Field Updates January 2022: Understanding Continuous Water Quality Data

Creek water quality monitoring

One of the primary ways that the Estuary Program tracks creek health data is by conducting routine water quality monitoring. Staff and volunteers visit sites throughout the Morro Bay watershed each month and collect a variety of data points from each site. These water quality parameters include temperature, dissolved oxygen, conductivity, turbidity and flow velocity.

This type of sampling is known as “grab sampling” because the data provides information only the moment in time when you collected the sample or took a meter reading. While grab sampling can help illustrate ambient conditions at each site, this approach can leave gaps in our datasets, especially outside of our normal staff working hours.

To better understand what conditions look like outside of monthly monitoring site visits, the Estuary Program uses continuous monitoring equipment. These water quality data collection devices remain stationed in the creek and collect data on either fifteen-minute or thirty-minute intervals.

Nick downloads TIDBIT data — *One of our Monitoring Coordinators, Nick, collects data from a continuous water temperature logger in a local creek.*

Types of continuous monitoring

The Estuary Program currently has three types of continuous monitoring equipment. The first are our temperature data loggers, also called TIDBITs. These tiny but mighty devices log water temperature every thirty minutes, all year-round. You can check out this blog post for more information about these temperature loggers.

The second and longest running of our continuous datasets comes from our pressure transducers. These devices are stationed in creeks to measure changes in water depth. When we track the water depth over time, we can begin to identify how rainfall, lack of rainfall, and air temperature might affect creek depth.

The pressure transducer looks simple, but it provides important data that would be very difficult to collect by hand. — *This is the type of pressure transducer that the Estuary Program uses to gather continuous data on water depth. This data would be nearly impossible to collect by hand.*

A staff gauge measures water depth in a creek. — This is a staff gauge, a very large measuring stick that is placed in a creek to measure water depth. They are good for monitoring water depth only when staff are out in the field collecting data by hand.

Using the hydrograph from Chorro Creek below, can you find which month we received the most rainfall?

graph that shows water depth in feet at a local water quality monitoring site — This graph shows an example of continuous water depth data from a pressure transducer. The blue line indicates the depth of water in the creek over time. The steep increase on this graph indicates that water levels rose rapidly due to rainfall during a storm.

New monitoring equipment

The last and most recent addition to the continuous data logger ensemble is our water quality sonde. Unlike our temperature loggers, which collect only one type of data, the sonde can collect five different types of data in a single measurement!

The newest addition to the Estuary Program’s continuous data collection devices is a water quality sonde, pictured here. — *The newest addition to the Estuary Program’s continuous data collection devices is a water quality sonde, pictured above.*

The new sonde’s sensors can collect five types of data every 15 minutes: temperature, conductivity (or salinity), dissolved oxygen, pH, and water depth.

Why is continuous data so valuable?

Sondes and other pieces of continuous logging equipment provide valuable water quality information and can identify exactly when and for how long conditions might persist.

For example, if the dissolved oxygen levels are abnormally low for a long period of time, these conditions are likely to have an adverse effect on aquatic species, like rainbow and steelhead trout (both fish are the same species, Oncorhynchus mykiss, with different lifestyles) and California red-legged frogs (Rana draytonii).

Because the sonde measures multiple water quality parameters during the same logging cycle, we can also start to see trends in the data and better understand the relationship between indicators like temperature and dissolved oxygen, or conductivity and dissolved oxygen.

A red legged frog sits facing away from the camera. This is a side view with the frog's back left leg closest to the camera. It is sitting on what appears to be mud. — *Continuous data collected by the Estuary Program can help identify conditions that might affect native aquatic species, like the California red-legged frog pictured above.* Photograph courtesy of Marcia Grefsrud, California Department of Fish and Wildlife, and shared via Flickr under a Creative Commons license.

Data quality is key

Any data we collect must be accurate in order to be useful. While each of the loggers has slightly different quality assurance measures, one of the more interesting methods is built into our new water quality sonde.

One of the most common issues with submerged equipment is the potential for biofouling, which is the accumulation of algae, microorganisms, or plants on the surface of the sensors. This buildup can interfere with the sensors’ ability to collect accurate data.

To prevent biofouling, the water quality sonde has an internal wiper brush that prevents any fouling organisms from accumulating on the sensors and affecting readings. This small wiper operates in a circular-fashion, automatically cleaning the surface of all of the sensors as it runs.

Check out the video below to see how the anti-fouling wiper works!

What we do with the data we collect

The water quality monitoring data we collect by hand and from continuous monitoring equipment serves multiple purposes. We share it with partners at other organizations and agencies, including local oyster farms, and the California Water Board. We use it to inform our restoration project plans and gauge the effectiveness of past projects. It also forms the foundation of our many memos and reports that assess the health of the Morro Bay estuary and watershed. To see this data in action, check out our most recent State of the Bay report from 2020, and stay tuned for State of the Bay 2023 early next year. Additional technical memos and data reports can be found in our online library.

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Feb 11, 2022