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  • Isotopes
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  • 1
    Language: English
    In: Journal of Applied Ecology, 1 August 2011, Vol.48(4), pp.916-925
    Description: 1. Shoreline development and the associated loss of littoral habitats represent a pervasive alteration of the ecological integrity of lakes and have been identified as major drivers for the loss of littoral biodiversity world-wide. Little is known about the effects of shoreline development on the structure of, and energy transfer in, littoral food webs, even though this information is urgently needed for management and mitigation measures. 2. We measured macroinvertebrate biomass and analysed potential food resources using stable isotopes (δ¹³C, δ¹⁵N) and mixing models to compare the complexity and the trophic base of littoral food webs between undeveloped and developed shorelines in three North German lowland lakes. 3. The lower diversity of littoral habitats found at developed shorelines was associated with lower diversity of food resources and consumers. Consequently, the number of trophic links in food webs at developed shorelines was up to one order of magnitude lower as compared with undeveloped shorelines. 4. Mixing model analysis showed that consumer biomass at undeveloped shorelines was mainly derived from the particulate organic matter (FPOM) and coarse particulate organic matter of terrestrial origin (CPOM). The contribution of CPOM to consumer biomass was twofold lower at developed shorelines, and consumer biomass was mainly derived from FPOM and suspended particulate organic matter. 5. Synthesis and application. Shoreline development impacts the flow of organic matter within littoral food webs primarily through the reduction in littoral habitat diversity. These effects are exacerbated by clearcutting of the riparian vegetation, which disrupts cross-boundary couplings between the riparian and the littoral zone. Lakeshore conservation should focus on preserving the structural integrity of the littoral zone, while restoration of coarse woody debris, reed and root habitats can be a cost-efficient measure to improve degraded lakeshores. The local effects of shoreline development demonstrated in this study might lead to whole-lake effects, but future studies are needed to derive thresholds at which shoreline development has consequences for the structure and functioning of the entire ecosystem.
    Keywords: Vegetation and Community ecology
    ISSN: 00218901
    E-ISSN: 13652664
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  • 2
    In: Canadian Journal of Fisheries and Aquatic Sciences (Journal canadien des sciences halieutiques et aquatiques), 2011, Vol.68(1), pp.74-88
    Description: We compared the invertebrate production and stable isotope signatures of key ecosystem compartments of urban sites subjected to the input of tertiary-treated wastewater with those of upstream sites in an agricultural lowland stream. We detected a significant shift in the trophic basis of invertebrate production from upstream, natural and agricultural resources, to urban resources, i.e., wastewater-derived organic matter as well as autochthonous primary production based on wastewater-derived nutrients. Invertebrate production was higher at urban sites than at agricultural sites. However, the median contribution of the most important secondary producer, the shredder Gammarus roeseli , to total invertebrate production was lower at urban sites (9%) than at agricultural sites (61%). The low production of G. roeseli at urban sites was associated with the absence of allochthonous coarse particulate organic matter (CPOM) habitats, rather than the loss of CPOM as a food resource. Our results suggest that contemporary urban stressors in developed countries affect secondary producers less severely than historically recorded, but still profoundly change the matter fluxes and ecosystem functioning of running waters. Restoration of the native riparian vegetation, channel naturalization, and adequate dilution of tertiary-treated wastewater may partially mitigate adverse effects on invertebrate communities and their secondary production.
    Description: Nous comparons la production d'invertbrs et les signatures d'isotopes stables de compartiments cls de l'cosystme dans des sites urbains soumis l'apport d'eaux uses de traitement tertiaire par comparaison des sites d'amont dans un cours d'eau agricole de plaine. Nous dtectons un changement significatif dans la base trophique de la production d'invertbrs, partir des ressources naturelles et agricoles en amont vers des ressources urbaines, c'est--dire de la matire organique drive des eaux uses, ainsi qu'une production primaire autochtone base sur des nutriments provenant des eaux uses. La production d'invertbrs est plus leve dans les sites urbains que dans les sites agricoles. Cependant, la contribution mdiane du producteur secondaire le plus important, le dchiqueteur Gammarus roeseli , la production totale des invertbrs est plus basse aux sites urbains (9 %) qu'aux sites agricoles (61 %). La faible production de G. roeseli aux sites urbains est associe l'absence d'habitats matire organique particulaire grossire (CPOM) allochtone, plutt qu' la perte de CPOM comme ressource alimentaire. Nos rsultats laissent croire que les facteurs urbains actuels de stress dans les pays dvelopps affectent les producteurs secondaires moins svrement que signal dans le pass, mais qu'ils modifient nanmoins profondment les flux de matire et le fonctionnement de l'cosystme dans les eaux courantes. La restauration de la vgtation riveraine indigne, la naturalisation du chenal et la dilution adquate des eaux uses aprs un traitement tertiaire peuvent en partie rduire les effets ngatifs sur les communauts d'invertbrs et leur production secondaire.
