Polyhaline Regions Research Articles

A Modeling Study on the Influence of Sea-Level Rise and Channel Deepening on Estuarine Circulation and Dissolved Oxygen Levels in the Tidal James River, Virginia, USA

The impact of channel deepening and sea-level rise on the environmental integrity of an estuary is investigated using a three-dimensional hydrodynamic-eutrophication model. The model results show that dissolved oxygen (DO) only experienced minor changes, even when the deep channel was deepened by 3 m in the mesohaline and polyhaline regions of the James River. We found that vertical stratification decreased DO aeration while the estuarine gravitational circulation increased bottom DO exchange. The interactions between these two processes play an important role in modulating DO. The minor change in DO due to channel deepening indicates that the James River is unique as compared with other estuaries. To understand the impact of the hydrodynamic changes on DO, both vertical and horizontal transport timescales represented by water age were used to quantify the changes in hydrodynamic conditions and DO variation, in addition to traditional measures of stratification and circulation. The model results showed that channel deepening led to an increase in both gravitational circulation strength and vertical stratification. Saltwater age decreased and vertical exchange time increased with increases in channel depth. However, these two physical processes can compensate each other, resulting in minor changes in DO. A comparison of the impact of a sea-level rise of 1.0 m with channel deepening scenarios was conducted. As the sea level rises, the vertical transport time decreases slightly while the strength of gravitational circulation weakens due to an increase in mean water depth. Consequently, DO in the estuary experiences a moderate decrease.

Comparison of Thermohaline Optima for Juveniles of Two Sympatric Paralichthyid Flounders: Ecophysiological Evaluation of Estuarine Nursery Quality

Juvenile summer flounder Paralichthys dentatus and southern flounder Paralichthys lethostigma exhibit ontogenetic segregation during spring and summer in southeastern USA estuaries, with summer flounder remaining primarily in polyhaline regions and southern flounder migrating to oligohaline habitat. To determine physicochemical conditions contributing to optimal nursery ground function for each species, growth rates, feeding rates, and gross growth efficiencies were examined in common-garden experiments at spring and summer thermohaline regimes. Experiments were conducted on young-of-the-year (45–100 mm total length; 0.9–8.9 g) summer flounder (15–25 °C, 10–30‰) and southern flounder (15–30 °C, 0–30‰) from North Carolina, and juvenile summer flounder from Delaware (15–25 °C, 30‰ only). Over the 15–25 °C and 10–30‰ conditions common to both species, means of all dependent variables were greater in summer flounder than southern flounder. Summer flounder grew best at 21–23 °C and 21–28‰. Low salinity (0–10‰) was physiologically suboptimal, especially at high (25 °C) summer temperatures. There was a significant direct effect of location (North Carolina vs Delaware) on growth efficiency of juvenile summer flounder, but not on growth rate, feeding rate, or linear growth rate. Growth potential of southern flounder was maximum at 25–26 °C and 10–30‰, and growth efficiency was highest at mesohaline salinities; yet growth was maintained at moderate levels over a broad range of oligohaline conditions, including ≤ 10‰, even at 30 °C. Differences in thermohaline conditions that affect growth potential illustrate spatiotemporal patterns and dynamics of optimal nursery potential for these two paralichthyid flounders.

Diversity and distribution of tintinnid ciliates along salinity gradient in the Pearl River Estuary in southern China

Tintinnid community structure in the Pearl River Estuary were investigated 6 times (10, 29 October 2014; 11, 30 June 2015 and 15 March, 1 April 2017) from upstream freshwaters to polyhaline waters. A total of 43 tintinnid species in 15 genera were identified. Freshwater, brackish and marine species occurred in sequence along salinity gradient. Tintinnopsis mayeri, T. tubulosa and Tintinnidium fluviatile were freshwater species. Fourteen and 15 tintinnid species were considered as brackish and marine species, respectively. The preferred salinity of freshwater species was <3, and the abundance of freshwater species decreased along salinity gradient. Preferred salinity of brackish species ranged in 3–23. High abundance of brackish species occurred at mesohaline regions and decreased towards both oligohaline and polyhaline regions. Marine species abundance dropped sharply with the decrease of salinity, and seldom appeared when salinity was <15. Tintinnid species richness was low at low salinity areas. With the increase of salinity, tintinnid species richness showed different variation patterns in different seasons. Tintinnid abundance showed bimodal-peak along salinity gradient. The first abundance peak was mainly contributed by brackish species and occurred where salinity was < 15. While the second abundance peak appeared where salinity was around 25 or > 30, which was mainly contributed by marine species. Low salinity, brackish and coastal tintinnid communities were divided based on the abundance percentage variations of different tintinnid types. Complexities of those communities increased along salinity gradient.

