D2.Geo.4.9-12: Reciprocal Influences Between Human and Physical Systems

Overview

Lesson Procedure

70-75 minutes of class time across 5 phases.

1. Warm-Up5-10 minutes
2. Direct Instruction20 minutes
3. Guided Practice15 minutes
4. Independent Practice20 minutes
5. Closure10 minutes

1. Warm-Up5-10 minutes

   Warm-Up Prompt

   "A town builds a wall to keep a river from flooding it. Name one way the wall changes the river, and one way the changed river might later change the town."

   Take answers and draw them as a circle of arrows on the board. Name the idea: reciprocal influence, an effect that comes back around. Tell students they will test this idea against 84 years of USGS measurements from one coast.

2. Direct Instruction20 minutes

   Key terms for D2.Geo.4.9-12 (working definitions)

   Term	Meaning in this lesson
   System	A set of parts that affect one another, such as a river and its sediment, or a regional economy
   Human system	People and what they build and decide: settlements, economies, transportation, laws and policies
   Physical system	Natural processes and features: rivers, sediment, land, sea level, climate, storms, plants
   Interaction within a system	Two parts of the same system affecting each other, such as storms and subsidence in the physical system
   Interaction between systems	A human part and a physical part affecting each other
   Reciprocal influence (feedback)	A change that returns to its starting point through the other system, so each system both causes and receives change
   Sediment and delta	Sediment is sand, silt and clay carried by water; a delta is land built where a river drops its sediment
   Subsidence	Gradual sinking of the land surface
   Levee	A raised bank along a river that keeps floodwater in the channel
   Hydrologic basin	An area drained by one set of rivers and bays; the USGS report divides the coast into nine basins

   Part 1: Read Diagram 1. Walk the loop with students: physical box, human box, physical box, human box. Ask after each arrow, "Is this within one system or between systems?" Every arrow in Diagram 1 crosses between systems; stress that each box also contains its own internal interactions, which students will find in the sources.

   Part 2: Worked examples. Model one example of each kind of analysis.

   • Computing change (coastwide)

     Source 5 gives coastal Louisiana's land area as 19,544 km² in 1932 and 18,400 km² in 1956. What was the change, and what percent of the 1932 area is that?

     Result: 18,400 - 19,544 = -1,144 km², and 1,144 / 19,544 = 0.0585, a loss of about 5.9% in 24 years, or about 48 km² a year.

   • Interaction within the physical system

     Source 2 lists sea-level rise and subsidence among the stressors. How do these two physical processes work together?

     Result: Both raise the water relative to the land: the sea rises while the land sinks. Their effects add up, so a wetland must build up faster to stay above water. Neither involves a human decision.

   • Interaction within the human system

     Source 2 notes that 5 of the nation's top 20 ports are in coastal Louisiana and lists "navigation infrastructure" as a stressor. How are these two human parts connected?

     Result: Ports need channels deep enough for ships, so the port economy depends on navigation infrastructure. The link is economic and runs inside the human system; its effect on the wetlands is a separate, between-system interaction.

   • Reading a loop in a source

     Source 1, paragraph 1, says river floods "would carry these sediments" and built "a vast expanse of fertile deltaic wetlands." Which way does the influence run here?

     Result: Physical to physical first (floods to sediment to land), and that land then became the ground on which the human system built ports, fisheries and towns. This is the starting point of the loop in Diagram 1.

   Teacher tip. Students often call every arrow "human impact." Insist that each arrow name both its start and its end, and that at least one arrow in every loop points from the physical system to the human system.

3. Guided Practice15 minutes

   Sources 1 and 2. Read both passages aloud, one paragraph at a time. Students highlight human-system parts in one color and physical-system parts in another. SLR means sea-level rise; "anthropogenic" means caused by people.

   1Coastal Louisiana was built by sedimentary material sourced from fluvial and tidally redistributed deposits. The bulk of these deposits were delivered via the Mississippi River as a result of upper catchment glaciation and melting associated with sea-level changes. As glaciers retreated (from about 12,000 until 6,000 years ago), meltwater inundated valleys and transported much of the upper catchment sediments to the lower catchment floodplains that compose coastal Louisiana today. Periodic floodwaters would carry these sediments, and as the floodwaters retreated, rich sediment left behind formed a vast expanse of fertile deltaic wetlands (Fisk and McFarlan, 1955). Hydrology continues to dictate the geomorphic structure and vegetation distribution of this landscape but in a drastically altered fashion.

