Turbid Estuary Research Articles

Bottom fine sediment boundary layer and transport processes at the mouth of the Changjiang Estuary, China

Summary Improved understanding of fine sediment transport processes within turbid estuaries has been of interest to both the coastal engineer and coastal oceanographer. The continuous measurement of fine suspended sediment concentration profiles is central to the study of transport processes. With this in mind, we utilise acoustic backscatter measurements to infer continuous vertical profiles of suspended sediment concentration. The acoustic profiling method has the advantage that it senses suspended sediment concentrations remotely and non-intrusively with a high degree of temporal and spatial resolution. Observational studies were undertaken to obtain more insight into the importance of bottom fine sediment boundary layer and transport processes to the seaward part of the North Passage in the Changjiang Estuary, China. Field measurements were made in October 1994 during spring, moderate and neap tides, respectively. Time series data of tidal elevations, current speed, and directions were measured. Vertical profiling of fine suspension concentration was made hourly by an acoustic suspended sediment monitor. Three dominant physical processes were identified: (1) the near-bed periodic resuspension by the tidal currents via tidal pumping; (2) the asymmetric stratifications due to fine suspension; and (3) the exchange of sediment between the bed and water column. The study also has its regional significance in estuarine morphodynamics, regulation of navigational channel, and water quality at the North Passage in the Changjiang Estuary.

Colloidal Metals in the Tamar Estuary and their Influence on Metal Fractionation by Membrane Filtration

Environmental Context. Trace metals play an essential role in the growth and function of aquatic organisms; however, enhanced metal concentrations can have detrimental effects on ecosystems. The distribution of metals between filterable and filter-retained phases is key to their bioavailability and biogeochemical cycling. Studies on rivers have shown that separating dissolved metals from particle-associated metals may introduce significant artefacts in the resulting filtrate concentrations. Comparable studies on turbid estuarine waters are necessary to improve the design of water sampling programmes. Abstract. Total filterable and colloidal metals were measured in the Tamar Estuary. The colloidal fraction (Mc) was highly variable for each metal, both spatially and temporally. In April 2001, Alc and Coc were higher in the river than the estuary, Cdc, Crc and Pbc were lower, and Mnc and Uc were similar. In September 2001, Cdc was higher in the river than the estuary. Colloidal Al and Mn were positively correlated with concentrations of suspended particles, whereas the colloid contents of the other metals were primarily determined by additional factors. The effect of the colloidal metal content on resultant metal filtrate concentrations, as a function of sample volume filtered, was examined. The amount of Al, Cd, Cu, Pb, and U in the filtrate decreased significantly in at least one case, whereas Mn initially increased in some cases. There was no change for Co, Cr, and Zn. The implications of these results for the study of trace metals in moderately turbid estuaries are discussed.

Phytoplankton production modelling in three marine ecosystems—static versus dynamic approach

Phytoplankton productivity is usually determined from water samples incubated at a number of irradiance levels during several hours. The resultant productivity-irradiance ( P– E) curves are then used to estimate local and/or global phytoplankton production. However, there is growing evidence that these curves, referred as static, underestimate phytoplankton photosynthesis to a great deal, by assuming a stable response to light over the incubation period. One of the drawbacks of static P– E curves is the overestimation of photoinhibition. In this work, three one-dimensional vertically resolved models were developed as simply as possible, to investigate differences between static and dynamic phytoplankton productivity in three marine ecosystems: a turbid estuary, a coastal area and an open ocean ecosystem. The results show that, when photoinhibition development time is considered (dynamic model), the primary production estimates are always higher than when calculated with the static model. The quantitative importance of these differences varies with the type of ecosystem and it appears to be more important in coastal areas and estuaries (from 21 to 72%) than in oceanic waters (10%). Thus, these results suggest that primary production estimates, obtained under the assumption of a static behaviour response to light, may underestimate the real values of global phytoplankton primary production. Calculations suggest that the quantitative importance of this underestimation may be larger than the global missing carbon sink.

