Exercises: Waste and biodiversity

Define what a xenobiotic is and give two examples, explaining why decomposing organisms find it difficult to degrade these substances.

Differentiate between bioaccumulation and biomagnification using a three-level marine food chain of your choice.

List the waste management hierarchy (reduce, reuse, recycle, recover, and dispose) ordered from most to least recommended, and give an everyday example of each level.

The diagram shows the concentration of a persistent pesticide in a bay food chain. Calculate the biomagnification factor between water and fish-eating birds (marked with '?'), and explain why apex predators are always the most affected.

Explain what microplastics are, what their two main sources are, and why it is so difficult to remove them from the ocean. Propose two effective measures to reduce their entry into the sea.

Relate loss of biodiversity to loss of ecosystem services using two specific examples (for example pollinators, wetlands, or reefs), and indicate which type of service is degraded in each case.

A landfill closed 15 years ago on fractured karst limestone lacks a basal geomembrane. Located 800 m downslope is a spring that supplies a town and feeds a protected wetland. Analysis of the spring water shows: electrical conductivity of 2400 µS/cm (natural baseline value: 450 µS/cm), ammonium at 12 mg/L (legal limit: 0.5 mg/L), traces of benzene, and a drop in dissolved oxygen to 1.8 mg/L in the wetland.

1. a) Justify hydrogeologically why the lithology of the substrate accelerates the impact, and predict the consequences of this chemical cocktail on the wetland's food web.
2. b) A town councillor proposes "pumping clean water into the landfill to dilute the groundwater contamination". Refute his proposal technically, demonstrating what hydrogeological risks it would trigger.
3. c) Design an urgent three-phase action plan (immediate hydraulic containment, leachate sealing/collection, and bioremediation), justifying the chronological order of each measure to prevent the collapse of the ecosystem.

The zebra mussel and tiger mosquito are invasive alien species in Mexico. Explain what characteristics make a species invasive, how these two damage biodiversity and ecosystems, and what control measures are applied against them.

Following a diesel spill in a peri-urban sandy soil, three in situ bioremediation plots are tested over 90 days, monitoring the concentration of total petroleum hydrocarbons (TPH) starting from an initial value of 15 000 mg/kg:

• Plot A (natural attenuation, no intervention): final TPH = 13 800 mg/kg; degrading bacterial population = 10⁴ CFU/g.

• Plot B (biostimulation with the addition of N and P at a C:N:P ratio of 100:10:1 and periodic tilling for aeration): final TPH = 1200 mg/kg; degrading population = 10⁸ CFU/g.

• Plot C (bioaugmentation with a commercial inoculum of allochthonous degrading bacteria, without nutrient correction or tilling): final TPH = 11 500 mg/kg; introduced bacteria drop to undetectable levels after 20 days.

1. a) Interpret the results by comparing B and C: justify which factor was limiting biodegradation in the original soil and identify why bioaugmentation failed.
2. b) Reasonably predict what would have happened in Plot B if the soil had become waterlogged due to continuous torrential rains, indicating which microbial metabolic pathways would be affected.
3. c) If the hydrocarbons had migrated to the saturated zone (a deep anoxic aquifer), justify why physicochemical methods (such as multi-phase extraction or permeable reactive barriers) would compete advantageously against standard aerobic biostimulation.