Climate Change and the European Water Dimension - Agri ...

Pressures) deriving from these Drivers are reported (see Table VI.C.2) (ABP, 1999)
in terms of “Potential” and “Effective” loads for both nitrogen and phosphorous.
Table-2 suggests that the contribution of diffuse sources is higher (69%) than point
sources (31%) for nitrogen, whereas for phosphorous point sources contribute with
62% of the total and diffuse sources with
the remaining 38%.
Nutrient drivers
It is well known that Nitrogen (N) and
Phosphorous (P) are present in the
environment and that their inorganic forms
are ‘reactive’ and therefore potential
pollutants when in excess or in the wrong
place (Hatch et al., 2002). Nitrogen is an
essential nutrient to both plants and
animals, it is found in different organic and
inorganic forms, and its biogeochemical
cycle occurs in the soil, water and
atmospheric compartments. Water is the
main carrier of N but the atmosphere is
the major source and the cycle is soil
based. Anthropogenic activities interact
with the natural N cycle by introducing
inorganic fertilizers and spreading
manure. Waste water also increases N
input to the catchment. Meanwhile,
atmospheric nitrogen reaches the soil
through atmospheric scavenging by
precipitation and it is transformed into
inorganic forms. Other natural inputs of N
are related to chemical and biological
transformations of organic material. The
major chemical and physical processes
that occur in the nitrogen cycle include
denitrification, volatilization, runoff and
Figure-VI.C.7: The nitrogen cycle
(from: Edwards & Alken-Murray
Corporation, http://www.alkenmurray.com/Phosphorous.html).
184
Table-VI.C1: Drivers affecting the nutrients transport
pathways related to anthropogenic and natural forces.
Drivers Catchment Coastal zone
Agriculture +
Human activities
Livestock +
Industry +
Population + +
Tourism +
Legislation + +
Socio-economic
framework and Institutions + +
governance
Policies + +
Natural Conditions Climate + +
Table-VI.C.2: Potential and effective nutrient loads in the
Po catchment estimated for diffuse and point sources
(from ABP, 1999).
Source
Point
Nitrogen Phosphorus
Sector t/y % t/y %
Potential Loads
Civil 78000 11 10000 6
Indstrial 25000 4 1000 1
Livestock 260000 39 50000 33
Diffuse Agriculture 310000 46 90000 60
Point
Diffuse
Total 673000 100 151000 100
Effective Loads
Civil 61000 23 6000 56
Industrial 22000 8 700 6
Livestock 105000 40 2100 20
Agriculture 60000 23 1200 11
Superficial runoff 15000 6 750 7
Total 263000 100 10750 100
leaching (Figure-VI.C.7).
Bacterial activity
(denitrification) transforms
nitrates present in soil to
gaseous nitrogen (N2) which is
released to the atmosphere;
similarly, urea fertilizers and
manures emit gaseous
nitrogen to the atmosphere
(volatilization); both processes
have a strong effect on soil
fertility. The runoff process is
an important transport
mechanism that carries
nitrogen loads to rivers, lakes
and the sea; while leaching is