Effects of pesticides on the ecological function of benthic grazing
Marcus Rybicki, Carola Winkelmann, Dirk JungmannTU Dresden, Faculty of Forestry, Geo- and Hydrosciences, Institute of Hydrobiology
Background:•Modernapproachesoftheeffectanalysisofchemicalsare based on structural parameters (e.g mortality,reproduction)
• Functional parameters (e.g. primary production) aredeemedtobemoretolerantagainstdisturbance,duetothebufferingcapacity,thenstructuralones
• But functionalparameterscanbe » Well buffered -highnumberofperformingspecies,e.g.primaryproduction
» Less buffered-onlylimitednumberofperformingspecies,e.g.benthicgrazing
•Lessbufferedfunctionsmightbelesstolerantagainststressorswiththeresultof
» Reduced effort » Loss of the function
Weusedthefunctionofbenthicgrazingasamodeltoinvestigatewhetherdisturbancesbypesticidesareabletonegativelyinfluenceecosystemfunctions
The function of benthic grazing:•Importantecologicalfunctionofstreamecosystems•Performedbymacroinvertebrateswithmayflieslarvaeasmostimportantgroup Rhithrogena semicolorata (highly abundant species)
•Mostimportantduringspringtocontrolthegrowthofaufwuchscausedbyincreasingwatertemperaturesandlightavailability
•Uncontrolled growth of aufwuchs leads to clogging of the streambed(organiccolmation)» Reducedwaterexchangebetweenstreamandthehyporheicinterstitial» Degradinglivingconditionsfororganismswithintheinterstitial
Methods:• Experimentsinmicro-andmesocosms• Organisms(aufwuchs/R. semicolorata)fromasecondordermountainstreamnearDresden(Gauernitzbach)
• Herbicide(Terbutryn,0.006–6µgL-1)1.experimentNov2007–Feb2008(glassvessels)2.experimentNov2009–Feb2010(artificialstreams)
• Insecticide(lambda-Cyhalothrin;0,009–9µgg-1OC)1.experimentFeb2010–March2010(beakers)2.experimentFeb2010–May2010(artificalstreams)
Hypothesis I falsified
Herbicide (Terbutryn)
Direct effects of Terbutryn on aufwuchs
0.0
0.5
1.0
1.5
2.0
2.5
3.0
time [d]
graz
er −
dry
wei
ght [
mg]
6 13 27 41 55 69
control0.0060.060.66
control 0.06 0.6 6graz
er −
trig
lyce
ride
cont
ent [
µMol
g−1
DW
]
0
200
400
600
800
* **
treatment control 0.006 0.06 0.6 61.experiment(microcosms)
17±6 - 19±5 12±5 8±1
2.experiment(art. streams)
1.1 1.1 3.3 6.7 6.7
grazer mortality[%] in both experiments:
Insecticide (lambda-Cyhalothrin)
0
1
2
3
4
5
6
time [d]
graz
er −
dry
wei
ght [
mg]
0 6 13 27 41 55 69
control0.0090.090.99
control 0.009 0.09 0.9 9
graz
er −
mor
talit
y [%
]
0
20
40
60
80
100
0.0
0.2
0.4
0.6
0.8
1.0
time [d]
PO
C [m
g C
cm
−2]
−15 −8 0 6 13 20 27 41 55 69
control0,0090,090,99 control 0.009 0.09 0.9 9 µg g-1OC
control 0.009 0.09 0.9 9graz
er −
trig
lyce
ride
cont
ent [
µMol
g−1
DW
]
0
500
1000
1500
2000
Direct effects of lambda-Cyhalothrin (LCH) on grazers
» Aufwuchs biomass increased (1. experiment: 0.9 & 9 µg g-1OC, 2. experiment: 9 µg g-1OC)
» Concentration response of mortality with LCH (LC50 = 1.6 µg g-1OC) » Change of feeding behavior:
• Reduced growth (dry weight) of grazers (0.9 µg g-1OC)• Reduced triglyceride content of grazers (0.09 & 0.9 µg g-1OC)
Hypothesis II falsified
Hypothesis IHerbicides might change the quantity and quality of aufwuchs, but an indirect effect on the grazers will not
occurr
Hypothesis IIThe function of benthic grazing will be affected by in-secticides just due to the direct mortality of the grazers
0.00
0.05
0.10
0.15
time [d]
PO
C [m
g C
cm
−2]
−15 −8 0 6 13 20 27 41 55 69
control0.0060.060.66
Figure 2: Development of particulate organic carbon as parameter for the aufwuchs biomass during the 2. Ter-butryn experiment [mean ± se]. Error bars indicate variation within the streams. Terbutryn concentrations in µg L-1. The red circle indicates the difference at the end of the experiment.
