High Freshwater Inflow Research Articles

The hydrodynamic response of the York River estuary to Tropical Cyclone Isabel, 2003

Hurricane Isabel made landfall along the North Carolina coast on September 18, 2003 (UTC 17:00) and the storm surge exceeded 2.0 m in many areas of the Chesapeake Bay and in the York River estuary. River flooding occurred subsequently, and the peak river discharge reached 317 and 104 m 3 s −1 in the Pamunkey and Mattaponi rivers, respectively. The York River estuary experienced both storm surge and river flooding during the event and the estuary dynamics changed dramatically. This study investigates the hydrodynamics of the York River estuary in response to the storm surge and high river inflows. A three-dimensional model was used to investigate the changes of estuarine stratification, longitudinal circulation, salt flux mechanisms, and the recovery time required for the estuary to return to its naturally evolved condition without the storm. Results show that the salt flux was mainly caused by advection, which was induced by the barotropic gradient during the storm event. The net salt flux increased by a factor of 30 during the rise of the storm surge. However, the large amount of salt transported into the estuary was quickly transported out of the estuary as the barotropic gradient reversed during the descent of the storm surge. Subsequent high freshwater inflow influenced the estuarine circulation substantially. The estuary changed from a partially mixed estuary to a very stratified estuary for a prolonged period. The model results show that it will take about 4 months for the estuary to recover to its naturally evolved salinity distribution after the impacts of the storm surge and freshwater pulse.

Late Pleistocene to Holocene marine transgression and thermohaline control on sediment transport in the western Magellanes fjord system of Chile (53°S)

In the Western Strait of Magellan in southernmost Chile marine transgression occurred between 14,500 and 13,500 cal. BP. This is indicated by strongly increased accumulation of biogenic carbonate and first appearance of foraminifers in sediment records. From that time until 11,500 cal. BP, sedimentation in the western fjords became predominant autochthonous, due to higher salinity and clay flocculation, and Late Glacial glacier retreat. Present day thermohaline zonation pattern, extensively representative for the Holocene, and sedimentation rates indicate that westerlies hampered westward outflow of superficial (0–30 m water depth) glacial clay-rich freshwater from glaciated areas. During the Holocene, isostatic uplift of the Andes overcompensated sea level rise. In areas with high Glacial glacier loading this led to shallowing fjord sills and restricted exchange with marine water, especially since high freshwater inflow produced strong pycnoclines and preserved old saline water in fjord bottoms. To the east of the climate divide the Seno Skyring fjord system shows a year-round stable stratification, despite a strong wind-induced eastward superficial current in the upper 30–50 m of the water column. Such currents enabled significant Late Glacial eastward transport of glacial clay. Sediment cores from this area indicate that east-ward sediment flux slowed down during the Holocene, probably due to less intense westerlies. Investigated present day thermohaline characteristics of the fjord system across the superhumid climate divide of the Southern Andes indicate details of the exchange between marine and freshwater which are fundamental for evaluation of sediment transport pathways, biogenic productivity and interpretation of paleoclimate records in this area.

