The importance of mixotrophy for estuarine primary production in the Chesapeake Bay

Eutrophication is often associated with nutrient pollution, reduced biodiversity, hypoxia, and increases in algal biomass and primary production (PP). Although insights into PP are crucial to understand eutrophication, the main processes affecting PP are not always known. More specifically, the importance of mixotrophy (i.e., combining autotrophy and phagotrophy) to PP has been understudied. Here we identify some of the main processes affecting PP (e.g., mixotrophy, nutrient limitation) and their variation in time and space along a large-scale gradient of environmental conditions (e.g., salinity, temperature, and nutrients). We apply an empirical-model integrated approach; we calibrate various PP models including the effects of mixotrophy to multi-decadal PP observations from the Chesapeake Bay (U.S.A.), focusing on specific regions and seasons. When mixotrophy is not included, the optimal model fit to the data suggests an absence of nitrogen limitation in the Bay, which contradicts the observations and results in autotrophic PP to be overestimated by ∼ 40 % in fall and ~ 75 % in spring in the polyhaline region. Mixotrophy is required to realistically capture nitrogen limitation. The relative contribution of mixotrophy to total PP strongly varies depending on season and region (∼ 10 - 75 %). Our results are one of the first estimates of the relative contribution of mixotrophy along a large-scale gradient of environmental conditions and may be important for both experimental scientists and modelers given that they often focus on autotrophy only.

Presentation Preference: Oral

Primary Presenter: Dante Horemans, Virginia Institute of Marine Science (dmlhoremans@pm.me)

Authors:

Dante Horemans, Virginia Institute of Marine Science, William & Mary  (dmlhoremans@vims.edu)

Marjorie Friedrichs, Virginia Institute of Marine Science, William & Mary  (marjy@vims.edu)

Pierre St-Laurent, Virginia Institute of Marine Science, William & Mary  (pst-laurent@vims.edu)

Raleigh Hood, Horn Point Laboratory, University of Maryland Center for Environmental Science  (rhood@umces.edu)

Christopher Brown, Earth System Science Interdisciplinary Center, University of Maryland and Global Science and Technology, Inc.  (cbrown12@umd.edu)