   2Flood-control structures including dams and levees were built, not only in Louisiana but throughout the Mississippi River catchment, particularly after the flood of 1927. The construction of these features has led to an overall decrease in the amount of sediment carried by the Mississippi River as a result of dam and levee construction throughout the drainage basin (Meade and others, 1990; Kesel and others, 1992). Anthropogenic controls also vary the distribution of sediment within the river by redirecting or altering the amount of sediment distribution at channel mouths, along channel banks, and across floodplains. These flood-control structures have contributed to a reduced capacity for sediment accretion and thereby reduced the ability of wetlands to maintain elevation in response to SLR and subsidence.

   1The U.S. Geological Survey (USGS) analyzed landscape changes in coastal Louisiana by determining land and water classifications for 21 datasets. Coastal Louisiana has been losing wetlands because of multiple compounding and interacting stressors including sea-level rise (SLR), subsidence, storms, sediment deprivation, oil and gas extraction and infrastructure, navigation infrastructure, saltwater intrusion, altered hydrology, and others (Penland and others, 2001). The purpose of this study is to provide updated estimates of persistent land change and historical land change trends for coastal Louisiana and for each hydrologic basin from 1932 to 2016. The use of 21 datasets plus the application of consistent change criteria in this study provide opportunities to better understand the timing and causal mechanisms of wetland loss that are critical for forecasting landscape changes in the future.

   2The Louisiana coastal zone encompasses approximately 37,780 square kilometers (km²) of lowland plains, deltaic lobes, and open water (fig. 1). Coastal Louisiana wetlands are generally considered one of the most important environments in the United States because they support more than 30 percent of the commercial fisheries in the United States, 5 of the Nation’s top 20 ports are located in coastal Louisiana, and 20 percent of the Nation’s oil and gas comes from or is transported through these wetlands (Costanza and others, 2008; Feagin and others, 2010; Gedan and others, 2011; NOAA, 2010; Twilley, 2007). This coast is also considered to be one of the most “at-risk” environments in the Nation because approximately a quarter of these wetlands have been lost in the past 84 years (Couvillion and others, 2011).

   1. Time scale. Prompt: Source 1, paragraph 1, says glaciers retreated "from about 12,000 until 6,000 years ago." How long did that take, and what does it say about how fast the physical system built the land? Teacher note: about 6,000 years; the land was built slowly, while the changes in Source 4 happened within one lifetime.
   2. Where. Prompt: Source 1, paragraph 2, says flood-control structures were built "not only in Louisiana but throughout the Mississippi River catchment." Why does that matter for a coast? Teacher note: decisions made far upstream affect how much sediment reaches the coast, so the human system involved is much larger than Louisiana.
   3. Size. Prompt: Source 2, paragraph 2, gives the coastal zone as about 37,780 km². What fraction of it was land in 2016 (Source 5)? Teacher note: 14,711 / 37,780 = 0.389, about 39%; the rest of the zone was water.
   4. Sort the stressors. Prompt: put each stressor in Source 2, paragraph 1, into a Human, Physical or Both column. Teacher note: accept reasoned placements; "altered hydrology" and "saltwater intrusion" are physical processes, but the source does not say what caused them here, so students should say what extra evidence would settle it.
4. Independent Practice20 minutes

   Change across space and time. Source 4 compares the nine basins of the coast, and Source 5 gives coastwide land area for selected years. Source 3 is the report's own summary of how rates of change have varied.

   Source 4: Land area by hydrologic basin, 1932 and 2016 (USGS, observed, km²)

   Basin	1932	2016	Change (km²)	Change (% of 1932)
   Atchafalaya Delta	551	567	+16	+3.0%
   Barataria	3,833	2,713	-1,120	-29.2%
   Breton Sound	1,108	682	-426	-38.4%
   Calcasieu-Sabine	2,137	1,619	-518	-24.2%
   Mermentau	2,482	1,994	-488	-19.7%
   Mississippi River Delta	679	304	-375	-55.2%
   Pontchartrain	2,862	2,390	-472	-16.5%
   Teche-Vermilion	1,422	1,273	-149	-10.5%
   Terrebonne	4,472	3,170	-1,302	-29.1%
   Coastwide total	19,544	14,711	-4,833	-24.7%

   Source 5: Coastwide land area in selected years (USGS, observed, km²)

   Year (decimal)	Land area (km²)
   1932	19,544
   1956	18,400
   1973.9	17,482
   1985.1	15,501
   1990.8	15,593
   1999.9	15,345
   2004.9	15,066
   2006.8	14,524
   2008.8	14,120
   2010.8	14,666
   2016.1	14,711

   Sources 4 and 5: Couvillion and others (2017), USGS Scientific Investigations Map 3381, Table 1, observed values, rounded to the nearest square kilometer. The change columns in Source 4 are computed from the unrounded values, so a percent worked from the rounded figures can differ by 0.1 (Atchafalaya Delta: 16 / 551 = 2.9%). Years after 1956 are decimal dates of the satellite images (1973.9 is late 1973).

