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Interaction between sea surface chlorophyll a and seawater indicators in the sea ranching area: A case study in Haizhou Bay
Abstract
Chlorophyll A (Chla) is a key parameter that reflects phytoplankton biomass and estimates red tide intensity. Studying the distribution characteristics of Chla concentrations and their correlation with various environmental indicators is of great significance. In this study, we analysed environmental monitoring data of Haizhou Bay, Lianyungang, Jiangsu Province, from 2004 to 2021 using a generalized additive model (GAM) to investigate the spatiotemporal variation in sea surface chlorophyll a (Chla) and its correlation with other sea water indicators. The results showed that the concentration of Chla increased gradually over the years but varied within the year, with the highest concentration in summer (July to September). With the passage of years, the fitting results of the model may be more consistent with the actual situation of Chla concentration distribution in this region. Compared with univariate GAM, multivariate GAM could effectively explain the variation in Chla concentration in the region over 20 years. Generally, the variation in Chla concentration is influenced by nutrients, BOD5 and salinity, depth, temperature and DO. BOD5 and depth are significant variables that can explain the variation in Chla concentration, but their interactions should be avoided in the analysis. We believe that the Chla concentration not only is affected by the rapid change in the estuarine environment but also has a potentially positive effect on the time lag effect of sea ranching construction, indicating that the interannual change in sea ranching construction plays a positive role in the potential change in the offshore environment. This study can provide a theoretical basis and an important reference for the further construction and management of sea ranching in the coastal waters of the world.
... Chla increased notably in the estuary during spring and summer, confirming that the Chla concentration in the sea area was influenced by the rapid changes in the estuarine environment and time-lag effects. These spatial and temporal variations were dynamic in nature [11,48]. ...
Dissolved inorganic nutrients are pivotal in maintaining the material and energy balance of marine ecosystems, impacting the survival and dynamic succession of marine organisms. To gain a deeper understanding of the source and sink characteristics of dissolved inorganic nutrients in bays affected by human activities and to elucidate the processes involving filter-feeding shellfish in relation to these nutrients, this study investigated the source and sink dynamics of dissolved inorganic nutrients in the Dapeng Cove sea area of Shenzhen. Over the past decade, a significant change in the N/P ratio within the survey area has been observed, suggesting a shift in nutrient limitation from nitrogen to phosphorus or phosphorus–silicon limitation. This induced change in the N/P ratio, along with Si/N and Si/P ratios, may facilitate the growth of cyanobacteria and, subsequently, alter the proportions of diatoms, dinoflagellates, and cyanobacteria. Seasonal fluctuations in human disturbance intensity and precipitation determine the seasonal and spatial distribution of nutrients in the bay, thereby influencing the bay ecosystem metabolism. The Land–Ocean Interactions in the Coastal Zone (LOICZ) model analysis revealed that the bay represents a major source of inorganic nitrogen and a source of phosphate in spring, summer, and autumn, while acting as a sink for phosphate in winter. Furthermore, rivers and groundwater represent the primary sources of phosphate and inorganic nitrogen in the bay. The bay exhibits an annual net ecosystem metabolic rate of 7.06 mmol C/m2/d, with denitrification dominating the nitrogen cycle at 12.65 mmol C/m2/d. Overall, the Dapeng Cove ecosystem displays net production exceeding respiration, classifying it as an autotrophic system. Additionally, the nitrogen cycle in the sea area is predominantly driven by denitrification. The analysis also revealed that the impact of oyster proliferation on the physical and chemical factors in the surveyed area is relatively weaker than that of surface runoff and groundwater inputs.
The Haizhou Bay in eastern China, for a long time, is seriously polluted with heavy metals (HMs) due to intensive anthropic pressure. The river runoff is the dominant pathway of HM transport in the coastal region. However, the information on HM pollution in coastal rivers flowing into Haizhou Bay was still limited, and potential risks and possible sources raised by HMs in this area were neglected up to now. To fully understand the distribution and ecological risks of sediments in seven rivers along the bay, surface sediments were collected and seven HMs (Cr, Mn, Ni, Cu, Zn, Cd, and Pb) were investigated. The results showed that HM concentrations generally met the primary standard criteria of China (marine sediment quality), except for Cu and Zn. On the other hand, Zn and Cu tended to exhibit probable adverse biological effects in the Shawang River comparison with some sediment quality guidelines (SQGs). Moreover, the enrichment factor and geo-accumulation index demonstrated that there was no or slight contamination to be found for Cr, Mn, Ni, Cu, Zn, and Pb and moderate pollution for Cd. The contamination factor (Cfⁱ), integrated contamination degree (CF), modified degree of contamination (mCd), and modified pollution index (MPI) revealed individual metal contamination in localized areas. In these river sediments, the potential ecological risk (RI) was low to moderate, except Cd posted a considerable ecological risk because of its high enrichment. Furthermore, the Shawang River and Linhong River were seriously polluted with HMs among seven rivers. These results provided a new direction for controlling HM pollution in Haizhou Bay which suggested substantial measures should be implemented to alleviate the potential risk of HMs, to these rivers sediments.
Graphical abstract
Anthropic changes in coastal watersheds affect the quantity and quality of water in estuaries. Based on an analytical model of saline intrusion and load balance, we have evaluated the effects of effluent discharge (mean of 285 L·s−1 and peak of 495 L·s−1) from a wastewater treatment plant (WWTP) in an island estuary. Saline intrusion at low tide, without actual anthropic discharge, will increase by 22%, whereas with increasing discharge, reductions of 16% and 28%. The reduction of saline intrusion may affect biogeochemical processes and the distribution of species in regions further up the estuary. When the WWTP reaches the mean projected discharge, it will increase its BOD and phosphorus loads by 90% and 82%, respectively, in relation to the current load. With the increase of WWTP discharge, there will be an expansion of hypoxic and anoxic conditions over the current areas, worsening the condition of this already jeopardized estuary. For the WWTP to lead to the expected environmental gains, it is necessary to consider the carrying capacity of the receiving body.
The habitat and feeding environment of freshwater fish in freshwater lakes have been destroyed, with the problem of miniaturization and simplification of catches being serious. An artificial reef is an effective technical measure to protect and proliferate offshore fishery resources, but little research has been conducted on its application in freshwater lakes. A small artificial reef for freshwater lakes was designed according to the water depth of the lake and the habits of benthic fish. The artificial reef is composed of biomass modules, each of which is 900 × 120 mm. The community structure of phytoplankton around the artificial reef and its adjacent waters was studied. The results showed that 77 species from seven phyla were identified, with a high number of species from the Chlorophyceae. In terms of density composition, the density of cyanobacteria decreased month by month, while the phylum Chlorophyta and Cryptophyta increased first and then decreased. As for biomass composition, Chlorophyta and Cryptophyta increased first and then decreased. RDA analysis showed that water temperature, dissolved oxygen, and total phosphorus were the main influencing factors. To sum up, the artificial reef can improve the algae phase in the surrounding water column, inhibit the growth and reproduction of cyanobacteria to a certain extent, and have a significant enrichment and promotion effect on diatoms. Artificial fish reef affects the phytoplankton community structure of the surrounding water bodies mainly through the absorption of phosphorus nutrients. Artificial reefs can be popularized and applied in freshwater lakes to provide foraging and shelter for benthic fish in the lake.
