02 Contents Frame

Land evaluation – towards a revised framework
98
or two fungicide applications are normally enough to protect wheat, but six to nine 
applications are required for potatoes. The regional crop statistics are combined with 
information on pesticide use on the basis of surveys or information from extension 
services. For each crop type a pesticide risk index is established, derived from a factorial 
model or a process model. 
Most pesticide risk models take into account runoff and spray drift as the two most 
important exposure paths. The diffuse exposure of humans, animals or overall habitats 
to a combination of locally applied pesticides can be mapped on a regional scale. The 
lower the resolution of the datasets, the more simplified the model that can be used and 
the more generalized the predictions.
Acidification and eutrophication
In many parts of the world deposition of sulphur and nitrogen pollution poses a 
serious risk to the environment. Various assessment and mitigation methods are 
being developed, using tools such as air quality guidelines for health and critical 
loads and levels for crops, forests and natural ecosystems. Impacts include effects on 
human health, corrosion of materials, reductions in crop yields, eutrophication and 
acidification. Acid deposition leads to acidification of sensitive terrestrial and aquatic 
ecosystems. Decreases in lake pH have caused huge losses of fish stocks, notably in 
Europe and North America, and decreases in soil pH have been implicated as a major 
cause of forest damage in these regions.
Large-scale acidification and eutrophication caused by human activities increasing 
the inputs of nitrogen and sulphur compounds into the earth’s atmosphere and 
hydrosphere were identified as important environmental problems. Emission sources 
need to be identified, their potential expansion assessed and options for mitigation 
and reduction developed. The most important sources of S emissions are fossil fuel 
burning and industry; for N the sources are industry, fossil fuel burning, transport and 
agriculture. Global deposition rates on the basis of emission estimates and weathering 
data should be combined with sensitivity maps on the basis of soil, ecosystem and 
climate data, and soil dust deposition, to arrive at risk assessment.
Both steady-state and dynamic models have been developed to predict the 
acidification of soils, lakes, streams and groundwater. In steady-state models, such as 
SMB (FOEFL 1994) or PROFILE (Warfvinge and Sverdrup 1992), all time-dependent 
processes and finite pools are neglected. Therefore, the models can be applied with a 
limited amount of information and are suitable for mapping at national to continental 
scales. Dynamic models, such as MAGIC (Cosby et al., 1985), SAFE (Sverdrup et al., 
1995), SMART (De Vries et al., 1989), SMART2 (Kros et al., 2002), ReSAM (De Vries 
et al., 1995) or NUCSAM (Kros et al., 1995), are used to predict the gradual chemical 
response of a receptor to changing depositions by including the various buffer and 
adsorption/desorption mechanisms, but have high data requirements.
Eutrophication risks can be assessed in greater detail than acidification. Eutrophication 
is defined as nutrient enrichment of the aquatic environment leading to increased 
primary productivity and related changes in ecological quality, ultimately reducing 
the utility of the waterbodies (Iversen et al., 1997). Nutrients enter the surface water 
from sewage, fertilizer runoff or industrial effluents. Agriculture is the major source of 
nutrient enrichment by nitrate and phosphate. Assuming adequate supplies of carbon 
and light, plant growth is limited by nutrients. Nutrient pollution can therefore have 
a fertilizing rather than a toxic effect. Considerable enrichment may result in massive, 
uncontrolled plant growth, which exceeds the grazing capacity of herbivorous fish. The 
decay of the excess plant biomass increases the oxygen demand for bacterial respiration 
to the extent that it may exceed its supply rate from the overlying atmosphere. The 
resulting de-oxygenation of water can be deadly to aquatic animals. Some of these 
effects on ecosystems can be used in biological measurement of pollution.

Annex 3 – Tools for land evaluation

tải về 0.57 Mb.

Chia sẻ với bạn bè của bạn: