Water is one of California’s most precious resources. Not because there isn’t enough of it–supply ebbs and flows with droughts and wet seasons–but because we need so very much of it for everything from washing dishes and taking showers to watering crops and making sure salmon have freshwater to spawn in. Unfortunately, keeping tabs on our water’s quality hasn’t proved easy. Years of fertilizing crops, building homes near watersheds, and other activities have led to a noticeable decline in water purity, something environmental engineers are working to reverse. But first, they have to understand what’s causing it.
“In California, we know where most of the flow is going because we need it all. But once we start getting into finer issues like the quality of the water and individual chemicals in the water, then we don’t track it as well,” explains Tom Harmon, an associate professor of environmental engineering at UC Merced whose research focuses on monitoring watersheds, areas of land that capture precipitation, draining it into marshes, streams, rivers, lakes, and groundwater.
Harmon and another CITRIS-affiliated researcher, UC Davis Civil and Environmental Engineering professor Geoff Schladow, are independently developing sensor networks that would enable them to conduct real-time monitoring of water quality–Harmon in the farming communities of the Central Valley and Schladow in the Lake Tahoe Basin. Improved scrutiny, they believe, would not only
deepen researchers’ understanding of the causes behind water pollution, but also show how to reverse it.
Nowhere is the situation’s seriousness clearer than on Lake Tahoe. Thirty years ago, visitors to the lake could gaze nearly 100 feet into its famous crystalline blue waters. Today, visitors can see only 60 feet down. For a long time, Schladow and other Tahoe researchers believed all the blame lay with phytoplankton, microscopic plants that blossom when fed nitrogen and phosphorous from excess application of fertilizer.
“In the last four or five years we’ve started to realize that the phytoplankton aren’t so important. Most of the damage is being done by extremely fine particles, just 1 or 2 microns, that have washed in from sources such as driveways or from stream erosion; some are even brought in by air currents which deposit them on the lake. It’s particles that seem to have increased and particles that have accounted for most of the loss of clarity,” says Schladow, who is director of UC Davis’ Tahoe Environmental Research Center (TERC).
Currently, a network of six meteorological stations (the kind used for weather reports) on floating rafts (four are operated jointly with NASA), eight additional stations along the lake’s shore, and several NASA satellites record the lake’s temperature, wind speed, infrared
radiation, and clarity, uploading the data at regular intervals to a Website available to anyone. However, in order to study the actual contaminants, Schladow and his team still have to paddle out onto the lake and collect samples by hand every ten days. Automating this process, says Schladow, is the obvious next step. To that end, he and his team of investigators are planning for the installation of a suite of new, automated samplers and sensors that may do just that. Additionally, they have a proposal to the National Science Foundation (NSF) to build a network of smaller sensors along a set of nearby streams to study the interaction between the annual snowpack, the groundwater, and the water quality in the streams.
Sensor networks along stream beds also play a key role in the work Harmon is doing. While it’s known that chemicals are trickling through California’s watersheds and into rivers, tracing their paths has been difficult because the sensors needed to detect these substances either don’t exist or aren’t hardy enough to survive long in nature. Among Harmon’s many research projects is one to modify fragile laboratory chemical sensors for just that purpose. Ultimately, he hopes that data from physical, chemical, and biological sensor networks along rivers that drain from the snowpack through agricultural land could be combined with information on streamflow, temperature, and salinity from existing watershed gauging stations and satellite imagery to produce a big-picture view of the state’s water quality.
“If all the data was on the table in an easily accessible way and integrated with some forecasting model so that, just as we forecast the weather, we’d be able to forecast stream quality over certain branches of the stream based on presumed practices, we might be able to adaptively manage those practices. For example, we someday might be able to forecast optimal conditions for applying fertilizer or pesticides in a particular region of the valley, so that the farmer reaps the necessary benefits while the impact on local groundwater and rivers is minimal,” Harmon says.
While building a real-time map of the state’s water supply is going to take a lot of time and effort, Schladow points out that in the meantime “Lake Tahoe is a really great place to study these watershed processes because it’s relatively confined.” For that reason, students and researchers from around the world have flocked to this natural laboratory to learn and, in many cases, apply it to bodies of water half a world away. But learning isn’t the only reason Schladow believes his work there is important. He says: “It is a bellwether for our societal commitment to environmental restoration. These things take effort by a lot of people and that effort needs to be funded. If we can’t understand how to improve Tahoe and we can’t find the resources to do it, what are the chances of finding it for places that aren’t so unique and special?”