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Env Geo midterm 2
The second midterm. I need a 90.
| Question | Answer |
|---|---|
| What % of rivers in the US are dammed? | 98% |
| What happens when supply is less than capacity? | erosion, and perhaps armoring. Happens in dams, downstream. River is trying to move stuff, but there’s nothing to move, so it moves the channel itself. |
| What happens when supply=capacity? | not much, homie |
| What happens when supply>capacity? | channel and floodplain aggradation (building up). Pools might fill in with sediment. |
| Where are most dams? | On the east coast but the storage to runoff ratio is much higher in the Midwest (effects are greater) |
| Case study - colorado river | states are entitled to more water than flows. empty by the time it reaches the gulf. |
| Upstream vs Downstream Damming issues | Above dam = warm, below dam = cold. Was muddy, now clear. Backwaters fill with sediment. Floods before, now no floods. All things that screw with native species survival/reproduction. |
| Benefits of flooding | -periodic floods retain sand -scour backwater, erode debris fans -control small compared to pre-dam, big compared to post-dam -creates range in velocity/stream poer -coarsing upward pattern in deposits -backwater ^, then smaller quickly afterward |
| Composition of an Eddie | -seperation bar (sandbar forms behind debris flow) -DF makes stuff slow down, drop sediment -reattachment bar down a bit further -between SB & RB is the backwater (deep water) • warmer because it’s still -backwaters get filled, turned into marshes |
| Syvitski paper notes | Humans increased sed transport 2.3 B MT/yr, reduced sed flux to coast B MT/yr. 100 B MT of sed, 1-3 B MT C in reservoirs in last 50 yrs. 20% of world sed trapped there. JJA has most sed. 1.4 BT/yr sed flux compared to prehuman |
| Sea level facts | 50% US pop. within 75 km of coast, 50% world pop. within 150 km. Controls of beach expansion/contraction - deposition, erosion, sea level. |
| Sediment sources | -in– rivers, coastline rock erosion, longshore drift, wind, offshore deposits (storms) -out – longshore drift, wind, offshore losses -usually, sed losses > gains (delta S is negative) -E coast worse than W in this respect -severity, active < passive |
| Timescales of sea level change | Last 200Ka, rise of 130m. 5Ma ago was last glacial minimum. 1880 rise rate 1.6 mm/yr, 1980 rr 2.6 mm/yr. Local variation (Brazil receding, Alaska uplifting, Baltimore rr more like 3.1 mm/yr) |
| Sea level rise reasons | Melting (ice caps, greenland), thermal expansion, temperature increase (since '78). 1+m in the next 90ish yrs possible. Flat, populated coastlands (FL, bangladesh) are screwed. |
| Syvitski presentation | -area, relief, temp to produce discharge -discharge in N Canada similar -predictions & not direct measurements -deposited in warm/wet areas, high relief, high precip, plate boundaries -natural & manmade hotspots different |
| Groundwater is what percent of the world's fresh liquid water? | 97% |
| Groundwater movement | Elevation head - surface water flows downhill bc elevation energy, groundwater has energy from elevation & pressure. Pressure head - 1 point may have more pressure above it than another. more stuff on top of it = more pressure (makes it able to flow up) |
| Aquifers | -unit that stores & transmits H2O -unconfined – no pressure head (on top), H2O moves ^ & v -confined – confining unit over it, has pressure head @ every pt -table mimics topo -head – energy/unit weight H2O -recharge zone – surface areas of high topo |
| Groundflow & Maps | -topo map of an unconfined aquifer (water table contours by elevation) gives you a map of elevation head -water flow lines perpendicular to groundwater table elevation contours -well – hole in water table map. Becomes a depression in your energy map |
| Mass Wasting & Groundwater | -transport solely under the influence of gravity -tectonic activity (steep slopes, earthquakes) -loose sediment (unconsolidated, coastal sediment) -Mediterranean climate (dry period/wet period) -not as much vegetation |
