When river levels drop, it can dramatically reshape aquatic food webs, suggests a study published yesterday in the journal Nature Climate Change.

Researchers used artificial streams to mimic drought conditions of varying severity, analyzing the resulting changes in the freshwater ecosystems they had created.

They discovered that critically low water levels brought about during severe droughts greatly reduced the composition of food webs, reducing the diversity of invertebrate organisms by about 25 percent.

Species loss -- and severing normal links between species in the environments -- led to partial collapse of the food webs, the scientists said.

"Our research demonstrates that drier climates could have far-reaching impacts on the functioning of freshwater ecosystems," wrote the study's authors, led by Mark Ledger of the University of Birmingham's School of Geography, Earth and Environmental Sciences.

The researchers conducted the study using eight artificial stream channels fed by a chalk stream near the research site in southern England.

They simulated drought by reducing flows six days per month in one of each grouping of two streambeds during the course of the two-year experiment.

To gauge the effect of changing flows on aquatic life, the researchers sampled invertebrates from each streambed every month.