Hydrological perturbations drive rapid shifts in phytoplankton biodiversity and population dynamics in Butte Lake (Lassen Volcanic National Park, California).

Howard K, Noble P. 2017. Hydrological perturbations drive rapid shifts in phytoplankton biodiversity and population dynamics in Butte Lake (Lassen Volcanic National Park, California). Lake Reserv Manage. 34:21-41.Extreme interannual fluctuations in precipitation affect the hydrologic balance of montane lake systems and impact phytoplankton community composition and biodiversity. The 2013 water year (WY) was the driest period on record for California and caused drought conditions that reduced the total volume of Butte Lake (Lassen Volcanic National Park) by ∼40% at the end of WY 2014. These conditions resulted in changing lake hydrology from an open system (surface outflow) in 2012 to a prolonged period of being a closed system (no surface outflow) in WYs 2013 and 2014. Hydrologic perturbations experienced by Butte Lake in WYs 2013 and 2014 resulted in degraded water quality and shifts in phytoplankton biovolume composition and diatom biodiversity. Chlorophyll <italic>a</italic>, NH₄⁺, TP, DP, Ca²⁺, Mg²⁺, Na⁺ concentrations and specific conductivity (>10 µS/cm) increased in Butte Lake from WY 2012 to WY 2014, while dissolved oxygen concentrations decreased, and the hypolimnion became anoxic by August 2014. Declining water quality corresponded with increasing lake trophic status from oligo-mesotrophic in 2012 to borderline eutrophic by end of 2014, where DIN>DP (from increased concentration of NH₄⁺). Total surface phytoplankton biovolume shifted from being diatom-dominated in August 2012 to being cyanobacteria dominated by August and September 2014. Diatom biodiversity was significantly different in August 2014 compared with August 2012, and demonstrated a trend of increasing species richness and evenness from WY 2012 to WY 2014. These observed shifts imply the need for an increased focus on water resource and aquatic ecosystem management in Lassen Volcanic National Park lakes. [ABSTRACT FROM AUTHOR]