首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献，搜索用时 31 毫秒
1.
Estuarine rearing has been shown to enhance within watershed biocomplexity and support growth and survival for juvenile salmon (Oncorhynchus sp.). However, less is known about how growth varies across different types of wetland habitats and what explains this variability in growth. We focused on the estuarine habitat use of Columbia River Chinook salmon (Oncorhynchus tshawytscha), which are listed under the Endangered Species Act. We employed a generalized linear model (GLM) to test three hypotheses: (1) juvenile Chinook growth was best explained by temporal factors, (2) habitat, or (3) demographic characteristics, such as stock of origin. This study examined estuarine growth rate, incorporating otolith microstructure, individual assignment to stock of origin, GIS habitat mapping, and diet composition along ~130 km of the upper Columbia River estuary. Juvenile Chinook grew on average 0.23 mm/day in the freshwater tidal estuary. When compared to other studies in the basin our growth estimates from the freshwater tidal estuary were similar to estimates in the brackish estuary, but ~4 times slower than those in the plume and upstream reservoirs. However, previous survival studies elucidated a possible tradeoff between growth and survival in the Columbia River basin. Our GLM analysis found that variation in growth was best explained by habitat and an interaction between fork length and month of capture. Juvenile Chinook salmon captured in backwater channel habitats and later in the summer (mid-summer and late summer/fall subyearlings) grew faster than salmon from other habitats and time periods. These findings present a unique example of the complexity of understanding the influences of the many processes that generate variation in growth rate for juvenile anadromous fish inhabiting estuaries.  相似文献   

2.
Estuarine habitat occupied by Alligator mississippiensis, a primarily freshwater species, is spatially and temporally heterogeneous largely due to a salinity gradient that fluctuates. Using long-term night light survey data, we examined seasonal patterns in alligators’ habitat use by size classes in midstream and downstream estuary zones of Shark River, Everglades National Park, in southern Florida. We observed predominantly large-sized alligators (total length?≥?1.75 m); observations of alligators in the small size classes (0.5 m?≤?total length?<?1.25 m) were rare especially in the higher-salinity downstream zone. The density of alligators in the downstream zone was lower than that of the midstream zone during the dry season when salinity increases due to reduced precipitation. Conversely, the density of the large size alligators was higher in the downstream zone than in the midstream zone during the wet season, likely because of reduced salinity. We also found a significant declining trend over time in the number of alligators in the dry season, which coincides with the reported decline in alligator relative density in southern Florida freshwater wetlands. Our results indicated high adaptability of alligators to the fluctuating habitat conditions. Use of estuaries by alligators is likely driven in part by physiology and possibly by reproductive cycle, and our results supported their opportunistic use of estuary habitat and ontogenetic niche shifts.  相似文献   

3.
This study aims to investigate the effects of region and three regional dominated mangrove species (Avicennia marina, Aegiceras corniculatum and Kandelia candel) on the distribution of inorganic nitrogen and phosphorus. Measurement of the inorganic nitrogen and phosphorus and enzymatic activities was carried out in soils covered by three mangrove species in the Quanzhou Bay estuarine wetlands, a typical coastal wetland in China. Species with a higher biomass in upstream and midstream absorb more nitrogen from soils, and the retention of the available phosphorus in the soils of different regions causes the regional variation of phosphorus. In areas dominated by A. marina, nitrate nitrogen is lower while available phosphorus is higher. Meanwhile, nitrate nitrogen and available phosphorus are higher in the soils covered by K. candel. Moreover, all three species affect the elemental and enzymic stoichiometry. The mangrove species influences the diversity of the elemental and enzymic stoichiometric relationship through differential microenvironments, which induce the biodiversity of wetland ecosystems. Thus, this study may facilitate a better understanding of the transformation ability of mangroves to nitrogen and phosphorus and will therefore be beneficial for providing a basis for the ecological restoration of estuarine wetlands.  相似文献   

4.
The assemblages of fossil charophyte fructifications from the La Huérguina Formation at the La Huérguina stratotype and the Las Hoyas section, along with some other samples from isolated outcrops are composed of Atopochara trivolvis var. triquetra, Globator maillardii var. trochiliscoides, Globator maillardii var. biutricularis var. nov., Clavator harrisii var. reyi, Ascidiella cruciata and Mesochara harrisii. Some reworked utricles of Ascidiella iberica var. iberica were also found. The in situ assemblage belongs to the Cruciata-Paucibracteatus Biozone, which is Late Barremian–Early Aptian in age. These results confirm that the entire deposition of the La Huérguina Formation took place within this biozone and not earlier, as previously thought. The top of the unit can be limited to the uppermost Barremian with biostratigraphic data from ostracods. Globator maillardii var. biutricularis var. nov. is defined as the end form for the Globator lineage according to present knowledge. It is characterised by its unique utricle morphology, showing a basal ring representing a second, external utricular layer. This layer shows a primitive structure, reminiscent of G. maillardii var. mutabilis, in contrast to the internal utricle, which is more derived and similar to G. maillardii var. trochiliscoides. In comparison with other non-marine formations of the same age in the Iberian Chain and in Europe, the charophyte assemblages from the La Huérguina Formation appear to be relatively poor and monotonous, suggesting that some of the species found elsewhere never reached this part of the basin owing to the brief development of non-marine facies there. The main differences in composition between the samples studied are indicative of the palaeoecological conditions. Atopochara trivolvis triquetra was found to be dominant in shallow lacustrine facies and Globator maillardii var. trochiliscoides and var. biutricularis are associated with temporary lakes from a well-drained palustrine area. Clavator harrisii and Mesochara harrisii thrived on floodplains whereas Ascidiella cruciata grew in palustrine environments with significant edaphic activity.  相似文献   

