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1.
Oxygen air-water gas exchange was measured using floating chambers in two shallow tidal estuaries of differing bathymetry and local terrain, near Waquoit Bay, Massachusetts (United States). The specific chamber design permitted measurements of gas flux in 15 min, allowing analysis of the relationship with wind speed and tidal stage. Exchange coefficients ranged from 0.5 to 2.5 g O2·m?2 h?1 atm?1 (equivalent to piston velocities of 1.5 to 7 cm h?1) for wind speeds of 0.3 to 9 m s?1 at 10 m elevation. While the relationships for each estuary appear linear (significant linear regressions with wind speed were shown for each estuary, and the slopes were different at the 99.5% confidence level), the range of speeds differed at the two sites and an exponential function of wind speed was consistent with the combined data from both estuaries. A power function of wind speed was not an acceptable model. The exchange coefficients for our estuaries are from 57% to as low as 9% of that predicted by previously published generic equations. Because the atmospheric correction can be significant in shallow, metabolically active coastal waters, we suggest that empirically determined relationships for gas exchange versus wind for a specific estuary are preferable to the predictions of the general equations. While the floating chamber method should be used cautiously, at low winds speeds (below 8 m s?1) and in slowly flowing waters, it provides a convenient approach for quantifying these site-specific differences. The differences, especially those between shallow sheltered systems and the open waters best fit by some published relationships, are ecologically important and do not appear yet to be measurable by other methods. 相似文献
2.
We developed generalised additive models (GAMs) to estimate standardised time-series of population abundance indices for assessment purposes and to infer ecological and behavioural information on northern Benguela hakes, Merluccius capensis and M. paradoxus, using haul-by-haul commercial trawl catch-rate data as proxies for hake densities. The modelling indicated that individual ship identifiers should be used rather than general vessel characteristics, such as vessel size. The final models explained 79% and 68% of the variability in the commercial catch rates of M. capensis and M. paradoxus, respectively. The spatial density patterns were consistent and confirmed existing knowledge about these species in the northern Benguela system. Furthermore, seasonal migration patterns were described for the first time and were found to correspond to the known spawning areas and seasons for M. capensis and M. paradoxus. Spatial density patterns were validated using the geostatistical modelling results of fisheries-independent trawl survey data. Improved understanding of the relationships between fleet dynamics and fish movement can be achieved by taking into consideration the present catch-rate model and spatial and seasonal distribution maps. We conclude that the yearly standardised CPUE time-series are problematic as proxies for total stock abundance because of spatial coverage issues. Consequently, such CPUE data should not be used for stock-size assessments and fisheries advice concerning northern Benguela hakes until this is solved. We generally recommend the exclusion of standardised CPUE time-series from stock assessments when important and changing parts of the stock distribution cannot be targeted by the fishery, such as due to closed areas or seasons. 相似文献
3.
Andreas Pack Katrina Kremer Nina Albrecht Klaus Simon Andreas Kronz 《Geochemical transactions》2010,11(1):4
Background
In aerodynamic levitation, solids and liquids are floated in a vertical gas stream. In combination with CO2-laser heating, containerless melting at high temperature of oxides and silicates is possible. We apply aerodynamic levitation to bulk rocks in preparation for microchemical analyses, and for evaporation and reduction experiments. 相似文献4.