| Darcy's Law | quantifies groundwater flow: [(h1-h2)/L] * hydraulic conductivity * cross sectional area |
| Resisting & Driving forces | -gravity (controlled by slope) – driving -friction (resistance to shear) – resisting •internal angle of friction -cohesion (function of veg, soil comp, etc) – resisting • bit of air, bit of water = cohesive • filled pore space = flow |
| Factor of safety | resisting forces/driving forces. >1 good, <1 bad. Or shear strength/shear stress |
| Elmore (owens valley CA plant communities) paper notes | 19% showed linear decline when groundwater was lowered. When grassy cover went down with drought, invasive shrubby stuff went up when the drought ended. Ecosystem drought buffer was stable groundwater, now sensitive to fluctuation. |
| Elmore methods | vegetation live cover, vegetation map, field observations, precipitation records, water table depth. |
| Elmore presentation | Groundwater depletion bc of aqueduct sneakily bought up in 10s. Lake dried by 20s. Largest source of small particulate matter on earth. Pumping during drought in late 80s. Past sediment loss quantified using radionuclide dating. |
| High plains aquifer | We won't be able to grow anything in 100 years. 270 B m of fossil water. Unconfined, supplied by past glacial melt. Supplies 30% of US irrigated groundwater. Withdrawal 6-7x recharge. |
| Schlesinger paper notes | Getting rid of native grass leads to heterogeneity of water, N, and other stuff soil needs. That then leads to invasive shrubs that create fertility islands around themselves & the soil loses good stuff through erosion & gaseous emissions. + feedback loop |
| Schlesinger paper methods & figures | Predicted 17% increase in desert area. 53% of rain happens between Jul & Sept. Nutrients measured: pH, saturation percentage, soil moisture, total N. Flash floods & dust storms likely |
| Biogeochem of great plains | 15.6 C average. • In o Dead organic matter o N fixation (soil bacteria, lightning) • Out o Ammonia volatilization o Denitrification o Aeolian processes |
| Global implications of desertification | • neutralization of acid rain • sed transport • more greenhouse gasses • increased albedo for region • decreased % of productive land • increased extreme weather events |
| Elements required by plants | -macro • N (<0.002% of crust) • P (0.1%) • K (2.1%) -secondary • Ca • Mg • S -micro • Fe • B • Zn • Cu • Mn • Mo |
| N, P, and terrestrial, marine, and freshwater ecosystems. | -P>N in Lake Benthos, Forest Shrubland -N>P in benthos (hard), pelagic, tundra, wetland -P&N < individually • P&N together always drive productivity ~1.6x • marine environments, N is more limiting than P • P&N are limiting everywhere |
| Eutrophication | -too many nutrients, fuels photosynthesis & carbon fixation, plants die, suck up O, fish die. -41% of continental US drains through same river -dead zones the size of NJ -bacteria community shift to ones who dont eat O -pyrite = anoxia |
| Cooper & Brush (CB anoxia since settlement) notes | Measured 2Ka of sed cores near CB to show anoxia has been getting worse since settlement. Measured Pollen, diatoms, organic C concentration, N, S, acid-soluble Fe, pyritization of Fe. Sedimentation +5-7x. Most C & N organic. CB anoxia 1st reported in 30s |
| Chesapeake Bay & Anoxia | 64k m^2, biggest estuary in US, >17M people, trillion $ resource. Wide hypoxia in winter (10mg/L), stratified anoxia (0-7mg/L) in summer. Salt & dead things sink. |
| Cooper & Brush presentation | Sharp increase in pollen concentration around 1760. Sed rates go from 3-14cm/ka pre to 13-27cm/ka post. Diatom diversity plummets. Degree of pyritization ^ early 1800s. |
| Turner notes | 2000 yr paleoreconstruction from plankton. 41% of US drains to same place. Watershed pop density^ w land clearing, Sed conc^, varied less w dams. Land use measured using runoff (suspended sed, nitrate, P) N>P always. The less marsh, the more N and P |
