TREHS: An open-access software tool for investigating and evaluating temporary river regimes as a first step for their ecological status assessment

Abstract

When the regime of a river is not perennial, there are four main difficulties with the use of hydrographs for assessing hydrological alteration: i) the main hydrological features relevant for biological communities are not quantitative (discharges) but qualitative (phases such as flowing water, stagnant pools or lack of surface water), ii) stream flow records do not inform on the temporal occurrence of stagnant pools, iii) as most of the temporary streams are ungauged, their regime has to be evaluated by alternative methods such as remote sensing or citizen science, and iv) the biological quality assessment of the ecological status of a temporary stream must follow a sampling schedule and references adapted to the flow- pool-dry regime. To overcome these challenges within an operational approach, the freely available software tool TREHS has been developed within the EU LIFE TRIVERS project. This software permits the input of information from flow simulations obtained with any rainfall-runoff model (to set an unimpacted reference stream regime) and compares this with the information obtained from flow gauging records (if available) and interviews with local people, as well as instantaneous observations by individuals and interpretation of ground-level or aerial photographs. Up to six metrics defining the permanence of water flow, the presence of stagnant pools and their temporal patterns of occurrence are used to determine natural and observed river regimes and to assess the degree of hydrological alteration. A new regime classification specifically designed for temporary rivers was developed using the metrics that measure the relative permanence of the three main phases: flow, disconnected pools and dry stream bed. Finally, the software characterizes the differences between the natural and actual regimes, diagnoses the hydrological status (degree of hydrological alteration), assesses the significance and robustness of the diagnosis and recommends the best periods for biological quality samplings.

Characteristics, Main Impacts, and Stewardship of Natural and Artificial Freshwater Environments: Consequences for Biodiversity Conservation

“…Similar results were found when checking for interannual variability, with lower values for the same biological index under reference conditions in dry years [481]. Therefore, the classification of the natural flow regime of Mediterranean streams is a crucial step prior to bioassessment [472]. For example, if a naturally perennial river shifted to temporary, biomonitoring methods for perennial rivers should be applied and restoration measures should be devoted to establish environmental flows.…”

“…In the case of primary producers, similar assemblage shifts are observed, from lotic to lentic and eventually with drying, to sub-aerial communities [474]. However, this temporal pattern might not be true for ephemeral and episodic streams and rivers, in which the terrestrial habitats predominate throughout the year and flow depends on pulse flood events [472]. In the case of fish, assemblages are typically similar between seasons in terms of composition but fish abundances change in relation to both floods and droughts [465].…”

“…Shifts in populations and communities respond to such flow dynamics, showing changes in species abundances, richness and composition between phases [465]. To define these transitory phases, Gallart et al (2017) [472] defined a six aquatic states based on the associated biotic changes in freshwater organisms. These are (1) hyperrheic, i.e., flood conditions; (2) eurheic, i.e., full prevalence of all the possible mesohabitats; (3) oligorheic, i.e., sequence of pools connected by flowing water threads; (4) arheic, i.e., occurrence of isolated pools; (5) hyporheic, i.e., disappearance of SW, with the wet alluvium still allowing underground aquatic life; and (6) edaphic, i.e., desiccation of the river bed and alluvium.…”

Quantifying spatial and temporal patterns of flow intermittency using spatially contiguous runoff data

“…2). Uncertainty exists in the measurement of discharge by stream gauging, especially at very low flows (Kennard et al, 2010a), as gauging stations are not normally well-calibrated to measure zero flows and small changes due to erosion/deposition of sediments in the gauging section can modify the estimate of zero flow (Gallart et al, 2017). We therefore defined the threshold of flowing water as 0.1 10 3 m 3 /day (McJannet et al, 2014).…”

Evaluating a landscape-scale daily water balance model to support spatially continuous representation of flow intermittency throughout stream networks

“…Intermittent streams have seen increasing research interest over the past decade (e.g. Costigan et al, 2016;Fritz et al, 2013;Gallart et al, 2017;Leigh et al, 2016), and there is a growing interest in conserving these unique ecosystems. The scarcity of spatially-explicit information on flow intermittency has been identified as one of the key issues confronting intermittent stream management (Acuña et al, 2017).…”