Landscape management - Ecological Applications: Toward a Sustainable World - page 296

adverse effect on the provision of water of high quality for drinking and contact
recreation. These ecosystem services, normally provided 'free' from a healthy land-
scape, can be lost because of the input of large quantities of nitrogen and phosphorus
(from fertilizers applied to the land), fi ne sediment (from eroding land) and an
increase in water-borne pathogens from farm animals that affect humans (such as
the Giardia parasite). In addition, intensive farming may be associated with higher
fl ooding probabilities because of the loss of vegetation that recirculates water from
the soil after storm events. Flood protection is another ecosystem service associated
with a healthy landscape.
The impact of agriculture depends on how much of the landscape is used for
production. A single small farm - even one involving the excessive use of plough,
fertilizer and pesticide - will have little effect on biodiversity and water quality in
the landscape as a whole. It is the cumulative effect of larger and larger areas of
intensive agriculture within a river's catchment area that depletes the region's bio-
diversity and reduces the quality of the water needed for other human activities. For
this reason, management of agricultural landscapes needs to be carried out on a
large scale. Management must also involve a wide range of disciplines, from farm
production and economics to biology, chemistry and public health. This ideal
approach has proved diffi cult to achieve.
Santelmann et al. (2004) show the way forward. They incorporated knowledge of
experts in the various fi elds into alternative visions of a particular landscape - the
catchment area of Walnut Creek in an intensively farmed part of Iowa, USA. They
mapped the present pattern of land use and also created three scenarios of the way
the area might look in 25 years if particular strategies are followed. They also
assessed how farm income, water quality and biodiversity would be expected to
change according to the three scenarios. A production scenario imagines what the
catchment will be like if continued priority is given to corn and soybean production
('row' crops), following a policy that encourages extension of cultivation to all highly
productive soils in the catchment. A water quality scenario envisions the catchment
under a new (hypothetical) federal policy that enforces chemical standards for river
and ground water, and supports agricultural practices that reduce soil erosion and
fl ooding. Finally, a biodiversity scenario assumes a new (hypothetical) federal policy
to increase the abundance and richness of native plants and animals. In this sce-
nario, a network of biodiversity reserves is established with connecting habitat cor-
ridors that include the riparian (bankside) zones of rivers.
Figure 10.16 compares for the three scenarios the distribution of agricultural and
'natural' habitats in 25 years time. Not surprisingly, the Production scenario pro-
duces the most homogeneous landscape. Compared with the current situation, there
is an increase in row crops (corn and soybean) at the expense of less profi table
pasture and forage crops. Note that pasture and forage crops provide year-round
perennial ground cover that is conducive to both higher water quality and biodiver-
sity. The Water Quality scenario leads to more extensive riparian strips of natural
vegetation cover and more perennial cover in total. Finally, the Biodiversity scenario
has even wider riparian strips as well as prairie, forest and wetland reserves, and
an increase in strip intercropping, a farming practice that is more sensitive to bio-
diversity because it helps increase connectivity between reserves.
The percentage change for each scenario, compared to the current situation, in
economic, water quality and biodiversity terms is shown in Figure 10.17. It is hardly