TU BSc First Year — Answers

1.1 Characteristics of Community and Measurement of Heterogeneity

Characteristics of a Community

An ecological community is an assemblage of populations of different species living together and interacting in a given area. Its main characteristics are:

1. Species composition — each community has a characteristic set of species; some are dominant, some rare.
2. Species diversity — includes species richness (number of species) and evenness (relative abundance).
3. Dominance — one or a few species exert the greatest influence by virtue of size, number or biomass (e.g., Shorea robusta in a sal forest).
4. Growth form and structure — stratification into layers (canopy, sub-canopy, shrub, herb, ground) and life forms (trees, shrubs, herbs, epiphytes).
5. Trophic structure — organisation into producers, consumers and decomposers, with food chains and food webs.
6. Periodicity — seasonal changes in flowering, fruiting, leaf fall and animal activity.
7. Succession and stability — communities change over time (seral stages) and resist or recover from disturbance.
8. Productivity — rate of organic matter production, differing between communities.
9. Ecological niches and interactions — competition, predation, parasitism, mutualism, commensalism.
10. Boundaries — communities may be sharply delimited (ecotone) or grade gradually (continuum).

Measurement of Heterogeneity in an Ecosystem

Heterogeneity means the variety and spatial/temporal variability of species and habitats. It is measured as:

(a) Species richness (S) — total number of species present in the sample.

(b) Diversity indices

• Shannon–Wiener index: $H' = -\sum_{i=1}^{S} p_i \ln p_i$ where $p_i$ = proportion of individuals of the i-th species. Higher $H'$ = greater heterogeneity.

• Simpson's index of dominance: $D = \sum p_i^2 \qquad \text{and} \qquad 1-D \text{ (Simpson's diversity)}$

• Evenness: $E = \frac{H'}{\ln S}$ Values near 1 indicate even distribution of individuals among species.

(c) Alpha, beta and gamma diversity (Whittaker)

• Alpha (α) diversity — diversity within a single community.
• Beta (β) diversity — turnover of species between communities; measured as $\beta = \frac{\gamma}{\bar{\alpha}} \quad \text{or by } \beta_w = \frac{S}{\bar{\alpha}} - 1$
• Gamma (γ) diversity — total diversity of a large region.

(d) Habitat/structural heterogeneity — measured by quadrat sampling, point-intercept method, remote sensing, GIS, edge density, patch size and number, and by the coefficient of variation of environmental variables (light, moisture, nutrients).

(e) Species–area curve — the slope z of $\log S = \log c + z \log A$ indicates how rapidly richness increases with area, hence habitat heterogeneity.

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1.2 Measuring Primary and Secondary Productivity in a Terrestrial Ecosystem

Productivity is the rate of production of organic matter per unit area per unit time (g m⁻² yr⁻¹ or kcal m⁻² yr⁻¹).

Primary Productivity

Gross Primary Productivity (GPP) = total organic matter fixed by green plants in photosynthesis. Net Primary Productivity (NPP) = GPP − respiration of plants.

Methods of measurement:

1. Harvest method (dimension analysis) — the most widely used field method.

   • Vegetation is clipped from a known area (quadrat) at intervals.
   • Biomass is oven-dried at 65–80 °C to constant weight and weighed.
   • NPP is calculated from the change in biomass plus litter fall: $\text{NPP} = \Delta B + L + G$ where $\Delta B$ = change in standing biomass, L = litter production, G = grazing loss.
   • Below-ground productivity is estimated by soil coring and root washing.

2. Gas exchange / CO₂ flux method — an infrared gas analyser (IRGA) in a closed chamber measures CO₂ uptake and release. GPP is obtained from net CO₂ uptake plus respiration measured at night or from darkened chambers.

3. Oxygen method — changes in dissolved or gaseous O₂ in enclosed chambers (mainly aquatic, but applicable to soil/plant chambers).

4. Radioactive tracer method — ¹⁴CO₂ fed to plants; the labelled carbon incorporated gives a measure of photosynthetic rate.

5. Chlorophyll method — productivity estimated from chlorophyll content and light absorption, using light-use efficiency models.

6. Remote sensing / light-use efficiency models — NDVI from satellites combined with absorbed photosynthetically active radiation (APAR) and conversion efficiency gives large-scale NPP.

Secondary Productivity

Secondary productivity is the rate of formation of heterotroph biomass (herbivores, carnivores, decomposers).

Methods of measurement:

1. Population dynamics method — from changes in numbers and mean individual mass: $P = \Delta B + \text{deaths} + \text{emigration} - \text{immigration (biomass basis)}$ Requires mark–recapture, quadrat counts or trapping to estimate density and mortality.

2. Feeding/assimilation method — measured as: $P = I - (F + U + R)$ where I = ingestion, F = faeces, U = urine, R = respiration. Food consumption is measured by gut-content analysis or feeding trials; respiration by respirometry.

3. Growth increment method — animals are marked, weighed and recaptured at intervals; growth in biomass per unit time gives productivity.

4. Radioisotope labelling — ³²P or ¹⁴C labelled food traces the flow of energy into consumer trophic levels.

5. Consumption method (ecological efficiency approach) — secondary production estimated as a fixed fraction (ecological efficiency, ~10 %) of the energy ingested at the previous trophic level.

