Introduction

Ecological values refer to the level of benefits and services provided with the complex interactions among the biotic and abiotic components to sustain humans (Ramachandra et al. 2018a; Ramachandra et al. 2018b; Ramachandra et al. 2018c). Ecosystem services include services and benefits such as food, erosion control; climate regulation; water purification; bioenergy, etc. and are very crucial for the biota’s survival (Ramachandra et al. 2018; Ramachandra et al. 2018). The structural components of an ecosystem include physical features (such as land cover, water, sediment and soil profile, the gradient of conditions in water body), biotic compositions (like species, number of individuals and their biomass), etc. Interactions between these elements, i.e., the flow of nutrients, energy, etc. between different ecosystems constitute the functional aspects of an ecosystem. Ecosystems can be broadly categorized as aquatic and terrestrial ecosystems, on the basis of their major source and sink of nutrient, i.e., water or land (Ramachandra et al. 2018a; 2018b). Aquatic ecosystems with rich nutrient contents is substantially different from terrestrial ecosystems and both these ecosystems are dependent upon each other, as there is an overlap of the functional boundary between the two, irrespective of the physical boundaries (Ramachandra et al. 2018c).

An estuary is a dynamic zone between land and Sea with the salinity transitional to that of marine and fresh water, which makes them unique in their ecological and biological functions (Anoop et al. 2008). Estuaries support wide range of terrestrial and aquatic life with the distinctive ecological, geological, and biological domains of vital importance (Wilson, and Farber 2005). These are major specialized ecosystems where organic matter is built up in large quantities and offers ideal biotic conditions to sustain considerable aquatic population (Boominathan et al. 2008; Rao and Suresh 2002). Estuaries are the transition zones with salinity gradient where the water quality change from fresh water to saline as landscapes change from land to sea. These regions are protected by mangroves, reefs, barrier islands and land, mud or sand that define an estuaries seaward boundary and shield an estuary from the ocean waves, winds and storms (Ramachandra at al. 2018d). Most of the Western Ghats Rivers join Arabian Sea forming productive estuaries, which sustains the livelihood of millions of people.

Fresh water influx and density difference between the two merging water entities, a constant replenishment of nutrients and versatility in their structure make it a nursery ground for many marine organisms (Ramachandra 2018e). Diverse estuarine habitats include shallow open waters, fresh water and salt marshes, sandy beaches, mud and sand flats, rocky shores, mangrove forests, river deltas, tidal ponds, sea grass beds, etc. These habitats are essential for the survival of biota, which depend on the estuarine ecosystem for breeding, feed, living, etc.

Marine organisms including fish species and oysters, during various stages of their lifecycle, depend on the estuarine ecosystem (Bhat et al. 2010; Ramachandra et al. 2018d; Ramachandra et al. 2018c; Wilson and Farber 2005), while other species (salmon and shrimp) on a seasonal basis for reproduction and growth depend on estuaries (Wilson and Farber 2005).

Estuaries supports local livelihood through employment, goods (fish, fodder, sand, salt, etc.) and a variety of ecological services (Boominathan et al. 2008; Thomson, 2003; Wilson and Farber 2005). Majority of estuarine communities are dependent on the ecosystem for activities related to fishery (Anoop et al. 2008; Bhat et al. 2010; Thomson 2003). Diverse ecological services provided by an estuary include regulation of various gases, sequestration of carbon, water flow, retention and soil formation, nutrient cycling, pollination, related biological processes, bioremediation, recreation, repository of genetic resources, etc. (Boominathan et al. 2008; Ramachandra et al. 2017; Thomson 2003).

The estuaries are the repositories of mangroves biodiversity which serve as a wall for the coastline apart from providing numerous other benefits. Mangrove species grow in varied salinity levels and occur mainly in intertidal regions (Hirway and Goswami 2007; Kathiresan, and Narayanasamy 2005; Bhat et al. 2010; Prakash et al. 2010), receiving organic materials from estuarine or oceanic ecosystems. Goods provided by mangrove ecosystems are forestry products (firewood, charcoal, timber, etc.), non-timber produce (honey, etc.) and fishery produce (fish, prawn, crab, mollusk etc.). Twigs of mangroves are used for making charcoal and firewood due to high calorific worth. Mangrove swamps act as traps for the sediments, and sink for the nutrients. The root systems of the plants keep the substrate firm, and thus contribute to a lasting stability of the coast (Kathiresan, and Narayanasamy 2005).

