Assessing the ecological integrity after nutrient inputs in streams: the relevance of the descriptor and its associated scale

SABATER, S.; ACUNA, V.; ADONIS GIORGI; GUASCH, H.; GUERRA, E.; MUÑOZ, I.; ROMANI, A.

AQUATIC ECOSYSTEM HEALTH AND MANAGEMENT

Taylor & Francis

Año: 2005 vol. 8 p. 397 - 403

1463-4988

Two different streams receiving high nutrient content were compared in relation to the evidences provided by structural (chlorophyll concentration) and functional (community metabolism) descriptors. The first (Gaià) was an unshaded agricultural stream, where high Net Community Metabolism and chlorophyll concentrations were only modified by flood episodes which caused the sloughing of the benthic community. The second studied stream (Fuirosos) was forested, and an artificial nutrient addition was sustained for 44 days. In this case, the observations expanded also to bacteria and macroinvertebrate, and were compared to a control upstream stretch with low nutrient content.  Even though there was an increase of chlorophyll and algal density because of the nutrient addition, the macroinvertebrate community density as a whole was not affected. Moreover, metabolism (Net Community and Respiration) did not experience significant changes. Therefore, the nutrient addition under light limiting conditions was not causing remarkable effects on the stream functioning. However, the observations during a colonization experiment showed that chlorophyll and bacterial density became similar for the different substrata analyzed (sand, rocks) because of the nutrient addition. It is concluded that chlorophyll, algal communities or macroinvertebrate communities may be accurate descriptors of the effect of nutrients on unshaded streams, but that in shaded streams a more precise time scale is necessary to detect structural effects in the system. These structural changes may be associated with significant modifications of the stream functioning (such as the nutrient retention) in the longer term.