Ecohydrology: how water and ecosystems interact

"Water is life" is a most common phrase. Our bodies are 70% water; we humans cannot survive without water for more than a few days. Other forms of life (such as in arid deserts) have adapted to do with less, still, most life on Earth would perish soon without water. 

Now, the dance of life with water, energy and nutrients on Earth has resulted in a dizzying array of ecological adaptations in both terrestrial and aquatic communities. Each species and community has evolved to handle a certain range of conditions of water availability. Mosses and epiphytes in cloud forests depend upon fog, tropical rainforest plants transpire away water freely, while cacti in arid deserts hold on to whatever water they acquire in the infrequent rain showers, and have thorns to discourage animals from getting to them.

Plant and animal communities also have feedbacks upon water quantity, flow and quality. Natural forest cover in a valley intercepts rainfall, decreases instantaneous runoff and flash floods, promotes percolation and usually has flowing streams even in the dry season. Wetlands store large quantities of water during rain events and from inflowing streams, and recharge streams and groundwater. They also intercept and store excess nutrients from inflowing streams, and thereby are known as the kidneys of the landscape. The presence of forested tree islands in wetlands leads to changes in flow patterns, and along with that the formation of gullies and channels. Any large scale changes to vegetation almost always is acompanied by changes in the retention and flow of water, as well as water quality. These in turn can considerably affect organisms living in these areas. 

Hence, ecohydrology is a very rich area of basic ecological, biogeochemical and hydrological investigations, that are directly relevant as inputs to the wise management and conservation of our ecosystems, and with that, our most precious basic resources that make life possible. 

 Some typical questions in ecohydrology are:

--  what happens to streamflow and aquatic ecosystems when a native forest is cut down and replaced by single         species tree plantations (like eucalyptus/australian pine/teak, etc) or agriculture or pasture or urban                 settlements 
--  can deforestation lead to reduced precipitation locally ?
--  how can riparian vegetation buffer streams from excess sedimentation/nutrients in runoff, and how can they         be managed ?
--  how can wetlands be managed to preserve their ecosystem services of maintaining water quantity and flow ?
--  how would climate variability affect water availability ?
--  what minimum range of flows is necessary in rivers to maintain aquatic ecosystems in rivers and estuaries ?

and so infinite list !


Forests and wetlands maintain both water quality and water availability (year-round flow). They also maintain the aquatic ecosystem which in turn contributes to maintaining water quality. This saves humans effort and expense in treating water before consumption. There are numerous other benefits from forests/wetlands, such as maintaining perennial streamflow, reducing soil erosion/sedimentation and landslides, and provisioning food/fuelwood/timber and other resources that humans have depended upon for millenia. 

The role of ecohydrology in sustainable water resources management, document from UNEP

Ecohydrology: both an old and a new subject

Just like water, ecohydrology is both old and new (Jackson et al. 2009)Since the dawn of settlement, people have been using ecosystem services provided by forests. The tradition of sacred groves in Africa. Asia and South America successfully protected old growth forests from wanton logging and degradation. In India, Terminalia arjuna trees have been considered as sacred; these trees grow on streambanks and provide a host of benefits to water quality and stream ecosystems.

However, the degradation of forests, wetlands and other natural ecosystems over the past half a century has both decreased the ecosystem services that regulate hydrology and water quality, as well as brought into prominence the active effort now necessary, worldwide. to protect and restore ecosystems so as to avail their services. 

Thus ecohydrology is a new subject. New, also because of recent advances in sciences that has yielded useful tools to monitor environmental processes, such as laser spectroscopy for stable isotope analysis, time domain reflectometry for soil moisture analysis, sapflow probes for plant water uptake, remote sensing and GIS. Also. new perspectives from ecology, hydrology, soil science, civil engineering, social sciences, climate science, agriculture, environmental law and policy and sustainable development are converging. This is critical so that experts in different fields can communicate with each other, as natural resource management is interdisciplinary.

So, whats unique about ecohydrology in the  tropics/subtropics ?

High biodiversity: Tropical regions have the greatest diversity of life, caused by a range of climatic conditions, ample sunshine, high temperatures that support growth and a stunning variety of microclimates ranging from humid lowland ecosystems to cloud forests to high altitude grasslands and plateaus with cold temperatures and strong solar radiation. Threats: At the same time, the pressures on natural resources are far greater in the tropics and subtropics owing to large poverty-stricken populations who lack a safety net (access to resources in other regions or countries, unlike the developed world). Furthermore, The Himalayas and the Andes are witnessing unprecedented melting of glaciers, that can decrease dry season flow in rivers, on which depend more than a billion people. Tropical mountain ecosystems (such as the high paramo in the Andes or the Eastern Arcs in Kenya/Tanzania) are changing, often towards impoverishment because of a lower period of cloud /mist cover, extreme rainfall interspersed with long rainless periods and other reasons.

