Jesús Pozo | University of the Basque Country, Euskal Herriko Unibertsitatea (original) (raw)
Papers by Jesús Pozo
Annales De Limnologie-international Journal of Limnology, Dec 1, 2003
Methods and materials Study site The Agüera is a third-order stream that drains a small basin (14... more Methods and materials Study site The Agüera is a third-order stream that drains a small basin (144 km 2) located between Cantabria and
International Review of Hydrobiology, Aug 1, 2009
ABSTRACT The aim of our study was to evaluate the effects of Eucalyptus plantations on population... more ABSTRACT The aim of our study was to evaluate the effects of Eucalyptus plantations on population and biochemistry parameters of 3 stream invertebrates. The shredder Echinogammarus spp. had significantly lower densities, proportion of adults and lower accumulation rates of mass, lipid, carbon and nitrogen in eucalypt sites than in native deciduous sites. For the shredder Sericostoma pyrenaicum (Pictet) similar densities were found in both site types, but mass accumulation rate was again lower in eucalypt sites than in the native ones. Contrastingly, density of the collector/grazer Habroleptoides confusa (Sartori and Jacob) was higher in eucalypt sites than in native sites and maximum body length and protein accumulation rate was better explained by soluble reactive phosphorus content in the water than with eucalypt cover. (© 2009 WILEY-VCH Verlag GmbH &amp; Co. KGaA, Weinheim)
Limnetica, Dec 15, 1997
Leaf-litter budgets have been studied in two contrasting forested streams, one flowing under a de... more Leaf-litter budgets have been studied in two contrasting forested streams, one flowing under a deciduous forest and the other one flowing under an Eucalyptus globulus plantation. Inputs (vertical and lateral) of terrestrial CPOM to the streams, and CPOM storage in each stream bed were measured from September 93 to September 94. A model incorporating leaf-litter storage, terrestrial inputs and breakdown rates was applied to study leaf-litter dynamics in both streams. The relative importance of breakdown and transport as proceses affecting the availability of leaf-litter in the stream bed was assessed. Our data suggest that 10-17 % of leaf litter entering these streams annually is processed in place. Significant relationships between organic matter storage and the rate of terrestrial input were found at both cites. However, because of the different timing of leaf fa11 between both forest types, relationships between stream flow and leaf-litter storage were site-dependent. Eucalyptus plantations, together with the hydrologic regime, modify the availability of benthic leaf-litter, the leaf-litter turnover and the ecosystem efficiency.
Hydrobiologia
Detritivores are pivotal in forest streams as they process detritus and promote secondary product... more Detritivores are pivotal in forest streams as they process detritus and promote secondary production. Many studies have addressed the preference of freshwater detritivores towards materials of differing quality. Nevertheless, few studies compare the resource preferences in the laboratory with the availability in the field. In the present study, feeding preferences of two stream detritivores (the caddisfly Sericostoma pyrenaicum and the amphipod Echinogammarus tarragonensis), over three native leaf species (alder, chestnut and oak) and an exotic species (eucalypt) were quantified in the laboratory. Preference for eucalypt leaves conditioned for 1, 2 and 3 weeks was also described. We then contrasted the preference patterns in the laboratory feeding experiments with a 15-month-long benthic standing stock time series of a stream below a native deciduous forest and another below a eucalypt plantation. Both detritivores preferred consuming alder leaves and more conditioned eucalypt leave...
Global Biogeochemical Cycles, 2022
Microbes play a critical role in plant litter decomposition and influence the fate of carbon in r... more Microbes play a critical role in plant litter decomposition and influence the fate of carbon in rivers and riparian zones. When decomposing low‐nutrient plant litter, microbes acquire nitrogen (N) and phosphorus (P) from the environment (i.e., nutrient immobilization), and this process is potentially sensitive to nutrient loading and changing climate. Nonetheless, environmental controls on immobilization are poorly understood because rates are also influenced by plant litter chemistry, which is coupled to the same environmental factors. Here we used a standardized, low‐nutrient organic matter substrate (cotton strips) to quantify nutrient immobilization at 100 paired stream and riparian sites representing 11 biomes worldwide. Immobilization rates varied by three orders of magnitude, were greater in rivers than riparian zones, and were strongly correlated to decomposition rates. In rivers, P immobilization rates were controlled by surface water phosphate concentrations, but N immobil...