5.
《Organic Geochemistry》1987,11(3):169-175
This paper discusses results from laboratory experiments designed to study possible effects of migration on the distribution of biomarkers in oils and source rock extracts and on the various biomarker indicators which have been used to discuss the source, maturity, biodegradation and depositional environments. The results of the study showed that lower molecular weight n-alkanes eluted from the alumina column faster than higher molecular weight n-alkanes, tricyclic terpanes faster than pentacyclic terpanes and 14β,17β steranes faster than 5α20R steranes. Gammacerane eluted extremely slowly and could be obtained almost as a pure component. Many of these observations duplicate those previously observed in nature and ascribed to migration. The evidence suggests that the effects of migration must be carefully considered when discussing biomarker-based maturity parameters of oils and source rocks. It is proposed that the biomarkers remaining in the source rock after expulsion of oil show low maturity values which might not reflect the actual maturity of the rock.  相似文献   

6.
Tidal wetlands are affected by sea level rise. In the tidal freshwater stretches of estuaries in the temperate zone, willows (Salix spp.) form tidal freshwater forests above the mean high water level. Willows tolerance to prolonged periodic flooding in riverine systems is well documented, whereas effects of tidal flooding on willows are largely unknown. Flooding stress may play a major role in regeneration failure of willows in tidal forest stands along estuarine shores, and juvenile willows might be specifically affected by partial or total submergence. To assess the tolerance of juvenile willows to tidal flooding, we conducted a mesocosm experiment with cuttings from Salix alba and Salix viminalis, which are both characteristic species for tidal freshwater forests in Europe. Cuttings originating from either fresh or brackish tidal forest stands were grown under four tidal treatments with up to a tidal flooding of 60 cm. A general tolerance to a tidal flooding of 60 cm was observed in chlorophyll fluorescence, growth rates, and biomass production in both willow species. Overall, S. alba showed higher leaf and shoot growth, whereas S. viminalis produced more biomass. S. alba with brackish origin performed worst with increasing tidal flooding, suggesting a possible pre-weakening due to stressful site conditions in tidal wetlands at the estuarine brackish stretch. This study demonstrates that juvenile willows of S. alba and S. viminalis tolerate tidal flooding of up to 60 cm. It is concluded that tidal inundation acts as a stress by causing submergence and soil anaerobiosis, but may also act as a subsidy by reestablishing aerobic conditions and thus maintaining willows performance. Therefore, we suggest investigations on Salix tidal flooding tolerance and possible effects of willows on tidal wetland accretion under estuarine field conditions.  相似文献   

7.
《Applied Geochemistry》1993,8(3):245-254
The Porphyrin Maturity Parameter (PMP), which is derived from the vanadyl porphyrin distribution, is an excellent parameter for: (1) identifying the zone of hydrocarbon generation from marine source rock extracts; and (2) determining from oils the thermal maturity of their source rocks at expulsion.The PMP is measured using a methodology which is inexpensive, reliable and faster than earlier methods, allowing it to be used as a routine exploration tool. The PMP may be a more reliable maturity indicator for marine organic matter than some conventional methods such as vitrinite reflectance. Unlike most conventional maturity parameters guided by processes other than kerogen conversion, the reactions causing PMP evolution directly monitor the generation of bitumen and the concurrent thermal degradation of kerogen.Measurements on hydrous pyrolyzates from the Monterey Formation (offshore California), source rock bitumens from the Devonian-Mississippian Bakken Shale (Williston Basin), and Miocene Monterey equivalent source strata (San Joaquin Basin, California) illustrate the method. In all cases reviewed so far, PMP begins increasing at the onset of hydrocarbon generation and increases systematically and predictably as kerogen decomposition proceeds.In oils generated from high-S marine kerogens, PMP reflects the maturity of the source rock at the time of oil expulsion, provided that the oil does not undergo subsequent reservoior maturation or mixing with in-situ bitumen.  相似文献   