Figure 3: View into the living aufwuchs communi-ty with a fluorescent stereobinocular microscope (magnification: 1.6x11.25).
rela
tive
abun
danc
e [%
]
cont
rol
0.06 0.6 6
cont
rol
0.06 0.6 6
cont
rol
0.06 0.6 6
0
25
50
75
100t0 - start t27 t55 - end
diat
oms
cyan
ophy
ta
Figure 4: Change of the aufwuchs composition during the 1. Terbutryn experiment. Terbutryn concentrations in µg L-1.
» Aufwuchs biomass reduced (NOEC = 0,6 µg L-1, LOEC = 6 µg L-1) » Aufwuchs composition shifted to cyanophyts
Quantity Quality
Indirect effects of Tebutryn on grazers
Table 1: Mortality of grazers during the Terbutryn experiments [mean ± se]. Terbutryn concentrations in µg L-1
Figure 5: Development of grazer dry weight during the 2. Ter-butryn experiment [mean ± se]. Error bars indicate variation within the streams. Terbutryn concentrations in µg L-1
Figure 6: Triglyceride content of grazers at the end of the 1. Terbutryn experiment [mean ± se]. Error bars indicate variation between replicates. Terbutryn concen-trations in µg L-1. */** significance level: 0.05/0.01. » No effect on grazer mortality
» Growth (dry weight) of grazers reduced (6 µg L-1) » Triglyceride content of grazers reduced (0.6 & 6 µg L-1)
Figure 7: Mortality of grazers during the 2. LCH experiment [mean ± se]. LCH con-centrations in µg g-1 OC.
Figure 8: Development of grazer dry weight during the 2. LCH experiment [mean ± se]. Error bars indicate varia-tion within the streams. LCH concentrations in µg g-1 OC
Figure 9: Triglyceride content of grazers at the end of the 2. LCH experiment [mean ± se]. Error bars indicate variation within the streams. LCH concentrations in µg g-1 OC
Indirect effects of lambda-Cyhalothrin on aufwuchs
Figure 12: Aufwuchs biomass at the end of the 2. LCH experiment. LCH concentrations in µg g-1OC.
Figure 11: Development of particulate organic carbon as parameter for aufwuchs biomass during the 2. LCH ex-periment [mean ± se]. Error bars indicate variation within the streams. LCH concentrations in µg g-1OC.
control 0.009 0.09 0.9 9
PO
C [m
g C
cm−2
]
0.0
0.1
0.2
0.3
0.4
*
***
Figure 10: Particulate organic carbon as pa-rameter for aufwuchs biomass at the end of the 1. LCH experiment [mean ± se]. Error bars indicate variation between rep-licates. LCH concentrations in µg g-1OC. */*** significance level: 0.05/0.01.
Conclusion:• Herbicides indirectly decrease the physiological fitness of grazers,duetothereductionoffoodqualityandquantity
• Insecticides directly reduce the feeding activityofgrazersinsublethalconcen-trationsand decrease their physiological fitness
•Adecreased physiological fitness migth increase the sensitivity of grazers
againstotherenvironmentalstressorsand reduce their reproductive effort
Prospects:•Experimentswithcombinedexposureofherbicidesandinsecticidesinartificalstreamsandinbatchexperimentswithhigherreplication
Contact: [email protected] – Project Nr.080940733
DFG – Project Nr.Be 1671/14-1 FKZ
Possible disturbances of benthic grazing by pesticides:
insecticide
herbicide
aufw
uchs
− a
sh fr
ee d
ry w
eigh
t [m
g cm
−2]
Sep Nov Jan Mar May Jul
0
0.5
1
1.5
0
0.02
0.04
0.06
0.08
0.1
graz
er −
bio
mas
s [m
g cm
−2]
grazeraufwuchs
time of herbicide use
time of insecticide use
egg/hatch growth emergence
biomass of grazer and aufwuchs 2005/06
Figure 1: Development of aufwuchs and grazer biomass dur-ing the life cycle of Rhithrogena semicolorata. Colored lines indicate possible times of disturbance of grazers by pesticides (dotted = indirect, solid = direct).
only slight increase
decreased triglycerids without change of dry weight
decreased triglycerides
A negative effect of pesticides on the function of benthic grazing is possible!
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