Limnetica, 1995
TROPHIC STATE EVALUATION AND COMPARISON OF MODELS RELATED TO PHOSPHORUS IN CERNADlLLA AND VALPARA... more TROPHIC STATE EVALUATION AND COMPARISON OF MODELS RELATED TO PHOSPHORUS IN CERNADlLLA AND VALPARAISO RESERVOIRS (TERA RIVER, ZAMORA) Cernadilla (1965) and Valparaíso (1988) reservoirs, located in the river Tera which is a tributary within the Duero basin (Zamora), are used to produce electric energy and provide irrigation. The trophic state of the headwater reservoir (Cernadilla) has became worse since Valparaíso construction. In 1991, the interna1 phosphorus loading was 120,97 mg TP.m summer in Cernadilla, and 30,92 mg TP.m2 summer in Valparaíso. These estimates were calculated from the increased mass of hypolimnetic phosphorus divided by the surface area of the reservoir. The rates of phosphorus release from anoxic sediment surfaces were 14,40 and 6,2 mg TP.m2 d ', in Cernadilla and Valparaíso respectively. Both reservoirs were classified as mesotrophic in 1991.
Limnetica, 1995
DISSOLVED ORGANIC CARBON IN THE AGUERA STREAM (NORTHERN SPAIN) UNDER HYDOLOGICAL STABILITY COMDIT... more DISSOLVED ORGANIC CARBON IN THE AGUERA STREAM (NORTHERN SPAIN) UNDER HYDOLOGICAL STABILITY COMDITIONS. Concentrations of dissolved organic carbon (DOC) were measured monthly from November 1992 to December 1993 at four sites of the Agüera stream (Northern Spain). Longitudinal differences in DOC seem to be related to the existing urban sewage and environmental disturbances, as well as the self-purifying capacity of the stream. In spite of the human disturbances, concentrations of DOC are low, about 2.9 mg I ' in headwaters and a mid reach, and about 3.6 mg 1.' at sites after human settlements. From a temporal point of view, biological processes seem to be important in regulate the availability of DOC as increases mainly occurred in spring and summer. When concentrations of dissolved organic carbon and suspended particulate organic carbon (POC, fine fraction, < 1 mm) are compared, DOC appears as the main fraction of the transported carbon by the stream, although its relative importance decreases downstream. Our estimates of carbon export to the estuary result in three times more DOC than POC.
Science of The Total Environment, 2019
Science Advances, 2019
An experiment in >1000 river and riparian sites found spatial patterns and controls of carbon ... more An experiment in >1000 river and riparian sites found spatial patterns and controls of carbon processing at the global scale.
Fundamental and Applied Limnology, 1999
We studied the amount, size and dynamics of woody debris in 4 reaches of the Agtiera stream catch... more We studied the amount, size and dynamics of woody debris in 4 reaches of the Agtiera stream catchment (northern Iberian Peninsula) : three sites (lst-, 2nd-and 3rd-order) surrounded by deciduous forests, and one 1st-order site under a plantation of Eucalyptus globulus. From July 1995 to February 1997, on six occasions, all wood pieces larger than 1 cm in diameter were measured; logs (diameter > 5 cm) were tagged and their positions recorded. The volume of wood was relatively low and decreased downstream: 13,700 cm 3 /m 2 at the headwater deciduous site, 490 cm 3 /m 2 in the 2nd order reach, and 100 cm 3 /m 2 in the 3rd-order reach. The woody standing crop at the headwaters within eucalyptus plantations was only 960 cm 3 /m 2 The average size of individual pieces decreased downstream. The mobility of logs was lowest in the head waters: 47 % of the logs tagged in the 1st-order reaches moved during the year, 86 % in the 2nd-order reach, and 76 % in the 3rd-order reach. Te mporal variations were small and associated with sporadic events such as floods or human activities. Mid and low reaches of Basque streams have few old-growth riparian forests, and most fallen logs are removed; this results in low amounts of wood, thus limiting the role of woody debris in organic matter retention or habitat diversity. Similarly, plantations of eucalyptus seem to result in low volume and small size of woody debris in the head waters.
