Effects of recent increases in salinity and nutrient concentrations on the microbialite community of Lake Clifton (Western Australia): are the thrombolites at risk?

There has been a strong research focus on optical properties in temperate estuaries but very much less in tropical estuaries. These properties comprise light and beam attenuation dominated by suspended particulate matter, Chl a, and CDOM. Spatially and temporally distributed data on optical properties in a tropical wet and dry estuary are compared and discussed in relation to those of temperate estuaries. Sampling in the Nha Phu estuary, Vietnam, consisted of five stations on a transect from head to mouth that was sampled four times during dry conditions and three times during wet conditions between May 2006 and April 2008. Methods comprised CTD, optical measurements, and water sampling for suspended matter, Chl a, and CDOM. Results showed high light attenuation—K _d(PAR)—in wet conditions and low in dry. K _d(PAR) was highest at the estuary head and lower in the outer part. Spatial and temporal variations in K _d(PAR) were in general dominated by variations in suspended particulate matter concentrations in both wet and dry conditions. Chl a concentrations were low and showed no strong variations between wet and dry conditions. CDOM absorption coefficients were higher in wet conditions with high values at the head and lower in the central part of the estuary. The depth of the photic zone was reduced by up to 50% during wet conditions. A residence time in the estuary of 5–6 days was derived from the rate of change of K _d(PAR) after a period of heavy rain and discharge of freshwater into the estuary. This complied with a residence time of four and a half days derived from a basic physical relation. Optical properties were in general comparable to temperate estuaries in dry conditions although Chl a concentrations were lower in Nha Phu. A second distinctive point, as compared to temperate estuaries, was the episodic character with days of strong rainfall followed by longer periods of dry weather. All sampling, both wet and dry, was carried out in the dry season which implies a less definitive perception of wet and dry seasons.     

Predicting the light attenuation coefficient through Secchi disk depth and beam attenuation coefficient in a large, shallow, freshwater lake

The diffuse attenuation coefficient of photosynthetically active radiation (PAR) (400–700 nm) (K _d(PAR)) is one of the most important optical properties of water. Our purpose was to create K _d(PAR) prediction models from the Secchi disk depth (SDD) and beam attenuation coefficient of particulate and dissolved organic matter (C _t−w(PAR), excluding pure water) in the PAR range. We compare their performance and prediction precision by using the determination coefficient (r ²), relative root mean square error (RRMSE), and mean relative error (MRE). Our dataset comprised 1,067 measurements, including K _d(PAR), SDD, and C _t−w(PAR) taken in shallow, eutrophic, Lake Taihu, China, from 2005 to 2010. The prediction models of K _d(PAR) were based on the linear model with an intercept of zero, using the inverse SDD, and the nonlinear model using SDD. The linear model generated a slope of 1.369, which was not significantly different from 1.7, the index used worldwide, but significantly lower than the value of 2.26. The nonlinear model gave a slightly more reliable prediction of K _d(PAR) with a r ² of 0.804. Compared to the SDD, C _t−w(PAR) was more significantly correlated to K _d(PAR) based on the linear model, with a significantly higher r ² and lower RMSE and RE. Considering the measurement simplicity of C _t−w(PAR) and data acquisition feasibility from high-frequency autonomous buoys and satellites, our results demonstrated that this prediction model reliably estimates K _d(PAR), and could be used to significantly expand optical observations in an environment where the conditions for underwater PAR measurement are limited.     

Optically active components and light attenuation in an offshore station of Harima Sound, eastern Seto Inland Sea, Japan

In the eastern Seto Inland Sea, Japan, phytoplankton abundance in the surface water has gradually declined, whereas Secchi depth has risen in recent years, particularly in offshore areas. Therefore, it may be hypothesized that phytoplankton dominate light attenuation in the offshore area, and that other constituents are less important. To test this hypothesis, we examined the roles of seawater, colored dissolved organic matter (CDOM), non-algal particles (tripton), and phytoplankton in the light attenuation at an offshore station of Harima Sound in the eastern Sea. The magnitude of light attenuation was then determined from the attenuation coefficient of photosynthetically available radiation (PAR) through the water column (K _d). During a 13-month period, K _d ranged from 0.179 to 0.507 m^?1, with a mean of 0.262 m^?1. The mean relative contributions of seawater (15%) and CDOM (13%) to K _d were small, while the most dominant K _d constituent was tripton (45%). The mean contribution of phytoplankton to K _d (27%) was consequently less than that of tripton. However, 75% of the temporal variability in K _d was attributed to phytoplankton, measured as chlorophyll a. Our results emphasize that the main component of light attenuation does not always govern the temporal variation of light attenuation in coastal regions.     

