EEMB 148: Midterm 2

what are the two sources of phosphorus in rivers?

1. drainage basin (runoff)

2. some anthropogenic (i.e. insecticides, pesticides, fertilizer…)

what is the one additional source of phosphorus in rivers?

pacific salmon

• live in the ocean, breed in freshwater (less predators, but less food)

• mass breeding migrations brings organic phosphorus into rivers

• death of adult salmon releases additional nitrogen and phosphorus into the system

  • helps to supply a nutrient poor system

• promotes algae growth → feeds insects → feeds juvenile fish

what are the two major forms of phosphorus in a river?

• dissolved inorganic phosphorus (PO43-)

  • uptake by autotrophs and bacteria

  • soluble reactive phosphorus (SRP)

    • able to pass through the cell membrane

• organic phosphorus (RNA, DNA, etc.)

  • phosphatase enzyme (extracellular release)

  • index of phosphorus limitation (high conc. of enzymes = P limited)

is phosphorus a limiting nutrient in rivers? how does that effect the way bacteria and algae interact with phosphorus?

Yes. P is usually the primary limiting nutrient in freshwater (limits primary production and decomposition)

• bacteria can efficiently uptake phosphorus at low concentrations, but have little storage

• algae rapidly uptake phosphorus at high concentrations and can store it

how do large rivers complicate the amount of phosphorus present?

inorganic turbidity - phosphorus is adsorbed (sticks) to suspended sediments

what does sediment, light, phosphorus, and algal production look like in a turbid river?

high sediment; low light; high phosphorus; low algal production

what does sediment, light, phosphorus, and algal production look like in a clear river?

low sediment; high light; low phosphorus; low algal production

how does sediment, light, phosphorus, and algal production change where turbid and clear rivers mix?

phosphorus is able to desorb from the sediment (due to change in concentration gradient)

• phosphorus become SRP which, in combination with less turbidity, can be used by algae in the river

• results in algal blooms (river-reservoir interface)

what is the nutrient spiraling concept? what does it measure?

nutrients are moved downstream (TRANSPORT) and processed by the organisms in a river (CYCLED)

• this combination of transport and cycling leads to SPIRALS moving down a river

spirals allow us to measure the retentiveness of a river

what is the general concept behind nutrient spiraling?

the slower the downstream movement, the more times an atom can be utilized (fuels production)

what is the spiraling length and how is it calculated?

spiraling length: the average distance traveled by a nutrient atom during one complete cycle

• product of downstream velocity and time

S = V * T

• S = spiraling length; V = velocity; T = time for one cycle

what are the two implications based on the spiraling length equation?

1. increase the velocity = longer spiraling length (moves downstream faster)

2. decrease the time = shorter spiraling length (moves downstream slower)

how do we measure nutrient deposition?

S = Sw + Sb

• Sw = spiraling length in water (uptake length)

• Sb = spiraling length in biota

what is the “in-theory” equation for Sw and how is it actually measured?

in-theory: Sw = Vw * Tw

in practice: plot flux versus distance of radioactive tracer

• Fw (flux) = mass/time (g/sec)

what is kI and what does a larger kI indicate?

kI = slope of decline in flux with distance

• larger kI = greater rate of decline = steeper slope

  • indicates MORE uptake and SHORTER spiraling length

what is the rearranged equation for spiraling length in water? what are the two major outcomes from that rearrangement?

Sw = Fw / U

• Fw = flux rate

• U = uptake rate

increased Fw = increased spiraling length

increased U = decreased spiraling length

what is the “in-theory” equation for Sb and how is it actually measured?

in-theory: Sb = Vb * Tb

in practice: measure the loss of a label (sample over time)

what is kb and what does a larger kb indicate?

kb = slope of decline in flux with time

• larger kb= greater rate of decline = steeper slope

  • indicates MORE uptake and SHORTER spiraling length

how do you measure Vb?

Fb = Vb * Nb

• Fb = flux rate; Vb = average velocity of biota; Nb = concentration

what is the rearranged equation for spiraling length in biota? what is the major outcome from that rearrangement?

Sb = Vb / kb

increase in biota = decreased spiraling length

which value has a larger affect on spiraling length?

the spiraling length in water

what are the four factors that affect spiraling length?

1. stream geomorphology

2. discharge

3. algal and bacterial biomass / growth rate

4. consumers

how does stream geomorphology affect spiraling length?

impacts adsorption by sediment and downstream trends (typically high to low retentiveness)

• sand = travels long

• course sediment = travels short

• lots of organics = travels short

how does discharge affect spiraling length?

low flow = high uptake = high retentiveness = travels long

high flow = low uptake = high flux = ravels short

how does algal and bacterial biomass affect spiraling length?

lots of algae = increases uptake = decreases flux = travels short

lots of bacteria = increases uptake = decreases flux = travels short

how do consumers affect spiraling length?

sedimentary consumers = stays in one place = travels short

mobile consumer = decreases retention = travels long

what are the three size classifications for matter in a river?

