Conclusion

Watershed of a river plays a vital role in sustaining the hydrologic regime. Analyses of landscape dynamics across the west flowing major rivers of Uttara Kannada district (Central Western Ghats), reveal degradation of forests from 74.19% (1973) to 48.04% (2018) with the loss of evergreen forests from 56.07% to 24.85% due to the large scape developmental activities such as construction of dams, power projects, forest based industries - paper mills, road expansions, urbanization, encroachment for horticultural and agricultural practices. The forests are currently confined to the Ghats and protected areas.

River basin wise land use analyses reveals that anthropogenic activities involving monoculture (both forest plantation and horticulture) plantations and exploitation of timber in the Aghanashini river basin have led to the decline in the forest cover from 86.08% (1973) to 50.65% (2018), followed by river basins of Kali (37.8%), Gangavali (37.7%) and Sharavati (23.3%). Evergreen forest cover in Aghanashini riverscape has declined from 72.15% (1973) to 24.09% (2018), while moist deciduous forest cover has increased from 9.79% to 25.76% during this period. Construction of a series of dams in the Kali river basin at Supa, Kodasalli, Kadra, etc⁵² has resulted in loss of forest cover (from 87.26% to 54.24%) and in particular the evergreen forests (from 61.82% to 30.5%). Similar level of anthropogenic stress was witnessed in the Sharavati river basin which has led to the decline in forest cover (from 61.97% to 47.55%) with the loss of evergreen forests (from 52.68% to 27.11%) and an increase in deciduous forests by two fold. Human animal conflicts have increased due to the disruption of animal movement paths with the decline of the contiguous or intact (interior) forests from 45.88% to 23.97% and loss of fodder, water, etc. with decline of native vegetation.

Fragmentation analyses reveals a decline in the interior or contiguous forests in the district from 62.71% (in 1970) to 24.74% (2018) and consequent increase in patch, transitional, edge and perforated forests. Kali and Aghanashini Rivers have forests of native species covering more than 50% with the contiguous intact forests over 14% of the catchment area.

Alterations of landscape structure in the catchment areas influences the hydrological regime leading to variations in the hydrological status. Assessment of sub-basin wise eco-hydrological footprint across river basins with the varied levels of anthropogenic stress emphasizes the role of forests on infiltration and evapotranspiration capabilities. Sub-basins with higher forest cover with native species have higher eco-hydrological index suggesting that the availability of water can satisfactorily maintain the biotic demands, whereas sub-basins dominated by monoculture have low index, which indicates water scarcity. Inter annual variability of water availability and demand footprints indicate that the sub basins between coasts and Ghats are with perennial river streams, whereas the transition zones between Ghats and plains towards east show deficit of water for 6 to 10 months in a year with intermittent and seasonal flow. Occurrence of streams with 12 months flow in the ecologically sensitive region (1 and 2) confirms the linkages of hydrologic regime with the ecological sensitivity of a region. This highlights that streams are perennial in the catchments with native forest cover > 65% having higher proportion of endemic plant species. The significance of land cover with native undisturbed forests (interior forests) in maintaining the flow regime in the rivers, microclimate and biodiversity is evident with the comparative analysis of temperature, biodiversity, water quality, forests and hydro-ecological flows. The catchments with perennial rivers support rich biodiversity with higher number of species of both flora and fauna.

Assessment of spatial patterns of biodiversity across the four river basins studied reveal the occurrence of endemic flora and fauna in the catchments with perennial streams. Similarly, aquatic diversity across these four river estuaries indicates that due to the natural flow regime, Aghanashini has highest diversity followed by Gangavali, Kali and Sharavati, which have altered salinity conditions due to river flow that is regulated by reservoirs.

Anthropogenic activities (industries, horticulture, etc.) in the upper reaches of rivers have a negative impact on the pristine nature of water, i.e., high pollution levels have been observed in the catchments with towns/cities with high population (Hubli, Dharwad, Sirsi, Sagar), industries (Dandeli). Forests help in remediation and maintenance of water quality in the downstream regions. Forests also help in moderating microclimate as evident from the lower surface temperatures in the forested catchments compared to the degraded landscapes. Regulation of water flow in the river impacts the people’s livelihood downstream as evident from the lowered values of ecosystem goods and services as in Kali and Sharavati estuaries (TEV <2.5 Million Rupees./year/hectare) compared to river basins with the natural flow as in Aghanashini estuary (with the higher fish diversity and TEV of >5 Million Rupees./year/hectare).

The study provides insights on the role of native vegetation in i) sustaining the water availability during all seasons to meet biotic demands, ii) supporting rich endemic biodiversity, iii) maintaining water quality through bioremediation, iv) promoting higher ecosystem goods and services and (v) supporting livelihood of people dependent on indigenous resources. Understanding these linkages would help the planners/decision makers with valuable knowledge for integrated river basin management in an era dominated by indiscriminate development of river catchment areas involving enhanced deforestation, frequent instances of altering natural regime, inappropriate cropping and poor water efficiency.

The study highlights the vital ecological function of a riverscape in sustaining the hydrologic regime when covered with vegetation of native species. The presence of perennial streams in sub-catchment is dominated by native vegetation compared to the seasonal streams in the catchment dominated by anthropogenic activities with monoculture plantations. Hence, the premium should be towards conservation of the forests with native species in order to sustain water and biotic diversity in the water bodies, which are vital for food security. There still exists a chance to restore the lost natural evergreen to semi-evergreen forests through appropriate conservation and management practices. Eco-hydrological assessment across the riverscapes of varied levels of anthropogenic stress, highlights the water retention capability of a riverscape dominated by the vegetation of native species to sustain the local societal and ecological demands, which is useful in the integrated management of riverscapes (watershed, catchment or basin) in India by the respective government agencies.

Acknowledgement

We acknowledge the financial support for ecological research in Western Ghats from (i) UNSD and The Ministry of Statistics and Programme Implementation; (ii) NRDMS division, The Ministry of Science and Technology (DST), Government of India, (iii) Indian Institute of Science and (iv) ENVIS division, The Ministry of Environment, Forests and Climate Change, Government of India. We thank Vishnu Mukri and Srikanth Naik for the assistance during field data collection.