Science of The Total Environment, 2017
River ecosystems are subject to multiple stressors that affect their structure and functioning. E... more River ecosystems are subject to multiple stressors that affect their structure and functioning. Ecosystem structure refers to characteristics such as channel form, water quality or the composition of biological communities, whereas ecosystem functioning refers to processes such as metabolism, organic matter decomposition or secondary production. Structure and functioning respond in contrasting and complementary ways to environmental stressors. Moreover, assessing the response of ecosystem functioning to stressors is critical to understand the effects on the ecosystem services that produce direct benefits to humans. Yet, there is more information on structural than on functional parameters, and despite the many approaches available to measure river ecosystem processes, structural approaches are more widely used, especially in management. One reason for this
Fundamental and Applied Limnology, 2002
Science of The Total Environment, 2016
Four polymers were characterized by MALDI-TOF/MS. • Polycaprolactonediol 1250 polymer was used as... more Four polymers were characterized by MALDI-TOF/MS. • Polycaprolactonediol 1250 polymer was used as probe to assess ecosystem functioning. • Polycaprolactone diol 1250 probes were tested in mesocosoms and in river. • MALDI-TOF/MS spectra reflect changes undergone by probes after exposure.
Microbial Ecology, Jun 2, 2022
Ongoing global warming is expected to alter temperature-dependent processes. Nevertheless, how co... more Ongoing global warming is expected to alter temperature-dependent processes. Nevertheless, how co-occurring local drivers will influence temperature sensitivity of plant litter decomposition in lotic ecosystems remains uncertain. Here, we examined the temperature sensitivity of microbial-mediated decomposition, microbial respiration, fungal biomass and leaf nutrients of two plant species varying in litter quality. We also assessed whether the type of microbial community and stream water characteristics influence such responses to temperature. We incubated alder (Alnus glutinosa) and eucalypt (Eucalyptus globulus) litter discs in three streams differing in autumn-winter water temperature (range 4.6-8.9 °C). Simultaneously, in laboratory microcosms, litter discs microbially conditioned in these streams were incubated at 5, 10 and 15 °C with water from the conditioning stream and with a water control from an additional stream. Both in the field and in the laboratory, higher temperatures enhanced litter decomposition rates, except for eucalypt in the field. Leaf quality modified the response of decomposition to temperature in the field, with eucalypt leaf litter showing a lower increase, whereas it did not in the laboratory. The origin of microbial community only affected the decomposition rates in the laboratory, but it did not modify the response to temperature. Water quality only defined the phosphorus content of the leaf litter or the fungal biomass, but it did not modify the response to temperature. Our results suggest that the acceleration in decomposition by global warming will be shaped by local factors, mainly by leaf litter quality, in headwater streams.