• CPOM

  • > 1mm, slowest velocity, most from leaf fall

• FPOM

  • <1 mm to >0.45 um, intermediate velocity, most from soil organic matter

• DOM

  • < 0.45 um, fastest velocity, most from leaching of soil/leaves, dominant form of organic matter

what is labile organic matter?

• rapidly degraded

• simple molecules (proteins, amino acids, fats, sugar, carbohydrates)

• low C:N ratio

• small fraction of organic matter

what is refractory organic matter?

• slowly degraded

• complex molecules (cellulose, lignin, organic acids)

• high C:N ratio

• large fraction of organic matter

what is an allochthonous source?

carbon fixed OUTSIDE the stream

• leaching of DOM, erosion of POM

• pulsed inputs (fall and early spring due to falling of leaves and snow/floods)

• refractory

• fuels respiration

• bacteria and fungi colonize leaves

what kind of food chain is associated with an allochthonous source?

detrital food chain - donor control

• bottom up effects

• increased leaves → increased bacteria/fungi → increased detritivores → increased fish

• most macrophytes enter via detrital food web

what is an autochthonous source?

carbon fixed INSIDE the stream

• primary production of algae and macrophytes

• POM and DOM

• importance of light (canopy cover)

• pulsed inputs (early spring, late fall)

• labile

what is the order of the lability index?

periphyton > macrophytes > herbs vegetation > woody vegetation

what kind of food chain is associated with an autochthonous source?

grazing food chain

• top down effects

• increased fish → decreased grazers → increased algae

what are the two assumptions of the RCC created by Vannote et al. in 1980?

1. a gradient of physical conditions exist from headwaters to mouth

2. organism distribution is determined by organic inputs and processing of organic inputs by upstream organisms

what are the two predictions of the RCC created by Vannote et al. in 1980?

1. the relative importance of allochthonous, autochthonous, and downstream transport as sources of organic energy

2. the community composition of heterotrophs based on mechanisms to harvest organic matter

what does the RCC predict the characteristics of a head water to be?

physical: small, forested, low light, cold, low turbidity, low velocity

energy: allochthonous, P/R < 1

biota: shredders and collectors (mostly filter feeders)

fish: fusiform, cold adapted, feed on invertebrates

what does the RCC predict the characteristics of a mid water to be?

physical: intermediate size, open canopy, intermediate light, warmer, intermediate turbidity, intermediate velocity

energy: autochthonous, P/R > 1

biota: grazers and collectors (equal filter and deposit feeders)

fish: laterally compressed, variable temperature adapted, feeds on everything

what does the RCC predict the characteristics of a tail water to be?

physical: large, no canopy, high light, warmest, high turbidity, high velocity

energy: downstream transport, P/R < 1

biota: collectors (mostly deposit feeders)

fish: dorsoventrally compressed, warm adapted, fusiform filter feeding fish

what are the three general patterns predicted by the RCC?

1. water temperature increases downstream

2. particle size decreases downstream

3. ratio of FPOM / CPOM increases from head waters to tail waters

in the carbon budget approach, what form of carbon input dominates in most rivers?

allochthonous inputs

why are desert streams, some springs, slow rivers, and rivers with extensive floodplains exceptions to the idea that allochthonous inputs generally dominate?

• desert streams: no surrounding vegetation

• some springs: clear water, no particulates, light penetrates all the way down

• slow rivers: accumulates organic matter and nutrients, high light and sedimentation settling on the bottom allows for the phytoplankton populations to persist

• rivers with extensive floodplains: sediment drops, high nutrients combined with high light

what are the three limitations of the carbon budget approach?

1. no distinction between labile and refractory organic matter

2. indicates total input and output of organic matter, but NOT how much is useful

3. most organic matter transport is highly refractory

what is the general carbon budget percentages?

25% of carbon entering rivers is processed in the system

25% of carbon is stored as sediment

50% is transported to the oceans

what are the two main ways that organic matter can enter the food chain?

organisms (bacteria, fungi)

invertebrates (shredders, gougers)

what are the four stages of CPOM breakdown?

leaf fall / wetting → microbial colonization → invertebrate colonization → conversion to FPOM

what is leaching in CPOM breakdown? how much dry mass is lost in this step?

leaching: all soluble materials dissolve

• typically, the first 24 hours

• 25% dry mass lost

what is mineralization in CPOM breakdown? how much dry mass is lost in this step?

mineralization: bacteria and fungi take dead organic and convert it into living

• increases the nitrogen content

• about 10 days

• 50% dry mass lost

what is fragmentation in CPOM breakdown? how much dry mass is lost in this step?

fragmentation: ate by organisms

• fully broken down / gone in about 100 to 250 days

• 25% dry mass lost

how does a leaf pack work?

1. dry and weigh leaves

2. incubate

3. dry, re-weigh, and calculate loss

explain this graph about the decomposition rates of leaves.

• early biomass that is lost is the labile components = days

• late biomass that is lost is the refractory components = weeks, months

what was the first experiment researchers did on the rate of decomposition by animals versus microbes in leaf packs?