The effect of freshwater inflow on net ecosystem metabolism in Lavaca Bay, Texas

Estuaries and other coastal ecosystems depend on freshwater inflow to maintain the gradients in environmental characteristics that define these transitional water bodies. Freshwater inflow (FWI) rates in many estuaries are changing due to changing land use patterns, water diversions for human consumption, and climate effects, but there are no standard criteria to determine minimum inflow rates. An ecological indicator is required so models can be produced to predict how changing hydrology might affect estuarine metabolic rates, productivity, or impairment. One indicator of estuarine metabolic rates is net ecosystem metabolism (NEM). It is hypothesized that metabolic rates (as indicated by NEM) will depend on recently delivered FWI. To test this hypothesis, daily NEM was calculated from high frequency changes in dissolved oxygen measurements in a shallow water estuary, Lavaca Bay, Texas, USA and related to FWI and other environmental conditions. There was a significant relationship between NEM and cumulative ten-day FWI in upper Lavaca Bay, with more heterotrophic conditions occurring after high FWI events. No significant relationship existed between NEM and FWI in lower Lavaca Bay, where other environmental conditions, such as tidal forcing, may be more influential. An empirical model simulating NEM's response to FWI in upper Lavaca Bay was more accurate during moderate to high flows than during low base-flow conditions. Thus, quantity of FWI and distance from the inflow point source constrained the dependence of NEM on FWI. NEM can be quite variable over time and within a bay dominated by a river at one end and ocean exchange at the other end. The range of environmental gradients over time and within an estuary will determine how representative NEM at a single location is for an entire estuary. However, during high flow period pulses NEM can accurately predict shifts from balanced to heterotrophic conditions. Therefore, use of the NEM model as an indicator of FWI effects is constrained to regions in estuaries that are most effected by FWI because of proximity to the source or the size of FWI pulse events. The unique geologic, geographic, and climate signature's of individual estuaries will dictate the fit of this model in space and time. Inclusion of other environmental factors, such as temperature or irradiance, is necessary to improve the NEM model during low base-flow conditions. It is concluded that the NEM model does provide a useful indicator of FWI effects on ecosystem metabolic rates as it works well in the upper regions of Lavaca Bay and during freshwater inflow pulses where and when freshwater inflow has more influence than other environmental factors.

Using stable isotope analyses to assess carbon dynamics in a shallow subtropical estuary

The sources of carbon, which fuel water column respiration, remain unresolved for most estuaries; our objective was to examine carbon dynamics in a shallow subtropical estuary. We sampled the Sabine-Neches estuary, Texas, during low (November 1999) and high (May 2000) freshwater inflow and measured stable carbon isotope ratios of the dissolved inorganic and orgnaic carbon (δ13C-DIC, δ13C-DOC), as well as quantifying accessory parameters (salinity, nutrients, total suspended solids, and photosynthetic pigments). Pigment analysis indicated that diatoms were the predominant phytoplankton. Data from the May 2000 sampling event exhibited conservative mixing, indicating that the system was acting as a conduit between the watershed and the Gulf of Mexico. During November, mixing was generally nonconservative indicating extensive recycling of allochthonous and autochthonous carbon sources. Our data imply that both carbon sources had similar isotope, ratios that made it impossible to unambiguously determine the dominant source supporting respiration. The nonconservative DIC concentration data indicating an autotrophic sink as well as the strong relationship between δ13C-DOC and chlorophylla, suggest that in situ production was an important component of the DOC pool. We hypothesize that uncharacteristically calm wind conditions during sampling may have promoted phytoplankton settling, removing autotrophs, from the water column, but leaving behind a dissolved biogeochemical signature. Interpretation of carbon dynamics may be confounded by spatial and temporal decoupling of producers and consumers from biogeochemical indicators.

Spatial and overwinter changes in clam populations of San Pablo Bay, a semiarid estuary with highly variable freshwater inflow

In many estuaries worldwide, climate trends together with human diversion of fresh water have dramatically impacted the benthos. Such impacts have sometimes been complicated by exotic species, whose invasion and persistence can be mediated by wide variations in freshwater inflow. Monitoring such changes usually involves periodic samples at a few sites; but sampling that does not recognize variation at a range of spatial and seasonal scales may not reveal important benthic trends. San Pablo Bay, in northern San Francisco Bay, has extreme fluctuations in freshwater inflow. This bay also experienced a major benthic change with introduction of the Asian clam ( Potamocorbula amurensis) in 1986. This species initially displaced the former community, but later appeared to vary in abundance depending on site and freshwater inflow. To investigate such patterns and provide guidelines for research and monitoring, we took 1746 core samples at six sites around San Pablo Bay from 19 October to 17 December 1999 and from 6 March to 19 April 2000. Most biomass consisted of the clams P. amurensis, Macoma balthica and Mya arenaria. Potamocorbula amurensis dominated the benthos at most sites in the fall and recruited a new cohort during winter, while there was weak recruitment in M. balthica and none in M. arenaria. At most but not all sites, densities of P. amurensis and M. arenaria declined dramatically over winter while M. balthica declined only slightly. The dominant clams had patch diameters >5 m at most but not all sites, and some showed inconsistent patch structure at scales of 100–1400 m. In this semiarid estuary with highly variable freshwater inflow, samples for research and monitoring should include multiple sites and seasons, and samples within sites should be ≥5 m apart to account for between-patch variation. Species abundance in winter 1999–2000 appeared to be affected by high freshwater inflows in 1997–1999, while spatial patterns were probably most affected by post-settlement dispersal and mortality.

