Alumni Riley Pratt
What’s in the water? It can be easy to overlook the simple necessity of water as a resource especially when it is as easy to obtain as turning on the tap for those of use fortunate enough to have access to clean water. However, when water becomes scarce or polluted the effects on human well-being become apparent. Water is not only critical for us to drink but sustains all life on the plant, and for that reason when we study water we find clues about ecosystem functionality, about geologic process and the impact we have on the environment we inhabit.
An island is as close to a truly closed system as an ecologist can hope to find. At CSU Channel Islands, we are fortunate enough to study the unique and beautiful Santa Rosa Island, part of the Channel Islands National Park. While at first glance, the island seems pristine and untouched, SRI has a rich history of human inhabitants. From indigenous Chumash inhabitants to Spanish ranchers to National Park visitors, humans have left their mark on the island in various ways that are still apparent today. While certain aspects of history are still debated, it is understood that ranching practices had profound effects on the ecosystem of SRI. One such impact was that on water in the stream channels on the island. Remember how water quality gives us clues to the functionality of the ecosystem? Heavily grazed land lacks a health vegetation community. When vegetation is impacted, roots that once held erodible stream banks become vulnerable and fall into the stream. Thus, particulate matter, or dissolved solids, increase in concentration. By quantifying and analyzing dissolved solids over time, we can glean an idea of erosion rates and streambank vegetation.
To collect data on water quality, we used YSI water quality probes. One probe is handheld and collects data instantaneously in the field on parameters like dissolved oxygen and pH (the acidity of the water). The other probe can be deployed for months continuously collecting data points over time. Both feature removable probes that can measure for a variety of different parameters.
To assess the recovery of Santa Rosa Island’s stream health, we compared our data collected in 2014 and 2015 to studies performed in 2002 by the National Park Service. Figure 1 compares three parameters (pH, conductivity and dissolved oxygen) in three streams over this time. Across watersheds tested on the island, we observed wide variations in parameters. Some remained stable, especially pH which tends to be alkaline due to the chemical makeup of rocks that characterize the island. Dissolved oxygen, as evidenced by continuous data, changes greatly throughout the day and is evidence of thriving aquatic organisms. Conductivity, a measure of dissolved ions, has decreased by 12% in Water Canyon, while increasing by 7% in Quemada Canyon. Many historical testing reaches were dry during our monitoring period, especially in Quemada Canyon. The acceptable levels of pH were not found to exceed EPA guidelines of 6.5-9 and showed little change over time. Dissolved oxygen measurements at mid-day showed a decrease from 2002 levels. This could be due to seasonal variation, drought or changes in plant and algae communities.
Water quality monitoring on Santa Rosa Island, like any ecological study, is a long-term endevor and is influenced my many variables. Seasonal variability and precipitation rates have great impacts on the chemical concentrations in streams. Drought has significant impacts on the arid island ecosystem, and limited the number of streams we could reliably test. Future studies will hopefully examine these streams in wetter conditions and have more access to flowing water. We suggest further study in wet years across the island for a better understanding of overall water quality. Additionally, the relationship between roads and vehicle traffic to water quality is a potential research topic. However, in conjunction with vegetation and geomorphological surveys indicate that progress is slowly but surely happening on Santa Rosa Island.