AVIRIS Measurements of Chlorophyll, Suspended Minerals, Dissolved Organic Carbon, and Turbidity in the Neuse River, North Carolina

Abstract

Many aquatic ecosystems in the United States and worldwide are impaired by the over-enrichment of waters by nutrients. In advanced stages, the process of eutrophication can cause harmful algae blooms. This research retrieved the concentrations of suspended chlorophyll (Chl), suspended minerals (SM), colored dissolved organic carbon (DOC), and turbidity (total attenuation) from AVIRIS imagery of a severely overenriched waterway in North Carolina, and evaluated if these parameters could be used as indicators of conditions leading to algae blooms. A digital image processing algorithm called QSC1 (Quantitative Shoreline Characterization, Version 1.0) was used. The retrieved water quality parameter values were tested by statistical comparisons to field measurements made at the time of the AVIRIS data collection. Applying QSC1 to AVIRIS imagery resulted in measurements of Chl that correlated well with field measurements (r � 0.84). Problems with field sampling prevented the assessment of retrieved SM and DOC. The statistical correlation analysis indicated that, for comparison to remotely sensed data, field measurements in the steadily flowing Neuse River must be collected within two hours of the imagery. Thematic maps of each water quality parameter were generated from the imagery and evaluated. The maps of Chl showed spatial patterns consistent with the field data and circulation of the river, and indicated potential point and non-point sources. Statistical and principle component analyses were used to assess whether the AVIRIS water quality measurements were directly or indirectly related to parameters and conditions indicative of nutrient loading and algae blooms that were measured in the field. The AVIRIS measurements were used to create a new index of eutrophication, the Algae Production Potential Index (APPI), for the purpose of mapping where conditions of high nutrient loading and potential algae blooms exist. The index uses direct measurements of Chl, DOC, and SM (as a surrogate for phosphate). These measurements are combined in a GIS model based on ecological relationships. Although not field verified, the APPI map shows patterns of algae bloom conditions that are similar in size, scale, and location to previous blooms in the Neuse.