一维热扩散湖模式在太湖的应用研究 总被引：2，自引：1，他引：1
利用在太湖获得的2010年8月11-28日的观测资料研究了一维热扩散湖模式在太湖的适用性,通过对比模拟进一步研究了影响太湖湖表温度模拟的主要因子。该湖模式对太湖最初的模拟结果并不理想,模拟的湖表面温度与观测有较大的系统性偏差,温度的日变化幅度与观测相比也偏小。通过分析该模式对太湖的模拟效果不理想的可能原因,针对太湖的生态环境和污染情况,设计了18个测试参数的敏感性试验,从敏感性试验的结果分析得到,适用于太湖的、依赖于湖泊类型的3个参数应做如下修改:消光系数（η0）应放大3倍,湖泊表层吸收的太阳辐射系数（β）应取0.8,粗糙长度（z0）采用公式计算得到。用新得到的适用于太湖的3个参数,模拟得到的结果与最初的模拟结果和观测资料对比,发现采用新的参数后,模拟结果比最初的模拟结果有了很大的改进,模拟的湖表温度基本接近观测,模拟的湖水垂直剖面时间序列图也跟观测吻合得较好,随之的感热、潜热通量的模拟也都与观测接近。最后,对输入湖模式的主要大气参量（太阳辐射、2 m气温及风场）±10%的误差引起的模式模拟的湖表面温度误差进行分析,结果表明该湖模式对大气强迫场的误差敏感度不高;相比之下,模拟结果对风场敏感性最小,对辐射和气温的敏感度相当。 相似文献
5.
Pascal Kremer Jan Schlüter Paolo Racca Hans-Joachim Fuchs Christian Lang 《Climatic change》2016,135(3-4):481-491
6.
JN Kathena A Kokkalis MW Pedersen JE Beyer UH Thygesen 《African Journal of Marine Science》2018,40(3):293-302
There is global interest in providing scientific advice on optimal harvesting of all commercially exploited fish stocks. Nevertheless, many commercially important stocks lack analytical assessments. Therefore, we evaluate a data-moderate stock assessment method: the stochastic surplus production model in continuous time (SPiCT). The method was applied to two Namibian stocks: (i) the data-rich Cape monkfish Lophius vomerinus, where results are compared to a new data-rich assessment using a state–space assessment model (SAM); and (ii) the data-moderate west coast sole Austroglossus microlepis, which is an important bycatch species in the Cape monkfish fishery, but currently unassessed. The information available to the data-moderate assessment is total commercial catch, commercial catch per unit effort (CPUE), and survey CPUE. SPiCT and SAM gave largely consistent estimates of relative fishing mortality (F/FMSY) and relative exploitable biomass (B/BMSY) for the Cape monkfish stock, although with some discrepancies. Differences in the biomass estimates between the two assessments suggest that further investigation is required to understand the cause, and that some caution is necessary when considering the biomass of the stock. SPiCT shows that the west coast sole may be overexploited, although the confidence bounds were too wide for a firm conclusion. Similarity in the estimates of F/FMSY for Cape monkfish in recent years, using SPiCT relative to SAM, likewise indicates the suitability of SPiCT for managing west coast sole. 相似文献
7.
青海锡铁山铅锌矿床硫同位素地球化学研究——深源与海水硫的混合 总被引：5，自引：0，他引：5
锡铁山铅锌矿床发育较为完整的喷流沉积系统,包括管道相、近喷口相、远端沉积相及各种喷流沉积岩,并有后期改造作用形成的脉状铅锌矿体。本文通过喷流沉积系统各部位硫化物硫同位素的分析,不同部位硫化物硫同位素组成不同,且规律性变化。以黄铁矿分析结果为例,网脉状石英钠长岩δ34S=+0.8‰,代表供给系统的硫化物脉2.95‰,非层状矿体4.48‰,层状矿体3.25‰,炭质片岩为+6.26‰,后期改造型铅锌矿脉为+2.93‰。代表管道相的网脉状石英钠长岩黄铁矿具有深源(幔源)的硫同位素组成,而矿体或大理岩上盘炭质片岩具有海水硫来源的特点。矿体的硫介于二者之间,更靠近炭质片岩的硫化物同位素组成,其来源可能更多受海水硫酸盐的制约,即锡铁山矿床硫具有混合来源性质,主要是海水硫酸盐的还原,部分来源于深部卤水的供给。硫的还原方式以生物细菌还原为主。层状矿体中硫同位素组成由早至晚δ34S逐渐降低,表明层状矿体成矿作用过程中,发生了生物成因的H2S的大量加入。 相似文献
8.