Sea ranching is one of the promising sustainable ways to restore depleted stocks and increase production of sea cucumber. Before, only high price species were exploited but now the demand is extended to many other low-value species, such as Teripang Hitam, H. atra . The present work were aimed to observed the growth and survival of H. atra ranching using pen system. Sea pens system size of 5meter x 5meter x 1.8meter was set up in Teluk Awur Waters, Jepara, Indonesia. They were designed as mesocosms that mimic sea ranching location. Wild young H. atra (average weight of 100 g) from Panjang Island, located adjacent to Teluk Awur waters were stocked at 3 individu.m ⁻² , reared for five months without food addition. Sea cucumber was weighed and counted monthly to determine their growth and survival rate. The results of present experiment revealed that sea cucumber increased their weight with the time of rearing, the average weight gain and survival rates were 212 g and 83% respectively. It showed that their adaptation to the new environment was went well. The sea cucumber got intake of food that naturally grew in the sea pens or transported by the sea current from surrounding area. This result showed promising application on sea ranching for marine natural conservation.
This paper focuses on the atmospheric dust transport effect on the changes in chlorophyll-A concentration in the Black Sea surface layer. In order to assess the input of nutrients with atmospheric precipitations at the Crimean coast of the Black Sea, the collected samples were analyzed for the content of inorganic nitrogen, phosphates, and silicon. The samples were taken into a wet-only sampler and into a permanently open one, to assess the effect of dust on the nutrients concentration in dry depositions. Cases of multi-fold excess of the nutrients content in the open sampler collected precipitation over that in the wet-only sampler were identified. For such high concentration cases, the 7-day back-trajectories analyses was carried out using the model of the international network AERONET and the HYSPLIT model. The results of our research showed that the influx of nutrients with the atmospheric depositions can result in increasing of chlorophyll-A concentration in 11–36% in the surface layer of the Black Sea. After atmospheric depositions, concentration of phosphates in the surface layer can increase more than five times compared with the background concentration. The increase of silicon concentration can reach 30%. The influx of atmospheric precipitation containing significant amounts of nutrients into the bay can shifts the Redfield ratio compared with background value up to three times.
In the management of lakes for a healthy environment, it is crucial to assess the limiting nutrient(s) and understand its use efficiency of the phytoplankton production. We hypothesized that dissolved inorganic phosphorus (DIP) and/or nitrogen concentrations (DIN) describe the state of nutrient limitations on phytoplankton production. Using the 38 years of monthly limnological data at eight stations in Lake Kasumigaura, we analyzed the relationships between the available nutrients for building phytoplankton biomass and chlorophyll a (Chla). Better correlations were obtained by subtracting the nutrients in tripton (non-living particulate matter) from the total P and N (available nutrients: TP′ and TN′). We determined the thresholds for P and N limitation (DIP: 0.01 mg l⁻¹; DIN: 0.15 mg l⁻¹) using the slopes of regression, and we examined this assessment in one of four limitation conditions (only P, only N, both, or none) for the respective times and stations. Close relationships between TP′ and Chla for only the P limitation data and between TN′ and Chla for only the N limitation data were observed. Multiple regression models confirmed that TP′ and TN′ predominantly determined Chla in only the P and N limitation conditions, respectively. Factors affecting nutrient use efficiency were also discussed.
Remote sensing retrieval is an important technology for studying water eutrophication. In this study, Guanting Reservoir with the main water supply function of Beijing was selected as the research object. Based on the measured data in 2016, 2017, and 2019, and Landsat-8 remote sensing images, the concentration and distribution of chlorophyll-a in the Guanting Reservoir were inversed. We analyzed the changes in chlorophyll-a concentration of the reservoir in Beijing and the reasons and effects. Although the concentration of chlorophyll-a in the Guanting Reservoir decreased gradually, it may still increase. The amount and stability of water storage, chlorophyll-a concentration of the supply water, and nitrogen and phosphorus concentration change are important factors affecting the chlorophyll-a concentration of the reservoir. We also found a strong correlation between the pixel values of adjacent reservoirs in the same image, so the chlorophyll-a estimation model can be applied to each other.
Low-level jet (LLJ) significantly affects the synoptic-scale hydrometeorological conditions in the South China Sea, although the impact of LLJs on the marine ecological environment is still unclear. We used multi-satellite observation data and meteorological reanalysis datasets to study the potential impact of LLJs on the marine biophysical environment over the Beibuwan Gulf (BBG) in summer during 2015–2019. In terms of the summer average, the sea surface wind vectors on LLJ days became stronger in the southwesterly direction relative to those on non-LLJ days, resulting in enhanced Ekman pumping (the maximum upwelling exceeds 10 × 10–6 m s–1) in most areas of the BBG, accompanied by stronger photosynthetically active radiation (increased by about 20 μmol m–2 s–1) and less precipitation (decreased by about 3 mm day–1). These LLJ-induced hydrometeorological changes led to an increase of about 0.3 °C in the nearshore sea surface temperature and an increase of 0.1–0.5 mg m−3 (decrease of 0.1–0.3 mg m−3) in the chlorophyll-a (chl-a) concentrations in nearshore (offshore) regions. Intraseasonal and diurnal changes in the incidence and intensity of LLJs potentially resulted in changes in the biophysical ocean environment in nearshore regions on intraseasonal and semi-diurnal timescales. The semi-diurnal peak and amplitude of chl-a concentrations on LLJ days increased with respect to those on non-LLJ days. Relative to the southern BBG, LLJ events exhibit greater impacts on the northern BBG, causing increases of the semi-diurnal peak and amplitude with 1.5 mg m−3 and 0.7 mg m−3, respectively. This work provides scientific evidence for understanding the potential mechanism of synoptic-scale changes in the marine ecological environment in marginal seas with frequent LLJ days.
Urban river runoff carrying various anthropogenic sources of heavy metals (HMs) is the most important input pathways for HM pollutions in the coastal region, apportioning sources of environmental pollutants is key to controlling coastal HM pollution. In the study, surface sediments were collected from seven urban rivers flowing through Lianyungang City and discharging into Haizhou Bay, Eastern China. The concentrations of HMs of the river sediments were, in mg/kg (mean value ± standard deviation): Mn (550 ± 227) > Zn (67 ± 61) > Cr (33 ± 12) > Ni (21 ± 8.5) > Cu (16 ± 7.6) > Pb (15 ± 5.6) > Cd (0.11 ± 0.06), which were slightly to moderately polluted. As important outlets for municipal and industrial sewages, the Shawang River and Linhong River were the most polluted. Based on the multivariate statistical analysis, HMs were attributed to anthropogenic source (industrial, domestic, and agricultural discharges) and natural source (soil parent materials and atmospheric deposition). Based on isotope source apportionment, Pb was mainly from natural source, exhausts of leaded gasoline vehicles, and coal combustion, with the mean contributions of 39.3%, 23.7%, and 37.0%, respectively, and Sr originated from natural source and anthropogenic source, with mean contributions of 31.8% and 68.2%, respectively. Pb-Sr isotopes illustrated that anthropogenic inputs were the dominant source for HMs in urban river sediments flowing into Haizhou Bay, and the isotope tracing results make up the discriminating deficiency of the multivariate statistical analysis.
