1. |
- Chauvet, Eric, et al.
(author)
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Litter decomposition as an indicator of stream ecosystem functioning at local-to-continental scales : insights from the European RivFunction project
- 2016
-
In: Large-scale ecology. - London : Academic Press. - 9780081009352 ; 55, s. 99-182
-
Book chapter (peer-reviewed)abstract
- RivFunction is a pan-European initiative that started in 2002 and was aimed at establishing a novel functional-based approach to assessing the ecological status of rivers. Litter decomposition was chosen as the focal process because it plays a central role in stream ecosystems and is easy to study in the field. Impacts of two stressors that occur across the continent, nutrient pollution and modified riparian vegetation, were examined at > 200 paired sites in nine European ecoregions. In response to the former, decomposition was dramatically slowed at both extremes of a 1000-fold nutrient gradient, indicating nutrient limitation in unpolluted sites, highly variable responses across Europe in moderately impacted streams, and inhibition via associated toxic and additional stressors in highly polluted streams. Riparian forest modification by clear cutting or replacement of natural vegetation by plantations (e.g. conifers, eucalyptus) or pasture produced similarly complex responses. Clear effects caused by specific riparian disturbances were observed in regionally focused studies, but general trends across different types of riparian modifications were not apparent, in part possibly because of important indirect effects. Complementary field and laboratory experiments were undertaken to tease apart the mechanistic drivers of the continental scale field bioassays by addressing the influence of litter, fungal and detritivore diversity. These revealed generally weak and context-dependent effects on decomposition, suggesting high levels of redundancy (and hence potential insurance mechanisms that can mitigate a degree of species loss) within the food web. Reduced species richness consistently increased decomposition variability, if not the absolute rate. Further field studies were aimed at identifying important sources of this variability (e.g. litter quality, temporal variability) to help constrain ranges of predicted decomposition rates in different field situations. Thus, although many details still need to be resolved, litter decomposition holds considerable potential in some circumstances to capture impairment of stream ecosystem functioning. For instance, species traits associated with the body size and metabolic capacity of the consumers were often the main driver at local scales, and these were often translated into important determinants of otherwise apparently contingent effects at larger scales. Key insights gained from conducting continental scale studies included resolving the apparent paradox of inconsistent relationships between nutrients and decomposition rates, as the full complex multidimensional picture emerged from the large-scale dataset, of which only seemingly contradictory fragments had been seen previously.
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2. |
- Chauvet, Eric, et al.
(author)
-
Litter decomposition as an indicator of stream ecosystem functioning at local-to-continental scales : insights from the European RivFunction project
- 2016
-
In: Large-scale ecology. - London : Academic Press. ; 55, s. 99-182
-
Book chapter (pop. science, debate, etc.)abstract
- RivFunction is a pan-European initiative that started in 2002 and was aimed at establishing a novel functional-based approach to assessing the ecological status of rivers. Litter decomposition was chosen as the focal process because it plays a central role in stream ecosystems and is easy to study in the field. Impacts of two stressors that occur across the continent, nutrient pollution and modified riparian vegetation, were examined at > 200 paired sites in nine European ecoregions. In response to the former, decomposition was dramatically slowed at both extremes of a 1000-fold nutrient gradient, indicating nutrient limitation in unpolluted sites, highly variable responses across Europe in moderately impacted streams, and inhibition via associated toxic and additional stressors in highly polluted streams. Riparian forest modification by clear cutting or replacement of natural vegetation by plantations (e.g. conifers, eucalyptus) or pasture produced similarly complex responses. Clear effects caused by specific riparian disturbances were observed in regionally focused studies, but general trends across different types of riparian modifications were not apparent, in part possibly because of important indirect effects. Complementary field and laboratory experiments were undertaken to tease apart the mechanistic drivers of the continental scale field bioassays by addressing the influence of litter, fungal and detritivore diversity. These revealed generally weak and context-dependent effects on decomposition, suggesting high levels of redundancy (and hence potential insurance mechanisms that can mitigate a degree of species loss) within the food web. Reduced species richness consistently increased decomposition variability, if not the absolute rate. Further field studies were aimed at identifying important sources of this variability (e.g. litter quality, temporal variability) to help constrain ranges of predicted decomposition rates in different field situations. Thus, although many details still need to be resolved, litter decomposition holds considerable potential in some circumstances to capture impairment of stream ecosystem functioning. For instance, species traits associated with the body size and metabolic capacity of the consumers were often the main driver at local scales, and these were often translated into important determinants of otherwise apparently contingent effects at larger scales. Key insights gained from conducting continental scale studies included resolving the apparent paradox of inconsistent relationships between nutrients and decomposition rates, as the full complex multidimensional picture emerged from the large-scale dataset, of which only seemingly contradictory fragments had been seen previously.
