Transcript No Slide Title

Phosphorus inputs to
Lough Neagh.
The increasing impact of
agriculture
Introduction
• This slide-show shows how phosphorus inputs to
Lough Neagh have changed since 1974.
• The data presented are based on monitoring of
Lough Neagh and the inflowing rivers to Lough
Neagh undertaken by the staff of AESD.
• Comments should be addressed to Bob Foy
([email protected])
Why does phosphorus create
water quality problems?
1 Phosphates are non toxic - indeed they are vital for
life.
2 That is the problem. Small amounts of phosphorus
promote more plant life than a lake can cope with.
3 The phosphorus problem usually manifests itself
by excessive amounts of algae.
4 Leading to decline in fish stocks, low oxygen
levels, toxins, tastes and poor amenity value.
An algal bloom
Eutrophication and phosphorus
Eutrophication is the term used to describe
the process of phosphorus enrichment.
It can be defined as:
The over-enrichment of lakes and rivers with
nutrients, usually phosphorus, leading to
excessive growth of algae and other aquatic
plants.
How bad is the problem in lakes
in Northern Ireland?
Proposals for a strategy to control
nutrient enrichment published by DOE
(NI) 1999 stated that:
Eutrophication is considered to pose
the most widespread single threat to
good water quality in Northern Ireland.
A standard for lake phosphorus
• There is no legislative standard for phosphorus in
lakes as there is for nitrates.
• The classification system given in the OECD report
of 1980, Eutrophication of Waters is widely used.
• This defines lakes as eutrophic when annual lake P
exceeds 35 mg P/l.
• By this standard both Lough Neagh and Lough Erne
are highly eutrophic
Phosphorus concentrations of Irish lakes
Total Phosphorus (mg P l-1)
0
50
100
Neagh
Upper Erne
Lower Erne
Derg
Sheelin
Macnean (lower)
Macnean (upper)
Melvin
Ennell
Corrib
Mask
Leane
Conn
OECD eutrophic
lakes limit
150
Is the problem getting worse?
• Yes
• Current trends over the past 10 years show
a 50% increase in lake P in both Lough Erne
and Lough Neagh.
Phosphorus trends 1987-1999
Lough Neagh and Lough Erne
Lake Phosphorus (1987 =100)
180
Neagh
Erne
140
100
60
1987
1989
1991
1993
1995
1997
1999
Where does this phosphorus
come from?
Phosphorus principally originates from:
1 Towns
2 Septic tanks serving the rural population.
3 Industry - mostly creameries.
4 Agriculture - which is now the biggest single
source to Lough Neagh and Lough Erne
Rainfall is a very small (c1%) direct input to
Lough Neagh and Lough Erne.
Phosphorus sources
Lough Neagh and Lough Erne
Lough Neagh
Major towns 9%
Lough Erne
Minor towns 14%
Minor
towns 10%
Industry
2%
Industry
1%
Septic
tanks 12%
Septic
tanks 14%
Agriculture 62%
Major town 3%
Agriculture 73%
What is being done to reduce
phosphorus coming from
towns and industry?
• Phosphorus reduction began in 1981 at
major sewage treatment works in the
Lough Neagh catchment.
• It now removes about 100 tonnes P /yr.
• Plant closures and a switch from P based
cleaning agents has reduced the P load
from industry.
-1
Phosphorus (tonnes P yr )
Point source phosphorus loadings
Lough Neagh catchment 1974-1997
Major towns
Other towns
Industry
200
100
0
1974
1977
1980
1983
1986
1989
1992
1995
What about detergents?
• SOME detergents contain significant
amounts of phosphorus.
• Washing up liquids do not.
• Dishwasher powders contain a lot of P.
BUT
• Since 1985 the amount of P used in these
products has declined by 50%.
Detergent P (kg P person-1 yr-1)
UK detergent phosphorus
consumption 1950-1998
0.8
0.6
0.4
0.2
0
1950
1955
1960
1965
1970
1975
1980
1985
1990
1995
Septic tanks as a phosphorus
source
• If a septic tank discharges to a soakaway, it
should lose little phosphorus to streams and
rivers.
• BUT many tanks discharge to drains etc.
• Best “guesstimate” is that 60% of septic
tank discharges reach surface waters.
Diffuse river loading and septic tank
phosphorus loadings
Lough Neagh catchment 1974 vs1997
Phosphorus loading
(tonnes P yr-1)
Septic tanks
Diffuse loading
400
200
0
1974
1997
Increase
Septic tanks as a driver of
change?
It is unlikely that septic tanks are the cause of
change seen in Loughs Neagh and Erne
given the:
• modest increase in rural population and
• the decline in detergent P usage,
.
Since 1974 annual losses of phosphorus to
Lough Neagh from diffuse sources have
increased by 143 tonnes P
Equivalent to
• A rural population
increase of 274,000
Actual changes
• The rural population
increased by
14,000.
or
and a
• An urban population • P reduction from
towns equivalent to
increase of 165,000.
an urban population
decrease of 102,000
Are agricultural phosphorus
losses increasing?
• Yes - Since 1974, there has been a steady
increase in agricultural P losses.
• This increase has been more than enough to
cancel out the benefits of reducing P from
other sources.
• Annual P losses are highly related to river
flow. Losses are much higher in winter than
in summer.
300
3
200
2
100
1
Diffuse loading
Diffuse trend
Flow
0
0
1975
1980
1985
1990
1995
River Flow (*109 m3 yr-1)
River phosphates (tonnes P y-1)
Soluble phosphates from diffuse
sources & river flows:
Lough Neagh rivers 1974-1997
What causes agricultural phosphorus
losses? Is it farm-yards?
