Urbanisation reduces litter breakdown rates and affects benthic invertebrate structure in Pampean streams

GIORGI, ADONIS; TORREMORELL, ANA; TAGLIAFERRO, MARINA; ALBARIÑO, RICARDO

INTERNATIONAL REVIEW OF HYDROBIOLOGY

WILEY-V C H VERLAG GMBH

Lugar: Weinheim; Año: 2020 vol. 105 p. 33 - 43

1434-2944

The Pampean region became one of the most urbanised areas in South America with more than 91% of the Argentinean population. This region was ideal for human settlement that have historically chosen riverine grassland areas to settle. Consequently, urban streams are increasingly subjected to pressures affecting their functioning. The aim of this study was to assess urbanisation effects on two proxies of stream integrity: leaf litter decay and benthic invertebrate assemblage colonizing litter in streams draining urbanised vs. reference grassland areas. We placed plastic coarse-mesh and fine-mesh bags containing Populus nigra leaf litter along three urban and three reference reaches, which were retrieved periodically to determine remaining leaf mass and the identity and quantity of detritivore assemblage colonizing bags. Decay rate was negatively affected by urbanisation, and it followed a negative relationship with increasing Nitrogen concentration (mostly ammonia) and a hump-shape relationship against soluble reactive phosphorus. Urban invertebrate assemblages were significantly different from reference reaches, and were species-poorer and characterized by tolerant taxa belonging to Naididae, Glossiphoniidae and Nematoda. Hyalellidae, Aeglidae, Chironomidae, Caenidae, Baetidae, and Hydrobiidae represented reference reaches. Our proxies of structural (i.e. invertebrate assemblages) and functional (i.e. leaf litter breakdown) stream integrity were mostly driven by a nutrient enrichment gradient and responded with similar direction but different magnitude to urban alterations.