Answers to Any Three (3 × 10 = 30)

1.1 Water Quality Indices for Local Units

A water quality index (WQI) combines many parameters into a single rating. For a local unit I would sample drinking sources (taps, wells, springs) and rivers, and use physico-chemical and biological indicators.

(a) Physico-chemical parameters [5]

The weighted arithmetic index is

$WQI=\frac{\sum_i W_iQ_i}{\sum_i W_i},\qquad Q_i=100\,\frac{V_i-V_{ideal}}{S_i-V_{ideal}},\qquad W_i=\frac{K}{S_i}$

where $V_i$ is the measured value, $S_i$ the standard and $V_{ideal}$ the ideal value (0, except pH 7 and DO 14.6 mg/L). A WQI below 50 is excellent, 50–100 good, 100–200 poor, and above 300 unfit.

(b) Biological parameters [5]

• Total and faecal coliform / E. coli: indicators of faecal contamination; must be 0 per 100 mL in drinking water.
• Streptococcus faecalis (faecal streptococci) and Clostridium perfringens: confirm faecal pollution and longer-term contamination.
• Total plate count: general bacterial load.
• Benthic macroinvertebrates: the biotic indices used for Nepal's rivers are the Biotic Score / NEP-BMWP and ASPT (average score per taxon), plus EPT richness (Ephemeroptera, Plecoptera, Trichoptera). High EPT and ASPT mean clean water; dominance of tubificid worms and chironomids means heavy organic pollution.
• Chlorophyll-a and phytoplankton (Saprobic index): measure of eutrophication.
• Fish diversity and algal blooms: supporting indicators.

Interpretation: sites are classified into excellent, good, medium, poor or bad classes, and mapped so the local unit can target treatment and protect sources.

1.2 Design Flood and Flood Frequency Analysis

Definition of Design Flood

Design flood is the flood discharge (peak flow, volume, or water level) that a hydraulic structure — such as a dam, spillway, bridge, culvert, embankment, or drainage channel — is designed to safely accommodate without failure or unacceptable damage. It is selected on the basis of an acceptable risk level, usually expressed as a return period (recurrence interval), and depends on the importance of the structure, its design life, and the consequences of failure. For example, a minor culvert may be designed for a 25-year flood, whereas a major dam spillway may be designed for a 1000-year flood or the probable maximum flood (PMF).

Concept of Flood Frequency Analysis

Flood frequency analysis is a statistical technique used to estimate the probability of occurrence of flood events of various magnitudes at a given river site. It involves:

1. Collection of data: Gathering annual peak discharge records (annual maximum series) over a sufficiently long period (usually ≥ 20–30 years).
2. Ranking: Arranging the annual peak flows in descending order of magnitude, with rank ( m = 1 ) for the largest, ( m = 2 ) for the next, and so on, where ( n ) is the total number of years of record.
3. Plotting position: Assigning each ranked event a plotting position (empirical probability) using a suitable formula such as Weibull's.
4. Fitting a probability distribution: Fitting a theoretical frequency distribution — commonly Gumbel (Extreme Value Type I), Log-Pearson Type III, or Log-Normal — to the observed data.
5. Estimation: Using the fitted distribution to estimate the flood magnitude corresponding to any chosen return period, or vice versa.

The basic assumption is that flood peaks are independent, identically distributed random variables, and that the underlying statistical population is stationary (no long-term trend or change in the catchment).

Weibull's Formula

Weibull's formula gives the plotting position (empirical exceedance probability) of the ( m )-th ranked flood event in a record of ( n ) years:

$P(X \geq x_m) = \frac{m}{n+1}$

where:

• ( m ) = rank of the flood event (1 for largest, 2 for second largest, …),
• ( n ) = total number of years of record,
• ( P(X \geq x_m) ) = probability that a flood equal to or greater than ( x_m ) occurs in any given year (exceedance probability).

