<p>Global warming is turning clear mountain lakes green in the western United States because of an increase in algae blooms "without historical precedent", researchers reported on Tuesday.</p>.<p>The concentration of algae in two remote mountain lakes more than doubled in the past 70 years, researchers at Colorado State University found.</p>.<p>Their results, published in the British Royal Society journal <em>Proceedings B</em>, highlight the potentially harmful effects of climate change on pristine and remote ecosystems.</p>.<p>"Even in relatively remote lakes located in protected areas... the fingerprint of human perturbation of Earth System is evident," lead researcher Isabella Oleksy of Colorado State University told AFP.</p>.<p>"Rapid warming of high elevation environments has resulted in the rapid acceleration and dominance of green algae, which until recently were found in low abundance in these lakes."</p>.<p>The team of scientists led by Oleksy examined algae concentrations in lakes in a mountain range about 100 kilometres (65 miles) from Denver, using a tool called a gravity corer to collect sediment cores without damaging the lakebed.</p>.<p>Drawing on measurements going back to the 1950s, they found "dramatic changes" in algal abundance in the form of green algal blooms called chlorophytes, which thrive in warmer temperatures.</p>.<p>The high level of algae "came as an ecological surprise", Oleksy said.</p>.<p>She noted that the amounts of algae documented in the study would more typically be found in highly polluted areas, such as those prone to agricultural run-off, and not in unsullied mountain environments.</p>.<p>"While we documented these changes in two lakes in Colorado, it is likely that this is not an isolated phenomenon," she said.</p>.<p>The results are not a smoking gun, the researchers acknowledged, but point to climate change as driving the excess accumulation of nutrients -- such as phosphorus and nitrogen -- that cause algal blooms.</p>.<p>In lakes and oceans, algae blooms sicken wildlife if ingested and destabilise aquatic environments by blocking out sunlight, the United States Environmental Protection Agency says on its website.</p>.<p>Fresh water and marine algae blooms have a huge negative economic impact, affecting fisheries, tourism and human health.</p>
<p>Global warming is turning clear mountain lakes green in the western United States because of an increase in algae blooms "without historical precedent", researchers reported on Tuesday.</p>.<p>The concentration of algae in two remote mountain lakes more than doubled in the past 70 years, researchers at Colorado State University found.</p>.<p>Their results, published in the British Royal Society journal <em>Proceedings B</em>, highlight the potentially harmful effects of climate change on pristine and remote ecosystems.</p>.<p>"Even in relatively remote lakes located in protected areas... the fingerprint of human perturbation of Earth System is evident," lead researcher Isabella Oleksy of Colorado State University told AFP.</p>.<p>"Rapid warming of high elevation environments has resulted in the rapid acceleration and dominance of green algae, which until recently were found in low abundance in these lakes."</p>.<p>The team of scientists led by Oleksy examined algae concentrations in lakes in a mountain range about 100 kilometres (65 miles) from Denver, using a tool called a gravity corer to collect sediment cores without damaging the lakebed.</p>.<p>Drawing on measurements going back to the 1950s, they found "dramatic changes" in algal abundance in the form of green algal blooms called chlorophytes, which thrive in warmer temperatures.</p>.<p>The high level of algae "came as an ecological surprise", Oleksy said.</p>.<p>She noted that the amounts of algae documented in the study would more typically be found in highly polluted areas, such as those prone to agricultural run-off, and not in unsullied mountain environments.</p>.<p>"While we documented these changes in two lakes in Colorado, it is likely that this is not an isolated phenomenon," she said.</p>.<p>The results are not a smoking gun, the researchers acknowledged, but point to climate change as driving the excess accumulation of nutrients -- such as phosphorus and nitrogen -- that cause algal blooms.</p>.<p>In lakes and oceans, algae blooms sicken wildlife if ingested and destabilise aquatic environments by blocking out sunlight, the United States Environmental Protection Agency says on its website.</p>.<p>Fresh water and marine algae blooms have a huge negative economic impact, affecting fisheries, tourism and human health.</p>