The influence of catchment management on salinity, nutrient stochiometry and phytoplankton biomass of Eastern Cape estuaries, South Africa

Three estuaries with differing catchment use and freshwater input were investigated in terms of their nutrient status, phytoplankton biomass, freshwater inflow and salinity between 1993 and 1995. The nutrients analysed include phosphate, nitrate, nitrite, ammonia and total particulate nitrogen. All the parameters were investigated for their relationship with land-use and freshwater abstraction. The Kromme River catchment area is relatively pristine, the river is impounded for ca. 133% of its mean annual runoff, and consequently, freshwater input into the estuary is only episodic. Nutrient and chlorophyll- a concentrations are low, but become elevated when freshwater does reach the estuary. The Geelhoutboom tributary contributes nutrients to the Kromme estuary during high freshwater inflow conditions, but is not a viable nutrient contributor during low flow conditions. Freshwater abstraction from the Swartkops River catchment is limited, and it is characterised by urbanisation and industrial development. The Swartkops River was the main source of phosphate in the estuary, whereas other small tributaries along the estuary were additional point sources for nitrate, ammonia and nitrite. The third system, the Sundays estuary, has no tributaries or other point sources except the Sundays River, where the catchment is extensively used for agriculture and freshwater input relatively high. The phytoplankton biomass (in terms of chlorophyll- a) was highest in the Sundays estuary, although phosphate concentrations were as low as in the Kromme estuary. Trends over time indicated a decrease in phosphate concentrations and showed variations for inorganic dissolved nitrogen concentrations since the previous 15 years in all the three estuaries. Nutrient stochiometry had changed in favour of inorganic dissolved nitrogen.

Current Structure and Behavior of the River Plume in Suo-Nada

The behavior of a river plume in Suo-Nada, Japan, has been studied using a primitive equation numerical model, the Princeton Ocean Model. Special attention has been paid to the current structure and behavior of the anticyclonic eddy (bulge) induced by high freshwater inflow changing on a timescale of one week. First, the freshwater is supplied from a river to a rectangular basin with a simple topography. When the river discharge subsides after reaching its peak value, the bulge propagates upstream (i.e., opposite to the direction of the Kelvin wave propagation). Next, the freshwater is supplied from eight major rivers to the basin with realistic topography. The less saline water mass in the southern part of Suo-Nada propagates to the west (i.e., upstream) after the river discharge subsides. This is consistent with an observed phenomenon, viz., that the less saline water mass appears in the western part of Suo-Nada, suggesting that the upstream propagation of the bulge is possible in the real ocean. Finally, the cause of the upstream propagation is considered. Onshore currents appear in the bottom layer beneath the bulge, propagating upstream. They produce an anticyclonic barotropic eddy due to the conservation of potential vorticity. The current component associated with the eddy crosses normally to the isohaline in the upper layer, and therefore transports the bulge upstream. No other current component (such as surface current velocity minus vertically-averaged value) is responsible for the upstream propagation of the bulge.

Influence of water allocation and freshwater inflow on oyster production: a hydrodynamic-oyster population model for Galveston Bay, Texas, USA.