| Behman notes | Balance between N, P, and Fe determines phytoplankton growth. Tropics/subtropics defined by N depletion, so very sensitive. By 2050, 27-59% of all N fertilizer will happen upstream of sensitive ecosystems. 80% of alg blooms within days of fertilzation |
| Turner presentation | -25% of US $ fishing offshore of MS river -N sources (tile drainage, soil N pools, fertilizer) -diatoms have silica cell walls, limited by 1:1 silica to dissolved N ratio (no more N than that) and they’re the base of the food chain -decades to recover |
| Cooper presentation | • Organic detritus increased in late 1700s • Increased sediment, organic matter, but maybe not anoxia • Increased pyritization in 1940 -shark attacks near TX bc of limited habitat due to dead zones. Red tides cause respiratory illness, kill stuff |
| Behman presentation | -there should be 16N : 1P in a normal ecosystem, but some ecosystems are N deficient on purpose Chl up, temp down. More chl because of upwelling. -residuals are the difference between the observation & predicted model |
| Vitousek paper notes | ^ N2O concentrations (greenhouse gas), - in soil nutrients (Ca, N), acid soil/water, increased N transport (rivers → estuaries → coastal shelf), loss of biodiversity (esp plants), changed biology of estuaries and coastal ecosystems, decline in fisheries. |
| Janzen paper notes | ~500Pg C in plants, 2000Pg C in soil. Oceans have more. Atmosphere has 785. Atmospheric CO2 has increased at 3Pg C/yr, and will soon double pre-industrial levels. |
| Vitousek presentation | • deforestation • CO2 release o Fossil fuel burning • Industrial N fertilizer • N fixing crops • Mobilization of stored N • nitrous oxide o greenhouse effect o thins ozone • ammonia o poor air quality • nitric oxide o acid rain o smog |
| N cycle (naturally) | -Atm → bacteria & ocean -bacteria → soil → plants -animal decomposition & waste → soil -runoff from fertilizers & animal waste → water -ocean → atmosphere -n fixation through electric storms -factories |
| Janzen presentation | • land use o ag • fossil fuels o lots since industrial revolution o + 3.2 Pg of C/yr o - CO2 energy use o fossil -> bio o increase sequestration • what will it look like in the future? o Climate change, population growth, farming practices |
| C cycle (naturally) | 3 sinks – ocean, terrestrial, atm • soil has 2k in 1 m of depth o decomp o photosynthesis o respiration o burning plants • ocean has 39k o algae (photosynthesis, respiration, decay) o gas exchange (mixing through waves) • atmosphere has 760 |
| Carbon on a longer scale | 40 Ma, CO2 was not 280 (which is pre-industrial) but thousands (2500-4000) as we came out of Mz and into Cz Change in pools of organic matter has the capability for huge change. Coal is hundreds of millions of years old. |
| Syvitski calculated that humans have reduced the flow of sediment by 1.4 billon tons/yr, which is weird because we're accelerating erosion. Where is it all going? | It's getting sequestered in manmade structures like reservoirs & dams |
| What measurements (data) did Syvitski use to calculate sediment flux on such a large scale? | Drainage basin model based on Area, Relief, Temperature (ART) and Climate |
| What is the broader relevance to Syviski's calculations for society? | Sed isn't being deposited, so we're losing landmass |
| What did Elmore measure to show how plant communities have changes in Owens Valley, CA? | Vegetation maps & surveys, Remote sensing of vegetation live cover, water table depth, precipitation records |
| Give an example of a plant community that is groundwater dependent | Meadow communities are adapted to environments with short, frequent droughts & a steady groundwater level |
| What soil resources did Schleisinger measure in his paper on desertification & heterogeneity? | total N content, water (saturation % and soil moistness), pH |
| What human disturbance that leads to desertification did the Schleisinger paper focus on? | Overgrazing |
| Why would a decrease in soil infiltration lead to a decrease in N accumulation in soil? | Runoff, which carries away nutrients. Also aeolian processes. Also dry soils like ammonia NH2 volitilization |
