Landscapes Forest and Global Change - ESA - Escola Superior ...

P.C. Goebel et al. 2010. How important are riparian forests to aquatic foodwebs in agricultural watersheds
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non-forested reaches. This may be related to the fact that we did not observe clear differences
between δ 13 C signatures for some of the autochthonous resources (epilithon) and allochthonous
resources (CPOM and riparian plants). It has been observed elsewhere that variation in stream
flows, dissolved CO 2 concentrations, and δ 13 C concentrations in dissolved inorganic C can
result in higher than expected algal δ 13 C values that overlap with detrital δ 13 C values which tend
to be more consistent both spatially and temporally (Finlay 2004). Consequently, disentangling
energy pathways in this system may require additional study or the use of other stable isotopes
such as hydrogen (δD) (Finlay et al. 2010).
We did observe differences in levels of consumer 15 N enrichment between the forested and nonforested
riparian areas. However, we did not observe these differences with the higher-level
consumers as anticipated. We had hypothesized that the increased diversity of basal food web
resources associated with the forested sites would result in δ 15 N signatures of higher-level
consumers. The fact that we did not detect such a relationship suggests a possible linkage with
diet quality and stoichiometry associated with the different environments rather than trophic
position. Similar linkages have been suggested by others observing similar patterns in streams
of Arkansas (Dekar et al. 2009). This pattern may also be related to seasonality and differences
associated with diet (i.e., more reliance on algae and macrophyte sources during the spring as
these basal resources may have higher C:N ratios than detrital sources). However, more
research on these mechanisms is clearly needed to better understand the patterns of 15 N
enrichment in these headwater streams and how that may relate to riparian management and
restoration.
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