China’s offshore habitats are seriously degraded, leading to continuous decrease in fishery resources. Marine ranching, which can not only conserve diverse fishery resources, but also restore the ecological environment, play an important role in the harmonious development of China’s marine fishery resources and offshore ecosystems. In this study, the definition and methods of the major technologies for the construction of marine ranching were introduced, their application in various sea areas were reviewed, and combined with the development stage of marine pasture in China, the problems faced by marine pasture in research foundation, scientific and technological level and supporting development in China were expounded. The development trend and research direction of marine pasture technology in China are prospected. Suggestions for the improvement of marine-ranching technologies in the future were proposed also.
Haizhou Bay is an open bay located in northern Jiangsu Province, China. This study analyzes the changes in the coastline, coastal development, and water quality of Haizhou Bay between 2006 and 2016. The box model method and numerical simulation are adopted to calculate the environmental capacities of Haizhou Bay in 2006 and 2016, analyze changes to environmental capacity features, and assess the influencing factors over this period. The scenario analysis method is used to discuss the influencing mechanism and degree of influence of factors (e.g., the water quality difference inside and outside the bay, and sea reclamation) on the environmental capacity and calculate the contribution of each influencing factor. The changes in terrain triggered by sea reclamation and water quality from 2006 to 2016 reduced the total environmental capacity of Haizhou Bay, with an influencing ratio of 0.198:0.802. In other words, poorer water quality inside the bay reduces the environmental capacity by a degree of 4.05 times that of sea reclamation. This study can offer guidance on related future research aiming to protect the marine environment of Haizhou Bay and control the total amount of pollutants discharged into the sea.
Many previous studies of the impact of oceanic environmental factors on chlorophyll (CHL) in a specific region focused on sea surface temperature (SST), mixed-layer depth (MLD), or wind stress (WS) alone. In this study, relationship between CHL and all those environmental factors (SST, MLD, and WS) in the open ocean was quantified for five regions within the subtropical gyres and the variation trend of 13-year (2003–2015) was analyzed using satellite observations and Argo measurements. The correlation analysis results show that MLD was correlated positively with CHL, SST was correlated negatively with CHL, and the correlation between CHL and WS was either positive or negative. Based on the significance of the correlations, models representing the relationships were established using the multiple linear regression and analyzed, showing that the environmental factors were the major determinants of CHL change. The regression coefficients show that both SST and MLD have remarkable effect on CHL. Our derived models could be used to diagnose the past changes, understand present variability, and predict the future state of CHL changes based on environmental factors, and help us understand the dynamics of CHL variation in the open ocean.
A powerful investigative tool in biology is to consider not a single mathematical model but a collection of models designed to explore different working hypotheses and select the best model in that collection. In these lecture notes, the usual workflow of the use of mathematical models to investigate a biological problem is described and the use of a collection of model is motivated. Models depend on parameters that must be estimated using observations; and when a collection of models is considered, the best model has then to be identified based on available observations. Hence, model calibration and selection, which are intrinsically linked, are essential steps of the workflow. Here, some procedures for model calibration and a criterion, the Akaike Information Criterion, of model selection based on experimental data are described. Rough derivation, practical technique of computation and use of this criterion are detailed.
Better understanding of the temporal-spatial distribution of chlorophyll-a concentration (Chla) is crucial in controlling harmful water blooms. In this study, the dynamical change of Chl-a over the Bohai Sea and Yellow Sea from 2003-2017 were analyzed by using the MODIS/Aqua satellite data, and the effects of sea surface temperature (SST), wind and wave were investigated. The typical distribution modes of long-term surface Chl-a were extracted by using the Self-organizing Mapping (SOM), neural network model. The results showed distinct seasonal variations of the Chl-a along with a gradual increase in the study period. The total Chl-a of the whole area reached the lowest value of 2.41mg/m3 in July, and the highest value 3.43mg/m3 in April; though in Laizhou Bay, the Chl-a concentration was significantly higher than other regions and the value reached at the peak in September. The spatial distribution showed that Chla decreased from inshore to offshore. Meanwhile, from clear mode to low, medium, and high concentration modes, the Chl-a gradually increased in coverage and concentration, and modes extracted by the SOM neural network have effectively elucidated the trend of Chl-a in spatial, seasonal, and interannual variability. The Generalized Additive Model (GAM) was used to evaluate the effect of SST, wind, and wave on the changing patterns of Chl-a. It was found that there is a significant nonlinear correlation between Chl-a and SST, wind speed, mean wave direction and significant height of the wave. These influencing factors accounted for 47.9% of the change of Chl-a, which had significant effects on Chl-a change. Compared with wind speed, mean wave direction and significant height of wave, SST can better explain the change of Chla. Besides, wind direction and increased human activity (e.g., river discharge) played a significant role in changing the Chl-a distribution in the Bohai Sea and Yellow Sea.
Two Ecopath mass-balance models were implemented for evaluating the structure and function of Haizhou Bay Ecological Restoration Area ecosystem using 14 ecological indicators in two distinctive years (2003 and 2013). The results showed that the size of HZERA ecosystem became larger as total biomass was increased in last decade, especially in primary producer and zooplankton groups. Total system throughput increased from 7496.00 t km−2 yr−1 to 9547.54 t km−2 yr−1. The P/R (production/respiration) ratio decreased over the decade. Finn’s cycling index and Finn’s mean path length increased over the decade. No keystone species (KS) occurred during ten years; however, evidences of top-down control in 2003 and 2013 models were demonstrated by high KS value belonging to Lophius litulon group in food web. Drawing upon Odum’s theory of ecosystem maturity, the structured, web-like ecosystem of 2013 model had developed into a highly mature system compared with that of 2003 model.
When an ocean current encounters a vertical structure, such as an artificial reef (AR), it can create a plankton-rich upwelling that provides a reliable feeding spot for fish. The fish attracted into the AR zones depends largely on the size, structure, and layout of the ARs. Thus, this study was conducted to demonstrate the effect of different layouts on the flow field around cubic ARs, a common type of AR in China. Water tank tests and numerical simulations were used to study the flow field around the cubic ARs. Experiment of hydrogen bubble was conducted in a water tank to observe the effect of the reef spacing on the flow field around the reefs. Using computational fluid dynamics, a three-dimensional numerical model was established based on the Navier-Stokes equation. The standard k-ϵ model was adopted to simulate the flow field around the ARs. On comparing the streamlines of the flow field around the ARs, it was found that the numerical results were in good agreement with the hydrogen bubble results. Using the numerical model, the flow around the ARs with different transverse or longitudinal spacing was simulated. When the transverse spacing distance is equal to the width of the AR, the upwelling becomes stronger. When the distance increases to 7L, the interaction between the reefs can be ignored. When the longitudinal spacing distance is equal to 1L, the effect of the interaction of the reefs on the back eddy is quite significant. However, as the distance increases, the interaction between two reefs gradually weakens.
