Impact of the Spring 2000 phytoplankton bloom in Chesapeake Bay on optical properties and light penetration in the Rhode River, Maryland

Abstract

Accelerating eutrophication manifest as increasing frequency and magnitude of phytoplankton blooms threatens living resources in many estuaries. Effects of large blooms can be difficult to document because blooms are often unexpected and do not always coincide with scheduled sampling programs. Here we use continuously monitored salinity distributions and optical properties to study the spring bloom of the red tide dinoflagellate, Prorocentrum minimum, in the Rhode River, Maryland, a tributary embayment of upper Chesapeake Bay. Salinity distributions, together with weekly cruise measurements of nutrient concentrations, indicate that the bloom commenced with an influx of nitrate at the mouth due to the arrival of a freshet from the Susquehanna River. Arrival of this freshet at the mouth set up 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 due to 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 re-establishment 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 d, the elevated attenuation coefficients due to the bloom exceeded values that would permit growth of submersed vascular plants for a period of about 45 d.

Eutrophication of Chesapeake Bay: historical trends and ecological interactions

“…Gallegos 2001). Sharp declines in Bay water clarity during spring and summer can be directly related to algal blooms stimulated by watershed nutrient inputs (Gallegos & Jordan 2002). Reductions in depth distribution of conspicuous benthic plants (e.g.…”

Interannual variation in submerged aquatic vegetation and its relationship to water quality in subestuaries of Chesapeake Bay

“…High levels of chl a can block light from reaching SAV, especially during dense algae blooms , Smayda 1997, Carstensen et al 2007. Although blooms are typically short-lived, they can be devastating to young SAV (Gallegos & Jordan 2002), as documented in a well-studied May 2000 mahogany tide Prorocentrum minimum bloom that decimated upper Chesapeake Bay SAV (Gallegos & Bergstrom 2005). The more common summer blooms are less damaging because mature SAV plants have grown closer to the surface and have carbo hydrate reserves to survive temporary periods of lower light (Gallegos & Bergstrom 2005).…”

“…The 1994 drop followed high river nitrogen load and March chl a levels from the spring 1993 snowstorm and melt event in the Susquehanna watershed (see previous section). Such events deliver high nitrogen loads that cause spring algae blooms , 2002 (Orth et al 2006. Despite the documented effects of heat stress, average growing season temperature was not significantly cross-correlated with polyhaline SAV abundance,becauseafewdaysofheat stress in shallow water can have devastating biological effects without shifting seasonal average temperature .…”

Long-term variations in primary production in a eutrophic sub-estuary. II. Interannual variations and modeling

“…It has been demonstrated by high frequency automated monitoring of salinity (a surrogate for NO 3 input) and optical properties (showing response of phytoplankton chlorophyll, Gallegos & Jordan 2002) that such blooms are triggered by nutrients delivered when the spring freshet of the Susquehanna River causes a reversal of the normal salinity gradient, leading to rapid exchange of water in the sub-estuary (Schubel & Pritchard 1986). Such detailed observations are not available for most years, but both years having EB in this study (1992,2000) were categorized as having dry spring flows (Table 1).…”