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Scientists report low pelagic chlorophyll, explore nutrient, microbialite and lab-method causes
Summary
Researchers reported lower-than-normal pelagic chlorophyll this winter and outlined hypotheses (nutrient dilution, microbialite recolonization and altered north-arm nutrient flux) along with an interlab plan to harmonize nutrient analyses.
Researchers from university and state labs reported unusually low pelagic phytoplankton (chlorophyll) this winter and outlined hypotheses and laboratory work to explain the pattern.
Gary (surname given in meeting) presented phytoplankton counts showing 2025 values below the long-term (1994–2023) averages and below last year’s values. He said the low chlorophyll is unlikely to be driven by temperature alone and suggested multiple hypotheses: dilution of nutrients due to increased lake volume, recolonization of exposed microbialite biofilms that immobilize nutrients, and changes in north-arm connectivity that alter nutrient delivery to the south arm. "I can't prove either of those statements," he said, offering them as working hypotheses that require nutrient data.
Hannah described an interlaboratory comparison and spike-and-recovery study intended to resolve differences between results produced by NHS/Chesapeake/High Sierra/NWQL (USGS) laboratories. She said the labs have different processing times and that Chesapeake Biological Lab results for some phosphorus species ran higher than NWQL; Hannah said they will run serial-dilution spike-recovery tests and send matched samples (with matched salinity conditions) to multiple labs for method comparison and calibration. "This is a huge priority for us," Hannah said, referring to the need for consistent nutrient analyses.
Presenters discussed decomposition experiments and biofilm work: lab trials testing decomposition rates of phytoplankton, shrimp bodies, feces and biofilm showed decomposition varied with temperature and salinity and that method artifacts (for example, insufficiently killed phytoplankton samples) can bias results. Gary described adjustments to sample preparation (longer freezing protocols) that produced more consistent decomposition estimates for biofilm material.
Researchers also presented emerging brine-fly larvae counts and nitrogen-content data for pelagic and benthic components; student projects will compare microbialite recolonization data to earlier records (2011 and 2016) to assess changes in biofilm community composition. No regulatory actions were proposed — the session focused on research findings and planned lab comparisons.
