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- 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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- Johnson, Matthew F., et al.
(författare)
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Accounting for the power of nature: Using flume and field studies to compare the capacities of bio-energy and fluvial energy to move surficial gravels
- 2024
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Ingår i: Earth Surface Processes and Landforms. - : John Wiley & Sons. - 0197-9337 .- 1096-9837.
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Tidskriftsartikel (refereegranskat)abstract
- River channels, riparian and floodplain forms and dynamics are all influenced strongly by biological processes. However, the influence of macroinvertebrates on entrainment and transport of river sediments remains poorly understood. We use an energy-based approach to explore the capacity of benthic animals to move surficial, gravel-bed particles in field and laboratory settings and use the results to assess the relative significance of biological and physical benthic processes. Our results showed that in 11 British gravel-bed rivers, the maximum energy content (i.e., calorific content) of macroinvertebrate communities generally matched the flow energy associated with median discharges and, at multiple sites, exceeded that of the 10-year return interval flood. A series of laboratory experiments used to estimate the minimum energy expended by signal crayfish (Pacifastacus leniusculus) when performing geomorphic work established that crayfish move gravel particles at energy levels below that expected of the flow, complicating direct comparisons of the capacity for macroinvertebrates and fluvial flows to influence bed mobility. Our findings suggest that the influence of macroinvertebrate communities in either promoting or suppressing, the mobilisation of the bed may be large compared to equivalent values of fluvial energy. Based on these findings, we conclude that in the gravel-bed rivers studied, the macroinvertebrate community's potential to perform geomorphic work matches or exceeds the stream power during most of the year. Although our study examined biological and fluvial energy systems separately, it is important to recognise that in nature, these systems are highly interactive. It follows that utilising the energy framework presented in this paper could lead to rapid advances in both fluvial biogeomorphology and river management and restoration.
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- Pilotto, Francesca, et al.
(författare)
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Diversification of stream invertebrate communities by large wood
- 2014
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Ingår i: Freshwater Biology. - : John Wiley & Sons. - 0046-5070 .- 1365-2427. ; 59:12, s. 2571-2583
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Tidskriftsartikel (refereegranskat)abstract
- To evaluate the effects of large wood (LW) on benthic habitats and macroinvertebrates in sand-bed lowland rivers, we compared invertebrate communities recorded on four pieces of LW (12 samples in total) and around them (60 samples) with those in four control sites in the same river (four samples). Mean flow velocity was 32% lower in the channel areas surrounding the LW than in control sites, while median sediment grain size was 50% higher, and the organic matter content of the riverbed sediments was 287% higher. At the same time, habitat conditions showed threefold to 1000-fold increases in variance for five key abiotic habitat descriptors in the surrounding channel extending at least 60 cm upstream and 160 cm downstream of the LW. Three habitat patches typically occurred around the LW pieces: scouring pools, sand bars and accumulations of organic matter. These patches were colonised by distinctive invertebrate communities (e.g. accumulations of organic matter and gravel hosted 15 and 2 indicator taxa, respectively) that overall harboured 110% more taxa and exhibited a 168% higher diversity than control sites. The LW itself contributed only a small fraction to these increases, exhibiting a 15% increase in taxa richness and a 21% increase in species diversity compared to the control sites. The diversification of benthic invertebrate communities colonising streambed sediments around LW could be directly linked to the much more heterogeneous habitat conditions recorded there. Thus, local additions of large wood within river restoration programmes have the potential to promote the establishment of diverse invertebrate communities in extended areas of a river channel.
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| 5. |
- 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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