Procedure for Calculating Return Period and Probability of Reoccurrence

Return period (recurrence interval), ( T ): The average number of years in which a flood of given magnitude is expected to be equalled or exceeded once. It is the reciprocal of the exceedance probability:

$T = \frac{1}{P(X \geq x_m)} = \frac{n+1}{m}$

Probability of reoccurrence: The probability that a flood of magnitude ( x_m ) or greater occurs in any single year is:

$P = \frac{1}{T} = \frac{m}{n+1}$

Probability of occurrence at least once in ( N ) years (risk):

$P_{\text{at least once in } N \text{ years}} = 1 - \left(1 - \frac{1}{T}\right)^{N}$

Procedure:

1. Rank the ( n ) annual peak flows in descending order (( m = 1, 2, \ldots, n )).
2. Compute the exceedance probability of each event using Weibull's formula, ( P = m/(n+1) ).
3. Compute the return period, ( T = 1/P = (n+1)/m ).
4. Plot the flood magnitude ( x_m ) against the return period ( T ) (on Gumbel or log-probability paper) to obtain the frequency curve.
5. Fit a theoretical distribution (e.g., Gumbel) to the plotted points.
6. Read from the fitted curve the flood magnitude for the desired return period (design flood), or compute the probability of reoccurrence for a known flood magnitude.

Example: If ( n = 50 ) years and a flood is ranked ( m = 5 ), then: $P = \frac{5}{51} = 0.098 \approx 9.8\%, \qquad T = \frac{51}{5} = 10.2 \text{ years}$

This means a flood of that magnitude has about a 9.8% chance of occurring in any given year, and on average occurs once every 10.2 years. The probability that it occurs at least once in the next 20 years is: $1 - \left(1 - \frac{1}{10.2}\right)^{20} \approx 1 - (0.902)^{20} \approx 0.87 \text{ (87\%)}$

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1.3 Land Use Planning and Sanitary Landfill Siting

Land use planning is the systematic assessment of the physical, social and economic potential of land to select and adopt the best use options, so that land is used sustainably and conflicts are minimised.

Steps

1. Set goals and identify issues with stakeholders.
2. Collect and analyse data (topography, soils, geology, hydrology, climate, land cover, socio-economic data).
3. Evaluate land suitability (GIS overlay, land capability classes).
4. Develop alternative land use plans.
5. Select and approve the best plan.
6. Implement through zoning and regulation.
7. Monitor, review and revise.

Factors for a sanitary landfill

A site that combines gentle slope, deep water table, low rainfall, clay-rich geology and distance from water bodies is the best choice; if natural conditions are poor, an engineered liner, leachate treatment and gas collection must compensate.

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1.4 Köppen's Climate Classification

Köppen (1900, modified by Geiger) classifies climate using monthly temperature and precipitation, linked to natural vegetation. It uses a code of up to three letters: main class, precipitation sub-class, temperature sub-class.

Main classes

Sub-classes

• A: Af (tropical rainforest, no dry season), Am (monsoon), Aw (savanna, dry winter).
• B: BW (desert) and BS (steppe); with h (hot) or k (cold).
• C: Cfa/Cfb/Cfc (humid, no dry season, hot, warm or cool summer), Cwa/Cwb (dry winter), Csa/Csb (dry summer, Mediterranean).
• D: Dfa–Dfd (no dry season), Dwa–Dwd (dry winter), Dsa–Dsd (dry summer).
• E: ET (tundra, warmest month $0$–$10^\circ$C) and EF (ice cap, all months $<0^\circ$C).

Second letters: f = no dry season, w = dry winter, s = dry summer, m = monsoon. Third letters: a = hot summer, b = warm summer, c = cool short summer, d = very cold winter; h = hot, k = cold (for B).

Nepal: Terai is Cwa (humid subtropical, dry winter); the Middle Hills are Cwb; high mountains are Dwc/ET/EF; Mustang and Dolpa are BS or BW-like cold semi-arid.

TU BSc — Bachelor Level (4 Yrs.) 2nd Year

2.1 Impacts of Dam on Lacustrine Environment

A dam built on a river creates or modifies a lake (lacustrine) environment, mainly through the reservoir it forms. The key impacts are:

1. Change in flow regime: The dam traps water and releases it in a regulated manner. Downstream flow becomes uniform, losing the natural seasonal flood pulse that sustained lake-fed wetlands and floodplains.
2. Sediment trapping: Reservoirs act as giant sediment traps. Coarse and fine sediments settle behind the dam, so downstream channels become sediment-starved, causing bank erosion and bed degradation. The reservoir itself gradually loses storage capacity through siltation.
3. Water quality changes: Impounded water has longer residence time. This leads to thermal stratification, reduced dissolved oxygen in the hypolimnion, and increased nutrient retention. Eutrophication (algal blooms) is common in nutrient-rich reservoirs.
4. Temperature alteration: Released water is often colder than natural river water (from the deep layer), which harms native aquatic organisms downstream.
5. Habitat fragmentation: Migratory fish (e.g., salmon, mahseer) cannot move upstream to spawn. Lacustrine species may invade and displace riverine species.
6. Greenhouse gas emission: Decomposition of submerged vegetation in reservoirs releases methane and carbon dioxide.
7. Socio-ecological effects: Displacement of people, loss of riparian forest, and changes in local fisheries.

