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Murky Waters: multidimensional issues linkingmacronutrient sources & impacts in catchments
Helen Jarvie, Andrew Sharpley, Paul Withers
Exploring uncertainties & expectations.....
(1) Point sources are being addressed, so we need tofocus efforts on diffuse transfers to meet river waterquality & ecological targets
(2) Catchments are inherently leaky: P losses fromagriculture are a primary cause of nuisance algal growthin rivers
(3) Reducing P losses from agriculture will achievedesired improvements in river water quality & ecology
Beliefs driving catchment management policy:
A UK river water quality perspective
Use of background tracers: boron (detergents)as a tracer of sewage effluent
Across 54 major UK lowland rivers: Pshows a dominant sewage fingerprint
For P, dissolved reactive (DRP) concentrations during periods of ecologicalsensitivity pose the greatest risk for nuisance algal growth in lowland rivers
0 20 40 60 80 100
500
1000
1500
2000
120
Flow (m3s-1)
DR
P(µ
g-P
l-1)
Thames
…Coupled with flow dependence:
Jarvie et al, 2006. Science of theTotal Environment, 360, 246– 253
Dilution with flow – dominance ofpoint sources at low flows
.....BUT even in headwater agricultural catchments, point sources dominate TPloads most of the time (especially under baseflows, periods of ecological sensitivity)
Jarvie et al, 2010. Agriculture, Ecosystems and Environment 135, 238-252.
Yes, diffuse sources dominate annual TP loads......
Successes in P remediation: point source P controls
Ju
n-9
7
Se
p-9
7
De
c-9
7
Ap
r-98
Ju
l-98
Oct-9
8
Ja
n-9
9
Ma
y-99
Au
g-9
9
No
v-99
Ma
r-00
Ju
n-0
0
Se
p-0
0
De
c-0
0
Ap
r-01
Ju
l-01
Oct-0
1
Fe
b-0
2
Ma
y-02
Au
g-0
2
0
100
200
300
400
500
600
700
800
DR
P(μ
gl-
1) Upgrade to STW (P-stripping)
River Kennet
River reach mass balance studies (R. Lambourn):%
ch
an
ge
inD
RP
load
-100
-50
0
50
100
150
200
DRP release
DRP retention
May Aug Dec
2003
Feb June Oct
2004
Recovery phase~8 months
‘Legacy P’: responses to point source P remediation in rivers
P inputremoved
Short water & sediment residence times - rapid recovery
Jarvie et al., 2006. J Hydrology, 330, 101– 125
In-l
ake
Pco
ncen
trati
on
(µg
L-1
)
0
50
100
150
200
250
300
1990 1995 2000 2005 2010
2010
Point-source P inputsreduced 60%
Recovery phaseInternal recycling of ‘legacy’ P
(10-15 y)Waterquality
target met
Water quality target40 µg/L
Legacy P: longer residence times mean delayed WQ responses in lakes
Loch Leven, Scotland (Source: Linda May, CEH)
1992 2010
Farmyard
Spring House roofwater
Field drain
Road drain
• Multiple sources & forms of P
• ‘Landscape filtering’ of P along thewatershed-river continuum
• Storage & re-release of ‘legacy’ P
Longer legacy ‘lag’ effects after agricultural controls?
Evaluating P retention & release at the watershed scale
Extended End-member Mixinganalysis (E-EMMA)
Simple & versatile tool, reliessolely on routinely-measured Pconcentration and flow data.
Up to 50% retention of annualTotal P loads
Up to 80% retention of Total Ploads under ecological-criticallow flows (spring & summer)
Buffering along the watershed-river continuum regulatesdelivery of P to help reduceecological impactsdownstream
J. Environmental Quality, 40, 492-504
BMP successes: Conservation tillage
No-till reduced erosion from wheat fields (2 ha) by 95%
Convertedto no-till
1980 1985 1990 1995
Conventionaltill wheat
6
4
2
0
-
-
Total P (mg L-1)
From: Sharpley and Smith, 1994 – El Reno, OK
Runoff
1980 1985 1990 1995
20
15
10
0
-
5
-
Total N (mg L-1)
Convertedto no-till
Conventionaltill wheat
-
Conservation tillageConservation tillage
Maumee River - Annual flow-weighted Total P (mg/L)
Dave Baker & Peter Richards, OH
50% decrease
1975 1985 1995 2005
0.8
0.6
0.4
0
0.2
Adoption of mulch and no-till soybeans, %Annual flow-weighted dissolved P, ppm
75% decrease
80
60
40
20
Trends in P – Maumee River
1975 1985 1995 2005
0.12
0.09
0.06
0
0.03
Process mechanisms: coupled macronutrient cyclesD
epth
(cm
)
SRP (µg-P/l) NH4 (mg/l) SO4 (mg/l)
Palmer-Felgate et al (2011), Sci. Tot. Environ., 409, 2222-2232
P thresholds for nuisance algal (periphyton) growth
Bowes et al (2007) Canadian J. Fisheries and Aquatic Sciences 64 (2): 227-238
0.0
0.2
0.4
0.6
0.8
1.0
1.2
0 50 100 150 200 250 300 350 400 450
SRP conc (μg L-1)
Ch
loro
ph
yllc
on
c(s
tan
dar
dis
ed
)
P-stripped Control P-addition
River Thames
100 µg-P L-1
Even murkier - ecological responses to P remediation
DR
P(μ
gl-
1)
800
100 µg-P L-1
0
100
200
300
400
500
600
700River Kennet
DR
P(μ
gl-
1)
1997: Healthy chalk stream ecosystem; SRP c. 600 µg L-1
1999-2005: proliferation ofnuisance algae; SRP c. 80 µg L-1
Loss of invertebrate grazers?Increased stocking of brown trout
Ecosystem response?
Murky waters....
Aquatic ecologistsSoil scientists
Water quality scientists
Policy makers
Biogeochemists
• Resource & aquatic habitat management• Wider range of physico-chemical controls on river ecology• Coupled macronutrient cycles & ‘self-cleansing’ capacity of rivers
Current focus on diffuse-source P controls & nutrient criteria alonemay not necessarily achieve the desired ecological & water qualityoutcomes within short policy-relevant timescales….
But opportunties for more integrated approaches....
Source: Colin Neal, CEH & Ian Bateman, UEASource: Colin Neal, CEH & Ian Bateman, UEA
Which do you prefer?
Source: Colin Neal, CEH & Ian Bateman, UEASource: Colin Neal, CEH & Ian Bateman, UEA
1980 1985 19951990
0.5
1.0
0
Infiltration increased 33%
Convertedto no-till
Runoff - Dissolved P (mg L-1)
Conventionaltill wheat
Conservation compromises
1980 1985 19951990
Nitrate (mg L-1)
30
20
10
0
Convertedto no-till
Conventionaltill wheat
Leached -