Reconciling biodiversity conservation and flood risk reduction : The new strategy for freshwater protected areas

Aim: Natural disaster risk reduction (DRR) is becoming a more important function of protected area (PAs) for current and future global warming. However, biodiversity conservation and DRR have been handled separately and their interrelationship has not been explicitly addressed. This is mainly because, due of prevailing strategies and criteria for PA placement, a large proportion of PAs are currently located far from human-occupied areas, and habitats in human-occupied areas have been largely ignored as potential sites for conservation despite their high biodiversity. If intensely developed lowland areas with high flooding risk overlap with important sites for biodiversity conservation, it would be reasonable to try to harmonize biodiversity conservation and human development in human-inhabited lowland areas. Here, we examined whether extant PAs can conserve macroinvertebrate and freshwater fish biodiversity and whether human-inhabited lowland flood risk management sites might be suitable to designate as freshwater protected areas (FPAs). Location: Across Japan. Methods: We examined whether extant PAs can conserve macroinvertebrate and freshwater fish biodiversity and analysed the relationship between candidate sites for new FPAs and flood disaster risk and land use intensity at a national scale across Japan based on distribution data for 131 freshwater fish species and 1395 macroinvertebrate species. Results: We found that extant PAs overlapped with approximately 30% of conservation-priority grid cells (1 km2) for both taxa. Particularly for red-listed species, only one species of freshwater fish and three species of macroinvertebrate achieved the representation target within extant PAs. Moreover, more than 40% of candidate conservation-priority grid cells were located in flood risk and human-occupied areas for both taxa. Main conclusions: Floodplain conservation provides suitable habitat for many freshwater organisms and helps control floodwaters, so establishing new FPAs in areas with high flood risk could be a win-win strategy for conserving freshwater biodiversity and enhancing ecosystem-based DRR (eco-DRR)

Fish and macroinvertebrate assemblages reveal extensive degradation of the world's rivers

Rivers suffer from multiple stressors acting simultaneously on their biota, but the consequences are poorly quantified at the global scale. We evaluated the biological condition of rivers globally, including the largest proportion of countries from the Global South published to date. We gathered macroinvertebrate- and fish-based assessments from 72,275 and 37,676 sites, respectively, from 64 study regions across six continents and 45 nations. Because assessments were based on differing methods, different systems were consolidated into a 3-class system: Good, Impaired, or Severely Impaired, following common guidelines. The proportion of sites in each class by study area was calculated and each region was assigned a Köppen-Geiger climate type, Human Footprint score (addressing landscape alterations), Human Development Index (HDI) score (addressing social welfare), % rivers with good ambient water quality, % protected freshwater key biodiversity areas; and % of forest area net change rate. We found that 50% of macroinvertebrate sites and 42% of fish sites were in Good condition, whereas 21% and 29% were Severely Impaired, respectively. The poorest biological conditions occurred in Arid and Equatorial climates and the best conditions occurred in Snow climates. Severely Impaired conditions were associated (Pearson correlation coefficient) with higher HDI scores, poorer physico-chemical water quality, and lower proportions of protected freshwater areas. Good biological conditions were associated with good water quality and increased forested areas. It is essential to implement statutory bioassessment programs in Asian, African, and South American countries, and continue them in Oceania, Europe, and North America. There is a need to invest in assessments based on fish, as there is less information globally and fish were strong indicators of degradation. Our study highlights a need to increase the extent and number of protected river catchments, preserve and restore natural forested areas in the catchments, treat wastewater discharges, and improve river connectivity

Flood disturbance and predator-prey effects on regional gradients in species diversity

The effects of both abiotic factors and biotic interactions among guilds (i.e., inter-guild effects) have been suggested to be important for understanding spatial variation in species diversity; however, compared to the abiotic effects, the processes by which the inter-guild effects are mediated have been little described. Hence, we investigated stream invertebrate assemblages on Hokkaido Island, Japan, and assessed how the processes of determining regional patterns in species diversity differed among guilds (collector-filterers, collector-gatherers/shredders, scrapers, and predators) by taking both inter-guild and abiotic effects into consideration using Bayesian networks. Collector-gatherers/shredders, collector-filterers, and predators exhibited significant regional gradients in taxonomic richness. Gradients in the former two guilds can be generated by variation in flood disturbance regardless of interactions with other guilds. The gradient in predator taxonomic richness was indirectly related to the disturbance and was directly generated by bottom-up effects through their prey (collector-gatherers/shredders and collector-filterers). We found that not only environmental factors, but also inter-guild effects may be essential for forming the regional gradient in predators, unlike those for collector-gatherers/shredders and collector-filterers. The processes underlying the regional variation in taxonomic richness of the three guilds are interpreted in terms of the more individuals hypothesis, facilitation, and predator-prey relationships

Latitudinal gradients in stream invertebrate assemblages at a regional scale on Hokkaido Island, Japan

1. Although a latitudinal gradient in species diversity has been observed for various taxa, the factors generating the latitudinal gradient at broad spatial scales are difficult to identify because several candidate factors change simultaneously with latitude. We investigated latitudinal gradients in stream invertebrate assemblages in 30 headwater streams in Hokkaido Island, Japan, focusing on the regional scale to discount historical factors and to extract the effects of environmental factors on latitudinal gradients in diversity. 2. Taxon diversity (Shannon index) and taxon richness (number of taxa per unit area) increased with latitude. Abundance showed a similar latitudinal gradient, whereas evenness (D1) did not. Hence, we conclude that the observed latitudinal gradient in taxon richness was generated by directional variation in abundance (passive accumulation), leading to that in taxon diversity. 3. Precipitation, which is strongly related to flood disturbances, decreased with latitude and was an important factor explaining variation in taxon diversity, taxon richness and abundance. The probability of a taxon being present tended to increase from south to north, suggesting that the higher taxon richness observed in northern sites may be because of the presence of rare species. These findings indicate that flood disturbance varying with latitude may influence abundance and local extinction rates of rare species, consequently affecting taxon richness and taxon diversity. 4. By detecting the effects of an environmental factor (precipitation) on the latitudinal gradients in taxon diversity and taxon richness without interference by historical factors, this study demonstrates processes that can produce latitudinal gradients in the diversity of stream invertebrate assemblages

Appendix A. Characteristics of the study streams on Hokkaido Island, Japan.

Characteristics of the study streams on Hokkaido Island, Japan