Changes in phytoplankton biomass and primary production between 1991 and 2001 in the Westerschelde estuary (Belgium/The Netherlands)

The Westerschelde estuary is a very polluted and turbid estuary, but the last decade the waterquality improved. Dredging activity also increased in 1997 to allow bigger ships to enter the port of Antwerpen. This could potentially decrease the light conditions for the phytoplankton. Because of all these recent changes in the estuary we studied primary productivity in 2001 and compared it to values in 1991. The results show that due to a decrease in discharge in particulate and dissolved organic carbon the oxygen concentrations in general have increased in the upstream region, although in spring and summer low oxygen concentrations (10–30% saturation) can still be found. Phosphate and ammonia concentrations have decreased and the zone of nitrification which was very large in 1991 has become very small and is now located in the uppermost upstream region of the estuary. Si-concentrations have remained the same. All nutrient concentrations are still high enough not to limit phytoplankton growth. Turbidity remained unaltered as a result of the dredging works, and as a result phytoplankton biomass in most of the estuary did not show a decrease, although there were signs that in the upstream region phytoplankton biomass decreased, possible caused by increased grazing pressure. The relationship between phytoplankton biomass and primary productivity did not change, and from the data it can be concluded that the dredging activity will not influence the gross and net primary productivity of the phytoplankton.

Hydrophobicity and reactivity of trace metals in the low‐salinity zone of a turbid estuary

We chemically fractionated water samples from the low‐salinity zone of a turbid estuary (Tamar, UK) using C18 columns to examine the controls on the complexation, hydrophobicity, and reactivity of dissolved trace metals (Co, Cu, Mn, and Pb). The hydrophobic (C18‐retained) fraction of metal was related to the solubility of metal in the amphiphilic solvent, n‐octanol, and in acid‐base titrations and for all metals this fraction exhibited a peak centered around pH 7–8 in both freshwater and brackish water. In freshwater, hydrophobicity decreased in the order Pb > Cu > Mn > Co, and in brackish water, hydrophobicity was either reduced (Cu and Pb) or enhanced (Co and Mn) compared to freshwater, but in all cases peaks were more distinct. Salinity distributions of dissolved trace metals in the estuary indicated significant removal of Co, Cu, and Mn, and a source of Pb that was coincident with the onset of the turbidity maximum, and all distributions could be accounted for empirically by end‐member water mixing and sediment resuspension. Salinity distributions of the hydrophobic fraction of metal were not consistent with any variation in water composition (including pH), but revealed that this fraction was preferentially removed from (Co, Cu, and Mn) or added to (Pb) the aqueous phase in the vicinity of the turbidity maximum. Removal implies that hydrophobic species are more reactive than hydrophilic species, and that either re‐equilibration between these fractions is not attained within the hydrodynamic timescales of the upper estuary, or new equilibria are established by the buffering effects of additional anions and ligands in the water column. Addition of hydrophobic species of Pb coincided with minimum total and hydrophobic concentrations of Co, Cu, and Mn, and could, therefore, be explained in terms of reduced competition for nonspecific hydrophobic ligands from these and other (e.g., Al) metals in this region of the estuary.

High resolution mapping and classification of oyster habitats in nearshore Louisiana using sidescan sonar

Sidescan sonar holds great promise as a tool to quantitatively depict the distribution and extent of benthic habitats in Louisiana’s turbid estuaries. In this study, we describe an effective protocol for acoustic sampling in this environment. We also compared three methods of classification in detail: mean-based thresholding, supervised, and unsupervised techniques to classify sidescan imagery into categories of mud and shell. Classification results were compared to ground truth results using quadrat and dredge sampling. Supervised classification gave the best overall result (kappa=75%) when compared to quadrat results. Classification accuracy was less robust when compared to all dredge samples (kappa=21–56%), but increased greatly (90–100%) when only dredge samples taken from acoustically homogeneous areas were considered. Sidescan sonar when combined with ground truth sampling at an appropriate scale can be effectively used to establish an accurate substrate base map for both research applications and shellfish management. The sidescan imagery presented here also provides, for the first time, a detailed presentation of oyster habitat patchiness and scale in a productive oyster growing area.

