Eutrophication risk assessment in coastal embayments using simple statistical models.

A statistical methodology is proposed for assessing the risk of eutrophication in marine coastal embayments. The procedure followed was the development of regression models relating the levels of chlorophyll a (Chl) with the concentration of the limiting nutrient--usually nitrogen--and the renewal rate of the systems. The method was applied in the Gulf of Gera, Island of Lesvos, Aegean Sea and a surrogate for renewal rate was created using the Canberra metric as a measure of the resemblance between the Gulf and the oligotrophic waters of the open sea in terms of their physical, chemical and biological properties. The Chl-total dissolved nitrogen-renewal rate regression model was the most significant, accounting for 60% of the variation observed in Chl. Predicted distributions of Chl for various combinations of the independent variables, based on Bayesian analysis of the models, enabled comparison of the outcomes of specific scenarios of interest as well as further analysis of the system dynamics. The present statistical approach can be used as a methodological tool for testing the resilience of coastal ecosystems under alternative managerial schemes and levels of exogenous nutrient loading.

Analysis of phytoplankton community structure using similarity indices: a new methodology for discriminating among eutrophication levels in coastal marine ecosystems.

Nine similarity indices based on phytoplankton community structure were examined for their sensitivity to assess different levels of eutrophication. Two phytoplankton data sets, one from an open coastal system and one from a semi-enclosed gulf, associated with different nutrient dynamics and circulation patterns were used for evaluating the indices. The results have shown that similarity indices, measuring interspecific association and resemblance of phytoplankton communities between enriched areas and control sites, were effective for detecting spatial and temporal dissimilarities in coastal marine ecosystems. The structure of the oligotrophic habitat as a potential source of ambiguity for the results was discussed, whereas the validity ranges and the potential applicability of this method were deemed to be dependent on the size of the fraction of the common species among the samples, and the similarity of the classification patterns resulted from this subcategory and those extracted from the overall community data. Furthermore, the study provides a new technique based on the use of the "Box and Whisker Plot" designed to distinguish opportunistic and rare phytoplanktonic species. The similarity indices, applied solely to the dominant species abundance, were more sensitive to resolve eutrophic, mesotrophic and oligotrophic conditions. This procedure can be proposed as an effective methodology for water characterization and can also be used as a qualitative tracer for detecting renewal processes of coastal marine ecosystems.

Developing an optimal sampling design. A case study in a coastal marine ecosystem.

The development of a sampling design for optimising sampling site locations collected from a coastal marine environment has been the purpose of the present work; application of statistical analysis and spatial autocorrelation methods have been carried out. The dataset included data collected from 34 sampling sites spaced out in the Strait of Lesbos, Greece, arranged in a 1 x 1 NM grid. The coastal shallow ecosystem was subdivided into three zones, an inner one (7 stations), a middle one (16 stations) and an offshore zone (11 stations). The standard error of the chlorophyll-a concentrations in each zone has been used as the criterion for the sampling design optimisation, resulting into reallocation of the sampling sites into the three zones. The positions of the reallocated stations have been assessed by estimation of the spatial heterogeneity and anisotropy of chlorophyll-a concentrations using variograms. Study of the variance of the initial dataset of the inner zone taking into account spatial heterogeneity, revealed two different sub-areas and therefore, the number of the inner stations has been reassessed. The proposed methodology eliminates the number of sampling sites and maximises the information of spatial data from marine ecosystems. It is described as a step-by-step procedure and could be widely applied in sampling design concerning coastal pollution problems.

Marine eutrophication: a proposed data analysis procedure for assessing spatial trends.

A methodology for the discrimination of the different trophic levels at a spatial scale in the marine environment is proposed using spatial analysis methods and non-parametric statistics. Phytoplankton cell number, being a representative parameter to express trophic trends in the marine ecosystem is selected for the methodology development; Saronicos Gulf, Greece is used for the case study. The proposed stepwise methodology includes interpolation for assessing the spatial distribution of phytoplankton cell number, division of the Gulf into a number of quadrates, development of a scale characterising trophic levels and finally characterisation of the trophic state of each quadrate using non-parametric statistics. The advantages of this methodology and the potential applications in coastal management studies are also discussed.

