Piet Verdonschot Freshwater Ecology Group Group of Aquatic Ecology and Ecotoxicology Effects of wooded riparian zones on stream water temperature and stenothermic macroinvertebrates along a European latitudinal climate gradient GA no.:

Why is temperature an issue? Reduced oxygen solubility Increased respiration (oxygen consumption) Loss of aquatic biodiversity Functional “hypoxia” Lethal limits Increased water temp (Rutherford et al. 2004) Indicator cold stenothermic macroinvertebrates

Research question Primary production Stream temperature) Terrestrial habitat Food Growth rates & life cycles (Warner et al. 1984) Wooded riparian zone Supply detritus (energy) Shading Water quantity & quality Habitat quality 1.How do stretches with wooded riparian zones alter stream water temperature at different air temperatures? 2.And what are the effects on macroinvertebrates?

Experimental stream sites 8 streams per temperature regime low slope (< 1 m/km) sand bottom bank full width < 5 m no groundwater influx no tributaries, dams or impoundments Temperature SE DK D NL F SP Air temperature decrease Experimental set-up SE DK D D NL F F SP

Experimental set-up Open to shaded stretches Country = Temperature regime: Sweden, Denmark, Germany, Netherlands, France, Spain Number: 8 streams per country,10 sites per stream Time period: Year sampling site flow -2 km2 km Measurements: Temperature ( o C), Shading (mean leaf area index), Latitude (temperature regime), Current velocity (m/s), Width (m), Depth (m) & Physico-chemical parameters, Macroinvertebrates (once: 3 replicates form soft and hard substrates, respectively)

Data analyses (I) Mean daily average temperature (Mean) daily maximum temperature Calculated for the 5% warmest days (upstream): Temperature change in daily mean average and maximum m

Data analyses (II) m Rate of change ( o C) m m Model for the rate of change in water temperature No effectLinear modelQuadratic model Point of no change (cooling stops) Steepest slope m

Results: open -> shaded m T avg decrease o C T max decrease o C Initial rate of change (cooling) over the first 100 m Rate of change ( o C)

Distance to reach maximal achievable cooling Quadratic T avg o C T max o C Linear T avg o C T max o C Results: open -> shaded Rate of change ( o C)

Effect of environmental variables? Not significant:Latitude, Current, Width, Depth, W:D Significant for both mean and max:Leaf Area Index (LAI) Results: open -> shaded Reduced rank regression

Results: open -> shaded Macroinvertebrates * * Stream zonation preference (crenal-potamal species) Temperature range preference (cold and warm stenothermic species) * Shaded stretch: > crenal and < potamal species (significant for soft sediments) < warm stenothermic species (significant for soft sediments) Wilcoxon signed rank test

Conclusions More crenal species in streams: o that are shaded o that are smaller o in colder climates (with lower yearly maximum in temperature) More cold-stenothermic species in streams: o in colder climates (on soft substrates) Temperature regime Wooded riparian zones cool the water in a stream Cooling depends on the LAI, the higher the faster the cooling takes place Cooling is relatively equal in colder and warmer climates (At a higher current velocity a longer stretch is needed) Planting trees along streams mitigates temperature rise and favours cold water species

Thank you for your attention LAI matters Questions?