A hydrodynamic-oyster population model was developed to assess the effect of changes in freshwater inflow on oyster populations in Galveston Bay, Texas, USA. The population model includes the effects of environmental conditions, predators, and the oyster parasite, Perkinsus marinus, on oyster populations. The hydrodynamic model includes the effects of wind stress, river runoff, tides, and oceanic exchange on the circulation of the bay. Simulations were run for low, mean, and high freshwater inflow conditions under the present (1993) hydrology and predicted hydrologies for 2024 and 2049 that include both changes in total freshwater inflow and diversions of freshwater from one primary drainage basin to another. Freshwater diversion to supply the Houston metropolitan area is predicted to negatively impact oyster production in Galveston Bay. Fecundity and larval survivorship both decline. Mortality from Perkinsus marinus increases, but to a lesser extent. A larger negative impact in 2049 relative to 2024 originates from the larger drop in fecundity under that hydrology. Changes in recruitment and mortality, resulting in lowered oyster abundance, occur because the bay volume available for mixing freshwater input from the San Jacinto and Buffalo Bayou drainage basins that drain metropolitan Houston is small in comparison to the volume of Trinity Bay that presently receives the bulk of the bay's freshwater inflow. A smaller volume for mixing results in salinities that decline more rapidly and to a greater extent under conditions of high freshwater discharge.Thus, the decline in oyster abundance results from a disequilibrium between geography and salinity brought about by freshwater diversion. Although the bay hydrology shifts, available hard substrate does not. The simulations stress the fact that it is not just the well-appreciated reduction in freshwater inflow that can result in decreased oyster production. Changing the location of freshwater inflow can also significantly impact the bay environment, even if the total amount of freshwater inflow does not change.

Impact of channelization on oyster production: a hydrodynamic-oyster population model for Galveston Bay, Texas

A hydrodynamic-oyster population dynamics model was developed to assess the effect of a change in ship channel configuration under different freshwater inflow regimes and different future hydrologies on oyster (Crassostrea virginica) populations in Galveston Bay, Texas. The population dynamics model includes the effects of environmental conditions, predators, and the oyster parasite Perkinsus marinus on oyster populations. The hydrodynamic model includes the effects of wind stress, river runoff, tides, and oceanic exchange on the circulation of the Bay. Simulations were run for low, mean, and high freshwater inflow conditions under the present (1993) hydrology and predicted hydrologies for 2024 and 2049 that include anticipated water diversion projects to satisfy the freshwater demands of population growth in metropolitan Houston, Texas. Simulation results show that oyster biomass was predicted to increase after enlargement of the ship channel. Oyster biomass is expected to increase on about 53% of total reef acreage when averaged over a 50-yr time span. Oyster reef acreage characterized by increased biomass after channel enlargement increases moderately under the present hydrology and the 2049 hydrology, but decreases slightly in 2024. Lower biomass in 2024 is due to reduced freshwater inflow and increased saltwater intrusion that pushes the optimal areas for oyster growth somewhat farther upbay than in 2049. Declines in oyster biomass, noted in most simulations in downbay reaches, were more than balanced by increased oyster biomass upbay. The differential between upbay and downbay reefs can be explained by an increase in mortality from Perkinsus marinus downbay and saltwater intrusion upbay that expands the area characterized by moderate salinities. The 20th century history of Galveston Bay is one of expansion of isohaline structure and increased oyster production as a result of anthropogenic modification of bay physiography. The salinity gradient of the 1990s, however, is not in equilibrium with the distribution of hard substrate required for oyster growth, that reflects an earlier equilibrium with the pre-1900s hydrodynamics. Increased saltwater intrusion is normally disadvantageous to oyster populations; but, in this case, channel enlargement further expands the salinity gradient upbay and outward (east and west) from the channel. As a result, in most years, oyster biomass is increased because moderate salinities cover more of the pre-1900s reef tracts where hard substrate is plentiful.

