Roman S. Stanley

Dredging impact on an urbanized Florida bayou: effects on benthos and algal-periphyton

Environmental effects of dredging events have been uncommonly reported for shallow, residential estuaries characteristic of the Gulf of Mexico region. The objective of this study was to determine the impact of hydraulic dredging on an urbanized estuary. Physicochemical quality, benthic community composition, whole sediment toxicity, periphytic algal community composition and trace metal tissue quality were determined prior to and after dredging. The effects on surface water pH, dissolved oxygen, and temperature were negligible but photosynthetically active radiation was decreased at several stations. Dredging significantly reduced benthic diversity and density (P < 0.05). However, the sediments were not acutely toxic to the epibenthic, Americamysis bahia (formerly Mysidopsis bahia); survival averaged 93% (post-dredging) and to 98% (pre-dredging). There were several post-dredging taxonomic structural changes in the diatom-dominated, periphyton community but differences in mean density and three diversity indices were not significant. Trace metal concentration in periphyton after dredging were reduced from an average of 4-65% and significantly for mercury, zinc and chromium in several areas. It was concluded that the environmental impact of small-scale dredging events in urbanized near-coastal areas, based on the selected parameters, are likely to be localized and of short-term environmental consequence. The choice of the target biota, response parameters and chemical analysis are important considerations in the environmental impact assessment of these periodic episodic events.

Linkage between microzooplankton grazing and phytoplankton growth in a Gulf of Mexico estuary

Microzooplankton dilution grazing experiments were conducted with water collected from Pensacola Bay, Florida (USA) on 12 dates at 2 sites. Statistically significant grazing rates were observed in 22 of 24 experiments. Grazing rates in Upper Bay and Lower Bay were similar averaging 0.54 and 0.51 d−1, respectively. Phytoplankton growth rates were also similar at the two sites, averaging 1.02 and 1.00 d−1 at Upper Bay and Lower Bay, respectively. Phytoplankton growth rates usually exceeded grazing rates by about a factor of two, though microzooplankton grazing represented a significant mortality for phytoplankton. The literature suggests a linkage between phytoplankton growth and microzooplankton grazing that spans a wide variety of aquatic environments. While individual growth and grazing rates were variable, growth frequently exceeded grazing by about two-fold. This implies that the role of microzooplankton is similar across a wide variety of aquatic systems.

THE EFFECTS OF URBANIZATION ON THE CHEMICAL QUALITY OF THREE TIDAL BAYOUS IN THE GULF OF MEXICO

Water and sediment quality in threetidal bayous located near Pensacola, Florida, wereassessed during 1993–1995. The primary objective wasto determine the environmental condition of therelatively small urban bayous by comparing thechemical quality of the sediments and surface waterwith published guidelines and criteria developed toprotect marine life. Surface water concentrations ofmost potential toxicants such as heavy metals,organochloride pesticides, PAHs and PCBs were usuallybelow method detection limits. The major exception tothis trend was for copper which consistently exceededFlorida and National acute and chronic water qualitycriteria. Nickel, cadmium and chromium intermittentlyexceeded these criteria. Sediment contamination wassite-specific and chemically diverse. Theconcentrations of as many as 17 compounds exceededproposed Florida sediment quality assessmentguidelines indicating the potential for adversebiological effects. Nutrient concentrations, with oneexception, were below average levels found in otherFlorida estuaries. Seasonal variation in contaminantconcentrations for sediment collected from the samesampling station was less than an order of magnitude. The differences in the concentrations of the sameanalytes as measured for the multiple samplingstations located within the same bayou varied 1 to 2orders of magnitude and over 2 orders of magnitude forthe 20 sampling stations located in the three bayous. A within-bayou sediment contaminant gradient wasevident; sediment quality generally improved seaward.