In Nepal, dams such as Kulekhani and proposed storage projects on the Karnali and Budhi Gandaki illustrate these effects on lake and river ecology.

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2.2 Spatial Pattern of Climate of Nepal

Nepal's climate varies strongly with altitude, latitude, and monsoon influence. The spatial pattern can be described as follows:

A. Altitudinal variation (vertical zonation):

B. Longitudinal (east–west) variation: The eastern part receives more rainfall than the western part because the monsoon enters from the Bay of Bengal in the east and loses moisture as it moves west. Thus, Ilam and Dhankuta are wetter than Jumla and Humla.

C. North–south variation: Rainfall increases from the Terai toward the Middle Hills (maximum on south-facing slopes), then decreases sharply in the rain-shadow Trans-Himalaya (Mustang, Manang, Dolpa), which are dry and cold deserts.

D. Seasonal pattern: Four seasons — pre-monsoon (Mar–May, hot and dry), monsoon (Jun–Sep, ~80% of annual rainfall), post-monsoon (Oct–Nov, clear and mild), and winter (Dec–Feb, cold and dry with occasional snow).

E. Climatic controls: Altitude, latitude, monsoon direction, relief (rain shadow), and distance from the sea together produce this pattern. Nepal has five climatic zones from tropical Terai to arctic Himalayan peaks within a north–south distance of about 200 km.

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2.3 Remote Sensing in Snow Hydrology Study

Remote sensing (RS) is the acquisition of information about the Earth's surface without physical contact, using sensors on satellites or aircraft. In snow hydrology it is valuable because snow-covered regions are high, remote, and inaccessible.

Applications:

1. Snow cover mapping: Optical sensors (Landsat, MODIS, Sentinel-2) use the high reflectance of snow in visible and near-infrared bands to map snow-covered area (SCA). The Normalized Difference Snow Index (NDSI) distinguishes snow from clouds and water.
2. Snow extent and depletion curves: Repeated satellite passes give time series of snow cover, allowing snow depletion curves (SDC) to be drawn for a basin. These curves are used to estimate snowmelt runoff.
3. Snow water equivalent (SWE): Passive microwave sensors (SSM/I, AMSR-E) measure microwave emission, which is sensitive to snow depth and liquid water content, giving estimates of SWE.
4. Snowline and glacier monitoring: RS tracks the position of the snowline and changes in glacier area, useful for climate change studies.
5. Snowmelt runoff modelling: Snow cover data from RS are used as input to hydrological models (e.g., SRM — Snowmelt Runoff Model) to forecast streamflow.
6. Avalanche and hazard mapping: RS helps identify avalanche-prone slopes and monitor snow stability.

Advantages: Large area coverage, repeatability, access to inaccessible terrain, and cost-effectiveness. Limitations: Cloud cover obstructs optical sensors, coarse resolution of microwave data, and difficulty in distinguishing wet snow from dry snow.

In Nepal, RS is widely used to study snow and glacier melt in the Himalayan basins that feed major rivers.

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2.4 Stream Simulation Models

Stream simulation models are mathematical or computer-based tools that represent the hydrological, hydraulic, and water-quality processes of a stream or river system. They simulate how water moves and how materials are transported through a channel network.

Types:

1. Hydrological models: Simulate rainfall–runoff processes. Examples: SWAT (Soil and Water Assessment Tool), HEC-HMS, and TOPMODEL. They predict discharge from a catchment.
2. Hydraulic models: Simulate water flow in channels using equations such as the Saint-Venant equations (1-D) or 2-D/3-D flow equations. Examples: HEC-RAS, MIKE 11, and Delft3D. They give water level, velocity, and flood extent.
3. Water quality models: Simulate transport of sediments, nutrients, and pollutants. Examples: QUAL2K and WASP.
4. Sediment transport models: Simulate erosion, transport, and deposition of sediment (e.g., HEC-RAS with sediment module).