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1.3 Ion-Exchange Reaction in Soils and Effect of Pesticides

Ion Exchange in Soil

Soil colloids (clay minerals and humus) carry negative charges from isomorphous substitution and dissociation of –OH and –COOH groups. These charges attract and hold exchangeable cations (Ca²⁺, Mg²⁺, K⁺, Na⁺, H⁺, Al³⁺) in the diffuse double layer. Cations are held electrostatically but are not fixed; they can be replaced by other cations in the soil solution. This reversible replacement is cation exchange:

$\text{Clay}^-\text{Ca}^{2+} + 2\,\text{K}^+ \rightleftharpoons \text{Clay}^-2\text{K}^+ + \text{Ca}^{2+}$

The total amount of exchangeable cations a soil can hold is the Cation Exchange Capacity (CEC), expressed in cmol(+)/kg. It is high in clay and organic soils and low in sandy soils. The readiness with which a cation is replaced is its lyotropic series:

$\text{Al}^{3+} > \text{Ca}^{2+} > \text{Mg}^{2+} > \text{K}^+ = \text{NH}_4^+ > \text{Na}^+ > \text{H}^+$

Soils at low pH also show anion exchange on positively charged sites (iron and aluminium oxides), where OH⁻ is replaced by H₂PO₄⁻, SO₄²⁻ or Cl⁻.

Significance: cation exchange controls nutrient retention and availability, soil pH, base saturation, fertilizer response and soil fertility.

Effect of Pesticides on Ion Exchange

1. Cationic pesticides (e.g., paraquat, diquat) are adsorbed strongly on negatively charged clay and humus surfaces by cation exchange, replacing Ca²⁺, Mg²⁺ and K⁺. This reduces the availability of these nutrient cations and makes the pesticide less mobile and less biodegradable.
2. Anionic pesticides (e.g., 2,4-D, MCPA) are repelled by negative colloids and are adsorbed on positively charged oxide surfaces by anion exchange with OH⁻, raising soil pH slightly.
3. Non-ionic pesticides are held by weak van der Waals and hydrogen bonding, not by true ion exchange, but they still compete for adsorption sites.
4. Displacement of nutrient ions into the soil solution increases leaching losses of K⁺, Ca²⁺ and Mg²⁺, lowering base saturation and CEC over time.
5. Change in soil pH caused by pesticide residues alters the charge on variable-charge colloids, thereby changing CEC and anion exchange capacity.
6. Reduced microbial activity by pesticides slows organic matter decomposition, which lowers the formation of humus colloids and hence lowers CEC in the long run.

OR — Composition of the Atmosphere and Processes Affecting Its Chemistry

Composition of the Atmosphere (dry air, by volume)

Water vapour is variable (0–4 % by volume). Aerosols, dust and particulate matter are also present in small amounts.

Processes Affecting Atmospheric Chemistry

1. Photochemical reactions — solar UV radiation breaks O₂ into oxygen atoms, forming ozone; it also drives smog formation (NOₓ + VOCs → PAN, ozone).
2. Volcanic activity — releases CO₂, SO₂, H₂S and ash; SO₂ forms sulphate aerosols.
3. Biological processes — photosynthesis fixes CO₂; respiration and decomposition release CO₂; denitrification and nitrogen fixation control N₂O and N₂.
4. Industrial and anthropogenic emissions — burning of fossil fuels releases CO₂, SO₂, NOₓ, CO and soot.
5. Atmospheric transport and mixing — winds and convection distribute gases and pollutants globally.
6. Wet and dry deposition — rain, snow and dust remove gases and particles, forming acid rain (H₂SO₄, HNO₃).
7. Photolysis and oxidation by OH radicals — the hydroxyl radical is the main "cleaning agent" that oxidises CH₄, CO and VOCs.
8. Ocean–atmosphere exchange — oceans absorb CO₂ and release dimethyl sulphide and sea salt aerosols.
9. Radioactive decay — radon and carbon-14 production affect trace composition.
10. Greenhouse effect and radiative forcing — rising CO₂, CH₄ and N₂O alter the thermal structure and hence reaction rates.

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1.4 Processes and Factors Affecting Soil Genesis

Soil genesis is the formation of soil from parent material through the combined action of climate, organisms, relief, parent material and time (Jenny's equation):

$S = f(Cl,\ O,\ R,\ P,\ T)$

Processes of Soil Genesis

1. Weathering — physical (temperature, frost, water, wind), chemical (hydration, hydrolysis, oxidation, carbonation, solution) and biological (roots, microbes, lichens) breakdown of rock into regolith.
2. Humification — decomposition of plant and animal residues by microorganisms to form dark, colloidal humus.
3. Eluviation — downward leaching of clay, iron, aluminium and organic matter from the A horizon, leaving it sandy and pale.
4. Illuviation — deposition of leached materials in the B horizon, making it clay-rich and coloured.
5. Podzolization — leaching of Fe and Al oxides under acid, coniferous conditions, giving a bleached E horizon and a dark B horizon.
6. Laterization — intense leaching of silica and bases under hot, humid conditions, leaving Fe and Al oxides (laterite).
7. Calcification — precipitation of CaCO₃ in the B horizon under semi-arid conditions.
8. Salinization and alkalization — accumulation of soluble salts or sodium in arid, poorly drained soils.
9. Gleization — reduction of iron under waterlogged, anaerobic conditions, producing grey, mottled colours.
10. Pedoturbation — mixing of soil by roots, earthworms, frost action or cultivation.