Patterns and Trends in Secchi Disk Depth over Three Decades in the Chesapeake Bay Estuarine Complex

Water clarity is an important ecosystem indicator of eutrophication in Chesapeake Bay and other coastal and estuarine systems across the globe. Although a variety of measures are available to quantify light availability in water, Secchi disk depths have been the most consistent and frequent measure employed in water monitoring programs. Because light availability is influenced by multiple variables, such as phytoplankton biomass, non-living suspended particles, and colored dissolved organic matter (CDOM), understanding the factors driving long-term variability and trends in water clarity is critical for targeting watershed management actions related to eutrophication. Thus, we conducted a comprehensive statistical analysis of spatial and temporal variations in Secchi disk depth and the key internal and external variables that influence its variability in Chesapeake Bay and its tidal tributaries over the past 30 years. Our results indicate that although watershed nutrient, sediment, and freshwater inputs did not correlate with Secchi depth on a monthly timescale outside of low-salinity regions near river outflows, water-column variables that represent the consequences of those inputs (CDOM, chlorophyll-a, and total suspended solids [TSS]) were strongly associated with Secchi depth variability. The inconsistency of these two findings may be explained by controls on chlorophyll-a and TSS that are not directly related to watershed input, such as grazing and resuspension, and by lags of several months between watershed inputs and the associated water-column concentrations. While salinity (a proxy for CDOM) was a dominant spatial covariate with Secchi depth bay-wide, TSS concentrations were strongly associated with temporal changes in Secchi depths in low-salinity regions and indicators of phytoplankton biomass were more important in mesohaline and polyhaline regions. These findings related to spatially dependent controls on Secchi depth enhance our understanding of long-term changes in estuarine light availability and suggest a region-specific response of Secchi depth to variables (TSS and chlorophyll-a) targeted by watershed restoration actions designed to limit nutrient and sediment inputs to Chesapeake Bay.

Impacts of Atmospheric Nitrogen Deposition and Coastal Nitrogen Fluxes on Oxygen Concentrations in Chesapeake Bay

AbstractAlthough rivers are the primary source of dissolved inorganic nitrogen (DIN) inputs to the Chesapeake Bay, direct atmospheric DIN deposition and coastal DIN concentrations on the continental shelf can also significantly influence hypoxia; however, the relative impact of these additional sources of DIN on Chesapeake Bay hypoxia has not previously been quantified. In this study, the estuarine‐carbon‐biogeochemistry model embedded in the Regional‐Ocean‐Modeling‐System (ChesROMS‐ECB) is used to examine the relative impact of these three DIN sources. Model simulations highlight that DIN from the atmosphere has roughly the same impact on hypoxia as the same gram‐for‐gram change in riverine DIN loading, although their spatial and temporal distributions are distinct. DIN concentrations on the continental shelf have a similar overall impact on hypoxia as DIN from the atmosphere (~0.2 mg L−1); however, atmospheric DIN impacts dissolved oxygen (DO) primarily via the decomposition of autochthonous organic matter, whereas coastal DIN concentrations primarily impact DO via the decomposition of allochthonous organic matter entering the Bay mouth from the shelf. The impacts of atmospheric DIN deposition and coastal DIN concentrations on hypoxia are greatest in summer and occur farther downstream (southern mesohaline) in wet years than in dry years (northern mesohaline). Integrated analyses of the relative contributions of all three DIN sources on summer bottom DO indicate that impacts of atmospheric deposition are largest in the eastern mesohaline shoals, riverine DIN has dominant impacts in the largest tributaries and the oligohaline Bay, while coastal DIN concentrations are most influential in the polyhaline region.