Lack of knowledge:Unlike ecosystems in the temperate zone ( and a few tropical regions such as Panama,  Costa Rica and Hawai'i), by and large most tropics and subtropics have large blank areas as regards ecohydrological studies and understanding. While basic laws of ecology and hydrology operate worldwide, existing studies indicate a very wide range of ecohydrological interactions in different ecosystems, suggesting that one cannot extrapolate results from one ecosystem to another.  

Sustainable water and land management needs a detailed understanding of the linkages between water, land, human activities and biodiversity. Ecosystems such as forests and wetlands naturally regulate water flow and quality; hence preserving these ecosystems, and understanding the specific processes that maintain water should form part of the strategy for water and environmental management in the developing countries. Practical (let nature take care of the processes), cheap (no expensive structures or energy required) with a host of other benefits from preserving ecosystems, such as biodiversity, carbon sequestration, forest-based natural resources and tourism.

This site aims to:
1.  compile news on ecohydrology research and application in the sub/tropics and developing countries
2. develop an online course in the principles and applications of Ecohydrology as applicable to the sub/tropics.

First, some F U N D A M E N T A L  concepts! 

 a watershed  
 Watershed/Catchment/Drainage basin

The land area around a stream that contributes water into the stream via rainfall-surface runoff and/or groundwater seepage.

Water cycle

precipitation - infiltration - transpiration - runoff - evaporation - condensation - precipitation and so on and long as the sun keeps shining on earth !

The BIG picture (scope) of Ecohydrology:

The myriad interactions between water, environment and life are best visualized in a framework with overlapping components (Figure 1). 

Ecohydrological framework

1. Water cycle, hydrology and ecosystems

Managing water needs for humans and ecosystems requires knowing how much water there is available in a catchment, and how does that vary over season and place. This leads to identifying the various forms of water (like surfacewater, groundwater, wetland storage, rain etc), as well as the processes like rainfall, evaporation, streamflow, etc. This is known as stocks and fluxes of water. A water balance or water budget attempts to relate these different processes to understand water availability at various time scales.

Water balance calculations for watersheds - a range of techniques from simple accounting in a spreadsheet,  to complex spatial hydrological models, the choice of which depends upon the objectives of analysis, resources available, and mainly, how much DATA is there.

2. BIogeochemistry, nutrient cycles and water quality

Looking at how is the cycling of elements (primary and secondary production, and decomposition of organic matter, mineralization and uptake of inorganic forms by living creatures) is linked with the presence of water. For instance, flooding of soils in wetlands leads to anerobic conditions which changes the pathways of nitrogen in decomposition. Anerobic conditions, by depriving oxygen to aerobic bacteria ( fast decomposers) slows down decomposition of organic matter resulting in vast quantities of peat being stored - natural sequestration of carbon which otherwise would get released into the atmosphere as carbon dioxide (greenhouse gas).

3. Plants, animals, ecosystems, local communities and water

All life depends on water; hence drastic changes to the seasonality of water availability and water quality can affect reproduction, growth and the very survival of life forms. However, not much is known about  the linkages between hydrology, water availability, ecosystem function and species requirements of water and nutrients/prey, especially in tropical and subtropical ecosystems. It is vital to get the water right to ensure conservation of ecosystems along with the services they provide mankind. Ecohydrology studies can increase our knowledge and understanding of how ecosystems function with respect to water, and thereby devise tools such as Environmental Flow Assessments and Biomonitoring to help us monitor and manage ecosystems better. Also critical is to involve local indigenous communities in ecosystem preservation, by a two-way knowledge exchange on ecosystem function, generation of sustainable livelihoods and the formation of trust.

4. Water needs by humans (Pressures on water quality and availability)

Growing human population, synergistically coupled with increasing per capita resource consumption is posing increasing stresses and demands on the finite freshwater resources. More water is being abstracted especially from aquifers, while increasing pollution is compromising water quality in both surfacewater and groundwater. Monitoring is critical to get a realtime idea of the conditions of water quality and availability, and is increasingly necessary as proactive steps to buffer water resources from the uncertainity in rainfall increasingly associated with climate change. 

5. Water resources management
Ecosystems having their natural species diversity and function are known to positively affect water availability and quality on the landscape. Forested catchments regulate water flow, with greater availability of baseflow in the dry season, while also minimizing soil erosion. Wetlands not only store water in the rainy season, they also act as pollutant filters on the landscape. Utilizing such ecosystem services is the only sustainable way for ensuring water availability and quality especially in developing countries that lack the massive amount of capital and energy costs associated with conventional physicochemical treatment plants.Hence, ecosystem service- based water treatment is once again emerging as a sustainable and feasible means of treating wastewater, such as the East Kolkata wetlands in India that treat more than 50% of sewage of the city of Kolkata, and in turn also produce a large amount of the vegetables and fish consumed in the city of 14 million.