NCOS during rain storm March 28th 2022.
North Campus Open Space not only provides a safe space to walk, bike, run, and enjoy nature; the wetland is also working to improve water quality. Nutrients such as Nitrogen and Phosphorus that accumulate on the ground from fertilizer, animal waste and car exhaust, leaches into the local watershed during heavy precipitation events. In the realm of biogeochemistry, wetlands are considered a “sink,” or a location in which these nutrients are removed from the water by natural processes. Nitrogen in the water is typically in the form of Nitrate (NO3-) which could be harmful if consumed. Aerobic and anaerobic microbes work together in a process called “denitrification” to transform this soluble nutrient into a harmless gas, N2-, which makes up more than 70% of the air we breathe. Soluble phosphate (PO4) is removed from the water by settling out in the calm water of the estuaries and by binding to clay particles. These two processes are shown in the diagram below. Many features at NCOS promote denitrification and phosphate reduction such bioswales, seasonal ponds and the estuary itself. These features promote denitrification, by decreasing flow and increasing surface area for water and particles to settle. They also promote phosphorus reduction because the clay soils provide a substrate for the solutes to bind to. By reducing nutrient and sediment runoff this wetland is making the ocean a safer place for swimmers and wildlife.
Nutrient cycle http://www.wetlands-initiative.org/nutrient-removal
NCOS staff and student researchers are working to quantify the nutrients fluxes in the wetland. To do this we need to grab our rain gear and chase the storm! We have been collecting water samples and stream flow measurements during rain events over the past four years. Collecting stream flow will help us convert nutrient sample concentrations received in mg/L to total pounds of nitrogen and phosphorus entering the system per storm. This research has been made possible with the help of UCSB professor John Melack and his lab equipment. Students have also been working to characterize the watershed by collecting dissolved oxygen and salinity data, measuring groundwater depth and identifying aquatic flora and fauna.
Hayden Vega helping collect stream flow measurements at Phelps creek Marymont bridge during a lower flow time period.
Preparing to take stream flow measurements from Whittier pond outflow.
Ulva intenstinalis, a type of algae that responds to nutrient influxes and takes up nutrients. Because Devereux Slough opens to the ocean periodically after large storms, there is an opportunity for the decayed, organic matter to leave the system each year.
We intend to synthesize the data we have to write a scientific paper on the findings which will quantify the multitude of benefits that the restoration project is providing to the larger Goleta watershed. In the hydrograph below you can see how nutrients (green dots) typically increases with flow rate, as indicated by stream stage (e.g. water level). You can also see that the concentration of nutrients coming in to the system at Phelps and Whittier, for example, is much higher (0.5-1 mg/L) than that flowing out of the NCOS portion of the wetland at Venoco Bridge (0.01 mg/L).
However, concentration is not the whole story! As mentioned earlier, we are working on measuring stream flow so we can quantify the volume of water entering the system by multiplying flow rate by time at that flow rate. If you have stood at Phelps Bridge during a rain event you know how fast the flow rate can jump up and also drop. We can then multiply the volume of water by the nutrient concentration at each flow rate to characterize the total weight of nitrates and phosphates entering the system. This data will allow us to compare the nutrient inputs to other systems and to follow the fate of those nutrients in Devereux Slough. Because the mouth of the slough only opens to the ocean after significant rain volumes, there is more time for denitrification to happen in the calm estuary. But, because it only opens to the ocean once or twice a year , there are also fewer times to quantify the nutrients leaving the Devereux Slough system, so we have to be ready to collect when those events happen.
Nutrient concentrations from the inlets of Devereux Slough.
Lastly, here are just a few ways you can help to reduce nutrients in your wetland: always clean up your pet waste, decrease your fertilizer application, use phosphorus free fertilizer, and if you do need fertilizer be sure to avoid applying it right before big storms.