    Keywords: Rivers ; Isotopes ; Ecosystems ; Environmental Impact ; Pollution Effects ; Trophic Structure ; Particulate Organic Matter ; Freshwater Organisms ; Secondary Production ; Waste Water ; Agricultural Runoff ; Chemical Analysis ; Pollution ; Gammarus Roeseli ; Germany, Erpe R. ; Freshwater ; Mechanical and Natural Changes ; Productivity;
    ISSN: 0706-652X
    E-ISSN: 1205-7533
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  • 3
    Language: English
    In: Hydrobiologia, 2017, Vol.799(1), pp.37-48
    Description: Ephemeral ponds are often dominated by species with both terrestrial and aquatic life phases. Such species have the potential to strongly alter the food web structure of ponds, particularly if they are predators. Here we experimentally tested the effects of salamander larvae ( Salamandra salamandra ) on invertebrate communities in ephemeral forest ponds. We repeatedly split two ponds into salamander enclosure- and exclosure-segments, and compared the diversity and biomass of potential prey organisms. We used stable isotopes of carbon (δ 13 C) and nitrogen (δ 15 N) of resources and consumers to characterise the food web structure. The presence of salamander larvae did not affect abundances of culicid larvae, their preferred prey. The population dynamics of most insect larvae was independent of the presence of salamander larvae, and was instead driven by the timing of hatching and emergence. However, a significant reduction resulting from salamander predation could be detected in the less abundant chironomid larvae. There was no substantial alteration of the food web structure as indicated by stable isotopes. However, the stable isotope results suggest a strong trophic subsidisation from the terrestrial system, which is probably the reason for the weak top-down effects of the salamander larvae on the invertebrate food web.
    Keywords: Biodiversity ; Salamandra salamandra ; Top-down ; Trophic cascades ; Aquatic-terrestrial linkage
    ISSN: 0018-8158
    E-ISSN: 1573-5117
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  • 4
    Language: English
    In: PLoS ONE, 2016, Vol. 11(5)
    Description: Hydrogen stable isotopes (δ2H) have recently been used to complement δ13C and δ15N in food web studies due to their potentially greater power to separate sources of organic matter in aquatic food webs. However, uncertainties remain regarding the use of δ2H, since little is known about the potential variation in the amount of exchangeable hydrogen (Hex) among common sample materials or the patterns of δ2H when entire food webs are considered. We assessed differences in Hex among the typical sample materials in freshwater studies and used δ2H, δ13C and δ15N to compare their effectiveness in tracing allochthonous matter in food webs of two small temperate lakes. Our results showed higher average amounts of Hex in animal tissues (27% in fish and macroinvertebrates, 19% in zooplankton) compared to most plant material (15% in terrestrial plants and 8% in seston/periphyton), with the exception of aquatic vascular plants (23%, referred to as macrophytes). The amount of Hex correlated strongly with sample lipid content (inferred from C:N ratios) in fish and zooplankton samples. Overall, the three isotopes provided good separation of sources (seston, periphyton, macrophytes and allochthonous organic matter), particularly the δ2H followed by δ13C. Aquatic macrophytes revealed unexpectedly high δ2H values, having more elevated δ2H values than terrestrial organic matter with direct implications for estimating consumer allochthony. Organic matter from macrophytes significantly contributed to the food webs in both lakes highlighting the need to include macrophytes as a potential source when using stable isotopes to estimate trophic structures and contributions from allochthonous sources.
    Keywords: Natural Sciences ; Earth And Related Environmental Sciences ; Oceanography, Hydrology And Water Resources ; Naturvetenskap ; Geovetenskap Och Miljövetenskap ; Oceanografi, Hydrologi Och Vattenresurser
    ISSN: 1932-6203
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  • 5
    In: Freshwater Biology, October 2018, Vol.63(10), pp.1240-1249
    Description: Trophic interactions are important pathways of energy and matter fluxes in food webs and are commonly quantified using stable isotopes of carbon (δ13C) and nitrogen (δ15N). An important prerequisite for this approach is knowledge on the isotopic difference between consumer and resource (trophic discrimination, Δ13C and Δ15N). The range and mechanism causing variation of trophic discrimination factors remain unclear. We conducted a controlled feeding experiment with 13 freshwater benthic invertebrate taxa fed with six resources to test if the C:N, C:P and N:P ratios of consumer, resources and consumer‐resource imbalances are significant predictors of Δ13C and Δ15N. We compiled the available literature on discrimination factors for aquatic invertebrates from controlled feeding experiments and field studies to compare the variation in trophic discrimination. Molar C:N and C:P ratios of resources as well as consumer‐resource imbalances of C:N were significantly related to Δ13C and explained more than 40% of variation of Δ13C, respectively. Resource %N was unrelated to Δ15N, but consumer N:P explained 20% of variation of Δ15N. Our data taken together with the literature compilation provide a mean Δ13C of 0.1‰ (SD = 2.2, N = 157) and a mean Δ15N of 2.6‰ (SD = 2.0, N = 155) for aquatic invertebrates to be used in mixing model analysis for estimating dietary proportions. Our study bridges the currently separated disciplines of stable isotope discrimination and ecological stoichiometry and shows that resource C:N:P and consumer‐resource imbalances are powerful predictors of invertebrate trophic discrimination. Including these stoichiometric predictors into stable isotope mixing models may improve the estimates of the contribution of organic matter sources to the diet of invertebrate consumers. The overall discrimination factors for aquatic invertebrates derived from this study may help to produce precise estimates in trophic ecology if taxon‐specific discrimination factors are unavailable.