Distance‐based mixing models of δ18 and δ18 in a marsh‐lined estuary with multiple, distinct sources (Murderkill Estuary, Delaware, USA)

AbstractThe Murderkill Estuary (Delaware, USA) receives principally from its upland watershed and from a wastewater treatment facility. Due to disparate sources, one‐dimensional salinity‐based mixing models were inadequate for describing distributions of , δ15 , and δ18 . Distance‐based mixing models with multiple, spatially‐specified inputs were, therefore, applied to describe conservative mixing of these constituents and determine the extent to which biogeochemical reactions lead to non‐conservative behavior of . These models closely matched Si observations in both winter and summer, consistent with high wastewater silicate loads and light limitation, and serve to validate modeling parameters for both seasons. A close fit of distance‐based models to estuarine observations suggested a lack of uptake and fractionation in early winter. In the summer, modeled predictions of , δ15 , and δ18 diverged from estuarine observations, particularly in the oligohaline and polyhaline regions, consistent with in situ nitrogen cycling or additional sources and sinks. Effluent from an adjacent marsh in the lower estuary contained with low δ15 and δ18ONO3, low DO and high concentrations in late summer. This data and previous studies of adjacent Delaware Bay suggest that reactions in marshes and Bay waters likely drove the non‐conservative behavior of and its stable isotopes. Potential uncertainty in watershed discharge, however, limited explicit quantitation of loss in the estuary. Nonetheless, distance‐based models are useful tools for the study of , δ15 and δ18 distributions and cycling patterns in complex marsh‐lined estuaries with multiple inputs.

Spatio-temporal distribution of Acartia (Copepoda: Calanoida) species along a salinity gradient in the Seomjin River estuary, South Korea

The spatio-temporal distribution of four coexisting Acartia (Copepoda: Calanoida: Acartiidae) species, A. hudsonica, A. omorii, A. ohtsukai and A. forticrusa was examined along a salinity gradient in the Seomjin River estuary, during the spring tide of each month for one year from January to December 2000. Most of the Acartia species were found in mesohaline (5–18 psu) and polyhaline regions (>18 psu), but their densities varied seasonally both along the salinity gradient and with chlorophyll a concentration. Acartia hudsonica showed a high density in mesohaline and polyhaline regions in March and April when chlorophyll a concentration was >20 µg l–1, but A. omorii showed high density only in the polyhaline region in April. Acartia ohtsukai occurred both in mesohaline and polyhaline regions after June, but its peak density occurred in the polyhaline region in October when there was an autumn diatom bloom in the mesohaline. Acartia forticrusa showed peak density in the mesohaline in June when the water temperature was >20°C. These results indicate that food can be an important factor in controlling spatio-temporal distributions in the Seomjin River estuary, in addition to other environmental factors.

Contribution of Nutrient and Organic Matter Sources to the Development of Periodic Hypoxia in a Tributary Estuary

The seasonal formation of periodic hypoxia within tributary estuaries is influenced by multiple nutrient and organic matter sources, both autochthonous and allochthonous. In contrast to lakes and flowing rivers, allochthonous inputs to estuaries include those from near-field sources in the watershed as well as far-field sources from adjacent marine systems that contribute nutrients, organic matter, and hypoxic water via estuarine circulation. This study utilized a reduced-complexity eutrophication model to quantify the contribution of individual sources to hypoxia in the York River estuary (YRE), and assess the reductions necessary to mitigate hypoxic conditions. Results indicate that portions of the oligohaline YRE are influenced by organic loading from the watershed, while the lower mesohaline region is influenced by both internal phytoplankton production and watershed loads. In the high mesohaline, watershed organic matter and internal phytoplankton production play an equally important role during the spring; however, in summer and fall oxygen concentrations appear to respond strongly to dissolved organic carbon (DOC) entering via advection from Chesapeake Bay (CB). The polyhaline region, which is frequently the site of reoccurring hypoxia, responded primarily to advected DOC from CB. Results indicate that different regions of the YRE may require different management strategies, and highlight the strong relationship between periodic hypoxia in the lower YRE and advection of labile organic matter from CB, a far-field input that requires a regional management approach. A cross-system comparison of nutrient budgets indicates that far-field sources can comprise a large portion of total system inputs in numerous tributary estuaries.

