1/17/2023 0 Comments Ephemeral stream![]() Many such streams were excluded from federal environmental laws under former President Donald Trump’s administration. Others say the results highlight the need for stronger legal protections for intermittent tributaries that form the headwaters of many rivers. “We should have many more gauges in small streams,” says Albert Ruhi, a freshwater ecologist at the University of California, Berkeley. “I definitely didn’t expect the pattern to be so regionally clear.”īroader monitoring of intermittent streams would help researchers and policymakers better understand the sometimes subtle impacts that climate change is having on water quantity and quality, scientists say. But a warming climate appears to be “the overarching organizer” of the shifts, Zipper says. In some cases, human activities such as operating dams, irrigation, and groundwater pumping could be contributing to dewatering. One possible reason: Winters are warmer and shorter, meaning frozen landscapes thaw earlier, allowing streams to flow. In contrast, in the northern United States ephemeral rivers are now flowing longer. But even in the Southeast, which is relatively wet, streams are drying earlier and staying dry longer. The drying trend is clearest in arid regions, such as the Southwest. It also has implications for water quality, as microbes in damp sediments can remove nitrogen pollution even after the last puddles have disappeared. “Just because the channel is dry does not make it biologically dead,” says river scientist Ellen Wohl of Colorado State University. That is bad news for the many plants and animals that time their reproduction to the availability of water, especially in deserts. At some 7% of gauges, dry periods expanded by 100 days or more. Some now shrivel earlier in the year and remain dry for longer, for example, or they dwindle more quickly than before. ![]() More than half of the gauges showed changes in the streams’ flow patterns since 1980. Still, the analysis revealed some eye-opening regional shifts, says Sam Zipper, one of the authors and an ecohydrologist with the Kansas Geological Survey. The sample covered just a small fraction of intermittent streams, the authors note, and left out some states, such as Nebraska and Maine, that don’t have any long-term gauges on these streams. Most of the gauges were on small waterways in river headwaters, but a few tracked large rivers that are intermittent in places, such as the Rio Grande, which flows sporadically in New Mexico and Texas. The findings, reported last month in Environmental Research Letters, come from a study of data collected between 19 by flow gauges on 540 intermittent streams around the United States. “That’s really shocking,” says Sarah Null, a watershed scientist at Utah State University. Some are dry for 100 days longer per year than in the 1980s. Now, a study has found that ephemeral streams across the continental United States have become less reliable over the past 40 years, likely as a result of climate change. They help purify surface water and provide crucial habitat for creatures such as the Sonoran Desert toad, fairy shrimp, and Wilson’s warbler. But these intermittent streams are everywhere, making up more than half of Earth’s waterways. The many small, unnamed ephemeral streams in the piedmont of the Huachuca Mountains and Barry Goldwater Range have high conservation value.Small streams that dry up for part of the year are easy to overlook. The results demonstrate the need to conserve a variety of stream flow types to meet the sometimes mutually exclusive goals of high ecosystem productivity and high species richness. Ground dwelling arthropods were strongly influenced by flow permanence, with effects being seasonally dynamic. Along the continuum from ephemeral to semiperennial stream flow, trade-offs were apparent between riparian plant biomass high at wetter sites and plant species diversity high at dry sites with sparse canopy. ![]() Decomposition and nutrient release were tightly coupled to stream flow for the narrow band along the stream channel, but not for the associated riparian zone. ![]() Duration of flow and precipitation were decoupled for intermittent and semiperennial streams because of contributions from groundwater discharge and the vadose zone. Relationships between rainfall and stream flow permanence varied by stream flow type. Data were collected on stream hydrology, litter decomposition, nutrients, vegetation, seed banks, and ground-dwelling soil arthropods. Abstract: This projects goal was to improve understanding of the hydroclimatic drivers of biotic communities and ecosystem processes in ephemeral stream channels as a basis for projecting response to regional climate change. ![]()
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