Agriculture Reference
In-Depth Information
is obviously contentious. There is no single best
method available to estimate load reduction allo-
cation for multiple pollutants but most aim for
uniformity in reducing load for all types of
sources, and selection of sources with minimal
regulation costs. Uncertainties in the model are
acknowledged by inclusion of a margin of safety
(MOS). Practices must be adopted by sources
that will reduce pollutant loads to meet their
assigned reductions. These practices include
BMPs such as stream bank fencing, as well as
tightened discharge limits for factories and
wastewater treatment plants and improvements
in septic systems of local homes.
Efficient implementation of TMDL plans
demands stakeholders' active involvement. Early
TMDLs suffered from lack of buy-in; increased
efforts to elicit stakeholder input have resulted in
more accurate assessment of sources of pollut-
ants and more equitable allocation of load
reductions. Effluent standards, subsidized BMPs,
public education and effluent trading are among
the tools used to restore water quality. The uncer-
tainty in estimating MOS for N and P makes it
almost impossible to set numeric criteria accu-
rately for nutrient-based TMDLs. The lack of
numeric set point for the nutrients may make the
problem more aggravated but progress has been
made in reducing nutrient pollution with TMDLs.
The proportion of TMDLs focused on N and P
decreased from 23.8% in 1996 to 7.7% in 2008
and 6.4% in 2012 (US EPA, 2012).
the USA) and samples from the same wells
obtained during 2000-2004 (Rupert, 2008).
Denmark serves as a lesson for long-term
effects of stringent policy measures intended to
reduce N losses from farms. The agriculture
industry in Denmark is particularly intense, and
that country was early to realize the problems
associated with N losses to water resources.
With its relatively small population and agricul-
ture industry, strict enforcement of regulations
is possible. Beginning in 1985 and continuing
for 20 years, Denmark enacted seven national
action plans to reduce N pollution of water
bodies. The instruments of these regulations
were mandatory improvement in wastewater
treatment plants, mandatory implementation
of fertilizer and crop rotation plans to limit
plant-available N application, and development
of statutes codifying assumed plant available
N proportion in manures.
Following implementation of these policies
in Denmark, land application of manure N
decreased from 244,000 to 237,000 t over
13 years, resulting in a 34% reduction in N sur-
plus as measured by field balance (Kronvang
et al
., 2008). In those 13 years, model-simulated
N leaching (Danish DAISY model) from 86 small
agricultural catchments representing eight geo-
regions was reduced by 28% to 45%, annual
total N concentration in streams draining in
those same 86 catchments was lower in nitrate-
N than the target concentration (50 mg l
−1
) and
annual N load was reduced by 32%. Thus, strict
national regulations enabled Danish agriculture
to reduce N leaching and N loads to surface
waters while maintaining crop production and
increasing livestock production.
The Water Framework Directive (WFD)
was developed by the EU to collect information
throughout the Europe in order to provide policy
makers with the data to develop policies address-
ing water related issues (Collins and McGonigle,
2008). Three approaches were used: long-term
water quality assessment by surveillance moni-
toring, identification of water-bodies failing to
meet water quality standards, and understand-
ing of the primary cause of failing to meet the
standards. These data were used to develop effi-
cient modelling and decision support tools.
A primary challenge with this and other
monitoring and modelling efforts is the time lag
between the implementation of a management
Do more stringent regulations result
in improved water quality?
Despite accelerated regulatory activity since
the mid-1990s, no consistent improvement has
been observed in ground and surface water in
the USA. Flow of total N decreased from a base-
line period of 1980 to 1996 through subsequent
moving 5-year average periods through 2006.
Using an updated statistical model, nitrate
N transport to the Gulf of Mexico increased by
9% between 1980 and 2008 (Sprague
et al
.,
2011). The rate of change was greater between
2000 and 2008 than in the 20 years previous.
Flows of total P increased compared with
baseline. Similarly, groundwater nitrate-N con-
centration increased significantly between sam-
ples obtained in 1988-1995 (495 wells across