Seasonal dynamics of Mesodinium rubrum in Chesapeake Bay

The photosynthetic ciliate Mesodinium rubrum is a common member of coastalphytoplankton communities that is well adapted to low-light, turbid ecosystems.It supports the growth of, or competes with, harmful dinoflagellate species forcryptophyte prey, as well as being a trophic link to copepods and larval fish. Wehave compiled data from various sources (n ¼ 1063), on the abundance and distri-bution of M. rubrum in Chesapeake Bay and its tributaries. Because M. rubrumrelies on obtaining organelles from cryptophyte algae to maintain rapid growth,we also enumerated cryptophyte algae in the portion of these samples that we col-lected (n ¼ 386). Mesodinium rubrum occurred in oligohaline to polyhaline regions ofChesapeake Bay and throughout the year. Blooms (.100 cells mL

Calibration of a bioenergetics model linking primary production to Atlantic menhaden Brevoortia tyrannus growth in Chesapeake Bay

Growth and potential productivity of young-of-the-year (YOY) Atlantic menhaden Brevoortia tyrannus, a key forage fish, were investigated in Chesapeake Bay. A coupled foraging and bioenergetics model was developed to predict the dependency of menhaden size on chloro- phyll a (chl a) and water temperatures in the bay. Substantial improvements were made to func- tional responses previously developed to describe YOY menhaden filtering efficiency on phyto- plankton and swimming speed while filter feeding. Model output was calibrated to correspond to observed lengths of field-collected menhaden over an 11 yr period (1995 to 2005) by adjusting the percentage of chl a available to menhaden in the model. The model effectively represents vari- ability in menhaden length in response to changes in chl a and temperature, indicating that only 9.2% of available chl a was required for menhaden to grow to lengths observed in the bay. In simulations of growth potential by bay region, the oligohaline (upper) region had the highest growth potential with decreasing potential in the mesohaline (middle) and polyhaline (lower) regions of the bay. Our results represent the first rigorous calibration and evaluation of a coupled foraging-bioenergetics model for Atlantic menhaden and establish a quantitative link between chl a standing stock and menhaden growth potential.

Water Quality within the York River Estuary

Key water quality management issues and threats within the Chesapeake Bay and its tidal tributaries include excess loadings of sediment and nutrients, and the introduction of toxic chemicals and microbial agents. Poor water clarity, principally controlled by suspended sediments and phytoplankton, is a persistent and widespread problem in the York River estuary with the oligohaline and middle mesohaline regions failing to meet submerged aquatic vegetation (SAV) habitat requirements (SAV criteria: ~10 NTU and TSS < 15 mg L−1). Both the primary and more localized secondary estuarine turbidity maximum are associated with these regions where elevated surface (30–35 mg L−1) and bottom (80–105 mg L−1) water TSS levels are observed. While nonpoint agriculture sources dominate riverine sediment load inputs, tidal and nearshore erosion are a significant source of suspended sediment in the York River estuary. As with sediment, nonpoint agricultural sources dominate nutrient inputs and streamflow is a dominant controlling factor in explaining variability in annual loads. Within mainstem surface waters, TDN and TDP concentrations exhibit a decreasing trend with increasing salinity. TDN and TDP concentrations are on the order of 40–45 μmol L−1 and 1.2 μmol L−1, respectively, in the tidal freshwater reaches of the Pamunkey and Mattaponi Rivers and 22–24 μmol L−1 and 0.6 μmol L−1 in the polyhaline regions of the York River. Mean DON exhibits little variation between salinity regimes. Seasonal phytoplankton biomass and productivity vary between salinity regimes with mean monthly peak chlorophyll a concentrations on the order of 9–10 μg L−1 in the tidal freshwater reaches, 14–18 μg L−1 in the transition zone below the freshwater region, 25–28 μg L−1 in the upper and middle mesohaline reaches, and 15 μg L−1 in the lower mesopolyhaline region. Based on DIN:DIP molar ratios and limited nutrient enrichment studies, tidal freshwater regions experience year-round phosphorus limitation, shifting to seasonal nitrogen limitation in the lower oligo, meso and polyhaline regions of the York River. Harmful algal bloom (HAB) producing dinoflagelletes have resulted in “red tides” that generally occur annually (summer, early fall) in the lower York River. With respect to low dissolved oxygen levels, hypoxia derived from oxidation of organic matter and sediment oxygen demand has also been observed repeatedly in the bottom waters of the lower, high salinity reaches when water temperatures exceed 20 °C. While studies have indicated limited toxic chemical contamination, mercury and PCB fish consumption advisories and restrictions have been issued within the York River estuary. Mercury impacted regions of the Mattaponi and Pamunkey Rivers receive significant wetland drainage that can enhance the potential for bioaccumulation of mercury in fish. Sediments in the York River proper exhibit PCB levels ranging from 1–5 ppb with more elevated levels (25 ppb) being observed in some contributing tidal creeks. In contrast to mercury where atmospheric deposition is a primary pathway, PCBs are generally released into the environment from runoff processes occurring at hazardous waste sites. With varying sources of fecal pollution, 20 percent (31.1 km2) of the York River's assessed shellfish waters has been designated as impaired. Condemned waters are restricted to major industrial and defense facility sites, and contributing smaller tidal creek systems.

