Drought affects pH of water, creating changes in quality

By Danielle Kalisek

Studies conducted by Baylor University scientists accidentally determined how drought affects water and its pH levels, therefore affecting water quality and aquatic life among other things. Results from ongoing studies may soon help answer more questions.

“These recent field studies we were performing were not timed to intentionally encompass drought-type conditions,” said Dr. Bryan Brooks, professor of environmental science at Baylor University. “As it turns out, because of the timing of these wadeable stream and reservoir studies, they encompassed our last major drought in 2006.”

Brooks, Dr. Ryan King, Dr. Robert Doyle and Baylor graduate students originally set out to study water quality gradients in reservoirs and streams to support environmental assessment and management efforts. However, when the 2006 drought conditions became prevalent, what turned out to be a problem for the scientists’ studies ended up allowing them to develop a better understanding of how droughts influence historical and emerging contaminants of water quality for compounds, toxicity and bioaccumulation (or the accumulation of a substance in a living organism’s tissues), and how aquatic organisms can be influenced by site-specific pH.

“Though our important findings weren’t part of our original study design, as it turns out, these projects gave us the opportunity to examine how, under extreme drought scenarios, various water quality indicators and ecological functions in these different habitats would respond,” Brooks said. “We noticed there was fairly substantial pH variability in back waters of reservoirs and in wadeable streams that were more nutrient-enriched under those drought scenarios.”

He added that the timing of the 2006 and 2011 droughts was not anticipated, but looking back he feels fortunate these studies were being performed in the field, allowing the scientists to capture what the variability and effects of these droughts look like across different levels of surface waters, as well as the implications of the historical and emerging contaminants. Many emerging contaminants are ionizable weak acids and weak bases, which is important because site-specific pH of surface waters can influence chemical toxicity and bioaccumulation.

“Our study is the first to integrate a number of factors associated with climate, urbanization, industry processes, pH variability and the implications for environmental assessment of these ionizable chemicals,” Brooks said. “We’re in a unique situation because we have such a strong normal rainfall annual gradient from the western part of the state to the eastern part of the state and our major river basins are flowing across that gradient from an arid to a more pronounced precipitation regime, and then you’ve got a bunch of people right in the middle. So the inter-annual climate variability of Texas is something that provides unique opportunities to examine the influences of climatic changes on surface water quality.”

The studies took place in a variety of habitats—wadeable streams, rivers that are flowing into reservoirs, gradients in reservoirs from the river to the dam locations and eight reservoirs in the state—and conditions varied within each situation.

“In wadeable streams under lower flow conditions there was much more variability in pH and then greater potential influences on water quality as far as toxicity of various types of contaminants are concerned,” Brooks said. “In reservoirs there were some patterns that were a bit more reservoir-specific.

“In the wadeable streams, we observed the range of pH variability to be more enhanced under nutrient-rich conditions, which is actually not surprising but also suggests when stream flows are lower, especially close to low flow conditions, we may want to examine pH site variability much more closely especially in areas where chemicals whose toxicity and bioaccumulation potential would be influenced in pH shifts.”

Their results from the 2006 study identify that under extreme drought conditions, scientists may want to examine site-specific pH a little more closely because for some compounds, their toxicity to aquatic organisms will be greater, while for other compounds they may be less.

“The way we interpret degradation of water quality, based on our work, indicates that we should look at the interaction between climatological changes, nutrient enrichment and in-stream flows,” he said.

Since the 2006–2007 study, Brooks and fellow scientists have been involved in various other water quality studies during the 2010–2011 drought, which shaped up to be a more severe drought than they saw a few years ago.

“What we’re doing now is focusing specifically on developing a better understanding of how pH influences the bioaccumulation and toxicity of these types of chemicals to aquatic organisms,” Brooks said. “The work we’re doing right now includes some field studies as well as some carefully-controlled lab studies to identify how pH shifts can increase or decrease bioaccumulation of these ionizable contaminants to aquatic life.”

They are in the process of examining the most current data in hopes of relaying this information and their findings in reports in the coming months.

“At the very least the studies from a few years ago provided us a sound platform on which to start interpreting data from this most recent extreme drought,” Brooks said. “It identified potential hot spots where impacts of pH on bioaccumulation and toxicity of historical contaminants and contaminants of emerging environmental concern are likely to be greatest, which can help focus our management efforts when appropriate and in a reasonable way.”