Date of Graduation

Spring 5-2013

Level of Access

Open Access

Degree Name

Bachelor of Arts

Department or Program

Geology

Number of Pages

98

First Advisor

Beverly Johnson

Abstract

Anadromous fish, such as alewives (Alosa pseudoharengus) can provide an important link between coastal watersheds and the Atlantic Ocean along the Gulf of Maine. Alewives contribute marine-derived nutrients (MDN) in the form of nitrogen to freshwater lakes via excretion and mortality as they migrate upstream during spawning season. Previous attempts to detect MDN in the sedimentary record have provided equivocal results. Freshwater biota or the size of current alewife migrations may have a significant effect on the sedimentary MDN signal. The focus of this project is to determine the degree to which MDN were imported into Nequasset Lake, Woolwich Maine. These data represent the initial findings of an expanded, multi-institutional, multi-year study currently underway. The Nequasset Lake watershed covers an area of ~50 square kilometers and provides drinking water to the city of Bath and three other communities in Maine. Every spring, alewives return to Nequasset Lake to spawn, accessing the lake through a fish ladder adjacent to the water control dam. In April and May 2012, alewife counts were performed at the top of the fish ladder by volunteers of Trout Unlimited and Kennebec Estuary Land Trust. Water samples were collected from the top of the fish ladder, and from the 4 major stream inlets, and analyzed for nutrient concentrations (TDN, NO3-, NH4+) to construct a nitrogen budget. Additional samples were collected for δ15N of water NO3- analysis from April to June to trace marine-derived nitrogen from the alewives in the lake. δ15N of water NO3 (+1.6 ‰) suggests the only detectable MDN signal is at the top of Nequasset Dam. However, NH4+ concentrations may suggest Nequasset Brook and Sucker Brook be targeted for restoration management. Nutrient cycling models shows that the implications of MDN may be insignificant because nutrient loading from the 2012 migration only accounts for approximately 1% of the total nitrogen inputs.

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