Scientists report unusual nutrient and chlorophyll patterns, link to berm and lab-method shifts

Scientists at the meeting detailed an unexplained decline in chlorophyll in January–February and discussed hypotheses about nutrient inputs, export and microbial dynamics that may be reshaping Great Salt Lake’s pelagic food web.

Christine (USGS partnership) and Gary Golowski (laboratory presenter) summarized monitoring and lab work underpinning the discussion. Christine said the USGS nutrient mass-balance draft identifies the north arm as the largest source of phosphorus and nitrogen into the lake and highlighted ongoing discrete inflow and salinity measurements. "Our most recent measurement was around 30 CFS," she said when describing low uncertainty flows near detection limits for some cross-sections.

Participants flagged an uncharacteristic suppression of chlorophyll in early winter despite minimal grazing and expected growth conditions. Kyle Stone and others proposed three broad explanations heard in the meeting: reduced nutrient delivery into the south arm, export of nutrients to the north arm, or rapid uptake or sequestration by microbial mats or other benthic components. Gary presented lab experiments showing brine fly larvae accelerate decomposition of brine shrimp pellets — increasing decomposition rates by roughly 300% — and emphasized that brine flies can substantially alter nitrogen cycling. "What this is telling us is that the brine flies are playing a tremendous impact on the nitrogen cycling within the lake," Gary said.

Gary and colleagues compared model forecasts to observed chlorophyll and SIS time series since 1996 and noted the model fits well for many years but diverged during earlier troubled years and again after 2022, when managers modified the berm. Presenters said those changes could be altering the timing and pathways of nutrient inputs, allowing microbialites and biofilms to release cyanobacteria and diatoms into the water column during cold or high-wind events — processes the current forecast model does not fully capture.

Separately, speakers announced an operational change in laboratory analyses: the national water-quality laboratory will no longer run hypersaline nutrient samples. "They’re now refusing to do it," a presenter said, noting the program will move hypersaline nutrient analyses to Chesapeake Biological Labs and run a formal lab-comparison to document any step changes in the long-term record.

Researchers emphasized the need to account for lab-method shifts, improve sampling near inflows, and incorporate stochastic wind and cold events into retrospective model evaluation. They proposed building cyst-hatching dynamics and microbial-source terms into future model iterations and pledged to publish updated nutrient-mass-balance results and a lab-comparison for historical continuity.