Advances in Ecological Research, 2016
RivFunction is a pan-European initiative that started in 2002 and was aimed at establishing a nov... more 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 100 E. Chauvet et al. 101 Litter Decomposition in European Streams carbon from land-derived allochthonous organic matter, which ultimately also fuel the lower reaches into which the headwaters flow (Hladyz et al., 2011a*; Wallace et al., 1997). The decomposition of this litter is mainly a biological process, driven by microbial decomposers (fungi and bacteria) and macroinvertebrate detritivores (Gessner et al., 1999; Hieber and Gessner, 2002; Webster and Benfield, 1986), and it is highly sensitive to changes in environmental conditions (Ferreira et al., 2015a; Rosemond et al., 2015; Webster and Benfield, 1986). The central role of litter decomposition in streams, which represents the major 'brown pathways' in the food web, means that this process needs to be considered in order to capture and assess the broader ecological status of these ecosystems (Gessner and Chauvet, 2002*). Despite seminal work by Odum (1956), for many years stream ecosystems have been considered mere conduits instead of biologically active ecosystems in their own right (Battin et al., 2009; Raymond et al., 2013). This view is changing and the necessity to incorporate ecosystem functioning into stream assessment and environmental management schemes has become increasingly evident (Christensen et al., 1996; Giller, 2005). The RivFunction initiative developed against this backdrop and evolved into a large-scale EU-funded project that aimed at elaborating a novel methodology for assessing the ecological status of European rivers in functional terms by focusing on leaf litter decomposition as a key ecosystem-level process. The goal was to unravel the relationships between environmental drivers, community structure and litter decomposition in streams at unprecedented scale. This was achieved by conducting coordinated large-scale field experiments and bioassays across Europe (Hladyz et al., 2011a*; Woodward et al., 2012*), as well as smaller-scale field studies and controlled microcosm experiments (e.g. McKie et al., 2008*) within five Workpackages (Fig. 1). Emphasis of the large-scale field studies was on two types of widespread impacts in European streams: pollution by high nutrient inputs and modification of riparian vegetation. Two potential pathways affecting ecosystem functioning as indicated by leaf litter decomposition were examined, where: (i) stressors directly affect the activities of organisms and (ii) shifts in community structure towards species with intrinsically different activity potentials lead to changes in the emergent properties of the community (Fig. 1). The importance of the second pathway was elucidated in microcosm and field experiments, especially by focusing on the diversity of plant litter, fungi and litter-consuming macroinvertebrates as one important aspect of *References marked with an '*' are derived from the RivFunction project.
Annales De Limnologie-international Journal of Limnology, Dec 1, 2003
Methods and materials Study site The Agüera is a third-order stream that drains a small basin (14... more Methods and materials Study site The Agüera is a third-order stream that drains a small basin (144 km 2) located between Cantabria and
International Review of Hydrobiology, Aug 1, 2009
ABSTRACT The aim of our study was to evaluate the effects of Eucalyptus plantations on population... more ABSTRACT The aim of our study was to evaluate the effects of Eucalyptus plantations on population and biochemistry parameters of 3 stream invertebrates. The shredder Echinogammarus spp. had significantly lower densities, proportion of adults and lower accumulation rates of mass, lipid, carbon and nitrogen in eucalypt sites than in native deciduous sites. For the shredder Sericostoma pyrenaicum (Pictet) similar densities were found in both site types, but mass accumulation rate was again lower in eucalypt sites than in the native ones. Contrastingly, density of the collector/grazer Habroleptoides confusa (Sartori and Jacob) was higher in eucalypt sites than in native sites and maximum body length and protein accumulation rate was better explained by soluble reactive phosphorus content in the water than with eucalypt cover. (© 2009 WILEY-VCH Verlag GmbH &amp; Co. KGaA, Weinheim)
Limnetica, Dec 15, 1997
Leaf-litter budgets have been studied in two contrasting forested streams, one flowing under a de... more Leaf-litter budgets have been studied in two contrasting forested streams, one flowing under a deciduous forest and the other one flowing under an Eucalyptus globulus plantation. Inputs (vertical and lateral) of terrestrial CPOM to the streams, and CPOM storage in each stream bed were measured from September 93 to September 94. A model incorporating leaf-litter storage, terrestrial inputs and breakdown rates was applied to study leaf-litter dynamics in both streams. The relative importance of breakdown and transport as proceses affecting the availability of leaf-litter in the stream bed was assessed. Our data suggest that 10-17 % of leaf litter entering these streams annually is processed in place. Significant relationships between organic matter storage and the rate of terrestrial input were found at both cites. However, because of the different timing of leaf fa11 between both forest types, relationships between stream flow and leaf-litter storage were site-dependent. Eucalyptus plantations, together with the hydrologic regime, modify the availability of benthic leaf-litter, the leaf-litter turnover and the ecosystem efficiency.
