Grantee Research Project Results

Seagrass, Seaweed and Water Quality Management in the Great Bay Estuary

EPA Grant Number: R840932
Title: Seagrass, Seaweed and Water Quality Management in the Great Bay Estuary
Investigators: Matso, Kalle , Matsuoka, Atsushi
Institution: University of New Hampshire , University of New Hampshire
EPA Project Officer: Hoysala, Sneha
Project Period: September 1, 2024 through August 31, 2028
Project Amount: $1,150,000
RFA: Congressionally Directed Spending (2024)
Research Category: Estuarine Studies , Coastal Water Quality , Watersheds , Endocrine Disruptors , Water , Climate Change , Environment

Description:

EPA, the NH Department of Environmental Services, and many municipalities in the Piscataqua Watershed struggle to quantify the relationship between nitrogen and sediment pollution and decreased seagrass habitat. One aspect of this question is characterizing changes in seagrass distribution in relation to changes in seaweed abundance, as well as those things that block light. Decreased light is most often implicated as the cause of seagrass loss. The constituents that often block light are phytoplankton, non-algal particles (NAP), and colored dissolved organic matter (CDOM).

The 2021 EPA Total Nitrogen Permit has created some general goals, but it is recognized by everyone that further quantification of stressors and reduction goals is required. The municipalities with wastewater treatment plants have committed to an Adaptive Management framework, which required increased monitoring of the ecological variables mentioned in the first paragraph. Therefore, this will work will help galvanize community efforts to address pollution cost-effectively.

Objective:

The goal of the proposed project is to develop a Great Bay Estuary (GBE) specific bio-optical model that includes chlorophyll fluorescence due to eelgrass and seaweed. This will be built upon the first version of the bio-optical model being successfully developed for the GBE, which presently includes phytoplankton, non-algal particles (NAP), colored dissolved organic matter (CDOM), and pure water molecules as optically significant constituents. Field work as well as tank experiments planned in the proposed project will provide the baseline data for the model development.

Approach:

Fieldwork will be conducted at representative stations distributed in the GBE from spring to fall when ice is not present. At each station, eelgrass coverage, biomass, and several water quality variables (pH, oxygen, as well as temperature, salinity, etc.) along with the light diffuse light attenuation will be measured. Water and seagrass samples will also be collected. The water samples collected will be brought back to the Jackson Estuarine Lab where optical properties of each optically significant constituent (chlorophyll, CDOM, NAP) will be determined. The seagrass samples will be used for a series of tank experiments where different healthy status of seagrass will be placed in the tank to characterize its water reflectance.

Using data to be obtained from the above-mentioned field work and tank experiments, we will develop a bio-optical model by incorporating the eelgrass and seaweed fluorescence signatures observed in the red and near-infrared parts of the spectrum into the calculation of the reflectance
spectra based on Matsuoka et al. (2022). By applying the new model to a single point measurement, the physiological status of eelgrass will be retrieved through the optimization procedure. When upscaled, we will be able to provide a better estimate of eelgrass and seaweed coverage for the entire GBE by applying the new model to remotely sensed reflectance spectra using an operational satellite ( or occasionally available airborne) sensor.

The approach described below focuses on eelgrass before seaweed because pilot work has already occurred, providing information on eelgrass fluorescence signatures. After eelgrass is assessed using this approach, we will move on to focusing on seaweed. The overall deliverable for the community will be: 1) increased ability to assess changes in light; 2) increased ability to assess the constituents that block and/or absorb light, 3) increased ability to assess eelgrass coverage and health, 4) increased ability to assess changes in seaweed abundance and distribution.

Expected Results:

The health of eelgrass is a critical indicator in the Great Bay Estuary and has been a key consideration in regulations that are of significant concern to municipalities and citizens of the Piscataqua Watershed. Changes in light and seaweed competition are two aspects of eelgrass health that have been noted in previous studies as requiring more research. This problem will be addressed through this work, putting regulators, concerned citizens and municipalities in a much stronger position to address the health of this estuary of national significance.

Outputs:
• A bio-optical model that includes chlorophy 11 fluorescence due to eelgrass and seaweed.
• Pilot results of new method for assessing eelgrass cover and health as compared to seaweed cover.

Outcomes:
• Increased ability to assess changes in light Shared understanding on how to monitor the estuary going forward to evaluate potential changes to the Nitrogen Permit.
• Increased ability to assess the constituents that block and/or absorb light.
• Increased ability to assess eelgrass coverage and health.
• Increased ability to assess changes in seaweed abundance and distribution.

Supplemental Keywords:

Ecosystem protection; methods/techniques; public policy; risk management.

Progress and Final Reports:

2025