Ecological Approach: Key concepts in understanding Watershed
Landscape as a Mosaic
The land is always spatially heterogeneous (an uneven, non-random distribution of objects), that always has structure. The key is solar energy. Over geologic time it produces landforms, and today it grows different plants, which provide structure or heterogeneity to the land.
Three mechanisms create Mosaic pattern
Substrate Heterogeneity – hills, wet spots and different soil types, causes vegetation patchiness.
Natural Disturbance – fire, heavy rains, pest explosions etc.
Human Activity – Plowing Fields, cutting woodlots, building roads, creating patches, corridors, boundaries.
Various biological processes commonly modify and enhance the pattern .
The chemical elements, including all the essential elements of protoplasm, tend to circulate in the biosphere in characteristic paths from environment to organisms and back to the environment. These more or less circular paths are known as biogeochemical cycles.
The movement of those elements and inorganic compounds that are essential to life can be conveniently designated as nutrient cycling.
Example – Nitrogen cycle, Phosphorous cycle, Sulfur cycle etc.
The rate of release of nutrients from the solids, the solar input and the cycle of temperature, day length and other climatic conditions are the most important processes, which daily regulate the rate of function entire ecosystem.
Four Ecosystem processes :
Water cycle, Mineral cycle, Energy flow, Community dynamics (also called succession).
Modifying any one of these processes automatically changes all of them because in reality, they are only different aspects of the same thing.
Natures services which are essential for human life, are generated by a complex of natural cycles driven by solar energy, that constitute the workings of the biosphere, the thin layer near earth’s surface that contains all known life.
Following are few important natural services
Purification of air & water
Mitigation of floods & droughts
Detoxification & decomposition of wastes
Generation & renewal of soil & soil fertility
Pollination of crops & natural vegetation
Control of vast majority of potential agricultural pests
Dispersal of seeds and translocation of nutrients
Maintenance of biodiversity, from which humanity has derived key elements of its agricultural, medicinal & industrial enterprise
Maintaining the global atmosphere, regulating the earth’s weather patterns
India covers about 2% the land area of the world but possesses more than 8% of world’s Bio-Diversity. High endemism is the character of the Indian Biodiversity. Hence Biodiversity loss is irreversible.
As explained earlier together with physical conditions, biodiversity also helps to define characters of nature’s services . If an area atmosphere, soil and water are polluted, nature’s services will be affected. The existing biodiversity will be an indicator of disturbed condition.
The variety of species provides a gigantic gene bank which becomes an unlimited source of food & fiber, medicines, antibiotics, pesticides and raw materials for different industries.
Wild genes are much stronger in resisting diseases and can impart this strength to domesticated plants such as crops to make them pest resistant.
Present Threat :
Ecological knowledge is inadequate
For Biodiversity it is not only the number and variety of species and sub-species of plants and animals, higher and lower but also, includes the variety of habitats & niches available in particular area. Habitat is the address & niches available is the profession of each species.
It is extremely difficult to separate out and count each and every habitat and niche as they are connected to each other & to larger divisions like biomes in a maze of linkages.
Hence conservation of Biodiversity through protection and elimination of human impacts, which means a kind of relapse into conditions that existed sometimes in the past. The same can be called Restoration of natural processes.
The study of the patterns of distribution of organisms in space and time is called biogeography.
India – A Tropical Country
Characteristics of the Tropics
Acute Water Shortage
Fragile Soils – poor moisture retention and organic content
High Evaporation Rate
High Decomposition Rate
Bio-Geographic zones of Maharashtra – A case study I Konkan – Narrow strip between Arabian Sea and Western Ghats (Sahyadri), II Crestline of Western Ghats (Sahyadri), III Slopes, IV Dry Deciduous Zone of Marathwada and Khandesh, V Dry evergreen Zone of Vidarbha
Areas of natural vegetation, such as forests or grasslands, have distinctive climate, which is a modification of the general climate typical of the geographical region in which they are situated. These modifications are the result both of small-scale geographical variation in terrain—slope, aspect, etc. – and of the shading and deflection of wind and rain by the community itself. Such local climates are called Microclimates.
Important factors in development of Microclimates are the extent of penetration into the vegetation of sunlight energy, of heat, and of wind and rain (which cause cooling and control humidity).
