Date of Graduation

5-2016

Level of Access

Open Access

Degree Name

Bachelor of Arts

Department or Program

Geology

Number of Pages

97

First Advisor

Beverly Johnson

Abstract

Nequasset Lake, in Woolwich Maine, is a coastal lake that serves as a spawning habitat for the anadromous fish Alosa Pseudoharengus, commonly known as alewives. Migrations of anadromous fish provide a source of allochthonous nutrients from the sea into freshwater systems. These nutrients, known as marine derived nutrients (MDN) are incorporated into both the sedimentary record and the biota of the impacted system. Nitrogen, one of these nutrients, plays a vital role in primary production and other geochemical processes within freshwater environments. In 2012 and 2013, monitoring efforts were put into place in order to assess the impact of the alewife migration on the nitrogen budget of the lake. In 2014, as an effort to increase alewife accessibility into the lake, the fish ladder present at Nequasset Lake was renovated to a more durable model. This is expected to increase the MDN influx in the lake, as more fish are able to reach spawning habitat. The purpose of this study is to assess the effects of increasing migration sizes on Nequasset Lake, and determine how MDN are changing the nitrogen cycling within the lake. In 2015 the largest migration of alewives was seen at Nequasset Lake. Water samples were taken from the outlet of the lake for and tested for changes in δ15N values in nitrate over time using the EA-GC-IRMS at the Bates College Environmental Geology Laboratory. 15N serves as an indicator of MDN due to an enriched nitrate pool at sea. These measurements were compared to δ15N values of the particulate organic matter, chlorophyll concentrations, nutrient concentrations, as well as the data from previous years, in order to observe any changes within the lake. Three different phases of nitrogen cycling were identified: the spring bloom, influx of MDN, and a restoration of natural nitrogen cycling. Increases in these forms of cycling were observed each year, likely an effect of increasing alewife population sizes.

Components of Thesis

1 pdf file

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