Title

Microbial Patterns in the Metalimnion of Lake Whatcom, Washington

Date of Award

2004

Document Type

Thesis

Degree Name

Master of Science (MS)

Department

Environmental Science

First Advisor

Robin A. Matthews

Second Advisor

Leo R. Bodensteiner

Third Advisor

Craig Moyer

Abstract

Over the past several years, Matthews et al. (2004) observed two phenomena: a metalimnetic oxygen maximum in Basin 1, and a metalimnetic ammonia maximum in Basin 3. These phenomena may be related to microbial metabolism in the metalimnion of Lake Whatcom, Washington. The purpose of my thesis research was to evaluate the nature and cause of the metalimnetic oxygen maximum in Basin 1 and the metalimnetic ammonia maximum in Basin 3. To accomplish this, I measured water quality parameters, phytoplankton abundance (density and biovolume to genus), and bacterial abundance (4,6-diamidino-2-phenylindole cell counts and 2-(p-iodophenyl)-3-(p-nitrophenyl)-5- phenyltetrazolium chloride violet active counts) within basins 1 and 3 of Lake Whatcom during the summer of 2003. Graphical analyses using isopleths and scatter plots, and non-parametric correlation analyses (Kendall’s 𝜏) were used to evaluate these phenomena.

Lake Whatcom water quality parameters displayed significant seasonal trends during the summer of 2003. Of particular importance were trends associated with dissolved oxygen and chlorophyll. Hypolimnetic oxygen depletion was apparent towards the end of summer at Site 1 (Basin 1). This anaerobic environment altered hypolimnetic water quality parameters such as ammonia, nitrate, soluble reactive phosphate, and total phosphorus. The hypolimnetic oxygen concentrations at Site 4 (Basin 3) did not drop to zero, and therefore did not have as much influence on other water quality parameters. Chlorophyll concentrations were positively correlated with month in the epilimnion at Site 1, indicating an increase in concentration as summer progressed. Epilimnetic nitrate concentrations at Site 1 were negatively correlated with chlorophyll, indicating that nitrate concentrations decreased as chlorophyll concentrations increased. All correlations, including monthly correlations and correlations among water quality parameters were predictable given the biological activity that occurs in Lake Whatcom.

Monitoring during the summer of 2003 revealed that a temporary metalimnetic oxygen maximum was present in Basin 1 from approximately mid-June to mid-August. Chlorophyll measurements indicated a chlorophyll maximum within and below the metalimnetic oxygen maximum. Graphical and correlation analyses indicated a higher biovolume abundance of phytoplankton in the metalimnetic oxygen maximum. The most likely source of the metalimnetic oxygen maximum was a band of mixed diatoms and cyanobacteria represented by Cyclotella, Anacystis, and Chroococcus.

The metalimnetic ammonia maximum was present in Basin 3 on all sampling dates. Ammonia in the water column of lakes is usually the primary end product of the decomposition of organic matter by heterotrophic bacteria. Significant correlations existed between ammonia and active bacteria on all dates except 26 August. Graphical and correlation analyses indicated that ammonification by heterotrophic bacteria in the metalimnion was the most likely cause of the metalimnetic ammonia maximum.

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