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101.
102.
The pattern and influence of low dissolved oxygen in the Patuxent River,a seasonally hypoxic estuary
Denise?L.?BreitburgEmail author Aaron?Adamack Kenneth?A.?Rose Sarah?E.?Kolesar Beth?Decker Jennifer?E.?Purcell Julie?E.?Keister James?H.?Cowan 《Estuaries and Coasts》2003,26(2):280-297
Increased nutrient loadings have resulted in low dissolved oxygen (DO) concentrations in bottom waters of the Patuxent River,
a tributary of Chesapeake Bay. We synthesize existing and newly collected data to examine spatial and temporal variation in
bottom DO, the prevalence of hypoxia-induced mortality of fishes, the tolerance of Patuxent River biota to low DO, and the
influence of bottom DO on the vertical distributions and spatial overlap of larval fish and fish eggs with their gelatinous
predators and zooplankton prey. We use this information, as well as output from watershed-quality and water-quality models,
to configure a spatially-explicit individual-based model to predict how changing land use within the Patuxent watershed may
affect survival of early life stages of summer breeding fishes through its effect on DO. Bottom waters in much of the mesohaline
Patuxent River are below 50% DO saturation during summer. The system is characterized by high spatial and temporal variation
in DO concentrations, and the current severity and extent of hypoxia are sufficient to alter distributions of organisms and
trophic interactions in the river. Gelatinous zooplankton are among the most tolerant species of hypoxia, while several of
the ecologically and economically important finfish are among the most sensitive. This variation in DO tolerances may make
the Patuxent River, and similar estuaries, particularly susceptible to hypoxia-induced alterations in food web dynamics. Model
simulations consistently predict high mortality of planktonic bay anchovy eggs (Anchoa mitchilli) under current DO, and increasing survival of fish eggs with increasing DO. Changes in land use that reduce nutrient loadings
may either increase or decrease predation mortality of larval fish depending on the baseline DO conditions at any point in
space and time. A precautionary approach towards fisheries and ecosystem management would recommend reducing nutrients to
levels at which low oxygen effects on estuarine habitat are reduced and, where possible, eliminated. 相似文献
103.
Tracy?N.?WiegnerEmail author Sybil?P.?Seitzinger Denise?L.?Breitburg James?G.?Sanders 《Estuaries and Coasts》2003,26(2):352-364
Responses of autotrophic and heterotrophic processes to nutrients and trace elements were examined in a series of experimental
estuarine food webs of increasing trophic complexity using twenty 1-m3 mesocosms. Nutrients (nitrogen and phosphorus) and trace elements (a mix of arsenic, copper, cadmium) were added alone and
in combination during four experimental runs spanning from spring 1997 to spring 1998. Diel changes in dissolved oxygen were
used to examine whole system gross primary production (WS-GPP), respiration (WS-RESP), and net ecosystem metabolism (NEM).
Nutrient and trace element additions had the greatest effect on WS-GPP, WS-RESP, and NEM; trophic complexity did not significantly
affect any of these parameters (p>0.3). Effects of trophic complexity were detected in nutrient tanks where bivalves significantly
(p=0.03) reduced WS-GPP. Nutrient additions significantly enhanced WS-GPP and to a lesser extent WS-RESP during most mesocosm
runs. The system shifted from net heterotrophy (−17.2±1.8 mmol C m−3 d−1) in the controls to net autotrophy (29.1±7.6 mmol C m−3 d−1) in the nutrient tanks. The addition of trace elements alone did not affect WS-GPP and WS-RESP to the same extent as nutrients,
and their effects were more variable. Additions of trace elements alone consistently made the system more net heterotrophic
(−24.9±1.4 mmol C m−3 d−1) than the controls. When trace elements were added in combination with nutrients, the nutrient-enriched system became less
autotrophic (1.6±3.1 mmol C m−3 d−1). The effects of trace elements on NEM occurred primarily through reductions in WS-GPP rather than increases in WS-RESP.
Our results suggest that autotrophic and heterotrophic processes respond differently to these stressors. 相似文献
104.
Luis M. Sender Jos B. Diez Javier Ferrer Denise Pons Cristbal Rubio 《Cretaceous Research》2005,26(6):898-905
A newly discovered plant fossil assemblage in the Albian Escucha Formation, located at Valle del Río Martín (Teruel, Spain), shows similarities with the classic early Cretaceous flora of the Potomac Group in the USA. This is the first time that a flora of this age and composition has been found in Spain. It comprises representatives of ferns, Ginkgoales, Bennettitales, Caytoniales, conifers and angiosperms and suggests a possible mixing of the European and Potomac provinces in the early Cretaceous within the Iberian Peninsula, in a subtropical, semi-arid climate. 相似文献
105.
Surface films on marsh creeks form water-air interfaces of high biological activity. The development, movement, deposition, and breakup of the tidal creek surface film in a naturalSpartima alterniflora-dominated salt marsh in Delaware were followed seasonally over tidal cycles. The metabolic activity, i.e., photosynthesis and respiration, of the surface film and underlying water were determined in the field at the time of peak film formation, just prior to high tide, and the particulate material and chlorophylla were quantified over the tidal cycles. The quantities of organic and inorganic components of the particulate material were all significantly higher in the surface film than in the underlying water (on a volume basis). Numbers of algal cells and quantities of chlorophyll were orders of magnitude greater in the surface film than in the water column. Photosynthesis and respiration were significantly higher in the surface film than in the underlying water. The spectrum of fatty acids was more diverse and their total content was significantly greater in the surface film than in the water column, indicating a concentrated food source contributed by the film as well as a biological richness of the film. When water in the creek flooded the marsh plain at high tide, film deposition was greatest on simulated creek bankS. alterniflora stems, compared to stems along rivulets in the marsh and those in the marsh plain. Using surface film dry weight measurements on an areal basis and film velocity in the creek, both measured throughout a tidal cycle during the summer, it was determined that approximately 12 kg (dry weight) of particulate material moved on the creek surface (2 m wide) past a given point on the flood tide, and 14 kg moved in the opposite direction on the ebb tide. The biological and physical data collected in this study illuminate the contribution of the surface film to the biological (food web) and physical (sediment transport and deposition) functions of a salt marsh. 相似文献
106.
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108.
We propose a general method for evaluating, and possibly improving, the interface between scientific research and policy-making institutions. The method considers the adequacy of both institutional structures for incorporating research, and research for addressing institutional needs. It involves both interviews (with policy makers and scientists) and formal analyses of the links between the research and the decisions described in the interviews. A case study applies the method in analyzing the usefulness of climate change research for managing salmon runs in the Pacific Northwest. It shows these policy makers to be receptive to the research, which is, in principle, relevant to them. However, they are unable to use it because the research is not currently formulated in ways compatible with current decision-making models. For their part, these models are not comprehensive enough to capture the full range of potentially relevant environmental forcers, including climate change. 相似文献