Optical properties and optical constituents of the Faroe Islands shelf and off-shelf waters,North East Atlantic

The study comprises a data set of CTD, optical properties—K ₀(PAR), c _p, a(PAR), b(PAR)—and optical constituents—Chl a, SPM, CDOM—from 72 shelf and off-shelf stations in the Faroe Islands (62°N, 7°W) North East Atlantic, in early spring 2005. Results showed that shelf waters surrounding the islands were cold and low saline, whereas off-shelf waters were warmer (~1°C) and more saline (~0.05) PSU. A pronounced oceanographic front separated the two waters, and diffuse light attenuation K ₀(PAR), beam attenuation c _p, Chl a, absorption a(PAR), and scattering coefficient b(PAR) were all significantly higher on the shelf. Analyses showed that off-shelf light attenuation K ₀(PAR) was governed by Chl a, shown by a high (r ² = 0.64) Chl a–K ₀(PAR) correlation, whereas light attenuation on the shelf was governed by both Chl a, SPM, and CDOM in combination. A Chl a specific diffuse attenuation coefficient K₀^* ( \textPAR ) K_{0}^{*} \left( {\text{PAR}} \right) of 0.056 (m² mg⁻¹ Chl a) and a Chl a specific beam attenuation ( c_\textp^* c_{\text{p}}^{*} ) of 0.27 (m² mg⁻¹ Chl a) coefficients were derived for the off-shelf. It is pointed out that Chl a is the single variable that changes over time as no rivers with high SPM and CDOM enter the shelf area. Data were obtained in early spring, and Chl a concentrations were low ~0.5 mg Chl a m⁻³. Spring bloom Chl a are about 10 mg Chl a m⁻³ and estimations showed that shelf K ₀(PAR) will increase about 5 times and beam attenuation about 10 times. The Faroe Islands shelf–off-shelf waters is a clear example where physical conditions maintain some clear differences in optical properties and optical constituents. The complete data set is enclosed.     

Effects of seston on ultraviolet attenuation in Lake Biwa

We examined the attenuation of underwater ultraviolet (UV) radiation and photosynthetically available radiation (PAR) in Lake Biwa, Japan, at offshore and inshore sites and under contrasting stratification and mixing regimes. There were large spatial differences in the water column transparency to both wavebands, despite little change in concentrations of dissolved organic carbon (DOC). The 1% of surface irradiance depth varied from 0.3 to 2.7 m at 305 nm, from 0.8 to 6.3 m at 380 nm, and from 2.3 to 12.8 m for PAR. Both PAR and UV transparency declined abruptly in the South Basin of the lake when a typhoon caused the resuspension of sediments. The water column ratio of UV to PAR increased by 30% at all stations over the course of a 3-week sampling period associated with the general increase in phytoplankton concentrations. At several sites, the diffuse attenuation coefficient for UV radiation deviated substantially from that predicted from UV-DOC models. A significantly positive linear relationship was found between UV attenuation (K _d determined with a profiling UV radiometer) and the beam attenuation coefficient at 660 nm as measured by transmissometer. These results indicate that scattering and absorption by particulate matter can reduce UV transparency to below that inferred from DOC concentrations, and that current UV-exposure models should be modified to incorporate this effect. Received: March 21, 2001 / Accepted: August 17, 2001     

A Neural Network Model for K(λ) Retrieval and Application to Global K par Monitoring

