cycles are effected by clear cuts (long term disturbances)

78
Q

Which watershed was used as the experiment in the second model?

A

watershed 2 was clearcut

78
Q

What is the overall trend of nitrogen retention in HB?

A

in every season, there’s a decrease in the years between 1960-1985ish or so

there was overall, less nitrogen being retained annually in those years, but has since increased (due to increased buffering capacity of system and decreased S and NO emissions in P) to more seasonal variation than annual

varied in fall, spring and winter, stable in summer

79
Q

What is ecosystem succession? How was the second model based on this?

A

it’s the gradual succession of plant growth after a major disturbance over many years

a disturbance was induced on watershed 2, it was clear cut, then the scientists studied how it rebounded

80
Q

What are the 4 stages of forest succession?

A

disturbance - watershed 2 clearcut

  1. reorganization phase - new plant species begin to grow
  2. aggradation phase -
  3. transition phase - dominant species begin to replace pioneer species
  4. steady state phase - decomposition = production (production has slowed down to the rate of decomposition) -mature forest
81
Q

How does decomposition compare to production during the reorganization phase?

A

D&raquo_space; P

82
Q

How does decomposition compare to production during the aggradation phase?

A

D &laquo_space;P

83
Q

How does decomposition compare to production during the transition phase?

A

D < P

84
Q

How does decomposition compare to production during the steady state phase?

A

D = P

85
Q

How were the succession phase boundaries measured?

A

by determining tree community composition

defining the forest structure by determining importance values of trees

86
Q

What are importance values? how are they calculated?

A

the weight of contribution of trees to the forest community structure

calculated by measuring

Diameter at Breast Height (DBH)
frequency (# of a single species/total trees)
density (# single species species/ rn^2)

87
Q

What method was used or could be used to measure importance values of trees?

A

Transects of different trees at different elevations

88
Q

What were the types of trees in this HB study?

A

Large DBH:
Sugar maple (Acer saccharum)
Yellow birch (Betula alleghamensis)
Beech (Fagus grandifolia)

Paper birch
balsam fir
red spruce
mountain maple
striped maple
mountain ash

89
Q

Which trees had highest importance values overall and therefore dominate the forest?

A

Sugar maple and beech mostly but
also yellow birch

their values decrease at high elevations

90
Q

Which species were more dominant at higher elevations (still with low IV)?

A

Paper birch
balsam fir
red spruce
mountain maple
striped maple
mountain ash

91
Q

what is unique about American Beech’s leaves?

A

they do not lose their browning leaves until the following season - they have incomplete abscission

92
Q

What does looking at the flow of energy (carbon) in the control (watershed 6) show us for what we would expect in a healthy, uncut ecosystem?

A

High carbon input (high NPP) and very low carbon output

carbon is highly retained in the system

93
Q

How did the clearcut effect P, S, and ET in watershed 2 compared to watershed 6? explain

A

Precipitation didn’t change (they’re in the same geographic region)

Streamflow rapidly increased in W2 (way above W6)

ET rapidly decreased in W2 compared to W6

S increase in W2 would be caused by less plants present to uptake water entering as P

ET decreases for the same reason, there’s nothing there to retain the water

94
Q

How did the clearcut effect Ca, K, and nitrate in S in watershed 2 compared to watershed 6? explain. Which of the 3 was the most significant loss?

A

Ca, K, and nitrate all increased significantly in S in W2 and remained relatively constant in W6

with no plants present to assimilate these nutrients, they would easily leach out of the system through streamflow

nitrate was lost most significantly, NO3- is very water soluble and easily lost

95
Q

which nutrient was most significantly lost from W2 after the clearcut?

A

Nitrate

96
Q

What explains this massive loss of nitrate from W2 after the clearcut? which succession phase does this occur in?

A

Microorganisms are continuing to decompose OM and mineralize ammonium and convert it into nitrate, but now there’s no plants present to uptake the nitrate and because it’s water soluble, it’s easily lost

occurs in the reorganization phase

97
Q

Approximately how long was the reorganization phase?

A

~6 years to resemble something like the prior forest

98
Q

How did they determine the forest was recovering from the clearcut?

A

after ~6 years of increased losses of Ca, K, nitrate and OM in streamwater

the streamwater started showing decreasing concentrations of these = more were being retained

99
Q

what did they find in terms of forest community structure after 20 years?