Steps in stream simulation:

1. Define the study reach and objectives.
2. Collect data — topography, cross-sections, discharge, rainfall, and channel roughness.
3. Build the model geometry and set boundary conditions.
4. Calibrate the model using observed data.
5. Validate the model with independent data.
6. Run scenarios (e.g., flood, land-use change) and interpret results.

Applications: Flood forecasting and mapping, design of dams and bridges, reservoir operation, water allocation, pollution control, and environmental flow assessment.

Limitations: Models are simplifications of reality; accuracy depends on data quality; uncertainty arises from parameters and boundary conditions.

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2.5 Sustainable Soil Management

Sustainable soil management (SSM) means using soil in a way that maintains its productivity, biodiversity, and ecological functions for present and future generations without degrading it.

Principles:

1. Maintain soil organic matter: Add compost, farmyard manure, and crop residues to improve fertility and structure.
2. Minimize soil erosion: Use terracing, contour ploughing, strip cropping, and cover crops, especially on sloping land.
3. Maintain soil nutrients: Use balanced fertilization, crop rotation with legumes, and organic amendments.
4. Conserve soil moisture: Mulching, conservation tillage, and rainwater harvesting.
5. Avoid soil pollution: Reduce excessive use of chemical fertilizers and pesticides; manage waste properly.
6. Maintain soil biodiversity: Encourage earthworms, microbes, and beneficial organisms through organic practices.
7. Prevent salinization and waterlogging: Proper irrigation and drainage management.

Practices in Nepal:

• Terrace farming on hillslopes.
• Use of compost and green manure.
• Agroforestry and agro-ecological farming.
• Conservation agriculture (zero tillage in Terai).
• Watershed management programmes.

Importance: Healthy soil supports food security, reduces poverty, mitigates climate change (carbon sequestration), and maintains water and nutrient cycles. Soil is a non-renewable resource on a human timescale, so its sustainable management is essential for sustainable development.

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2.6 Application of Microbes in Environment

Microorganisms (bacteria, fungi, algae, protozoa, and viruses) play essential roles in environmental management. Their applications include:

1. Bioremediation: Microbes degrade pollutants such as petroleum hydrocarbons, pesticides, and heavy metals. Example: Pseudomonas degrades oil spills; Thiobacillus oxidizes sulfur.
2. Sewage and wastewater treatment: Activated sludge process uses bacteria to break down organic matter. Trickling filters and oxidation ponds also rely on microbes.
3. Biogas production: Anaerobic bacteria (e.g., Methanobacterium) convert organic waste into methane-rich biogas.
4. Composting: Aerobic microbes decompose organic waste into nutrient-rich compost.
5. Biofertilizers: Rhizobium, Azotobacter, and Azospirillum fix atmospheric nitrogen; Mycorrhiza improves phosphorus uptake.
6. Biopesticides: Bacillus thuringiensis (Bt) controls insect pests; Trichoderma controls fungal pathogens.
7. Bioremediation of heavy metals: Bacteria like Geobacter and Shewanella reduce and immobilize metals.
8. Indicator organisms: E. coli and coliforms indicate water contamination.
9. Carbon and nutrient cycling: Microbes drive decomposition, nitrogen fixation, nitrification, and denitrification.
10. Biodegradation of plastics: Certain bacteria and fungi can degrade polythene and other plastics.

Conclusion: Microbes are eco-friendly, cost-effective tools for pollution control, waste management, and sustainable agriculture. Their use reduces dependence on harmful chemicals and supports a cleaner environment.

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2.7 Microbial Interaction in Environment

Microorganisms do not live in isolation; they interact with each other and with other organisms. These interactions determine the structure and function of ecosystems. Major types are:

1. Mutualism: Both partners benefit. Example: Lichens (algae + fungi); Rhizobium in legume root nodules fixes nitrogen and gets shelter and food.
2. Commensalism: One benefits, the other is unaffected. Example: Nitrosomonas and Nitrobacter in the nitrogen cycle; many gut microbes.
3. Parasitism: One benefits at the expense of the other. Example: Plasmodium in humans; Agrobacterium tumefaciens in plants.
4. Predation: One microbe kills and consumes another. Example: Bdellovibrio attacking other bacteria; protozoa eating bacteria.
5. Competition: Both compete for the same limited resource (nutrients, space). This controls population size.
6. Amensalism (Antagonism): One is harmed, the other unaffected. Example: Penicillium produces penicillin that inhibits bacteria.
7. Synergism: Two microbes together produce an effect neither can produce alone. Example: breakdown of complex substrates by consortia.
8. Syntrophy: One organism lives on the metabolic products of another. Example: methanogens using products of fermentative bacteria.

