Grantee Research Project Results
1999 Progress Report: Rhode River CISNet: Estuarine Optical Properties as an Integrative Response to Natural and Anthropogenic Stressors
EPA Grant Number: R826943Title: Rhode River CISNet: Estuarine Optical Properties as an Integrative Response to Natural and Anthropogenic Stressors
Investigators: Gallegos, Charles L. , Jordan, Thomas E. , Neale, Patrick J. , Correll, David L.
Current Investigators: Gallegos, Charles L. , Jordan, Thomas E. , Neale, Patrick J.
Institution: Smithsonian Environmental Research Center
EPA Project Officer: Packard, Benjamin H
Project Period: October 1, 1998 through September 30, 2001
Project Period Covered by this Report: October 1, 1998 through September 30, 1999
Project Amount: $510,181
RFA: Ecological Effects of Environmental Stressors Using Coastal Intensive Sites (1998) RFA Text | Recipients Lists
Research Category: Environmental Statistics , Aquatic Ecosystems , Ecological Indicators/Assessment/Restoration
Objective:
The primary objective of this work is to utilize recent advances in the monitoring of estuarine spectral optical properties to develop the capability to continuously monitor concentrations of optically active parameters as an integrated measure of estuarine response to perturbations on time scales ranging from individual storms or phytoplankton blooms to seasonal, decadal, or longer responses to increased disturbance or to management efforts. Research to interpret continuously monitored optical properties is focused on: (1) interpretation of optical properties in terms of the concentrations of suspended particulate matter (SPM), phytoplankton chlorophyll, and colored dissolved organic matter (CDOM); (2) manipulative experiments to establish the response of in situ concentrations of chlorophyll, SPM, and CDOM to inputs of nutrients on event to interannual time scales; and (3) process level research to examine the effects of solar ultraviolet (UV) radiation on nearshore plankton communities, as influenced by potential changes in estuarine optical properties.Progress Summary:
Research in the first year has focused on establishing a system for monitoring estuarine optical properties and installation of salinity monitors to gauge mixing and exchange in the system. We have installed a WETLabs Spectral AC-9 absorption and attenuation meter in a monitoring shed on the Rhode River. The instrument measures absorption and beam attenuation coefficients at nine wavelengths. A self-cleaning, flow-through system has been designed to supply water to the instrument at hourly intervals.In situ profiles of downwelling and upwelling spectral irradiance have been conducted approximately weekly since mid-January 1999. Water samples for the determination of optical water quality parameters and inherent optical properties in the laboratory are collected along with profiles. Samples have been analyzed for total, volatile, and fixed suspended solids, chlorophyll a, turbidity, absorption by CDOM, and absorption by particulate matter.
Based on optical and water quality data collected during weekly underwater irradiance profiles, we have begun to develop algorithms for determining concentrations of optical water quality parameters from continuously monitored optical properties. In data collected to date, absorption at 676 nm, near the peak of chlorophyll absorption in the red, is highly correlated with the concentration of chlorophyll a. Data from the Lower St. John's River in Florida, collected in another project, extend the range of available measurements, and indicate that the relationship may be quite robust. The slope of the relationship, 43.5 [mg Chl m-3 (m-1)-1] implies a very reasonable value of 0.022 m2 mg-1 for the specific absorption of chlorophyll a at 676 nm (Figure 1).
Monitoring data collected with the AC-9 indicate that the system will be useful for resolving changes in phytoplankton chlorophyll over a wide range of time scales. Daily sampling, before the automated system was running, captures the main features of a chlorophyll rise to a minor peak in mid-May, followed by a decline over the next 2?3 weeks to a local minimum in early June. Analysis in connection with data on water motions and streamflow will enable us to distinguish advective changes, and will assist in identification of nutrient inputs resulting in phytoplankton blooms (Figure 2).
The automated data reveal a high degree of variability at short time scales (Figure 3). The longest time series currently available is 13 days in October 1999. Some of that variability appears to be advective, as several of the absorption local maxima align with minima in water depth. The usual gradient in chlorophyll concentration is increasing up estuary, so that low water would tend to bring higher concentration water past the monitor. Lower frequency changes, not obviously related to advection, occur at an approximately weekly time scale, indicated by a steady decline over the first 4 days of the series, followed by a rise over the next 3 days. Continuing research utilizing the full spectrum of measured absorption and scattering coefficients will help interpret changes in optical properties in terms of suspended particulate matter and CDOM, in addition to chlorophyll a.
Absorption coefficient (m-1)
Figure 3. Time series of absorption at 676 nm (corrected for baseline absorption at 715 nm) measured using WETLabs Spectral AC-9 in monitoring mode at hourly intervals. Rhode River, Octber 1?13, 1999. Superimposed are water level readings (solid line). Some changes in a (676) appear to be advective, with some absorption peaks aligning with water level minima.
