Date of Award

Fall 2021

Project Type

Thesis

Program or Major

Natural Resources

Degree Name

Master of Science

First Advisor

William H McDowell

Second Advisor

Danielle Grogan

Third Advisor

Kalle Matso

Abstract

Estuaries are threatened by eutrophication due to increasing anthropogenic nutrient loading from surrounding coastal watersheds. The Great Bay Estuary, NH/ME, has been designated as nitrogen impaired primarily due to a 44% loss in eelgrass coverage since 1996. Since 2014, wastewater treatment plants in the watershed have begun upgrading to reduce nitrogen loads to Great Bay. This region has also experienced changes in climate, with multiple, consecutive years of low annual precipitation totals. The loss of eelgrass, increased variability in precipitation, and continued anthropogenic land-use influence on the region have biogeochemical consequences for Great Bay. Solute budgets for a portion of Great Bay Estuary were developed at annual and monthly timescales for nitrogen, orthophosphate, dissolved organic carbon, and total suspended solids. Inputs and outputs of nutrients, carbon, and sediments have been monitored monthly since 2008, across both point and nonpoint sources. Results show total annual nitrogen input loads are less than output loads, indicating net export from Great Bay. Dissolved inorganic nitrogen annual inputs exceeded outputs on average, resulting in positive Δ storages values and indicating net import. Net ecosystem metabolism is an important driver of patterns in dissolved organic carbon, orthophosphate, and dissolved inorganic nitrogen retention. Black box models can aid resource managers with understanding the relative amounts of nutrients, carbon, and sediments an estuary is biogeochemically capable of retaining or exporting to the coastal ocean.

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