Practise IB ESS HL Topic 4 Water by analysing hydrological systems, interpreting pollution and scarcity data, and evaluating management choices with evidence from aquatic food…
Outline how energy drives the hydrological cycle.
primary source of energy driving hydrological cycle is solar energy; solar energy causes changes of state in water eg evaporation/sublimation/melting/transpiration; condensation of water releases (latent) heat energy causing air to rise/hurricanes; solar energy causes the temperature differences that create winds/cause movement of water vapour in the atmosphere/advection; kinetic/wind energy moves clouds (from ocean over land, usually); solar energy melts ice producing streams/lakes/rising ocean levels; solar energy causes both transfers (eg advection) and transformations (eg evaporation) in hydrological cycle; precipitation/run-off/streamflow occurs due to gravitational energy/difference in potential energy between the high and low positions; transpiration is driven by opening of leaf stomata which is due to chemical energy (cellular respiration in mitochondria);
Explain, with the use of a system diagram, how human activities affect flows in the global water cycle.
Possible impacts of human activities on flows in the global water cycle:
melting (1) will increase due to global warming/climate change/increased greenhouse gas emissions;
freezing (2) will decrease due to global warming/climate change;
precipitation (4,6,8) will be polluted due to acid formation/emissions of NOx and SOx/combustion of coal;
precipitation (4,6,8) could change/increase/decrease due to climate change;
percolation/infiltration (8) will decrease due to urbanisation/soil compaction caused by eg overgrazing;
run-off (5) will increase due to urbanization/deforestation;
warmer/polluted streams (5) due to thermal/toxic pollution from industrial effluent;
evaporation (3,7,9) will increase due to global warming/climate change;
evapotranspiration (10) will increase due to global warming/climate change;
evapotranspiration (10) will be reduced due to deforestation;
uptake by plants (11) will be reduced due to deforestation/urbanization/long fallow periods;
groundwater flow/aquifers (12) will change dependent on climatic impacts/precipitation/rate of human extraction;
cloud seeding increases precipitation (4,6,8), addressing problems of drought/fog around airports;
Figure:Integrated aquaculture system
the integrated-aquaculture diagram shown above represents a system of aquaculture with four groups of harvestable species.
Identify one producer in the system illustrated in the integrated-aquaculture diagram shown above.
algae/seaweed/sea grass;
Outline one reason why aquaculture production has increased globally.
increased food demand from increasing population/affluence; health benefits / change of diet preferences;
depletion of marine fisheries / considered more sustainable;
limited arable land for food production;
more economically efficient/profitable; requires less resources/expertise (boats, fishermen, etc) than wild fisheries; technology/technological methods have improved;
Marking guidance:
Award [1 max].
Describe two negative environmental impacts that may arise from integrated aquaculture.
escaped fish impact wild stocks through genetic degradation/disease/competition; high density populations lead to more disease; farmed species may consume/displace food species for local populations; loss/degradation of habitat due to clearance for aquaculture / nets/cages may trap/endanger local species; introduction of non-native species; pollution due to use of medication/growth hormones/pesticides;
NB do not credit high nutrients/eutrophication/low diversity/high BOD or any other impacts that integrated agriculture actually limits or reduces (as indicated in responses to 3d below).
Marking guidance:
Award [1] for each correct answer identified, up to [2 max].
Explain why this system may cause fewer environmental impacts than systems that farm only fish.
polyculture helps maintain biodiversity/complexity/resilience in the environment; (polyculture) allows for species to recycle wastes of other species; lobsters/mussels will reduce particles of organic waste/faecal matter/excess feed; (reduction of particles will) reduce BOD/decomposition and oxygen consumption; filtration by the mussels will improve water clarity/photosynthesis; cropping/harvesting algae will prevent build-up of nutrients/eutrophication; algae will absorb excess CO2 reducing acidification of water; algae will release oxygen limiting anaerobic conditions; food is provided naturally from within system/feeds made up from wild populations are not required;
Marking guidance:
Award [1] for each correct answer identified, up to [4 max].
Part (c) questions in Section B are all to be assessed using the markbands on page 21 with the guidance given below for each question.
Outline two point sources and two non-point sources of water pollution in a city.
Point sources [2 max]:
a. Factories/manufacturing plants may release pollutants directly into water bodies;
b. Inadequately treated sewage and wastewater from treatment plants can contain pollutants and be released directly into water bodies;
c. Accidental spills of oil/petroleum products from pipelines/storage tanks/tankers;
d. Improper disposal of hazardous waste/garbage/chemicals into storm drains or waterways.
Non-point sources [2 max]:
a. Urban runoff can carry litter/oil/chemicals from streets/parking lots/rooftops into storm drains/water bodies;
b. Urban greenspace runoff can carry excess fertilizers/pesticides from agricultural activities into rivers and streams;
c. Sediment/debris/construction materials from building sites can be washed into water bodies;
d. Urbanization/land development can increase impervious surfaces like roads and buildings, reducing natural infiltration/increasing surface runoff that can carry pollutants into waterways, impacting water quality in the city;
Note to examiners: Accept any other relevant example to those given.
Evaluate the strategies that can be used to meet an increasing demand for freshwater.