Julian Day, 1999
Figure 3. Time series of absorption at 676 nm (corrected for baseline absorption at 715 nm) measured using WETLabs Spectral AC-9 in monitoring mode at hourly intervals. Rhode River, Octber 1?13, 1999. Superimposed are water level readings (solid line). Some changes in a (676) appear to be advective, with some absorption peaks aligning with water level minima.
Profiles of in situ spectral irradiance have been conducted on 51 occasions. These are utilized to calculate spectra of diffuse attenuation coefficients. Diffuse attenuation spectra are quite conservative in shape, with maximal attenuation in the UV region, a minimum at about 555 nm, and increasing again in the red region due to water and chlorophyll (Figure 4). Comparison of relatively clear and more turbid profiles illustrate the extreme sensitivity of attenuation in the UV portion of the spectrum to changes in water quality (Figure 4).
A wide range of optical conditions have been observed. The diffuse attenuation spectra are providing an additional check on the validity of the AC-9 readings. We have used equations that predict diffuse attenuation coefficient from absorption and scattering coefficients to verify measurements made with the AC-9 (Figure 4). The absorption and scattering coefficients measured by the AC-9 generally provide very good estimates of spectral diffuse attenuation coefficients, indicating that reliable estimates of absorption and scattering coefficients are being obtained.
Diffuse attenuation coefficient (m-1)
Figure 4. Spectra of measured (squares) diffuse attenuation in the Rhode River for some of the more turbid and clear conditions encountered, compared with estimates derived from measurements of absorption and scattering coefficients made with a WETLabs Spectral AC-9 (circles). Note: The AC-9 measurements do not extend into the UV region of the spectrum.
Wavelength (nm)
Figure 4. Spectra of measured (squares) diffuse attenuation in the Rhode River for some of the more turbid and clear conditions encountered, compared with estimates derived from measurements of absorption and scattering coefficients made with a WETLabs Spectral AC-9 (circles). Note: The AC-9 measurements do not extend into the UV region of the spectrum.
Publications/ Presentations: None.
Future Activities:
In the coming year, we will begin to post data on the World Wide Web. We are in the process of creating an FTP site that will be linked to the main research page of our local site (http://www.serc.si.edu).
Measurements of benthic nutrient release rates will continue through the fall and commence again in the spring (Figure 5). In spring 2000, we anticipate conducting experiments to manipulate salinity and nitrate concentration of water overlying sediment cores to determine whether there is an interaction between denitrification and phosphate release rates, as is indicated by correlative analyses. Materials and methods for measuring nutrient release rates in core samples will be tested during the winter. Measurement of biological weighting functions for sensitivity to ultraviolet irradiance will commence this winter.
Journal Articles:
No journal articles submitted with this report: View all 15 publications for this projectSupplemental Keywords:
ecological effects, precipitation, nutrients, indicators, environmental chemistry, marine science, modeling, monitoring, Chesapeake Bay., RFA, Scientific Discipline, Water, Geographic Area, Ecosystem Protection/Environmental Exposure & Risk, Water & Watershed, Nutrients, Ecology, estuarine research, Environmental Chemistry, Ecosystem/Assessment/Indicators, Ecosystem Protection, State, Chemistry, Ecological Effects - Environmental Exposure & Risk, Air Deposition, Environmental Monitoring, Ecology and Ecosystems, Ecological Risk Assessment, Watersheds, Ecological Indicators, Chesapeake Bay, anthropogenic stress, aquatic ecosystem, coastal ecosystem, dissolved organic matter, nutrient supply, ecological exposure, anthropogenic stresses, monitoring, CISNet, estuaries, UV effects, bioavailability, natural stressors, esturarine eutrophication, Rhode River, phytoplankton dynamics, UV radiation, environmental decision-making, aquatic ecosystems, nutrient cycling, water quality, plankton, stress responses, UV-B, atmospheric deposition, Maryland, UV-B radiationRelevant Websites:
A preliminary Web site has been established as a link to the Smithsonian Environmental Research Center (SERC) Photobiology Laboratory at the address http://www.serc.si.edu/uvb_web_html/CISnet.html. It contains the project objectives and abstract, and is being revised to link to downloadable data and research results. When completed, the location will be changed to be accessed from the Coastal Ecosystems Project descriptions of the main SERC Web Site.Progress and Final Reports:
Original AbstractThe perspectives, information and conclusions conveyed in research project abstracts, progress reports, final reports, journal abstracts and journal publications convey the viewpoints of the principal investigator and may not represent the views and policies of ORD and EPA. Conclusions drawn by the principal investigators have not been reviewed by the Agency.