How people are changing Earth's systems

Grade 9 Science Worksheet

Circle the best answer.

1. Read this first

   Where rain goes as land is paved (USGS, from FISRWG 1998)

   Ground cover	Evapotranspiration	Runoff	Shallow infiltration	Deep infiltration
   Natural ground cover	40%	10%	25%	25%
   10–20% impervious	38%	20%	21%	21%
   35–50% impervious	35%	30%	20%	15%
   75–100% impervious	30%	55%	10%	5%

2. 1.

   Model data: 2 inches of rain fall on a town at 35–50% impervious cover. How much soaks in (shallow plus deep), by Bo's math?

   • About 0.7 inch
   • About 0.4 inch
   • About 7 inches
   • About 1.3 inches
3. 2.

   Model data: 2 inches of rain fall on 50 acres (1 acre-inch is 1 inch over 1 acre). How much more runs off at 35–50% impervious cover than on natural ground, by Esme's math?

   • About 2 acre-inches more
   • About 40 acre-inches more
   • About 30 acre-inches more
   • About 20 acre-inches more
4. 3.

   EPA says a city block makes more than 5 times the runoff of woodland. Does the USGS table fit that, by Jun's math?

   • Yes; 55% ÷ 10% is about 5.5 times, which fits more than 5 times
   • Yes; 30% ÷ 10% is 3 times, which fits more than 5 times
   • No; 55% − 10% is 45 times, which is far above 5 times
   • No; the table shows less runoff on paved ground than on woodland
5. 4.

   Paving cuts infiltration and raises runoff. Runoff from sewers gains speed and erosional power. A new parking lot drains to a creek. Which chain of changes fits, by Kira's reasoning?

   • More soaking in, less runoff, a slower stream rise and less bank erosion
   • Less soaking in, more runoff, a faster stream rise and more bank erosion
   • More runoff, a slower stream rise, then more sediment dropped on the banks
   • The pavement changes, but the creek stays the same
6. 5.

   The ocean absorbs about 30% of released CO₂, surface pH has fallen 0.1, and shell builders find fewer carbonate ions. Fuel burning adds CO₂ to the air. Which chain across systems fits NOAA, by Milo's reasoning?

   • The air gains CO₂, the ocean absorbs about 30% and turns more acidic, and shell builders find fewer carbonate ions
   • The ocean releases 30% of its CO₂ into the air, so the air and the ocean both turn more acidic
   • The air gains CO₂, the ocean absorbs about 30% and turns less acidic, and shell builders gain carbonate ions
   • The air gains CO₂ and the ocean is unaffected, since the CO₂ stays in the atmosphere
7. 6.

   pH is a logarithmic scale, so each drop of 1.0 means 10 times more acidic. 10^0.1 is about 1.26. Surface pH fell by 0.1, which NOAA calls about 30% more acidic. Why does a 0.1 drop mean so large a rise, by Pia's reasoning?

   • A 0.1 drop makes seawater about 26% more acidic, near NOAA's 30%
   • pH is linear, so a drop of 0.1 out of about 8 is about 1% more acidic
   • A drop of 0.1 makes seawater 10 times more acidic, since pH counts tens
   • A lower pH means seawater turns more basic, so acidity falls by about 26%
8. 7.

   The ocean absorbs about 30% of released CO₂. Surface pH has fallen 0.1. The ocean takes up CO₂ from the air. Which statement describes both effects, by Ren's reasoning?

   • The ocean slows the rise of CO₂ in the air but becomes more acidic
   • The ocean slows the rise of CO₂ in the air and stays at the same pH
   • The ocean slows the rise of CO₂ in the air and becomes less acidic
   • The ocean speeds up the rise of CO₂ in the air and becomes more acidic

9. Card (USGS)

   Reservoir water moves too slowly to keep sediment suspended, so reservoirs slowly fill. Model data: capacity 50 million m³; sediment arriving 0.5 million m³ a year; 90% trapped.

10. 8.

    Model data: a reservoir holds 50 million m³. A river brings 0.5 million m³ of sediment a year and the dam traps 90% of it. About how long until the reservoir fills, by Tala's math?

    • About 100 years
    • About 10 years
    • About 1,100 years
    • About 110 years

11. Card (example)

    Sediment settles in the reservoir. The river below the dam carries little sediment but still has the energy to pick more up.

12. 9.

    Water leaving a reservoir carries little sediment. What may happen to the river bed and banks just below the dam, by Zee's reasoning?

    • They may build up, since the river drops extra sediment below the dam
    • They may erode, since the river can pick up more sediment than it carries
    • They harden, since clear water cannot move any rock
    • They stay the same, since the dam changes just the water above it

13. Card (USGS)

    Reservoir water moves too slowly to keep sediment suspended, so reservoirs slowly fill. Floodplain sediment makes farmland. A reservoir stores water (example).

14. 10.

    Which statement fairly states one benefit and one cost of a reservoir, by Ari's reading?

    • It stores water and sediment, and both pass freely on to the downstream floodplain
    • It stores water, but it adds fresh sediment to the floodplain soils and does not fill up
    • It stores water, but it traps sediment that builds floodplain soils and slowly fills
    • It traps sediment and slowly fills, but it has no benefit to people who live nearby