Ecological relevance of non‐perennial rivers for the conservation of terrestrial and aquatic communities

Abstract

River conservation efforts traditionally focus on perennial watercourses (i.e., those that do not dry) and their associated aquatic biodiversity. However, most of the global river network is not perennial and thus supports both aquatic and terrestrial biodiversity. We assessed the conservation value of nonperennial rivers and streams (NPRS) in one of Europe's driest regions based on aquatic (macroinvertebrates, diatoms) and terrestrial (riparian plants, birds, and carabid beetles) community data. We mapped the distribution of taxa at 90 locations and across wide environmental gradients. Using the systematic planning tool Marxan, we identified priority conservation sites under 2 scenarios: aquatic taxa alone or aquatic and terrestrial taxa together. We explored how environmental factors (runoff, flow intermittence, elevation, salinity, anthropogenic impact) influenced Marxan's site selection frequency. The NPRS were selected more frequently (over 13% on average) than perennial rivers when both aquatic and terrestrial taxa were considered, suggesting that NPRS have a high conservation value at the catchment scale. We detected an underrepresentation of terrestrial taxa (8.4–10.6% terrestrial vs. 0.5–1.1% aquatic taxa were unrepresented in most Marxan solutions) when priority sites were identified based exclusively on aquatic biodiversity, which points to a low surrogacy value of aquatic taxa for terrestrial taxa. Runoff explained site selection when focusing on aquatic taxa (all best‐fitting models included runoff, r2 = 0.26–0.27), whereas elevation, salinity, and flow intermittence were more important when considering both groups. In both cases, site selection frequency declined as anthropogenic impact increased. Our results highlight the need to integrate terrestrial and aquatic communities when identifying priority areas for conservation in catchments with NPRS. This is key to overcoming drawbacks of traditional assessments based only on aquatic taxa and to ensure the conservation of NPRS, especially as NPRS become more prevalent worldwide due to climate change and increasing water demands.

Integrating spatiotemporal hydrological connectivity into conservation planning to protect temporary rivers

“…Given the high rate of taxa turnover in our dataset, with most taxa restricted to a few sites, high representation targets could only be achieved for all taxa at the same time by selecting almost all sites simultaneously. To address this problem, a bootstrap analysis was conducted (Bruno et al, 2022), by attempting to achieve the targets for a given proportion of all taxa each time. For this, 1,000 random samples were selected containing 50% of the taxa from the total pool and identified the minimum set of locations to cover the representation targets explained above.…”

“…For this, 1,000 random samples were selected containing 50% of the taxa from the total pool and identified the minimum set of locations to cover the representation targets explained above. This decision was based on the work of Bruno et al (2022), who tested three different thresholds (50%, 75%, 90%) and found that the results were consistent across the different bootstrap thresholds used. Given the lack of estimates of conservation costs across the study area, a constant cost across all locations were used (e.g., Hermoso et al, 2021) and no connectivity penalty measure was included, similar to Bruno et al (2022).…”

“…This decision was based on the work of Bruno et al (2022), who tested three different thresholds (50%, 75%, 90%) and found that the results were consistent across the different bootstrap thresholds used. Given the lack of estimates of conservation costs across the study area, a constant cost across all locations were used (e.g., Hermoso et al, 2021) and no connectivity penalty measure was included, similar to Bruno et al (2022). With this configuration, Marxan was ran 100 times, using a million iterations each, and kept the solution with the lowest objective function score across those runs as our best solution, for each of the bootstrap selection of taxa.…”

“…An alternative approach for selecting and prioritising sites to be conserved are systematic planning (Margules & Pressey, 2000), which have been used in rivers (Linke et al, 2011) and, only recently, in TRs (Bruno et al, 2022). Among these tools, one of the most widely used is Marxan (Ball et al, 2009), which relies on the principle of complementarity to find the best combination of sites to be protected to meet a set of conservation targets at the minimum cost.…”

“…Additionally, TRs are among the most damaged and vulnerable freshwater habitats in the world (Datry et al, 2014; Fovet et al, 2021; Skoulikidis et al, 2017). Despite some efforts have been done in some parts of the world (e.g., partial recognition in the EU Water Framework Directive and Habitats Directive; Fritz et al, 2017), they still remain neglected by policy‐makers (Datry et al, 2023; Leigh et al, 2015), and conservation plans have largely ignored them (Bruno et al, 2022). The few existing studies on the conservation of TRs argue that priority sites for conservation can vary over time in these ecosystems (Rodríguez‐Lozano et al, 2023; Ruhí et al, 2017).…”