Grantee Research Project Results
Final 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 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 overall objective of this research project was 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 responses to increased disturbance, or to management efforts. The specific objectives were to: (1) establish a system for monitoring estuarine optical properties and conduct research to interpret optical properties of the concentrations of suspended particulate matter (SPM), phytoplankton chlorophyll, and colored dissolved organic matter (CDOM); (2) relate variation in estuarine optical properties to natural and anthropogenic inputs of nutrients across a wide range of time scales; and (3) conduct research to predict the response of key components of the ecosystem to changes (both increases and decreases) in penetration of visible light and ultraviolet-B (UV-B) as impacted by global change and long-term changes in estuarine optical properties. Research to interpret continuously monitored optical properties focused on: (1) interpretation of optical properties in terms of the concentrations of SPM, phytoplankton chlorophyll, and CDOM; (2) observations to establish the response of in situ concentrations of chlorophyll, SPM, and CDOM to inputs of nutrients on events and interannual time scales; and (3) process level research to examine the effects of solar UV radiation on nearshore plankton communities, as influenced by potential changes in estuarine optical properties.
Research in year 1 focused on establishing a system for monitoring estuarine optical properties, installing salinity monitors to gauge mixing and exchange in the system, and determining the response of optical properties to experimental additions of nutrients. Research in Years 2 and 3 emphasized the continued collection of continuously monitored optical properties, development of data analysis procedures, and collection and Web posting of salinity data. Research in Year 2 extended measurements out into the Chesapeake Bay, and converted the system for temporal monitoring into a system for spatial mapping of surface optical properties. This transformation will assist in scaling up observations made at a single location, and will be an important adjunct to remote sensing studies.
Summary/Accomplishments (Outputs/Outcomes):
A flow-through system for measuring spectral absorption and attenuation coefficients was installed at the Smithsonian pier in Rhode River. For analyzing the data, a series of three mathematical procedures was derived for discriminating the light absorption by phytoplankton, CDOM, and non-pigmented particulates. The procedures differ in the amount of ancillary measurements incorporated to reduce the variability of the estimates. The procedure that incorporates no ancillary information is expected to be unbiased only over long time periods. Application of the procedures to a 15-day time series of continuously monitored data from the Rhode River, revealed the presence of large (approximately two-fold) changes in absorption at 440 nm during periods of a few hours. Hourly sampling during a 24-hour period confirmed that the changes in measured optical coefficients corresponded to changes in water quality. Errors in estimates of absorption components were of a magnitude consistent with those observed in the development of procedures, and confirmed the progressive improvement achieved by incorporation of additional information. During the time period observed, changes in optical properties appeared to be driven by advective processes.
We operated the optical monitoring station for nearly a 2-year period to characterize the causes and time scales of variability in an optically complex environment. A distinct seasonal pattern was observed in both years. The seasonal pattern was characterized by an increase in absorption and scattering coefficients during the spring phytoplankton bloom, followed by a relatively clear water phase in early June, a gradual rise in coefficients to an annual maximum in early September, and a rapid decline in late fall to winter. Interannual differences were attributable primarily to differences in magnitudes of spring and fall blooms. Short-term (diurnal to weekly) variability was a substantial fraction of the seasonal variance, and was driven by a combination of advection of steep spatial gradients and meteorological forcing, though these were difficult to differentiate. Application of the above described inversion procedure to determine the components of absorption indicated that the largest component of the seasonal trend was driven by an increase in absorption by non-algal particulate matter during summer months; absorption by chlorophyll attributable to phytoplankton blooms was the second largest component. Absorption by colored dissolved organic matter was the smallest and least variable constituent. These broad trends in estimated components of absorption were confirmed by optical analysis of discrete water samples. The extreme variability observed on short-time scales indicates that it would be very difficult to document long-term (i.e., decadal) trends in water clarity with fortnightly or monthly sampling. In this system, the similarity in overall magnitude of absorption and scattering coefficients during summer months of the 2 years indicates that effort is best expended documenting interannual differences in magnitudes and duration of spring and fall phytoplankton blooms.
Effects of large blooms can be difficult to document because blooms often are unexpected and do not always coincide with scheduled sampling programs. We utilized continuously monitored salinity distributions and optical properties to study the spring bloom of the red tide dinoflagellate, Prorocentrum minimum, in the Rhode River. Salinity distributions, together with weekly cruise measurements of nutrient concentrations, indicated that the bloom commenced with an influx of nitrate at the mouth because of the arrival of a freshet from the Susquehanna River. Arrival of this freshet at the mouth setup provided an unstable, inverse salinity gradient within the Rhode River. Continuously monitored absorption and scattering spectra indicated that increases in chlorophyll within the Rhode River initially were because of the influx of chlorophyll that had developed in the main stem of the Bay. After the influx, much higher concentrations and steep spatial gradients developed within the Rhode River, subsequent to reduced mixing that accompanied reestablishment of a normal estuarine salinity gradient. We used the monitored absorption and scattering coefficients to determine the effect of the bloom on light attenuation coefficients in the Rhode River. The bloom resulted in a nearly three-fold increase in attenuation coefficient. Attenuation was dominated by chlorophyll in the early stages of the bloom, and by detritus after the termination of the bloom. Although the bloom lasted only 20 days, the elevated attenuation coefficients as a result of the bloom exceeded values that would permit growth of submersed bay grasses for a period of about 45 days.