Categorical mapping of marine eutrophication based on ecological indices.

The present work is concerned with the development of methodological procedures for studying the spatial distribution of eutrophication in the marine environment. Seven ecological indices (S, number of phytoplankton species; N, total number of individuals; D(Mg), Margalef's index; D(Mn), Menhinick's index; D(Od), Odum's species per thousand individuals; H', Shannon's Diversity index; E, Evenness index), based on phytoplankton community data collected from Saronicos Gulf, Greece were used for describing the eutrophication state of the sea environment. A representation of the spatial distribution for each ecological index was developed using the Inverse Distance Weighted (IDW) interpolation method. A eutrophication scale for each index was also developed for indicating four different trophic levels in the marine environment (eutrophic, upper-mesotrophic, lower-mesotrophic, oligotrophic); categorization of the interpolated values of each index resulted in a clear illustration of these trophic levels on seven thematic maps. Two methodological procedures were finally applied for synthesizing the information of these thematic maps. The purpose was the development of a final map illustrating the spatial distribution of eutrophication in the study area. The first procedure was based on the integration of unsupervised and supervised classification methods, widely used in the field of remote sensing, while the second one on the overlay technique, simply carried out within the frame of a Geographical Information System (GIS). The hybrid unsupervised/supervised classification method can assess the optimal number of classes in which data values from simultaneously considered parameters could be allocated, while the overlay technique is an additive procedure not taking into account existing trends in the dataset. The advantages and disadvantages of each procedure are further discussed.

Evaluation of Phytoplankton Community Indices for Detecting Eutrophic Trends in the Marine Environment.

Twenty two diversity, evenness and dominance indices based on phytoplankton community structure were examined for their sensitivity to assess eutrophic conditions. Data from two sampling sites, one eutrophic and one oligotrophic, were used as reference data-sets for evaluating the indices. McNaughton's dominance index, cell number, species number (Hill's N0), Kothe's species deficit, Odum's species per thousand individuals and Evenness E2, E3 seemed to be the most sensitive indices for discriminating between eutrophic and oligotrophic conditions. A case study was also performed using a data-set from ten stations spaced along the coastal area of the city of Rhodes, Aegean Sea, Greece to find out which of the indices were appropriate to assess different levels of eutrophication. Kothe's species deficit, Hill's N0 (species number), Margalef's and Gleason's indices have shown the highest sensitivity to resolve oligotrophic, mesotrophic and eutrophic conditions.

Quantitative assessment of eutrophication: A scoring system for characterising water quality in coastal marine ecosystems.

A scoring system based on nutrient concentrations was developed to assess coastal water quality according to the trophic level. Three nutrient data sets from eutrophic, mesotrophic and oligotrophic waters were used as the reference information for setting up a semi quantitative water quality scale (from 0 to 5) to express different nutrient loadings. The validity and sensitivity of the method was applied to a number of stations spaced out along the coastal area of Rhodes (Greece). A score for each nutrient/sampling site was calculated and the scorecard formed, was the data matrix used for numerical classification of the stations. The results showed (a) good discrimination between cutrophic, mesotrophic and oligotrophic waters (b) nitrate among the nutrients showed the maximum sensitivity in characterising pollution levels. The reference data sets used for assessing eutrophication levels ensured the objectivity of the method. The proposed method is described step-by-step and it is suggested that the method can be further adapted to describe other forms of pollution becoming a useful quantitative technique in coastal management practices.

Application of multicriteria choice-methods in assessing eutrophication.

Multicriteria choice-methods, often used in policy analysis, were examined as a methodological procedure for eutrophication assessment. Multicriteria analysis ranked the sampling sites along two coastal areas, according to nutrient and chlorophyll concentrations. Three levels of nutrient loading were revealed, characterizing eutrophic, mesotrophic and oligotrophic waters. These results have been compared to station grouping based on multivariate analysis which indicated similar trends. Multicriteria choice-methods were shown to be an effective methodological tool in assessing eutrophication. In addition, this approach is compatible with multicriteria methods applied on policy-making and therefore the problem of eutrophication can be integrated with plan and project evaluation in environmental management.

Scaling methods in assessing environmental quality: A methodological approach to eutrophication.