Knowledge of the chlorophyll-a dynamics and their long-term changes is important for assessing marine ecosystems, especially for coastal waters. In this study, the spatial and temporal variability of sea surface chlorophyll-a concentration (Chl-a) in the Bohai Sea were investigated using 13-year (2000–2012) satellite-derived products from MODIS and SeaWiFS observations. Based on linear regression analysis, the results showed that the entire Bohai Sea experienced an increase in Chl-a on a long-term scale, with the largest increase in the central Bohai Sea and the smallest increase in the Bohai strait. Distinct seasonal patterns of Chl-a existed in different sub-regions of the Bohai Sea. A long-lasting Chl-a peak was observed from May to September in coastal waters (Liaodong bay, Qinhuangdao coast, and Bohai bay) and the central Bohai Sea, whereas Laizhou bay had relatively low Chl-a in early summer. In the Bohai strait, two pronounced Chl-a peaks occurred in March and September, but the lowest Chl-a was in summer. This pattern was quite different from those in other regions of the Bohai Sea. The water column condition (stratified or mixed) was likely an important physical factor that affects the seasonal pattern of Chl-a in the Bohai Sea. Meanwhile, increased human activity (e.g., river discharge) played a significant role in changing the Chl-a distribution in both coastal waters and the central Bohai Sea, especially in summer. The increasing trend of Chl-a in the Bohai Sea might be attributed to the increase in nutrient contents from riverine inputs. The Chl-a dynamics documented in this study provide basic knowledge for the future exploration of marine biogeochemical processes and ecosystem evolution in the Bohai Sea.
The variance inflation factor (VIF) is used to detect the presence of linear relationships between two or more independent variables (i.e. collinearity) in the multiple linear regression model. However, the traditionally used VIF definitions encounter some problems when extended to the case of the ridge estimation (RE). This paper presents an extension of the VIF in RE by providing two alternative VIF expressions that overcome these problems in the general case. Some characteristics of these expressions are also presented and compared with the traditional expression. The results are illustrated with an economic example in the case of three independent variables and with a Monte Carlo simulation for the general case.
The Southern Ocean (SO) plays a primary role in global climate by storing and transporting anthropogenic carbon dioxide through the meridional overturning circulation and the biological pumping process. In this study, we aim to investigate interannual variability of summer chlorophyll concentration in the SO and its relation with the El Niño Southern Oscillation (ENSO), using satellite ocean color data covering 16 years from 1997 to 2012. During El Niño periods, chlorophyll concentration tends to increase in the subtropics (north of the subantarctic front). This chlorophyll increase is likely linked to El Niño-induced surface cooling that increases nutrient supply through enhanced vertical mixing in the subtropics. On the other hand, the subpolar gyres show localized chlorophyll changes in response to the ENSO. The localized response seems to be primarily attributed to changes in sea-ice concentrations. Our findings suggest that ENSO contributes interannual variability of chlorophyll in the SO through different mechanisms depending on regions.
Biochemical Oxygen Demand (BOD) is a typical parameter used in assessing organic pollution strength in surface waters and is normally tested over a 5-day period at an incubation temperature of 20°C (BOD 5). The accuracy of this constituent, in assessing organic contamination under brackish conditions has always been known to be somewhat limited as elevated concentrations of chloride (Cl -) disrupts microbial activity from osmotic cellular degradation, causing the bottle decay rate, k 1 , to be effected. The aim of this study was to quantify the effects of induced salinity on k 1 , with varying levels of sodium chloride (NaCl) concentration (5 – 25 ppt), towards six mildly polluted to polluted tropical river water samples. The observed variations ranged between 0.10 – 0.25/day of k 1 for the stipulated samples using the Thomas graphical method for determination of the k 1 rate constant. Sg. Rawang depicted the highest quantum of difference in k 1 , with decrement from 0.754/day (0 ppt) to 0.513/day (25 ppt), whereas Sg. Klang showed the lowest quantum, from 0.306/day (0 ppt) to 0.265/day (25 ppt).
Several different classifications to characterize estuarine systems have been proposed. In this present paper, one of the most important estuaries in North Africa, the Oued Loukkos (Morocco), forms a case-study for proposing a systematic classification of this particular tidal estuary according to the vertical salinity gradient.
This study, conducted using a CTD, shows that the spatial-temporal distribution of salinity depends on the stage of the tide and the upstream distance from the mouth of the river. In this case, it is also evident that the morphology of the bottom was capable of impacting the distribution of salinity by locally changing the water circulation.
Based on the vertical salinity gradient measurement, the Oued Loukkos represents an estuarine environment with one section near its mouth that can be characterized as a mixed mesotidal estuary and another section upstream which can be characterized as a stratified mesotidal estuary. Between, there is an intermediate zone with a low vertical gradient of salinity, classified as a partially mixed mesotidal estuary. When the effect of terrestrial inputs is low compared to marine inputs, the river bed topography plays a role in the stratification of salinity by either disrupting the vertical stratification of the water or by changing the lateral distribution of salinity.
The proposed classification deepens our hydrological knowledge and provides descriptive labels to the Oued Loukkos estuary. It provides a valid starting point for predicting the environmental impact of future recreational, agricultural and commercial activities on the estuary.
Many researchers have studied the properties of chlorophyll-a vertical distribution in open ocean waters by now, and little is found for coastal waters. In the study, the chlorophyll-a vertical distribution of Yantai coastal waters is analyzed and a polynomial model is used to appraise the trend. Furthermore, the Gaussian model according to open waters is used to testify the practicability for coastal waters. The ratio between chlorophyll-a and turbidity is also discussed in order to predict the distribution trend. Finally, some conclusions could be achieved: A chlorophyll-a maximum in vertical direction could be seen and the maximum appears at about 6 8 meter depth in our research areas. The chlorophyll-a vertical distribution is similar to open ocean waters. Secondly, the euphotic layer is about 6~8 meter depth. Thirdly, under the depth of maximum chlorophyll-a concentration, chlorophyll-a concentration has negative correlation to the turbidity concentration in vertical direction. Based on above conclusion, the total chlorophyll-a could be achieved by calculating definite integrate of the simulation functions. This verifies the relationships of the surface and total chlorophyll-a concentration, which is the basis of primary production by the method of remote sensing.
[1] Precipitation over the ocean surface in the vicinity of industrialized and populated coastlines can increase the ocean nitrate concentration and consequently enhance ocean primary productivity. Using satellite data and a meteorological reanalysis product, we evaluated the impact of precipitation events on the chlorophyll-a concentration in coastal and offshore waters located downwind of the eastern United States. We found that in low-nutrient areas (defined as having nitrate concentrations < 1 μM) precipitation events were associated with increased levels of chlorophyll-a (up to approximately 15%), but in high-nutrient areas (nitrate concentrations > 1 μM) they were associated with decreased levels. These contrasting responses of chlorophyll-a concentration to precipitation were attributed to the correlation of precipitation with wind speed and to other factors (nutrients and light) limiting phytoplankton growth. Increases in wind speed accompanied by precipitation events typically deepen the mixed layer, which can entrain additional nutrients into the mixed layer but simultaneously reduce light availability. We suggest that in nutrient-depleted areas (south of 36°N) the added nutrients were a dominant factor increasing the chlorophyll-a concentration, whereas in the nutrient-replete areas (north of 36°N), where phytoplankton growth was light limited, reduced light availability was the dominant factor determining reduced chlorophyll-a concentration. Our results indicate that an increase in wind speed accompanied by precipitation events was a major contributor to the observed changes in chlorophyll-a concentration during wet days, whereas the wet deposition of pollutant nitrogen slightly increased the chlorophyll-a concentration (< 5%) only in nutrient-depleted areas.