Nitrogen Budget for Low and High Freshwater Inflows, Nueces Estuary, Texas

Nueces Estuary is a relatively shallow, microtidal estuary which receives inputs from a significant industrial and urban area and from a semi-arid drainage basin. Nitrogen (N) loadings were compiled using FLUX model and flow x concentration calculations for four annual periods spanning a range of inflow volumes. For each annual period, N budgets were developed, supported by water and total dissolved solids dudgets. Budget compilations include materials transported in tidal exchange with the Gulf of Mexico and with neighboring bays. Wastewater discharge contributes twice as much N to the bay than inflows from the Nueces River. Net flows and tidal entrainment of materials from neighboring bays contribute 24–32% of total loadings except during flood flows of the Nueces River. Atmospheric deposition to the estuary surface provides 8% of N loading. Despite low tidal amplitude and a restricted Gulf pass tidal entrainment losses are the main vehicle of export, except during flood flows, when net flows to the Gulf become important. The system exports much more of its total N load than would be expected from its water residence time, possibly facilitated by ship channel longitudinal transport. Denitrification accounts for 30–40% of all N lost. Uncertainties in components of the budget are estimated and included in compilations of confidence bounds for N budget components.

Assessment of changes to saltwater/freshwater habitat from reductions in flow to the Richmond River estuary, Australia

The Australian climate is highly variable and many Australian estuaries lack a seasonal pattern of freshwater flow. During periods of low freshwater inflow, saline waters enter from the ocean through the estuary mouth. These saline waters enter as density currents or as a result of tidal mixing. During periods of high freshwater inflow from the estuary catchment, salt water is flushed towards the estuary mouth. As a consequence, the saline structure of Australian estuaries can be highly variable, depending on the antecedent rainfall. The Richmond River in northern New South Wales in such an estuary. The biota inhabiting estuaries have varying levels of freshwater and saltwater tolerance and reducing the freshwater flow into and along an estuary will favour saltwater species. However, if extractions of freshwater from an estuary are sufficiently high, freshwater habitat could be eliminated entirely for short periods (-one month) but with consequent, and perhaps long-standing, damage to the environment. This contribution describes a new approach to quantify the impact of changes to freshwater flows to the Richmond River estuary. This approach includes a review of hydrological data gathered over the past century and includes a detailed assessment of: changes to the highly variable freshwater inflows and freshwater extraction below the tidal limit; consequent changes to the highly variable saline structure; and the risk to aquatic biota. The crucial factors of magnitude, frequency and duration of short-term intrusions of saline water into freshwater habitat and their impact are quantified by the methods developed.

Estuarine Nutrient Fluxes to the Humber Coastal Zone, UK, during June 1995

Measurements are presented of salinity, temperature and dissolved inorganic nutrient concentrations from an intensive survey of the near-mouth region of the Humber Estuary and coastal zone during a tidal cycle on 6 June 1995. The tidal movement of water in this area is illustrated with model results and used to interpret the observations. Variable–salinity plots showed that while estuarine-derived nitrate and silicate mixed conservatively with seawater, nitrite and phosphate showed evidence of sources within the mouth region of the estuary. A temperature–salinity scatter plot showed elevated temperatures within the shallow, estuarine waters due to solar heating. Despite the relatively small range of salinities encountered, from 34.2 to 29.6 progressing from the coastal zone into the estuary mouth, the suspended particulate matter concentration increased from 2 to 80 mg l −1 and the temperature from 10°C to 14°C. Nitrate concentration increased from 1.4 to 106 μM; nitrite, 0.1–0.4 μM; phosphate, 0.3–1.7 μM and silicate, 0.3–11.3 μM. The residence time of the Humber was approximately 60 days during summer 1995. Using freshwater inflows averaged over the residence time gave estimates of the seaward transport rates for nitrate–nitrogen, phosphate–phosphorus and silicate–silicon of 9.9 × 10 3, 73 and 1.1 × 10 3 k mol d −1. However, significantly greater nutrient fluxes from the Humber system are likely to occur during winter and spring, high freshwater inflow periods.