   1[...] Of note is the slowing of the rate of wetland change since its peak in the mid-1970s. Not only have rates of wetland loss been decreasing since that time, a further rate reduction has been observed since 2010. Possible reasons for this reduction include recovery from lows affected by the hurricanes of 2005 and 2008, the lack of major storms in the past 8 years, a possible slowing of subsidence rates, the reduction in and relocation of oil and gas extraction and infrastructure since the peak of such activities in the late 1960s, and restoration activities. In addition, many wetlands in more exposed positions in the landscape have already been lost. Most notable of the factors listed above is the lack of major storms over the past 8 years. The observed coastwide net “stability” in land area observed over the past 6–8 years does not imply that loss has ceased. Future disturbance events such as a major hurricane impact could change the trajectory of the rates. Sea-level rise is projected to increase at an exponential rate, and that would also expedite the rate of wetland loss.

   [...]

   2Finally, the Atchafalaya Delta Basin experienced an increasing land area trend (positive land change slope) since 1961 (fig. 5). Prior to 1961, this basin was initially on a negative trajectory; however, following the opening of the Wax Lake Outlet in 1942, sediment deposition increased, and a subaerial active delta emerged after the flood of 1973.

   Task (pairs). (1) Describe the spatial pattern in Source 4: which parts of the coast changed most and least? (2) Describe the pattern over time in Source 5 in three phases. (3) From Source 3, list every possible reason for the slowing of loss and label each H (human system), P (physical system) or H/P (an interaction between them). (4) Choose one reason and draw it as a loop with at least three arrows.

   Look for: patterns described with numbers and basin names, three distinct phases supported by values, every reason in Source 3 labeled with a justification, and a loop whose arrows each name a start and an end.

5. Closure10 minutes

   Exit ticket: "One human decision on this coast changed the physical system by ... In turn, that change affected people by ..."

   Teacher note on the sources: all three passages are quoted exactly from the USGS report, including the authors' citations of other studies and references to the report's figures, which are not shown here. The report presents several causes and does not rank human decisions as right or wrong; keep the class discussion on how the systems interact. Flood control protects people and property from floods, and the same structures change where sediment goes: both facts belong in any evaluation. Coastal policy in Louisiana is debated today, so use the sources to analyze trade-offs rather than to take a side on any current project.

Differentiation Strategies

Assessment Guidance

1. Question 1 of 20 · Multiple Choice

   According to Source 1, paragraph 1, what delivered the bulk of the sediment that built coastal Louisiana?

   AHurricanes that pushed sand onshore from the open water over many centuries BLevees that trapped silt along the river's banks CWaves that wore down rocky cliffs and spread the pieces along the coast DThe Mississippi River, fed by melting glaciers upstream

2. Question 2 of 20 · Multiple Choice

   Source 1, paragraph 2, says flood control reduced the amount of sediment in the river. What else, according to the paragraph, do "anthropogenic controls" do?

   AChange where sediment ends up at river mouths, banks and floodplains BAdd new sediment from behind the dams to the river's lower course each year CStop subsidence by holding the land surface of the delta firmly in place DRemove salt water from the wetlands behind the levees

3. Question 3 of 20 · Multiple Choice

   Which stressor listed in Source 2, paragraph 1, is clearly part of the human system?

   ASubsidence of the land surface BOil and gas extraction CStorms that reach the coast DSea-level rise along the coast

4. Question 4 of 20 · Multiple Choice

   Source 2, paragraph 1, describes the stressors as "multiple compounding and interacting." What does this mean for anyone explaining the land loss?

   AOne stressor, once it is found, will explain all of the land that was lost BOnly the human stressors need to be studied, since people can change them CCauses add up and affect one another, so they must be studied together DThe stressors cancel out, so the loss is mostly random

5. Question 5 of 20 · Multiple Choice

   Which statistic in Source 2, paragraph 2, most directly shows the physical system supporting a part of the human economy that depends on living wetlands?

   AThe coastal zone covers about 37,780 square kilometers of land and water BAbout a quarter of the coast's wetlands were lost over the past 84 years CThe study combined 21 different datasets of land and water from 1932 to 2016 DMore than 30 percent of U.S. commercial fisheries depend on these wetlands

6. Question 6 of 20 · Multiple Choice

   Source 3, paragraph 1, lists possible reasons that wetland loss has slowed. Which of these reasons is a change in the human system?

