Table S2. Identification, levels and description of moderator variables used in this review Moderator variable *
Levels
Description
Study reference
Several
References can be found in Appendix S1.
Year
Several
Publication year.
Study type
Field
Study in the field.
Laboratory
Study in the laboratory.
Correlative
Correlative study over a gradient of nutrient concentrations already existing in the field.
Manipulative
Manipulative study with experimental nutrient enrichment.
Catchment
Manipulative field study in which experimental nutrient enrichment is made to the entire catchment by addition of dry ammonium sulphate (Chadwick & Huryn, 2003).
Stream
Manipulative field study in which experimental nutrient enrichment is made to the whole stream by dripping a nutrient solution (e.g. Ferreira et al., 2006).
Side channel
Manipulative field study in which experimental nutrient enrichment is made to artificial stream side channels by dripping a nutrient solution (e.g. Piggott et al., 2012).
Bag
Manipulative field study in which experimental nutrient enrichment is made inside or near the mesh bag used to incubate the litter using nutrient-diffusing substrates (e.g. McKie et al., 2009).
N
Nutrient added in field manipulative studies: N only (e.g. Ferreira et al., 2006).
P
Nutrient added in field manipulative studies: P only (e.g. Ardón et al., 2006).
Both
Nutrient added in field manipulative studies: N and P (e.g. Gulis & Suberkropp, 2003c).
Leaves
Leaves from angiosperm species (includes entire leaves or leaf discs) and needles from gymnosperm species.
Wood
Wood; includes bark, twigs, veneers, and toothpicks.
Several
Litter genus.
Field type
Manipulation type
Nutrient added
Litter type
Litter identity
1 of 3
Aquatic community type
Microbial
Litter was enclosed in fine mesh bags (≤ 0.5 mm mesh), which excludes macroinvertebrates (organisms > 0.5 mm), and therefore litter decomposition was mainly carried out by the microbial community (e.g. Gulis et al., 2006). Litter might also have been incubated in coarse mesh bags (> 0.5 mm mesh) but the incubation procedure excluded macroinvertebrates (Li, 2011; Pearson & Connolly, 2000; Spänhoff et al., 2007a; Suberkropp & Chauvet, 1995).
Total
Litter was enclosed in coarse mesh bags (> 0.5 mm mesh) or assembled as litter packs (no mesh), which allows the access of macroinvertebrates to the litter, and therefore litter decomposition was potentially carried out by both microbial and invertebrate communities (e.g. Gulis et al, 2006). Litter might also have been incubated in fine mesh bags (≤ 0.5 mm mesh), where macroinvertebrates were experimentally enclosed (McKie et al., 2009).
Cold
Cold regions include polar (> 66.32º), boreal (59º– 66.32º) and alpine areas.
Temperate
Temperate regions between 23.5º and 59º, including Mediterranean areas.
Tropical
Tropical regions between the Tropic of Cancer and the Tropic of Capricorn, 23.5ºN – 23.5ºS.
Mean DIN concentration in REF
Continuous
Mean DIN concentration in REF (µg l ); when the primary study did not report DIN this was calculated as NO3-N+NO2-N+NH4-N. However, in many papers NO2-N and/or NH4-N were not reported and therefore DIN = NO3-N, DIN = NO3-N+NO2-N or DIN = NO3-N+NH4-N; this was based on the assumption that NO3 was the main contributor to DIN.
Mean SRP concentration in REF
Continuous
Mean PO4-P or SRP concentration in REF (µg l ); SRP ~ PO4-P.
Proportional increase in DIN
Continuous
Magnitude of the increase in DIN in NUT versus REF: (DIN in NUT – DIN in REF)/DIN in REF.
Proportional increase in SRP
Continuous
Magnitude of the increase in SRP in NUT versus REF: (SRP in NUT – SRP in REF)/SRP in REF.
Literature type
Mainstream
Studies published in indexed journals.
Grey literature
Unpublished studies (V. Gulis, V. Ferreira & M. A. S. Graça, unpublished) or studies reported in thesis or reports (e.g. Fernandes, 2011; Geraldes, 2011; Young, 2007).
Reported
Litter decomposition was reported as exponential decomposition rate per day (k, d ) and variation was reported as standard deviation (S.D.) in the primary studies or supplied by the authors after contact. –1 Exponential decomposition rates per day (k, d ) and standard deviation (S.D.) were estimated from data available in the primary studies or requested from the authors.
Climate
Origin of values
Estimated
–1
–1
–1
2 of 3
N: nitrogen; P: phosphorus; DIN: dissolved inorganic nitrogen; SRP: soluble reactive phosphorus; REF: reference condition; NUT: nutrient-enriched condition. * Some potentially important moderator variables were not included in the analyses because information was available only for a few cases or because there was not enough variability between moderator (e.g. type of N compound added in manipulative studies, duration of incubation, initial litter N concentration, initial litter lignin concentration, initial litter C/N ratio, latitude or stream order) levels to render the analysis meaningful.