Few illustrations South facing slopes in Northern Hemisphere receive more sun than north facing ones, for instance, and thus are warmer and tend to be drier. They are also often more sheltered from the cold North-East winds, and these factors influence the biotic community that develops on them. The vegetation itself greatly influences the climate and community. Tall plants, for instance, provide smaller members of the community with shade and protection from wind and rain. The Microclimate of grassland is very much influenced by the height and density of the vegetation. When the height of the vegetation varies in different seasons, the microhabitats will also vary. The activities of herbivorous insects such as caterpillars, grasshoppers are very much influenced by the conditions of humidity and temperature among the grasses on which they feed.
Core Objectives in Present Management
Present point of view - Ridge to Valley
Protect the upper reaches to avoid erosion and reduce runoff
Avoid siltation of structures in the middle and lower catchments
Ensure the cost effectiveness of structures in the valley
Improve over all efficiency of measures
Continuous Contour Trenches
Staggered Contour Trenches
Continuous Contour Benches
Reduce Soil erosion
Provide vegetation cover
Trenches on slopes will accelerate erosion sources from internet
Soil Conservation- Ecological Point of View Every landscape has variety of vegetation cover spread all over the landscape through variety of land features right from upper reaches to bottom of any slope for example some where depressions, some where steep and medium slopes, rocky out crops etc. These cover types have a specific character and role to play with that land feature for example reducing erosion, absorbing rain shocks etc. . Shola Forests in ravines
Cover Type Management- a Missing Component
Objectives Maintain an association between different land features and their vegetation cover over the landscape , so as to maintain the biological and physical processes (erosion etc.) over the landscape. Significance Contour trenches or benches as a generalized and uniform approach all over the slopes from top to bottom is ecologically incorrect and consideration of physical as well as biological processes according to land classes is important
Ecological Point of View – Ridge to Valley through Stream and Cover Types
Stream plays an important role of connection between Ridge and Valley.
Stream processes that create habitats, integrate the physical and biological processes across watershed.
Cover types over different land classes plays important role in maintaining physical and biological processes.
Before studying measures lets study Stream as an Ecosystem
Every ecosystem has structures and functions, if the balance between them is maintained we get services from it. Any change in structures or functions hampers the balance and hence the services.
Meander, Pools, Riparian Vegetation, Medium size boulders, Medium size channel – Stream in Middle reaches
Structures of Stream Ecosystem
Steps in upper reaches,
Pools in all reaches,
Riffles in middle and lower reaches,
Meanders in plains,
Point Bars in stream channel,
Banks on both sides,
Components of Stream Ecosystem
Functions or Processes of Stream Ecosystem
Transportation of water from land towards sea,
Transportation of sediment load from land towards sea
Services from Stream Ecosystem
Purification of water,
Ground water recharge,
Rich soil in floodplains,
Habitats and Corridors for aquatic as well as other fauna
Dynamic Equilibrium of Stream
A naturally stable stream channel maintains its dimension, pattern and profile such that the stream does not degrade or aggrades i.e. maintains its structures and functions .
Stable streams migrate across the landscape slowly over geologic time while maintaining their form and function.
Naturally stable streams must be able to transport the sediment load supplied by the watershed.
This stable state is called Dynamic Equilibrium of Stream.
sources from internet sources from internet
Instability occurs when scouring causes the channel bed to erode (degrade) or excessive deposition causes the channel bed to rise (aggrade).
The product of sediment load and sediment size is proportional to the product of stream slope and discharge—or stream power.
A change in any one of these variables causes a rapid physical adjustment in the stream channel i.e. Stream Instability.
Stream Instability causes stream to adjust towards new equilibrium state.
This transition may take long time and cause big changes in water quality, habitat and adjacent property i.e. Stream Services .
Water Harvesting in Streams Conventional Approach
Reduce velocity of flow
Infiltration of water in soil
Reduction in stream velocity results into stream instability, hence hampering the services .
Permanent Dam obstructing the stream flow, Instream cultivation and Loss of riparian vegetation
What is Stream Restoration?
Stream restoration is the re-establishment of the general structure, functions and self-sustaining behavior of the stream system that existed prior to disturbance.
It is a holistic process that requires an understanding of all physical and biological components of the stream system and its watershed.
Temporary Half moon shaped pool where flow is retained for a while Restoration includes a broad range of measures, including the removal of the watershed disturbances that are causing stream instability; installation of structures and planting of vegetation to protect streambanks and provide habitat; and then reshaping or replacement of unstable stream reaches into appropriately designed functional streams and associated floodplains.