Seasonality of the Turbidity Maximum in the Humber–Ouse Estuary, UK

A 3-year campaign of field measurements in the Humber–Ouse Estuary was undertaken as part of the UK's Land Ocean Interaction Study. The measurements identified a persistent, high concentration turbidity maximum (TM) in the upper estuary that was generally associated with the freshwater–saltwater interface (FSI) region. Seasonal variability in the locations of the FSI and TM was pronounced and consistent from year to year. The TM was located more than 90 km down-estuary from the Ouse's tidal limit following freshwater spates during February 1995, whereas it was located less than 30 km down-estuary following the drought of summer 1995. Taken over the whole record, the mean positions of the FSI and TM were 47 and 52 km from the tidal limit, respectively, and their standard deviations were 13 and 20 km, respectively. There was a lag between the movements of the FSI and the TM. Maximum and minimum locations of the TM, relative to the tidal limit, occurred about one month after those for the FSI. During winter months the TM was located further down-estuary than the FSI, and was relatively weak, whereas during summer and early autumn the reverse was true and the TM was much stronger and located much closer to the tidal limit. Statistical relationships are derived that describe the FSI and TM in terms of freshwater inflows, tidal range and location. These results indicate that tidal `pumping' effects are important to the formation and migration of the TM, particularly during low inflow conditions, and that sediment `trapping' due to gravitational circulation may also play a significant role, especially during high freshwater inflow conditions.

Seasonal and inter-annual plankton variability in the Gulf of Trieste (northern Adriatic)

Seasonal and inter-annual variability of environmental characteristics and of plankton were analysed based on monthly surveys of the physical structure of the water column, nutrients, phytoplankton, and zooplankton biomass and abundance in the Gulf of Trieste (1989-1995). Seasonal plankton dynamics were related to Soca River run-oV, the main freshwater source, and peaks of autotrophic biomass were associated with extended periods of high freshwater inflow. Our results indicate that the freshwater discharge during spring was more important for annual phytobiomass than total yearly input. In 1993, which was characterized by a relatively high total annual freshwater input but by a dry spring, the lowest average chlorophyll biomass (0.85 Ig l 1 ) and cumulative monthly mesozooplanktonic biomass (123 mg AFDW m 3 ) were observed over the entire period. Annual peaks of phytoplankton biomass were mainly due to increases in diatom abundance, while small-sized cells (microflagellates, coccolithophores) dominated during periods of low Chl a concentrations. Consumer community patterns followed autotrophic biomass evolution with high abundance of herbivores and mixed feeders in spring, and fine-filter feeders and planktonic protists during summer. A large inter-annual variability emphasizes the importance of long-term monitoring in areas like the Gulf of Trieste for distinguishing anthropogenic trends from natural variations of plankton. ? 1998 International Council for the Exploration of the Sea

Differences in Radiocarbon Age between Shell and Charcoal from a Holocene Shellmound in Northern California

The West Berkeley shellmound, the oldest well-dated archaeological site in the San Francisco Bay region, contains shell and charcoal ranging in age from ca. 1200 to 5700 cal yr B.P. Radiocarbon ages of marine shell and charcoal collected from fifteen stratigraphic levels in the West Berkeley shellmound suggest changes in the14C content of San Francisco Bay surface waters relative to the atmosphere (the oceanic reservoir age) over the past 5000 yr. The reservoir age of San Francisco Bay waters fluctuated between 870 and −17014C yr over the past 5000 yr, with the lowest values occurring 2900 to 3800 cal yr B.P. and the highest values between 1200 and 2000 cal yr B.P. Changes in the radiocarbon reservoir age may be due to changes in the strength of seasonal wind-driven upwelling off coastal California, where upwelling brings14C-depleted waters to the surface. The period of lowest ΔRvalues (at 3500 to 3900 cal yr B.P.) is coincident with relatively low salinity in San Francisco Bay (indicating high freshwater inflow) and wet climate in California based on lake level records. The period of high ΔRvalues (1200–2000 cal yr B.P.) is coincident with one of the driest periods in California during the late Holocene. These data suggest a link between coastal upwelling and precipitation over central California. The age of the top of West Berkeley mound and several other mounds in the San Francisco Bay region (1100 to 1300 cal yr B.P.) coincides with a prolonged dry period in California and low river inflow to San Francisco Bay. Perhaps the sites were abandoned because of the drought.