• Dirty water from farm-yards, leaking tanks
etc are the most visible form of P losses.
• Results from the Colebrooke catchment
suggest they may contribute 15-20% of P
losses.
• It is unlikely that P losses from farm-yards
are increasing. Farm pollution incidents are
down since 1987.
Farm pollution (incidents yr-1)
Farm pollution incidents in
Northern Ireland 1987-1998
750
500
250
0
1987
1989
1991
1993
1995
1997
Could it be manures then?
• Land spreading of manures will lead to P
losses to water if the ground is wet or
spreading is followed by rainfall and drainflow.
• Manure P produced in the Neagh catchment
has increased by only 25% since 1974.
• This is a smaller increase compared to the
diffuse P increase measured in rivers.
300
6000
200
3000
100
Manure P (tonnes P yr-1)
-1
9000
Water Phosphorus (tonnes P yr )
Manure P and diffuse phosphate loads
Lough Neagh catchment 1975-1998
Manure P
0
1975
Diffuse water P
loading
1979
1983
1987
1991
1995
0
Fertilisers??
• Fertilisers are spread in spring and summer
when runoff and diffuse P losses are small.
• The direct impact of fertiliser P applications
on P in lakes and rivers is likely to be small.
• There has been no real increase in fertiliser
P use since 1974 (or since the 1940s).
Phosphorus (103 tonnes P yr-1)
Phosphorus fertiliser use
Northern Ireland 1974-1998
18
12
6
P fertiliser
0
1974
1978
1982
1986
1990
1994
1998
So fertilisers aren’t a problem?
• Except that NI Agriculture imports a large
amount of P in animal feed-stuffs - referred to
as “concentrate P”.
• Combined with fertiliser P, inputs of P to
agriculture exceed outputs in crops, meat,
milk products and wool.
• This means agriculture operates a P surplus.
Phosphorus (tonnes P yr-1)
Phosphorus balance in agriculture
Northern Ireland 1998
20000
Rain P
15000
C Denotes concentrate P
Fertiliser P
10000
5000
C
C
C
Diffuse P
Crops
Pigs
Poultry
Grazing systems
0
Input P
Output P
Is it the phosphorus surplus?
• As inputs have consistently exceeded
outputs of P in farm production, there has
been a P surplus.
• The P surplus has remained fairly constant
since 1974.
• Almost all of this P surplus accumulates in
the soil.
Phosphorus (103 tonnes P yr-1)
Northern Ireland Farm Phosphorus
Budget 1974-1998
25
P inputs
P outputs
P surplus
20
15
10
5
0
1974
1978
1982
1986
1990
1994
1998
Surplus phosphorus and
fertiliser phosphorus
• The annual P surplus in Northern Ireland
agriculture is roughly equal to annual P
fertiliser use.
• Changes in the P fertiliser use are clearly
reflected in the P surplus for Northern
Ireland agriculture.
Phosphorus (103 tonnes P yr-1)
Phosphorus surplus & fertiliser trends
Northern Ireland agriculture: 1974-98
18
12
6
P fertiliser
0
1974
1978
1982
P surplus
1986
1990
1994
1998
Surplus phosphorus and soil
phosphorus
• A long-term effect of this surplus is an
increase in soil P levels in Northern Ireland
soils since the 1940s.
• Soil P can now be classed as at “excess”
levels on more than 40% of soils.
• Grass grown on soils which have “excess” P
will not respond to more P added either as
fertiliser or manure P.
Impact of P surplus on soil P
1940s vs 1990s
50
1940s
1990s
% of samples
40
30
20
10
0
Deficient
Low
Adequate
Soil P status for grass production
Excess
Increasing soil P Is it a phosphorus “time-bomb”?
• The sustained annual P surplus is resulting
in an increase in soil P.
• This increase is related statistically to the
increase in soluble P from diffuse sources
measured in the Lough Neagh rivers.
• The P surplus could be reduced by cutting
back on fertiliser P use on high P soils.
-1
Cumulative Phosphorus (kg P ha )
500
Cumulative soil P
0.8
Diffuse river soluble phosphate
0.7
400
0.6
0.5
300
0.4
200
0.3
0.2
100
0.1
0
1974
1978
1982
1986
1990
1994
0
1998
Water phosphorus (kg P ha-1)
Soil P accumulation & L. Neagh
diffuse phosphate loss rates
Since 1974 soils in the Lough Neagh
catchment have accumulated a surplus
76,000 tonnes of phosphorus.
Annual phosphate losses to Lough Neagh from
agriculture have increased by 143 tonnes P.
This is represents 0.2% of the accumulating
phosphorus.
Assuming that soil phosphorus cannot move from
soil to water may only be 99.8% true.
So we can forget about
manures then? - No!
• Halting the P surplus may only stop the
situation getting worse.
• Tackling manure P losses will be crucial in
achieving significant improvements.
So we can forget about
manures then?
• P losses from a field drain at Greenmount
show annual P losses varying at least tenfold
• High P losses were caused by slurry
applications followed by high drain-flows.
• The highest single manure P application
was during a dry summer.
• It produced the lowest annual P loss.
What can we learn?
• There is no prospect for improving water quality
unless P losses from agriculture are substantially
reduced.
• P use in agriculture must be critically reviewed - as
many farms now have fields with high soil P levels.
• This review is best done in the context of nutrient
management planning - when crop requirements for
all nutrients are assessed - a field that is rich in soil
P may not be rich in potash or sulphur.
• The plant nutrient value of manures must be better
recognised and utilised on farms.
• The storage, containment and spreading of manures
must be improved if river P loads are to decline.