Ecological Surveys, Restoration Measures and Monitoring in three important areas of stream ecosystem i.e. watershed, stream channel and riparian vegetation.
Surveys are carried out to understand present conditions of stream (stable or unstable) by assessing physical and biological components of stream in above mentioned areas.
Riparian Vegetation in good condition on one bank and disturbed on other bank Survey of Riparian Vegetation A survey of riparian vegetation is carried out to study condition of present vegetation over there, its association with the aquatic as well as terrestrial fauna over there. For example it can serve as a breeding habitat, feeding habitat or corridors for all types of faunas etc.
Survey in Watershed
Study of variety of vegetation cover spread all over the watershed, through variety of land features right from upper reaches to bottom of any slope, some where depressions, some where steep and medium slopes, rocky out crops, wetlands etc.
Survey of Stream Channel
This survey is done in three reaches particularly upper (high slope), middle (medium slope), lower (plains)
Highly Eroded Stream Banks Purpose: To assess condition of Stream banks, check whether erosion is taking place and if yes at what rate. To assess condition of stream channel, check whether degradation or aggradations is taking place. To assess human Interferences on stream channel like dams, instream cultivation, degradation or aggradations, use of stream as for waste disposal, pathways for livestock etc.
Natural Cover Type Management,
Maintaining Enclosures or protected areas
Identifying anchoring places and introducing native species
Creating and Maintaining Natural Cover Type over Gullies and Ravines, which plays important role of moisture retention and corridors for fauna.
Building Half Moon Shaped Pools In Stream Channel For Bank and Channel Protection from erosion: Root wads, Rock Vanes (Single, Cross, J-shaped vanes), Point Bars, Rip-Rap etc. For Habitats creation and Pathways for aquatic fauna: Half moon shaped pools, fish ladders.
In Riparian Vegetation
Protection from cutting and grazing,
Plantation of suitable riparian tree species decided from the survey, in areas where stream banks have lost their riparian vegetation,
Stream banks where riparian vegetation is lost and sever erosion has taken place, initially plantation of grasses is required and later on plantation of trees,
A naturally stable stream channel maintains its dimension, pattern and profile such that the stream does not degrade or aggrades.
Following are the methods used for measuring dimensions, pattern and profile of stream channel
Stream Cross Sectional Profile,
Pool to Pool distances,
Riffle to Pool distances,
Riffle to Riffle distances,
Over the years changes in these measurements helps in deciding whether the stream is heading toward stability or instability and whether any changes are required in measures taken.
Cross Section of Stream
Forest Cover Design for Watershed
Before starting the forest cover design lets have a quick look at Ecological groups of Plants
Hydrophytes – Water loving plants
Mesophytes – Normal plants - Evergreen, Deciduous forests.
Drought escaping - ephemerals
Drought resisting - succulents
Drought enduring - hardy, spiny, thorny.
Halophytes – Waterlogged conditions
Forest Cover Design for Watershed
Every watershed is composed of various land forms or features from ridge to valley through stream.
We can divide watershed into two areas, Elevated Areas and Plain Areas where we get different land features.
For Elevated Areas following are the land features
Gullies and Ravines,
Pioneer Plants on Rubble Heap Forest on slopes
Forest Cover Design for Watershed
For Plain Areas following are the land features
Hill base areas and pediments,
Flood plain area,
Stream course and river basin,
Forest Cover Design
An association between these land features and naturally occurring flora, resulting into relative fauna over there can be called as forest cover design .
Significance of forest cover is that they play important role in keeping both the physical and biological processes over landscape intact.
Forest Cover Design for Watershed
Wind movement, Rains, cooling structures
Tall Trees obstruct the wind movement which results into lesser evaporation loss of nearby water bodies. Tall Trees are also responsible for rains.
Presence of good Riparian vegetation results into cooling of water in stream reducing evaporation loss. In Dry season leaf litter of these trees fallen into the stream channel also results into reducing the evaporation loss through soil.
Riparian Vegetation Few Cover Types and their Ecological roles Shrubs – Faunal diversity Insects Shrubs provide habitats for lesser fauna like insects etc. Clusters – Gene bank Clusters as an association of shrubs, herbs, tall trees, climbers serve as a gene bank over any landscape.
Forest Cover Design for Watershed
Example of cover types in Semi arid regions and their ecological successions
For Ridge top and slopes
Dry deciduous type of forest as the climax ecosystem composition-