Quantifying Nutrient Mass and Internal Cycling in Great Salt Lake

Science Center Objects

The Great Salt Lake (GSL) is an indispensable economic and ecological resource.  It provides critical habitat and food for millions of migratory birds, and generates nearly $200 million per year from recreational activities and the brine shrimp harvest industry (Bioeconomics, 2012).  These uses, habitat and aquaculture, rely on a balanced supply of nutrients in the Great Salt Lake to support phytoplankton growth and healthy brine shrimp populations (Belovsky et al., 2011).  However, little is known about processes controlling nutrient availability that would inform nutrient management policy (Naftz et al., 2008.)

We know that many factors affect nutrient loading, availability, and cycling in the lake (Figure 1), but the relative importance of each process is still unknown. Nutrients enter the system via river inflows, atmospheric deposition, and groundwater, but because the GSL is a terminal lake, most nutrients come from the internal cycling of a resident nutrient mass (Belovsky et al., 2011; Naftz, 2017).

This study seeks to provide a better understanding of the nutrient cycle in the lake by quantifying nutrients at key interfaces.

Cycling occurs through the food web as algae use nutrients for growth and are consumed by brine shrimp. As organisms die, organic matter sinks to the bottom of the lake, transporting nutrients to the deep brine and sediment layers where they undergo chemical transformations. Nutrients are then buried in lake sediments or recycled back into the water column, and potentially volatilized to the atmosphere. It is unknown how much nutrient mass is recycled back into the water column vs. lost to sedimentation, mineral precipitation/sorption, or volatilization processes. A better understanding of nutrient dynamics in the GSL would inform nutrient management policy and be useful to agencies managing GSL industries, ecosystems, and water quality. The proposal for this study outlines tasks for an initial phase (Phase1) of nutrient investigation on the lake. Future nutrient questions and research directions will build on information gained through this effort.

Schematic shows brine interface and potential nutrient sources

Figure 1. Schematic diagram of nutrient loading and internal cycling in Great Salt Lake that will be monitored.

Objectives

Objectives of Phase 1 are to better understand nutrient pools in GSL.  Data will be collected to: 1) quantify nutrient mass from multiple pools of the GSL (Figure 1), 2) estimate nutrient flux rates, and 3) estimate nutrient burial in sediments. Additionally, we will pilot the use of isotopes to explore internal nutrient cycling. 

Approach

To begin to understand nutrient cycling and loading, it is necessary to quantify the relative nutrient mass in different pools of the lake, including lake sediments, sediment pore water, particulate matter, biota, river inflows, the water column (upper brine layer (UBL) and deep brine layer (DBL)), and atmospheric deposition (Figure 1). 

Quantifying carbon (C), nitrogen (N), phosphorus (P), and sulfur (S), analytes and their ratios from several nutrient reservoirs will improve our ability to understand and identify processes important for nutrient cycling in GSL.  High-resolution sampling across the UBL/DBL interface will be piloted to better understand nutrient mass transfer between the UBL and DBL.  Stable isotope ratios of 34S/32S will be used as a proxy to understand mixing from anoxic sediments.  Stable isotope ratios of 13C/12C and 15N/14N will be used selectively in biota to begin to identify important in-lake biogeochemical processes. 

Due to the unique characteristics of the GSL, some analytical methods may need additional development; therefore some analyses proposed in this study may be delayed.  Sampling will occur at locations identified in figure 2 during a single event and will provide a detailed “snapshot” of nutrient processes that can be expanded upon in future studies during other lake conditions. 

Image of Great Lake

Figure 2.  Map of proposed sampling locations.

References

Bioeconomics, Inc.  2012.  Economic significance of the Great Salt Lake to the State of Utah.  Prepared for the State of Utah Great Salt Lake Advisory Council, Salt Lake City, Uta. 50 p.  https://documents.deq.utah.gov/water-quality/standards-technical-services/great-salt-lake-advisory-council/Activities/DWQ-2012-006864.pdf, accessed 16 July 2018.

Belovsky, G. E., Stephens, D., Perschon, C., Birdsey, P., Paul, D., Naftz, D., Baskin, R., Larson, C., Mellison, C., Luft, J., Mosley, R., Mahon, H., Van Leeuwen, J., Allen, D.  2011.  The Great Salt Lake Ecosystem (Utah, USA):  long term data and a structural equation approach.  Ecosphere, 2(3):  1-40.  https://doi.org/10.1890/ES10-00091.1

Naftz, D., Angeroth, C., Kenney, T., Waddell, B., Darnall, N., Silva, S., Perschon, C., Whitehead, J.  2008.  Anthropogenic influences on the input and biogeochemical cycling of nutrients and mercury in Great Salt Lake, Utah, USA.  Applied Geochemistry, 23(6):  1731-1744.  doi:10.1016/j.apgeochem.2008.03.002

Naftz, D. 2017.  Inputs and internal cycling of nitrogen to a causeway influenced, hypersaline lake, Great Salt Lake, Utah, USA.  Aquatic Geochemistry, 23:  199-216.  (accessible from Publications at top of page)

 

Partners

Below are partners that have generously supported this work.

*  Utah Deptartment of Natural Resources, Division of Forestry, Fire, and State Lands

Utah Department of Environmental Quality, Division of Water Quality, Great Salt Lake Advisory Council

*  Utah Department of Natural Resources, Division of Wildlife Reources, Great Salt Lake Ecosystem Program