Biomass and composition of the phytoplankton in the Río de la Plata: large-scale distribution and relationship with environmental variables during a spring cruise

The distributions of phytoplankton taxa and biomass were recorded to assess their association to environmental variables in the Río de la Plata, a shallow and highly turbid estuary. Forty-seven CTD stations covering the whole estuary were sampled from 5 to 16 November 2001. At 31 stations, dissolved oxygen concentration, pH, and light intensity at 50 cm depth intervals were recorded in situ; also, samples were taken for measurement of dissolved nutrient levels (nitrate, ammonium, phosphate, and silicate), suspended particulate matter and particulate organic matter loads, chlorophyll ( a, b, and c) concentration, and phytoplankton identification. Stations ordination (multi-dimensional scaling, MDS, analysis) on environmental data suggested two main groups (upper–middle and lower estuary) but stressed the gradual change of conditions along the ecosystem. MDS on pigment data suggested a tendency for higher biomass levels in the lower estuary; MDS based on species indicated two main groups corresponding to lower and upper–middle estuarine stations. Spearman rank correlations of environmental and pigment similarity matrices suggested that salinity, the ratio of mixed to photic depth, and nitrates were the variables best explaining pigments distribution; in turn, the variables best explaining species distribution were salinity and seston. Results suggest an overriding importance of salinity-light gradients in modulating biomass levels and species distribution in the Río de la Plata. This result is consistent with processes known to modulate phytoplankton distribution and production in other highly turbid estuaries.

A massive dissolved inorganic carbon release at spring tide in a highly turbid estuary

In September 2003, the highly turbid Loire estuary (France) showed drastic oxygen depletions (down to 11% of saturation), high pCO2 (up to 3740 μatm) and high CO2 fluxes (280 ± 100 mmol.m−2.d−1). A rapid rise in Dissolved Inorganic Carbon (DIC) was observed when the tidal amplitude increased from 3.8 m to 5.8 m. In two days, average concentrations in the 0.1–25 salinity range increased by 106 ± 17 μmol.kg−1 for DIC, by 80 ± 14 μeq.kg−1 for Total Alkalinity (TA) and by 684 ± 142 μatm for pCO2. In parallel, oxygen decreased by 65 ± 12 μmol.kg−1. These changes in concentrations were attributed in majority to a massive fluid mud resuspension in the estuarine turbidity maximum. At spring tide, this DIC input was 30% higher than the river input. When averaged over the neap‐spring period, resuspension contributed to only 10% of the atmospheric CO2 flux from the estuary, but to 60% to the net TA production in the estuary.

Photoresponses of the marine protist Ulkenia sp. zoospores to ambient, artificial and bioluminescent light

Ulkenia sp. zoospores are attracted to 492 nm wavelength light produced by the marine bacterium Vibrio fischeri. Zoospores are positively photoresponsive to wavelengths of 440, 460 and 480 nm and contain a pigment that absorbs blue light. The average velocity of the zoospores is 0.47 m h−1. Stimulatory intensities of these wavelengths ranged from 0.5 to 3.5 μEm−2 s−1 in both laboratory and field studies. The response of this protist to bioluminescence produced by Vibrio fischeri may direct zoospores to a nutrient rich environment colonized by these bacteria. In addition, the greatest responses were found at intensities associated with the light regime found near the bottom of naturally turbid estuaries or at greater depths of nonturbid, offshore waters. Positive phototaxis was not seen in zones of high light intensity either in field or laboratory studies, and there is some indication that zoospores may swim away from high light intensities.