• fine mesh exclusion of animals reduced the decay rates

• decay rate is also vegetation species specific

  • thin/wide vegetation breaks down more by microbes

  • thick/smaller vegetation breaks down more by animals

alternative explanation: the extremely small mesh size blocked the flow of nutrients and oxygen into the system and waste out of the system

what was the second experiment researchers did on the rate of decomposition by animals versus microbes in leaf packs?

• insecticide → resulted in the same curve as the first experiment meaning that the mesh bag was not an issue

alternative explanation: small difference in microbial respiration due to the dead insects decomposing and acting as fuel

what are the main primary producers in rivers?

aquatic photosynthetic organisms with chlorophyll or other photosynthetic pigments

what is periphyton?

benthic algae

what is a biofilm made up of?

bacteria, fungi, algae in a polysaccharide matrix

what is the difference between epilithic, episammic, epipelic, and epiphytic?

• epilithic: rocks

• episammic: sand

• epipelic: mud

• epiphytic: plants

what are the characteristics of bacillariophyta?

• silica, bivalve, protection, binary fission

• rapid reproducers (asexual) → cost of genetic diversity BUT good in a constant environment

• R-selected

what are the characteristics of chlorophyta?

• chlorophyll absorbs red, reflects green

• rapid reproducers (sexual)

• all energy into growth, none into defense

what are the characteristics of cyanophyta?

• fix their own nutrients

• gel coat increases surface area and grazing resistance

what are the characteristics of euglenophyta?

• part animal, part plant

• heterotrophic

• mobile with a flagella

what are the characteristics of rhodophtya?

• chlorophyll absorbs green, reflects red

• deep water or shaded conditions → less competition

• green light moves through water further than red light

what is the difference between submerged, floating, and emergent macrophytes?

submerged: all photosynthetic parts are underwater

floating: photosynthetic parts float above water

emergent: rooted in water and penetrate to to the surface, photosynthetic parts can be above or below

what are the three methods to estimate biomass of primary producers? what are the benefits or drawbacks to those approaches?

1. ash free dry mass (AFDM) (combust it, measures ALL biomass, cheap/fast BUT inaccurate for only primary production)

2. chlorophyll A (separate pigments based on concentration, more accurate BUT more work and less effective)

3. cell volume (count every algal cell, high accuracy BUT a ton of work and flow cytometry is expensive)

how can we measure productivity?

gross primary production = total energy fixed per unit time

net primary production = gross primary production - plant respiration

what is the first method to measure primary productivity? what are the two problems with this method?

light and dark chambers → O2 production / O2 consumption

• light chamber allow for both photosynthesis and respiration to occur

• dark chamber only allows for respiration to occur

problems:

1. measures community metabolism (underestimate NPP)

2. reduces flow rate of nutrients which decreases metabolic rates

easy, cost effective, easy labor

what is the second method to measure primary productivity?

uptake and assimilation of radioactive carbon (C14) → rate of CO2 production

• assumes uptake of C14 is proportional to uptake of C12

time costly, expensive, labor intensive

what is the third method to measure primary productivity? what group does it work the best for and what group does it not work for?

changes in biomass over time

• works for: macrophytes

  • more biomass = more productivity

  • more defensive features means they are harder to eat

• does not work for: periphyton

  • constant predation of periphyton means there is no increase in biomass

  • all energy into growth and not into defenses

how can we measure the primary production of periphyton?

biomass change: rate change in biomass = gain - loss

• gains: immigration (initial colonization), growth rate (productivity)

• losses: cell death, emigration via sloughing (suffocates under other algae), scouring (abrading algae off substrates), grazing

what do these two curves show?

A. logistic growth rate of algae and carrying capacity→ reaches a maximum population based on the amount of resources

B. division rate decreases over time as resources decrease

C. net primary productivity curve as there is initially a TON of resources but at some point those resources become limiting and production drops

explain this light intensity graph and how it relates to primary productivity.

light limited region: low light meaning it is a critical resource controlling the amount of production

light saturated: algal cells cannot absorb any more light, fully productive

photo inhibition: light is high energy and too much light damages the cell

how do light and nutrients effect algal biomass?

rivers vary in nutrient load (high vs. low) and canopy (open and closed canopy)

what were the results from the Hill and Knight experiment exploring the effects of canopy cover on rivers?

open canopy stream was COVERED → no decrease in biomass

• suggested it was nutrient limited as there was normally unlimited amounts of light allowing them to photosynthesize at maximum rates

closed canopy stream had trees CUT → biomass increased

• suggested that it was light limited as there was normally plenty of nutrients to photosynthesize but they cannot be used without light

do nutrients limit algal growth? what is the first hypothesis?

• if nutrient concentration is low and the delivery rate is high, then it does not affect primary productivity

• no nutrient limitation as it is constantly replaced by upstream sources

do nutrients limit algal growth? what is the second hypothesis?

• boundary layer may have reduced exchange and delivery rate is dependent on nutrient concentration

• most algae at the bottom

  • not an accurate representation by sampling at the middle/top

• nutrient limitation creates a curve that initially increases then plateaus