Factors Affecting Soil Genesis

1. Climate — temperature and rainfall control weathering rate, leaching, organic matter and soil type; the most active factor.
2. Parent material — determines texture, mineral composition, pH and nutrient status; e.g., basalt gives clayey, fertile soil, sandstone gives sandy soil.
3. Organisms — vegetation supplies organic matter; microbes decompose it; earthworms and burrowing animals mix soil; humans modify soil through tillage and fertilization.
4. Relief (topography) — slope affects drainage, erosion and depth; steep slopes give shallow, eroded soils; flat, poorly drained areas give waterlogged soils.
5. Time — soil develops through youth, maturity and old age; older soils are deeper, more weathered and more leached.
6. Groundwater — its depth and quality affect gleization, salinization and moisture regime.
7. Human activity — deforestation, terracing, irrigation, fertilizer and pesticide use accelerate or retard soil formation.

2.1 Major land-related issues in Nepal

• Fragmentation and landlessness: repeated division of holdings among heirs leaves most farms under 0.5 ha, while many Terai and hill households (Kamaiya, Haliya and Dalit families) have little or no land.
• Unequal distribution and tenancy: a few owners hold large areas, and dual ownership (landlord and tenant) causes disputes.
• Degradation: soil erosion, landslides and nutrient loss on steep Siwalik and Mahabharat slopes; river cutting and flooding in the Terai.
• Encroachment: forest, public and riverbank land is occupied for settlement, and fertile land is lost to unplanned urbanisation.
• Abandonment: out-migration leaves terraces fallow.
• Weak governance: poor land records, weak implementation of land reform and land-use policy.

2.2 Societal development and the environment

Development raises living standards but increases pressure on nature. Negative impacts: resource depletion (forests, minerals, water), land-use change, air, water and soil pollution, greenhouse gas emission and climate change, ozone depletion, biodiversity loss, solid waste, and disruption of biogeochemical cycles. Positive impacts: better technology, cleaner energy, environmental education and laws, and conservation programmes (e.g. community forestry in Nepal). Sustainable development is needed to balance the two.

2.3 Factors regulating population size in ecosystems

Population size changes through natality, mortality, immigration and emigration.

• Density-dependent factors: act more strongly as density rises, e.g. food and space competition, predation, parasitism and disease, accumulation of wastes, emigration. They produce logistic (S-shaped) growth up to the carrying capacity $K$.
• Density-independent factors: act regardless of density, e.g. floods, drought, fire, earthquakes, frost, human activity. They cause J-shaped growth followed by a crash.

2.4 Anthropogenic effects on the phosphorus cycle

Phosphorus has no gaseous phase, so human activity changes it mainly through: mining phosphate rock for fertilizer; heavy fertilizer use and runoff; detergents, sewage and animal waste adding phosphate to water, causing eutrophication and algal blooms; deforestation and erosion increasing P loss from soil; intensive livestock farming; and depletion of finite phosphate reserves.

2.5 Volumetric and gravimetric analysis in water quality

• Volumetric (titrimetric): a reagent of known concentration is added until the end point. Used for alkalinity, acidity, hardness (EDTA), chloride (argentometric), dissolved oxygen (Winkler) and COD.
• Gravimetric: the constituent is isolated and weighed. Used for total dissolved solids (TDS), total suspended solids (TSS), sulphate (as $\text{BaSO}_4$), and silica.

Volumetric methods are quick and suit routine work; gravimetric methods are accurate but slower.

2.6 Extreme weather events and tornado formation

Extreme weather events are rare, severe weather phenomena such as cyclones, tornadoes, floods, droughts, heat waves, cold waves, hailstorms and cloudbursts.

A tornado is a violently rotating column of air extending from a thunderstorm cloud to the ground. Formation: (1) warm moist air near the surface meets cold dry air aloft, giving strong instability; (2) a supercell thunderstorm develops with a strong updraft; (3) wind shear (wind changing speed and direction with height) creates a horizontal rolling tube of air; (4) the updraft tilts it vertical, forming a rotating mesocyclone; (5) the rotation tightens and stretches, spinning faster; (6) a funnel descends from the cloud base; (7) when it touches the ground it is a tornado.

2.7 Stability conditions in the atmosphere

Stability depends on the environmental lapse rate (ELR) compared with the dry (DALR, about $9.8\,^\circ$C/km) and saturated (SALR, about $4$-$6\,^\circ$C/km) adiabatic lapse rates.

2.8 Mountain building processes

Orogeny results mainly from plate tectonics. (1) Plate collision: continent-continent collision (India-Eurasia gave the Himalaya), oceanic-continental subduction (Andes) and island-arc formation. (2) Folding and thrusting shorten and thicken the crust. (3) Faulting and block uplift create fault-block mountains. (4) Volcanism builds volcanic mountains. (5) Isostatic uplift raises thickened crust as it rebounds. (6) Erosion later sculpts the relief.

2.9 Abundance of minerals in the Earth

The crust is about 46.6% O, 27.7% Si, 8.1% Al, 5.0% Fe, 3.6% Ca, 2.8% Na, 2.6% K, 2.1% Mg. So silicate minerals make up about 90% of the crust, mainly feldspars (about 50%), quartz, pyroxene, amphibole, mica and olivine. Oxides, carbonates, sulphides, sulphates and halides are minor. The mantle is mostly olivine and pyroxene (Mg-Fe silicates), and the core is Fe-Ni metal. Abundance is controlled by element abundance, crystallisation conditions and mineral stability.

