Plankton studies in Buzzards Bay, Massachusetts, USA. VI. Phytoplankton and water quality, 1987 to 1998

Abstract

From October 1987 through September 1998, phytoplankton composition, inorganic nutrients, temperature, salinity, water clarity, and chlorophyll a (chl a) + phaeopigments were monitored during 141 monthly cruises in Buzzards Bay, Massachusetts, USA. There were large seasonal and interannual variations in nitrate, silicate and phytoplankton abundance and composition. There were no consistent interannual patterns of recurrent spring blooms, measured as either chl a or phytoplankton cell abundance. Rather, blooms of various taxa were sporadic, particularly diatom blooms in the late summer and fall. Other parameters were similar bay-wide on a given day, and over seasons and years for stations away from New Bedford Harbor, but concentrations of ammonium, phosphate, and chl a were elevated at the New Bedford sewage outfall, prior to its conversion to secondary treatment in September 1996. After conversion, increased water transparency and decreased levels of ammonium indicated improved water quality at the outfall. Bay-wide chl a and nitrate had significant declines over time from the late 1980s to the late 1990s. There were no significant linear trends with time for annual means of temperature, but there was a significant trend of increased warming in spring. Phytoplankton abundance (0.012 to 26.0 × 10 6 cells l -1, 1988 to 1998) was higher than reported in other coastal waters of New England, due to preservation that did not destroy the delicate microflagellates and phytoflagellates which dominated phytoplankton abundance. Potentially harmful algal species included diatoms of the genus Pseudo-nitzschia, and the dinoflagellate Alexandrium fundyense. Buzzards Bay is a favorable habitat for phytoplankton in that it is wellmixed and well-illuminated, and nutrient-replete.KEY WORDS: Buzzards Bay · Phytoplankton · Nutrients · Estuary · Water quality · Long-term trends Resale or republication not permitted without written consent of the publisherMar Ecol Prog Ser 376: [103][104][105][106][107][108][109][110][111][112][113][114][115][116][117][118][119][120][121][122] 2009 cate dinoflagellates, which do not disintegrate upon formalin preservation (e.g. Turner & Hopkins 1974). Studies of either live phytoplankton samples, or those using preservatives that do not destroy most athecate phytoplankton, have revealed that small athecate cells (typically designated as 'microflagellates') often dominate phytoplankton abundance (Durbin et al. 1975), particularly during warmer periods. High abundance of athecate microflagellates was found in several recent studies of phytoplankton assemblages in coastal waters from the northeastern United States (Narragansett Bay, Rhode Island: Karentz & Smayda 1984, Smayda 1983 Peconic Bay, Long Island, New York: Turner et al. 1983; Boston Harbor, Massachusetts Bay, and Cape Cod Bay, Massachusetts: numerous reports from the Massachusetts Water Resources Authority at www.mwra.state.ma.us/harbor/ enquad/trlist.html).It is often difficult to compare responses of estuarine phytoplankton ass...

Long-term declines in chlorophyll a and variable phenology revealed by a 60-year estuarine plankton time series

“…Furthermore, the annual maximum chl a concentration decreased over time suggesting a waning intensity of phytoplankton bloom events. Long-term declines of chl a concentrations in NBay mirror those observed in diverse locations including other estuaries ( 19 , 39 ), the Gulf of Maine ( 27 ), the Australian coast ( 40 ), and the Black Sea ( 41 ), where blooms have also decreased in intensity over time ( 41 , 42 ). Reductions in annual and event-scale chl a concentrations have both ecological and biogeochemical implications for ecosystem functioning, with decreases in organic matter deposition resulting in a less efficient biological pump ( 43 , 44 ), and decline in nutrient cycling and benthic production within estuaries ( 45 , 46 ).…”

Selecting a suitable diversity index for a tropical Ramsar wetland site

“…The opposite also may occur, as observed for algal blooms from seasonal or anthropogenic releases of nutrients (Turner et al. ). The results of the present study confirm this observation.…”

Connectivity of the bay scallop (Argopecten irradians) in Buzzards Bay, Massachusetts, U.S.A.

“…Turner et al . () found that the biomass of diatoms and microflagellates, principal elements of the bay scallop diet, is highly variable, both seasonally and interannually. The Buzzards Bay Coalition has used data on nitrogen (organic and inorganic), water clarity, dissolved oxygen and algal pigments acquired since 1992 to derive a health index of the bay and its embayments (http://www.savebuzzardsbay.org/BayHealthData).…”