CHAPTER 4 Anthropogenic effects on ecosystems

Learning Outcomes

  • Students will be able to understand:
    • Ecosystem goods & services and the implications of disturbance/destruction.
    • Short-term threats to ecosystems.
    • Long-term threats to ecosystems.

Key Definitions & Core Concepts

  • Anthropogenic: Environmental change caused or influenced by humans (directly/indirectly).
  • Ecosystem: Biotic + abiotic components and their interactions.
  • Human-dominated techno-ecosystems: Human-created arrangements replacing natural systems in modern society.
  • Carrying capacity: Maximum population size Earth can sustain; difficult to estimate, must consider multiple constraints (food, fuel, wood, clothing, transport).
  • Ecological footprint (Wackernagel & Rees, 1996): Hectares needed to support a given population.
  • Three pillars of ecosystem health:
    1. Challenge of invasive species.
    2. Measurement of ecosystem services.
    3. Concept of sustainability.

Human Population & Growth Trends

  • Earth’s population in early 2000s ≈ 6.4 billion6.4\,\text{billion}; in 20142014 > 7.3 billion7.3\,\text{billion}.
  • Grew by 2 billion2\,\text{billion} in 25 years; projected > 9.3 billion9.3\,\text{billion} by 20502050 (UN).
  • Current net increase ≈ 80\,\text{million yr^{-1}} though growth rate is slowing.
  • Economic growth highly unequal within/between nations.

Human Motivations & Activities

  • Secure food, shelter, economic security, social protection.
  • Resultant activities: agriculture, industry, housing, transport, mining, energy production, war, etc.

Invasive Species Examples & Significance

  • Kudzu vine overrunning farm equipment; red imported fire ant (Solenopsis invicta).
  • Not all introduced species are harmful, but a few cause massive ecological & economic damage.

Ecosystem Goods & Services (EGS)

  • Goods: food, freshwater, wood, fuel, fibers, oils, raw materials.
  • Services: waste breakdown, climate regulation, erosion control, pest regulation, nutrient cycling, pollination.
  • Categories (Millennium Ecosystem Assessment, MEA):
    • Provisioning (goods).
    • Regulating (processes).
    • Cultural (non-material benefits).
    • Supporting (primary productivity, habitat)—underpin the other three.
  • Largest single service value: nutrient cycling.
  • Pollination & freshwater easiest to quantify.
  • Without EGS, societies collapse; artificial self-sustaining ecosystems currently impossible.

Millennium Ecosystem Assessment (2005)

  • Involved 360360 scientists from 9696 countries.
  • Found >60%60\% of EGS classes degrading/used unsustainably (Table 1-1 synopsis):
    • 17 % enhanced, 20 % mixed, 63 % degraded.
  • Concluded worsening trends will threaten human well-being within 50 years unless reversed.
  • Other global/regional assessments (e.g., GEO, IPBES, IUCN Red List) echo similar results.

Ecosystem Health: Divergent World-Views

  • Technological optimists: Believe innovation will solve environmental stresses.
  • Technological skeptics: Doubt technology alone can offset degradation; emphasize limits and ecological thresholds.

Climate Change as a Long-Term Threat

  • Fossil-fuel combustion in 20132013: 91.3\,\text{Mbbl oil day^{-1}}, 324\,\text{Bcf natural gas day^{-1}}, 11.6\,\text{Mt coal day^{-1}} ➔ 80\,\text{Mt CO_2 day^{-1}}.
  • Atmospheric CO2CO_2 rose from 280 ppm280\,\text{ppm} (1900) to 400 ppm400\,\text{ppm} (2014); \approx 2\,\text{ppm yr^{-1}}.
  • Greenhouse effect warms lower atmosphere; documented by IPCC (Fifth Assessment, 2013-14).
  • Impacts: ice melt, sea-level rise, stronger storms, ocean acidification (declining pH, carbonate ions).
  • Mitigation = emissions reduction; needs binding treaty + unilateral national actions.

Natural Resources, Valuation & Public Goods

  • Natural resources = ecosystem capital when assigned monetary value.
  • Markets price provisioning goods well, but fail on regulating/supporting/cultural services (public goods: non-excludable, non-rival).
  • Example: small-scale logging seems profitable locally but large-scale removal causes long-term regional climate loss.
  • Property rights shape consumptive vs productive use.

Types of Ecosystem Uses

  • Consumptive use: Direct harvest for survival (food, fuel, shelter).
  • Productive use: Harvest for economic markets (timber, fish, domestication).

Comprehensive List of Human Threats (A–K)

A. Modern agriculture (deforestation, monocultures, irrigation, agro-chemicals).
B. Animal husbandry (feed demand, GHG emissions).
C. Fishing (overfishing, community alteration).
D. Energy industry: fossil, thermal, petroleum, nuclear, hydro, wind.
E. Manufactured products: detergents, nanotech, paints, paper, pesticides, PPCPs.
F. Mining (erosion, sinkholes, contamination).
G. Housing (resource consumption, habitat loss).
H. Transport (energy use, habitat fragmentation, pollution).
I. Forestry (invasive species, monocultures, biodiversity loss).
J. Tourism/recreation (sensitive-area damage).
K. War (pollution, habitat destruction).