   ARestoration activities BThe lack of major storms CA possible slowing of subsidence rates DRecovery from the lows after the 2005 and 2008 hurricanes

7. Question 7 of 20 · Multiple Choice

   Why does Source 3, paragraph 1, say that recent coastwide "stability" in land area "does not imply that loss has ceased"?

   ABecause the satellites that measured the coast stopped working after the year 2010 BBecause the land area grew every year after 2010 CBecause all restoration projects on the coast ended in the year 2016 DBecause a major hurricane or faster sea-level rise could change the trend

8. Question 8 of 20 · Multiple Choice

   Source 3, paragraph 1, notes that "many wetlands in more exposed positions in the landscape have already been lost." What kind of interaction does this describe?

   AA human decision, made on purpose, to slow the loss in the exposed places BAn interaction between the human and physical systems CA feedback within the physical system: past loss leaves less vulnerable land DA change in how the USGS measured land in the later satellite images that it used

9. Question 9 of 20 · Multiple Choice

   Which statement best describes the chain in Source 3, paragraph 2, about the Atchafalaya Delta Basin?

   AA flood alone built the delta, and people played no part in the change BA human decision sent more sediment, and a later flood helped new land emerge CLevees blocked the river's sediment, so the basin lost land after 1942 DHurricanes carried large amounts of sediment in from the open water and built the delta

10. Question 10 of 20 · Multiple Choice

    Use Source 4. The coast lost about 4,833 km² from 1932 to 2016. That loss equals what percent of the coast's 2016 land area?

    A3.3% B24.7% C32.9% D75.3%

11. Question 11 of 20 · Multiple Choice

    Use Source 4. Which statement about the basins is correct?

    ATerrebonne lost the most land, and Mississippi River Delta lost the largest share BMississippi River Delta lost both the most land and the largest share CBarataria lost the most land, and Breton Sound lost the largest share of its 1932 area DTerrebonne lost both the most land and the largest share of its 1932 area

12. Question 12 of 20 · Multiple Choice

    Source 2 says about a quarter of the wetlands were lost "in the past 84 years." Using the coastwide loss of about 4,833 km², what was the average loss per year over those 84 years?

    AAbout 232.7 km² per year BAbout 48.3 km² per year CAbout 175.1 km² per year DAbout 57.5 km² per year

13. Question 13 of 20 · Multiple Choice

    Use Source 5. How much land did the coast lose between the 2004.9 and 2006.8 images?

    AAbout 404 km² BAbout 542 km² CAbout 546 km² DAbout 946 km²

14. Question 14 of 20 · Multiple Choice

    Which pair is an interaction within the human system?

    ASubsidence of the land and sea-level rise along the coast BLevees along the river and the amount of sediment it carries COil and gas infrastructure and the nation's energy supply DHurricanes and the area of wetlands left after each storm season

15. Question 15 of 20 · Short Answer

    The Atchafalaya Delta Basin is the only basin that gained land. Use Source 3, paragraph 2, and Source 4 to explain this exception as a reciprocal influence.

    Show model answer

16. Question 16 of 20 · Short Answer

    Source 2, paragraph 2, calls the coast one of the most "at-risk" environments. Using the paragraph's evidence about ports, explain how a change in the physical system in one state can feed back on people far away.

    Show model answer

17. Question 17 of 20 · Short Answer

    Use Source 5 to compare the average yearly loss from 1932 to 1973.9 with the average yearly loss from 1990.8 to 2016.1. Then use Source 3 to suggest two reasons for the difference.

    Show model answer

18. Question 18 of 20 · Short Answer

    A student writes, "Building the levees was a mistake." Evaluate this claim using Source 1 and one other source. Your answer may agree or disagree, but it must weigh effects on both the human and the physical system.

    Show model answer

19. Question 19 of 20 · Short Answer

    Name three interactions from Sources 1-3: one within the physical system, one within the human system and one between systems. Explain each classification.

    Show model answer

20. Question 20 of 20 · Short Answer

    The USGS used 21 datasets from 1932 to 2016 instead of comparing just two years. Use Sources 2, 3 and 5 to explain why.

    Show model answer

These standards connect to D2.Geo.4.9-12: prerequisites to review first, parallel standards at the same level, and next steps that build on it.

Standard text: National Council for the Social Studies (NCSS), The College, Career, and Civic Life (C3) Framework for Social Studies State Standards: Guidance for Enhancing the Rigor of K-12 Civics, Economics, Geography, and History (Silver Spring, MD: NCSS, 2013). NCSS was not involved in the production of this lesson and does not endorse it.