History of Olympia Oysters (Ostrea luridaCarpenter 1864) in Oregon Estuaries, and a Description of Recovering Populations in Coos Bay

ABSTRACT Historical evidence indicates that Olympia oysters (Ostrea lurida)† are indigenous to at least three of Oregon's estuaries. Populations of O. lurida occur in Yaquina Bay, Netarts Bay, and Coos Bay, although only the population in Yaquina Bay seems likely to have been continuous since prewestern settlement. The historical occurrence of Olympia (native) oysters in Yaquina and Netarts Bays is confirmed by numerous records of fishery landings. In contrast, historic populations in Coos Bay are inferred by the presence of large shell deposits buried in sediments throughout the polyhaline (salinity > 18–30) region of the estuary. Other Oregon estuaries (such as Tillamook, Alsea, and Umpqua/Winchester Bay) may have had ambient environmental conditions suitable to support self-sustaining populations of O. lurida, but none of these estuaries are currently inhabited by natural populations, nor do they exhibit clear historical records of occupation in the past. We conducted searches of background information...

Ammonia‐oxidizing bacterial community composition in estuarine and oceanic environments assessed using a functional gene microarray

The relationship between environmental factors and functional gene diversity of ammonia-oxidizing bacteria (AOB) was investigated across a transect from the freshwater portions of the Chesapeake Bay and Choptank River out into the Sargasso Sea. Oligonucleotide probes (70-bp) designed to represent the diversity of ammonia monooxygenase (amoA) genes from Chesapeake Bay clone libraries and cultivated AOB were used to construct a glass slide microarray. Hybridization patterns among the probes in 14 samples along the transect showed clear variations in amoA community composition. Probes representing uncultivated members of the Nitrosospira-like AOB dominated the probe signal, especially in the more marine samples. Of the cultivated species, only Nitrosospira briensis was detected at appreciable levels. Discrimination analysis of hybridization signals detected two guilds. Guild 1 was dominated by the marine Nitrosospira-like probe signal, and Guild 2's largest contribution was from upper bay (freshwater) sediment probes. Principal components analysis showed that Guild 1 was positively correlated with salinity, temperature and chlorophyll a concentration, while Guild 2 was positively correlated with concentrations of oxygen, dissolved organic carbon, and particulate nitrogen and carbon, suggesting that different amoA sequences represent organisms that occupy different ecological niches within the estuarine/marine environment. The trend from most diversity of AOB in the upper estuary towards dominance of a single type in the polyhaline region of the Bay is consistent with the declining importance of AOB with increasing salinity, and with the idea that AO-Archaea are the more important ammonia oxidizers in the ocean.

Depth-related patterns in benthic community condition along an estuarine gradient in Chesapeake Bay, USA

Abstract We tested whether macrobenthic community condition varies significantly with water depth in a variety of regions of Chesapeake Bay, USA. Benthic community condition was characterized using the Benthic Index of Biotic Integrity (B-IBI) previously developed for the Bay. We applied two water depth thresholds intended to emphasize the ecological importance and/or anthropogenic impacts upon shallow-water regions. The first threshold of 2 m emphasizes restoring and supporting submerged aquatic vegetation while the second threshold of 4 m emphasizes the zone of maximum anthropogenic impact upon natural ecosystem functions. An a priori expectation is that benthic community condition may worsen with increasing depth, specifically in regions (1) where water column stratification at depth results in prolonged low dissolved oxygen levels or (2) where net deposition at depth results in higher levels of hydrophobic, sediment-bound contaminants. Samples collected from a major tributary of Chesapeake Bay, the York River estuary, spanned the entire salinity range from tidal freshwater to polyhaline. We also tested the shallow-water depth thresholds using data from the Virginia Mainstem of Chesapeake Bay and the Southern Branch of the Elizabeth River. These two polyhaline regions are characterized as having the best and worst benthic community condition in Chesapeake Bay. At the scale of the entire tidal York River system, there were no significant differences in benthic community condition with water depth. However, two salinity regions, low mesohaline and polyhaline, had significant depth effects with the shallowest water depth zone significantly different from the other two depth regions. For the low mesohaline region benthic community condition was worse at the shallowest depth and for the polyhaline region the shallowest depth was better comparing the three depth regions. No depth-related differences in the B-IBI were found for the two additional Chesapeake Bay strata, the Virginia Mainstem characterized with the lowest levels of benthic community degradation and for the Southern branch of the Elizabeth River, characterized by the highest levels of benthic community degradation. We conclude that the ecological state of Chesapeake Bay subtidal benthic communities is adequately characterized by randomly sampling all depths without further stratification into shallow and deeper regions.

