Title

Effects of light, nutrients and Dreissena (Dreissena polymorpha and Dreissena bugensis) on benthic ecosystems in lakes

Date of Award

2007

Degree Type

Dissertation

Degree Name

Doctor of Philosophy (PhD)

Department

Biology

Keywords

Nutrients, Lakes, Benthic ecosystems, Dreissena, Light penetration, Periphytons

Subject Categories

Ecology and Evolutionary Biology | Life Sciences | Terrestrial and Aquatic Ecology

Abstract

Filtration by invasive mollusks ( Dreissena spp. ) and nutrient reductions (e.g., phosphorus abatement) have dramatically increased water clarity and successfully lowered phosphorus inputs in the Great Lakes in recent decades. Field studies have shown that high Dreissena filtration greatly decreased phytoplankton biomass. However, we conducted field, mesocosm and lab experiments to examine light, Dreissena and nutrient effects on benthic algal biomass, production, and stoichiometry and benthic invertebrate biomass. This thesis consists of four chapters: (1) a series of field experiments to test effects of light and nutrients on periphyton food quantity and quality in lakes, (2) a mesocosm experiment to separate synergistic effects of Dreissena filtration and phosphorus abatement on benthic primary producers, (3) a mesocosm experiment to compare effects on benthic ecosystem of Dreissena to those of native grazers, and (4) three lab and field light experiments to test if single and natural periphyton stoichiometry response to light same as its production response to light.

Our field experiments showed that both light and nutrients affected periphyton biomass and stoichiometry. Periphyton biomass increased and periphyton C:P decreased as total phosphorus increased under high light. Periphyton biomass and C:P were higher in light than shade. Benthic invertebrate biomass was higher with high periphyton biomass and low periphyton C:P. Three lab and field light experiments also indicated that periphyton C: nutrients increased under high light due to more carbon fixation.

The two mesocosm experiments suggest that Dreissena are ecosystem engineers that modify habitat in a unique way by increasing light, habitat complexity and available P. Dreissena had a strong positive effect on periphyton PP, and biomass of macrobenthos on hard substrate. Light and Dreissena increased benthic invertebrate biomass. P1 alone did not affect biomass of periphyton and macrobenthos in ourutrophic mesocosms. High light and low P increased periphyton C:P on rock, but Dreissena did not affect periphyton stoichiometry, because it increased both C and P content of periphyton.

Together, these results showed Dreissena locally increased periphyton and benthic invertebrate biomass on hard substrate and increased benthic production lake-wide by mediating water clarity and light penetration. Our experiments allow us to tease apart concurring environmental stressors that Dreissena but not P abatement increased periphyton and benthic invertebrate biomass. Additionally, light should be considered as an important factor affecting periphyton stoichiometry on hard substrate and macrobenthos biomass lake-wide.

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