δ13C Of Periphyton Research Articles

Does rapid glacial recession affect feeding habits of alpine stream insects?

Abstract Glacial retreat, accompanied by shifts in riparian vegetation and glacier meltwater inputs, alters the energy supply and trophic structure of alpine stream food webs. Our goal in this study was to enhance understanding of dietary niches of macroinvertebrates inhabiting different alpine streams with contrasting glacial and non‐glacial (groundwater, precipitation, snowmelt) water inputs in conjunction with seasonal and habitat‐specific variation in basal resource availability. We measured a range of stream physico‐chemical attributes as well as carbon and nitrogen isotopes (δ13C, δ15N) of macroinvertebrates and primary food sources at seven sites across seasons within a Swiss glaciated catchment (Val Roseg) undergoing rapid glacial retreat (1–2 km between 1997 and 2014). Sampling sites corresponded to streams used in a previous (1997/1998) study within the same alpine catchment. Physico‐chemical attributes showed wide variation in environmental conditions across streams and seasons. Significant correlation among physico‐chemical proxies of glacier meltwater (phosphate‐P, total inorganic carbon, conductivity, turbidity) and macroinvertebrate δ13C, δ15N, and size‐corrected standard ellipse area (a proxy for feeding niche width) values showed that the extent of glacial water input shapes the energy base among alpine streams. Feeding niche differences among common alpine stream insect taxa (Chironomidae, Baetidae, Heptageniidae) were not significant, indicating that these organisms probably are plastic in feeding behaviour, opportunistically relying on food resources available in a particular stream and season. Seasonal trends in macroinvertebrate δ13C largely followed patterns in periphyton δ13C values, indicating that autochthonous resources were the main consumer energy source within the stream network, as shown previously. The overall range in macroinvertebrate δ13C (−33.5 to −18.4‰) and δ15N (−6.9 to 6.7‰) values also corresponded to values measured in the previous study, suggesting that macroinvertebrates altered diets in line with changes in environmental conditions and food resources during a period of rapid glacial retreat. Our results suggest that environmental changes brought on by rapid glacial retreat have not yet caused a profound change in the trophic structure within these fluvial networks.

Consumer‐diet discrimination of δ13C and δ15N: Source‐ and feeding‐oriented patterns based on gut content analysis in a large subtropical river of China

AbstractUnderstanding the trophic discrimination (∆13C and ∆15N) between consumers and diets in fluvial systems remains difficult because of the variable food sources and complex predator–prey interactions from headwaters to the estuaries. Here, stable carbon (δ13C) and nitrogen (δ15N) isotopes in fish and invertebrates from a large subtropical river in southern China were determined to explore trophic discrimination in conjunction with a gut content analysis. The ∆13C values showed significant differences (p < .05) among functional feeding groups, with fish, shrimp, and insect scrapers presenting higher ∆13C values (1.20 ± 0.23‰ to 1.51 ± 0.31‰) than other groups. The ∆15N values varied significantly between invertebrates (0.64 ± 0.17‰ of insect collector‐gatherers to 1.63 ± 0.36‰ of shrimp predators) and fish (1.98 ± 0.19‰ of detritivores to 2.71 ± 0.43‰ of crustaceavores) and exhibited an increasing tendency from primary to secondary consumers. A linear regression analysis revealed that the longitudinal changes in ∆13C and ∆15N were closely associated with the δ13C of periphyton, the δ15N of particulate organic matter (POM) in water, and the relative contribution (%) of periphyton and organic detritus to the diet composition of consumers. These results indicated that discrimination factors might not only be influenced by the isotope signatures of basal food sources but also downstream shifts in dominant food items utilized by consumers. In particular, trophic discrimination between periphyton– and detritus–based food chains, such as “epilithic diatoms–shrimp scrapers–crustaceavorous fish” and “POM–bivalves–molluscivorous fish,” displayed regionally specific patterns. When back‐calculating to the diet assimilation and trophic position in subtropical streams and rivers, we suggest using the basin‐scale ∆13C value of 0.96 ± 0.26‰ for all consumers and ∆15N values of 1.07 ± 0.32‰ for invertebrates and 2.38 ± 0.37‰ for fish.