Photoresponses of the Marine Protist Ulkenia sp. Zoospores to Ambient, Artificial and Bioluminescent Light

Ulkenia sp. zoospores are attracted to 492 nm wavelength light produced by the marine bacterium Vibrio fischeri. Zoospores are positively photoresponsive to wavelengths of 440, 460 and 480 nm and contain a pigment that absorbs blue light. The average velocity of the zoospores is 0.47 m h−1. Stimulatory intensities of these wavelengths ranged from 0.5 to 3.5 μEm−2 s−1 in both laboratory and field studies. The response of this protist to bioluminescence produced by Vibrio fischeri may direct zoospores to a nutrient rich environment colonized by these bacteria. In addition, the greatest responses were found at intensities associated with the light regime found near the bottom of naturally turbid estuaries or at greater depths of nonturbid, offshore waters. Positive phototaxis was not seen in zones of high light intensity either in field or laboratory studies, and there is some indication that zoospores may swim away from high light intensities.

Metal mobilization in the Gironde Estuary (France): the role of the soft mud layer in the maximum turbidity zone

Vertical profiles of heavy metals (Cd, Cu, Cr, Fe, Mn, Ni and Pb) in the particulate and dissolved phases and redox sensitive parameters (dissolved oxygen, nitrate, nitrite and ammonium) were analyzed for the first time in the continuum Maximum Turbidity Zone (MTZ)–Fluid Mud (FM; 50 g l −1<suspended particulate matter (SPM)<500 g l −1)-consolidated sediment of a macrotidal, highly turbid estuary: the Gironde. The results show that the fluid mud is a layer of intense metal mobilization due to redox induced dissolution, releasing trace metals into the water column. This newly identified phenomenon creates a transient situation characterized by the onset of diagenetic sequences in the FM, i.e. in the lower part of the water column. These sequences overlie permanent diagenetic sequences in the consolidated sediment, similar to those typically observed in marine and estuarine sediments. The discontinuity of dissolved Cd, Ni and Pb concentrations at the sediment surface indicates that Mn reduction is faster in the FM than in the upper sediment, isolated from the oxic water column by the suboxic FM. Two separate diagenetic signals are preserved, as the installation of the diagenetic sequence in the FM is faster than the molecular diffusion of dissolved compounds through the FM–sediment interface. The diagenetic signal of trace metals (e.g. dissolved Cr maximum) in the upper sediment layer near the FM–sediment interface is interpreted as a transient record of past hydrologic situations, during which the absence of the FM layer permitted the installation of an oxic/suboxic front in the upper sediment. The resuspension of the FM during the spring tide probably results in a new distribution of these elements in the estuary, where they may be stabilized in the dissolved phase (e.g. by chloride complexes or dissolved organic compounds) or be adsorbed onto reactive particles (e.g. freshly precipitated Mn oxyhydroxides).

Phytoplankton community growth-rate response to nutrient pulses in a shallow turbid estuary, Galveston Bay, Texas

Phytoplankton growth is a physiological process often limited by temperature, nutrients or light, while biomass accumulation is a function of growth rates, grazing and deposition. Although primary productivity measurements are usually used to assess responses to limiting factors, the rates are proportional to biomass and inversely related to grazing pressure during experimental incubations. Alternatively, carbon-specific growth-rate determinations provide insights into physiological responses without the confounding acts of biomass and grazing. The objective of this study was to quantify the growth-rate responses of phytoplankton to enhanced nutrient availability (nitrate and phosphate) over a range of in situ irradiances. Growth rates were determined based on chlorophyll a-specific 14 C-uptake rates by phytoplankton. Phytoplankton demonstrated high (24 h) growth rates when exposed to increased concentrations of limiting nutrients, independent of the surface irradiances (12-41%). Growth-rate responses were also compared zenith the biomass (chlorophyll a) responses and community composition. Observed and estimated phytoplankton biomass changes during the incubations differed, emphasizing the structural role of graders on the phytoplankton community. The phytoplankton community in Galveston Bay has the potential to instantaneously respond to nutrient pulses, facilitating diatom biomass accumulations in spring and summer and small, flagellated species and cyanobacteria during periods of low nutrient inputs. Thus, Galveston Bay phytoplankton biomass and community composition reflect a dynamic balance between the frequency of nutrient pulsing and grazing intensity.

