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Nutrient enrichment and stream salmonids in Ireland Conor Graham & Simon Harrison School of Biological, Earth & Environmental Sciences, University College Cork, Ireland
Nutrient enrichment and stream
salmonids in Ireland
Conor Graham & Simon HarrisonSchool of Biological, Earth & Environmental Sciences, University College
Cork, Ireland
INPUTS
Nutrients Organic matter
Secondary
Production
Fish
Decay
Respiration
Dissolved
oxygen
Temperature
Flow
+
_
Impacts of eutrophication in streams
Primary
Production
Change in fish communities
Coregonid/Salmonid Percid Cyprinid
Fish responses to eutrophication
Siltation and deoxygenation of
spawning gravels
Summer fish kills
Average number of wet days ranges from about 150 days per year in the east to about 225 days per year in the west. Irish skies are completely covered by cloud for >50% of the time.
Irish climate – cool and moist
INPUTS
Nutrients Organic matter
Secondary
Production
Fish
Decay
Respiration
Dissolved
oxygen
Temperature
Flow
+
_
Impacts of eutrophication in Irish
streams
Primary
Production
1. What effect does nutrient enrichment have on salmon and trout in Irish rivers?
2. Does the effect differ between salmon and trout?
3. What are the mechanisms underlying any response?
Impacts of eutrophication on salmonids
Study Sites
Seven study sites were selected from some 100 candidate streams in
Munster
All study streams had similar geology (Old Red Sandstone),
gradient, riparian cover, substrate and morphological characteristics.
River Tourig,
Youghal
Dungourney
River , Midleton
Methods
• Water chemistry: May, June, August & September at base flow
• Biological sampling: May, July, September
Surber samples of invertebrates from gravel & macrophytes
Multi-pass deplete electrofishing
Fish growth, production & ration consumed (Elliot’s equations)
Water Chemistry - PCA
Eigenvalues: PCA axis 1 = 39.4, PCA axis 2 = 25.4
-4 -2 0 2 4
PC1
-4
-2
0
2
4
PC
2
river
Ow
Bl
To
Au
Go
Du
Cu
Ammonia
TON
TPSS
K
CapH
Stream nutrient gradient
Nutrient gradient based on TP levels. Range <0.02 – 0.075 mg/L
0
0.02
0.04
0.06
0.08
0.1
SRP
TP
mg
/L P
ho
sph
oru
s
Ow Bl To Au Go Du Cu
Chlorophyll a & Ash-Free Dry Mass
mg
/m2
g/m
2
0
10
20
30
40
50
Spring Summer
Autumn Average
0
20
40
60
80
100
120
140
160
Ow Bl To Au Go Du Cu
Spring Summer
Autumn Average
Chlorophyll
AFDM
Dissolved oxygen levelsD
isso
lved
ox
yg
en (
mg
/l)
0
3
6
9
12
15
18
Ow Bl To Au Go Du Cu
EU Directive for salmonid waters 78/659/EEC: 50% of
samples >9mg/l
TP
Macroinvertebrate NMS ordination:
Gravel Surber data
P
Q value and BMWP scoresQ
va
lue
BM
WP
sco
re
Q value
0
1
2
3
4
5
BMWP
40
60
80
100
120
WASPT
5
6
7
8
Ow Bl To Au Go Du Cu
Benthic macroinvertebrate density
0
20000
40000
60000
80000
Ow Bl To Au Go Du Cu
No.
of
inver
teb
rate
s p
er m
2
r2 = 0.33, d.f. = 5, p = 0.18
TP
0
20000
40000
60000
80000
Ow Bl To Au Go Du Cu
Gravel
Macrophyte
No.