Large variation in periphyton δ13C and δ15N values in the upper Great Lakes: Correlates and implications

Stable isotope ratios of carbon (δ13C) and nitrogen (δ15N) are frequently used to examine food web structure. Despite periphyton's importance to lake food webs, little is known about spatial variation of periphyton δ13C and δ15N values in the Great Lakes. We present periphyton δ13C and δ15N values from 28 sites the upper Great Lakes, including Lake Superior, the north shore of Lake Michigan, and Green Bay. We also examined variation in periphyton isotope values relative to several water quality parameters (TP, TN, TKN, NO3−, Kd) as well as periphyton C:N. There was a large range in both periphyton δ13C (range = 13.5‰) and δ15N (range = 10.2‰) among sites. Periphyton in more eutrophic sites had more depleted δ13C and more enriched δ15N compared to more oligotrophic sites. Our finding of high variability in periphyton isotope values in the Upper Great Lakes has implications for stable isotope-based reconstructions of food web structure.

Stable isotope compositions of aquatic flora as indicators of wetland eutrophication

Abstract Carbon and nitrogen stable isotopes (δ13C and δ15N) have been used as indicators for environmental changes in aquatic ecosystems. In this study, δ13C and δ15N values of select flora taxa were evaluated as indicators of human-induced eutrophication in an Everglades wetland which has been impaired by the source and quality of inflow and the alteration of hydrological pattern. Results showed that δ13C of cattail (Typha domingensis Pers.) increased with the decrease in total phosphorus (TP) concentration. Limited data for sawgrass (Cladium jamaicenses Crantz) collected at three study sites along the nutrient gradient also show a similar change in δ13C. However, δ13C of periphyton and bladderwort (Utricularia sp.) decreased with the decrease in TP concentration. The elevated δ13C values of emergent vascular plants (cattail and sawgrass) were likely the results of decreases in stomatal conductance, carboxylation and 13C fractionation under nutrient stress. This is supported by corresponding decreases in photosynthetic rate of cattail along the decreasing nutrient gradient. In contrast, δ15N values of all flora taxa increased with the increase in TP concentration. Findings from this study indicate that δ13C of emergent plants is a sensitive indicator for nutrient stress while δ15N of major flora species may serve as a robust indicator for wetland eutrophication.

Depth‐specific variation in carbon isotopes demonstrates resource partitioning among the littoral zoobenthos

Summary Benthic animals readily consume benthic algae, phytoplankton and terrestrial organic matter and are themselves a major component of fish diets. However, the effect of variation in resource availability on resource use by littoral macroinvertebrates remains poorly resolved. Using stable isotopes of carbon, we quantified depth‐specific resource use by zoobenthic functional feeding groups in five lakes in northern Wisconsin. The littoral zoobenthos was collected from soft sediments at several depths in conjunction with samples of bulk periphyton (top 5 mm of sediment and biofilm) and measurements of benthic algal primary productivity. Periphyton δ13C was positively correlated with depth‐specific benthic algal primary productivity, but grazer δ13C was consistently higher than that of the periphyton. The δ13C of infaunal collectors and predators was tightly correlated with, and nearly identical to, bulk periphyton δ13C (collectors: R2, 0.88; slope, 0.97; P < 0.0001; predators: R2, 0.78; slope, 0.88; P < 0.0001). Reliance of collectors and predators on benthic algal carbon varied between 43 and 100%, depending on whether grazers or bulk periphyton was used as the benthic algal end‐member. Despite the apparent homogeneity of the sediments, benthic grazers and collectors partitioned resources in a consistent way in our study lakes, indicating either selective ingestion or assimilation of different components of the biofilm.

Spatial and Temporal Variation in Stable Isotopes Signatures of Periphyton and an Endangered fish in a flow-reduced River Reach

The environmental and ecological issues in the flow-reduced river reach are very serious and arereceiving increasingly attention. In this study, we investigate the temporal and spatial changes in δ13C and δ15N of Periphyton and isotopic relationship between Periphyton and the endangered fish (Ayu, Plecoglossusaltivelis) in a flow-reduced river reach in Japan. Much of the spatial and temporal variation in δ13C ofendangered fish was explained by variation in Periphyton, indicating a strong link between primary production and higher order consumers. The Periphyton δ13C was correlated with current velocity while it was not correlated with the Periphyton biomass (Chl.a). Spatially, the relatively high δ13C and δ15N of Periphyton in the lower sites of the flow-reduced river reach might be due to high level of anthropogenically derived N and C introduced from the surrounding agricultural activities and human settings. The trophic position of the endangered fish in was estimated to be 1.5-2.2(1.8±0.3), which agrees with the previous stomach content analysis suggesting that the ayu mainly feed on Periphyton.