Patricia Kremer 《Estuaries and Coasts》1979,2(2):97-105
The impact ofMnemiopsis leidyi as a predator was studied quantitatively to determine their feeding rates on mixed natural zooplankton. These studies showed that feeding rate was independent of food concentration, but a function of both temperature and size of ctenophore. The feeding rate (liters cleared per mg dry weight per day) ranged from about 0.01 for larger ctenophores at lower temperatures (10–15°C) to about 0.1 for smaller ctenophores at higher temperatures (20–25°C). Combining these results with ctenophore biomass estimates from three years of sampling, numerical estimates were made of zooplankton mortality due to ctenophore predation. The maximum summer cropping byM. leidyi was calculated to be an average of 5–10% per day for the bay as a whole. Although substantial, this predation pressure alone does not account for the observed summer decline of zooplankton. 相似文献
9.
The availability of underwater light is a critical factor in the growth and abundance of primary producers in shallow embayments.
The goal of this study was to examine the relative importance of factors influencing light availability in this type of water
body. Many simulation models of aquatic ecosystems predict light attenuation from chlorophyll or phytoplankton stock. In the
three southern New England sites studied here, no useful relationship was found to exist between chlorophyll and KPAR (the diffuse attenuation coefficient of photosynthetically active radiation; Kirk 1994; Mobley 1994). In 40 of 53 cases,
a regression of chlorophyll versus KPAR was not statistically significant. Variation in KPAR did demonstrate a correlation to salinity, implicating a freshwater source of light attenuating material. This was true even
in a system with little freshwater inflow. Colored dissolved organic matter (CDOM) is one such terrestrial input that enters
estuaries from their watersheds and can strongly influence the availability of light to aquatic primary producers. This study
demonstrated that over 70% of the variability in the KPAR coefficient can be attributed to CDOM in the shallow estuaries studied. This illustrates the need for improved model formulations
that include CDOM in the prediction of light attenuation in shallow coastal systems. A new equation has been developed to
predict KPAR with CDOM. 相似文献
10.
Daily and annual integrated rates of primary productivity and community respiration were calculated using physiological parameters
measured in oxygen-based photosynthesis-irradiance (P-I) incubations at 8 stations throughout central and western Long Island
Sound (cwLIS) during the summer and autumn of 2002 and 2003 and the late spring of 2003. Each calculation takes into account
actual variations in incident irradiance over the day and underwater irradiance and standing stock with depth. Annual peak
rates, ±95% confidence interval of propagated uncertainty in each measurement, of gross primary production (GPP, 1,730±610
mmol O2 m−2 d−1), community respiration (Rc, 1,660±270 mmol O2 m−2 d−1), and net community production (NCP, 1,160±1,100 mmol O2 m−2 d−1) occurred during summer at the western end of the Sound. Lowest rates of GPP (4±11 mmol O2 m−2 d−1), Rc (−50±300 mmol O2 m−2 d−1), and NCP (−1,250±270 mmol O2 m−2 d−1) occurred during late autumn-early winter at the outer sampled stations. These large ranges in rates of GPP, Rc, and NCP throughout the photic zone of cwLIS are attributed to seasonal and spatial variability. Algal respiration (Ra) was estimated to consume an average of 5% to 52% of GPP, using a literature-based ratio of Ra:Rc. From this range, we established that the estimated Ra accounts for approximately half of GPP, and was used to estimate daily net primary production (NPP), which ranged from 2
to 870 mmol O2 m−2 d−1 throughout cwLIS during the study. Annual NPP averaged 40±8 mol O2 m−2 yr−1 for all sampled stations, which more than doubled along the main axis of the Sound, from 32±14 mol O2 m−2 yr−1 at an eastern station to 82±25 mol O2 m−2 yr−1 at the western-most station. These spatial gradients in productivity parallel nitrogen loads along the main axis of the Sound.
Daily integrals of productivity were used to test and formulate a simple, robust biomass-light model for the prediction of
phytoplankton production in Long Island Sound, and the slope of the relationship was consistent with reports for other systems. 相似文献