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The Skidaway River estuary, GA (USA), a tidally dominated subtropical system surrounded by extensive Spartina salt marshes, is experiencing steady increases in nutrients, chlorophyll, and particulate matter and decline in dissolved
oxygen, associated with cultural eutrophication. A long-term study is documenting changes in these parameters: previous papers
Verity (Estuaries 25:944–960, 2002a, Estuaries 25:961–975, b) reported on hydrography, nutrients, chlorophyll, and particulate matter during 1986–1996; plankton community responses are
reported here. Phytoplankton, bacteria, heterotrophic nanoplankton and dinoflagellates, ciliates, and copepods exhibited strong
seasonal cycles in abundance driven by temperature and resource availability, typically with summer maxima and winter minima.
However, cultural eutrophication coincided with altered planktonic food webs as autotrophic and heterotrophic communities
responded to increasing concentrations and changing ratios of inorganic and organic nutrients, potential prey, and predators.
Small (<8 μm) photosynthetic nanoplankton increased in absolute concentration and also relative to larger cells. In contrast,
diatoms did not show consistent increases in abundance, despite significant long-term increases in ambient silicate concentrations.
Mean annual bacteria concentrations approximately doubled, and eukaryotic organisms in the microbial food web (heterotrophic
and mixotrophic flagellates, dinoflagellates, ciliates, and metazoan zooplankton) also increased. All plankton groups except
copepods showed trends of increasing annual amplitudes between seasonal high and low values, with higher peak concentrations
each year. These observations suggest that the eutrophication signal was gradually becoming uncoupled from regulatory mechanisms.
Theory and evidence from other more impacted waters suggest that, if these patterns continue, changes in the structure and
function of higher trophic levels will ensue. 相似文献
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Between 1991 and 2000, Boston Harbor, a bay–estuary in the northeast USA, experienced a decrease in loadings of total nitrogen
(TN), total phosphorus (TP), and particulate organic carbon (PC) of between ∼80% and ∼90%. The average concentrations of TN
and TP in the harbor water column were decreased in linear proportion to the loadings. The changes to the chlorophyll-a (chl-a), PC, and bottom water DO concentrations were curvilinear relative to the loadings, with larger changes at low than high
loadings. For TN and TP, the starts of the decreases in concentrations coincided with the starts of the decreases in loadings.
For the three variables that showed curvilinear responses, the starts of the changes lagged by 2 to 3 years the starts of
the decreases in TN loadings. Total suspended solid concentrations and water clarity in the harbor were unchanged. The study
shows that for systems such as Boston Harbor, decreases in nutrient loadings will have quite different effects depending on
the base loadings to the system. 相似文献
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Carlton D. Hunt David G. Borkman P. Scott Libby Richard Lacouture Jefferson T. Turner Michael J. Mickelson 《Estuaries and Coasts》2010,33(2):448-470
The Massachusetts Water Resources Authority (MWRA) conducts a comprehensive multidisciplinary monitoring program in Massachusetts
Bay, Cape Cod Bay, and Boston Harbor to assess the environmental effects of a relocated secondary-treated effluent outfall.
Through 2007, 8.7 years of baseline data and 7.3 years of postdiversion data (16 total years), including species level estimates
of phytoplankton and zooplankton abundance, have been collected. MWRA’s monitoring program and other studies make this region
one of the most thoroughly studied and well-described marine systems in the world. The data show that the diversion of MWRA
effluent from the harbor to the bay has decreased nutrients concentrations and improved water quality in the harbor (e.g.,
higher dissolved oxygen, lower chlorophyll). The diversion also resulted in an increase in dissolved inorganic nutrients (especially
ammonium) in the vicinity of the bay outfall, but no obvious impacts such as increased biomass or decreased bottom water dissolved
oxygen have been observed. Regional changes in phytoplankton and zooplankton unrelated to the diversion have been seen, and
it is clear that the bays are closely connected both physically and ecologically with the greater Gulf of Maine. Direct responses
to modifications of the nutrient field within a 10 × 10-km area centered near the midpoint of the 2-km long outfall diffuser
in Massachusetts Bay (a.k.a. the nearfield) have not been seen in the plankton community. However, plankton variability in
the bays has been linked to large regional to hemispheric scale (NAO) processes. 相似文献
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David G. Borkman P. Scott Libby Michael J. Mickelson Jefferson T. Turner Mingshun Jiang 《Estuaries and Coasts》2016,39(4):1084-1099
Abundance of the prymnesiophyte Phaeocystis pouchetii was quantified via light microscopy at 2-week to monthly intervals in Massachusetts Bay (southern Gulf of Maine, NW Atlantic) during 1992–2012. Variability in the abundance and seasonal cycle of Phaeocystis are described and synoptic hydrographic, nutrient, and meteorological data were analyzed to identify factors that may influence Phaeocystis abundance. The maximum Phaeocystis abundance was 14?×?106 cells L?1 (10 Apr 2008). It was frequently (5 of 8 years) absent prior to year 2000, but not thereafter. Seasonally, it first appeared in February to early March, reached peak abundance in mid-April, and persisted until May or early June for a duration of 0–112 days (mean 34 days). A long-term alternation between Phaeocystis and centric diatom abundance was apparent, suggesting winter-spring selection of either Phaeocystis or centric diatoms. Phytoplankton community analysis suggested that blooms affected the rest of the phytoplankton community. Phaeocystis blooms were manifest as a substantial increase in particulate nutrients above normal levels. Phaeocystis blooms were preceded in February by a slightly elevated concentration of NO3 (9.3 vs. 6.5 μM when absent) and PO4 (0.99 vs. 0.79 μM when absent). Blooms were also preceded by elevated ratios of NO3/PO4, NO3/Si, and PO4/Si, and warmer, saltier waters reflecting reduced river discharge. The correlation with salinity and river discharge suggests that Phaeocystis bloom variability is partially determined by annually varying circulation processes that determine the degree of low nutrient, low salinity coastal water intrusion into Massachusetts Bay. 相似文献
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