EFFECTS OF HURRICANE ON LEAF BREAKDOWN AND METABOLIC PROCESSES IN NEOTROPICAL HEADWATER STREAMS

Steve Strella Pedro J. Torres Rubenstein School of Environment and Natural Resources Odum School of University of Vermont Hurricanes have been demonstrated to be important disturbance regimes for many Caribbean forests, but how do they affect freshwater Ecosystems?

Goals: Discussion • To investigate how changes in Methods Continued Litter Breakdown: proportions of energy inputs to Artificial: A Parallel experiment was arranged in artificial stream pools. Four treatments consisted of exposed or shaded lighting rates (k’) in the field experiment were streams, such as those resulting conditions in combination with high or low litter densities. not significantly different among treatments (F6=1.755, from canopy disturbance, p= .2392). The limitations of small scale manipulations influence ecosystem processes. Leaf packs were also deposited as in the field experiment; the total change in mass was measured after three weeks. may have limited the influence of treatments in the

• Exploring how ecosystem Metabolic processes were calculated after measuring the change in dissolved oxygen through time within a water-tight chamber field. processes relate to each other. containing a fixed area of substrate. The artificial environment was under more consistent • To support field treatments using • respiration was measured with total exclusion of light conditions that the field treatments, and the results artificially simulated • Photosynthesis was measured under natural lighting conditions; photosynthesis rates were calculated as the sum of the net may suggest an inverse relationship between environments gain of DO under light and the net loss of DO in darkness. decomposition and litter density (f3= 3.5652, p=.0602).

Metabolic Processes Results Light was not significant for both photosynthesis and

120 84 respiration. However, litter density was significant for Methods 82 both photosynthesis (p=0.0117) and respiration 100 Decomposition was studied in both 80 (p=0.0092). a field experiment and within an 80 78 76 artificial environment: 60 Bruquena Results suggest that benthic ecosystems have high TdA 74 Prieta B potential to rebound from hurricane disturbance 40 72 Field: Three first order streams with following an initial starving phase; breakdown of debris

Remaining Mass Leaf Percent Avg. 70 similar physical and chemical Remaing Mass Leaf Percent Avg. 20 provides both detrital food source and stimulates algal 68 characteristics were selected 0 growth via nutrient release. 6 12 18 24 30 HH HL LH LL Variables were combined, with a Time (days) Figure 2: Average percentage dry mass (% DMr) in leaf packs for high litter density (Toma de Agua) Figure 1: Average percentage of ash free dry mass remaining over time in the four treatments: high litter-high light (HH), high litter-low and a low litter treatment leaf packs for each study stream, high light reduced litter(Bruquena), high light (HL), low litter-low light (LL), and low litter-high light (LH). light added litter (Toma de Agua) and Control (Prieta B). Error bars represent Error bars represent +/- 1SE. (Buruquena). Canopies were +/- 1SE. disturbed at both site by removing 0.025 low-lying branches. Prieta B served 0.02 Acknowledgments 0.02 EPSCoR VT and the Streams Project Staff

as a control stream, free of

0.01

/Hour) Alonso Ramirez- program Director manipulation. 0.015 3 /Hour 3 /cm 2

/cm El Verde Field Station Staff 2

0.01 (mg O 0.01 mg O Freshly fallen Cecropia schreberiana Respiration Karleen Wagner leaves were arranged into bundles 0.005 For Assistance in the field: of known mass and deposited within 0.00 Marisa Cross

0 0.01 0.015 0.02 0.025 each 25m reach of stream (5 HH HL LH LL Ashley Curry Photosynthesis

3 replicates per stream). Photosynthesis Rate Respiration Rate (mg O2/cm /Hour) Lelanee Ortiz T.J. Hegan Figure 4: Photosynthesis and respiration rates for the four treatments: high Figure 6: Regression of community respiration rate to photosynthesis rate One leaf pack from each replicate litter-high light (HH), high litter-low light (HL), low litter- low light (LL), and low among all artificial pool treatments. Jacob Menkin was retrieved every six days to litter-high light (LH). Error bars represent +/- 1SE. Whitney Reyes develop a decomposition rate (k’). Stephanie Simpson