Stream foodweb δ13C and geomorphology are tightly coupled in mountain drainages of northern Idaho

The relative influence of landscape vs local processes on variation in stream C and energy sources to lotic consumers remains unresolved, but is a key component in understanding pathways through stream food webs. I investigated potential linkages between the distribution of δ13C signatures of primary producers (periphyton), terrestrial organic matter (detritus), and secondary consumers (aquatic invertebrates and fish) and: 1) drainage area and 2) stream reach geomorphology in 3 mountain watersheds of northern Idaho, USA. When considered alone, drainage area explained variation in the δ13C signatures of periphyton (R2 = 0.30) and sculpin (R2 = 0.15) only. Subsequent General Linear Models (GLMs) showed that stream morphology explained significant variation in δ13C of periphyton (79%), Diptera (93%), sculpin (51%), and trout (63%). Drainage area was not significant in these models, a result indicating that once δ13C signatures are explained as a function of geomorphic type, the contribution of drainage area becomes less important. On the whole, consumer δ13C signatures related more strongly to periphyton δ13C than detrital δ13C, though this relationship varied among geomorphic types. Collectively, results indicate that the morphology of a stream reach (including factors such as substrate size and storage elements, floodplain development, etc.) may be an important factor in the assimilation and distribution of C in food webs in forested mountain streams.

Use of carbon‐13 and carbon‐14 natural abundances for stream food web studies

AbstractWe review the use of stable carbon isotope ratios (δ13C) and radiocarbon natural abundances (Δ14C) for stream food web studies. The δ13C value of primary producers (e.g., periphytic algae, hereafter periphyton) in streams is controlled by isotopic fractionation during photosynthesis and variable δ13C of dissolved CO2. When periphyton δ13C differs from that of terrestrial primary producers, the relative contribution of autochthony and allochthony to stream food webs can be calculated. Moreover, the variation in periphyton δ13C can reveal how much stream consumers rely on local resources because each stream habitat (e.g., riffle vs. pool, open vs. shaded) usually has a distinctive δ13C. However, periphyton δ13C often overlaps with that of terrestrial organic matter. On the other hand, periphyton Δ14C is less variable than δ13C among habitats, and reflects the Δ14C of dissolved CO2, which could be a mixture of “aged” (Δ14C < 0 ‰) and “modern” (Δ14C > 0 ‰) carbon. This is because the Δ14C is corrected by its δ13C value for the isotopic fractionation during photosynthesis. Recent studies and our data indicate that many stream food webs are supported by “aged” carbon derived from the watershed via autochthonous production. The combined use of δ13C and Δ14C allows robust estimation of the carbon transfer pathway in a stream food web at multiple spatial scales ranging from the stream habitat level (e.g., riffle and pool) to watershed level (autochthony and allochthony). Furthermore, the Δ14C of stream food webs will expand our understanding about the time frame of carbon cycles in the watersheds.

Natural C-14 provides new data for stream food-web studies: a comparison with C-13 in multiple stream habitats

In stream food-web analysis, the contributions of carbon from periphyton (an autochthonous source) and terrestrial litter (an allochthonous source) are estimated by isotopic difference. We hypothesised that periphyton δ13C varies among stream habitats, whereas Δ14C does not because Δ14C is corrected with δ13C, by definition. To test this hypothesis, we compared the variability of δ13C and Δ14C of periphyton and dissolved inorganic carbon (DIC) in four habitats (open v. shaded, riffle v. pool) within a limestone-based upland stream in Japan. Periphyton δ13C values (from –31.9‰ to –16.3‰) were significantly different among the habitats whereas the Δ14C values (from –379‰ to –141‰) were not. Periphyton δ13C values depended on both algal photosynthetic activity and δ13C of the DIC, whereas periphyton Δ14C depended only on DIC Δ14C. The δ13C and Δ14C values of litter were constant. Thus, the difference between the periphyton and litter δ13C values (Δδ13C) varied among habitats, but their Δ14C differences (ΔΔ14C) did not. Our results indicate that Δ14C is spatially stable among stream habitats and that Δ14C measurements can be used to precisely determine carbon sources for stream food-web analysis within individual reaches.