Importance: These interactions regulate nutrient cycling, decomposition, disease dynamics, and bioremediation. They also maintain ecological balance in soil, water, and the atmosphere. Understanding them helps in agriculture, waste treatment, and public health.

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2.8 Factors Affecting Growth of Microorganisms

Microbial growth is influenced by physical, chemical, and biological factors:

A. Physical factors:

1. Temperature: Psychrophiles (below 20 °C), mesophiles (20–45 °C), thermophiles (45–80 °C), and hyperthermophiles (> 80 °C). Optimum temperature gives maximum growth.
2. pH: Most bacteria grow at pH 6.5–7.5; fungi prefer acidic pH (5–6). Extreme pH denatures enzymes.
3. Osmotic pressure/water activity: High salt or sugar causes plasmolysis. Halophiles tolerate high salt.
4. Radiation: UV and ionizing radiation damage DNA.

B. Chemical factors:

1. Nutrients: Carbon, nitrogen, phosphorus, sulfur, and trace elements are essential.
2. Oxygen: Obligate aerobes, facultative anaerobes, obligate anaerobes, microaerophiles, and aerotolerant anaerobes.
3. Water: Available water is essential for all metabolic activities.

C. Biological factors:

1. Competition: Other microbes compete for nutrients and space.
2. Antagonism: Antibiotics and toxins from other microbes inhibit growth.
3. Symbiosis: Mutualistic partners may promote growth.

D. Other factors: Hydrostatic pressure, salinity, and host factors (for pathogens).

Conclusion: Understanding growth factors is important in food preservation, disease control, industrial fermentation, and environmental microbiology.

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2.9 Methods of Surveying Forest

Forest survey is the systematic collection of data on forest resources — area, volume, species composition, and condition. Main methods are:

1. Complete enumeration (Total census): Every tree in the forest is measured. Accurate but costly and time-consuming; suitable for small areas or valuable forests.
2. Sampling methods: Only a part of the forest is measured and results are extrapolated. Types:
   • Simple random sampling: Plots are selected randomly.
   • Systematic sampling: Plots are laid at regular intervals (e.g., every 100 m).
   • Stratified sampling: Forest is divided into homogeneous strata and sampled separately.
   • Cluster sampling: Groups of plots are selected as clusters.
   • Multistage sampling: Sampling in two or more stages (e.g., district → block → plot).
3. Plot-based methods:
   • Fixed-area plots (quadrats): Square or circular plots of fixed size.
   • Circular plots: Common in forest inventories.
   • Strip plots: Long narrow strips.
4. Plotless methods:
   • Point-centred quarter method: Distances from a point to nearest trees in four quadrants.
   • Nearest neighbour method: Distance between nearest trees.
   • Angle count (Bitterlich) method: Uses a wedge prism to estimate basal area.
5. Remote sensing and aerial survey: Satellite imagery and aerial photographs for large-area forest cover mapping.
6. GPS and GIS-based survey: Digital mapping and spatial analysis of forest resources.

Steps: Reconnaissance survey → map preparation → plot layout → data collection (species, DBH, height) → data analysis → volume and biomass estimation → report preparation.

Importance: Provides data for sustainable forest management, biodiversity conservation, and national forest policy.

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2.10 Protoplast Fusion Technology and Its Application

Protoplast is a plant cell without a cell wall, obtained by enzymatic digestion of the cell wall using cellulase and pectinase. Protoplast fusion (somatic hybridization) is the fusion of two protoplasts from different species or varieties to form a hybrid cell called a heterokaryon, which can regenerate into a hybrid plant.

Steps:

1. Selection of parent plants.
2. Isolation of protoplasts from leaf or callus tissue using enzymes.
3. Fusion of protoplasts — chemical (PEG — polyethylene glycol) or electrical (electrofusion).
4. Selection of hybrid cells (heterokaryons).
5. Culture of hybrid cells on suitable medium to form callus.
6. Regeneration of hybrid plants (somaclones).
7. Verification of hybridity by molecular markers or chromosome analysis.