Terrestrial Ecosystems

Forests

  • Supply diverse goods & critical services (biodiversity conservation, carbon storage, hydrology control).
  • Deforestation = greatest threat; 100 M ha degraded since 20002000, e.g., Indonesian palm-oil expansion, Haiti vs Dominican Republic border contrast.
  • Short-term impacts: ↓productivity, livelihood loss, nutrient depletion, soil erosion, altered hydrology.
  • Long-term impacts: regional drying, desertification, loss of carbon sinks, biodiversity decline.
  • Additional stresses: air pollution, invasive species, pests, disease, fire.

Grasslands

  • Up to 80%80\% of U.S. native grasslands converted to agriculture.
  • Short-term impacts: wildlife decline (antelope, bison), erosion, ↓carbon storage, ↓groundwater recharge.
  • Practices such as plowing, over-grazing, over-irrigation ➔ erosion, salinization, eventual desertification.

Ocean Ecosystems

  • Provide food (fish), climate regulation (heat transport, carbon uptake), coastal protection (mangroves, reefs), biodiversity.
  • Conveyor belts (thermohaline circulation) moderate global climate.

Short-Term Ocean Threats

  • Overharvest of fish, loss of coastal habitats, coral degradation, localized pollution (trash, oil, sediment).

Long-Term Ocean Threats

  • Climate change, acidification, deoxygenation (dead zones), governance gaps ➔ lawlessness.
Overfishing & Food-Web Collapse
  • ~50%50\% of stocks at max sustainable; ~33%33\% beyond.
  • High-tech fleets (sonar, 200-ft trawls) ➔ habitat destruction.
  • Bycatch often exceeds target catch.
  • Fishing down the food chain: sequential depletion from top predators to lower trophic fish, altering ecosystems.
  • Restoration could add ≥10 Mt\ge 10\,\text{Mt} catch if temporary moratoria/sustainable management enforced.
Coastal Habitat Loss
  • Salt marshes: ≈50%\approx 50\% lost; mangroves: ≈50%\approx 50\% cut since 19831983.
  • Mangroves offer storm protection (e.g., 2004 tsunami), nurseries, carbon sequestration; conversion to shrimp farms, rice paddies, fuelwood ongoing.
Coral Reefs
  • Protect shores; biodiversity hotspot; tourism magnet.
  • ≈20%\approx 20\% destroyed; threats: dynamite/cyanide fishing, trawling, warming, acidification, bleaching (loss of algal symbionts).
  • Ocean acidification: ↓carbonate ions ➔ harder skeleton formation, potential reef wipe-out.
Pollution & Dead Zones
  • Plastics, oil, agricultural nutrients cause hypoxia; large "dead zones" unsuitable for life.
Lawlessness on High Seas
  • UN Law of the Sea (1982) left high seas as common property; illicit fishing 20–32 % of U.S. seafood imports.
  • Linked crimes: black-market fish, slavery, drug/weapons smuggling.
  • Need updated treaties as tech enables deep-sea exploitation.

Aquaculture: Promise & Problems

  • Rapid growth supplies seafood, reduces poverty, restores functions (oyster reefs).
  • Issues: mangrove destruction (shrimp), inefficient fish-in-fish-out protein conversion, disease transfer, nutrient pollution.
  • Nearshore space limited ➔ interest in open-ocean aquaculture; still under-developed.

Ethical, Philosophical & Practical Implications

  • Poverty drives over-exploitation; conservation strategies must meet human needs sustainably.
  • EGS are undervalued; calls for new stewardship ethic (Kofi Annan, 2000).
  • Technological fixes alone insufficient; require policy, global cooperation, valuation reform.

Key Numbers & Formulas (LaTeX)

  • Global population milestones: 6.4 billion→7.3 billion6.4\,\text{billion} \rightarrow 7.3\,\text{billion} (2014); projected >9.3\,\text{billion} (2050).
  • Atmospheric CO$_2$ increase: Δppm=400−280=120\Delta \text{ppm} = 400 - 280 = 120 over 1900–2014; \approx 2\,\text{ppm yr^{-1}}.
  • Fossil-fuel CO$_2$ flux (2013): 80\,\text{Mt day^{-1}}.
  • Marine fishery potential increase if restored: \ge 10\,\text{Mt yr^{-1}}.

Examples, Analogies & Case Studies

  • Kudzu engulfing tractor illustrates invasive takeover.
  • Haiti vs Dominican Republic border: stark visual of deforestation consequences.
  • Trawling likened to "clear-cutting" forests (destroying benthic habitats).
  • Shrimp farm vs mangrove loss: short-term private gain vs long-term communal loss.

Connections to Previous Principles

  • Energy flow & nutrient cycling governed by same ecological laws across biomes.
  • Greenhouse effect relates to basic radiative forcing learned in climate science.

Conclusion & Stewardship

  • Human exploitation rising with population; protective measures must scale accordingly.
  • Developing-world poverty makes conservation hardest; requires leadership + international aid.
  • "New ethic of stewardship": preserve forests, fisheries, biodiversity before irreversible collapse.

References for Further Study

  • Krebs, C.J. (2014) Ecology: The Experimental Analysis of Distribution and Abundance.
  • Wright, R.T. & Boorse, D.B. (2017) Environmental Science: Toward a Sustainable Future.