Accurate estimation of diffuse attenuation coefficients in the visible wavelengths K _d(λ) from remotely sensed data is particularly challenging in global oceanic and coastal waters. The objectives of the present study are to evaluate the applicability of a semi-analytical K _d(λ) retrieval model (SAKM) and Jamet’s neural network model (JNNM), and then develop a new neural network K _d(λ) retrieval model (NNKM). Based on the comparison of K _d(λ) predicted by these models with in situ measurements taken from the global oceanic and coastal waters, all of the NNKM, SAKM, and JNNM models work well in K _d(λ) retrievals, but the NNKM model works more stable and accurate than both SAKM and JNNM models. The near-infrared band-based and shortwave infrared band-based combined model is used to remove the atmospheric effects on MODIS data. The K _d(λ) data was determined from the atmospheric corrected MODIS data using the NNKM, JNNM, and SAKM models. The results show that the NNKM model produces <30% uncertainty in deriving K _d(λ) from global oceanic and coastal waters, which is 4.88-17.18% more accurate than SAKM and JNNM models. Furthermore, we employ an empirical approach to calculate K _par from the NNKM model-derived diffuse attenuation coefficient at visible bands (443, 488, 555, and 667 nm). The results show that our model presents a satisfactory performance in deriving K _par from the global oceanic and coastal waters with 20.2% uncertainty. The K _par are quantified from MODIS data atmospheric correction using our model. Comparing with field measurements, our model produces ~31.0% uncertainty in deriving K _par from Bohai Sea. Finally, the applicability of our model for general oceanographic studies is briefly illuminated by applying it to climatological monthly mean remote sensing reflectance for time ranging from July, 2002- July 2014 at the global scale. The results indicate that the high K _d(λ) and K _par values are usually found around the coastal zones in the high latitude regions, while low K _d(λ) and K _par values are usually found in the open oceans around the low-latitude regions. These results could improve our knowledge about the light field under waters at either the global or basin scales, and be potentially used into general circulation models to estimate the heat flux between atmosphere and ocean.     

Spatial variability of chlorophyll-a and abiotic variables in a river–floodplain system during different hydrological phases

Chlorophyll-a (Chl-a) and abiotic variables were measured in the main channel and floodplain waterbodies of the Middle Paraná River to analyse the system dynamics and to assess their spatial variability during different hydrological phases, including an extreme flood. We wanted to test that the flood does not always have a homogenising effect in a river–floodplain system. An explanatory model for Chl-a was performed according to Akaike’s Information Criterion (AIC), and the relation of water level with the coefficient of variation (CV) among sites for each variable was explored. The model explained 64% of Chl-a variability. Water level, depth:euphotic zone ratio (Z _d:Z _eu) (inverse correlation) and conductivity (direct correlation) were the significant explicative variables. The CV of Chl-a decreased with flood from the main channel to the floodplain, but for turbidity, Z _d:Z _eu, pH, dissolved oxygen, soluble reactive phosphorus and Chl-a:pheophytin-a ratio, it increased. However, within the floodplain, CV of turbidity, Z _d:Z _eu and pH decreased during flood. These suggest that the homogenising effect frequently observed during inundation cannot be generalised and that the floodplain may maintain its identity even during flood. The extreme flood and its overlap with the warm season and sedimentological pulse probably contributed to the heterogeneity in the spatial gradient.     

Spatial and temporal analyses of water quality and phytoplankton biomass in an urbanized versus a relatively pristine salt marsh estuary

The robust growth of coastal communities in the southeastern United States is putting unique pressures on estuarine resources. Urbanization of estuarine systems may alter ecosystem function and thus affect the spatial scale and magnitude of nutrient concentrations and primary production temporally and spatially. We examined the spatial and temporal patterns of nutrient and chlorophyll a (Chl a) concentrations in two shallow well-mixed estuaries, (1) a developed estuary, Murrells Inlet (MI), South Carolina, and (2) a relatively pristine estuary, North Inlet (NI), South Carolina. The summer chlorophyll a maximum in MI was characteristically higher than in NI, which may be indicative of eutrophication. Correlations between salinity and inorganic nutrients (N and P) suggest that nutrient import from upland sources may be more pronounced in MI during stochastic precipitation events. Although inorganic nutrient concentrations between the estuaries were similar overall, during a wet period, inorganic N concentration in MI was increased to a greater extent than in NI, while only minimal increases in inorganic P were observed in both estuaries. Chlorophyll a concentrations decreased from the dry to wet period. Geographic Information System (GIS) plots of intensive spatial sampling in MI indicated spatial gradients of nutrient concentrations within this estuary that appeared to be consistent over time. These observations were investigated in more detail using regression analyses to examine the influences of coastal dilution and nutrient sources on relationships between water quality constituents. Results indicate the importance of stochastic rain events in affecting the linkages of estuarine processes to upland runoff in the urbanized estuary, MI.     