One mark for naming a valid water conservation/supply enhancement strategy [1 max]
One mark per each outlined strength [2 max per strategy]
One mark per each outlined weakness [2 max per strategy]
See examples below:
Example strategy:
a. Implementation of water-saving technologies in households/low flow shower heads/dual flush toilets;
Strengths [2 max]:
b. Reduces the amount of water used, so there is more water available;
c. Often can be inexpensive fixes;
d. Easy to implement at a small scale;
e. Reduces water bills;
Weaknesses [2 max]
f. Individuals may not like the resulting effects (e.g. low water pressure etc)
g. Requires wide adoption to be effective on a large scale;
Example strategy:
h. Rainwater harvesting;
Strengths [2 max]:
i. Low setup costs/low-cost supply of water;
j. Low environmental impact/not high technology;
k. Renewable supply / reduces the use of potable water;
Weaknesses [2 max]:
I. Quantity limited for agricultural uses;
m. Weather/climate dependent;
n. May contain atmospheric pollutants / isn't generally potable;
Marking guidance:
Award one mark overall for a balanced conclusion; Example: Meeting an increasing demand might involve both water conservation strategies and enhancing the water supply; [1 max]
Note to examiners: Credit up to three valid and specific water conservation/supply enhancement strategies. If they list more than three, credit the highest scoring strategies. Examples might include agricultural practices, infrastructure improvements, awareness campaigns, taxes, legislative policies, desalination, aquifer recharge, wastewater treatment, etc:
Explain how the hydrological cycle influences climate around the Earth.
a. evaporation/evapotranspiration is higher at regions with higher insolation;
b. evaporation absorbs heat from the atmosphere (negative latent heat flux)...;
c. ...water vapour carries (via convection currents/tropical cyclones) heat to higher latitudes/altitudes...;
d. ...condensation of vapour releases heat (positive latent heat flux) to colder latitudes/altitudes...;
e. ...stabilizing the heat deficit between Tropics and Poles;
f. condensation of vapour (as rising air cools) forms clouds...;
g. ...leading to higher precipitation (e.g. in the Equatorial Belt) / snowfall (higher altitudes/latitudes);
h. oceans/inland waters effectively store heat (positive sensible heat flux) during periods of high insolation (day/summer)...;
i. ...and release it back (negative sensible heat flux) during night/winter;
j. ...thus ameliorating regional temperature differences (seasonal/diurnal);
k. overall, oceans warm the planet (by absorbing solar radiation)...;
I. ...due to water's high thermal capacity...;
m. water masses increase humidity of adjacent region (due to higher evaporation);
n. warm ocean currents transfer heat from equator to poles / cold ocean current absorb heat from atmosphere as they move from Poles toward Equator...;
o. ...(warm currents) increasing temperatures in certain regions/e.g. Gulf Stream / (cold currents) decreasing temperatures in certain regions/e.g. Labrador current;
p. warm ocean currents also increase precipitation in coastal regions/e.g. Southwest Monsoon Current / cold ocean currents decrease precipitation in coastal regions/e.g. Peru Current...;
q. ...(warm) due to increased evaporation during the summer (period of higher insolation)/e.g. monsoons in Bay of Bengal, which is helped by...;
r. ...advection of vapor by prevailing onshore winds;
s. ...(cold currents) due to cold air holding less moisture;
t. formation of ice / increased cloud cover increases albedo, thus may stabilize global warming (negative feedback) / reduce regional temperature;
u. melting of ice / reduced cloud formation decreases albedo, thus may contribute to global warming (positive feedback) / increase regional temperature;
v. increased evaporation may contribute to global warming, as water vapour is a greenhouse gas;
w. ocean acts as a carbon sink sequestering CO2, thus reducing global warming;
Note: Description of the tri-cellular model of air circulation should gain marks as above; i.e. no separate mark for stating e.g. "Hadley cell". No credit for wind effects not linked to water (as, for example, in MPr).
Marking guidance:
Allow up to [2max] for reference to global warming.
Evaluate management strategies for reducing the impact of agricultural pollution on an aquatic ecosystem.
The following guide for using the markbands suggests certain features that may be offered in responses. The five headings coincide with the criteria in each of the markbands (although ESS terminology has been conflated with "understanding concepts"). This guide simply provides some possible inclusions and should not be seen as requisite or comprehensive. It outlines the kind of elements to look for when deciding on the appropriate markband and the specific mark within that band.
Answers may demonstrate:
- understanding concepts \& terminology of agricultural pollution; inorganic fertilizers; organic run-off/slurry; persistent pesticides; biomagnification; erosion; spraying; biological control; buffer zones; organic fertilizers; eutrophication; mud-pumping; re-introduction of aquatic species; levels of pollution management etc.
- breadth in addressing and linking different forms of agricultural pollutants with effective management strategies to protect or clean-up different aquatic ecosystems.
- examples of different pollutants; agricultural practices; management strategies; aquatic systems etc.
- balanced analysis evaluating advantages and disadvantages of management strategies employed to reduce impacts of agricultural pollution.
- a conclusion that is consistent with, and supported by analysis and examples given e.g. The most effective management strategies are those that prevent pollutants being released in the first place e.g. replacing inorganic with organic fertilizers, but this is not always the most economically feasible for farmers.
Please see markbands on page 18