Seasonal changes in eelgrass functions: current velocity reduction,prevention of sediment resuspension,and control of sediment–water column nutrient flux in relation to eelgrass dynamics

We assessed seasonal changes in eelgrass (Zostera marina) functions, i.e., reduction of current velocity, buffering of sediment resuspension, and control of dissolved inorganic nitrogen flux between the sediments and the water column, using field observations and experiments in the Akkeshi-ko estuary, Hokkaido, Japan. We also analyzed the relationships between eelgrass traits and functions. The efficiency of the reduction in current velocity increased with the development of the eelgrass canopy. Sediment resuspension was inhibited from May to August, during which time the eelgrass canopy developed. Eelgrass controlled the NH₄ ⁺ concentration of sediment porewater through root nutrient uptake, affecting NH₄ ⁺ flux between the sediments and the water column. Fluctuations in eelgrass functions and coincident changes in dynamics resulted in seasonal changes in the eelgrass environment, which may in turn affect the dynamics of organisms inhabiting eelgrass beds, e.g., mysids and epiphytic algae. Moreover, the developed eelgrass canopy trapped a large amount of material during spring and summer, which was resuspended into the surrounding ecosystem in autumn when the canopy and its functions (i.e., reduction of current and sediment resuspension) diminished. These results suggest that seasonal changes in eelgrass functions also affect communities within marginal coastal ecosystems through the control of allochthonous resources. Handling editor: P. Viaroli     

Uncertainties in Data and Spurious Correlations Related to the Redfield Ratio

Spurious correlations is a fundamental problem in situations where the y‐variable is a function of x, such as ratios u/x versus x or u, or products, such as u × x versus x or u, or expressions such as (u–x) versus x. The theory of spurious correlations was developed more than 100 years ago and yet there are numerous papers in aquatic ecology presenting results as if they were mechanistically meaningful when they, in fact, are clearly spurious. This is specifically so in contexts related to some of the most important issues in aquatic ecology namely the question of “limiting” nutrient and the Redfield ratio, defined as either TN/TP or DIN/DIP (TN = total‐N, TP = total‐P, DIN = dissolved inorganic N, DIP dissolved inorganic P). We have demonstrated by systematic tests using randomly generated data that the patterns in spurious relationships can be identical to patterns in empirical data that have been interpretated in mechanistic terms. We have collected empirical data from the Baltic Sea, Kattegat and Skagerack and tested those data to see if spurious relationships exist. The r² ‐values vary from 0.90 (TN/TP versus TP), 0.67 (DIN/DIP versus DIN), 0.40 (DIN/DIP versus DIP) to 0.014 (TN/TP versus TN). Very little mechanistic understanding about “limiting nutrient” and/or the role of TN/TP or DIN/DIP‐ratios can be deduced from these – and similar results – because they are spurious. We have also shown that the ratios TN/TP and DIN/DIP have significantly higher coefficients of variations (CV) than TN, TP, DIN and DIP individually. This explains why these ratios generally are poor predictors in contexts of nutrient limitation and in modeling of primary production. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Assessment of nutrient limitation in Rijeka Bay, NE Adriatic Sea, using miniaturized bioassay

In this paper we consider the trophic state and ambient nutrient limitation by the trophic index (TRIX) calculation and nutrient enrichment bioassay using the diatom Phaeodactylum tricornutum at two differently eutrophicated NE coastal Adriatic locations (in the Rijeka Bay area). The first station in Rijeka Port had significantly higher concentrations of dissolved inorganic nutrients and TRIX indices (up to 7.53) than the station near Opatija. The DIN/TP ratios in Rijeka Port were lower (11.03 to 44.47) than those in Opatija (38.67 to 82.00), indicating P limitation in Opatija. The nutrient enrichment bioassays revealed P as the key limiting nutrient for the diatom growth at both sites. In addition, silica limitation was found in all water samples with the exception of the surface water samples in Rijeka Port. Nitrogen limitation was rarely evident.     

Characterization of a novel DNA damage-inducible gene of Saccharomyces cerevisiae , DIN7 , which is a structural homolog of the RAD2 and RAD27 DNA repair genes

A number of DNA damage-inducible genes (DIN) have been identified in Saccharomyces cerevisiae. In the present study we describe isolation of a novel gene, Din7, the expression of which is induced by exposure of cells to UV light, MMS (methyl methanesulfonate) or HU (hydoxyurea). The DNA sequence of DIN7 was determined. By comparison of the predicted Din7 amino acid sequence with those in databases we found that it belongs to a family of proteins which includes S. cerevisiae Rad2 and its Schizosaccharomyces pombe and human homologs Rad13 and XPGC; S. cerevisiae Rad27 and its S. pombe homolog Rad2, and S. pombe Exo I. All these proteins are endowed with DNA nuclease activity and are known to play an important function in DNA repair. The strongest homology to Din7 was found with the Dhs1 protein of S.␣cerevisiae, the function of which is essentially unknown. The expression of the DIN7 gene was studied in detail using a DIN7-lacZ fusion integrated into a chromosome. We show that the expression level of DIN7 rises during meiosis at a time nearly coincident with commitment to recombination. No inducibility of DIN7 was found after treatment with DNA-damaging agents of cells bearing the rad53-21 mutation. Surprisingly, a high basal level of DIN7 expression was found in strains in which the DUN1 gene was inactivated by transposon insertion. We suggest that a form of Dun1 may be a negative regulator of the DIN7 gene expression. Received: 30 May 1996 / Accepted: 26 September 1996     