Variability in the sub-surface light climate at ecohydrodynamically distinct sites in the North Sea

This paper shows that the sub-surface light regime in the offshore North Sea varies spatially and seasonally between different ecohydrodynamic regions, which is likely to have important implications for primary production and carbon and nutrient fluxes in different areas of the North Sea. Measurements of downward irradiance were collected using different instruments (i.e. water column-profiling instruments, semi-autonomous moorings, and remote sensing) at three ecohydrodynamically distinct sites in the North Sea: in the southern Bight (SB), at the Oyster Grounds (OG) and north of the Dogger Bank (ND). The ND site was the deepest, and had the lowest and least variable light attenuation coefficients (mean K_d(PAR) = 0.11 m^?1). The onset of the phytoplankton spring bloom was earlier than at the other two sites. In summer, ND had low K_d(PAR) ~ 0.07 m^?1 and light penetration was shifted towards blue-green wavelengths (490–560 nm), with water itself being one of the strongest contributors to overall attenuation. In contrast, the SB site was characterised by the highest and most variable values of K_d(PAR) (mean = 0.54 m^?1), comparable to near-coastal waters, and the spring bloom started almost a month later than at the ND site. The vertical variability of the attenuation coefficient and the strong PAR attenuation in the blue region of the spectrum were the result of higher concentrations of phytoplankton, CDOM and SPM, due to riverine inputs, shallow depth and strong tidal mixing. The OG site showed intermediate conditions between the ND and SB sites with a mean K_d(PAR) = 0.23 m^?1, and deepest penetration of irradiance in the green region of the spectrum at 560 nm. The implications of these results for phytoplankton growth and ecosystem modelling are discussed.     

Invertebrate communities in dry-season pools of a large subtropical river: patterns and processes

In order to develop an optical model to map the extent of coastal waters, the authors analyzed variations in bio-optical constituents and submarine optical properties along a transect from the nutrient-enriched coastal bay, Himmerfjärden, out into the open Baltic Sea. The model is a simple implementation of the “ecosystem approach,” because the optical constituents are proxies for important components of ecosystem state. Yellow substance or colored dissolved organic matter (CDOM) is often a marker for terrestrial freshwater or decay processes in the littoral zone. Phytoplankton pigments, especially chlorophyll a, are used as a proxy for phytoplankton biomass that may be stimulated by fluvial or coastal inputs of anthropogenic nutrients. Suspended particulate matter (SPM) is placed in suspension by tidal or wind-wave stirring of shallow seabeds, and is therefore an indicator for physical forcing. It is the thesis of this article that such constituents, and the optical properties that they control, can be used to provide an ecological definition of the extent of the coastal zone. The spatial distribution of the observations was analyzed using a steady-state model that assumes diffusional transport of bio-optical variables along an axis perpendicular to the coast. According to the model, the resulting distribution along this axis can be described as a low-order polynomial (of order 1–3) when moving from a “source” associated with land to the open-sea “sink.” Order 1 implies conservative mixing, and the higher orders imply significant biological or chemical processes within the gradient. The analysis of the transect data confirmed that the trend of each optical component could be described well using a low-order polynomial. Multiple regression analysis was then used to weigh the contribution of each optical component to the spectral attenuation coefficient K _d(490) along the transect. The results showed that in this Swedish Baltic case study, the inorganic fraction of the SPM may be used to distinguish between coastal and open-sea waters, as it showed a clear break between coastal and open-sea waters. Alternative models may be needed for coastal waters in which fronts interrupt the continuity of mixing.     

Lake optics and depth limits for photogenesis and photosynthesis in charophyte meadows

Two series of lakes with increasing attenuation were examined for trends in spectral composition. They became the basis for an evaluation of the light environment at the lower boundary (LB) of Nitella meadows in three other series of lakes. Increased attenuation (K _d PAR) was marked by progressive erosion of the blue window and caused primarily by humic substances. An increase in K _d PAR from 0.06 to 0.81 produced, at the floor of the euphotic zone, a shift in K _d min from 440 to 580 nm. Regressions of boundary depths of Nitella meadows on water clarity produced similar slope coefficients for the three series of lakes. Several trends became evident: 1, PAR irradiance at the LB increases with depth of the LB; 2, red light (E _d 660) declines from richness at shallow LB to near extinction in deep water LB in clear lakes; while 3, blue light (K _d 450) increases to an asymptote. Blue light appears to substitute, although less effectively, for red light irradiance in the growth regulation of charophytes. These data support an hypothesis that spectral quality is involved in the determination of lower boundary depths for benthic macro-algae.     

