MANAGEMENT OPTIONS: A WATERSHED APPROACH

In order to ensure the quality and integrity of the river basin; it is necessary to practice watershed approaches taking into account the topography, vegetation and hydrology. This approach in planning ensures the sustainable management of renewable natural resources. Water as well as extent of vegetation and soil are the most important constituents in watershed characterisation the status of the watershed decides the drainage systems in the catchment as is evident from poor drainage network and seasonal water in degraded ecosystems (eastern parts of the upper basin) and existence of higher order streams with perennial water in good evergreen patches in the western part of the Sharavathi river basin. Land use changes during the last three decades (especially in the eastern side of the river basin) have contributed tothi8 situation, which is mainly due to conversion of forests to agricultural lands. Eventually these lands have been transformed to unproductive wastelands because of poor agricultural practices (uncontrolled, unplanned, unscientific land and fertiliser use). The deterioration of micro and mini watershed is posing serious threat to the integrity of the river basin and the environmental consequences are:

• low productivity of land (food, fuel, forage, fibre and fruits),
• degradation of forest,
• erosion and denudation within and outside the watershed,
• soil nutrient degradation (desertification),
• quick siltation of streams, reservoir, lakes, ponds etc.,
• poor water quality yield due to heavy sediment,
• decline in aquatic ecosystem productivity,
• frequent flood and droughts and
• poor health of people and cattle.

The conservation and restoration of a watershed involves the management of biotic and abiotic components of the ecosystem involving personnel from diverse backgrounds. The planning is to be done considering the present status of the catchment including infrastructure and socio-economic status.

Integrated watershed management approaches can be employed either by preventive or rehabilitative approaches. In preventive approach, conservation of soil and water resources is achieved by legal regulations and proper use of land according to capability classes. While in rehabilitative approach, technical measures like gully control structures, channel stabilisation and terracing are employed. Rehabilitation and afforestation, erosion and sedimentation and watershed economics can be achieved by participatory approach and through education, awareness and training. This would help in enhancing the quality of biotic and abiotic components of the catchment.

The main threat to Sharavathi river and its tributaries (upstream) is from soil erosion and siltation due to lack of vegetative cover and non point sources of pollution (due to agricultural activities). This is resulting in loss of productive top layer of soil and pollution of ecosystems. The management options of Sharavathi river basin are described hereunder.

Turbidity at sites Keshwapura, Nandihole and Sampakai were high, due to the soil erosion in the catchment and could be minimised by adopting the best management practices listed below:

• The use of contour ploughing, which has the ability of reducing the runoff in rainy season. (26% reduction in runoff in the case of contour ploughed catchment compared to the untreated catchment. Similarly, soil loss was reduced from about 30 tonnes to less than 20 tonnes/ha during the rainy season.
• Leaving unploughed grass strips between ploughed hind.
• Maintaining soil cover by vegetative means, so that soil will be rich in humus and organic matter (decaying plant and animal remains). Organic matter acts as chelating agent that binds the soil particles together and plays an important role in preventing erosion. Apart from this, the vegetation cover of soil:
• slows down runoff and facilitates infiltration,
• prevents siltation as plant roots hold the soil in position,
• reduces the impact of a raindrop before it hits the soil, thus reducing its ability to erode,
• prevents erosion (due to the presence of plants in wetlands and on the banks of rivers) and
• trees intercept rainfall and reduce its velocity and the force with which   the raindrops strike the soil surface. The interception value for Acacia is 15 to 20% and for Shorea robusta 14%.

Catchment management also involves

• avoiding overgrazing and the over-use of crop lands;
• allowing indigenous plants to grow along the river banks instead of ploughing and planting crops right up to the water edge;
• encouraging biological diversity by practicing polyculture by planting different types of plants together; and
• conservation and sustainable management of wetlands in the Sharavathi river basin which will have a great capacity to recharge the ground water, maintain stream flow and augment the availability of soil water to vegetation.

The biological coliform in water samples at sites-Sharmanavathi, Haridravathi, Valagare, Keshwapura, Nandihole and Sampakai-indicate that water is unfit for human and animal consumption. This necessitates prevention of human and animal waste getting into water bodies.

The soil samples were rich in organic matter and with optimum pH for plant growth and low values for the primary nutrients like Nitrates, Phosphate, Potassium (NPK) and secondary nutrients like sulphates, sodium and calcium at all the sampling sites.

The primary nutrients like nitrogen enhance the plant growth and leaves, seeds, and tubers. Phosphorus stimulates early root and plant growth and hastens maturity. Potassium enhances ability to resist diseases, insect attacks, and adverse weather. It helps in the formation and movement of carbohydrates and oils and improves fruit quality. The secondary nutrients like sulphur, magnesium and calcium are also key nutrients as sulphur is involved in energy producing process and responsible for the flavour and odour of compounds, magnesium is responsible for chlorophyll and seed production and calcium is responsible for root health, growth of new roots, root hair and development of leaves.