Phytoplankton assemblages associated with water quality and salinity regions in Chesapeake Bay, USA

Based on an 18-year data base (1984–2002), seasonal (spring, summer) phytoplankton relationships to specific environmental determinants were identified within different salinity regions of Chesapeake Bay. Growth conditions in these areas were identified as either less favorable (Impaired) or favorable (Least Impaired) for phytoplankton development. Diatoms represented the greatest cellular abundance and biomass during spring in different salinity regions and water quality conditions. In contrast, the dominant summer floral biomass was produced by a combination of diatoms, chlorophytes, and cyanobacteria in tidal freshwater and oligohaline waters, with diatoms and dinoflagellates representing the major algal biomass in mesohaline and polyhaline regions. Chlorophyte and cyanobacteria abundance and biomass decreased with the increasing salinities of the mesohaline and polyhaline regions, in contrast to increased biomass and abundance by dinoflagellates and diatoms. The common background taxa and an additional biomass source throughout these seasons were cryptophytes. Increased summer cyanobacteria abundance and biomass in the Impaired water of the tidal fresh and oligohaline regions were associated with reduced light availability and higher nutrient concentrations. The summer diatoms and dinoflagellates had increased mean cell sizes in the Least Impaired mesohaline and polyhaline waters compared to their populations in Impaired regions. This relationship was enhanced by increased abundance of neritic diatoms and dinoflagellates entering the Bay from Atlantic coastal waters. The data suggested a general reduction of existing nutrient levels and improved light availability in the Impaired waters would still continue the dominance of diatom flora over any additional cyanobacteria development.

Long-term trends in mesozooplankton abundance in Chesapeake Bay, USA: influence of freshwater input

Analyses of a 16 year time-series (1985-2000) of mesozooplankton abundance in the Chesapeake Bay reveal the influence of freshwater flow on species composition and abundance. Trend analysis and linear mixed-effects regression models were used to assess long-term variation in, and influence of water-quality parameters (modulated by freshwater input) on, the monthly mean abundance of the 2 dominant copepod species Acartia tonsa and Eurytemora affinis. There were no long-term trends in abundance of either copepod species, with the exception of a slight downward trend for A. tonsa in the mesohaline region of the northern Chesapeake Bay. There were no long- term trends in temperature, but there was a downward trend in salinity related to a wet period in the late 1990s. Linear mixed-effects models showed a negative correlation between freshwater input and A. tonsa abundance in the oligohaline region, and no significant relationship between other water- quality parameters and A. tonsa abundance in the mesohaline region. A. tonsa abundance was posi- tively correlated with temperature in the polyhaline region. E. affinis abundance in the oligohaline region was negatively correlated with biovolume of the ctenophore Mnemiopsis leidyi and positively correlated with phytoplankton abundance. A negative correlation with salinity and a positive corre- lation with turbidity were found for E. affinis in the mesohaline region. While years of above-average freshwater input were characterized in the spring by high abundances of E. affinis in the mesohaline region and low abundances of A. tonsa in the oligohaline region, the former may show a lagged response depending on the time and magnitude of the input. Freshwater input appears to be mainly influencing habitat parameters specific to each copepod species and top-down control by predators.