    Keywords: Consumer‐Resource Elemental Imbalance ; Ecological Stoichiometry ; Lipids ; Macroinvertebrates ; Stable Isotopes
    ISSN: 0046-5070
    E-ISSN: 1365-2427
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  • 6
    Language: English
    In: Hydrobiologia, 2019, Vol.841(1), p.121(11)
    Description: The role of hydromorphological degradation and temporal variation for food webs in human-modified rivers is still not fully evaluated. We tested the hypothesis that man-made engineering structures alter macroinvertebrate resource use in the Elbe River (Germany) in relation to seasonal variation. Stable isotopes (δ13C, δ15N) and mixing models revealed that dietary contributions of benthic organic matter (BOM) and phytoplankton were driven by engineering structure. Contributions of biofilm were driven by season, while contributions of terrestrial particulate organic matter (t-POM) were driven by both engineering structure and season. Contributions of t-POM were larger than those of phytoplankton in spring and summer, but not in autumn, which adds to the debate about the sources of organic matter fuelling riverine benthic food webs. Resource availability was not systematically related to resource use, indicating that factors other than resource limitation were responsible for the observed results. By demonstrating that human alterations determine consumer resource use independently from resource availability, our study links hydromorphological modifications to fluxes of matter in riverine food webs. Future studies should quantify organic matter fluxes from various autochthonous and allochthonous pathways in human-modified and natural rivers to allow for a robust synthesis of how hydromorphological modifications alter benthic food webs.
    Keywords: Life Sciences ; Freshwater & Marine Ecology ; Ecology ; Zoology ; Elbe River ; Food Web ; Stable Isotopes ; Mixing Model ; Non-Native Species ; River Engineering ; Biology ; Oceanography ; Zoology ; Ecology;
    ISSN: 0018-8158
    E-ISSN: 15735117
    Source: Cengage Learning, Inc.
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  • 7
    Language: English
    In: Aquatic Sciences, 2015, Vol.77(2), pp.307-314
    Description: Stable isotope techniques are widely applied in aquatic food web research to infer trophic position or to estimate the relative contributions of different dietary resources. The accurate consideration of carbon (C) and nitrogen (N) discrimination in organisms is a critical prerequisite for such studies. Isotopic discrimination of invertebrates may differ systematically between temperate and tropical freshwater environments, but there are little data available on discrimination factors of tropical invertebrates. Here, we analyzed the C (Δ 13 C) and N discrimination (Δ 15 N) of eight taxa of benthic freshwater invertebrates from a Southeastern Brazilian tropical catchment, six predator and two shredder species. Predators showed a high variability in Δ 13 C (−1.5 to 1.3; min–max), but shredders exhibited a lower variability and had negative Δ 13 C values (−2.1 to −1.8). Values of Δ 15 N were also highly variable among both predators and shredders, but shredders had negative and lower values (−0.9 to −0.1) than predators (0.0 to 9.1). Tissue turnover rates were equal to or higher than 0.02 d −1 for all invertebrates, suggesting that experiment durations of 50 days may be sufficient for future isotopic discrimination experiments with tropical freshwater invertebrates. Our results suggest that Δ 13 C enrichment, and to a minor degree also Δ 15 N enrichment, may not always occur in tropical freshwater invertebrates.
    Keywords: Carbon and nitrogen fractionation ; Stable isotopes ; Riverine food webs
    ISSN: 1015-1621
    E-ISSN: 1420-9055
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  • 8
    Language: English
    In: Ecosystems (New York. Print), 2016, Vol.19(2), pp.311-325
    Description: Ecosystems are generally linked via fluxes of nutrients and energy across their boundaries. For example, freshwater ecosystems in temperate regions may receive significant inputs of terrestrially derived carbon via autumnal leaf litter. This terrestrial...
    Keywords: Natural Sciences ; Naturvetenskap
    ISSN: 1432-9840
    E-ISSN: 14350629
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