Nutrient efficiency is a measure of crop produced per unit of nutrients supplied. Higher the efficiency, more the product per unit of nutrients supplied. The nutrient use efficiency is affected by the quality of soil. The factors affecting nutrients use efficiency are:

1. Erosion and runoff both are detrimental to nutrient management as it is contained in the topsoil along with soil organic matter and these being washed away with the runoff water and eroding action of wind. Organic matter is transported by water or wind because of its lower specific gravity. Additional nutrients are required to maintain the lost productivity.

2. Deposition of sediments by wind or water in the fields has both positive and negative effect. If the sediment is fine clay particles and contains organic matter, this brings in nutrients and if it is coarser like sand, it does not have high nutrient content, and lacks moisture holding capacity.

3. Compaction: compact soil restricts the movement of roots and the usage of available nutrients by plants. Compaction als6 restricts the diffusion and flow in soil. The limited roots and nutrient movement results in the stunted growth of plants and retards the air movement and gas exchange in root zone and can lead to denitrification.

4. Soil aggregation favours water and nutrient movement in soil. More aggregation means more surface area of the soil particles has capacity to adsorb the nutrients. Surface aggregation allows pore space for water infiltration, gas exchange, retain organic matter and enhance biological activities for better nutrient cycling.

5. Infiltration: since nutrient transfer takes place in moist soil, soil with good infiltration capacity is capable of making the nutrients available to plant roots. Only those nutrients susceptible to leaching are not carried to the root zone. Percolating water carries the nutrients deeper into the root zone and also removes harmful salt that may accumulate there.

6. Soil crusting seals the soil surface and restricts water infiltration, seed germination, gas exchange etc. Due to crusting, nutrients are susceptible to runoff and wind erosion.

7. Nutrient imbalance: over application of nutrients can lead to plant toxicity, poor pH reactions, excess nutrients available for runoff, leaching and volatilisation, because the whole quantity of nutrients   applied are not used by the crops. For example, if phosphorous is applied in large quantity it will restrict the availability of zinc for com and too much potassium may interfere with the uptake of magnesium by corn and other grasses. Additional application of fertilisers or manure to boost soil nutrient levels into the optimum range not only result in unsatisfactory economic returns, but also can adversely affect plant growth, animal health and environmental quality.

8. Pesticide carryover: pesticides with residual soil activity can stunt growth of subsequent crops. If roots are affected, their ability to absorb nutrients will be lessened. Any effect on plant photosynthesis will reduce the nutrients uptake and metabolism.

9. Organic matter: it is a very important component of the topsoil. Organic matter store nutrients, feed decomposers, return the basic nutrients to the soil, retain soil moisture etc. Hence, maintaining organic matter in soil matrix is helpful in retaining nutrients.

10. Biological activity: a healthy soil system has diverse sets of macro and microorganisms that assure a well functioning soil food web. Microorganisms decompose organic matter, store nutrients in their bodies and on decomposition release nutrients. Some small organisms like insects and crustacea carry organic material and related nutrients into soil and aid in its decomposition. Some microorganisms have symbiotic relationship with plants such as mycorrhiza. Microorganisms live in plant root and help the plants to assimilate water and nutrients.

11. Weeds and pathogens: the efficient utilisation of nutrients means it is converted into harvestable products. If insects or diseases attack crops the efficient utilisation of nutrients are stopped. Hence to overcome this problem weeds and pathogens should be controlled.

12. Extreme soil moisture conditions: soil moisture has a positive response in making the nutrients available to plants but excessive moist condition i.e. waterlogged situation affects the transformation of nutrients. 'Phosphorus becomes more mobile and less attached to minerals in waterlogged conditions. Nitrate nitrogen is denitrified by changing from liquid to gas and finally lost to atmosphere because gases are transported much more slowly through water (110,000th slower) than air. Some gases such as carbon dioxide can accumulate in the soil and are toxic to roots.

Effective nutrient management can be achieved by

• Preventing soil erosion and deposition of coarser sediment in the field
• Reducing soil compaction, soil crusting, nutrient loss or imbalance and augmenting soil aggregation and infiltration
• Increasing organic matter content and biological activity
• Preventing extreme moisture condition (water logging)
• Proper and timely use of fertiliser to prevent volatilisation and leaching .
• Selecting proper starter manure which does not cause toxic gas release to affect the seed germination seedlings growth
• Farm management based on manure production

Hence, management of the watershed at the micro level and integrating the entire aspects helps in achieving ecosystem sustainability.