Previous studies of the Rhode River estuary have quantified nutrient inputs via discharge from the local watershed and via direct atmospheric deposition (Jordan, et al., 1991a; Gallegos, et al., 1992). The current study demonstrated the impact of nitrogen input from the spring freshet of the Susquehanna River arriving at the mouth of the Rhode River (section 4). However, inputs of nutrients from benthic sources had not been measured previously, though the general magnitude of sediment P release rates may be inferred from Jordan, et al. (1991a). Here, we performed direct measurements of the net releases of NO3-, NH4+, and PO4-3 from sediments to determine their role in supporting primary productivity of phytoplankton and in promoting eutrophication. We also measured net uptake of dissolved oxygen and net release of dissolved inorganic carbon (DIC) from the sediments, to gain insights into biogeochemical processes in the sediments. Two regions of the estuary were examined in detail; the up-estuary mudflats, which receive the most discharge of suspended sediments from the watershed, and the area around the Smithsonian pier, where the optical monitoring was conducted.
Nutrient and DIC release rates were highly variable, but displayed a distinct seasonal pattern with the highest rates in the mid- to late summer, corresponding with the highest seasonal temperatures. Rates of dissolved inorganic nitrogen (DIN) release were similar in the two regions, but rates of dissolved inorganic phosphorus (DIP) release were considerably higher in the mudflat region than down-estuary near the pier and optical monitor. The ratio of DIN:DIP release near the pier was similar to the elemental composition of phytoplankton, while the ratio in the mudflat area was relatively enriched in DIP, reflecting the delivery of particulate inorganic P in sediments discharged from the watershed. The high DIP relative to DIN release contributes to the regular mid-summer peak in DIP concentrations in the water column of the upper Rhode River, and contributes to the shift from P to N limitation of phytoplankton growth that typically occurs from early spring to summer. Overall rates of nutrient release from sediments during the spring in the 2 years were observed. One had an extraordinary bloom of phytoplankton, and the other which only had a bloom of average magnitude for this system. Thus, we conclude that interannual differences in springtime nutrient release rates are not the main factor governing interannual differences in spring bloom magnitude in this system.
Changes in incident irradiance and in factors influencing water optical properties modify both the spectral composition and the intensity of UV exposure to aquatic biota in the Chesapeake Bay. Assessing the implications of these changes for aquatic ecosystem processes required the development of wavelength-dependent weighting functions. Biological weighting functions (BWFs) describe the effectiveness of radiation of different wavelengths to produce a biological response, such as inhibition of photosynthesis.
While working with phytoplankton in the Rhode River, we applied a wavelength-dependent description of UV effects on photosynthesis (BWF/P-I model) previously developed in work with cultures and natural populations in Antarctica. The model describes photosynthesis as a function of photosynthetically active radiation (PAR P-I), and photoinhibition as a function of both PAR and UV (BWF). The BWFs were measured experimentally using a series of polychromatic irradiance treatment, i.e., successively shorter wavelengths of UV-A then UV-B were added to a constant background of PAR, as occurs during environmental exposure. The results then were used to estimate the effect of UV under a range of conditions of varying optical transparency and incident irradiance (including the effects of ozone depletion).
Phytoplankton assemblages in the Rhode River were sensitive to UV radiation throughout the year, and both UV-A and UV-B contributed to inhibition, at least by surface irradiance. There was no significant inhibition of photosynthesis by PAR. A sensitivity analysis then was undertaken to understand the implications of variations in sensitivity (i.e., BWFs) relative to changes in exposure conditions for UV effects, focusing on the early summer period of highest UV exposure. The comparison entailed calculation of midday, total water-column photosynthesis from the surface, down to 1.6 m (total depth for this segment of the Rhode River) for each combination of measured irradiance, BWF, and spectral attenuation. Inhibition of midday production in the Rhode River averaged about 16 percent throughout all combinations of conditions, considerably less than the around 25-30 percent inhibition of daily production calculated in similar analyses for an area of the Southern Ocean and Antarctic Peninsula waters. On the other hand, the predicted inhibition of integrated production for the Rhode River is at a similar level as calculated for Lake Michigan (effect of <370 nm only) and lakes in the Swiss Alps. Interestingly, the depth penetration of biologically effective UV relative to PAR in the Swiss lakes was in the same range as the Rhode River (20-40 percent of the euphotic zone) despite the generally clearer water in the lakes. This reinforces the conclusion that the predicted effect of UV depends more on the relative penetration of UV and PAR rather than the UV transparency alone. Thus, inhibition by UV can be significant even in a turbid estuary with high attenuation coefficient for biologically effective wavelengths, especially under conditions of simultaneous low transparency for PAR.
Journal Articles on this Report : 3 Displayed | Download in RIS Format
Other project views: | All 15 publications | 5 publications in selected types | All 4 journal articles |
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Type | Citation | ||
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Gallegos CL, Jordan TE. Impact of the Spring 2000 phytoplankton bloom in Chesapeake Bay on optical properties and light penetration in the Rhode River, Maryland. Estuaries 2002;25(4A):508-518. |
R826943 (2001) R826943 (Final) |
not available |
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Gallegos CL, Neale PJ. Partitioning spectral absorption in case 2 waters: discrimination of dissolved and particulate components. Applied Optics 2002;41(21):4220-4233. |
R826943 (2001) R826943 (Final) |
not available |
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Neale PJ. Modeling the effects of ultraviolet radiation on estuarine phytoplankton production: impact of variations in exposure and sensitivity to inhibition. Journal of Photochemistry and Photobiology B-Biology 2001;62(1-2):1-8. |
R826943 (2001) R826943 (Final) |
not available |
Supplemental 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:
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.