Longitudinal changes in δ13C of riffle macroinvertebrates from mountain to lowland sections of a gravel-bed river

Summary 1. To understand longitudinal changes in the trophic base of benthic macroinvertebrates from mountain to lowland river sections, we investigated carbon stable isotopic compositions (δ13C) of macroinvertebrates and their food resources in riffles for four seasons at 14 sites along the main stem of the Toyo River, Japan. 2. At each site, δ13C was usually highest or nearly highest for periphyton (epilithic biofilm) and was lowest for transported leaf materials. Among macroinvertebrate groups, grazers usually had higher δ13C values than filterers or predators. 3. During all seasons, δ13C of periphyton and all macroinvertebrate groups increased downstream from mountain to upland sections, but decreased downstream from upland to lowland sections. In addition, the difference between grazer δ13C and filterer δ13C decreased from mountain to upland sections, but increased from upland to lowland sections. 4. The observed changes in δ13C of periphyton and macroinvertebrates from mountain to upland sections agree with previous reports: the δ13C of periphyton and consumers increased with stream size and productivity. The decrease in δ13C of periphyton and macroinvertebrates from upland to lowland sections has not been reported previously, and this may have resulted from an increased importance of terrestrial detritus relative to periphyton production in the lowland section, where riffles were infrequent and pools dominated the reach. 5. A simple mixing model of δ13C showed that grazers rely mostly on periphyton at all sites, whereas the importance of periphyton for filterers changed longitudinally increasing from mountain to upland sections and decreasing from upland to lowland sections. This longitudinal trend for filterers is possibly associated with the changes in the availability or quality of terrestrial detritus in transported particulate organic matter. 6. Longitudinal changes in the relative importance of autochthonous production and allochthonous detritus appear to be reflected in δ13C of riffle benthic communities. The longitudinal changes were not monotonic, and specific reach characteristics may be responsible for the greater importance of allochthonous detritus in mountain and lowland sections.

Influence of velocity and chlorophyll standing stock on periphyton δ13C and δ15N in the Ste. Marguerite River system, Quebec

In a previous laboratory experiment, water velocity had a strong negative effect on periphyton δ13C and δ15N, probably reflecting the effect of flow on boundary-layer exchange. To determine whether similar patterns could be detected in situ at different spatial scales, we examined several reaches, each with a wide range in water velocity and chlorophyll standing stock. Periphyton samples were uniform in composition, composed predominantly of living and dead diatoms of very few species. δ13C signatures were more variable (–17.7‰ to –31.5‰) than δ15N signatures (–0.4‰ to 5.7‰). Velocity and chlorophyll were significant predictors of periphyton δ13C within reaches, mainly at medium scales (10–500 m) where persistent alternations between fast and slow current (riffles–runs–pools) produced inverse fluctuations of periphyton δ13C. However, none of the variability in δ15N could be explained, possibly a result of severe boundary-layer N depletion. Similarly, the velocity and chlorophyll predictors could not explain the among-reach signature differences for either isotope. δ13C signatures tended to be13C-depleted in the tributary streams and13C-enriched in the downstream reaches.

Changes in carbon stable isotope ratios during periphyton development

Stable isotopes are widely used to infer trophic relationships with little attention paid to temporal variability at the base of the food web. We examined changes in the carbon-stable isotope composition during periphyton development, sampling periphyton that accumulated on ceramic tiles at four stream sites over a 2-month period. Periphyton 13C rose and fell in general concordance with rising and falling biomass at all four sites, resulting in significant correlations between periphyton Δ13C and chlorophyll a (Chl a). Mean Δ13C values at one site rose from -26‰ to -20‰ in 2 weeks, falling back to -24‰ the next week after a large scouring spate. Periphyton 13C also underwent a smaller, longer-term increase that correlated with a gradual rise in stream temperature. Multiple regression analysis with both Chl a and temperature as independent variables accounted for up to 88% of the temporal variability in Δ13C, with Chl a the largest source of variability. Water velocity, measured on each sampling occasion, was unrelated to temporal changes in 13C. Depletion of inorganic carbon within the periphyton matrix is the probable cause of increasing 13C in periphyton as biomass develops. Rising Δ13C values during periphyton biomass development suggest the possibility of carbon-limited periphyton growth, even in alkaline waters. The strong link between biomass and periphyton 13C helps explain the large range of Δ13C reported for periphyton in streams, where temporal and spatial variability in periphyton biomass are notorious.

