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The southwestern Florida shelf marine environment has often been characterized as oligotrophic, yet these waters can support large, high biomass, persistent phytoplankton blooms, including blooms of the toxin producing dinoflagellate Karenia brevis. Little is known regarding which major nutrient potentially limits primary production in these waters as both inorganic nitrogen and phosphorus concentrations are often near the limits of analytical detection and it is difficult to estimate what percentage of the dissolved organic pool is available for phytoplankton uptake. To assess the nutrient status of phytoplankton populations on the southwest Florida shelf, this project examines the particulate nutrient stoichiometry of ambient phytoplankton assemblages from 1998-2000 as part of the ECOHAB: Florida Program. Particulate C, N, P concentrations and particulate ratios display a large range of values across the West Florida Shelf (WFS). The average particulate stoichiometry is well above the classic Redfield ratio with a geometric mean of 410C:56N:1P. Frequency percentages of particulate ratio values to total sample number binned according to potential nutrient limitation indicate that 39% (C:N) of the data have values suggesting N limitation and that from 88% (N:P) to 95% (C:P) of the data have values which suggest P-limitation. It is difficult to discern whether phytoplankton biomass is truly P-limited as related to the nutrient regime on the WFS or whether detrital contributions, which can potentially be large on this shallow shelf, are skewing the N:P and C:P ratios towards higher values. Errors which could potentially be related to the different methodologies of determining C, N and P concentrations must also be considered when interpreting the particulate nutrient ratios. The data were also analyzed as subsets to determine near-shore to offshore, latitudinal, seasonal, inter-annual and K. brevis bloom versus non-bloom trends. The near-shore to offshore transect indicates decreasing concentrations of particulate C, N, P concentrations and increasing C:N, N:P, C:P ratios with increasing distance offshore. Particulate nutrient concentrations and particulate ratio values are very similar between the Tampa Bay, Sarasota and Fort Meyers transects indicating that these latitudes are not spatially distinct with regards to these variables. There does not appear to be any relationship between the particulate C, N, P concentrations or C:N, N:P, C:P ratios and rainfall as indicated by Spearman Ranking Correlation coefficients. However, there does appear to be monthly trends across the shelf where peak particulate nutrient concentrations and particulate ratio values occur during the spring, summer and fall. The average particulate nutrient concentrations and ratios differ for each year as well as each K. brevis bloom which occurred during the study period. In summary, the particulate C, N, P concentrations and particulate nutrient ratios vary both spatially and temporally on the WFS and are potentially related to the flexibility of phytoplankton uptake kinetics in response to the varying nutrient regimes of the WFS.

The purpose of this study was to determine the limiting nutrient in a set of coastal areas and estuaries in the Baltic Sea. Although the subject as been studied for several decades, no clear consensus has been reached in the scientific community as to whether primary production is limited by phosphorus or nitrogen. A total of five coastal areas, all located on the east coast of Sweden, were assessed regarding their limiting nutrient by using three methods. The first method was applying linear regression analysis on measured TP and TN concentration together with chlorophyll-a and Secchi depth. The data was collected from sampling programs stretching back to the 1970s and 80s, studying the summer period May to September for all sites but one, were the period April to October was studied. The second method calculated the TN/TP ratio during the summer period and compared it to the Redfield ratio. Thirdly, basic mass-balance calculations were carried out, with empirical data on the external loads and calibrated with the yearly average concentration in the surface water (0–10 m). From the calculations, both the annual external and internal load of TP and TN was obtained. The different TP and TN loads were likewise tested for a correlation with the measured summer chlorophyll-a concentration and Secchi depth. The results of using linear regression analysis on measured concentrations were mostly inconclusive, as the TP and TN concentrations for all sites and most years were related to each other. Consequently both nutrients often gave equal correlation coefficients. Similarly the TP and TN loads also matched each other for most sites and years, inherently obtaining the same inconclusive, but also contradictory results, as when using the measured concentrations. The TN/TP ratio indicated, for one site that it was limited by phosphorus and another site possibly nitrogen limitation. The ratio in the other sites periodically dropped between nitrogen and phosphorus limitation over the years. Thus it was difficult to draw an overall conclusion as to what nutrient was the limiting one for all the sites. However analysing the results from the individual sites showed that three of the five sites had signs of phosphorus limitation. Two factors were deemed as being the main reasons as to why the methods did not achieve more conclusive results. The first factor was the empirical data, which varied in frequency and extent over the studied time periods and between sites, making representative concentrations difficult to calculate and evaluate. The second was the matching trends between both the concentrations and the loads of TP and TN. To achieve a better result one nutrient could be increased or decreased while one remains relatively constant. The problem with such an experiment would be controlling the inflow of nutrients from the adjacent sea. / Syftet med detta projekt var att bestämma det begränsande näringsämnet för ett antal kustområden i Östersjön. Frågan huruvida fosfor eller kväve är det begränsande näringsämnet i kustområden runt Östersjön har varit omdiskuterad under flera år och undersökts vid ett flertal tillfällen. I denna studie testades tre metoder, i fem olika kustområden, med syftet att fastställa det begränsande näringsämnet. Först användes linjär regressionsanalys med uppmätta värden på TP och TN koncentrationer tillsammans med klorofyll-a och Secchidjup. Empirisk data insamlades från övervakningsprogram där prover tagits sedan 1970- och 80-talet. Medelvärden beräknades för perioden maj till september för alla områden förutom ett, där undersöktes perioden april till oktober. Sommarmedelvärdena för TN/TP kvoten analyserades också för alla områden med avseende på Redfield kvoten. Slutligen genomfördes massbalansberäkningar med data för de externa belastningarna av TP och TN, dessa beräkningar kalibrerades sedan med uppmätta värden på koncentrationen i ytvattnet (0–10 m). Utifrån beräkningarna erhölls värden på den externa och den interna belastningen. Dessa belastningar testades med linjär regression för ett samband med de uppmätta värdena på Secchidjup och klorofyll-a. Metoden att använda linjär regressionsanalys med empiriskt uppmätta koncentrationer och djup, gav generellt ett oklart resultat. Detta var en följd av att halterna av både TP och TN i regel följdes åt, vilket fick konsekvensen att korrelationskoefficienterna för TP och TN ofta var lika stora. Samma problem uppstod för regressionsanalysen med belastningarna, då även dessa ofta följde varandra, men även motsade resultatet med koncentrationerna. Analysen av TN/TP kvoten tydde på att ett område var fosforbegränsat och ett område möjligen var kvävebegränsat. För de övriga tre områdena skiftade TN/TP kvoten under åren mellan kväve- och fosforbegränsning. De oklara resultaten gjorde det svårt att dra en övergripande slutsats. Däremot vid analysen av de enskilda områdena uppvisade tre av de fem områdena tecken på fosforbegränsning, även om detta inte kunde med säkerhet fastställas. Det var huvudsakligen två faktorer vars inverkan anses ha haft stor betydelse för det oklara resultatet. Den första faktorn var uppmätt data, vars frekvens och omfattning skiljde sig avsevärt mellan år och platser. Följaktligen försvårades beräkningarna av koncentrationerna och tillförlitligheten i hur representativa värdena var. Den andra och avgörande faktorn var de matchande trenderna hos både koncentrationerna och belastningarna. För att förbättra resultatet kan ett näringsämne ändras, medan det andra näringsämnet hålls relativt konstant. Problemet med att genomföra ett sådant experiment skulle vara att kontrollera inflödet av näringsämnen från närliggande hav.