Recently compiled observational data suggest a substantial decline in the global median chlorophyll a concentration over the 20th century, a trend that appears to be linked to ocean warming. Several modelling studies have considered changes in the ocean's physical structure as a possible cause, while experimental work supports a biological mechanism, namely an observed increase in zooplankton grazing rate that outpaces phytoplankton production at higher temperatures. Here, we present transient simulations derived from a coupled ocean general circulation and carbon cycle model forced by atmospheric fields under unabated anthropogenic global warming (IPCC SRES A1FI scenario). The simulations account for both physical and biological mechanisms, and can reproduce about one quarter of the observed chlorophyll a decline during the 20th century, when using realistically parameterized temperature sensitivity of zooplankton metabolism (Q10 between 2 and 4) and phytoplankton growth (Q10 ~ 1.9). Therefore, we have employed and re-calibrated the standard ecosystem model which assumes a lower temperature sensitivity of zooplankton grazing (Q10 = 1.1049) by re-scaling phytoplankton growth rates and zooplankton grazing rates. Our model projects a global chlorophyll a decline of >50% by the end of the 21st century. While phytoplankton abundance and chlorophyll a experience pronounced negative effects, primary production and zooplankton concentrations are less sensitive to ocean warming. Although changes in physical structure play an important role, much of the simulated change in chlorophyll a and productivity is related to the uneven temperature sensitivity of the marine ecosystem.
The underwater topography in the offshore sea area of north Jiangsu is complicated, including the middle radial sand ridges and northern Haizhou bay underwater shoal. Therefore, it forms special marine dynamic conditions and typical shoal wetland ecosystem. Previous researches of these sea areas were mainly focused on the forms of morphogenesis and the characteristic of conformation of sand ridges. Few studies have done on three dimensional hydrodynamic and water quality simulation. This paper introduced EFDC (Environ-mental Fluid Dynamics Code) to study the tidal current fields, dilution and diffusion of the sewage outlet near Yangkou Port. Comparison between computation results and the observed data indicates that this model could reasonably simulate hydrodynamic fields. Based on the computed tidal current field, the distributions of COD concentration were simulated. The range of contamination diffusion derived from sewage outlet was very limited, and the influence range of sewage came to the maximum when ebb slacks in neap tide period.
Guðmundsson, K., Heath, M. R., and Clarke, E. D. 2009. Average seasonal changes in chlorophyll a in Icelandic waters. – ICES Journal of Marine Science, 66: 2133–2140.The standard algorithms used to derive sea surface chlorophyll a concentration from remotely sensed ocean colour data are based almost entirely on the measurements of surface water samples
collected in open sea (case 1) waters which cover ∼60% of the worlds oceans, where strong correlations between reflectance
and chlorophyll concentration have been found. However, satellite chlorophyll data for waters outside the defined case 1 areas,
but derived using standard calibrations, are frequently used without reference to local in situ measurements and despite well-known factors likely to lead to inaccuracy. In Icelandic waters, multiannual averages of 8-d
composites of SeaWiFS chlorophyll concentration accounted for just 20% of the variance in a multiannual dataset of in situ chlorophyll a measurements. Nevertheless, applying penalized regression spline methodology to model the spatial and temporal patterns of
in situ measurements, using satellite chlorophyll as one of the predictor variables, improved the correlation considerably. Day number,
representing seasonal variation, accounted for substantial deviation between SeaWiFS and in situ estimates of surface chlorophyll. The final model, using bottom depth and bearing to the sampling location as well as the
two variables mentioned above, explained 49% of the variance in the fitting dataset.
The Hilbert-Huang Transform was applied to the satellite-derived monthly surface chlorophyll-a data and monthly blended satellite wind products from September 1997 to April 2010 to examine temporal trends in these time series. Using this new approach, we found an overall increasing trend in both the surface chlorophyll-a concentration and surface wind speed averaged over the entire South China Sea. Chlorophyll-a concentration increased by 12% between September 1997 and September 2003, and then decreased by 3% by April 2010. Wind speed increased by 21% between September 1997 and December 2005, but then decreased by 11%. The increasing trends followed by a period of decrease in both chlorophyll-a and wind speed time series are likely driven by the El Nio Southern Oscillation signal. The biggest change occurred in the deep basin region where the area averaged chlorophyll-a concentration increased by 20% between 1997 and 2010. This trend was primarily attributed to a 19% increase of the surface area of waters with monthly averaged chlorophyll-a concentration greater than 0.2 mg m -3, called the high chlorophyll waters. The most pronounced change occurred in winter with the high chlorophyll surface area expanding from 56 to 64% of the South China Sea. Strong correlation between chlorophyll-a and wind speed in this region suggested that it is the enhanced wind-induced mixing in the winter that stimulates phytoplankton growth via increased vertical supply of nutrients. The obtained 13-year trends indicate that the physical-biological interactions also take place on inter-annual time scales in the South China Sea.
The northern Gulf of Mexico (NGOMEX) was surveyed to examine the broad-scale spatial patterns and inter-relationships between hypoxia (<2 mg L −1 dissolved oxygen) and zooplankton biovolume. We used an undulat-ing towed body equipped with sensors for conductivity, temperature, depth, oxygen, fluorescence, and an optical plankton counter to sample water column structure, oxygen, and zooplankton at high spatial resolution (1 m—vertical; 0.25–1 km—horizontal). We contrast the distribution of zooplankton during summer surveys with different freshwa-ter input, stratification, and horizontal and vertical extent of bottom-water hypoxia. Bottom-water hypoxia did not ap-pear to influence the total amount of zooplankton biomass present in the water column or the areal integration of zooplankton standing stock in the NGOMEX region sur-veyed. However, where there were hypoxic bottom waters, zooplankton shifted their vertical distribution to the upper water column during the day where they normally would reside in deeper and darker waters. When bottom waters were normoxic (>2 mg L −1 dissolved oxygen), the daytime median depth of the water column zooplankton was on average 7 m deeper than the median depth of zooplankton in water columns with hypoxic bottom waters. A reduction in larger zooplankton when there were hypoxic bottom waters suggests that if zooplankton cannot migrate to deeper, darker water under hypoxic conditions, they may be more susceptible to size-selective predation by visual predators. Thus, habitat compression in the northern Gulf of Mexico due to hypoxic bottom water may have implica-tions for trophic transfer by increasing the contact between predators and prey.
Chlorophyll-a is a pigment that is contained in phytoplankton. Through the photosynthesis process, chlorophyll-a plays an important role in the global carbon cycle. The purpose of this research is to investigate the effect of global warming on chlorophyll-a concentration in Indonesian waters. The data used includes the monthly data of sea surface temperatures from 1984-2013, CO2 concentrations from 1980-2014, and chlorophyll-a concentrations from 2003-2014. The method used is linear regression. The results show that sea surface temperatures in Indonesian waters increased by about 0.51 °C from 1984-2013. The effects of global warming on chlorophyll-a concentrations varies between different areas of Indonesian waters. From the 12 research sites, 9 showed a decrease in concentration and 3 showed an increase.