Interpreting the colour of an estuary

This paper explores the possibility of using water colour to quantify the concentration of coloured dissolved organic matter (CDOM), and through it, dissolved organic carbon (DOC) and salinity in a turbid estuary in which suspended sediments also influence water colour. The motivation of the work is that the method could be applied to water colour measurements made remotely from an aircraft (or, in larger estuaries, a satellite) enabling near-synoptic mapping of surface salinity and DOC distributions. The paper describes observations at 29 stations distributed along the salinity gradient of the Conwy estuary in North Wales. At each station, surface water samples were collected and analysed for salinity, concentrations of DOC, chlorophyll and suspended particles and absorption spectra of CDOM, or yellow substance. Profiles were made of both upwelling and downwelling irradiance in four narrow band channels, and these were used to calculate irradiance reflection and attenuation coefficients. Results show that spectrally averaged light absorption in the estuary is caused principally and equally by mineral suspended solids and yellow substance, with water and chlorophyll in third and fourth place. The CDOM is strongly correlated ( R 2=0.99) in a negative sense with salinity, and more weakly correlated with DOC. There is a linear relationship between CDOM and the ratio of reflection coefficients in the red (670 nm) and blue-green (490 nm) parts of the spectrum, which could be applied to remote sensing; the slope and intercept of the relationship are however different to those found in less turbid water bodies. It is shown that the change in slope and intercept are consistent with the presence, in the Conwy estuary, of suspended particles which influence the water colour. A method is described and tested for inverting water colour measurements in a turbid estuary to give estimates of CDOM in the presence of suspended particles. The solution, which has not been adjusted to fit the data, produces profiles of CDOM, DOC and salinity, which behave reasonably but which currently have a limited accuracy. RMS differences between measured and optically derived parameters for the entire data set are 0.27 m −1 (CDOM), 4 PSU (salinity) and 67 μM (DOC) although better accuracy is obtained on individual surveys. The fact that there is little bias between predicted and observed parameters indicates that much of the scatter is caused by random measurement error and that the approach is fundamentally sound.

Mercury transformations and exchanges in a high turbidity estuary:: The role of organic matter and amorphous oxyhydroxides

The speciation and partition of mercury in a macrotidal estuary (Seine estuary, France) was studied in order to explore the role of the high turbidity zone (HTZ) in mercury transfer to the adjacent coastal waters. Water and particles were analyzed to determine the concentrations of various mercury species, including monomethylmercury and the inorganic fraction. The exchangeable particulate mercury, which varies with salinity, and the mercury fraction associated with the amorphous oxyhydroxides were evaluated. The distribution of dissolved mercury species during early mixing suggests non-conservative behavior of organically bound mercury at the head of the estuary. Mercury in the particles covaried positively with suspended particulate matter concentrations up to a threshold, which constitutes the typical mercury load of particles and deposited sediments of the HTZ. This distribution pattern is well explained by a dilution model: a slowly settling, low metal population of particle, characterized by relatively invariant turbidity, becomes admixed with a variable amount of higher metal content particles derived from the resuspension in the HTZ. In addition, in the HTZ, which acts as a degradation reactor for particulate organic matter, particulate mercury concentrations increase with increasing C:N ratios and amorphous oxyhydroxides particles. Mercury reaches the estuarine HTZ mainly associated with the riverine and marine particles, including organic matter and oxyhydroxides, which are temporarily trapped in the HTZ and mixed with autochthonous HTZ particles. The largest particles periodically settle and undergo diagenetic reactions and resuspensions, which lead to their mercury enrichment. Depending upon hydrodynamic conditions, mercury escapes seaward as fine particulate within the plume, partially associated with the oxyhydroxides. A surface complexation model reproduces most of the partitioning observed. In the dissolved phase the model simulation suggests that a very strong ligand must be present to explain the field observations.