Periphyton and Sediment Bioassessment in North Florida Bay

Periphyton colonization and sediment bioassessment were used ina survey to compare the relative environmental condition ofsampling sites located in Florida Bay and four peripheral sloughareas during the summer of 1995. Periphyton biomass, pigmentcontent, tissue quality and community composition weredetermined. In addition, benthic community composition and thetoxicities of whole sediments and associated pore waters weredetermined for two species of rooted macrophytes, an epibenthicinvertebrate and bioluminescent bacteria. Several locational differences were observed for the response parameters.Periphyton biomass was significantly greater in the Taylor Riverand the least in Shell Creek (P < 0.05). Most sediments were notacutely toxic to mysid shrimp nor phytotoxic. However, sedimentsfrom the Taylor River were more phytostimulatory than others (P< 0.05). Contaminant bioresidues were similar at most sites,however, mercury, chromium and nickel concentrations weregreater for periphyton colonized in the Taylor River and TroutCreek areas. Structural characteristics of the periphytic algalcommunity usually were statistically similar but a consistenttrend of lower density and diversity was evident for ShellCreek. The benthic community was the least diverse and dense inthe Canal C-111. The results of this study provide an initialindication of differences in the role of several slough areas aspossible sources of bioavailable contaminants to Florida Baywhich warrants additional investigation.

Recolonization of estuarine organisms: effects of microcosm size and pesticides

Two six-week laboratory experiments were conducted to evaluate effects of pesticides and microcosm size on benthic estuarine macroinvertebrate recolonization. Sediments fortified with the pesticides (fenvalerate: controls, 5 (low) and 50 µg g−1 wet sediment (high); endosulfan: controls, 1 (low) and 10 µg g−1 wet sediment (high)) were fine-grained, organically rich (approximately 3.5% organic carbon and 22% dry weight) material. Relative dominance of the four most abundant taxa in both experiments was consistent among treatments with few exceptions. The amphipod,Corophium acherusicum, dominated abundance in both experiments.In the fenvalerate experiment, large trays (400 cm2) contained significantly (p<0.05) more total number of taxa (TNT) than small microcosms (144 cm2) but tray size was not significantly related to total number of organisms (TNO). When size was adjusted to a common unit area, small trays contained significantly more TNO than large containers. Adjusted abundance of small trays was 2.5 times that of large containers; a ratio close to that of microcosm sizes (i.e., 2.8). This result suggests that larval supply may have been inadequate to ‘aturate’ the available sediment in large containers. Fenvalerate significantly reduced abundance in the high treatment compared to both controls and low treatment but low treatment was not significantly different from controls. The amphipod,Corophium acherusicum, accounted for most of the decrease in abundance in response to fenvalerate. The holothruroid,Leptosynpta sp. and the polychaete,Mediomastus ambiseta, increased in abundance significantly with increased concentration of fenvalerate.Combined effects of actual microcosm size and concentration of endosulfan were not significant for TNO or TNT. As in the fenvalerate experiment, adjusted abundance of small microcosms was 2.6 times that of large trays which approximated the ratio of unit area between microcosm sizes. Abundance of a few taxa responded significantly to adjusted and unadjusted unit area. Abundance of the tunicate,Molgula manhattensis, increased significantly with increased concentration of endosulfan. Abundance was affected by sample location (e.g., interiorvs exterior cores) within microcosms. Abundance adjusted to unit area resulted in significantly greater TNO in externalvs internal cores. This has importance for sequential sub-sampling of microcosms to determine temporal dynamics.Statistically significant effects were measured in benthic community structure associated with microcosm size; however, the magnitude was relatively small. There appears to be no major biological reason to select one microcosm size over the other for screening for contaminant effects. Where feasible, the small trays provide savings in sample preparation and analysis, allow more replicates where laboratory space is limiting and generate less chemical waste. These benefits may be off-set by less ‘artifacts’ associated with edge effects of larger microcosms and the need for a larger mass of sediment to accommodate additional analytical requirements (e.g., thin vertical surficial samples to refine contaminant exposure at the sediment/water interface).

