Determining the nitrogen (N) status of phytoplankton is important for understanding primary production and N cycling in marine ecosystems. We assayed transcript levels of the N regulatory gene ntcA to assess the physiological N status of Synechococcus populations exposed to different N regimes in the meso-to oligotrophic Gulf of Aqaba, Red Sea. Synechococcus populations were N sufficient even in low-N environments when the ratio of dissolved nitrogen to phosphorus indicated that overall phytoplankton biomass was constrained by N. Ammonium supported Synechococcus N requirements under most conditions, but during a massive spring bloom in April 2000 alternative N sources were utilized. Evidence from ntcA clone libraries indicates changes in the genotypic makeup of Synechococcus populations under different N regimes, suggesting that the Synechococcus genotypes present in N-poor waters were those adapted for life in these environments. Thus, the success of Synechococcus in the open oceans is likely to be at least partially due to the selection of genotypes suited to life under prevailing N conditions rather than to prolonged manifestation of the N stress response, mediated by ntcA, in less well-adapted genotypes.Low photosynthetic biomass, prevalent in vast oligotrophic expanses of the world's oceans, is often attributed to 1 Corresponding authors (anton.post@huji.ac.il, dlindell@mit.edu).
This study focuses on the seasonal changes in the Gulf of Aquaba, Red Sea, in nitrite concentration and their relationship with phytoplankton activity, which is mainly controlled by an alternation of water-column stratification with vertical mixing. Within the euphotic zone, during thermal summer stratification, nutrient depletion was severe, and no nitrite could be detected in the upper 70 m. However, during stratification, nitrite was always associated with the nutriclines and formed a deep maximum at the bottom of the euphotic zone. In contrast, nitrite accumulated in the mixed water column during winter, closely paralleling the development of phytoplankton biomass. In the Gulf of Aqaba, maximum nitrite accumulation occurred when winter mixing reached its greatest depth, which in turn was coincident with the height of the phytoplankton spring bloom. Thus, our field data suggest that accumulation of nitrite is associated with nutrient-stimulated phytoplankton growth. This hypothesis was supported by nutrient-enrichment bioassays performed concomitantly: only when phytoplankton growth was stimulated by nutrient additions, did nitrite accumulate in the water. In the bioassays, the time-course of nitrite accumulation closely paralleled the development of phytoplankton biomass during the incubation period. We therefore suggest that the accumulation of nitrite in the mixed water column during winter is due to excretion by algal cells. Our field and experimental data show that between 10 and 15% of the total amount of nitrogen entering the mixed-water column is released as nitrite by phytoplankton. Further, our field and experimental data support the hypothesis that nitrite excretion by phytoplankton has a significant role in the formation of the deep nitrite maximum (DNM) during stratification in summer. In the bioassays, phytoplankton cells excreted nitrite even when ammonia was the nitrogen source. This indicates a so far unrecognised physiological pathway involved in nitrite excretion by phytoplankton cells. KEY WORDS: Nutrients · Nitrogen species · Nitrite · PhytoplanktonResale or republication not permitted without written consent of the publisher Mar Ecol Prog Ser 239: 233-239, 2002 In the well-oxygenated water column of the Gulf of Aqaba, the dissimilatory reduction of nitrate to nitrite by denitrifying bacteria is likely to be negligible. Thus, we consider the following processes as potentially responsible for the generation and consumption of ambient nitrite in the Gulf of Aqaba: (1) Excretion of nitrite during nitrate reduction, i.e. incomplete assimilatory reduction of nitrate by phytoplankton and bacteria (Vaccaro & Ruyther 1960, Wada & Hattori, 1971, Miyazzaki et al. 1973, Miyazzaki et al. 1975, Kiefer et al. 1976, Herbland & Voituriez 1979, Olson 1981a, Dore & Karl, 1996b, Collos 1998. (2) Ammonium oxidation to nitrite by autotrophic nitrifying bacteria (Brandhorst 1959, Miyazzaki et al. 1975, Olson 1981a,b, Ward 1986, Dore & Karl 1996b, Enoksson et al. 1996. (3) Nitrite assimilation by p...
