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611.
Many Gulf of Mexico estuaries have low ratios of water volume to bottom surface area, and benthic processes in these systems
likely have a major influence on system structure and function. The purpose of this study was to determine the spatiotemporal
distribution of biomass and community composition of subtidal benthic microalgal (BMA) communities in Galveston Bay, TX, USA,
compare BMA community composition and biomass to phytoplankton in overlying waters, and estimate the potential contribution
of BMA to the trophodynamics in this shallow, turbid, subtropical estuary. The estimates of BMA biomass (mean = 4.21 mg Chl
a m−2) for Galveston Bay were within the range of the reported values for similar Gulf of Mexico estuaries. BMA biomass in the
central part of the bay was essentially homogeneous, whereas biomass at the seaward and upper bay ends of the transect were
significantly lower. Peridinin, fucoxanthin, and alloxanthin were the three carotenoids with the highest concentrations, with
fucoxanthin having the highest mean concentration (1.82 mg m−2). The seaward and landward ends of the transect differed from the central region of the bay with respect to the relative
abundances of chlorophytes, cyanobacteria, and photosynthetic bacteria. Benthic microalgal community composition also showed
a gradual shift over time due to changes in the relative abundances of photosynthetic bacteria, cryptophytes, dinoflagellates,
and cyanobacteria. Major changes in community composition occurred in the spring months (March to April). On an areal basis,
BMA biomass in Galveston Bay occurred at minor concentrations (16.5%) relative to phytoplankton. Furthermore, the concentrations
of carotenoid pigments for phytoplankton and BMA (fucoxanthin, alloxanthin, and zeaxanthin) were correlated (r = 0.48 to 0.61), suggesting a close linkage between microalgae in the water column and sediments. The contribution of BMA
to the primary productivity of the deeper waters (>2 m) of Galveston Bay is probably very small in comparison to shallower
waters along the bay margins. The significant similarities in the community composition of phytoplankton and BMA illustrate
the potential importance of deposition and resuspension processes in this turbid, shallow estuary. 相似文献
612.
Macrofaunal Spatial Patterns in Relationship to Environmental Variables in the Richibucto Estuary,New Brunswick,Canada 总被引:1,自引:0,他引:1
Estuarine macrobenthos respond to a variety of environmental gradients such as sediment type and salinity, and organic enrichment.
A relatively new influence, organic loading from suspended bivalve culture, has the potential to alter this response. A study
on soft-bottom macrobenthic communities was carried out in the Richibucto estuary (46°40′N, 64°50′W), New Brunswick, Canada,
with samples collected from 18 stations in late September and early October 2006. The site consisted of a large tidal channel
originating upstream in a small river. The channel was punctuated by bag culture of oysters along its length. A total of 88
species were recorded. The mean values of abundance, species richness, and diversity (H′) of macrofauna were 11,199 ind. m−2 (ranged from 4,371 to 19,930 ind. m−2), 23.4 species grab−1 and 3.29 grab−1, respectively. In general species richness and H′ increased from the upper estuary to the estuarine mouth. Multivariate analyses clearly exhibited the spatial distribution
in community structure, which coincided with the locations along the estuary (the upper, the lower and the mouth), as well
as inside and outside the channel. Species richness and diversity H′ showed strong positive correlations with salinity (21.2–25.2 ppt), and abundance was positively correlated with water depth
(1.0–4.5 m). Abundance and species richness were negatively correlated with both of silt–clay fraction (3.3–24.8%) and sorting
(σI). Species richness was also negatively correlated with organic content (1.9–12.7%). The BIO-ENV analyses identified silt–clay
fraction, σI and salinity as the major environmental variable combination influencing the macrofaunal patterns, and silt–clay fraction
as the single best-correlated variable. 相似文献
613.
614.
Florencia Botto Agustina Mendez-Casariego Macarena Valiñas Oscar Iribarne 《Estuaries and Coasts》2008,31(1):134-143
We show that, as previously described, there are conflicts between areas used by people and shorebirds. However, we propose
that burrowing organisms add complexity to the shorebird–human interaction that should be taken into account for management
and conservation. This is because SW Atlantic mudflats are dominated by high densities (up to 60 crabs m−2) of a strong bioturbator, the burrowing crab Neohelice granulata (=Chasmagnathus granulatus). These crabs affect the habitat use and foraging performance of shorebird species. The two-banded plover Charadrius falklandicus feed more in burrow areas whereas the yellowlegs Tringa spp. and the white-rumped sandpiper Calidris fuscicollis tend to avoid burrow areas. We evaluated the effect of human recreational activities on shorebirds, taking into account shorebird–crab
interaction, during shorebird migratory periods (November to April) of 2001, 2002, and 2003. This study was performed at the
Mar Chiquita coastal lagoon (37° 40′ S, Argentina). Results showed that people only rarely used the extensive soft bottom
intertidals dominated by burrowing assemblages of N. granulata because the soft sediments make walking difficult. Therefore, human impact is reduced for the two-banded plover. However,
for several migratory shorebirds that also avoid burrow areas, these areas act as suboptimal alternative areas when human
impact is important in their preferred habitats. When human activity is low, shorebirds remain foraging in the area but they
decrease their feeding intakes. The extensions of burrow areas differ among estuaries and are likely to generate between-estuaries
differences as stopover sites for shorebirds. Also, other species that form large burrowing assemblages can have a similar
impact on shorebird–human interactions. 相似文献
615.
We developed light requirements for eelgrass in the Pacific Northwest, USA, to evaluate the effects of short- and long-term
reductions in irradiance reaching eelgrass, especially related to turbidity and overwater structures. Photosynthesis-irradiance
experiments and depth distribution field studies indicated that eelgrass productivity was maximum at a photosynthetic photon
flux density (PPFD) of about 350–550 μmol quanta m−2 s−1. Winter plants had approximately threefold greater net apparent primary productivity rate at the same irradiance as summer
plants. Growth studies using artificial shading as well as field monitoring of light and eelgrass growth indicated that long-term
survival required at least 3 mol quanta m−2 day−1 on average during spring and summer (i.e., May-September), and that growth was saturated above about 7 mol quanta m−2 day−1. We conclude that non-light-limited growth of eelgrass in the Pacific Northwest requires an average of at least 7 mol quanta
m−2 day−1 during spring and summer and that long-term survival requires a minimum average of 3 mol quanta m−2 day−1. 相似文献
616.
主要论述传统的人口分布专题地图方法及其不足,阐述了人口分布与土地利用之间的关系,运用人口在不同用地类型上的分配的理论,模拟人口分布,根据辽阳市的土地利用情况以及人口数字准备来绘制人口分布图。 相似文献
617.
单人智能测绘系统主要由野外用加固型便携式计算机、高精度GPS接收机、专业软件组成,可以实现单个测量员承担全流程测量作业,高效地进行成图与更新。系统集成创新了现代测绘技术手段,其精度适用于各种不同比例尺地图的测绘与更新,成为信息化测绘体系中的现代测绘技术装备之一。 相似文献
618.
619.
620.
指出了具有复杂分布的随机量的总体熵的估计问题,首次给出了估计熵的最小截断误差限.推导了样本熵的近似估计公式,引入最优窗宽、全局最优窗宽的算法,首次解决了样本熵的估计值不惟一的问题. 相似文献