Long-term streamflow trends in Hawai'i and implications for native stream fauna

Climate change has fundamentally altered the water cycle in tropical islands, which is a critical driver of freshwater ecosystems. To examine how changes in streamflow regime have impacted habitat quality for native migratory aquatic species, we present a 50‐year (1967–2016) analysis of hydrologic records in 23 unregulated streams across the five largest Hawaiian Islands. For each stream, flow was separated into direct run‐off and baseflow and high‐ and low‐flow statistics (i.e., Q10 and Q90) with ecologically important hydrologic indices (e.g., frequency of flooding and low flow duration) derived. Using Mann–Kendall tests with a running trend analysis, we determined the persistence of streamflow trends through time. We analysed native stream fauna from ~400 sites, sampled from 1992 to 2007, to assess species richness among islands and streams. Declines in streamflow metrics indicated a general drying across the islands. In particular, significant declines in low flow conditions (baseflows), were experienced in 57% of streams, compared with a significant decline in storm flow conditions for 22% of streams. The running trend analysis indicated that many of the significant downward trends were not persistent through time but were only significant if recent decades (1987–2016) were included, with an average decline in baseflow and run‐off of 10.90% and 8.28% per decade, respectively. Streams that supported higher native species diversity were associated with moderate discharge and baseflow index, short duration of low flows, and negligible downward trends in flow. A significant decline in dry season flows (May–October) has led to an increase in the number of no‐flow days in drier areas, indicating that more streams may become intermittent, which has important implications for mauka to makai (mountain to ocean) hydrological connectivity and management of Hawai'i's native migratory freshwater fauna

Relative change in stream discharge from a tropical watershed improves predictions of fecal bacteria in near-shore environments

<p>Statistical models poorly predict bacteria in near-shore environments of tropical islands due to inaccuracies in runoff and discharge characterization of storm events. Intense, short duration storms on small, steeply sloped watersheds produce high rates of runoff, resulting in rapid pulses of discharge that influence the physical and physiological conditions of the fate and transport of pathogens. As such, increasing rates of discharge are expected to have a different influence on sediment transport and pathogen load compared to decreasing rates of discharge. Regression modeling was used to examine the affect of antecedent streamflow on the interaction between environmental parameters and two fecal indicator bacteria, enterococci and <i>Clostridium perfringens</i>. Including the relative change in discharge incorporates a proximate representation of the energy available to transport particulates, improving predictions of near-shore water quality. Understanding factors that influence pathogen loads improves management of watersheds and protects public health.</p

Spatial analysis of domestic water use and rural livelihoods in a semi-arid African highland

Rural communities throughout sub-Sahara Africa are hampered by unequal access to water resources, economic markets, and transportation. Further, development programs do not always provide uniform access to water supply, especially in water scarce regions. With a growing concern over the limited supply of ecosystem services, the need to understand how the complex realities of water use is affected by socio-cultural factors—including household tenure, size, income, and resource management practices—is urgent. This study uses qualitative (e.g., group discussions, village community mapping, key-informant interviews) data to inform quantitative models that test for spatial relationships among factors governing rural livelihoods among water sources across a village in Northern Tanzania. Models identified the social, environmental, and economic factors that affect a households’: 1) ability to meet the UN's minimum per capita threshold for water use; and 2) total domestic water use. These results reinforce the importance of family size, access to transportation, and water governance strategies affecting rural water use. The integration of traditional resource management with regional governance policies improved water use and protected water supplies. Investments in water infrastructure need to consider how additional supplies affect access to and management of resources across water scarce landscapes

Shifting magnitude and timing of streamflow extremes and the relationship with rainfall across the Hawaiian Islands

Flooding is a significant threat to life and property in Hawaiʻi. As climate warming continues to alter precipitation patterns and hydrological processes in the tropics, characterizing the shifting patterns in magnitude, seasonality, and location of floods would improve our understanding of the consequences and better prepare us for future flood events. In this study, 84 rain gauges and 111 crest gauges across five major Hawaiian Islands were analyzed from 1970 to 2005. We estimated trends in the annual maximum daily rainfall (RFmax) and the annual peak flow (PFmax) using the Mann-Kendall test and Senʻs slope. Subsequently, we examined the association between PFmax and rainfall. Then, we assessed temporal shifting by combining circular analysis with Senʻs slope. The main identified trends were a decrease in RFmax and PFmax (67% and 61% of all gauges, respectively). The physiography of the Hawaii islands (i.e., windward vs. leeward) has little contribution to both trends. In addition, RFmax trend cannot be fully attributed to PFmax trend, and in many cases, RFmax and PFmax did not occur coincidently. The timing of RFmax and PFmax occurred earlier in the wet season during the El Niño years. Therefore, RFmax and PFmax’s timing have shifted earlier from 1970 to 2005 likely due to the change of El Niño. These findings have implications for assessing flood risk. Our finding will aid watershed management and flood mitigation, and can increase resilience of downstream communities and near-shore environments

A freshwater perspective on the United Nations decade for ecosystem restoration

Globally, ecosystems have suffered from anthropogenic stressors as we enter the sixth mass extinction within the Anthropocene. In response, the UN has declared 2020-2030 the Decade for Ecosystem Restoration, aiming to mitigate ecosystem degradation and biodiversity loss. Freshwater ecosystems are disproportionately impacted relative to marine or terrestrial systems and ecological restoration is needed to preserve biodiversity and ecosystem services. Paradoxically, freshwater is among Earth's most vital ecosystem services. Here we identify meaningful considerations from a freshwater perspective that will lead to progression toward the restoration of freshwater ecosystems: work across terrestrial and freshwater boundaries during restoration, emulate nature, think and act on a watershed scale, design for environmental heterogeneity, mitigate threats alongside restoration, identify bright spots, think long term (a decade is not long enough), and embrace social-ecological systems thinking. Further, we reflect upon the three implementation pathways identified by the UN to translate these considerations into practice in hopes of "bending the curve" for freshwater biodiversity and ecosystems. Pathway 1, building a global movement, could create a network to share experiences and knowledge promoting vicarious learning, ultimately leading to more effective restoration. Pathway 2, generating political support, will be necessary to institutionalize ecosystem protection and restoration by demonstrating the value of freshwater ecosystems and biodiversity. Pathway 3, building technical capacity, aims to improve the current and often ineffective restoration toolbox by incorporating evidence syntheses (i.e., appraisal of evidence base) and Indigenous ways of knowing (i.e., two eyed seeing). Given that freshwater ecosystems are in dire need of repair, it is our hope that these considerations and implementation pathways will contribute to an actionable and productive Decade for Ecosystem Restoration

The database of the PREDICTS (Projecting Responses of Ecological Diversity In Changing Terrestrial Systems) project

The PREDICTS project—Projecting Responses of Ecological Diversity In Changing Terrestrial Systems (www.predicts.org.uk)—has collated from published studies a large, reasonably representative database of comparable samples of biodiversity from multiple sites that differ in the nature or intensity of human impacts relating to land use. We have used this evidence base to develop global and regional statistical models of how local biodiversity responds to these measures. We describe and make freely available this 2016 release of the database, containing more than 3.2 million records sampled at over 26,000 locations and representing over 47,000 species. We outline how the database can help in answering a range of questions in ecology and conservation biology. To our knowledge, this is the largest and most geographically and taxonomically representative database of spatial comparisons of biodiversity that has been collated to date; it will be useful to researchers and international efforts wishing to model and understand the global status of biodiversity