Rainwater is considered a dependable source for domestic purposes within rural areas in Palestine. Harvested rainwater stored in cisterns is used to leverage deficits from municipal water supplies. Harvested rainwater in areas surrounded with industrial and agricultural activities is usually contaminated with heavy and trace metals. To study the effects of human exposure to heavy and trace metals, 74 harvested rainwater samples of rain-fed cisterns were collected from different localities in the Yatta area of Palestine in the months of January and February of 2016. The water samples were analysed for Ca, Mg, Al, Fe, K, Na, Ag, Li, Co, Ba, Bi, Sr, Ga, V, Rb, Mo, Beand Tl elements utilizing ICP-MS (inductively coupled plasma mass spectrometry). The selected trace metals were found within the concentration limits of the acceptable values, in accordance with WHO and Palestinian standards, except for K and Al, which were found above the allowed limits. The potential risks of the selected trace metals on the health of the local residents, as well as the possible sources of such heavy metals, were also studied. The Chronic daily intake (CDI) of each metal and health risk indexes (HRI) were calculated for both adults and children residents. The oral ingestion pathway was studied, including exposure via drinking water. The values for CDI were found in the descending order of: Ca > Mg > Na > K > Sr > Fe > Al > Ba > Li > V > Rb > Ag > Mo > Ga > Co > Bi > TI > Be. The values of HRI were below 1 for most of the selected heavy metals, expect for Li for children, indicating potential health risk. The study also predicted that the local residents have a higher chance of developing cancer in their lifetime, especially children, with respect to the carcinogenic risk (CRing) values for Na, Mg, Al, Ba, K, Ca, Fe and Sr, which were greater than standardized limits (>10−6). The rest of the selected elements were within the acceptable limit in the five different studied locations. Furthermore, univariate, multivariate and statistical analysis depending on one-way ANOVA, inter-metal correlation, cluster analysis (CA) and principal component analysis (PCA) results revealed that geogenic and anthropogenic activities were major sources of drinking water contamination by heavy metals in the Yatta area.
Heavy metal contamination of the groundwater of south West Bank in Palestine was assessed. The groundwater samples were analyzed for different trace heavy metals (Tl, Pb, Bi, Cr, Mn, Co, Ni, Cu, Zn, Mo, Ag, and Cd), and Al content by ICP/MS. This study was conducted to determine the water quality of ground water which is used for drinking in the study area. Water samples from ten groundwater wells were obtained in four different dates of the year (October 2012, November 2012, March 2013, and April 2013). Three water samples were obtained from each well for each sampling date. A total of 120 water samples were collected from the ten wells. The samples were analyzed for their pH, electrical conductivity, total dissolved solids, and different trace metals content. The pH, electrical conductivity, and total dissolved solids of all water samples were found to be within the US Environmental protection Agency limits. Results showed that Pb, Al, Cr, Co, Ni, Cu, Zn, and Mo were detected in all water samples analyzed in this study, while Tl, Bi, Mn, Ag, and Cd were detected in 80%, 88%, 90%, 75%, and 95% of the water samples analyzed in this study, respectively. In general, 93% of all samples analyzed contained one or more of the 13 metals studied each in varying concentration. Furthermore, results showed that the concentration of Cr, Mn, Ni, Cu, Zn, and Mo is within the allowed WHO limits in drinking water. However the concentration of Pb Cd, and Al are found to be higher than the allowed WHO limits in 40%, 8%, and 33% of the water samples analyzed in this study, respectively. Statistical analyses showed that concentrations of the metals studied in this study vary significantly between the ten ground water wells, indicating that the wells analyzed in this study is different from each other in terms of heavy metal content. Additionally, from the statistical results obtained, it was found that there is a significant difference in the concentration of the metals in each well for the four sampling times (October 2012, November 2012, March 2013, and April 2013), denoting that metal concentration in the wells vary significantly with sampling time. The results obtained from this study suggest a possible risk to the population of the study area given the toxicity of these metals, and the fact that for many people in the study area, ground water is a main source of their water supply.
Rainwater samples harvested for drinking from the west part of Hebron (south of West Bank in Palestine), the largest city in the West Bank, were analyzed for the content of different trace heavy metals (Cr, Mn, Co, Ni, Cu, Zn, Mo, Ag, Cd, Bi, and Pb) by inductively coupled plasma mass spectrometry (ICP-MS). This study was conducted to determine the water quality of harvested rainwater used for drinking of south West Bank (case study, Hebron area). A total of 44 water samples were collected in November 2012 from 44 house cisterns used to collect rainwater from the roofs of houses. The samples were analyzed for their pH, temperature, electrical conductivity, total dissolved solids, and different heavy metal contents. The pH of all water samples was within the US Environmental Protection Agency limits (6.5-8.5), while some water samples were found to exceed the allowed WHO limit for total dissolved solids (TDSs) in drinking water. Results showed that concentrations of the heavy metals vary significantly between the 44 samples. Results also showed that the concentration of five heavy metals (Cr, Mn, Ni, Ag, and Pb) is higher than the WHO limits for these heavy metals in drinking water. Overall, our findings revealed that harvested rainwater used for drinking of this part of south West Bank is contaminated with heavy metals that might affect human health.
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