TITLE PAGE - acumen - The University of Alabama
TITLE PAGE - acumen - The University of Alabama TITLE PAGE - acumen - The University of Alabama
Cambarus tenebrosus, the obligate cave salamander Gyrinophilus palleucus, and a facultative salamander, Eurycea cirrigera. This level of taxonomic and trophic diversity allowed us to test predictions about how a food web containing both obligate and facultative cave species would respond to increased energy supply. Experimental design A before-after control-impact (BACI) sampling design was used for this study. Two 100- m stream reaches, separated by 25 m, were chosen: an upper control reach and a lower manipulation reach. These stream reaches were located ~400m stream distance from the nearest cave entrance. Wetted channel width ranged from 0.5 to 4 m and depth ranged from 0.2 to 0.8 m. Following 1 yr of pre-treatment sampling in both reaches (Feb 2009 to Feb 2010), the manipulation reach was amended with corn stover (leaves, stalks, and husks left over from corn harvest) so that standing crop organic matter was maintained at ~500 g dry mass (DM) m -2 for 1 yr (Feb 2010 to Feb 2011). Corn stover was chosen as the carbon source because it was easily obtained, readily utilized by stream microbes and macroinvertebrates (Griffiths et al. 2009; Venarsky et al. 2012), and has a distinctive C4 δ 13 C signature (-11 ‰; Fry 2006) that allows it to be traced through the recipient food web using stable isotope analysis (Bender 1968). The corn variety chosen for the manipulation (variety W5280: Wyffels Hybrids Inc., Geneseo, Illinois, U.S.A) did not contain the Bacillus thuringiensis toxin, which could have affected invertebrate consumers in the manipulation reach (Rosi-Marshall et al. 2007). Immediately following the first addition of corn litter (Feb 2010), 20 mesh barriers were constructed at 5-m intervals to increase litter retention in the manipulation reach. Mesh barriers were positioned perpendicular to the stream channel and were constructed using a 1×0.5-m piece 43
of netting (mesh size 2.5×1.5-cm) attached between two sandbags filled with stream substrate. Fresh corn litter was occasionally added as needed to maintain the target addition level. Environmental characteristics Water temperature was recorded every 30 min using a HOBO Water Level Logger model U20-001-04 data logger (Onset Computer Corp., Pocasset, Massachusetts, USA). Water samples were collected from each reach on each sampling date and analyzed for NH + 4 -N, NO 3¯-N, soluble reactive phosphorus (SRP). All water samples were filtered through glass-fiber filters (0.7-µm nominal pore size). Water samples were transported to the laboratory on ice and frozen until analysis. Concentrations of NH + 4 -N were measured using the orthophthaldialdehyde fluorometric method (Holmes et al., 1999; Taylor et al., 2007). Concentrations of NO 3¯-N were measured using ion chromatography (Dionex ICS 2000 Ion Chromatograph; APHA, 1998). Soluble reactive phosphorus (SRP) concentrations were quantified using the ascorbic acid method (Murphy & Riley, 1962). Meio-, macro-fauna, and organic matter sampling Sampling occurred on nine dates prior to (Feb 2009 to Jan 2010) and eleven dates following (Mar 2010 to Feb 2011) the initiation of the litter amendment. On each date, the density of small macrofauna (amphipods, isopods, and insects), meiofauna (copepods and cladocerans), and standing crop organic matter was estimated from 10 random samples taken within each study reach. Samples were collected using a stove-pipe corer (22.5 cm diameter) to a depth of 30 cm or bedrock, whichever came first. Samples were preserved in 5% formalin. Densities of large macrofauna (salamanders and crayfish) were estimated by placing block nets at the ends of each study reach and making three collection passes. Individuals were measured 44
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Cambarus tenebrosus, the obligate cave salamander Gyrinophilus palleucus, and a facultative<br />
salamander, Eurycea cirrigera. This level <strong>of</strong> taxonomic and trophic diversity allowed us to test<br />
predictions about how a food web containing both obligate and facultative cave species would<br />
respond to increased energy supply.<br />
Experimental design<br />
A before-after control-impact (BACI) sampling design was used for this study. Two 100-<br />
m stream reaches, separated by 25 m, were chosen: an upper control reach and a lower<br />
manipulation reach. <strong>The</strong>se stream reaches were located ~400m stream distance from the nearest<br />
cave entrance. Wetted channel width ranged from 0.5 to 4 m and depth ranged from 0.2 to 0.8 m.<br />
Following 1 yr <strong>of</strong> pre-treatment sampling in both reaches (Feb 2009 to Feb 2010), the<br />
manipulation reach was amended with corn stover (leaves, stalks, and husks left over from corn<br />
harvest) so that standing crop organic matter was maintained at ~500 g dry mass (DM) m -2 for 1<br />
yr (Feb 2010 to Feb 2011). Corn stover was chosen as the carbon source because it was easily<br />
obtained, readily utilized by stream microbes and macroinvertebrates (Griffiths et al. 2009;<br />
Venarsky et al. 2012), and has a distinctive C4 δ 13 C signature (-11 ‰; Fry 2006) that allows it to<br />
be traced through the recipient food web using stable isotope analysis (Bender 1968). <strong>The</strong> corn<br />
variety chosen for the manipulation (variety W5280: Wyffels Hybrids Inc., Geneseo, Illinois,<br />
U.S.A) did not contain the Bacillus thuringiensis toxin, which could have affected invertebrate<br />
consumers in the manipulation reach (Rosi-Marshall et al. 2007).<br />
Immediately following the first addition <strong>of</strong> corn litter (Feb 2010), 20 mesh barriers were<br />
constructed at 5-m intervals to increase litter retention in the manipulation reach. Mesh barriers<br />
were positioned perpendicular to the stream channel and were constructed using a 1×0.5-m piece<br />
43
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