The identification of pollution levels by numerical classification-ordination and the statistical confirmation of the detected trends-were attempted in a eutrophication assessment study. Special emphasis was placed on the importance of data scaling and the selection of a distance coefficient that would accentuate discrete states within the system. Among metric, binary and ordinal variable scaling, ordinal numbers showed the maximum sensitivity in discriminating pollution levels; the observed trends were further enhanced by using the absolute distance coefficient as a resemblance measure. The eutrophic patterns identified were statistically confirmed by a non-parametric permutation test. Finally a step-by-step multivariate procedure is proposed for assessing environmental quality in aquatic ecosystems.

Environmental characteristics in oligotrophic waters: Data evaluation and statistical limitations in water quality studies.

Standard statistical tests of nutrient variability in the euphotic layer of an oligotrophic system in the S.E. Aegean Sea were performed. Practical problems resulting from data handling, such as high errors associated with low concentrations, nonlinearity and interaction among variables were examined. The practical problems in the analysis of environmental data, arising from statistical limitations were considered: linear correlations between chlorophyll α and nutrients were found to be significant only for ammonia, and the multiple regression model was found to be of limited value as a tool for a description of the system. By contrast, principal component analysis contributed significantly to the interpretation of each variable. The difficulties arising from the use of statistical methodology, and particularly the limited goodness-of-fit of the regression models, are discussed in relation to the suitability of oligotrophic waters as 'control sites' in eutrophication studies.

Use of multiple criteria for eutrophication assessment of coastal waters.

The quality assessment of coastal waters of a tourist resort, on the basis of water quality criteria was attempted by using different quantitative approaches. Five variables related to eutrophication, that is nitrate, nitrite, ammonia, phosphate and chlα were analyzed. Graphical methods were applied to all variables as well as unvariate statistical methods on the total inorganic nitrogen. Cluster analysis based on the five variables was also applied as an approach for numerical classification of the coastal waters. Comparison between the unvariate and multivariate methods used, was attempted to assess the validity of the procedures. The suitability of the methods used in coastal water management is also discussed.

Patterns of dark(14)CO 2 incorporation by natural marine phytoplankton communities.

The rates of dark(14)CO2 fixation by natural phytoplankton communities growing in eutrophic and oligotrophic waters were studied with short-term in situ experiments. Three aspects were investigated: (1) the time course incorporation of(14)CO2 in darkness, (2) the depth variability in dark(14)CO2 fixation, and (3) the variability in(14)CO2 fixation within a year. The highest dark(14)CO2 incorporation rates were observed during the first interval of incubation (20 min) after which they approached a constant rate with time. The observed differences in dark(14)CO2 fixation rates between populations from different depths were associated with differences in species composition as well as with physiological differences caused by exposure to different illumination conditions prior to their exposure to darkness. Autocorrelation coefficients were computed for the analysis of variability of dark(14)CO2 fixation rates within a year. It was suggested that dark(14)CO2 incorporation might be a periodic phenomenon depending mainly on the productive capacity of the phytoplankton community.

Physiological effects of hydrocarbons on the marine diatomCyclotella cryptica.

Effects of hydrocarbons on the marine diatomCyclotella cryptica have been studied in laboratory experiments. Low hydrocarbon concentrations (100 µg· l(-1)) stimulate growth whereas higher concentrations (l mg· l(-1)) inhibit growth. The aromatics are most toxic among the hydrocarbons, whereas the paraffins do not seem to have any serious effect on growth or photosynthesis of the algae. Both aromatic and paraffin fractions affected the chlorophyll a, protein, and sugar contents of the cells. Toxicity levels were affected by the presence of dissolved organic material in the medium. Studies on the ultrastructure ofC. cryptica have shown that paraffins affect the thickness of the cell wall.

Uptake of hydrocarbons by the marine diatomCyclotella cryptica.

The accumulation of exogenous hydrocarbons by the marine diatomCyclotella cryptica grown in culture has been studied using gas chromatography. Exposure of the alga to paraffins for 10 days results in accumulation of n-alkanes having between C13 and C16 carbon atoms. The C16 level in the accumulated fraction is twice as high as that in the original oil.