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Experimental thermocline deepening alters vertical distribution and community structure of phytoplankton in a 4-year whole-reservoir manipulation

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dc.contributor.authorLofton, Mary E.en
dc.contributor.authorHoward, Dexter W.en
dc.contributor.authorMcClure, Ryan P.en
dc.contributor.authorWander, Heather L.en
dc.contributor.authorWoelmer, Whitney M.en
dc.contributor.authorHounshell, Alexandria G.en
dc.contributor.authorLewis, Abigail S. L.en
dc.contributor.authorCarey, Cayelan C.en
dc.date.accessioned2023-05-10T13:35:03Zen
dc.date.available2023-05-10T13:35:03Zen
dc.date.issued2022-11en
dc.description.abstractFreshwater phytoplankton communities are currently experiencing multiple global change stressors, including increasing frequency and intensity of storms. An important mechanism by which storms affect lake and reservoir phytoplankton is by altering the water column's thermal structure (e.g., changes to thermocline depth). However, little is known about the effects of intermittent thermocline deepening on phytoplankton community vertical distribution and composition or the consistency of phytoplankton responses to varying frequency of these disturbances over multiple years. We conducted whole-ecosystem thermocline deepening manipulations in a small reservoir. We used an epilimnetic mixing system to experimentally deepen the thermocline via five short (24-72 hr) mixing events across two summers, inducing potential responses to storms. For comparison, we did not manipulate thermocline depth in two succeeding summers. We collected weekly depth profiles of water temperature, light, nutrients, and phytoplankton biomass as well as bottle samples to assess phytoplankton community composition. We then used time-series analysis and multivariate ordination to assess the effects of intermittent thermocline deepening due to both our experimental manipulations and naturally occurring storms on phytoplankton community structure. We observed inter-annual and intra-annual variability in phytoplankton community response to thermocline deepening. We found that peak phytoplankton biomass was significantly deeper in years with a higher frequency of thermocline deepening events (i.e., years with both manipulations and natural storms) due to altered thermal stratification and more variable depth distributions of soluble reactive phosphorus. Furthermore, we found that the depth of peak phytoplankton biomass was linked to phytoplankton community composition, with certain taxa being associated with deep or shallow biomass peaks, often according to functional traits such as optimal growth temperature, mixotrophy, and low-light tolerance. For example, Cryptomonas taxa, which are low-light tolerant and mixotrophic, were associated with deep peaks, while the cyanobacterial taxon Dolichospermum was associated with shallow peaks. Our results demonstrate that abrupt thermocline deepening due to water column mixing affects both phytoplankton depth distribution and community structure via alteration of physical and chemical gradients. In addition, our work supports previous research that phytoplankton depth distributions are related to phytoplankton community composition at inter-annual and intra-annual timescales. Variability in the inter-annual and intra-annual responses of phytoplankton to abrupt thermocline deepening indicates that antecedent conditions and the seasonal timing of surface water mixing may mediate these responses. Our findings emphasise that phytoplankton depth distributions are sensitive to global change stressors and effects on depth distributions should be taken into account when predicting phytoplankton responses to increased storms under global change.en
dc.description.notesFunding was provided by NSF grants CNS--1737424, DEB--1753639, DBI-1933016, DBI-1933102, and DGE-1651272, the Western Virginia Water Authority, the Global Change Center at Virginia Tech, the Virginia Tech College of Science Roundtable Make--A--Difference Scholarship, and the Virginia Water Resources Research Center.en
dc.description.sponsorshipNSF [CNS-1737424, DEB-1753639, DGE-1651272, DBI-1933016, DBI-1933102]; Global Change Center at Virginia Tech; Virginia Tech College of Science Roundtable Make-A-Difference Scholarship; Virginia Water Resources Research Center; Western Virginia Water Authorityen
dc.description.versionPublished versionen
dc.format.mimetypeapplication/pdfen
dc.identifier.doihttps://doi.org/10.1111/fwb.13983en
dc.identifier.eissn1365-2427en
dc.identifier.issue11en
dc.identifier.urihttp://hdl.handle.net/10919/115002en
dc.identifier.volume67en
dc.language.isoenen
dc.publisherWileyen
dc.rightsCreative Commons Attribution 4.0 Internationalen
dc.rights.urihttp://creativecommons.org/licenses/by/4.0/en
dc.subjectepilimnetic mixingen
dc.subjectfunctional traitsen
dc.subjectglobal changeen
dc.subjectstormen
dc.subjectwhole-ecosystem experimenten
dc.titleExperimental thermocline deepening alters vertical distribution and community structure of phytoplankton in a 4-year whole-reservoir manipulationen
dc.title.serialFreshwater Biologyen
dc.typeArticle - Refereeden
dc.type.dcmitypeTexten

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