Pre-classification improves relationships between water clarity, light attenuation, and suspended particulates in turbid inland waters

Relationships between water clarity, light attenuation, and concentration of suspended particulates are important in water optics and remote sensing, but are not well described yet, especially for optically complex turbid inland waters. In this study, based on 3-year data from Chinese lakes (Lake Taihu, Lake Chaohu, and Three Gorges reservoir), we propose a new approach to describe the inter-relationships of these bio-optical variables. This approach includes a pre-classification step of the waters into three types based on a semi-analytical parameter C _s before establishing the relationships. Our results showed that the pre-classification of waters increased model accuracies both for Z _SD (Secchi depth) versus K _d (diffuse attenuation coefficient) and K _d versus TSM (total suspended matter concentration). The quasi-theoretical model described better the relationship between Z _SD and K _d than the empirical model. For the K _d versus TSM relationship, linear models proved suitable for the Type 2 and Type 3 waters, whereas the power function model gave a better fit for the Type 1 water. Testing of the proposed relations with an independent dataset showed mean absolute percentage errors (MAPE) mostly below 30%. The findings of this study clarify the relationships between Z _SD, K _d, and TSM, and improve our bio-optical understanding of complex turbid inland waters.     

Spatial distribution and trophic ecology of dominant copepods associated with turbidity maximum along the salinity gradient in a highly embayed estuarine system in Ariake Sea, Japan

The present study aimed to investigate into the feeding ecology of the dominant copepods along a salinity gradient in Chikugo estuary. Copepod composition was studied from samples collected from stations positioned along the salinity gradient of the estuary. Copepod gut pigment concentrations were measured by fluorescence technique and hydrographical parameters such as temperature, salinity, transparency, suspended particulate matter (SPM); pigments such as chlorophyll-a (Chl-a), phaeopigment; and particulate nutrients such as particulate organic carbon (POC) and particulate organic nitrogen (PON) were measured. Two distinct zones in terms of nutrient and pigment concentrations as well as copepod distribution and feeding were identified along the estuary. We identified a zone of turbidity maximum (TM) in the low saline upper estuary which was characterized by having higher SPM, higher POC and PON but lower POC:PON ratios, higher pigment concentrations but lower Chl-a/SPM ratios and higher copepod dry biomass. Sinocalanus sinensis was the single dominant copepod in low saline upper estuary where significantly higher concentrations of nutrients and pigments were recorded and a multispecies copepod assemblage dominated by common coastal copepods such as Acartia omorii, Oithona davisae and Paracalanus parvus was observed in the lower estuary where nutrient and pigment concentrations were lower. Copepods in the estuary are predominantly herbivorous, feeding primarily on pigment bearing plants. However, completely contrasting trophic environments were found in the upper and the lower estuary. It was speculated from the Chl-a and phaeopigment values that copepods in the upper estuary receive energy from a detritus-based food web while in the lower estuary an algal-based food web supports copepod growth. Overall, the upper estuary was identified to provide a better trophic environment for copepod and is associated with higher SPM concentrations and elevated turbidity. The study demonstrates the role of estuarine turbidity maximum (ETM) in habitat trophic richness for copepod feeding. The study points out the role of detritus-based food web as energy source for the endemic copepod S. sinensis in the upper estuary, which supports as nursery for many fish species.     

The attenuation of ultraviolet and visible radiation in Dutch inland waters

The vertical attenuation coefficients (K _d) of downward ultraviolet (UV) and visible irradiance (PAR) were measured in 19 different inland waters in the Netherlands using a scanning spectroradiometer. Water chemistry variables such as dissolved organic carbon (DOC), absorbance of dissolved matter (a _d), chlorophyll-a, and particulate matter were measured to determine the relative contribution of dissolved and particulate components in explaining the variation in K _d. In addition to the field measurements, laboratory measurements were performed to test the relationships between water properties and light attenuation. The attenuation properties of Dutch inland waters vary. In most systems the penetration of UV-B radiation (280–320 nm) is limited to the upper decimetres. Lake Maarsseveen was the clearest waterbody in this study, with K _dUVB of 9.1 (m^–1). The DOC concentration had limited power in predicting UV attenuation in this study (r ²=0.33), because of the large differences in carbon-specific absorption. A _d300 was a much better predictor of UV attenuation (r ²=0.75). The relationships obtained in the laboratory experiments can be used to give a good prediction of in situ K _d values, based on 3 variables (chlorophyll-a, ash weight, and absorption of dissolved matter).     