Applications:

1. Production of hybrid plants between sexually incompatible species (e.g., tomato + potato = "pomato"; cabbage + radish).
2. Transfer of useful genes for disease resistance, stress tolerance, and quality traits.
3. Creation of novel crop varieties with combined desirable characters.
4. Cytoplasmic male sterility for hybrid seed production.
5. Study of cell genetics and gene expression.
6. Production of cybrids (cytoplasmic hybrids) for organelle transfer.

Limitations: Low fusion frequency, difficulty in regeneration, and genetic instability of hybrids. Despite this, protoplast fusion is a powerful tool in plant biotechnology and crop improvement.

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2.11 Alternative Methods of Pesticide Use

Chemical pesticides cause environmental pollution, pest resistance, and health hazards. Alternative methods include:

1. Integrated Pest Management (IPM): Combines biological, cultural, mechanical, and chemical methods with minimal chemical use. It monitors pest populations and acts only when needed.
2. Biological control: Use of natural enemies — predators (ladybird beetles), parasitoids (Trichogramma), and pathogens (Bt, Beauveria bassiana).
3. Botanical pesticides: Neem (azadirachtin), pyrethrum, tobacco extract, and garlic/chili extracts.
4. Cultural methods: Crop rotation, intercropping, mixed cropping, and resistant varieties reduce pest buildup.
5. Mechanical and physical methods: Hand picking, traps (light, pheromone, yellow sticky), and barriers.
6. Sterile insect technique (SIT): Release of sterilized males to reduce pest population.
7. Pheromone-based methods: Mating disruption and mass trapping.
8. Genetic methods: Bt crops and other genetically modified pest-resistant varieties.
9. Organic farming: Avoids synthetic pesticides and uses compost, biofertilizers, and natural repellents.
10. Habitat management: Maintaining natural vegetation to support beneficial insects.

Advantages: Eco-friendly, sustainable, reduces pollution, protects biodiversity, and lowers health risks. Limitations: Slower action, requires knowledge and monitoring, and may be less effective in severe outbreaks. Integration of these methods is the best approach for sustainable pest control.

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2.12 Application of GIS in Environmental Survey

GIS (Geographic Information System) is a computer-based system for capturing, storing, analyzing, and displaying spatially referenced data. In environmental surveys, GIS is widely used:

1. Land-use/land-cover mapping: GIS maps forests, agriculture, water bodies, and settlements, and detects changes over time.
2. Environmental impact assessment (EIA): GIS overlays project sites with sensitive areas (forests, wetlands, protected areas) to assess impacts.
3. Site suitability analysis: Identifies suitable locations for waste disposal, industries, and conservation areas.
4. Water resource management: Maps watersheds, drainage networks, and groundwater potential zones.
5. Pollution mapping: Displays spatial distribution of air, water, and soil pollution.
6. Biodiversity and habitat mapping: Identifies habitats of endangered species and corridors.
7. Disaster risk mapping: Maps flood-prone, landslide-prone, and earthquake-prone areas.
8. Forest inventory and management: Integrates field data with maps for volume and biomass estimation.
9. Climate change studies: Analyzes changes in snow cover, glaciers, and vegetation.
10. Public health and epidemiology: Maps disease incidence and environmental risk factors.

Advantages: Integrates data from multiple sources (RS, GPS, field survey), enables spatial analysis and modelling, supports decision-making, and produces accurate maps. Limitations: Requires trained manpower, software, and reliable data; high cost for large-scale surveys.

In Nepal, GIS is used by government agencies (Survey Department, ICIMOD, and Department of Forests) for environmental planning, disaster management, and natural resource management.

3.1 Long range and short range weather forecast

3.2 Class I and Class II of land capability classification

3.3 Physico-chemical and biological water quality index

3.4 Horton's and Kostiakov's equation for estimation of hydrologic budget

3.5 Remote sensing and Geographic Information System

3.6 Relief and elevation

3.7 Vadose zone and saturated zone of ground water

3.8 Phytoplankton and Zooplankton

3.9 Pre-monsoon and post-monsoon climate of Nepal

3.10 Microbes in soil and microbes in food