Sept. 22 (UPI) -- Scientists have published a global water quality database detailing the health of nearly 12,000 freshwater lakes, almost half the world's freshwater supply.
Compiled by researchers at York University, in Canada, the database offers water quality information on lakes in 72 countries and all seven continents, including Antarctica.
Researchers detailed the database compilation process in a new paper, published Tuesday in the Nature journal Scientific Data.
"The database can be used by scientists to answer questions about what lakes or regions may be faring worse than others, how water quality has changed over the years and which environmental stressors are most important in driving changes in water quality," lead author Alessandro Filazzola said in a news release.
To build the database, researchers mined some 3,322 studies for information on chlorophyll levels in lakes all over the world. Scientists often use chlorophyll as a proxy for measuring an ecosystem's health because it is a good predictor of primary production -- the amount of vegetation and algae growing in lakes.
Primary production sounds good, but more chlorophyll isn't always better than less chlorophyll. Rising chlorophyll levels is typically a sign of degraded water quality and declining ecosystems health, researchers say.
"Human activity, climate warming, agricultural, urban runoff and phosphorus from land use can all increase the level of chlorophyll in lakes," said Filazzola, a postdoctoral research fellow at York. "The primary production is most represented by the amount of chlorophyll in the lake, which has a cascading impact on the phytoplankton that eat the algae and the fish that eat the phytoplankton and the fish that eat those fish."
"If the chlorophyll is too low, it can have cascading negative effects on the entire ecosystem, while too much can cause an abundance of algae growth, which is not always good," he said.
Rising global temperatures have encouraged algae blooms in many lakes around the world, and extreme weather events have exacerbated agricultural runoff problems, flooding lakes with excess nutrients. The problem is especially pronounced in lakes near urban watersheds and agricultural areas.
In addition to chlorophyll data, researchers compiled information on phosphorous and nitrogen levels, which can help predict changes in chlorophyll. Scientists also collected data on each lake's physical characteristics, as well as climate data and land use information.
"In addition to drinking water, freshwater is important for transportation, agriculture, and recreation, and provides habitats for more than 100,000 species of invertebrates, insects, animals and plants," said senior researcher Sapna Sharma.
"The database can be used to improve our understanding of how chlorophyll levels respond to global environmental change and it provides baseline comparisons for environmental managers responsible for maintaining water quality in lakes," said Sharma, an associate professor of biology at York.