A

groundcover (herbs, shrubs) and saplings decreased significantly and trees increased significantly

a slow transition of components as trees replace one another

ex. Prunus replaced by Betula replaced eventually by Acer saccharum (sugar maple) and Fagus grandifolia (beech)

100
Q

How does GPP compare in an old-growth Douglas-fir forest to an eastern deciduous forest (like HB)?

A

DF > eastern

101
Q

How does NPP compare in an old-growth Douglas-fir forest to an eastern deciduous forest (like HB)?

A

similar NPP but eastern slightly higher

102
Q

How does net ecosystem production compare in an old-growth Douglas-fir forest to an eastern deciduous forest (like HB)?

A

NEP = GPP - ecosystem respiration

equivalent NEP even though different contributors and very different GPP

high GPP - high ecosystem respiration = low NEP (DF)

low GPP - low ER = low NEP (eastern)

103
Q

How does overall ecosystem productivity (NEP/GPP) compare in an old-growth Douglas-fir forest to an eastern deciduous forest (like HB)?

A

eastern deciduous forests are more productive overall than DF

104
Q

Why would eastern deciduous forests have lower maintenance efficiency and autotrophic respiration than an old-growth DF forest?

A

DF forests are mostly coniferous trees that do not lose leaves seasonally, whereas deciduous trees drop leaves seasonally = less respiration

105
Q

How do P, S, and ET compare in an old-growth Douglas-fir forest to an eastern deciduous forest (like HB)?

A

P is much higher in DF, so S and ET are both going to be higher (there’s just more water moving through the system)

but

ET % is higher in deciduous than in DF (48% in deciduous v. 34% in DF)

106
Q

How does net loss of Ca, Mg, and K compare in an old-growth Douglas-fir forest to an eastern deciduous forest (like HB)?

A

DF has much higher net losses of these nutrients than ED

107
Q

How does the total loss of nitrogen in a DF forest that has been burned by a wildfire compare to an undisturbed one?

A

undisturbed has no loss, actually accumulates

wildfire DF forest has significant loss (736 kg per ha per yr) via volatilization and leaching

108
Q

which lake did Likens and Bormann study for the HB experiments?

A

Mirror Lake, downstream from the watersheds

109
Q

why did they study a lake ecosystem?

A

because lakes receive inputs from terrestrial systems

110
Q

In lakes, how are O2 and CO2 affected with depth?

A

dissolved O2 decreases and CO2 increases

111
Q

which nutrients were very high in the lake during Spring months? why?

A

dissolved silica and nitrate

because snowmelt, increased streamflow input carrying these nutrients from the terrestrial systems

112
Q

What method is used to study bacterial populations in lake water columns?

A

there’s a few: microscopy, hemacytometer, or petroffauser method

113
Q

Which method to study bacterial populations did they use for mirror lake?

A

Petroffhauser method - a smaller volume of liquid
and DAPI (fluoro dye) to count live cells

114
Q

What did they find for bacterial populations in mirror lake?

A

the decrease of O2 with depth is correlated to increase of bacterial uptake of O2

bacteria concentrations increase with depth in summer but remain constant in winter

115
Q

How did phytoplankton biomass vary seasonally in mirror lake?

A

decreased in fall/winter with decreasing T

increased in spring/summer with increasing temperature

116
Q

What are the 3 important bacteria in Mirror lake? Which is most common?

A

all 3 are cyanobacteria

Anabena
Chroococcus (most common)
Merismopedia (least common)

117
Q

What depths are Anabena most common in Mirror Lake in summer and winter?

A

Summer most common at 3m (shallow)

None in winter

118
Q

What depths are Chroococcus most common in Mirror Lake in summer and winter?

A

Summer most common at 3m, but found at fairly high [] at all depths

None in winter

119
Q

What depths are Merismopedia most common in Mirror Lake in summer and winter?

A

Summer most common at 6m (deeper)

none in winter

120
Q

What is unique abut Anabena and Chroococcus and lacking in Merismopedia?

A

Anabena and Chroococcus (especially C) are N2 fixers

Merismopedia doesn’t fix N2

121
Q

Describe Chroococcus

A

it’s a unicellular cyanobacteria that contains nitrogenase for fixing N2 at night and does oxygenic photosynthesis with O2 and light

it is the most abundant N2 fixer in Mirror Lake

122
Q

describe Anabaena

A

it’s a filamentous colonial cyanobacteria that contains a heterocyst for fixing N2

less abundant in Mirror Lake

very efficient N2 fixing and photosynthesis because they can occur at the same time unlike Chroococcus

123
Q

Describe Merismopedia

A

polysaccharides surround cell walls to keep a bunch of cells together in a checkerboard like fashion

does not fix N2

124
Q

What makes Anabaena more efficient at N2 fixing and photosynthesis than Chroococcus?

