The U.S. Environmental Protection Agency has a research goal of improving its ability to quantify and predict aquatic (freshwater, estuarine, marine) ecosystem response and recovery to changing nutrient loads. This strategy calls for developing numeric thresholds for total nitrogen (TN) and total phosphorus (TP) as causal variables and dissolved oxygen and chlorophyll
a as nutrient-related response variables. The objective of this research is to quantify the relationship of nutrients with management response and recovery trajectories in aquatic ecosystems. In this study, we use light attenuation as a measure to determine the quality and clarity of New England estuarine waters in response to nutrient loading. The clarity of these waters is important to the sustainability of healthy seagrass habitats which support the stability, nursery function, biochemical cycling and trophic dynamics of coastal ecosystems. We suggest that numeric thresholds and management recovery trajectories can be derived for seagrass management based on light attenuation (K
d), colored dissolved organic matter (CDOM) absorption, and the concentrations of total suspended solids (TSS) and chlorophyll
a (chl
a) retrieved from remotely sensed data.
The Hyperspectral Imager for the Coastal Ocean (HICO) instrument onboard the International Space Station offered EPA the opportunity to model the quality and quantity of light for the Narragansett (Rhode Island) and Buzzards Bays (Massachusetts) estuarine systems. Using atmospherically corrected images, apparent (e.g., remote sensing reflectance (Rrs)) optical properties were retrieved and used to derive bio-optical models which estimated chl a concentrations, CDOM absorption and TSS concentrations. The chl a, CDOM absorption, and TSS estimates were then input into a regionally calibrated seagrass bio-optical model which predicted spatial and temporal patterns in PAR attenuation (KdPAR) and the potential distribution of Zostera marina during the 2013 and 2014 growing seasons.
