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排序方式： 共有229条查询结果，搜索用时 15 毫秒
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C.S. Hassler J.R. DjajadikartaM.A. Doblin J.D. EverettP.A. Thompson 《Deep Sea Research Part II: Topical Studies in Oceanography》2011,58(5):664-677
This study focuses on the comparison of oceanic and coastal cold-core eddies with inner-shelf and East Australian Current (EAC) waters at the time of the spring bloom (October 2008). The surface water was biologically characterised by the phytoplankton biomass, composition, photo-physiology, carbon fixation and by nutrient-enrichment experiments. Marked differences in phytoplankton biomass and composition were observed. Contrasted biomarker composition suggests that biomarkers could be used to track water masses in this area. Divinyl chlorophyll a, a biomarker for tropical Prochlorophytes, was found only in the EAC. Zeaxanthin a biomarker for Cyanophytes, was found only within the oceanic eddy and in the EAC, whereas chlorophyll b (Chlorophytes) was only present in the coastal eddy and at the front between the inner-shelf and EAC waters.This study showed that cold-core eddies can affect phytoplankton, biomass, biodiversity and productivity. Inside the oceanic eddy, greater phytoplankton biomass and a more complex phytoplankton community were observed relative to adjacent water masses (including the EAC). In fact, phytoplankton communities inside the oceanic eddy more closely resembled the community observed in the inner-shelf waters. At a light level close to half-saturation, phytoplankton carbon fixation (gC d−1) in the oceanic eddy was 13-times greater than at the frontal zone between the eddy and the EAC and 3-times greater than in the inner-shelf water. Nutrient-enrichment experiments demonstrated that nitrogen was the major macronutrient limiting phytoplankton growth in water masses associated with the oceanic eddy. Although the effective quantum yield values demonstrate healthy phytoplankton communities, the phytoplankton community bloomed and shifted in response to nitrogen enrichments inside the oceanic eddy and in the frontal zone between this eddy and the EAC. An effect of Si enrichment was only observed at the frontal zone between the eddy and the EAC. No response to nutrient enrichment was observed in the inner-shelf water where ambient NOx, Si and PO4 concentrations were up to 14, 4 and 3-times greater than in the EAC and oceanic eddy. Although results from the nutrient-enrichment experiments suggest that nutrients can affect biomass and the composition of the phytoplankton community, the comparison of all sites sampled showed no direct relationship between phytoplankton biomass, nutrients and the depth of the mixed layer. This is probably due to the different timeframe between the rapidly changing physical and chemical oceanography in the separation zone of the EAC. 相似文献
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O2, N, P and Si net ecosystem metabolism of the Ría de Ares-Betanzos (NW Iberian upwelling system) was estimated during two 3-wk periods of contrasting summer downwelling and autumn upwelling conditions by means of a transient 2-D kinematic box model. The subtidal circulation was positive in both situations, although it was depressed during downwelling and enhanced during upwelling. Concurrently, the ría was fertilised mainly by shelf bottom waters, which introduced from 69% (under downwelling) to almost 100% (under upwelling) of the limiting N nutrients. The ría was an efficient nutrient trap: about 70% of the N nutrients that entered the embayment were retained under downwelling conditions (average flushing time, 9 days) and about 50% under upwelling conditions (average flushing time 3 days). Although the trapping efficiency was lower, the net ecosystem production (NEP) was much higher under upwelling (from 1.0±0.3 to 1.5±0.4 g C m−2 d−1), than under downwelling favourable winds (from 0.2±0.1 to 0.3±0.1 g C m−2). The stoichiometry of NEP suggests that P and N compounds recycled faster than C compounds, specially in the inner segment of the ría. The net degree of silification was twice in the inner than in the outer segment of the ría. 相似文献
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The governments around the Baltic Sea have agreed on a new set of targets for nutrient load reductions. The major motive for this is new and better knowledge about the link between nutrient loads and water transparency in different parts of the sea. The Baltic Sea Action Plan (BSAP) defines target for transparency in different marine basins, the load reductions necessary to meet transparency targets and a scheme for the distribution of the abatement burden between countries adjacent to the sea. 相似文献
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Tropical rivers display profound temporal and spatial heterogeneity in terms of environmental conditions. This aspect needs to be considered when designing a monitoring program for water quality in rivers. Therefore, the physico-chemical composition and the nutrient loading of the Upper Mara River and its two main tributaries, the Amala and Nyangores were monitored. Initial daily, and later a weekly monitoring schedule for 4 months spanning through the wet and dry seasons was adopted. Benthic macro-invertebrates were also collected during the initial sampling to be used as indicators of water quality. The aim of the current study was to investigate the physico-chemical status and biological integrity of the Upper Mara River basin. This was achieved by examining trends in nutrient concentrations and analyzing the structure, diversity and abundance of benthic macro-invertebrates in relation to varying land use patterns. Sampling sites were selected based on catchment land use and the level of human disturbance, and using historical records of previous water quality studies. River water pH, dissolved oxygen, electrical conductivity (EC), temperature, and turbidity were determined in situ. All investigated parameters except iron and manganese had concentration values within allowable limits according to Kenyan and international standards for drinking water. The Amala tributary is more mineralized and also shows higher levels of pH and EC than water from the Nyangores tributary. The latter, however, has a higher variability in both the total phosphorus (TP) and total nitrogen (TN) concentrations. The variability in TP and TN concentrations increases downstream for both tributaries and is more pronounced for TN than for TP. Macro-invertebrate assemblages responded to the changes in land use and water quality in terms of community composition and diversity. The study recommends detailed continuous monitoring of the water quality at shorter time intervals and to identify key macro-invertebrate taxa that can be used to monitor changes of the water quality in rivers of the Mara basin as a result of anthropogenic changes. 相似文献
7.