A

Anabaena has a heterocyst that uses energy produced by photosynthesis to conduct N2 fixation - they occur simultaneously

whereas

Chroococcus does not have a separate domain for the two processes so N2 fixation must occur at night so photosynthesis can occur during the day

125
Q

Describe the succession of phytoplankton populations in Mirror Lake over a year (seasonal)

A

early summer: diatoms and Chrysophyceae (Dinobryon)

late summer: Cyanophyceae (cyanobacteria) and Peridineae (dinoflagellates)

Winter: Cryptophyta and Chrysophyceae (Dinobryon)

126
Q

Which of the dominant phytoplankton found in each season are mixotrophs?

A

Chrysophyceae (Dinobryon)
Peridineae (Dinoflagellates)
Cryptophyta

127
Q

Why do mixotrophs exist at both the water surface during the summer and throughout the water column in the winter?

A

Because they can photosynthesize and consume other organisms for energy

128
Q

What is the cell wall of cyanobacteria made of?

A

peptidoglycan

129
Q

Explain the C14 fixation by bacteria study

A

in a microcosm, 14CO2 is added to a sample of lake water and incubated

then filtered at 0.45 um

cells stick to filter and liquid scintillation can be used to measure 14C

130
Q

What month was daytime 14C fixation by phytoplankton the highest?

A

June-July - photosynthesis is at its peak so CO2 fixation is highest

131
Q

what is the seston in an aquatic system?

A

what is suspended in the water column

132
Q

What contributes the most to the mean annual standing stock in the seston of Mirror Lake?

A

detritus

133
Q

Do zooplankton or phytoplankton contribute the more to the mean annual standing stock in the seston of Mirror Lake? How does this compare to terrestrial ecosystems?

A

phytoplankton in aquatic

in terrestrial, zooplankton would contribute more

134
Q

Describe the microbial loop in the seston of Mirror Lake

A
135
Q

What contributes the most to mean annual standing stock in the benthic zone of Mirror lake? where in the benthic zone are they most active?

A

bacteria

in the sediment

136
Q

What is the input for the benthos of Mirror lake?

A

the detritus from the seston zone

137
Q

What contributes the most to the outputs of organic carbon from Mirror lake?

A

phytoplankton then zooplankton

138
Q

Why does a short term small-scale disturbance (such as clear cutting W2 at HB) result in such dramatic changes to nutrient dynamics?

A

because of the role of soil bacteria

139
Q

What is a consequence of mass nitrate leaching from stream systems into lakes?

A

eutrophication

140
Q

T or F: over time, after a disturbance like clear cutting, forests can recover

A

true

141
Q

What is the main reason there was high loss of Ca2+ in the forested ecosystem at HB?

A

the SO2 and NOx emissions

142
Q

What results from loss of Ca2+ in forested ecosystems?

A

acidification (increased H+ ions)

143
Q

What was the UN convention that addressed the SO2 and NOx emissions/acid rain?

A

Convention on long-range transboundary air pollution in 1979
- SO2 in 1985
- NOx in 1988

HB helped contribute to this understanding

144
Q

What was the UN convention that addressed CFCs and the ozone depletion?

A

Vienna convention on protection of the ozone layer (1985)

Montreal Protocol on Substances (CFCs) that deplete the ozone layer (1987)

145
Q

What did long term studies on ozone depletion 23 years after the Montreal Protocol (1987) show?

A

that over time, with decreased CFC emissions, the ozone layer could replenish

146
Q

What makes getting control over the emissions/responses of CO2, CH4, and N2O challenging?

A

they are all driven by microbial processes that we don’t fully understand

147
Q

What microbial organisms contribute mostly to CO2 in the atmosphere?

A

cyanobacteria in aquatic and bacteria in soil

148
Q

What microbial organisms contribute mostly to CH4 in the atmosphere?

A

methanogens (Archaea)

methanotrophs (bacteria)

149
Q

Are methanogens Archaea or Bacteria?

A

Archaea

150
Q

What microbial organisms contribute mostly to N2O in the atmosphere?

A

nitrifiers (proteobacteria, thaumarchaea, Brocadia)

denitrifiers (proteobacteria(

151
Q
A

Nutrient Cycling + Prokaryotes (13 decks)

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