Invasions by non-native species are an increasing problem, especially at valuable rangelands. In the present research, the suitable habitat of the invasive species of Leucanthemum vulgare Lam., in the rangelands of the Namin County in northwest Iran, was assessed using the topographic, climatic, and soil variables. Four machine learning models, including random forest (RF), boosted regression trees (BRTs), generalized linear model (GLM), and generalized additive models (GAM), were used in the R environment. This research was conducted in May and June 2019–2020. The presence and absence of the L. vulgare were recorded using a stratified random sampling method using a global positioning system. The soil samples were taken at a depth of 0 to 30 cm from the presence and absence sites of L. vulgare. The results showed that GAM performed with 95% Kappa, 91% AUC, 88% TSS better than others and, followed by GLM, BRTs, and RF in decreasing order among the implemented models. The predictive performance of the GAM model using tenfold cross-validation in the Caret package indicate that clay, organic matter, elevation, and phosphorus were the critical factors influencing the spread of L. vulgare. According to the GAM prediction, 12.95% (13,799.79 ha) of the Namin County is potentially suitable for the L. vulgare. The spatial pattern of invasive species in rangelands can help make sound decisions in controlling the expansion of invasive species and related ecological implications.
Holothuria scabra (sandfish) is a tropical sea cucumber that has been over-exploited because of its high-value in the bêche-de-mer trade. It is amenable to mariculture and the potential for community-based sea ranching has been investigated in the Tigak Islands of Papua New Guinea (PNG). A 5-ha trial sea ranch was established within the fishing grounds of an island community and protected from fishing for the duration of this study. Over 10 months, 5655 fluorochrome-marked H. scabra juveniles were stocked into the centre of the sea ranch. Line-transects were used to survey sea cucumber within and on the periphery of the sea ranch prior to stocking the sea ranch (October 2018) and at the conclusion of the study (February 2020). Additional collections of H. scabra were made at night in a 1-ha area around the stocking site. All H. scabra were weighed and checked for fluorochrome marks to determine cultured or wild origin. An estimated 3.7 ± 0.9% of cultured H. scabra were recoverable in the post-stocking survey. Cultured juveniles were found at a significantly higher density only around the stocking site. Factors potentially contributing to low recovery of cultured H. scabra include mortality, being overlooked, migration and misidentification of cultured and wild individuals. Species richness and density of the wild sea cucumber community increased in response to stocking and protecting the sea ranch. Our results highlight the importance of site-specific monitoring and evaluation to assess the success of sea ranching. Despite low recovery, H. scabra mariculture remains a promising option in PNG, as wild stocks are predicted to decline with increased fishing pressure, thus limiting recruitment. This will be aided by improved production of release-size juvenile H. scabra, improved release protocols to promote higher recovery of cultured juveniles and improved community capacity to manage cultured and wild sea cucumber stocks.
Particulate matter with aerodynamic diameter ≤2.5μm (PM2.5) concentrations vary between countries with similar carbon dioxide (CO2) emissions, which can be partially explained by differences in air pollution control efficacy. However, no indicator of air pollution control efficacy has yet been developed. We aimed to develop such an indicator, and to evaluate its global and temporal distribution and its association with country-level health metrics. A novel indicator, ambient population-weighted average PM2.5 concentration per unit per capita CO2 emission (PM2.5/CO2), was developed to assess country-specific air pollution control efficacy (abbreviated as APCI). We estimated and mapped the global average distribution of APCI and its changes during 2000-2016 across 196 countries. Pearson correlation coefficients and Generalized Additive Mixed Model (GAMM) were used to evaluate the relationship between APCI and health metrics. APCI varied by country with an inverse association with economic development. APCI showed an almost stable trend globally from 2000 to 2016, with the low-income groups increased and several countries (China, India, Bangladesh) decreased. The Pearson correlation coefficients between APCI and life expectancy at birth (LE), infant-mortality rate (IMR), under-five year of age mortality rate (U5MR) and logarithm of per capita GDP (LPGDP) were -0.57, 0.65, 0.66, -0.59 respectively (all P values <0.001). APCI could explain international variation of LE, IMR and U5MR. The associations between APCI and LE, IMR, U5MRwere independent of per capita GDP and climatic factors. We consider APCI to be a good indicator for air pollution control efficacy given its relation to important population health indicators. Our findings provide a new metric to interpret health inequity across the globe from the point of climate change and air pollution control efficacy.
Particulate matter with a diameter of ≤ 2.5 μm (PM2.5) is a critical air pollutant that adversely affects human health and the ecological environment. Using the data of daily air pollutant concentration and meteorological elements from 2013 to 2020 in Lanzhou, China, we employed the generalized additive model (GAM) and gradient boosting machine (GBM) approaches to analyze the relationship between PM2.5 concentration and environmental factors. The results revealed that the annual average PM2.5 concentration in Lanzhou, China, decreased by 3.98 μg/m³ per year during the study period and the variation of PM2.5 concentration was influenced by many factors. Mean temperature, air pressure, relative humidity, and O3 concentration had significantly negative effects on PM2.5 concentration, whereas CO and NO2 concentrations had significant positive effects. PM2.5 concentration was also high during static winds or high-speed winds. Among these influencing factors, the interactions of meteorological factors and air pollution also had strong correlations with PM2.5 concentration. We found that the multi-factor model could better explain the influence of environmental factors on PM2.5 concentration than the single-factor model. The fitting degree of the GAM was better than that of the GBM model; their mean absolute errors were 11.85 and 11.30, respectively. We also found that the GBM model was more precise for estimating daily PM2.5 concentration, whereas the GAM was more suitable for long-term trend analysis.
Variations in the physico-chemical characteristics of estuaries, such as surface water salinity and temperature, lead to the establishment of gradients that are closely related with the distribution of nutrients and suspended sediment. This affects light penetration, which in turn influences Chlorophyll-a (Chl-a) concentration and primary productivity. We used MODIS imagery to identify spatio-temporal patterns of sea surface salinity, temperature, and Chl-a concentrations from 2003 to 2017, to explore relationships between these variables and oceanographic factors, such as streamflows, winds and currents in the mouth of Colombia's Magdalena River, which discharges to the Caribbean Sea. Sea surface salinity (SSS) in the study zone varied in time and space from estuarine to marine. Mean SSS was 10.8 ± 3.4 at Bocas de Ceniza, and 28.4 ± 0.4 in the Caribbean Sea, with the horizontal salinity gradient providing evidence for the existence of a salinity plume. Mean monthly sea surface temperatures (SST) averaged across all years were 27.6 ± 1.5 °C at Bocas de Ceniza, and 27.6 ± 1.3 °C in the Caribbean Sea. A significant, increasing trend in temperature was observed throughout the years of the study period. Average Chl-a values were 3.3 ± 1.4 mg m⁻³ at Bocas de Ceniza, and 1.5 ± 1.2 mg m⁻³ in the Caribbean Sea and the calculated average Trophic State Index (TSI) for Bocas de Ceniza indicated that the estuary trophic state varied between oligo-mesotrophic (30 < TSI≤40) and mesotrophic (40 < TSI≤50). The highest concentrations of Chl-a were found in intermediate salinities in the estuarine zone. Outside the saline plume, there is a considerable decrease in Chl-a concentrations (<0.5 mg m⁻³). Winds played the most important role in influencing spatio-temporal distribution of chemical and physical variables in the study zone. Our results emphasize the importance of physical processes on biological dynamics in the Magdalena River mouth.