Brenda Moraska Lafrancois Suzanne Magdalene D. Kent Johnson 《Journal of Paleolimnology》2009,41(4):603-622
Long-term water quality monitoring data from two riverine lakes in the Upper Mississippi River basin, Lakes St. Croix and
Pepin, were analyzed to compare the long-term average water quality conditions and land use distributions, water quality trends
and loads at lake inlets and outlets, trends from long-term versus short-term monitoring records, and the ability of paleolimnological
cores to accurately infer lake water quality conditions. During the 1976–2004 period, the long-term average concentrations
of nutrients, suspended solids, and chlorophyll-a were consistently lower at the Lake St. Croix inlet versus the Lake Pepin inlet, which drains a greater proportion of urban
and agricultural runoff. Despite these differences, nutrient trends were similar at the inlets to both lakes; reductions in
total phosphorus and ammonium concentrations were attributed to improvements in point source technologies, whereas increasing
nitrate concentrations were attributed to both point source changes and nonpoint source increases. Despite improvements in
several water quality variables, nitrate concentrations are increasing in both lakes, sediment trends indicate persistent
nonpoint source inputs to Lake Pepin, and current total phosphorus concentrations remain well above pre-1950s levels in both
lakes. Since urban development and agriculture are increasing in the Lake St. Croix and Lake Pepin Watersheds, continued point
source regulation and additional nonpoint source control efforts will be needed to further improve water quality in these
lakes. The 1976–2004 trends for most water quality variables were similar at inlet versus outlet sites on Lake St. Croix.
Trends at Lake Pepin inlet versus outlet sites were less similar, but data availability limited the comparison to the 1993–2003
period. While the truncated data record highlighted short-term trends in both lakes, the full data record was most useful
for exploring general patterns in water quality. Length of monitoring record affected our ability to detect trends at the
inlets to both lakes, and altered the magnitude of detected trends. During the two decades of the 1980s and 1990s, paleolimnological
estimates of retained phosphorus loads were similar to those estimated from recent water quality monitoring. These similarities
support the use of paleolimnological approaches to infer past water quality conditions in Lakes St. Croix and Pepin.
This is one of eight papers dedicated to the “Recent Environmental History of the Upper Mississippi River” published in this
special issue of the Journal of Paleolimnology. D. R. Engstrom served as guest editor of the special issue. 相似文献
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《Marine Policy》2017
Heavy loads of the nutrients nitrogen and phosphorus cause severe damage in many waters in the world. Nutrient trading markets where capped firms can buy and sell nutrient load credits have been established in several countries in order to achieve certain nutrient reduction targets at minimum costs for society. The availability of multifunctional nutrient abatement measures that simultaneously reduce loads of both nutrients, such as wetland construction, raises the issue of credit stacking, i.e. whether a firm constructing the wetland should earn credits for both nutrients. This article examines theoretically and empirically the implications of establishing alternative nutrient trading market designs (markets with and without credit stacking, a market for a bundled payment of nutrients, and separate markets for either nutrient) for total costs and achievement of stipulated nutrient reduction targets for the Baltic Sea. The results show that the total abatement cost of achieving reduction targets of both nutrients is always lowest if a market design with credit stacking is established, that markets without credit stacking result in higher abatement cost and nutrient abatement in excess of the reduction targets, and that none of the single nutrient market systems is able to generate the required abatement of both nutrients. The application to the Baltic Sea shows that the total abatement cost can be 20% higher when credit stacking is not allowed than when it is allowed. 相似文献