2.10 Soil types in Nepal

• Terai: alluvial soils (fertile, rice, wheat, sugarcane); sandy/gravelly soils in the Bhabar belt at the foot of the Churia.
• Siwalik (Churia): coarse, sandy, porous residual soils, highly erodible.
• Dun valleys: Chitwan and similar, alluvial and colluvial.
• Middle hills: red-yellow (lateritic) soils on old terraces; brown forest soils; residual soils on slopes.
• Kathmandu valley: lacustrine clays and silts, fertile.
• High mountains: podzolic soils under coniferous forest, alpine meadow soils, and thin glacial/tundra soils at high altitude.

3.1 Agrarian and industrial society

3.2 Clumped and random distribution

3.3 Alpha and beta diversity

3.4 Spatial and hypervolume niche

3.5 Linear and Y-shaped energy flow model

3.6 Production and decomposition

3.7 Potentiometric and conductometric titration

3.8 Lapse rate and temperature inversion

3.9 Turbulence and diffusion

3.10 Crust and mantle

TU BSc First Year — Attempt All Questions

1.1 What is an ecosystem? Describe structural and functional components of a lentic ecosystem.

Ecosystem: An ecosystem is a self-regulating, interacting unit consisting of a biotic community (living organisms) and its abiotic environment (physical and chemical factors), through which energy flows and matter cycles. The term was coined by A. G. Tansley (1935).

Structural components of a lentic ecosystem (standing or slowly moving freshwater, e.g. pond, lake)

A. Abiotic (non-living) components

1. Inorganic substances: Water, dissolved CO₂, O₂, N₂, calcium, phosphorus, sulphur, and other mineral nutrients.
2. Organic substances: Humic acids, proteins, carbohydrates, lipids, and detritus dissolved or suspended in water.
3. Physical factors: Light (penetration depth), temperature (thermal stratification), pH, salinity, density, and depth.

B. Biotic (living) components

1. Producers (autotrophs): Phytoplankton (diatoms, Chlorella, Volvox), floating macrophytes (Eichhornia, Lemna), rooted submerged plants (Hydrilla, Vallisneria), and marginal plants (Typha).
2. Consumers (heterotrophs):
   • Primary consumers (herbivores): Zooplankton (Daphnia, Cyclops), snails, tadpoles, small fishes.
   • Secondary consumers (carnivores): Small carnivorous fishes, frogs, water insects.
   • Tertiary consumers (top carnivores): Large fishes, snakes, kingfishers, herons.
3. Decomposers (saprotrophs): Bacteria and fungi that break down dead organic matter and release nutrients.

Functional components

1. Energy flow: Unidirectional flow of energy from the sun → producers → consumers → decomposers, following the 10 % law of energy transfer at each trophic level.
2. Food chain and food web: Grazing food chain (phytoplankton → zooplankton → fish) and detritus food chain (dead matter → bacteria → detritus feeders).
3. Nutrient cycling: Biogeochemical cycles (carbon, nitrogen, phosphorus) recycle matter between biotic and abiotic pools.
4. Productivity: Primary productivity (gross and net) by producers and secondary productivity by consumers.
5. Decomposition: Fragmentation, leaching, catabolism, humification, and mineralization of dead organic matter.
6. Homeostasis / self-regulation: Feedback mechanisms maintain stability against disturbances.

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OR

Types of productivity

1. Primary productivity: Rate of organic matter synthesis by autotrophs.
   • Gross Primary Productivity (GPP): Total organic matter fixed by producers in unit time.
   • Net Primary Productivity (NPP): NPP = GPP − Respiration (R). This is the energy available to consumers.
2. Secondary productivity: Rate of organic matter formation by heterotrophs (consumers) at higher trophic levels.

Can we conclude that the cropland has higher productivity than the grassland?

No, we cannot conclude this from standing crop biomass alone.

Reasons:

1. Standing crop ≠ productivity. Standing crop is the amount of biomass present at a given moment, whereas productivity is the rate of biomass production per unit time. A large standing crop may simply mean that biomass is being removed slowly, not that it is being produced faster.
2. Harvesting in cropland. In cropland, biomass is removed periodically (harvest), so the standing crop measured at one time may actually under-represent total production. Conversely, a heavily grazed grassland has its biomass continuously removed by herbivores, so its standing crop stays low even though its productivity may be high.
3. Turnover rate. Grassland has a rapid turnover — biomass is produced and consumed quickly. Cropland has a slower turnover but accumulates more biomass before harvest.
4. Comparison requires annual NPP. Only by measuring net primary productivity over a full year (g/m²/yr) can productivity be compared fairly.

Conclusion: Standing crop is a poor index of productivity. The cropland may have a higher standing crop but not necessarily higher productivity; a heavily grazed grassland can have productivity equal to or even greater than cropland.

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1.2 Density-dependent population regulation; exponential and logistic growth models

Density-dependent population regulation: Regulation of population size by factors whose effect increases as population density rises. These are biotic factors such as competition for food and space, predation, parasitism, and disease. As density increases, birth rate falls and death rate rises, bringing the population back toward the carrying capacity (K). Such regulation keeps populations stable and is density-dependent.

Exponential (J-shaped) growth model

When resources are unlimited and the environment is ideal, population grows at a rate proportional to its size:

$\frac{dN}{dt} = rN$

where N = population size, r = intrinsic rate of natural increase, t = time.

Integrating: N_t = N₀ e^{rt}

The curve is J-shaped — growth is slow at first, then accelerates rapidly without limit. It occurs in newly introduced species or in laboratory conditions with abundant resources.