Ecosystem services transcend boundaries: estuaries provide resource subsidies and influence functional diversity in coastal benthic communities

Background

Estuaries are highly productive ecosystems that can export organic matter to coastal seas (the ‘outwelling hypothesis’). However the role of this food resource subsidy on coastal ecosystem functioning has not been examined.

Methodology/Principal Findings

We investigated the influence of estuarine primary production as a resource subsidy and the influence of estuaries on biodiversity and ecosystem functioning in coastal mollusk-dominated sediment communities. Stable isotope values (δ¹³C, δ¹⁵N) demonstrated that estuarine primary production was exported to the adjacent coast and contributed to secondary production up to 4 km from the estuary mouth. Further, isotope signatures of suspension feeding bivalves on the adjacent coast (Dosinia subrosea) closely mirrored the isotope values of the dominant bivalves inside the estuaries (Austrovenus stutchburyi), indicating utilization of similar organic matter sources. However, the food subsidies varied between estuaries; with estuarine suspended particulate organic matter (SPOM) dominant at Tairua estuary, while seagrass and fringing vegetation detritus was proportionately more important at Whangapoua estuary, with lesser contributions of estuarine SPOM. Distance from the estuary mouth and the size and density of large bivalves (Dosinia spp.) had a significant influence on the composition of biological traits in the coastal macrobenthic communities, signaling the potential influence of these spatial subsidies on ecosystem functioning.

Conclusions/Significance

Our study demonstrated that the locations where ecosystem services like productivity are generated are not necessarily where the services are utilized. Further, we identified indirect positive effects of the nutrient subsidies on biodiversity (the estuarine subsidies influenced the bivalves, which in turn affected the diversity and functional trait composition of the coastal sediment macrofaunal communities). These findings highlight the importance of integrative ecosystem-based management that maintains the connectivity of estuarine and coastal ecosystems.     

Parameterization of surface irradiance and primary production in Århus Bay,SW Kattegat,Baltic Sea

The aims of the present study were to develop a parameterization of a one-year-long observed PAR time-series, apply the PAR parameterization in a primary production relation, and compare calculated and observed time-series of primary production. The PAR parameterization was applied in the generally used relation for the primary production (P _d): P _d = a(BI ₀ Z ₀) + b with observed photic depth (Z ₀) and Chl-a concentrations (B). It was tested whether the PAR parameterization in combination with this simple relation for primary production was able to describe the actual measured primary production. The study is based on a one year long time-series of PAR, CTD-casts (n = 45), and primary production measurements (n = 24) from Århus Bay (56°09′ N; 10°20′ E), south west Kattegat. Results showed a high and positive correlation between observed and calculated primary production in the bay, as based on the present PAR parameterization combined with the simple primary production relation. The developed PAR parameterization, which calculates total daily surface irradiance per day (M photons m^?2 d^?1), can be applied in any ecological application taking into account that it was developed for the latitude of 56° N.     

Optical characterization of coastal lagoons in Tunisia: Ecological assessment to underpin conservation

Ghar El Melh is a shallow lagoon (average depth of 0.8 m) that has undergone a eutrophication process due to growing human pressures. To obtain a global frame of the ecosystem functioning, an optical and an ecological classification were used in parallel. Downwelling and upwelling spectral irradiances were measured in situ in 22 sampling stations across the water body; then Apparent Optical Properties (AOPs), namely reflectance R(λ) and vertical attenuation coefficient K_d(λ) were calculated for each wavelength of visible spectrum, furnishing typical spectra from turbid waters, rich in dissolved and suspended matter. From water samples of the same stations the concentrations of OASs (Optically Active Substances), i.e. Chromophoric Dissolved Organic Matter (CDOM), Non-Algal Particulate (NAP) and Phytoplankton, were assessed. The use of an optical classification for water bodies rich in TSM and CDOM, integrating AOPs and OASs, highlighted a great spatial heterogeneity, well overlapping with hydrology and human impacts patterns. A modified version of the Ecological Evaluation Index (EEI), considering the macrophyte distribution (based on a visual assessment of macrophyte coverage, without quantitative sampling) was then used, highlighting an intermediate ecological condition, despite high water turbidities. The integrated use of both systems thus furnished a complete characterization, rapidly detecting the most impacted sectors and the possible primary causes. The method might be applied as a monitoring procedure in other Mediterranean coastal lagoons, with the aim to adopt a common conservation strategy for these important transitional water bodies.     

