Lentic-lotic character

CNR-IRSA activities related to INHABIT

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Lentic-lotic character

Hydraulic and morphological features are crucial in structuring the habitats of aquatic organisms in rivers. The importance of hydraulic conditions in influencing freshwater biotic communities at the site scale is historically recognized by the scientific community. Water depth, velocity, turbulence, shear stress and flow types are among the major hydraulic parameters affecting biota distribution, along with channel substrate which obviously affects invertebrates, fish and macrophyte distribution
More recently, physical variables such as flow conditions, depth and substrate type have been considered as central to river management practices and a renewed accent is therefore being placed on describing or modelling the hydraulic preferences of benthic macroinvertebrates. It should be stressed however, that although the value of such information is currently accepted, no simple means for its comprehensive quantification is yet available for routine use in the monitoring, assessment and management of rivers. On this regard, a few methods of hydro-morphological and habitat survey, based on visual assessment of river features, e.g. the River Habitat Survey (RHS) and CARAVAGGIO protocols, support the collection of weighty scientifically-sound data during relatively short field surveys.
The significance of hydromorphology in supporting the interpretation of biological communities and in the establishment of management plans for European river ecosystems is now recognized and authoritatively stated by the Water Framework Directive. Together with morphological conditions and river continuity, the WFD indicates the hydrological regime - and thus the derived descriptors identified at the site scale - as one of the key supporting elements in the assessment of ecological status and interpretation of biological patterns. While flow-related aspects are indisputably relevant in all river systems, they are expected to be crucial in studies of the Mediterranean area.
In general terms, the outline and selection of cost-effective descriptors and indices is advocated for the interpretation of biological responses to habitat variability, especially in terms of local hydraulic conditions. In this regard, the concept and use of flow type categories represents relevant progress in visually assessing the hydraulic character of a river section at the micro and meso-scale. With this in mind, an index, which identifies the character of a river site in terms of its local hydraulic conditions was presented, based on visual habitat assessment in the field: the Lentic-lotic River Descriptor (LRD). This descriptor was originally applied at the Italian scale and successively employed at a European scale.
The lentic-lotic character illustrates the observed ratio between lentic and lotic in-channel habitats, resulting from the interaction between channel morphology, discharge and sediment transport. Based on CNR-IRSA studies, the lentic-lotic character of rivers - quantified by means of the LRD - resulted in being the most important factor in explaining benthic community differences among river sites across Mediterranean Italy. Its relevance is nonetheless expected to be high in all river types in Europe and worldwide. In spite of this, most current methods based upon invertebrates do not take of local hydraulic conditions into account in their assessment of ecological quality. As far as the influence of local hydraulic conditions on invertebrate community metrics and i.e. the evaluation of river quality status, the lentic-lotic character was found to be the most significant factor affecting invertebrate communities in the Mediterranean mountains, even if it is a relevant factor for most quality metrics also in the Alpine and Central European mountain rivers. Therefore, this character should be taken into account when assessing ecological quality of rivers because it can greatly affect the assignment of ecological status.

Selected papers

Buffagni A., Armanini D.G. & Erba S., 2009. Does the lentic-lotic character of rivers affect invertebrate metrics used in the assessment of ecological quality? Journal of Limnology, 68 (1): 92-105.
Buffagni A., Erba S. & D.G. Armanini, 2010. The lentic-lotic character of Mediterranean rivers and its importance to aquatic invertebrate communities. Aquatic Sciences Volume 72, Number 1, 45-60, DOI: 10.1007/s00027-009-0112-4.