Water Resources Research Act Program

Details for Project ID 2018MT327B

Student Research: Limitations to Photosynthesis in Silver Bow Creek

Institute: Montana
Year Established: 2018 Start Date: 2018-03-01 End Date: 2019-02-28
Total Federal Funds: $2,000 Total Non-Federal Funds: $670

Principal Investigators: Isaiah Robertson

Project Summary: Photosynthesis provides heterotrophic life on Earth with uptake of carbon dioxide and production of oxygen. The limits of photosynthesis are controlled by many factors including temperature, pH, and the availability of light, inorganic carbon, nutrients, and presence or absence of toxic metals and substances. Human influences can affect these variables and thus the fundamental process of photosynthesis (Cox, 2011). In our Clark Fork watershed, the fragile headwaters have been deeply impacted by mining wastes and have affected where microbial and macrophyte photosynthesis is occurring. This project aims to qualify and quantify microbial and macrophyte photosynthesis along the headwaters of the Clark Fork in relationship to changing controlling variables that have influence on ecosystem health throughout the entire watershed (NRDP, 2005; EPA, 2011). This project will take place along Silver Bow Creek, a stream that flows through the city of Butte, Montana until it reaches the Warms Spring Ponds to form the headwaters for the Clark Fork River. Silver Bow Creek has been used to remove mining and municipal wastes from the Butte area (NRDP, 2005). Since 2005 efforts to restore the creek’s banks have begun to shape the creek into a healthier environment (NRDP, 2005; EPA, 2011). This combination of pollutants and restoration efforts has created an environment that may cause unique limitations to photosynthesis. Heavy metals often exist as long-term pollutants, and lead has been found to limit growth in algae (Dao and Beardall, 2016). Also, cadmium has been shown to be toxic to cyanobacteria (Cox, 2011), while copper has a history as an algicide (Adamson, and Sommerfeld, 1980). The restoration efforts on the banks of Silver Bow Creek have left it with a wide variety of stream banks (EPA, 2011). The varying riparian regiments created by the restoration efforts allow the streambed different access to light at different sites. Light is a predominant limit on photosynthesis, and likely affects the degree of photosynthesis down the stream path (Roberts et al., 2004). Wastewater treatment and discharge of storm waters have altered the nutrient regiments within Silver Bow Creek. Nitrogen and phosphorus are usually limiting when light is saturated (Konopka, 1983). Plants have seasonal cycles and are less abundant and dormant in winter months. These cycles are driven by temperature and changes in light, and can create a shift in observed composition of photosynthetic communities (Luo et al., 2016). Preliminary data, collected by LEGEND, provides evidence of seasonal trends in Silver Bow Creek. However, the data plot opposite of what is expected. Photosynthesis preferentially utilizes lighter carbon isotopes enriching 13C in the aquatic inorganic carbon pools and increasing the 13C/12C ratio (δ13C). The enrichment in inorganic carbon isotopes in the cooler winter months, and depletion in warmer summer months, shown on this graph, suggests that photosynthesis is more active relative to respiration during the winter months (Fig. 1) (McConnaughey, et al., 1997). This is an interesting point that merits further investigation into the seasonal shifts in microbial communities.