30 Agricultural Harm to the Environment
There are more than 2 million hectares of paddy rice in Japan, and each of these
hectares holds about 1000 tonnes of water each year. In the Koshigaya City basin,
25 kilometres north of Tokyo, paddy fields close to the city have been steadily
converted to residential uses over the past quarter century. But as the area of paddy
has declined by about 1000 hectares since the mid-1970s, so the incidence of
flooding has increased. Each year, 1000–3000 houses are flooded. In whole water-
sheds, woods and farms on steep slopes have been identified as having the greatest
value in buffering and slowing water flow, and minimizing landslides. Diversity,
though, is critical. As Yoshitake Kato and colleagues have put it:
traditional villages in rural areas include settlements, paddy fields, crop fields and for-
ested hills or mountains, all as linked landscape. The systems were dependent on all
their parts. The decline of farming in the uplands, together with loss of forests, threatens
the stability of whole watersheds.^24In China, the 500,000 hectares of wetlands that have been reclaimed for crop pro-
duction in the past 50 years have meant the loss of flood-water storage capacity of
some 50 billion cubic metres, a major reason for the $20 billion flood damage
caused in 1998.^25 In many agricultural systems, over-intensive use of the land has
resulted in sharp declines in soil organic matter and/or increases in soil erosion,
some of which in turn threatens the viability of agriculture itself. In South Asia, for
example, a quarter of farmland is affected by water erosion, a fifth by wind erosion,
and a sixth by salinization and waterlogging.^26
Putting a value on wetlands and watercourses, so that we can calculate how
much is lost when they are damaged or destroyed, is not a trivial task. Economists
have no agreed value for wetlands, though various studies indicate that individual
bodies can provide several million dollars of free services to nearby communities for
waste assimilation and treatment. A recent US Department of Agriculture study
put wetland monetary value at $300,000 per hectare per year. Another way to assess
value is to investigate how much people pay to visit wetlands, whether to watch or
photograph biodiversity, or indeed to shoot it. In the US, it is estimated that 50
million people each year spend $10 billion observing and photographing wetland
flora and fauna, 31 million anglers spend $16 billion on fishing, and 3 million
waterfowl hunters spend nearly $700 million annually on shooting it. A recent
meta-analysis of economic studies of people’s willingness-to-pay for recreational
services of wetlands and watercourses puts the average value in Europe to be £20–25
per person per hectare per year.^27 Thus each hectare of wetland converted to another
purpose means the loss of at least £20 of value to the public. There are, of course,
limitations in these exercises, as monetary values cannot be allocated to all uses.
One of the most serious side effects of agriculture is the leaching and run-off
of nutrients, and their disruption of water ecosystems. Eutrophication is the term
used to describe nutrient enrichment of water that leads to excessive algal growth,
disruption of whole food webs, and in the worst cases complete eradication of all
life through deoxygenation. The most notorious example is the Gulf of Mexico