Hydrobiologia
Detritivores are pivotal in forest streams as they process detritus and promote secondary product... more Detritivores are pivotal in forest streams as they process detritus and promote secondary production. Many studies have addressed the preference of freshwater detritivores towards materials of differing quality. Nevertheless, few studies compare the resource preferences in the laboratory with the availability in the field. In the present study, feeding preferences of two stream detritivores (the caddisfly Sericostoma pyrenaicum and the amphipod Echinogammarus tarragonensis), over three native leaf species (alder, chestnut and oak) and an exotic species (eucalypt) were quantified in the laboratory. Preference for eucalypt leaves conditioned for 1, 2 and 3 weeks was also described. We then contrasted the preference patterns in the laboratory feeding experiments with a 15-month-long benthic standing stock time series of a stream below a native deciduous forest and another below a eucalypt plantation. Both detritivores preferred consuming alder leaves and more conditioned eucalypt leave...
Global Biogeochemical Cycles, 2022
Microbes play a critical role in plant litter decomposition and influence the fate of carbon in r... more Microbes play a critical role in plant litter decomposition and influence the fate of carbon in rivers and riparian zones. When decomposing low‐nutrient plant litter, microbes acquire nitrogen (N) and phosphorus (P) from the environment (i.e., nutrient immobilization), and this process is potentially sensitive to nutrient loading and changing climate. Nonetheless, environmental controls on immobilization are poorly understood because rates are also influenced by plant litter chemistry, which is coupled to the same environmental factors. Here we used a standardized, low‐nutrient organic matter substrate (cotton strips) to quantify nutrient immobilization at 100 paired stream and riparian sites representing 11 biomes worldwide. Immobilization rates varied by three orders of magnitude, were greater in rivers than riparian zones, and were strongly correlated to decomposition rates. In rivers, P immobilization rates were controlled by surface water phosphate concentrations, but N immobil...
Limnetica, 1995
TROPHIC STATE EVALUATION AND COMPARISON OF MODELS RELATED TO PHOSPHORUS IN CERNADlLLA AND VALPARA... more TROPHIC STATE EVALUATION AND COMPARISON OF MODELS RELATED TO PHOSPHORUS IN CERNADlLLA AND VALPARAISO RESERVOIRS (TERA RIVER, ZAMORA) Cernadilla (1965) and Valparaíso (1988) reservoirs, located in the river Tera which is a tributary within the Duero basin (Zamora), are used to produce electric energy and provide irrigation. The trophic state of the headwater reservoir (Cernadilla) has became worse since Valparaíso construction. In 1991, the interna1 phosphorus loading was 120,97 mg TP.m summer in Cernadilla, and 30,92 mg TP.m2 summer in Valparaíso. These estimates were calculated from the increased mass of hypolimnetic phosphorus divided by the surface area of the reservoir. The rates of phosphorus release from anoxic sediment surfaces were 14,40 and 6,2 mg TP.m2 d ', in Cernadilla and Valparaíso respectively. Both reservoirs were classified as mesotrophic in 1991.
