Date of Award


Document Type

Honors Thesis (Open Access)


Colby College. Environmental Studies Program


Denise Bruesewitz


The Messalonskee Stream in central Maine has five hydroelectric dams on 16.6km. Each dam drastically changes the flow regime of the stream, dividing it into segments with different patterns of sediment settling and organic matter retention. I investigated how these disruptions impact nitrogen cycling, specifically nitrification rates above and below each dam. I expected higher nitrification rates above the dams, where levels of organic matter are higher, and lower rates below the dam where scouring removes organic matter and fine sediment from the streambed. I measured sediment nitrification rates with a nitrapyrin-inhibition assay and potential drivers of nitrification including sediment organic matter and pore water ammonia (NH4 +) above and below each dam. Nitrification rates ranged from 0-1490 μg NH4 + g AFDM -1 day-1 with an average of 105μg NH4 + g AFDM -1 day-1 showing a wide range of variation with no consistent pattern between above and below sites. Variation among the five dam sites is due different distributions of sediment above and below the dams due to widely varying flow velocity.


dam, Messalonskee, Maine, nitrogen, impact

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