Logistic (S-shaped) growth model

In nature resources are limited, so growth slows as density increases. The model is:

$\frac{dN}{dt} = rN\left(\frac{K - N}{K}\right)$

where K = carrying capacity (maximum population the environment can support).

Integrating by partial fractions:

$N_t = \frac{K}{1 + \left(\frac{K-N_0}{N_0}\right)e^{-rt}}$

where $N_0$ is the initial population size.

The curve is S-shaped (sigmoid) with three phases:

1. Lag phase: slow initial growth.
2. Log (exponential) phase: rapid growth.
3. Stationary phase: growth levels off at K, where births = deaths.

The term (K − N)/K is the environmental resistance, which increases as N approaches K. Real populations generally follow the logistic model.

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1.3 Chemical and mineralogical composition of soil; soil types of Nepal

Chemical composition of soil

Soil consists of:

• Inorganic matter (~45 %): Weathered rock and mineral particles (sand, silt, clay).
• Organic matter (~5 %): Humus, dead and decaying plant and animal remains.
• Soil water (~25 %): With dissolved salts, forming the soil solution.
• Soil air (~25 %): O₂, CO₂, N₂ in the pore spaces.
• Living organisms: Bacteria, fungi, protozoa, earthworms, insects.

Chemically, soil contains oxides of Si, Al, Fe, Ti, Ca, Mg, K, Na, along with N, P, S and trace elements (Zn, Cu, Mn, B, Mo). The pH of soil ranges from acidic to alkaline and controls nutrient availability.

Mineralogical composition of soil

Soil minerals are of two types:

1. Primary minerals (from parent rock, unaltered): quartz, feldspar, mica, hornblende, augite, olivine.
2. Secondary minerals (formed by weathering): clay minerals — kaolinite, illite, montmorillonite, vermiculite; also gibbsite, goethite, haematite.

Clay minerals determine cation exchange capacity (CEC), water holding capacity, and fertility of soil.

Soil types of Nepal

Nepal has great variation in soil due to its varied relief and climate. Major types:

1. Alluvial soil: Found in the Terai and river valleys; fertile, rich in potash and lime, poor in nitrogen and organic matter. Best for agriculture.
2. Sandy and gravelly soil: Found in the Chure/Bhabar region; coarse, porous, low fertility.
3. Red and brown soil: Found in the mid-hills and inner Terai; rich in iron and aluminium oxides, moderately fertile.
4. Mountain and forest soil: Found in the hills and mountains; rich in organic matter, acidic, thin and stony.
5. Glacial / alpine soil: Found in the high Himalayas; immature, stony, low fertility, covered with snow most of the year.
6. Peaty / marshy soil: Found in marshy areas of Terai (e.g. Koshi Tappu); highly organic and acidic.

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1.4 Temperature lapse rate and its effect on pollutant dispersion

Temperature lapse rate: The rate at which atmospheric temperature decreases with increasing altitude. The normal (environmental) lapse rate in the troposphere is about 6.5 °C per 1000 m of ascent. This is also called the normal lapse rate.

Effect on dispersion of pollutants

The vertical temperature profile of the atmosphere controls how pollutants mix and disperse:

1. Normal lapse rate (temperature decreases with height): Warm air near the ground rises, carrying pollutants upward. This gives good vertical mixing and dispersion of pollutants.

2. Inversion (temperature increases with height): A layer of warm air lies above cooler air near the ground. This is a temperature inversion. It acts as a lid, preventing vertical mixing. Pollutants get trapped near the ground, causing severe air pollution (e.g. smog in Kathmandu Valley in winter mornings).

3. Neutral / isothermal conditions: Temperature is nearly constant with height; dispersion is moderate.

4. Unstable (superadiabatic) conditions: Temperature falls faster than normal; strong vertical mixing occurs, so pollutants disperse rapidly and are diluted.

Conclusion: A steep lapse rate (unstable atmosphere) favours pollutant dispersion, while an inversion strongly suppresses it and leads to pollutant accumulation near the ground.

2.1 Different Environmental Worldviews

An environmental worldview is a person's or society's basic set of beliefs about how the natural world works, what our place in it is, and how we ought to act towards it. Three broad categories are usually recognised.

1. Anthropocentric (human-centred) worldview. Humans are seen as the central and most important species, and nature exists mainly as a resource for human use. It is further divided into:

• Planetary management worldview: humans are separate from and superior to nature; nature is a resource to be managed for human benefit; technology and economic growth can solve environmental problems. This view dominates modern industrial societies.
• Stewardship worldview: humans have an ethical duty to care for the Earth as trustees for future generations, but may still use natural resources wisely.

2. Biocentric (life-centred) worldview. All living organisms have intrinsic value, not only humans. Every species has an inherent right to exist, and human use of nature must be restrained so that other life forms can survive. It is closer to the views of many indigenous and Eastern traditions.

3. Ecocentric (ecosystem-centred) worldview. The whole ecosystem — soil, water, air, organisms and their interactions — is valued, not just individual species. Humans are only one part of nature and are subject to ecological laws. It emphasises the carrying capacity of the Earth, limits to growth, and the need for sustainable, low-consumption lifestyles. Deep ecology and the "Earth-wisdom" worldview fall in this category.

In practice most people hold a mixture of these views. The worldview adopted by a society strongly influences its environmental policies — for example, forest nationalisation in Nepal reflected a planetary management view, while community forestry reflects a stewardship/ecocentric view.