Limnetica, 1995
DISSOLVED ORGANIC CARBON IN THE AGUERA STREAM (NORTHERN SPAIN) UNDER HYDOLOGICAL STABILITY COMDIT... more DISSOLVED ORGANIC CARBON IN THE AGUERA STREAM (NORTHERN SPAIN) UNDER HYDOLOGICAL STABILITY COMDITIONS. Concentrations of dissolved organic carbon (DOC) were measured monthly from November 1992 to December 1993 at four sites of the Agüera stream (Northern Spain). Longitudinal differences in DOC seem to be related to the existing urban sewage and environmental disturbances, as well as the self-purifying capacity of the stream. In spite of the human disturbances, concentrations of DOC are low, about 2.9 mg I ' in headwaters and a mid reach, and about 3.6 mg 1.' at sites after human settlements. From a temporal point of view, biological processes seem to be important in regulate the availability of DOC as increases mainly occurred in spring and summer. When concentrations of dissolved organic carbon and suspended particulate organic carbon (POC, fine fraction, < 1 mm) are compared, DOC appears as the main fraction of the transported carbon by the stream, although its relative importance decreases downstream. Our estimates of carbon export to the estuary result in three times more DOC than POC.
Science of The Total Environment, 2019
Science Advances, 2019
An experiment in >1000 river and riparian sites found spatial patterns and controls of carbon ... more An experiment in >1000 river and riparian sites found spatial patterns and controls of carbon processing at the global scale.
Fundamental and Applied Limnology, 1999
We studied the amount, size and dynamics of woody debris in 4 reaches of the Agtiera stream catch... more We studied the amount, size and dynamics of woody debris in 4 reaches of the Agtiera stream catchment (northern Iberian Peninsula) : three sites (lst-, 2nd-and 3rd-order) surrounded by deciduous forests, and one 1st-order site under a plantation of Eucalyptus globulus. From July 1995 to February 1997, on six occasions, all wood pieces larger than 1 cm in diameter were measured; logs (diameter > 5 cm) were tagged and their positions recorded. The volume of wood was relatively low and decreased downstream: 13,700 cm 3 /m 2 at the headwater deciduous site, 490 cm 3 /m 2 in the 2nd order reach, and 100 cm 3 /m 2 in the 3rd-order reach. The woody standing crop at the headwaters within eucalyptus plantations was only 960 cm 3 /m 2 The average size of individual pieces decreased downstream. The mobility of logs was lowest in the head waters: 47 % of the logs tagged in the 1st-order reaches moved during the year, 86 % in the 2nd-order reach, and 76 % in the 3rd-order reach. Te mporal variations were small and associated with sporadic events such as floods or human activities. Mid and low reaches of Basque streams have few old-growth riparian forests, and most fallen logs are removed; this results in low amounts of wood, thus limiting the role of woody debris in organic matter retention or habitat diversity. Similarly, plantations of eucalyptus seem to result in low volume and small size of woody debris in the head waters.
Science of The Total Environment, 2017
River ecosystems are subject to multiple stressors that affect their structure and functioning. E... more River ecosystems are subject to multiple stressors that affect their structure and functioning. Ecosystem structure refers to characteristics such as channel form, water quality or the composition of biological communities, whereas ecosystem functioning refers to processes such as metabolism, organic matter decomposition or secondary production. Structure and functioning respond in contrasting and complementary ways to environmental stressors. Moreover, assessing the response of ecosystem functioning to stressors is critical to understand the effects on the ecosystem services that produce direct benefits to humans. Yet, there is more information on structural than on functional parameters, and despite the many approaches available to measure river ecosystem processes, structural approaches are more widely used, especially in management. One reason for this
Fundamental and Applied Limnology, 2002
Science of The Total Environment, 2016
Four polymers were characterized by MALDI-TOF/MS. • Polycaprolactonediol 1250 polymer was used as... more Four polymers were characterized by MALDI-TOF/MS. • Polycaprolactonediol 1250 polymer was used as probe to assess ecosystem functioning. • Polycaprolactone diol 1250 probes were tested in mesocosoms and in river. • MALDI-TOF/MS spectra reflect changes undergone by probes after exposure.