The valuation of goods and services from the global terrestrial and aquatic ecosystems (Costanza et al. 1997; Costanza and Folke, 1997) reveals the annual value of 16 to 60 trillion USD with an estimated average of 33 trillion USD ($), which is about 1.8 times higher than the current global gross national product (GNP). The relative share of marine compared to the terrestrial (forests and wetlands) is about 62%. A detailed socio-economic appraisal of the traditional, modern, recreational and non-use values for Kali estuary, Karnataka and Cochin estuary, Kerala show aggregate value of Rs. 1163.56 lakhs and Rs. 44,380 lakhs (ten lakhs is equivalent to one million) respectively (Thomson, 2003).

The mangrove vegetation contribute significantly in the regional socio-economic development through commercial products, fishery resources apart from the prospects of eco-tourism (Kathiresan and Narayanasamy 2005; Prakash et al. 2010). Mangroves provide habitat to a wide array of diverse biota, which include bacteria, fungi, insects, fish, prawns, shrimps, birds, etc., including a variety of flora – sea weeds, small plants and creepers (Hirway and Goswami 2007). Valuation of mangroves per household based on the avoided damage cost is estimated as 116.28 USD and 983795.7 USD as land accretion value over a period of 111 years.

The overall benefits due to eco-services by mangroves is INR 2246.93 crores per year in Gujarat (Hirway and Goswami 2007), 18570 Rs/ha/year (lagoon fishery, Rekawa lagoon, Srilanka), 34,500 Rs/ha/year (coastal fishery) respectively (Gunawardena and Rowan 2004). The storm and erosion control of mangroves is about 21000 Rs/ha/year through replacement cost approach. The annualized value of coastal protection through replacement cost technique is about 3697 USD/hectare. The net present value for 20 year period with 15 % discount rate was obtained as US $ 632.27 /ha and including indirect use values is USD 27,264 - 21,610 /ha. (Sathirathai and Barbier 2001). Economic analysis of twelve year mangrove plantation in the Gazy bay in Kenya show the benefit of 379.17 USD/ha/yr (extractable wood products) US$ 44.42/ha/yr (carbon sequestration) to US$ 770.23/ha/yr (research and education). The total economic value for Rhizophora plantation of twelve years old is estimated as 2902.87 USD/ha/yr. An economic valuation mangrove resource utilization study of Gaz and Hara delta located in South Iran computed the total economic value as 10000-20000 US$/ha/year (Ghasemi et al. 2012).

The economic valuation of Aghanashini estuary considering bivalve production (Boominathan et al. 2008) reveals the revenue generation of 57.8 million per year, 497990 man days of fishing opportunity in the estuary with the annual income of 56695 INR/person (Bhat et al. 2010). The integrated value of tangible goods (fish, salt, shrimp culture, bivalve food, mangrove fodder, lime and sand) for an estuary is estimated as 2,97,813 INR/hectare/year (Prakash et al. 2010). The NPV of total direct benefit is about 1928 million INR in the Ashtamudi estuary (Anoop et al. 2008). The annual effort is estimated as 23000 man days for fishery through hand picking in Aghanashini estuary. Shells deposit of 7600 tons annually are being extracted from Tadri estuarine bed for industrial use (poultry feed, etc.) and the income is estimated as 40-50 million INR per year (Bhat et al. 2010).

1.1 Ecosystem goods and services: Ecosystem provides various vital benefits and services, which are very crucial for the endurance of dependent biological organisms and welfare of the human society (Ramachandra et al. 2017; MEA, 2005). Ecosystem functions include natural processes (hydrological, bio-geo-chemical cycling) that provide goods and services supporting directly as well as indirectly the society (de Groot and Vander Meer 2010; MEA, 2005). The ecosystem benefits include (i) provisioning services (food and water), (ii) regulating services (flood and disease control), (iii) cultural services (spiritual, recreational and cultural), and supporting services (maintaining conditions for sustaining life) (Fischlin Midgley et al., 2007; Hassan et al. 2005; MEA, 2005; Ramachandra et al. 2017a; Wilson and Farber 2005).

Estuarine and coastal ecosystems are vulnerable natural systems globally (Barbier et al. 2011) with the intense anthropogenic stress, evident from the loss (MEA, 2005) of salt marshes (by 50%), mangroves (35%), coral reefs (30%), and sea grasses (29%). In addition, propagation of invasive species, declining water quality, and decreased coastal protection from flooding and storm events, etc. are the agents for the loss of biodiversity, ecosystem functions, and coastal vegetation in estuarine and coastal ecosystems have contributed to (Barbier et al. 2011). Insights of the ecosystem function would aid in optimizing alternative uses of ecosystem functions and services (Barbier et al. 2011; Costanza 1997; Costanza and Folke 1997). This would aid in the evolving prudent policy and managerial decisions in favor of environmentally prudent practices (Barbier et al. 2011), which maximizes societal welfare (Turpie et al. 2010; Ramachandra et al. 2017; Ramachandra and Rajinikanth, 2003; Ramachandra et al. 2002).

