Abstract
The biomonitoring methods implemented by water authorities are mostly developed for perennial rivers, and do not apply to temporary rivers (TRs). We propose a new classification for TRs to better assess their ecological status. It arises from the LIFE+ TRivers project, which was conducted in the Catalan and the Júcar Mediterranean river basin districts (RBD). The European Water Framework Directive (WFD) provided two systems to set river types (systems A or B from Annex II), which have been officially used by water authorities across Europe to set “national river types” (NRTs). However, essential hydrological variables for TRs are largely omitted. NRTs established according to the WFD were compared with TR categories obtained by using a rainfall-runoff model, “natural flows prescribed regimes” (NFPRs), and with “aquatic phases regimes” (APRs) calculated by using TREHS software. The biological quality indices currently used in Spain, based on macroinvertebrates and diatoms (IBMWP, IMMI-T, and IPS), were compared with a “general degradation” gradient in order to analyze the two TR river classification procedures (NFPR and APR). The results showed that NRTs did not properly classify TRs, and that the APR classification identified ecologically meaningful categories, especially those related to stagnant phases. Four “management temporary river categories” based on APRs are proposed to be used for water managers to properly assess the ecological status of TRs.
Highlights
More than half of the river networks worldwide have temporary flow regimes
It arises from the LIFE+ TRivers project, which was conducted in the Catalan and the Júcar Mediterranean river basin districts (RBD)
national river types” (NRTs) established according to the Water Framework Directive (WFD) were compared with temporary rivers (TRs) categories obtained by using a rainfallrunoff model, “natural flows prescribed regimes” (NFPRs), and with “aquatic phases regimes” (APRs) calculated by using TREHS software
Summary
More than half of the river networks worldwide have temporary (or non-perennial) flow regimes. Temporary rivers (TRs), known as intermittent rivers and ephemeral streams, or IRES [1], are fluvial ecosystems that recurrently stop flowing and/or become completely dry at some time [2]. They should not be considered as hydrologically challenged perennial rivers, but as highly dynamic ecosystems with a large variability of flow patterns and shifts between wet and dry phases [3]. TRs are underestimated globally in number and relevance [7,8] This is because TRs are rarely included in flow gauging networks [9], and even when gauging stations are present, they are not designed for measuring low or zero flows [10]
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