The water quality of the backwater areas in the Xiangxi River and Shennong River, which are typical tributaries of the Three Gorges Reservoir, was monitored in September 2018. The vertical distribution characteristics of dissolved oxygen, chlorophyll a, and other indicators in the two rivers were analyzed and compared, and the environmental factors affecting their vertical distribution were discussed. The results showed that the dissolved oxygen concentration 0-10 m and 0-12 m from the surface of the Xiangxi River and Shennong River, respectively, showed significant stratification and decreased with increasing water depth. The dissolved oxygen saturation of surface water was 139.20% and 107.78%, respectively, reaching a state of supersaturation (SDO>100%).The dissolved oxygen concentration in the middle and bottom water was more stable without stratification. The vertical distribution characteristics of chlorophyll a were consistent with those of dissolved oxygen in the Xiangxi River and Shennong River, and the chlorophyll a concentration in the surface water showed moderate eutrophication (5μg·L-1 < Chl-a < 20 μg·L-1). According to Pearson correlation analysis, the vertical distribution of dissolved oxygen in the Xiangxi River and Shennong River was significantly correlated with that of water temperature and phytoplankton. The stratification of water temperature and the life activities of phytoplankton were the key factors affecting the vertical distribution of dissolved oxygen. Chlorophyll a was positively correlated with water temperature and pH, and negatively correlated with turbidity, indicating that the vertical distribution of phytoplankton was mainly affected by the attenuation of light intensity along the water depth and the stratification of water temperature.
Data on Secchi depth, chlorophyll a, total phosphorus (TP), and nutrient status of phytoplankton were collected at five nearshore sites (11–17 m deep) and two offshore sites (>100 m) between the Grand River and Muskegon River outflows during March-December 2014–2018 to describe seasonal patterns and to compare the two depth regions in southeastern Lake Michigan. In contrast to the offshore, where spring chlorophyll a and TP concentrations declined dramatically following the dreissenid mussel expansion, the nearshore region of southeastern Lake Michigan was still characterized by low Secchi depth and elevated chlorophyll a and TP in the spring. During May, median Secchi depth was 5 times higher in the offshore than the nearshore, whereas chlorophyll a and TP were over 9 and 3 times higher in the nearshore, respectively. Even though spring chlorophyll a and TP have declined substantially at some of the nearshore sites compared to 1996, particularly the sites closest to tributary outflows, the overall yield of chlorophyll a per unit TP did not change over time in the nearshore. There were indications of P-deficiency in the nearshore in 2014–2018, but P-deficiency was even more severe in the offshore during the spring where yield of chlorophyll a per unit TP was also lower than in the nearshore. Although dreissenid mussels can be abundant in the nearshore, their populations are patchy and inputs from tributaries provide conditions that apparently dampen any potential filtering impacts of mussels in the nearshore compared to the offshore, especially during the spring.
While bivalve farming is well recognized in terms of modifying the biogeochemical cycle through filter-feeding and biodeposition, its impacts on water column nutrient concentrations in various ecosystems may vary from depletion to addition. Hypothesizing that the variability arises from overlap of farming-associated impacts and pelagic processes, nutrient concentrations and phytoplankton biomass were investigated monthly in an offshore sea ranch, to detect the real impacts of bottom-seeding scallop farming. Nutrient concentrations in water column average increased from July to December following successive surface freshening and disappearance of thermal stratification. Abrupt decrease was observed in March, along with increase in chlorophyll a concentration. The silicate concentration decreased below 2 μM in all depth layers in the mariculture area in March and April, whereas silicate limitation in open waters was commonly observed in April. Compared to open waters, inorganic nitrogen and phosphate concentrations were significantly lower in the mariculture area on an annual cycle, whereas silicate concentration was lower in spring and higher in summer. Our results indicate that scallop farming in frequently refreshed waters can act as nutrient sink through top-down effects. Without exogenous supply, it can also introduce the limitation of nutrient (silicate) with low regeneration rate and stimulate shift in the phytoplankton community structure.
In this study, the generalized additive model (GAM) was used to analyze seasonal monitoring data from Lake Taihu, collected from 2010 to 2014, with the aim to explore the correlation between chlorophyll a (Chla) and other water quality parameters. The selected optimal multivariable GAM could effectively explain the concentration variation of Chla occurring during each season, and the interpretation degree followed the order: summer > autumn > spring > winter. The fitting results indicated that the concentration variation of Chla could reflect that of biochemical oxygen demand and chemical oxygen demand in all seasons. In addition, the total phosphorus showed strong ability to explain the concentration change of Chla in spring and summer, as the growth of algae would be affected when the concentration of phosphorus shifted high or low. Nitrogen showed strong ability to explain the variations in Chla concentration in autumn. The conclusions of the optimal multivariable GAM could provide decision basis for the eutrophication control. In other words, the prevention of eutrophication outbreaks could be carried out via the targeted control of key water pollutants. According to these results, the concentration of Chla was higher in northern and western lake during summer and autumn, the management should focus on nutrient input of adjacent rivers.
Nutrient reduction efforts have been undertaken in recent decades to mitigate the impacts of eutrophication in coastal and estuarine systems worldwide. To track progress in response to one of these efforts we use Generalized Additive Models (GAMs) to evaluate a diverse suite of water quality constituents over a 32-year period in the Chesapeake Bay, an estuary on the east coast of the United States. Model development included selecting a GAM structure to describe nonlinear seasonally-varying changes over time, incorporating hydrologic variability via either river flow or salinity, and using interventions to model method or laboratory changes suspected to impact data. This approach, transferable to other systems, allows for evaluation of water quality data in a statistically rigorous way, while being suitable for application to many sites and variables. This enables consistent generation of annual updates, while providing a tool for developing insights to a range of management- and research-focused questions.
Biochemical and physiological parameters in the croaker Micropogonias furnieri were evaluated as biomarkers of chemical contaminants in estuaries. Juvenile croakers (10-20 cm total body length) were collected in summer and winter (2011 and 2012), in two sites at the Lagoa dos Patos estuary (southern Brazil). Fish were also collected in summer (2011 and 2012) in one site at the Barra do Chui estuary (southern Brazil). Tissue (gills, muscle or liver) samples were dissected and analyzed for contaminants [metals, polycyclic aromatic hydrocarbons (PAHs) and organochlorine pesticides (OCPs)] and selected biochemical and physiological parameters [metallothionein-like proteins (MTLP), acetylcholinesterase (AChE) activity, ethoxyresorufin-O-deethylase (EROD) activity, and lipid peroxidation (LPO)]. Additionally, water samples were collected for water chemical analyses (salinity, pH, temperature, dissolved oxygen, total alkalinity, and sulfate concentration). Data obtained were integrated and analyzed, using Principal Component Analysis (PCA) and Generalized Additive Model (GAM) approaches. Results showed that changes in concentrations of chemical contaminants and responses of biochemical and physiological parameters did not show any pattern according to the site, season and year of fish collection. However, they were influenced by fish body length and water temperature and salinity. Liver LPO and EROD activity were not responsive to PAHs. However, liver LPO was responsive to HCB, p,p-DDD, p,p-DDT and endosulfan sulfate. In turn, gill MTLP concentration, muscle AChE activity and liver EROD activity were responsive to non-essential metals (Pb, Cd and Ag). Considering that the ecotoxicological modeling approach adopted (GAM) accounted for biological, spatial and temporal variability of data associated with fish body size and site, season and year of fish collection, gill MTLP concentration, muscle AChE activity, as well as liver LPO and EROD activity can be considered as reliable biomarkers of fish exposure to chemical contaminants in estuaries.