The importance of physical scaling factors to benthic marine invertebrate recolonization of laboratory microcosms

Five laboratory studies of benthic macroinvertebrate recolonization were conducted for six‐week periods to evaluate the effects of physical scaling factors (i.e. microcosm size, seawater flow rates and sediment depth) on benthic community structure. Design variables included four open‐faced acrylic containers of size‐7, ‐12, ‐20 and ‐32 cm/side; seawater flow rate—approximately 0.7 or 1.6 liters/min; and sediment depth of 2.5 or 5.0 cm. Response variables included: total number of organisms (TNO), and taxa (TNT) and dominant taxa. Effects of seawater flow rates were more apparent than those related to microcosm size and sediment depth. Both TNO and TNT gave significant positive responses to increasing flow. Size effects were non‐linear; size‐20 microcosms tended to average more organisms than size‐32 but effects were often not significant (P>0.05). Size‐20 microcosms averaged higher numbers of taxa than size‐32 and responses were usually significant (P<0.05). Dominant taxa in these experiments were the tu...

Interactions of Thalassia testudinum and sediment biogeochemistry in Santa Rosa Sound, NW Florida

Abstract Thalassia testudinum belowground biomass weights, leaf weights, leaf growth rates, areal shoot densities (m−2), and leaf C:N:P ratios were compared to a set of biogeochemical parameters to gain information on seagrass–sediment interactions that may influence seagrass growth. Data were compiled from three surveys conducted in Santa Rosa Sound, located in northwest Florida, at three different meadows in sequential years. Biomass measurements and leaf growth rates decreased between stations along transects from shallow to deeper water. Belowground biomass weights decreased and leaf C:P ratios increased with temperature reflecting a seasonal growth pattern. The T. testudinum parameters were highly correlated with each other. Sulfate reduction rates (at times exceeding 1000 nmol ml−1 day−1) were among the highest recorded for seagrass beds with temperature accounting for 79% of the variation. Even though sulfate reduction rates were high, total Fe:reduced S ratios indicated sufficient Fe to account for all reduced S as pyrite. Sediment Fe, C, N, and organic P concentrations increased with sediment depth, whereas inorganic P decreased with depth, suggesting burial of organic P and root uptake of inorganic P. Leaf C:N:P ratios indicated P-limited growth for two surveys. NH4 + was detected in water above the sediment surface during some surveys demonstrating T. testudinum meadows at times may serve as sources of inorganic N to the water column. Plant parameters correlated with concentrations of sediment organic C and N, Fe, S, and porewater NH4 +. These results highlight the importance of the organic matter and Fe contents of sediments to seagrass growth.

Wetland plant seedlings as indicators of near-coastal sediment quality: interspecific variation

The toxicities of whole sediments collected from an urbanized Florida bayou-estuary were determined for the epibenthic mysid, Mysidopsis bahia, and the infaunal amphipod, Ampelisca abdita. In addition, the phytotoxicities of the same sediments were evaluated using rooted macrophytes, Scirpus robustus Pursh and Spartina alterniflora Loisel. The results of the 24 bioassays conducted for 7-28 days, were compared for interspecific differences. Toxicity to the benthic invertebrate species was predicted to be likely in all cases, based on comparison to effects-based sediment quality assessment guidelines. However, acute toxicity was uncommon and occurred at only one of the six sampling stations. In contrast, several sediments were either significantly phytostimulatory or phytoinhibitory (P < 0.05) relative to a reference estuarine sediment. The results show the importance of considering interspecific variation and phytoassessment in contaminated sediment evaluations. Phytoassessment, the focus of this research, provided useful information that would have been missing if only the animal test species were used. For this reason, the phytotoxicity data base needs to be increased to better evaluate the relevance of most current contaminated sediment evaluations for coastal areas and also to determine the realism of proposed numerical sediment quality assessment guidelines and criteria.