How to make an ecologist #8

fieldwork_in_Bangladesh_Aug

During my PhD years, Brian Whitton was also running a project in Bangladesh, looking at the ecology of deepwater rice fields, and gave me the opportunity to exchange the bleak Pennine hills for the tropical lowlands of the Indian sub-continent for part of one summer.   The premise of the project was that the rice fields here typically flooded to 1.5 or even 2 metres depth. The varieties of rice that grow in these fields had been studied by traditional agronomists but the sheer quantity of water meant that the rice fields resembled shallow lakes and, perhaps, studying the rice from the perspective of a freshwater ecologist would yield better insights into their yield.

The British High Commission allocated us a house in the diplomatic suburb of Dhaka, and gave us use of a Land Rover to negotiate the noisy mêlée of bicycles, rickshaws, buses and lorries that congested the streets of the capital, before we broke free from the urban areas and drove along narrow tree-lined roads running along the ridges between rice fields.   About an hour to the south east of Dhaka, we pulled to the side of the road, close to a small village where the team had worked in previous years.   The village was on a small island about 300 metres away across the rice field, but the sight of our Land Rover arriving would prompt our boat boys to set off in their punts to join us.

Moving through the fields in their small boats, I was struck by the fecundity of the fields. Prolific growths of aquatic plants thrived amidst the rice plants. Some, such as the water lilies in the foreground of the picture above, were familiar from home, others, such as water hyacinth (Eichhornia crassipes) and water lettuce (Pistia stratiotes) I had only previously read about.   The rice plants, themselves, were intriguing: they had shallow roots in the sediments, relying on the water for support, but had clusters of “aquatic roots” growing at intervals along their long (up to two metre) stems.   The stems and leaves were also smothered, in places, with growths of nitrogen-fixing blue-green algae such as Rivularia. I wanted to illustrate this diversity with some of my photographs of this diverse ecosystem but have only managed to find a few very general shots.   Accepted wisdom was that the fertility of lowland Bangladesh was derived from silt deposited by the rivers Ganges and Brahmaputra; looking closely at a rice field and the situation looked far less straightforward.    The prolific aquatic roots, compared with the shallow true roots, suggested that the rice plants depended upon the water, and not the sediments.

Sonargen_boatman_Aug85

One of our boat boys at Sonargon in Bangladesh. The upper photograph shows fieldwork underway in the rice fields with (from left), Motaleb, Ashit Paul and Jo Rother.

The question we were trying to answer was how the rice plants got the nutrients they needed, given this situation.   The answer came, at least partly, from extensive measurements of the water chemistry of the rice fields using a combination of dataloggers, attached to a range of instruments measuring pH, temperature and oxygen concentration in the water. These sat in metal boxes on specially-constructed platforms, guarded by the village boys who were also our boatmen.   We also moved amongst the fields collecting other measurements to complete the picture.

The water in the rice fields was very soft, with little natural buffering capacity and this, along with the warm temperature and abundant sunlight, meant that the pH fluctuated dramatically between daytime (when plants were removing carbon dioxide from the water for photosynthesis) and night-time (when the carbon dioxide they produced during respiration reacted with the water to produce dilute carbonic acid).   There was a very neat relationship, too, with the concentration of oxygen in the water – high concentrations produced during daytime and low concentrations recorded at night.   This, in turn, is key to understanding the fertility of the fields as phosphorus, in particular, is more soluble in the anerobic conditions, so the deeper, darker areas of the rice fields were rich in phosphorus released from the sediments, which was then available to the aquatic roots. As the season progressed, so the extent of the anoxic areas within the field increased.   The “fields”, in other words, were behaving in exactly the same way as shallow lakes.

pH_v_DO_in_DWR

Graphs from one of the Durham University reports on deepwater rice ecosystems to the Overseas Development Administration and EEC on deepwater rice fields showing the relationship between dissolved oxygen and pH in deepwater rice fields in Bangladesh, 1985 and 1986.   All measurements on a graph were made on the same afternoon, showing the wide variation in conditions even in a small area.

In between our fieldwork, we had a spacious house in the diplomatic quarter of Bangladesh with a very competent cook, Swapan, who came from Chittagong, close to the border with Burma (now Myanmar).   Our diet was mostly local food, heavily biased towards fish and prawns, which also formed part of the rice field ecosystems.   I had a particular fondness for biryanis, but also for a rice and lentil dish called khichuri. Neither, however, was washed down with beer because Bangladesh was dry. Our only source of alcohol was the British Aid Guest House, populated by characters who could have walked straight off the pages of a Graham Greene novel.   Compared to experiences a few years later in Nigeria, attitudes amongst the aid community were antediluvian, bordering on racist at times. Fortunately, perhaps, our intensive work schedule left us with little time for socialising.

At a deeper level, this experience of tropical ecology brought me closer to the world of television natural history programmes that had excited my interest in ecology in the 1970s.   The lush vegetation and exotic landscapes had piqued my interest although fate seemed to have decreed that my world would rarely overlap with the charismatic megafauna that populated Attenborough’s documentaries.   My future seemed to lie at the unfashionable end of biodiversity.

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One thought on “How to make an ecologist #8

  1. Pingback: How to make an ecologist #9 – microscopesandmonsters

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