Light control on phytoplankton production in a shallow and turbid estuarine system

Tagus estuary is one of the largest estuaries of Western Europe. With the aim of unravelling the drivers of primary production in this shallow and turbid nutrient replete estuary, we tested the hypothesis that light availability is a major factor controlling phytoplankton production. Environmental parameters, phytoplankton biomass, community composition, and photosynthetic parameters were monitored at two sites in the estuary during a complete annual cycle. Despite the fact that nutrient concentrations were always above growth-limiting values, Chl a concentrations were relatively low throughout the study period. High water column turbidity, due to riverine inputs, promoted a rapid attenuation of light and created a compressed profile with optimal photosynthetic conditions. Therefore, the phytoplankton community, dominated by small cells, such as diatoms and cryptophycean flagellates, displayed highly photosynthetic efficiency and low light-saturated photosynthetic rates as a photo-acclimation response to low light conditions year-round. Primary production rate was unimodal, peaking in the summer months. In such estuarine system, gross primary production could thus be predicted by an existing robust empirical model based on pigment standing crop (Chl a), surface irradiance (E ₀) and optical depth (Z _eup). Compared to other shallow estuaries, the Tagus can be classified as a low- to moderately productive estuary, being the turbidity-induced low light conditions the principal factor limiting phytoplankton growth.     

Inorganic tripton in the Finger Lakes of New York: importance to optical characteristics

Inorganic particles in the upper waters of the 11 Finger Lakes of New York are morphometrically and elementally characterized by individual particle analysis conducted with scanning electron microscopy interfaced with automated image and X-ray analyses (IPA/SAX). Coupled measurements of Secchi disk transparency (SD), the attenuation coefficient for downwelling irradiance (K_d), the beam attenuation coefficient at 660 nm, and turbidity (T_n) were made to support evaluation of the importance of non-living, inorganic particles (inorganic tripton) in regulating these optical features of water quality. Wide differences in levels of inorganic tripton, represented in terms of particle projected area per unit volume (PAV_in), and the optical measures are reported for these lakes. However, generally similar size distributions are observed for the inorganic tripton for the lakes. Terrigenous suspensoids, in the form of clay minerals, dominated the inorganic tripton particle assemblage of nine lakes, while CaCO₃, formed autochthonously, dominated in the other two and was a noteworthy contributor in four others. PAV_in is demonstrated to be an important regulator of the optical properties of these lakes, performing substantially better than chlorophyll in predicting SD, and T_n, and interlake differences in these optical measures.Contribution No. 226 of the Upstate Freshwater Institute     

Subsurface chlorophyll maximum (SCM) location and extension in the water column as governed by a density interface in the strongly stratified Kattegat estuary

The aims of the study were to analyse the relations between the physics of a water column and the location of the subsurface chlorophyll maximum (SCM) peaks in a strongly stratified estuary. Could extension and depth location of the SCM be explained by the physical conditions in terms of water column stratification and density interface? Questions were addressed by obtaining data on water column density (CTD), chlorophyll a (Chl a), nutrients, (F _v/F _m), σ_PSII and K _d(PAR) at 15 positions along a 575 km transect in the Kattegat estuary. Results showed that the estuary was strongly stratified with mixed surface and bottom layers intercepted by a layer where density increased with depth. The SCM occurred only in this density interface, and widths of SCM and density interface were highly correlated. The surface waters were nearly depleted of inorganic nitrogen, phosphate and silicate though with significant higher concentrations in the waters below the interface. The Chl a concentration was comparatively higher in the SCM peak as well as maximum quantum efficiency (F _v/F _m) and functional cross sectional area (σ_PSII). The SCM was maintained at very low light levels and by a diapycnal nitrogen flux, with a stratified water column and nutrient depleted surface waters as predecessors. It was concluded that the depth location and vertical extension of the SCM in the estuary were closely linked to the physical structure of the water column in terms of density interface and stratification.