Characterization of riparian species and stream detritus using multiple stable isotopes

Abstract

Multiple stable isotopes were used to determine the effectiveness of distinguishing among several dominant riparian species and aquatic macrophytes both spatially (three sites) and temporally (three seasons) along an 8-km reach of a blackwater stream. The differences in isotopic composition were used to assess contributions of various organic matter sources to the detrital pool of the stream. Samples of riparian and aquatic macrophyte vegetation and detritus were collected at three times to represent early leaf-out (April), mid-summer (August), and just prior to abscission (October). Each sample was analyzed for stable isotopes of carbon δC, nitrogen δN, and sulfur δS Within a site and sampling date, δC-values were significantly different among certain riparian species and detritus samples. Species differences persisted between seasons. δS values were the most variable of the three elements examined although they remained fairly constant through time within each species and site. The results suggest that temporal changes in isotopic compositions of riparian species and aquatic macrophytes are site-specific. Discriminant analysis dissimilarity plots (based on all three isotopes) demonstrated that the contribution of species to the detrital pool depended on the site and season. At the upper site, detritus was isotopically most similar to Quercus laurifolia and Sparganium americanum in April, and the aquatic macrophytes (S. americanum and Potamogeton spp.) in August and October. At the middle site, detritus was most similar to Carpinus caroliniana and Q. nigra in April but no single source was similar to detritus in August or October. At the lower site, detritus was most similar to Taxodium distichum for all three seasons.

Autochthonous and allochthonous plant contributions to coastal benthic detritus deposits: a dual-stable isotope study in a volcanic lake

“…Amount and composition of detritus was sitespecific, both influenced by the littoral slope and reflecting the relative abundances of plant sources. The stable isotope ratios of the allochthonous species fell within the range of C 3 plants reported by many authors (Rounick and Winterbourn 1986;Ehleringer 1993;McArthur and Moorhead 1996;France 1995;Talbot 2001;Jones et al 2004;Benstead et al 2006). Submergent species and epilithon had higher d 13 C values than allochthonous plants, similar to those reported by Benstead et al (2006).…”

“…Stable isotope analysis (SIA) often allows the unequivocal identification of elemental sources of organic deposits (McArthur and Moorhead 1996), and thus the contribution to higher trophic levels (Boon and Bunn 1994;Loneragan et al 1997;McCutchan and Lewis 2002;Peterson and Fry 1987;Phillips and Gregg 2003;Benstead et al 2006). However, the presence of multiple organic sources hamper SIA because mathematical Mixing Models used to estimate the contribution of each source to the mixture are constrained by the number of isotopes that can be analysed.…”

“…Mixing Models have been mostly applied to diet analysis, only rarely have they been used on lake benthic deposits (McArthur and Moorhead 1996). The principal aim of this study was to analyse the stable isotope ratios (d 13 C and d 15 N) of the littoral benthic organic deposits and its potential sources at two sites of a volcanic lake (Lake Bracciano, Italy), which differed in bottom slope, geological substratum, and vegetation composition.…”

Seasonal variability of fine-grained sediment morphology in a salmon-bearing stream.

“…the floodplain (Hamilton and Lewis, 1992) and riparian (McArthur and Moorhead, 1996) regions. However, the utility of SIA for identifying sources can be limiting for several…”

“…This has led to the development of mixing models that enable more accurate determination of sources, but the relative contribution of each source must be known. Others have suggested that analysing multiple stable isotopes simultaneously McArthur and Moorhead, 1996), or combining other tracers such as C/N ratios (Andrews et al, 1998), could prove to mitigate this problem.…”