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2.2 Need of Multidisciplinary Approach to Environmental Problems

Environmental problems are not purely scientific, nor purely economic or social — they arise from the interaction of natural systems with human systems. Hence no single discipline can understand or solve them; a multidisciplinary approach is essential.

1. Complex, multi-causal nature of the problems. Problems such as air pollution, deforestation, climate change or solid waste management arise from physical, chemical, biological, economic, cultural and political causes acting together. For example, indoor air pollution in Nepal is caused by biomass burning (technology), poverty (economics), kitchen design and gender roles (society), and weak regulation (policy).

2. Need for knowledge from many disciplines.

• Natural sciences (biology, chemistry, physics, geology, ecology) explain the mechanism and extent of damage.
• Social sciences (sociology, anthropology, economics, political science) explain why people behave as they do and how they may be motivated to change.
• Engineering and technology provide technical solutions such as treatment plants, cleaner stoves and renewable energy.
• Law and ethics provide standards, rights and enforcement.
• Health sciences assess the effects on human well-being.

3. Interdisciplinary solutions. A problem like urban solid waste needs engineers (collection and disposal), chemists (recycling and composting), economists (cost recovery), sociologists (public participation), and lawyers (rules). A single-discipline answer, e.g. only building a landfill, usually fails.

4. Sustainable development demands integration. Sustainability has ecological, economic and social pillars; balancing them requires integrated assessment, environmental impact assessment (EIA), and stakeholder participation — all multidisciplinary exercises.

5. Global and transboundary issues. Climate change, biodiversity loss and ozone depletion cross national and disciplinary boundaries, requiring international scientific panels (IPCC, IPBES) and multi-sectoral policy.

Conclusion. Environmental problems are "wicked problems" with no single technical fix. Only a multidisciplinary (and often interdisciplinary) approach can diagnose causes, weigh trade-offs, and produce solutions that are ecologically sound, economically viable and socially acceptable.

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2.3 Environmental Issues of Rural and Urban Nepal — Comparison

Similarities

• Both rural and urban Nepal face air pollution, though of different types (indoor biomass smoke in villages; vehicular and industrial pollution in cities).
• Both suffer from poor sanitation and unsafe drinking water, leading to water-borne diseases.
• Both are affected by climate change — floods, landslides, droughts, and changing rainfall patterns.
• Both generate solid waste, though quantity and composition differ greatly.
• Both experience deforestation and land degradation, driven by fuelwood demand in rural areas and by construction/urban expansion in cities.

Contrasts

Conclusion. Rural issues are mainly poverty- and biomass-linked, while urban issues are mainly pollution- and infrastructure-linked. Both ultimately stem from weak environmental governance, so solutions must be area-specific — rural biogas and spring-shed management, urban mass transport, sewerage treatment and proper landfill.

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2.4 Types of Competition and their Ecological Significance

Competition is an interaction between two or more organisms (of the same or different species) that require the same limited resource, in which the fitness of at least one is reduced.

Types of competition

1. Intraspecific competition — between members of the same species. Since requirements are identical, it is usually intense. It regulates population size and is a major agent of natural selection (e.g., seedlings of the same tree competing for light; male deer competing for mates).

2. Interspecific competition — between individuals of different species. Two main outcomes:

   • Interference (contest) competition: one species directly harms or excludes the other (e.g., allelopathy in plants, territorial defence in animals).
   • Exploitation competition: species compete indirectly by consuming the shared resource faster (e.g., two grazers on the same pasture).

3. Exploitative vs. scramble competition — in scramble competition all competitors get a share but all may suffer; in contest competition some winners get enough and losers get little.

4. Direct vs. indirect competition — direct when the resource is contested at the same time and place; indirect when one species depletes a resource used later by another.

Ecological significance

• Regulation of population size — competition for food, space and mates keeps populations within the carrying capacity of the habitat.
• Natural selection and evolution — it favours the better-adapted individuals, leading to adaptation, character displacement and, ultimately, evolution.
• Resource partitioning and coexistence — to reduce competition, species specialise (different feeding times, diets or microhabitats), which increases species diversity and niche differentiation.
• Competitive exclusion — Gause's principle states that two species with identical niches cannot coexist indefinitely; one is eliminated or shifts its niche. This shapes community structure.
• Determination of dominant species — competition decides which species dominates a community, influencing succession and ecosystem function.
• Maintenance of ecosystem stability — by controlling numbers and promoting diversity, competition contributes to balanced, stable ecosystems.

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2.5 Changes in Ecosystem Characteristics during Ecological Succession

Ecological succession is the gradual, directional and predictable change in community structure and composition at a site over time. The ecosystem changes in the following ways from the pioneer stage to the climax stage:

1. Species diversity and richness — increase from a few hardy pioneer species to many species; food chains and webs become longer and more complex.

2. Biomass and standing crop — total biomass, especially of plants, increases steadily and reaches a maximum at climax.

3. Net primary productivity (NPP) — rises in early stages, peaks at the middle seral stage, and declines at climax, where gross production ≈ respiration (P/R ratio approaches 1).

4. Trophic structure — simple food chains of early stages give way to complex, interconnected food webs; the number of trophic levels increases.

5. Niche specialisation and diversity — niches become narrower and more specialised; ecological niches increase in number.