Impacts of drinking water pretreatments on the formation of nitrogenous disinfection by-products

The formation of disinfection by-products (DBPs), including both nitrogenous DBPs (N-DBPs) and carbonaceous DBPs (C-DBPs), was investigated by analyzing chlorinated water samples following the application of three pretreatment processes: (i) powdered activated carbon (PAC) adsorption; (ii) KMnO(4) oxidation and (iii) biological contact oxidation (BCO), coupled with conventional water treatment processes. PAC adsorption can remove effectively the precursors of chloroform (42.7%), dichloroacetonitrile (28.6%), dichloroacetamide (DCAcAm) (27.2%) and trichloronitromethane (35.7%), which were higher than that pretreated by KMnO(4) oxidation and/or BCO process. The removal efficiency of dissolved organic carbon by BCO process (76.5%)--was superior to that by PAC adsorption (69.9%) and KMnO(4) oxidation (61.4%). However, BCO increased the dissolved organic nitrogen (DON) concentration which caused more N-DBPs to be formed during subsequent chlorination. Soluble microbial products including numerous DON compounds were produced in the BCO process and were observed to play an essential role in the formation of DCAcAm in particular.     

长江口及邻近海域富营养化指标原因变量参照状态的确定

河口区参照状态的确定是营养盐基准制定的核心步骤.采用参照点或观测点指标频数分布曲线法,利用长江口及邻近海域1992-2010年的调查数据,针对长江口外海区及舟山海区富营养化指标的原因变量,即无机氮和活性磷酸盐,进行参照状态值的确定.经分析,长江口外海区无机氮各季节参照状态可确定如下:春季为0.317mg/L、夏季为0.273 mg/L、秋季为0.211mg/L,活性磷酸盐各季节参照状态:春季为0.014mg/L、夏季为0.009 mg/L、秋季为0.018 mg/L;舟山海区无机氮各季节参照状态确定如下:春季为0.372mg/L、夏季为0.273 mg/L、秋季为0.441 mg/L,活性磷酸盐各季节参照状态:春季为0.020mg/L、夏季为0.018 mg/L、秋季为0.029 mg/L.     

Modeling the influence of nutrients, turbulence and grazing on Pfiesteria population dynamics

A semi-idealized marine ecosystem model, designed as a heuristic tool for exploring the population dynamics of non-inducible versus toxic forms of Pfiesteria is described. The model is based on empirical evidence suggesting that these differing functional types of Pfiesteria also differ substantially in terms of what they eat and how they utilize it to optimize their growth. Non-inducible strains are similar to other mixotrophic dinoflagellates, whereas toxic strains may consume organic matter and detritus, produce toxins and attack fish. In our model formulation we represent these differences in a simplified way: the non-inducible strain is kleptochloroplastidic and it can take up DIN, but it cannot utilize DON, whereas the toxic strain is heterotrophic, it cannot utilize DIN, but it can utilize DON directly. These differences give rise to very different impacts on prey and nutrient concentrations in our model. Under high DIN/DON ratio conditions, the non-inducible cells grew much faster and were therefore more likely to bloom, but this advantage is substantially mitigated when the DIN/DON ratio is low. A turbulence parameterization was also incorporated into our model. The effect of this was to reduce the grazing rate of Pfiesteria when turbulence levels are high. According to our model, increased turbulence is more detrimental to the toxic functional type because it grows more slowly. The further imposition of microzooplankton grazing in the model showed that top-down control effects can be very significant, which is consistent with both laboratory and field studies and the general idea that plankton blooms can only happen in the absence of substantial grazing control. In general, our model results suggest that non-toxic blooms are more likely to occur in more turbulent inorganic-nutrient rich conditions, which are often found in more open coastal and estuarine waters that are subject to high inorganic loading. In contrast, toxic blooms are more likely to occur in calm, organic-nutrient rich conditions, which are often found in shallow, protected tributaries that are subject to high organic nutrient loading. Our model results also support the idea that the absence of strong grazing pressure is a prerequisite to bloom formation for both non-inducible and toxic strains of Pfiesteria. These results are generally consistent with observed patterns of toxic Pfiesteria blooms in Chesapeake Bay, the Neuse River of North Carolina and many other coastal and estuarine environments.