Microbial Ecology, Jun 2, 2022
Ongoing global warming is expected to alter temperature-dependent processes. Nevertheless, how co... more Ongoing global warming is expected to alter temperature-dependent processes. Nevertheless, how co-occurring local drivers will influence temperature sensitivity of plant litter decomposition in lotic ecosystems remains uncertain. Here, we examined the temperature sensitivity of microbial-mediated decomposition, microbial respiration, fungal biomass and leaf nutrients of two plant species varying in litter quality. We also assessed whether the type of microbial community and stream water characteristics influence such responses to temperature. We incubated alder (Alnus glutinosa) and eucalypt (Eucalyptus globulus) litter discs in three streams differing in autumn-winter water temperature (range 4.6-8.9 °C). Simultaneously, in laboratory microcosms, litter discs microbially conditioned in these streams were incubated at 5, 10 and 15 °C with water from the conditioning stream and with a water control from an additional stream. Both in the field and in the laboratory, higher temperatures enhanced litter decomposition rates, except for eucalypt in the field. Leaf quality modified the response of decomposition to temperature in the field, with eucalypt leaf litter showing a lower increase, whereas it did not in the laboratory. The origin of microbial community only affected the decomposition rates in the laboratory, but it did not modify the response to temperature. Water quality only defined the phosphorus content of the leaf litter or the fungal biomass, but it did not modify the response to temperature. Our results suggest that the acceleration in decomposition by global warming will be shaped by local factors, mainly by leaf litter quality, in headwater streams.
Advances in Ecological Research, 2016
RivFunction is a pan-European initiative that started in 2002 and was aimed at establishing a nov... more 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 100 E. Chauvet et al. 101 Litter Decomposition in European Streams carbon from land-derived allochthonous organic matter, which ultimately also fuel the lower reaches into which the headwaters flow (Hladyz et al., 2011a*; Wallace et al., 1997). The decomposition of this litter is mainly a biological process, driven by microbial decomposers (fungi and bacteria) and macroinvertebrate detritivores (Gessner et al., 1999; Hieber and Gessner, 2002; Webster and Benfield, 1986), and it is highly sensitive to changes in environmental conditions (Ferreira et al., 2015a; Rosemond et al., 2015; Webster and Benfield, 1986). The central role of litter decomposition in streams, which represents the major 'brown pathways' in the food web, means that this process needs to be considered in order to capture and assess the broader ecological status of these ecosystems (Gessner and Chauvet, 2002*). Despite seminal work by Odum (1956), for many years stream ecosystems have been considered mere conduits instead of biologically active ecosystems in their own right (Battin et al., 2009; Raymond et al., 2013). This view is changing and the necessity to incorporate ecosystem functioning into stream assessment and environmental management schemes has become increasingly evident (Christensen et al., 1996; Giller, 2005). The RivFunction initiative developed against this backdrop and evolved into a large-scale EU-funded project that aimed at elaborating a novel methodology for assessing the ecological status of European rivers in functional terms by focusing on leaf litter decomposition as a key ecosystem-level process. The goal was to unravel the relationships between environmental drivers, community structure and litter decomposition in streams at unprecedented scale. This was achieved by conducting coordinated large-scale field experiments and bioassays across Europe (Hladyz et al., 2011a*; Woodward et al., 2012*), as well as smaller-scale field studies and controlled microcosm experiments (e.g. McKie et al., 2008*) within five Workpackages (Fig. 1). Emphasis of the large-scale field studies was on two types of widespread impacts in European streams: pollution by high nutrient inputs and modification of riparian vegetation. Two potential pathways affecting ecosystem functioning as indicated by leaf litter decomposition were examined, where: (i) stressors directly affect the activities of organisms and (ii) shifts in community structure towards species with intrinsically different activity potentials lead to changes in the emergent properties of the community (Fig. 1). The importance of the second pathway was elucidated in microcosm and field experiments, especially by focusing on the diversity of plant litter, fungi and litter-consuming macroinvertebrates as one important aspect of *References marked with an '*' are derived from the RivFunction project.