Effect of salinity on biological concentrations of137Cs in phytoplankton inhabited in brackish Lake Obuchi, Japan, bordered by nuclear fuel facilities

Lake Obuchi is on the Shimokita Peninsula, Aomori Prefecture, Japan, near several nuclear fuel-related facilities. The lake contains from oligohaline to polyhaline regions, and the salinity fluctuates greatly both spatially and temporally. This study examined the possible effect of salinity on biological concentrations of 137Cs in phytoplankton on the basis of a culture experiment using stable Cs and phytoplankton species isolated from the lake. In both Cyclotellaand Skeletonema, the biological concentrations of Cs varied with salinity conditions, and a positive linear relation was found between maximum proliferation and biological concentrations of Cs.

Planktonic and bacterial respiration along an estuarine gradient: responses to carbon and nutrient enrichment

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 30:251-261 (2003) - doi:10.3354/ame030251 Planktonic and bacterial respiration along an estuarine gradient: responses to carbon and nutrient enrichment Erik M. Smith*, W. Michael Kemp University of Maryland Center for Environmental Science, Horn Point Laboratory, PO Box 775, Cambridge, Maryland 21613, USA *Present address: Département des Sciences Biologiques, Université du Québec à Montréal, CP 8888, succursale Centre-Ville, H3C 3P8 Montréal, Québec, Canada. Email: smith.erik@uqam.ca ABSTRACT: Previous observations have revealed that rates of plankton community respiration vary consistently along the main salinity gradient of Chesapeake Bay, USA, with maximum values occurring in the mesohaline region and significantly lower rates in both the oligohaline and polyhaline regions. This study tested the hypothesis that spatial variations in respiration are the result of differential resource limitation of the bacterial communities along the land-sea gradient. Effects of organic carbon and inorganic nutrients on microbial (<3 μm) respiration rate were assessed in short-term (6 h) enrichment bioassays. Responses of bacterioplankton to enrichment were also investigated by means of re-growth culture experiments. Both sets of experiments were conducted during summer in 3 regions along the main salinity gradient of the estuary. Within the re-growth cultures, there was little variation in, or effect of enrichment on, specific growth rates, which were roughly 2 d-1 in all cultures. In contrast, estimates of cell-specific respiration varied 2-fold along the salinity gradient (from 3.3 to 6.9 fg O2 cell-1 h-1 in the Upper and Mid Bay regions, respectively) and showed significant responses to substrate enrichment. Resulting estimates of bacterial growth efficiencies exhibited similar variability, ranging from 20.4 to 41.3%, with spatial variations in efficiencies apparently related to nutrient concentrations. Results of substrate enrichment in both short-term bioassays and bacterioplankton re-growth cultures demonstrated a pattern of stimulation by organic carbon in the Upper Bay and by inorganic nutrients in the Lower Bay, with no significant response to substrate enrichment in the Mid Bay. Patterns of bacterioplankton response to enrichment in the nutrient-poor polyhaline region suggested a propensity for the bacterial community to maximize growth, rather than efficiency, via changes in specific respiration rates. KEY WORDS: Respiration · Bacterioplankton · Nutrient effects · Growth efficiency · Estuaries Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 30, No. 3. Online publication date: January 23, 2003 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 2003 Inter-Research.

Toward a Predictive Understanding of Primary Productivity in a Temperate, Partially Stratified Estuary