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3. |
- Hladyz, Sally, et al.
(author)
-
Stream ecosystem functioning in an agricultural landscape : the importance of terrestrial-aquatic linkages
- 2011
-
In: Ecosystems in a human-modified landscape. - San Diego : Academic Press. - 9780123747945 ; 44, s. 211-276
-
Book chapter (peer-reviewed)abstract
- The loss of native riparian vegetation and its replacement with non-native species or grazing land for agriculture is a worldwide phenomenon, but one that is prevalent in Europe, reflecting the heavily-modified nature of the continent's landscape. The consequences of these riparian alterations for freshwater ecosystems remain largely unknown, largely because bioassessment has traditionally focused on the impacts of organic pollution on community structure. We addressed the need for a broader perspective, which encompasses changes at the catchment scale, by comparing ecosystem processes in woodland reference sites with those with altered riparian zones. We assessed a range of riparian modifications, including clearance for pasture and replacement of woodland with a range of low diversity plantations, in 100 streams to obtain a continental-scale perspective of the major types of alterations across Europe. Subsequently, we focused on pasture streams, as an especially prevalent widespread riparian alteration, by characterising their structural (e.g. invertebrate and fish communities) and functional (e.g. litter decomposition, algal production, herbivory) attributes in a country (Ireland) dominated by this type of landscape modification, via field and laboratory experiments. We found that microbes became increasingly important as agents of decomposition relative to macrofauna (invertebrates) in impacted sites in general and in pasture streams in particular. Resource quality of grass litter (e.g., carbon : nutrient ratios, lignin and cellulose content) was a key driver of decomposition rates in pasture streams. These systems also relied more heavily on autochthonous algal production than was the case in woodland streams, which were more detrital based. These findings suggest that these pasture streams might be fundamentally different from their native, ancestral woodland state, with a shift towards greater reliance on autochthonous-based processes. This could have a destabilizing effect on the dynamics of the food web relative to the slower, detrital-based pathways that dominate in woodland streams.
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4. |
- McKie, Brendan, et al.
(author)
-
Ecosystem functioning in stream assemblages from different regions : contrasting responses to variation in detritivore richness, evenness and density.
- 2008
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In: Journal of Animal Ecology. - : Wiley. - 1365-2656 .- 0021-8790. ; 77:3, s. 495-504
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Journal article (peer-reviewed)abstract
- 1. The diversity of species traits characterising a biological assemblage reflects not only its species richness but also its species evenness and total density, which together influence the concentration of traits within functional guilds, and is ultimately constrained by the regional species pool. Implications of such variation for spatio-temporal variability in biodiversity-ecosystem functioning relationships are potentially complex, but poorly understood.2. In separate microcosm experiments maintained at laboratories in Sweden, Romania and Ireland, we investigated effects of the species richness, evenness and density of stream-living detritivores on two related processes: detritivore leaf processing efficiency (LPE) and growth. Assemblage composition varied among the laboratories, with only one taxonomic order (Plecoptera) investigated in Sweden, whereas two orders, encompassing wider trait variation, were studied in Romania (Trichoptera and Plecoptera) and Ireland (Trichoptera and Isopoda).3. Relationships between density and both LPE and growth ranged from negative to positive across all the study species, highlighting the potential for density-dependent variation in process rates to alter ecosystem functioning, but indicating that such effects vary with species identity.4. Increased diversity was associated with 25-50% higher LPE in the two more heterogeneous assemblages, but whereas LPE in the Romanian study was generally enhanced as richness increased, LPE in the Irish study only increased in less even species mixtures dominated by particular species. Mechanisms underlying these diversity effects also contrasted. The Romanian results were predominantly attributable to the selection effect, whereas there was evidence for positive complementarity among species in Ireland.5. Growth was elevated in Romanian species mixtures, reflecting positive complementarity among species, but lower than expected growth in some Swedish mixtures was associated with negative complementarity.6. Our results emphasize the potential importance of detritivore diversity for stream ecosystem functioning across multiple contrasting assemblages, but variability in both the effects of diversity on the studied processes, and the mechanisms underlying those effects, highlight challenges in generalizing impacts of diversity change for the functional integrity of naturally dynamic stream ecosystems in situ.
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5. |
- Woodward, Guy, et al.