Resuspension, reactivity and recycling of trace metals in the Mersey Estuary, UK

Distributions of dissolved and non-detrital (available to 1 M HCl) particulate Cd, Co, Cu, Ni, Pb and Zn have been determined in samples collected from the Mersey Estuary, UK, during four high-resolution axial transects. With the exception of Cu, dissolved metal concentrations displayed positive deviations from conservative behaviour. Cobalt and Ni appeared to have a common source, while dissolved Pb peaks coincided with maximum turbidities in the upper estuary. Concentrations of Cd, Co, Ni and Pb in the <63-μm grain size fraction of bed sediment were greater than those in suspended particulate matter (SPM). Magnitudes of dissolved metal peaks reflected the extent of metal enrichment in fine bed sediment compared with SPM, suggesting that addition of dissolved metal was effected primarily by desorption from resuspendable bed particles. An empirical sorption model, based on the mass balance of metal resuspended from the bed, was able to reproduce the axial distributions of dissolved metals that exhibited the most pronounced peaks (namely, Co and Pb) with reasonable success. More generally, model results indicated that bed sediment need only be moderately enriched in trace metal compared with SPM to cause measurable addition of dissolved metal to the overlying water column. Addition of dissolved metals on estuarine mixing is a common observation in macrotidal environments of western Europe, and it is proposed that resuspension of metal-enriched, fine bed sediment may be a significant agency for metal remobilisation in contaminated, turbid estuaries.

Non‐conservative mixing behavior of colored dissolved organic matter in a humic‐rich, turbid estuary

The estuarine mixing behavior of colored dissolved organic matter (CDOM) absorbance was investigated in combined field and laboratory studies. From February to October 1998, surface water samples were collected along 9 transects in the Tyne estuary, Northeast England, from the tidal limit into the coastal North Sea. In 8 of these transects, mixing plots of absorbance vs. salinity indicated substantial removal of CDOM absorbance (average: 32%) in the upper estuary. Results from laboratory studies under simulated estuarine conditions suggest that an average of 21% (range: 9–39%) of riverine CDOM may be removed by adsorption onto suspended sediment, while CDOM flocculation accounted for an average removal of only 6% (range: 0–18%). We propose that adsorptive removal exerts a major control on CDOM in estuaries with elevated turbidity levels.

Is the copepod egg production in a highly turbid estuary (the Gironde, France) a function of the biochemical composition of seston?

The influence of the biochemical composition of particles originating from surface waters of the Gironde estuary on egg production rates of Eurytemora affinis zooplanktonic population was studied. In the high turbidity zone, suspended particulate matter had a low nutritional quality because the easily available organic fraction represented less than 15% of the overall particulate organic matter. In waters located seaward of the high turbidity zone, a slight increase in nutritional quality was observed. As a result, the sum of easily extractable organic macromolecules represented 15 to 33% of the overall particulate organic matter. The present study suggests that the low egg-production rate of Eurytemora affinis, occurring in the high turbidity zone, results from combined effects of temperature and bad feeding conditions in the area. Low copepod production can be explained by little phytoplankton growth due to light limitation and, therefore, restricted food availability, as well as difficulties in food selection, non-living particle may being dominant.

