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Effects of pesticides on the ecological function of benthic grazing Marcus Rybicki, Carola Winkelmann, Dirk Jungmann TU Dresden, Faculty of Forestry, Geo- and Hydrosciences, Institute of Hydrobiology Background: •Modern approaches of the effect analysis of chemicals are based on structural parameters (e.g mortality, reproduction) • Functional parameters (e.g. primary production) are deemed to be more tolerant against disturbance, due to the buffering capacity, then structural ones • But functional parameters can be » Well buffered - high number of performing species, e.g. primary production » Less buffered - only limited number of performing species, e.g. benthic grazing • Less buffered functions might be less tolerant against stressors with the result of » Reduced effort » Loss of the function We used the function of benthic grazing as a model to investigate whether disturbances by pesticides are able to negatively influence ecosystem functions The function of benthic grazing: • Important ecological function of stream ecosystems • Performed by macroinvertebrates with mayflies larvae as most important group Rhithrogena semicolorata (highly abundant species) • Most important during spring to control the growth of aufwuchs caused by increasing water temperatures and light availability • Uncontrolled growth of aufwuchs leads to clogging of the streambed (organic colmation) » Reduced water exchange between stream and the hyporheic interstitial » Degrading living conditions for organisms within the interstitial Methods: • Experiments in micro- and mesocosms • Organisms (aufwuchs/R. semicolorata) from a second order mountain stream near Dresden (Gauernitzbach) • Herbicide (Terbutryn, 0.006 – 6 µg L -1 ) 1.experiment Nov 2007 – Feb 2008 (glass vessels) 2.experiment Nov 2009 – Feb 2010 (artificial streams) • Insecticide (lambda-Cyhalothrin; 0,009 – 9 µg g -1 OC) 1.experiment Feb 2010 – March 2010 (beakers) 2.experiment Feb 2010 – May 2010 (artifical streams) 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] grazer − dry weight [mg] 6 13 27 41 55 69 control 0.006 0.06 0.6 6 control 0.06 0.6 6 grazer − triglyceride content [μMol g -1 DW] 0 200 400 600 800 * ** treatment control 0.006 0.06 0.6 6 1.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] grazer − dry weight [mg] 0 6 13 27 41 55 69 control 0.009 0.09 0.9 9 control 0.009 0.09 0.9 9 grazer − mortality [%] 0 20 40 60 80 100 0.0 0.2 0.4 0.6 0.8 1.0 time [d] POC [mg C cm -2 ] −15 −8 0 6 13 20 27 41 55 69 control 0,009 0,09 0,9 9 control 0.009 0.09 0.9 9 µg g -1 OC control 0.009 0.09 0.9 9 grazer − triglyceride content [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 -1 OC, 2. experiment: 9 µg g -1 OC) » Concentration response of mortality with LCH (LC50 = 1.6 µg g -1 OC) » Change of feeding behavior: • Reduced growth (dry weight) of grazers (0.9 µg g -1 OC) • Reduced triglyceride content of grazers (0.09 & 0.9 µg g -1 OC) Hypothesis II falsified Hypothesis I Herbicides might change the quantity and quality of aufwuchs, but an indirect effect on the grazers will not occurr Hypothesis II The 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] POC [mg C cm -2 ] −15 −8 0 6 13 20 27 41 55 69 control 0.006 0.06 0.6 6 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). relative abundance [%] control 0.06 0.6 6 control 0.06 0.6 6 control 0.06 0.6 6 0 25 50 75 100 t 0 - start t 27 t 55 - end diatoms cyanophyta 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 -1 OC. 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 -1 OC. control 0.009 0.09 0.9 9 POC [mg 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 -1 OC. */*** significance level: 0.05/0.01. Conclusion: • Herbicides indirectly decrease the physiological fitness of grazers, due to the reduction of food quality and quantity • Insecticides directly reduce the feeding activity of grazers in sublethal concen- trations and decrease their physiological fitness •A decreased physiological fitness migth increase the sensitivity of grazers against other environmental stressors and reduce their reproductive effort Prospects: • Experiments with combined exposure of herbicides and insecticides in artifical streams and in batchexperiments with higher replication Contact: [email protected] ESF – Project Nr. 080940733 DFG – Project Nr. Be 1671/14-1 FKZ Possible disturbances of benthic grazing by pesticides: insecticide herbicide aufwuchs − ash free dry weight [mg 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 grazer − biomass [mg cm -2 ] grazer aufwuchs 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!