(author)
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Continental-scale effects of nutrient pollution on stream ecosystem functioning
- 2012
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In: Science. - : American Association for the Advancement of Science. - 0036-8075 .- 1095-9203. ; 336:6087, s. 1438-1440
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Journal article (peer-reviewed)abstract
- Excessive nutrient loading is a major threat to aquatic ecosystems worldwide that leads to profound changes in aquatic biodiversity and biogeochemical processes. Systematic quantitative assessment of functional ecosystem measures for river networks is, however, lacking, especially at continental scales. Here, we narrow this gap by means of a pan-European field experiment on a fundamental ecosystem process—leaf-litter breakdown—in 100 streams across a greater than 1000-fold nutrient gradient. Dramatically slowed breakdown at both extremes of the gradient indicated strong nutrient limitation in unaffected systems, potential for strong stimulation in moderately altered systems, and inhibition in highly polluted streams. This large-scale response pattern emphasizes the need to complement established structural approaches (such as water chemistry, hydrogeomorphology, and biological diversity metrics) with functional measures (such as litter-breakdown rate, whole-system metabolism, and nutrient spiraling) for assessing ecosystem health.
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6. |
- Hladyz, Sally, et al.
(author)
-
Impacts of an aggressive riparian invader on community structure and ecosystem functioning in stream food webs
- 2011
-
In: Journal of Applied Ecology. - : Wiley. - 1365-2664 .- 0021-8901. ; 48:2, s. 443-452
-
Journal article (peer-reviewed)abstract
- P>1. Bioassessment in running waters has focused primarily on the impacts of organic pollution on community structure. Other stressors (e.g. invasive species) and impacts on ecosystem processes have been largely ignored in many riverine biomonitoring schemes, despite being required increasingly by environmental legislation. 2. Exotic riparian plants can exert potentially powerful stresses by altering both autochthonous and allochthonous trophic pathways. We examined the impact of Rhododendron ponticum on community structure and three key ecosystem processes (decomposition, primary production, and herbivory) in nine streams bordered by three characteristic vegetation types (deciduous woodland, pasture, or Rhododendron). 3. Community structure and ecosystem process rates differed among vegetation types, with autochthonous pathways being relatively more important in the pasture streams than in the woodland reference streams. Overall ecosystem functioning, however, was compromised in the invaded streams because both allochthonous and autochthonous inputs were impaired. Rhododendron's poor quality litter and densely shaded canopy suppressed decomposition rates and algal production, and the availability of resources to consumer assemblages. 4. Synthesis and applications. Combining measures of invertebrate abundance, rates of litter decomposition and algal production in future bioassessments of stream ecosystem functioning can help to make better informed management decisions and to develop more focused priorities for mediating the negative effects of riparian invasions. We provide a series of specific recommendations for dealing with invasive riparian plants in general, and Rhododendron in particular, in order to minimize their impacts on stream ecosystems. For instance, where the invader produces poor quality litter the canopy should be kept as open as possible over the stream channel to reduce impacts on algal production, thereby retaining alternative food chains that can be exploited by generalist consumers in the absence of viable detrital resources.
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7. |
- Hladyz, Sally, et al.
(author)
-
Stream ecosystem functioning in an agricultural landscape : the importance of terrestrial-aquatic linkages
- 2011
-
In: Ecosystems in a human-modified landscape. - San Diego : Academic Press. - 9780123747945 ; 44, s. 211-276
-
Book chapter (pop. science, debate, etc.)abstract
- The loss of native riparian vegetation and its replacement with non-native species or grazing land for agriculture is a worldwide phenomenon, but one that is prevalent in Europe, reflecting the heavily-modified nature of the continent's landscape. The consequences of these riparian alterations for freshwater ecosystems remain largely unknown, largely because bioassessment has traditionally focused on the impacts of organic pollution on community structure. We addressed the need for a broader perspective, which encompasses changes at the catchment scale, by comparing ecosystem processes in woodland reference sites with those with altered riparian zones. We assessed a range of riparian modifications, including clearance for pasture and replacement of woodland with a range of low diversity plantations, in 100 streams to obtain a continental-scale perspective of the major types of alterations across Europe. Subsequently, we focused on pasture streams, as an especially prevalent widespread riparian alteration, by characterising their structural (e.g. invertebrate and fish communities) and functional (e.g. litter decomposition, algal production, herbivory) attributes in a country (Ireland) dominated by this type of landscape modification, via field and laboratory experiments. We found that microbes became increasingly important as agents of decomposition relative to macrofauna (invertebrates) in impacted sites in general and in pasture streams in particular. Resource quality of grass litter (e.g., carbon : nutrient ratios, lignin and cellulose content) was a key driver of decomposition rates in pasture streams. These systems also relied more heavily on autochthonous algal production than was the case in woodland streams, which were more detrital based. These findings suggest that these pasture streams might be fundamentally different from their native, ancestral woodland state, with a shift towards greater reliance on autochthonous-based processes. This could have a destabilizing effect on the dynamics of the food web relative to the slower, detrital-based pathways that dominate in woodland streams.
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