| Increased preservation of what 3 elements in sediments were used as indicators of anoxia in the Cooper & Brush paper? | Carbon, Nitrogen, Sulfur |
| What biological evidence of anoxia did Cooper & Brush find in the sediment cores? | Increase in Diatom Diveristy |
| When did Cooper & Brush find that human activities began to cause an increase in CB anoxia? | Late 1700s (1760). Or early 1800s if you're looking at pyritization. |
| In schmidt, the recurrence interval of the controlled flood relative to pre-dam flows was about a _________, but compared to the post-dam flows was about a ___________. | 1.1 year flood (RI<1.25); 6 year flood (RI=5.1) |
| (Schmidt) Compared to previous natural floods, did this controlled flood occur relatively early or late in the season? | Relatively early |
| What effect did the controlled flood have on the number and area of backwaters in the Grand Canyon below the Glen Canyon Dam? | Area went up immediately after, and then significantly decreased from pre-flood levels. Number stayed relatively stable. |
| Approximately when did we see a substantial increase in (k) human population? | 1950, around the BABY BOOM YOU STUPID ASSHOLE |
| The new cropland/pasture "biome" covers what % of the earth's land surface? | 40% |
| What soil forming factor has the biggest control on distribution of fertile soils in north america? | CLIMATE |
| How fast does the top meter of fertile topsoil erode in order to collapse a civilization? | 650m/my YOU CAN SOLVE IT LIKE AN EQUATION YOU DUNCE |
| During the 20th century, how many people in the US died from flooding? | 100,000 FIVE ZEROES AND A ONE BITCH. SIX DIGITS. LIKE THE 6-0 YOU GOT ON THE LAST MIDTERM |
| 180 million tons/yr of N is fixed naturally. How much do human activities contribute every year? | THE SAME AMOUNT BECAUSE WE'VE DOUBLED IT IN TOTAL. WE'RE PUTTING AS MUCH N IN THE AIR AS NATURE EVERY YEAR. |
| According to Walter & Merrits if you walked in a mid-atlantic stream 400 yrs ago you'd be walking on what? | organic-rich silt loam |
| Trimble and Walter & Merrits both claimed that channel erosion is responsible for what percent of total stream sed load? | 60-80% ITS THE ONLY OPTION WITH A RANGE WHERE THEY'RE BOTH EVEN NUMBERS |
| In a northern deciduous forested watershed, in which month does evapotranspiration have the strongest control on stream discharge | IT'S AUGUST BECAUSE THAT'S WHEN EVERYTHING IS AT ITS BLOOMIEST AND IT'S USING ALL THE WATER YOU FUCKING MORON |
| WHat is a specific design goal of stormwater retention ponds? | to delay the peak inflow to outflow stormflow centroid of the 1-year event by 24 hours |
| Montgomery said conventionally plowed ag fields average how much larger erosion rates than rates of soil production, natural erosion, etc? | 10 to 100 times. IT'S A PRETTY BIG DEGREE OF MAGNITUDE |
| Find the factor of increase from plot | YOU JUST DO e TO THE POWER OF WHATEVER POINT AND DO DIVISION |
| What are the 3 reasons the retention ponds sucked? | pools underestimated annual runoff. they didn't consider future construction. they didn't think about piggybacking |
| what is the exponential growth rate equation (k)? | k = 1/time interval * ln(biggest time/smallest time) |
| What is the formula for doubling time? | 70/(k * 100) |
| how do you calculate residence time? | pool/flux |
| how do you calculate change in system (delta S)? | input - output |
| what is the formula for recurrence interval? | RI = #+1/rank |
| What are 2 human caused and 1 natural fuck up during the dust bowl? | Digging up grass, overtilling the soil, drought |
| What are 3 ways that ancient rivers are different than modern rivers and one consequence? | depth, flow rate, sediment. and water filtration |
| Where was pre-human erosion vs erosion now? | high relief, low relief |
| When they cleared the vegetation in experimental forest, what QUANTITATIVELY happened to discharge, suspended sediment export, and dissolved load export? | discharge wen up 30%, suspended sediment went up 6x, and dissolved losses went up 9x |
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