Global pressures, specific responses: effects of nutrient enrichment in streams from different biomes

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Global pressures, specific responses: effects of nutrient enrichment in streams from different biomes
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We assessed the effects of nutrient enrichment on three stream ecosystems running through distinct biomes (Mediterranean, Pampean and Andean). We increased the concentrations of N and P in the stream water 1.6–4-fold following a before–after control–impact paired series (BACIPS) design in each stream, and evaluated changes in the biomass of bacteria, primary producers, invertebrates and fish in the enriched (E) versus control (C) reaches after nutrient addition through a predictive-BACIPS approach. The treatment produced variable biomass responses (2–77% of explained variance) among biological communities and streams. The greatest biomass response was observed for algae in the Andean stream (77% of the variance), although fish also showed important biomass responses (about 9–48%). The strongest biomass response to enrichment (77% in all biological compartments) was found in the Andean stream. The magnitude and seasonality of biomass responses to enrichment were highly site specific, often depending on the basal nutrient concentration and on windows of ecological opportunity (periods when environmental constraints other than nutrients do not limit biomass growth). The Pampean stream, with high basal nutrient concentrations, showed a weak response to enrichment (except for invertebrates), whereas the greater responses of Andean stream communities were presumably favored by wider windows of ecological opportunity in comparison to those from the Mediterranean stream. Despite variation among sites, enrichment globally stimulated the algal-based food webs (algae and invertebrate grazers) but not the detritus-based food webs (bacteria and invertebrate shredders). This study shows that nutrient enrichment tends to globally enhance the biomass of stream biological assemblages, but that its magnitude and extent within the food web are complex and are strongly determined by environmental factors and ecosystem structure.
Specific weight Isotope separation Video Pressure Electric power distribution Global warming Effects unit
Day Neutronenaktivierung
Energy level
Constraint (mathematics)
Concentrator Temperaturabhängiger Widerstand
Turning Controller (control theory)
Astronomisches Fenster
Impact event Temperature Constraint (mathematics) Light
Temperature Orbital period Spring (season)
Isotope separation Concentrator Short circuit Astronomisches Fenster Light Wire
Isotope separation Year Angeregter Zustand
Isotope separation Apparent magnitude Cardinal direction Crystal structure Mediterranean climate
the day the in the end
human activities are resulting in global
environmental change 1 of the most worrying trends is an increasing nutrient
content worldwide you right from
agricultural fertilizers and urban waste water higher nutrient
levels threaten freshwater erectus
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availability in the Mediterranean stream is loud throughout the year except in a
short period in the spring before the leave that during the right area forest as a
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assistance to nutrient enrichment was higher specific the strongest biomass
responses acute in Gandhi's framed as a result of wire windows of opportunity the weakest independently and where the basal nutrient concentrations were already high in the Mediterranean the response was limited to short temporal windows of light availability and the
seasonality of biomass response was also highly specific algae for
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