6. Soil development — soil depth, humus, organic matter, nitrogen and other nutrients increase; soil texture and water-holding capacity improve; pH changes toward neutrality.

7. Nutrient cycling — becomes more closed and efficient; the proportion of nutrients held in living biomass and litter increases relative to that in soil.

8. Energy flow — the proportion of energy captured and used within the system increases; efficiency of energy transfer improves.

9. Stability and resilience — early communities are simple and unstable; climax communities are more complex, stable and resistant to disturbance.

10. Dominant life forms — change from small, fast-growing, short-lived pioneers (r-selected) to large, slow-growing, long-lived, shade-tolerant climax species (K-selected).

11. Microclimate — becomes more equable: temperature and humidity fluctuations are buffered, soil moisture improves, and light at ground level decreases.

12. Biomass : production ratio — increases, as more energy is tied up in maintenance of existing biomass than in new growth.

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2.6 Fate of Pesticides in the Environment

Pesticides applied to fields do not remain where they are applied. Their fate in the environment is governed by several processes:

1. Volatilization — pesticides with high vapour pressure escape into the atmosphere from soil, water and plant surfaces. They may travel long distances and return to the Earth's surface through dry and wet deposition, causing contamination far from the site of use (e.g., DDT found in Antarctic ice).

2. Spray drift — fine droplets are carried by wind to non-target areas during and soon after spraying.

3. Leaching — water-soluble pesticides are carried downward through the soil profile by rain or irrigation water and may reach groundwater. This is a major route of drinking-water contamination.

4. Surface runoff and erosion — pesticides adsorbed on soil particles or dissolved in water are washed into streams, ponds and lakes, causing aquatic pollution.

5. Adsorption — pesticides bind to soil organic matter and clay particles. Strongly adsorbed pesticides are less mobile but persist longer in soil.

6. Absorption by organisms — plants take up pesticides through roots and leaves; animals absorb them through skin, gills or gut. This leads to bioaccumulation (build-up within an organism) and biomagnification (increasing concentration along the food chain), as seen with DDT in birds of prey.

7. Microbial and chemical degradation — soil bacteria, fungi and chemical reactions break pesticides into metabolites. Some metabolites (e.g., DDE from DDT) are more persistent and toxic than the parent compound. Degradation may be by hydrolysis, oxidation, reduction or photolysis.

8. Photodegradation — sunlight breaks down pesticides on soil and plant surfaces.

9. Persistence — pesticides differ greatly in their half-life. Organochlorines such as DDT may persist for years or decades; organophosphates and carbamates break down within weeks. Persistent pesticides accumulate and cause long-term soil, water and food-chain contamination.

Conclusion. The fate of a pesticide depends on its chemical nature and on soil, climate and biological factors. The combined result is that pesticides spread from the point of application into air, soil, water and living organisms, producing widespread and long-lasting environmental and health hazards.

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2.7 Stratospheric Ozone Chemistry and Ozone Layer Depletion

Formation of the ozone layer. In the stratosphere, molecular oxygen absorbs ultraviolet radiation of wavelength below 240 nm and splits into two oxygen atoms:

$\text{O}_2 + h\nu \rightarrow \text{O} + \text{O}$

Each oxygen atom combines with an oxygen molecule in the presence of a third body (M) to form ozone:

$\text{O} + \text{O}_2 + \text{M} \rightarrow \text{O}_3 + \text{M}$

Ozone is destroyed by absorbing UV radiation of 240–320 nm:

$\text{O}_3 + h\nu \rightarrow \text{O}_2 + \text{O}$

This continuous formation and destruction is the Chapman cycle, which maintains a steady ozone concentration and shields the Earth from harmful UV-B and UV-C radiation.

Depletion by CFCs and other ozone-depleting substances. Chlorofluorocarbons (CFCs), halons, carbon tetrachloride and methyl bromide are stable in the troposphere but release chlorine and bromine in the stratosphere under UV light:

$\text{CFCl}_3 + h\nu \rightarrow \text{CFCl}_2 + \text{Cl}$

The chlorine atom then catalytically destroys ozone:

$\text{Cl} + \text{O}_3 \rightarrow \text{ClO} + \text{O}_2$ $\text{ClO} + \text{O} \rightarrow \text{Cl} + \text{O}_2$

Net result: $\text{O}_3 + \text{O} \rightarrow 2\text{O}_2$. A single chlorine atom can destroy thousands of ozone molecules before being removed. Bromine from halons is even more destructive. In the polar stratosphere, reactions on ice crystals of polar stratospheric clouds convert reservoir species into active chlorine, causing the severe seasonal ozone hole over Antarctica each spring.

Consequences. Increased UV-B reaching the Earth causes skin cancer, cataract, weakened immunity, damage to crops and phytoplankton, and disruption of aquatic food chains.

Control measures. The Montreal Protocol (1987) and its amendments phase out CFCs, halons and other ozone-depleting substances; substitutes such as HCFCs and HFCs are used instead. The ozone layer is now slowly recovering.

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2.8 Cation Exchange Capacity (CEC) of Soil and its Significance

Definition. Cation exchange capacity is the total quantity of exchangeable cations (positively charged ions) that a soil can hold and exchange, expressed in centimoles of charge per kilogram of soil (cmol(+)/kg) or milliequivalents per 100 g (meq/100 g).

