Internal phosphorus loading alters nutrient limitation and contributes to cyanobacterial blooms in a polymictic lake

• DOI: 10.1007/s00027-024-01045-2
• Publication Date: 2024-03-12T03:01:48Z
• Authors: Micah M. Swann; Alicia Cortes; Alexander L. Forrest; Nick Framsted; Steven Sadro; S. Geoffrey Schladow; Angela De Palma-Dow
• Keywords: Bloom

Abstract Clear Lake, a medium-sized hypereutrophic, polymictic lake in northern California, has had recurring harmful cyanobacteria blooms (HCBs) for over century despite reductions external phosphorus (P) loadings. Internal P loading can alter nutrient availability and limitation supporting HCBs but is rarely quantified or compared with loads. We have loads from 2019 to 2021 the three main tributaries (accounting 46% of flow) internal loadings using two methods: mass balance modeled release rates soluble reactive oxic anoxic sediments. In addition, we combined high-frequency situ measurements water temperature dissolved oxygen, discrete grab sampling chemistry, remote sensing explore potential drivers observed variability provide comprehensive view spatiotemporal dynamics HCBs. By understanding relative contribution relationship between environmental parameters HCBs, interannual bloom be better predicted. Comparative estimates indicate that sources accounted 70–95% total input into system during study period. Contrary other lakes, intensity summer season was correlated timing duration anoxia rather than magnitude spring runoff. Internally released shifted nitrogen summer, potentially favoring proliferation nitrogen-fixing cyanobacteria.