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Levels
Description
Study reference
Several
References can be found in Appendix S1.
Year
Several
Publication year.
Study type
Field
Study in the field.
Laboratory
Study in the laboratory.
Correlative
Correlative study over a gradient of nutrient concentrations already existing in the field.
Manipulative
Manipulative study with experimental nutrient enrichment.
Catchment
Manipulative field study in which experimental nutrient enrichment is made to the entire catchment by addition of dry ammonium sulphate (Chadwick & Huryn, 2003).
Stream
Manipulative field study in which experimental nutrient enrichment is made to the whole stream by dripping a nutrient solution (e.g. Ferreira et al., 2006).
Side channel
Manipulative field study in which experimental nutrient enrichment is made to artificial stream side channels by dripping a nutrient solution (e.g. Piggott et al., 2012).
Bag
Manipulative field study in which experimental nutrient enrichment is made inside or near the mesh bag used to incubate the litter using nutrient-diffusing substrates (e.g. McKie et al., 2009).
N
Nutrient added in field manipulative studies: N only (e.g. Ferreira et al., 2006).
P
Nutrient added in field manipulative studies: P only (e.g. Ardón et al., 2006).
Both
Nutrient added in field manipulative studies: N and P (e.g. Gulis & Suberkropp, 2003c).
Leaves
Leaves from angiosperm species (includes entire leaves or leaf discs) and needles from gymnosperm species.
Wood
Wood; includes bark, twigs, veneers, and toothpicks.
Several
Litter genus.
Field type
Manipulation type
Nutrient added
Litter type
Litter identity
1 of 3
Aquatic community type
Microbial
Litter was enclosed in fine mesh bags (≤ 0.5 mm mesh), which excludes macroinvertebrates (organisms > 0.5 mm), and therefore litter decomposition was mainly carried out by the microbial community (e.g. Gulis et al., 2006). Litter might also have been incubated in coarse mesh bags (> 0.5 mm mesh) but the incubation procedure excluded macroinvertebrates (Li, 2011; Pearson & Connolly, 2000; Spänhoff et al., 2007a; Suberkropp & Chauvet, 1995).
Total
Litter was enclosed in coarse mesh bags (> 0.5 mm mesh) or assembled as litter packs (no mesh), which allows the access of macroinvertebrates to the litter, and therefore litter decomposition was potentially carried out by both microbial and invertebrate communities (e.g. Gulis et al, 2006). Litter might also have been incubated in fine mesh bags (≤ 0.5 mm mesh), where macroinvertebrates were experimentally enclosed (McKie et al., 2009).
Cold
Cold regions include polar (> 66.32º), boreal (59º– 66.32º) and alpine areas.
Temperate
Temperate regions between 23.5º and 59º, including Mediterranean areas.
Tropical
Tropical regions between the Tropic of Cancer and the Tropic of Capricorn, 23.5ºN – 23.5ºS.
Mean DIN concentration in REF
Continuous
Mean DIN concentration in REF (µg l ); when the primary study did not report DIN this was calculated as NO3-N+NO2-N+NH4-N. However, in many papers NO2-N and/or NH4-N were not reported and therefore DIN = NO3-N, DIN = NO3-N+NO2-N or DIN = NO3-N+NH4-N; this was based on the assumption that NO3 was the main contributor to DIN.
Mean SRP concentration in REF
Continuous
Mean PO4-P or SRP concentration in REF (µg l ); SRP ~ PO4-P.
Proportional increase in DIN
Continuous
Magnitude of the increase in DIN in NUT versus REF: (DIN in NUT – DIN in REF)/DIN in REF.
Proportional increase in SRP
Continuous
Magnitude of the increase in SRP in NUT versus REF: (SRP in NUT – SRP in REF)/SRP in REF.
Literature type
Mainstream
Studies published in indexed journals.
Grey literature
Unpublished studies (V. Gulis, V. Ferreira & M. A. S. Graça, unpublished) or studies reported in thesis or reports (e.g. Fernandes, 2011; Geraldes, 2011; Young, 2007).
Reported
Litter decomposition was reported as exponential decomposition rate per day (k, d ) and variation was reported as standard deviation (S.D.) in the primary studies or supplied by the authors after contact. –1 Exponential decomposition rates per day (k, d ) and standard deviation (S.D.) were estimated from data available in the primary studies or requested from the authors.
Climate
Origin of values
Estimated
–1
–1
–1
2 of 3
N: nitrogen; P: phosphorus; DIN: dissolved inorganic nitrogen; SRP: soluble reactive phosphorus; REF: reference condition; NUT: nutrient-enriched condition. * Some potentially important moderator variables were not included in the analyses because information was available only for a few cases or because there was not enough variability between moderator (e.g. type of N compound added in manipulative studies, duration of incubation, initial litter N concentration, initial litter lignin concentration, initial litter C/N ratio, latitude or stream order) levels to render the analysis meaningful.
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