Basis. Clay minerals (especially 2:1 types such as montmorillonite) and humus carry negative charges on their surfaces. These attract and hold cations such as $\text{Ca}^{2+}$, $\text{Mg}^{2+}$, $\text{K}^+$, $\text{Na}^+$, $\text{NH}_4^+$ and $\text{H}^+$. These adsorbed cations can be replaced by other cations from the soil solution — this reversible replacement is cation exchange.

Factors affecting CEC

• Amount and type of clay: montmorillonite > illite > kaolinite.
• Organic matter content: humus has very high CEC.
• Soil pH: CEC increases as pH rises because more negative charges develop.

Significance

1. Nutrient holding and supply — soils with high CEC retain plant nutrients and release them slowly, reducing leaching losses and the need for frequent fertiliser application.
2. Fertility indicator — CEC is a measure of the soil's potential fertility; sandy soils with low CEC are poor in nutrients.
3. Buffering capacity — high CEC soils resist sudden changes in pH and in nutrient concentration, protecting plants from toxicity and deficiency.
4. Fertiliser management — knowledge of CEC helps decide the type and dose of fertiliser; potassium and ammonium fertilisers are retained better in high-CEC soils.
5. Soil reaction and liming — the percentage of base saturation (proportion of bases among exchangeable cations) indicates whether lime is needed.
6. Pollution control — high-CEC soils adsorb heavy metals and other pollutants, reducing their movement to groundwater.
7. Soil classification and land use — CEC is used in soil taxonomy and in deciding suitable crops.

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2.9 Climate Change and its Impacts

Climate change refers to a significant and lasting change in the statistical distribution of weather patterns (temperature, precipitation, wind) over periods ranging from decades to millions of years. In the present context it means the long-term warming of the Earth's climate caused mainly by the increase of greenhouse gases — carbon dioxide, methane, nitrous oxide and CFCs — released by human activities such as burning fossil fuels, deforestation, agriculture and industry. These gases trap outgoing infrared radiation and raise the average global temperature (enhanced greenhouse effect).

Impacts (any two)

1. Melting of glaciers and rise in sea level. Global warming melts glaciers and polar ice sheets and causes thermal expansion of ocean water. In Nepal, glaciers in the Himalaya are retreating rapidly and many glacial lakes (e.g., Imja Tsho) are growing, increasing the risk of glacial lake outburst floods (GLOF). Worldwide, sea level rise threatens low-lying coastal areas and island nations such as the Maldives and Bangladesh.

2. Changes in agriculture and water resources. Higher temperatures, erratic rainfall, longer droughts and shifting monsoon patterns reduce crop yields, cause crop failure and increase pest and disease attack. In Nepal, delayed or weak monsoon affects paddy transplantation and causes food insecurity. At the same time, snow-fed rivers may initially carry more water but later shrink as glaciers disappear, creating water scarcity for drinking, irrigation and hydropower.

Other impacts include more frequent floods, landslides and droughts; loss of biodiversity; spread of vector-borne diseases such as malaria and dengue; and displacement of people (climate refugees).

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2.10 Wind as a Geological Agent of Change

Wind is an important agent of erosion, transportation and deposition, especially in arid and semi-arid regions where vegetation is sparse and the ground is dry and loose. Its geological work includes the following.

1. Erosion

• Deflation: removal of loose, dry sand and dust particles from the surface by wind, producing hollows and depressions (deflation basins) and lowering the land surface. Over-grazing and deforestation accelerate deflation.
• Abrasion: sand particles carried by wind strike rock surfaces and wear them away, producing smooth, polished, faceted and pitted rock surfaces (ventifacts) and undercut rock masses.
• Attrition: sand grains collide with one another and become rounded and smaller.

2. Transportation. Wind carries fine material in three ways:

• Suspension — dust and very fine sand are carried high in the air over long distances (e.g., dust from the Sahara reaching Europe).
• Saltation — medium sand grains bounce along the ground in a series of jumps.
• Surface creep — coarser grains roll and slide along the surface. The load carried by wind is sorted by size, and the finest material may travel thousands of kilometres.

3. Deposition. When wind velocity falls or an obstacle is met, the load is deposited, forming:

• Sand dunes — mounds of sand; common types are barchan (crescent-shaped, horns pointing downwind), transverse, longitudinal (seif) and parabolic dunes. Dunes slowly migrate with the prevailing wind and can bury roads, fields and settlements.
• Loess — extensive, thick deposits of fine, wind-blown silt and clay. Loess is fertile and forms vertical cliffs (e.g., the loess plateau of China).
• Sand sheets and ripple marks on desert floors.

4. Landforms produced. Wind action produces characteristic desert landforms such as mushroom rocks (pedestal rocks), inselbergs, yardangs, zeugen, deflation hollows, oases in deflated basins, and extensive dune fields.

Significance. Wind erosion causes loss of fertile topsoil, desertification, damage to crops and burial of settlements. It is checked by planting shelter belts, stabilising dunes with vegetation, mulching, contour ploughing and controlled grazing. Thus wind, though a slow agent, is a powerful geological force in shaping the Earth's surface in dry regions.

3. Differentiate between:

3.1 Simple and Y-shaped energy flow model

3.2 Sympatric speciation and allopatric speciation

3.3 Sedimentary cycles and gaseous cycles

3.4 Volumetric and gravimetric analysis

3.5 Resistance and resilience

3.6 Mohorovicic discontinuity and Gutenberg-Weichert discontinuity

3.7 Birth rate and growth rate

3.8 Weather and climate

3.9 El Nino and ENSO

3.10 Metamorphic rock and sedimentary rock