Figure 1 illustrates a framework for assessing the ecosystem goods and services (Costanza, d’Arge, de Groot, 1997; Costanza, Folke, 1997; MEA, 2005; Ramachandra, Soman, Ashwath, et al., 2017), which are broadly classified into four different functions namely – regulation, production, habitat and information. These can be grouped as (i) ecological (determined by the regulation and habitat functions), (ii) socio-cultural (identifies vital environmental functions, physical and mental health, education, cultural diversity), (iii) heritage, freedom and spiritual values (Costanza, d’Arge, de Groot, 1997; Costanza, Folke, 1997; MEA, 2005; Ramachandra, Soman, Ashwath, et al., 2017) and (iv) economic values, i.e willing to give up in other goods and services (Ramachandra, Rajinikanth, 2003; Ramachandra et al. 2002; Ramachandra et al. 2017a; 2017b; Turpie et al. 2010).

Fig. 1. Assessment of ecosystem goods and services 🡪

1.2 Total Economic Value (TEV): The total economic value (TEV) is the sum of (i) use value (UV) and (ii) non-use value (NUV), accounting all benefits from an ecosystem. (UNEP/GEF 2007; UNEP 2013; TEEB 2011). Figure 2 outlines the framework for TEV of an estuarine ecosystem. Use value refers to the tangible or physical aspects of resources, which provide direct (personal) utility or satisfaction and which have direct market prices for quantification and indirect (consist of the various functions that a natural system may provide, such as shoreline protection functions, carbon sequestration, and nutrient or contaminant retention (Ramachandra et al. 2017a; UNEP/GEF 2007; UNEP 2013; TEEB 2011). This reflects changes in the value of production or consumption of the activity or property (that it is protecting or supporting) and the availability of this resource in the future (UNEP/GEF 2007; UNEP 2013; TEEB 2011), which relates to future direct or indirect use of the resource (Barbier et al. 2011; Ramachandra et al. 2017a). Non-use values of an ecosystem are bequest and existence values (related to aesthetic, cultural, and moral aspects), regardless of whether it will be used or not (UNEP/GEF 2007; UNEP 2013; TEEB 2011).

Fig. 2. Framework for economic valuation of estuarine ecosystems 🡪

1.3 Techniques for quantification of ecosystem goods and services: The techniques for valuation of ecosystem based on the type of goods and services are grouped into four basic types – (i) direct market valuation considering the market price of the resources that are being used directly and indirectly (UNEP/GEF 2007; UNEP 2013; TEEB 2011), (ii) indirect market valuation (assessing the values can be used for the availability through the willingness to pay (WTP) or loss of these services through willingness to accept compensation (WTA) (Barbier et al. 2011; Ramachandra et al. 2017a). The techniques include avoided cost (AC), replacement cost (RC), factor income (FI), Hedonic pricing (HP) and travel cost (TC) methods (Barbier et al. 2011; Costanza and Folke, 1997; Costanza et al. 1997; Ramachandra et al. 2017a), (iii) Contingent valuation via economic values for non–marketed goods, such as environmental assets, amenities, and services are estimated through surveys to ascertain respondents’ preferences regarding an increase or decrease in the level of environmental quality (UNEP/GEF 2007; UNEP 2013; TEEB 2011). The preferences are valued through surveys to ascertain willing to pay for the preservation or improvement of a certain resource or environment or to accept payment for doing away with said resources or environment, (iv) group valuation based on of deliberative democracy principles and the assumption that public decision making should result from open public debates (Barbier et al. 2011; Costanza and Folke, 1997; Costanza et al. 1997; Ramachandra et al. 2017a) and (v) benefit transfer method of using values estimated for an alternative policy context or location as a basis for estimating a value for the policy context or site location in question (Barbier et al. 2011; Ramachandra, et al., 2017a).

Benefit transfer technique involves (i) identification of resources or services to be valued, (ii) identifying relevant existing studies, (iii) evaluating applicability and (iv) conducting the benefit transfer. This method is used for damage assessment, where there is a need of existing estimate of value of the natural resource or services provided by the resource.

The main objective of the current communication is to estimate the total economic value of Aghnashini estuarine ecosystem of Uttara Kannada in order to enhance natural resource productivity through prudent management. This includes estimating values of (i) provisioning services; and (ii) indirect products and services of the estuarine ecosystem such as regulating, supporting and information services.