Date of Award

2019

Document Type

Open Access Master's Thesis

Degree Name

Master of Science in Biological Sciences (MS)

Administrative Home Department

Department of Biological Sciences

Advisor 1

Amy M. Marcarelli

Committee Member 1

Casey J Huckins

Committee Member 2

Molly A. Cavaleri

DOI

10.37099/mtu.dc.etdr/837

Abstract

Climate change and species invasion are two agents of global change altering aquatic ecosystems worldwide. Submerged aquatic macrophytes control lake ecosystem processes through their direct and indirect interactions with other primary producers, but how their interactions may be altered by species invasions or how they function over full seasonal cycles in temperate lakes is poorly understood. We first addressed whether the presence of invasive watermilfoil (IWM) altered standing crops and gross primary pro-duction (GPP) of other littoral primary producers (macrophytes, phytoplankton, attached algae or periphyton) in littoral zones of 6 Michigan lakes. We found no differences in primary producer standing crops or GPP between plots with or without IWM. Macrophyte standing crop predicted rates of benthic periphyton GPP and standing crops of all other primary producers across all study plots, along with water temperature, nutrient concentrations, and water clarity. Second, we studied year-round dynamics of littoral primary producers in 2 lakes located on the Keweenaw Peninsula of the Upper Peninsula of Michigan. Standing crops of primary producers were present all year and changed seasonally, although they were lowest during winter. Water temperature explained 34% of phytoplankton GPP and 57% of plot-level GPP, which incorporated all primary producers. Water under the ice was hypoxic during winter. Together, the results of these studies suggest that macrophyte biomass, temperature and ice cover are important drivers of littoral zone productivity among lakes and over seasons, which has implications for understanding possible effects of climate change on ecosystem processes in north temperate lakes.

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