Carbon Cycling in a Shallow Turbid Estuary of Southeast Texas: The Use of Plant Pigment Biomarkers and Water Quality Parameters

Particulate organic carbon (POC), dissolved organic carbon (DOC), and plant pigments (chlorophylls and carotenoids) were measured approximately bimonthly from March 1992 to October 1993 in the Sabine-Neches estuary (Sabine Lake region), located on the Texas-Louisiana border. High freshwater inflow into this shallow turbid estuary results in the shortest hydraulic residence time (ca. 7 d) of all Texas estuaries (Baskaran et al. in press). Annual averages of chlorophyll-a (3.0 μg l−1) and particulate organic carbon (1.1 mg l−1) in the water column were extremely low in comparison to other shallow estuaries. The highest chlorophyll-a concentrations were observed in October 1993, in the mid and lower regions of the estuary, during the lowest river discharge. Zeaxanthin and fucoxanthin concentrations suggested that much of the chlorophyll-a during this low flow period was represented by cyanobacteria and diatoms that entered from the Gulf of Mexico. The range of DOC concentrations was generally high (4.4–20.9 mg l−1) and were significantly correlated with POC, but not with chlorophyll-a concentrations. When total suspended particulate (TSP) concentrations were below 20 to 30 mg l−1, there were significant increases in %POC and %PON of the TSP. The unusually high POC: chlorophyll-a ratios (highest value of 1423) suggested that much of the POC contained low concentrations of chlorophyll-a that had degraded during transport from wetlands in the Sabine and Neches rivers. Based on these data, this estuary can be characterized as a predominantly heterotrophic system, with low light penetrance, short particle-residence times, high DOC, and low inputs from autochthonous carbon sources.

Sources and composition of particulate organic carbon in the Baltic Sea: the use of plant pigments and lignin-phenols as biomarkers

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 156:25-31 (1997) - doi:10.3354/meps156025 Sources and composition of particulate organic carbon in the Baltic Sea: the use of plant pigments and lignin-phenols as biomarkers Thomas S. Bianchi1,*, Carl Rolff2, Corey D. Lambert1 1Department of Ecology, Evolution, and Organismal Biology, Tulane University, New Orleans, Louisiana 70118-5698, USA 2Department of Zoology, Stockholm University, S-10691 Stockholm, Sweden *E-mail: tbianch@mailhost.tcs.tulane.edu Water samples were collected in the Baltic Sea, along a north to south transect that extended from Bothnian Bay to the Baltic proper, in July 1994--just after the period of peak freshwater discharge. Plant pigments and lignin-phenols were used as biomarkers to determine the dominant sources of phytoplankton and terrestrial inputs along the transect. A distinct gradient in chlorophyll a concentrations that increased from north (2.1 ug l-1) to south (18.9 ug l-1) indicated that the dominant blooms occurred from the southern Bothnian Sea to the Baltic proper. High fucoxanthin (3.9 ug l-1) and peridinin (1.9 ug l-1) concentrations in the Bothnian Bay and Sea reflected late stages of diatom and dinoflagellate blooms, respectively, that typically occur in summer months in the northern Baltic (Andersson et al. 1996). High zeaxanthin (8 ug l-1) concentrations in the southern Bothnian Sea and Baltic proper indicated dominance of cyanobacterial blooms in these regions. Decreasing concentrations of total lignin-phenols (Lambda) from north (0.22) to south (0.02) indicated that terrestrial inputs of organic carbon were associated with high freshwater inflow into the northern Baltic. Further examination of lignin-phenol ratios indicated that the dominant source of terrestrial material into the Baltic was from woody gymnosperms. Biomarkers · Baltic Sea · Carbon cycling · Plant pigments · Lignin-phenols Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 156. Publication date: September 25, 1997 Print ISSN:0171-8630; Online ISSN:1616-1599 Copyright © 1997 Inter-Research.