of
inver
teb
rate
s p
er m
2
r2 = 0.66, d.f. = 5, p = 0.03
TP
Benthic macroinvertebrate density
0
0.1
0.2
0.3
0.4
All trout
TP
Salmonid density
TP
Fish
de
nsi
ty (
no
. in
div
idu
als
m-2
)
Ow ToBl Au Go Du Cu0
0.4
0.8
1.2
1.6
2
Salmon & trout
r2 = 0.93d.f. = 3
p = 0.03
0
0.04
0.08
0.12
0.16
Older trout
r2 = 0.74d.f. = 4
p = 0.047
TP
Ow ToBl Au Go Du Cu0
0.4
0.8
1.2
1.6
2
All salmon
r2 = 0.95d.f. = 3
p = 0.02
Ow ToBl Au Go Du Cu
Ow ToBl Au Go Du Cu
Equations of Malclom Elliot and co-workers:
• Weight at beginning and end of study period
• Temperature
• Species-specific constants
1. Observed daily growth rate, Go (% d-1)
2. Potential maximum daily growth rate, Gw (% d-1)
Growth & Energetics of Salmonids
Proportion of maximum potential
growth realised (%)
0
20
40
60
80
100
0+ salmon 1+ salmon 0+ trout 1+ trout 2+ trout
Ow Bl To Au Go Du Cu
Pro
port
ion
of
max. p
ote
nti
al
gro
wth
rea
lise
d (
%)
r2 = 0.65d.f. = 5
p = 0.028
r2 = 0.97d.f. = 3 p = 0.02
r2 = 0.45d.f. = 5
p = 0.097
Fish Production
Fish production, P (g m-2)
P = t Go
Σ {(Bo
+ Bt) /2}/A
Where:
t = time in days
Go = Observed daily growth rate
Bo = biomass (g) at time0, the start of the study
Bt = biomass(g) at timet , at end of study
A = area of stretch of river samples (m2)
Fish Production (May-September)P
rod
uct
ion
(g/m
2)
0
1
2
3
4
5
6
7
0+ salmon 1+ salmon 0+ trout 1+ trout 2+ trout
Ow Bl To Au Go Du Cu
r2 = 0.63d.f. = 5 p = 0.03
r2 = 0.92d.f. = 5
p < 0.001
0
0.02
0.04
0.06
0.08
0.1
SRP
TP
mg
/L P
ho
sph
oru
s
Ow Bl To Au Go Du Cu
Pro
du
ctio
n (
g/m
2)
Fish Production (May-September)
TP
0
2
4
6
8
10
12
Ow Bl To Au Go Du Cu
Daily ration consumed
Equations of Elliot and co-workers:
• Weight at beginning and end of study period
• Temperature
• Constants
• Observed daily growth rate, Go (% d-1)
• Potential maximum daily instantaneous growth rate, Gw (% d-1)
Calculated actual daily food consumption
(Cactual mg dry weight d-1)
Biomass of daily ration consumed
0
20
40
60
80
100
Ow Bl To Au Go Du Cu
1+trout
0+ trout
1+ salmon
0+ salmon
mg d
ry w
eig
ht
d-1
/m2
Exploitative competition:
salmon over trout?
Interference competition:
trout over salmon?
TP
Salmon – r2 = 0.91, d.f. = 3, p = 0.02; Trout - r2 = 0.97, d.f. = 5, p<0.0001
P
With increasing nutrients
P
Food
availability
Increasing secondary production
P
Total salmonid
production
Food
availability
Initial increase in salmonid
production
P
Decrease in salmonid production
associated with trout
Total salmonid
production
Food
availability
P
Decrease in salmonid production
associated with trout
Food
availability
Total salmonid
production
P
Lost
Production?
Lost Production?
Total salmonid
production
Food
availability
P
Other fish
species?
Production of other species?
Total salmonid
production
Food
availability
P
Decrease in salmonid production
associated with trout through
interference competition
Food
availability
Total salmonid
production
Lost
Production
Conclusions
• In Ireland, the mild and wet maritime climate results in relatively
high dissolved oxygen levels in all rivers
• Trophic enrichment, rather than anoxia, appear to be the dominant
factor affecting stream biota in nutrient enriched rivers
• Whereas the density, growth, production and ration consumed by
trout generally increases linearly with phosphorus, the salmon
respond initially to increased phosphorus before these parameters
decline sharply midway along the gradient.
• It appears salmon out compete trout at lower nutrient levels
(exploitive competitive) whereas trout out compete salmon at higher
nutrient levels (interference competition)
• ‘Lost’ salmonid production at higher nutrient levels?
Thank you.
Acknowledgements
Science Foundation Ireland for funding this research
Ross Macklin & Marc Shorten for fieldwork and lab
support
(and Simon Harrison for giving the talk!)