Regulation of bacterial growth efficiency in a large turbid estuary

AME Aquatic Microbial Ecology Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsSpecials AME 20:31-38 (1999) - doi:10.3354/ame020031 Regulation of bacterial growth efficiency in a large turbid estuary Fabio Roland1,2, Jonathan J. Cole1,* 1Institute of Ecosystem Studies, Box AB, Millbrook, New York 12545, USA 2Institute of Biological Sciences - Biology Department/UFJF, Juiz de Fora, Minas Gerais, 36036-330, Brazil *Corresponding author. E-mail: colej@ecostudies.org ABSTRACT: Bacterial secondary production transforms organic C from the environment into new bacterial biomass. Bacterial respiration generates energy and converts assimilated organic C into CO2. Two decades of research have given us a good understanding of the magnitude and regulation of bacterial production in pelagic ecosystems, but much less is known about bacterial respiration. Bacterial growth efficiency [BGE = BP/(BP + BR)] relates measurements of bacterial production and respiration. Recent reviews demonstrate a large range in BGE among and within systems; the regulation of this variance is not well understood. We made direct measurements of both BP and BR over a full seasonal cycle in the Hudson River, New York, and in a series of manipulative experiments. BGE was well correlated with BP and ranged from 0.04 to 0.66, with a majority (69%) between 0.2 and 0.5. BR and BP were correlated (r = 0.65; p < 0.0001) but BR was less variable than BP. Thus, much of the variation in BGE could be explained by the variation in BP. The relationship (based on 24 h bioassays) between BP and BGE fit a rectilinear hyperbola [BGE = 0.10 + 0.68BP(5.21 + BP)] and explained 70% of the variation in BGE (p < 0.001). During the relatively long incubation (24 h) required to measure BR, conditions diverge from ambient. BP, BR and BGE all increase during this incubation period. We used the relationships between BGE and BP and BR (above) to calculate realistic ambient estimates of BGE from short-term measurements (<1 h) of BP. Based on this approach, modeled BGE for the Hudson averaged 0.16 ± 0.05 (range = 0.07 to 0.23), about 50% lower than the values based on 24 h bioassays. Using this relationship we estimate pelagic BR in the tidal, freshwater Hudson River to be between 176 and 229 g C m-2 yr-1. KEY WORDS: BGE · Bacterial metabolism · Production · Respiration · Estuary · River · Ecosystems Full text in pdf format PreviousNextExport citation RSS - Facebook - Tweet - linkedIn Cited by Published in AME Vol. 20, No. 1. Publication date: November 30, 1999 Print ISSN: 0948-3055; Online ISSN: 1616-1564 Copyright © 1999 Inter-Research.

Comments on "Carbon Cycling in a Shallow Turbid Estuary of Southeast Texas: The Use of Plant Pigment Biomarkers and Water Quality Parameters" by Bianchi, Baskaran, DeLord and Ravichandran, Estuaries 20:404-415

Comments on "Carbon Cycling in a Shallow Turbid Estuary of Southeast Texas: The Use of Plant Pigment Biomarkers and Water Quality Parameters" by Bianchi, Baskaran, DeLord and Ravichandran, Estuaries 20:404-415

Nutrient Uptake in a Highly Turbid Estuary (The Humber, United Kingdom) and Adjacent Coastal Waters

Surveys were conducted in April and June 1995 to quantify the uptake of dissolved nutrients in a highly turbid estuary (the Humber, United Kingdom) and to determine the factors controlling nutrient uptake rates. A combination of isotope labelling methods were used in conjunction with on-deck incubation techniques to estimate the uptake of dissolved nutrients (PO4 3−, NH4 +, NO3 −, and urea) in surface samples collected from coastal waters. Similarly, isotope labelling and laboratory incubgation techniques were employed to estimate dissolved nitrogen uptake (NH4 +, NO3 −, and urea) in surface samples collected from the estuary mouth. Nutrient uptake rates were at the low end of ranges for coastal and estuarine environments reported in the literature. Concentrations of chlorophyll and the availability of photosynthetically active radiation were identified as potentially important factors controlling the uptake rates of nutrients. Uptake rates of dissolved nitrogen in the Humber mouth appeared to be related to the location of smapling sites. Depletion rates of dissolved nutrients in situ were estimated on the basis of integrated water column nutrient uptake rates and indicated assimilation of up to 16% of nutrients in the entire water column. Estimated depletion rates did not indicate preferential loss of any of the nutrient species investigated.