The Influence of Freshwater Inflow on the Nature, Amount and Distribution of Seston in Estuaries of the Eastern Cape, South Africa

The influence of freshwater inflow in determining the particulate food resources for suspension-feeders in eastern Cape estuaries was investigated. The seasonal and spatial distribution of total particulate material (TPM), total particulate organic material (TPOM), chlorophylla, particulate protein and carbohydrate were compared in two hydrodynamically contrasting systems, the Kariega and the Great Fish estuaries, which differ markedly in respect of their freshwater inflow. As a result of high, sustained freshwater inflow, seston levels in the Great Fish estuary were of an order of magnitude higher than in the Kariega estuary which received minimal inflow. Chlorophyllameasurements showed that the Great Fish estuary is predominantly eutrophic/mesotrophic whereas the Kariega estuary is classified as oligotrophic. Correlation analyses indicated that the organic fraction of the seston was dominated by detritus in the Kariega estuary and by phytoplankton in the Great Fish estuary. Although the quality of organic seston was higher in the Great Fish estuary, the ‘masking’ effect of suspended inorganic particles associated with freshwater inflow was much greater. In both estuaries, the majority of seston occurred in the nanoplanktonic size range. The seasonal and spatial patterns of seston distribution differed markedly under conditions of contrasting freshwater inflow. Suspended particulates were more uniformly distributed along the length of the Kariega estuary and were seasonally elevated during the warmer months. By contrast, a pronounced spatial gradient was evident in the Great Fish estuary with highest values recorded towards the upper reaches. The nutrient status of the Great Fish estuary was considerably higher than that of the Kariega estuary and determined principally by freshwater inflow. High phytoplankton standing stocks generally developed episodically following high freshwater inflow. This was partly the result of an accumulation of phytoplankton of riverine origin by hydrodynamic trapping, however, species tolerant of brackish conditions responded to the enriched conditions by remaining viable and active for considerable periods within the estuary.

Flushing Times for the Providence River Based on Tracer Experiments

The flushing time of the Providence River was estimated using three different data sets and three different methodologies. Dye concentrations were measured following instantaneous dye releases during wet weather experiments performed by the Narragansett Bay Project between October 1988 and June 1989. These data were analyzed to obtain flushing time estimates. Salinity measurements collected during the Sinbadd (Sampling In Narragansett Bay All During the Day) cruises, Spray (Sampling the Providence River All Year) cruises and wet weather experiments were used with the fraction of fresh water method and box model to calculate flushing time. The Sinbadd cruises performed 4 seasonal surveys at 22 stations in Narragansett Bay during 1986 to obtain a view of the whole Narragansett Bay with respect to the concentrations of nutrients and trace metals. The Spray cruises collected data in the Providence River at 10 stations to determine the relationship of nutrients and trace metals concentrations in the Seekonk and Providence rivers as a function of point source inputs. Based on the flushing time estimates, an exponential relationship between freshwater inflow and flushing time was developed (correlation coefficient of 0.826). The flushing time ranged from 0.8 d at high (90 m3 m−1) freshwater inflows to 4.4 d at low (20 m3 s−1) freshwater inflows. The average flushing time of the Providence River was estimated as 2.5 d for the mean freshwater inflow of 42.3 m3 s−1.

Middle Weichselian to Holocene palaeoecology in the eastern Kattegat, Scandinavia: foraminifera, ostracods and 14C measurements

Examination of a 10 m piston core from the eastern Kattegat revealed marine sediments spanning a period from the late Middle Weichselian to the Early Holocene. The oldest marine unit in the core is 14C‐dated to about 30,000–36,000 years BP. These sediments represent the Middle Weichselian Sandnes/Denekamp‐Hengelo Interstadial (upper part of stable isotope stage 3) and can be correlated to marine deposits from several localities in the Kattegat region by means of foraminifera. The Late Weichselian deposits comprise sediments from the Oldest Dryas Stadial and the Allerød Interstadial. The intervening periods are not represented in the sequence (hiatuses). Sediments from the latest part of the Early Holocene Preboreal period succeeding the Allerod sequence indicate a considerable hiatus spanning 2000–3000 years around the Weichselian/Holocene boundary. The late Preboreal faunas document a high freshwater inflow during this period, and stable conditions seem not to have been reached in the area until a few hundred years later, in the Boreal period. Comparison with boxcore material from the same site documents a reduction of the energy level of the bottom currents some time between c. 8000 and 800 years BP.