| 1. |
- Cashman, Matthew J., et al.
(författare)
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Combined stable-isotope and fatty-acid analyses demonstrate that large wood increases the autochthonous trophic base of a macroinvertebrate assemblage
- 2016
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Ingår i: Freshwater Biology. - : Wiley. - 0046-5070 .- 1365-2427. ; 61:4, s. 549-564
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Tidskriftsartikel (refereegranskat)abstract
- Large wood (LW), defined as pieces of wood greater than 10 cm in diameter and 1 m long, is well known to alter river hydromorphology and the availability of potential food resources for consumers. However, there has been a lack of studies investigating whether these can cause shifts in the trophic base, which may explain alterations to the total abundance and taxonomic structure of the macroinvertebrate assemblage. We aimed to determine how the presence of LW altered the trophic base of the macroinvertebrate consumer assemblage in a lowland river, and to provide a methodological comparison of two assimilation-based food web methods: stable-isotope analysis (SIA) and fatty-acid biomarker profiles (FA). To do so, we quantified the contribution of trophic resources to the diets of macroinvertebrates colonising the surface of LW, present in this study as single logs, and surrounding bed sediments with those from bed sediments of a nearby control site with minimal amounts of LW. SIA showed that the macroinvertebrate food web, even for non-filter feeding taxa, was mostly sustained by seston exported from a lake 1 km upstream, highlighting a high degree of lake-river coupling. The presence of wood altered the trophic base from being predominantly seston-supported to one with increased support from epixylic autochthonous production (i.e. periphyton and bryophytes on wood). Terrestrial matter (i.e. leaves and grass) and organic sediments were a relatively unimportant fraction of the trophic base (\textless10%) in all locations. FA did not directly track the influence of seston, but instead differentiated between overall allochthonous (terrestrial) and autochthonous (aquatic) components of the trophic base. In particular, FA analysis demonstrated the higher nutritional value of autochthonous primary producers, and provided supporting evidence that most consumers, even seston-feeders, were primarily supported by autochthonous resources and not by allochthonous matter. FA indicated shifts in some taxa-specific diets not detected by stable isotopes alone. Our study demonstrated that the combined use of stable isotopes and fatty acids provides new insights into determining the trophic base of a complex food web with trophic resources of both terrestrial/aquatic and lacustrine/riverine origins. In addition, directly comparing results from both stable-isotope and fatty-acid analyses provided additional information on selective feeding by seston-feeding taxa on autochthonous and allochthonous fractions of the seston. The presence of LW in the river channel decreased lake-river coupling by providing alternative basal resources, primarily through increasing high-quality autochthonous production on wood and by providing a superior substratum for net-spinning caddisflies to feed on a fraction of the seston richer in essential fatty acids. River management strategies that incorporate instream LW therefore have the potential to alter energy flows and enhance ecosystem productivity by increasing the quantity and quality of available basal food resources.
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| 2. |
- Pilotto, Francesca, et al.
(författare)
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Simple large wood structures promote hydromorphological heterogeneity and benthic macroinvertebrate diversity in low-gradient rivers
- 2016
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Ingår i: Aquatic Sciences. - : Springer Science and Business Media LLC. - 1015-1621 .- 1420-9055. ; 78:4, s. 755-766
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Tidskriftsartikel (refereegranskat)abstract
- The presence of large wood (LW) in river channels adds an important habitat feature for benthic macroinvertebrates. However, there has been a lack of studies focusing on the effects of simple wood structures on hydromorphology and macroinvertebrate diversity in surrounding channel areas. This study explores whether consistent patterns in LW-related benthic habitat complexity and macroinvertebrate diversity can be identified across a set of low-gradient streams dominated by fine sediments. While the presence of LW did not change the average values of standard hydromorphological variables (flow velocity, turbulence, median sediment grain size and sorting index), the coefficients of variation of such variables for wood rich sites were consistently higher than those for wood poor sites (velocity: 85 % higher, turbulence: 89 %, grain size: 126 %, sorting index: 67 % higher). In parallel, beta diversity was on average 31 % higher in the wood rich sites, and positively correlated with the amount of LW at the site. The hotspots of local (alpha) diversity were located in the river-bed areas surrounding the LW, where taxonomic richness was 83 % higher and Shannon-Wiener diversity 39 % higher compared to the sites with less wood. These results demonstrate that the presence of LW in sandy lowland rivers induces consistent patterns of increased spatial variability of benthic habitats in the surrounding channel areas and this significantly enhances alpha and beta diversity of macroinvertebrate communities. Therefore, LW should be conserved in river channels wherever possible, and its potential for introduction into degraded systems should be explored further because even simple pieces of LW introduced to lowland streams can deliver benefits.
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