Stable isotope investigation of food use by Caridina spp. (Decapoda:Atyidae) in Hong Kong streams

Caridina spp. (Atyidae) are widespread and abundant omnivorous shrimps in tropical Asian streams. Spatial and seasonal variation in C and N stable isotope signatures of 2 species (Caridina cantonensis and C. serrata) and their potential food sources (leaf litter, fine particulate organic matter [FPOM], and periphyton) were investigated in 2 shaded and 2 unshaded Hong Kong streams. The objectives were to identify food sources used by shrimps and to determine whether food use changed according to riparian shading, season, developmental stage, and sex. Isotopic signatures of different species of leaf litter were similar to each other and distinct from FPOM signatures in all streams, whereas periphyton δ13C and δ15N signatures were similar to FPOM signatures. FPOM and periphyton showed seasonal variation in δ13C and δ15N signatures in all streams, but signatures of leaf litter showed relatively minor variation. δ13C signatures of FPOM were 7 to 12‰ (shaded streams) and 5 to 7‰ (unshaded streams) higher than those of leaf litter during the dry season, and 5 to 8‰ (shaded streams) and 4 to 7‰ (unshaded streams) higher during the wet than the dry season. δ15N signatures of FPOM were almost 2× those of leaf litter in all streams and seasons. Periphyton was generally ≤6‰ more 13C-enriched and ≤4‰ 15N-depleted than FPOM. Seasonal variation in δ13C signatures of shrimps and their food sources were consistent among streams, and were less 15N-depleted during the dry season. Dual-isotope multiple-source mixing models indicated that FPOM and periphyton were the main foods of adult (male and female) and juvenile C. cantonensis and C. serrata. Leaf litter contributed <10% to the biomass of C. cantonensis in unshaded streams and 10 to 20% to the biomass of both species in shaded streams. Periphyton contributed >60% to the biomass of C. cantonensis in unshaded streams in the wet season, with the proportion slightly higher during the dry season. In shaded streams, periphyton contributed 35 to 60% to Caridina spp. biomass. Our results indicate that the Hong Kong atyids feed as omnivores, with herbivory as a primary feeding mode supplemented by collection of FPOM and limited direct consumption of allochthonous leaf litter.

The effect of water velocity on stable carbon and nitrogen isotope signatures of periphyton

Water movement affects carbon and nitrogen isotopic signatures of algae, possibly through effects on boundarylayer thickness. We describe a laboratory experiment carried out in artificial streams, which supports this hypothesis. Periphyton δ13C and δ15N signatures were significantly depleted in 13C and 15N when grown at higher water velocity over the range of 5–62 cm s−1, the normal range found in small streams. δ13C signatures ranged between —16.7‰ and —28.1‰ from the lowest to the highest water velocity, respectively. Similarly, δ15N signatures ranged between 7.2‰ and 2.3‰ from the lowest to the highest water velocity, respectively. This pattern was found for algal communities growing on glass (mainly diatoms) as well as for those growing on rock (mainly filamentous green algae). For both C and N, the slopes of the responses were not different between the periphyton communities growing on each substrate, although the effect was statistically weaker for the communities on rocks. The intercept for δ13C was significantly higher for the communities on rocks, but not different for δ15N. Thus, while both isotopes are fractionated to a greater extent as velocity increases, the diatom communities growing on glass appeared to fractionate C isotopes more than the filamentous green algae growing on rock. This relationship between the stable isotopic signatures of aquatic plants and water velocity will hopefully allow a better understanding of the differences in isotopic signatures of fish in different habitats.

Carbon-13/Carbon-12 Variation in Subalpine Lake Aquatic Insects: Food Source Implications

Relative 13C concentrations were found to be significantly different among the three primary organic carbon sources for aquatic insect production within Findley Lake, Washington, USA. These three carbon sources were conifer tree detritus (mean δ18C = −27.3 per mil), periphyton (−34.6 per mil), and plankton (−45.9 per mil). Correspondingly, the δ18C of the adults of assumed autochthonous carbon feeders, Paraleptophlebia sp. (Ephemeroptera: Leptophlebiidae) and Chaoborus trivittatus (Diptera: Chaoboridae), well approximated the δ13C of periphyton and plankton, respectively. The remainder of the adult insect emergence, mostly Limnelphilidae and Chironomidae, exhibited δ13C values intermediate between the terrestrial and periphyton carbon. Approximately 38% of the 51 kg C of insect biomass annually emerging from this lake was conservatively estimated to originate from terrestrial plant sources.Key words: carbon-13, carbon pathways, lake, aquatic insects, feeding ecology, insect emergence, terrestrial detritus