Grantee Research Project Results
2000 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.
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, 1999 through September 30, 2000
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 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 UV radiation on near-shore plankton communities, as influenced by potential changes in estuarine optical properties.
Research in the first year focused on establishing a system for monitoring estuarine optical properties, installation of salinity monitors to gauge mixing and exchange in the system, and determining the response of optical properties to experimental additions of nutrients. In the second year, we emphasized the continued collection of continuously monitored optical properties, development of data analysis procedures, and collection and Web posting of salinity data.
Progress Summary:
The system for monitoring inherent optical properties developed in Year 1 has proceeded with only minor interruptions due to equipment failure since spring 2000. One especially significant area of progress has been the development of an algorithm for discriminating the light absorption by phytoplankton, CDOM, and SPM in waters in which absorption is dominated by factors other than phytoplankton (i.e., case 2 waters). A manuscript based on this development has been prepared. Although performance of the algorithm will continue to be evaluated and refinements will be made, development and publication of this algorithm essentially completes objective 1 of the research.
Salinity monitors to measure mixing and exchange in the Rhode River were operated at three locations in addition to the one preexisting probe. These probes have been operating since late March 1999, with interruption during periods of ice. The probes have been very reliable and have experienced very few interruptions. They were in place and measured the response of the system to the spring freshet in April 2000. The intrusion of this freshet from elevated flows of the Susquehanna River delivered a late season pulse of nitrate, which fueled an extraordinary bloom of the mahogany tide dinoflagellate, Prorocentrum minimum.
Mesocosm experiments were conducted in spring 2000. Experiments designed to gauge the response of optical properties in the system to nitrogen inputs in the spring were unsuccessful due to natural inputs just prior to commencement of the experiment. The starting date of the experiment coincided with arrival of the spring freshet of the Susquehanna River, which carried a seed population of P. minimum and about 70 µM of nitrate. Consequently, a significant bloom occurred in all mesocosm enclosures as well as in the natural system, overwhelming any treatment effects.
Absorption and scattering spectra monitored during the bloom indicated that increases in chlorophyll within the Rhode River initially were due to the influx of chlorophyll that had developed in the main stem of the Chesapeake Bay. Concentrations of chlorophyll imported into the Rhode River never exceeded about 50 mg m-3. Locally high concentrations (up to 270 mg m-3) and steep spatial gradients developed within the Rhode River, subsequent to reduced mixing that accompanied reestablishment of a normal estuarine salinity gradient.
We applied the components algorithm to absorption and scattering spectra monitored during the bloom. Prior to the bloom, chlorophyll, SPM, and CDOM contributed approximately equally to the total absorption coefficient at 440 nm. During the bloom, the total absorption coefficient more than doubled, and chlorophyll clearly became the dominant factor. Absorption by detritus increased in magnitude and dominated absorption after the decline in chlorophyll. Absorption by CDOM increased slightly in response to the bloom, but was never the dominant absorption component.
Studies of the temporal variation in the sensitivity of Rhode River phytoplankton photosynthesis to inhibition by ultraviolet radiation (UV, 280 to 400 nm) have been completed. The studies characterized the biological weighting functions (BWFs) that quantify the biological effect of different wavelengths of UV. Phytoplankton assemblages were sensitive to UV throughout the year. Rhode River assemblages were inhibited more strongly in the UV-B (280 to 320 nm), particularly below 300 nm, but there was a significant influence well into the UV-A (320 to 400 nm). There was no inhibition of phytoplankton photosynthesis by PAR. Comparison of the most sensitive assemblage (spring) with the least sensitive assemblage (winter) indicates that these BWFs are close to the upper and lower bounds in sensitivity for irradiance-dependent BWFs from all natural and cultured phytoplankton populations examined to date.
Future Activities:
Continuous monitoring of inherent optical properties will continue until the end of funding. Measurements of benthic nutrient release rates will commence again in the spring and continue into late summer 2001. Because there was no discernable effect of salinity and/or nitrate on sediment release rates, this spring we will investigate the role of the filamentous, coenocytic alga, Vaucheria sp., on benthic nutrient uptake and release rates. This alga forms thick benthic mats in the shallow tributaries of the upper Chesapeake Bay in late winter and early spring, and may be responsible for much of the nitrate uptake in spring, and phosphate release when they die in mid- to late spring.
Another change in emphasis will be to begin spatial mapping of surface inherent optical properties in the Rhode River and other upper bay tributaries. Experience gained from temporal monitoring during the Prorocentrum bloom of spring 2000 has shown the importance of remote locations and spatial gradients in initiation of blooms in tributaries. At the same time, the Bay water quality monitoring and remote sensing studies implicate the tributaries in exporting high concentrations of chlorophyll to the western shore Bay. We have adapted our flow-through system for mobile mapping of optical properties, and plan to use it in other tributaries and the upper Bay this year.
In developing the algorithm for discriminating absorption by CDOM, phytoplankton, and SPM, we discovered that the scattering-to-absorption ratio of nonalgal particulate matter is both variable and very important for accurate discrimination of the components. In the final year, we intend to measure the spectral backscattering coefficients of particulate matter, to better predict the scattering-to-absorption ratio of nonalgal particulate matter, and to determine its spatial variability around the upper Chesapeake Bay. We will continue posting of salinity data on the World Wide Web (see below, relevant Web pages). Posting of inherent optical properties will commence.
Journal Articles:
No journal articles submitted with this report: View all 15 publications for this projectSupplemental Keywords:
ecological effects, 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 Web site describing objectives and activities of the Rhode River CISNet site
has been created as a link to the research activities of the Smithsonian Environmental
Research Center. In addition to a description of projects, the Web page has
links for downloading of data from the automated salinity monitors. Additional
data will be made available on the Web page as the project progresses. The address
for the Rhode River CISNet Web page is:
http://www.serc.si.edu/estuarine/est_water_cisnet.htm Exit
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.