This paper addresses the development of a predictive understanding of phytoplankton primary productivity (PP) in estuaries, drawing on an extensive set of observations in Chesapeake Bay and contemporary modeling approaches coupled to empirical data. PP was measured at 575 stations on 68 cruises, 1982–2000. Descriptions presented here are based on PP data from 455 stations occupied 1982–1998, and from 120 stations occupied 1999–2000 that were used for model validation. The nearly two-decade sampling period encompassed a broad range of freshwater flow and nutrient loading to the Bay. Mean net14 C-PP for 1982–1998 was 1055mgCm−2d−1 (±SE=46·0) in the main stem Bay for all seasons and regions. Phytoplankton dynamics included a spring maximum of biomass, expressed as euphotic-layer chlorophyll (chla), and a summer maximum of net 14C-PP displaced by approximately 4 months from the biomass maximum. The annual maximum of euphotic-layer chla exceeded 100mgm−2 in mesohaline and polyhaline regions of the Bay during April and May, whereas highest net14 C-PP of 1700–2500mgCm−2d−1occurred in the mesohaline Bay in July and August. Euphotic-layer chla and net 14C-PP were much lower in the light-limited oligohaline Bay and no time lag was observed. Mean gross 14C-PP was 1564mgCm−2d−1 (±SE=85·0) for 1995–1998. Concurrent measurements using 14C and O2 methods generated estimates of the photosynthetic quotient (PQ) to confirm our interpretation of net and gross PP from 14C uptake in full- and partial-day incubations, respectively, and allowed us to reconcile apparent differences in 14C- and O2-determined PP in recent studies. PQ values (=O2 produced/CO2 fixed) were estimated as 1·48 from regression of stoichiometrically converted net O2-PP on net 14C-PP, and as 1·38 from the regression of gross O2-PP on gross 14C-PP. PQ values in this range typically correspond to phytoplankton that are using oxidized nitrogen (NO−3-N) as the main N source, consistent with the view that N-limitation occurs on an annual scale in the Bay. We used empirical data for net and gross 14C-PP to estimate annual integrated production (AIP) of 282 to 538gCm−2yr−1 (net) and 347 to 662gCm−2yr−1 (gross). Simple, linear regression of net AIP on annual, mean euphotic-layer chla was significant and explained ∼62% of the variance. Inter-annual variability of net AIP was related to the volume of freshwater flow and to total nitrogen (TN) and total phosphorus (TP) loading during February and March. We tested the performance of published models to estimate PP in Chesapeake Bay. The Vertically Generalized Productivity Model (VGPM) overestimated net and gross PP, and adjusted forms of VGPM termed VGPM-A for net and gross PP gave significantly improved performance for Chesapeake Bay. We explored an alternative approach to VGPM that allowed us to obtain non-unity exponents for independent variables, using step-wise and multiple regressions in log-space first to identify independent variables that predicted net and gross PP, and subsequently to determine coefficients of the terms. This approach resulted in the Chesapeake Bay Productivity Model (CBPM-1) that estimated net and gross PP with root mean square error (RMSE) of 28·3% and 34·9%, respectively. We then developed models of the physiological input, PBopt, a variable that expresses optimal photosynthesis in the water column normalized to chla, using several independent variables and measured values of PBopt. Substitution of the models of PBopt in CBPM-1 resulted in CBPM-2 that required no explicit input of PBopt and estimated net and gross PP with RMSE of 120% and 49·8%, respectively. Lastly, we validated CBPM-1 and CBPM-2 using observations from 1999–2000 not included in development of the models. CBPM-1 estimated net and gross PP with RMSE of 17·8% and 35·8%, respectively, and CBPM-2 estimated net and gross PP with RMSE of 80·3% and 47·6%, respectively. We believe the use of contemporary PP models that require simple inputs amenable to remote sensing, such as the adjusted VGPM, CBPM-1, and CBPM-2, should permit us to resolve spatial and temporal differences of net and gross PP in estuaries and give improved estimates of AIP, an essential measure of ecosystem health and productivity.

Prey selection by the hogchoker, Trinectes maculatus (Pisces: Soleidae), along summer salinity gradients in Chesapeake Bay, USA

We investigated feeding by the hogchoker, Trinectes maculatus (Bloch and Schneider), in freshwater, oligohaline, mesohaline, and polyhaline regions of Chesapeake Bay, USA, and examined prey selection in relation to food availability. Otter trawling for fish and Van Veen grab sampling for benthic macrofauna occurred in July and August 1992 and August and September 1993. Hogchokers exhibited both opportunistic and selective feeding patterns along the estuarine salinity gradient in four tributaries (Potomac, Rappahannock, York, and James Rivers) and in the mainstem Chesapeake Bay. Major prey taxa included annelids, arthropods, and tellinid siphons. In polyhaline habitat, polychaetes dominated both the benthos and gut contents numerically and gravimetrically. On the other hand, oligochaetes were numerically dominant in freshwater/oligohaline areas but were rarely eaten, perhaps because of their burial depth. Arthropods (mostly amphipods) occurred at most salinities, were common in gut contents in low-salinity areas, and were replaced as prey by larger proportions of polychaetes in polyhaline regimes. Although hogchokers ate tellinid siphons, they rarely consumed whole bivalves or gastropods. These diet patterns (and especially the importance of siphon nipping) are similar to those of juvenile or small flatfish elsewhere in Europe, Africa, and North America. A size–salinity relationship for hogchokers occurred along the summer salinity gradient, with smaller fish predominating upstream and larger fish downstream. It was not clear from our data if variation in diet composition reflected changes in prey composition along the salinity gradient rather than changes in fish size.