The problem of testing smooth components of an extended generalized additive model for equality to zero is considered. Confidence intervals for such components exhibit good across-the-function coverage probabilities if based on the approximate result, where f is the vector of evaluated values for the smooth component of interest and V f is the covariance matrix for f according to the Bayesian view of the smoothing process. Based on this result, a Wald-type test of f=0 is proposed. It is shown that care must be taken in selecting the rank used in the test statistic. The method complements previous work by extending applicability beyond the Gaussian case, while considering tests of zero effect rather than testing the parametric hypothesis given by the null space of the component's smoothing penalty. The proposed p-values are routine and efficient to compute from a fitted model, without requiring extra model fits or null distribution simulation.
A model in which the conditional expected value of a response variate is an unknown nonlinear function of an unknown linear combination of regressor variates is considered. It is shown that in the case that the regressors are stochastic and jointly Gaussian, or are deterministic and quasi-Gaussian, the ordinary least squares estimates provide useful estimates of the coefficients of the linear combination up to an arbitrary multiplier. The cases of both conditional and unconditional inference are investigated.
Physical forcing and biological response within the California Current System (CCS) are highly variable over a wide range of scales. Satellite remote sensing offers the only feasible means of quantifying this variability over the full extent of the CCS. Using six years (1997-2003) of daily SST and chlorophyll imagery, we map the spatial dependence of dominant temporal variability at resolutions sufficient to identify recurrent mesoscale circulation and local pattern associated with coastal topography. Here we describe mean seasonal cycles and interannual variation; intraseasonal variability is left to a companion paper (K. R. Legaard and A. C. Thomas, manuscript in preparation, 2006). Coastal upwelling dictates seasonality along north-central California, where weak cycles of SST fluctuate between spring minima and late summer maxima and chlorophyll peaks in early summer. Off northern California, chlorophyll maxima are bounded offshore by the seasonally recurrent upwelling jet. Seasonal cycles differ across higher latitudes and in the midlatitude Southern California Bight, where upwelling winds are less vigorous and/or persistent. Seasonality along south-central Baja is strongly affected by processes other than upwelling, despite year-round upwelling-favorable winds. Interannual variation is generally dominated by El Niño and La Niña conditions. Interannual SST variance is greatest along south-central Baja, although interannual variability constitutes a greater fraction of total variance inshore along southern Oregon and much of California. Patterns of interannual chlorophyll variance are consistent with dominant forcing through the widespread depression and elevation of the nutricline during El Niño and La Niña, respectively. Interannual variability constitutes a greater fraction of total chlorophyll variance offshore.
East China Seas locate in the East Asia Monsoon region, which have large seasonal variation. In this paper, we use the remote sensing data from AVHRR, SeaWiFS and MODIS to analysis the climatology and long-time change of sea-surface temperature and chlorophyll concentration in the East China Seas. First, the monthly-averaged sea-surface temperature and chlorophyll concentration remote sensing data sets from 1998 to 2009 are generated. Second, the climatology distributions of the sea-surface temperature and chlorophyll concentration in the East China Seas are analyzed both for the seasonal cycle and monthly cycle, and the results show that there is remark seasonal variation in the East China Seas. Finally, based on the long-time data sets we have generated, the annual variation of the sea-surface temperature and chlorophyll concentration in the East China Seas are analyzed, and results shows that sea-surface temperature generally decreases for the whole East China Seas in the last 10 years, but with spatial variation. The chlorophyll concentration increases in the Yellow Sea in the last 10 years; however, it is decreases in the shelf of the East China Sea and the Kuroshio region.
Consumer-mediated nutrient supply is increasingly recognized as an important functional process in many ecosystems. Yet, experimentation at relevant spatial and temporal scales is needed to fully integrate this bottom-up pathway into ecosystem models. Artificial reefs provide a unique approach to explore the importance of consumer nutrient supply for ecosystem function in coastal marine environments. We used bioenergetics models to estimate community-level nutrient supply by fishes, and relevant measures of primary production, to test the hypothesis that consumers, via excretion of nutrients, can enhance primary production and alter nutrient limitation regimes for two dominant primary producer groups (seagrass and benthic microalgae) around artificial reefs. Both producer groups demonstrated marked increases in production, as well as shifts in nutrient limitation regimes, with increased fish-derived nutrient supply. Individuals from the two dominant functional feeding groups (herbivores and mesopredators) supplied nutrients at divergent rates and ratios from one another, underscoring the importance of community structure for nutrient supply to primary producers. Our findings demonstrate that consumers, through an underappreciated bottom-up mechanism in marine environments, can alter nutrient limitation regimes and primary production, thereby fundamentally affecting the way these ecosystems function.
Pagasitikos Gulf (Greece), presents an interesting area as it depicts strongly non-linear ecosystem character-istics. It is a shallow coastal area where the marine ecosystem picture is strongly influenced by non-linear hydrodynamic interactions and instabilities. In this study, we explore and assess the major influential vari-ables of the surface phytoplankton biomass (Chlorophyll-a). Several different physical and biogeochemical parameters were used (sea surface temperature [SST], mixed layer depth [MLD], salinity, phosphates and nitrates) to identify which variables control or significantly affect the surface Chl-a of Pagasitikos Gulf for the period of 2001–2005. The variables were derived from a coupled hydrodynamic-biogeochemical model and remotely sensed data from SeaWiFS and AVHRR sensor. Generalised Additive Models (GAMs) were used to examine the relationships between Chlorophyll-a and the environmental regime. GAM analysis showed that the combined effects of the variables used, explained 71% of the surface chlorophyll variation. The order of importance of the variables (based on GAM probability) is p = 0.01 (for both phosphate and nitrate), MLD: p = 0.0197, salinity: p = 0.022, and SST: p = 0.046. The results clearly indicated the importance of deep mixing for Pagasitikos Gulf, as the surface phytoplankton blooms appeared to be favoured by cold, nutrient rich, well mixed and higher salinity waters. GAMs indicated that SST plays a significant role having a strong negative relationship with Chl-a, where the highest concentration is reached at 12–15 °C and min-imum at 22–26 °C. Chl-a ceases to increase after 37.9‰ of salinity and 40 m of MLD, while minimum concen-tration is found at 10 m of MLD, with a subsequent increase as the waters become more mixed. Phosphate and nitrates appeared to be of equal importance with Chl-a exhibiting an increase along with the nutrients.