8.
While many coastal ecosystems previously supported dense meadows of seagrass and dense stocks of bivalves, the impacts of overfishing, eutrophication, harmful algal blooms, and habitat loss have contributed to the decline of these important resources. Anthropogenic nutrient loading and subsequent eutrophication has been identified by some researchers as a primary driver of these losses, but others have described potential positive effects of eutrophication on some estuarine resources. The Peconic Estuary, Long Island, NY, USA, offers a naturally occurring nutrient-loading gradient from eutrophic tidal creeks in its western reaches to mesotrophic bays in the eastern region. Over 2 years, we conducted an experiment across this gradient to examine the effects of eutrophication on the growth of estuarine species, including juvenile bivalves (northern quahogs (Mercenaria mercenaria), eastern oysters, (Crassostrea virginica), and bay scallops (Argopecten irradians)) and slipper limpet (Crepidula fornicata). Water quality and phytoplankton community biomass and composition were concurrently monitored at each site, and the effects of these variables on the growth of estuarine species were analyzed with multiple regression model. Eutrophication seemed to impact shellfish through changes in the quality of food and not the quantity since the growth rates of shellfish were more often correlated with densities of specific cell types or quality of seston rather than bulk measures of phytoplankton and organic seston. Northern quahogs and eastern oysters grew maximally within eutrophic locales, and their growth was positively correlated with high densities of autotrophic nanoflagellates and centric diatoms in these regions (p?<?0.001). The growth rates of northern quahogs were also positively correlated with relative water motion, suggesting an important role for tidal currents in delivering seston to suspension feeders. Bay scallops and slipper limpets were negatively impacted by eutrophication, growing at the slowest rate at the most eutrophic sites. Furthermore, bay scallop growth was negatively correlated with densities of dinoflagellates, which were more abundant at the most eutrophic site (p?<?0.001). These results suggest that nutrient loading can have significant but complex effects on suspension-feeding molluscs with select species (e.g., oysters and clams) benefiting from eutrophication and other species performing poorly (e.g., scallops and slipper limpets). Future management approaches that seek to restore bivalve populations will need to account for the differential effects of nutrient loading as managers target species and regions to be restored.  相似文献   

9.
The growth of unstable structures was studied experimentally in layered wax models. The rheological properties of the two wax types were determined independently by a series of cylinder compression tests. Both waxes enhibited (1) a non-Newtonian stress vs strain-rate relationship (2) strain softening and (3) temperature-dependent viscosity. The stress-strain-rate relationships approximated a power-law, with stress exponents of 5 for the microcrystalline wax and 1.8 for paraffin wax.Blocks of paraffin with a single embedded layer of microcrystalline wax were deformed in two-dimensional pure shear with the layer oriented either parallel to the compressive strain axis so that it shortened and folded, or perpendicular to that axis so that it would stretch and boundinage would form. The growth rates of tiny initial disturbances were measured. The growth rates for folding and boudinage were much higher than could be accounted for by theories assuming Newtonian material properties. Theories taking non-Newtonian behaviour into account (Smith, R. B. 1975. Bull. geol. Soc. Am.86, 1601–1609; Fletcher, R. C. 1974. Am. J. Sci.274, 1029–1043) better describe the folding growth rates. Boudinage, however, grew almost three times faster than would be predicted even by existing non-Newtonian theory. A possible reason for this discrepancy is that the waxes do not exhibit steady-state creep as assumed in the theory. We, therefore, extend the theory to include strain-softening. The crucial step in this theory is the use of a scalar measure of the deformation as a state variable in the constitutive law. In this way the isotropic manifestation of strain-softening can be taken into account. The analysis shows that strain-softening can lead to greatly increased boudinage growth rates while having little influence on the growth rates of folds, which is in agreement with the experiments.  相似文献   

10.
王恩德 《地质与资源》2004,13(3):159-166
辽宁省阜新地区东北部有一片广阔的沼泽湿地区域,富有含多种动植物区系群的植被类型.然而,由于多年的河流改道、气候干燥使得原始沼泽地开始干涸.经济的发展导致湿地不断地被开发,湿地中有机物的衰减造成水禽类数量的锐减.因此,为适当地保护、规划和管理而对湿地区域进行判别并填图是十分重要的.国家已拥有许多根据航片判别的湿地图录,但这些图录中还存在着航片解译及填图过程中产生的人为误差.因为小型湿地一般不易与周围小规模的高地区别开来,所以它们可能未被绘在地形图上.卫星数据的应用提供了一种解决此问题的方法,因为计算机能够判别最小的潜在的湿地区域,这是人类裸眼所不能辨别出来的.本研究正是以此为基础的.随着一种利用陆地卫星TM数据来判别湿地的新技术的应用,对于高植被区域或水体的识别受到了更多的重视,因为这些区域成为湿地的可能性较高.所获得的结果根据地面实情并利用现有资料如地形图和航片等进行了评估.陆地卫星TM数据为湿地填图提供了一种既快捷又具成本效益的方法.在中国,所有地区的这种图像一般都可获得,并且有保存完好的历史档案,这便容许我们选择最合适的不同季节的图像进行分析.  相似文献   

11.
A depositional model of the lower Pliocene Hagul formation, which is exposed in the East Cairo district (Egypt), is proposed with more than 10 depositional cycles recognized. Field occurrence, detailed petrographic investigation and geochemical analysis revealed that the sediments within each cycle are the result of three sequential sedimentological processes: (1) alluvial sedimentation, (2) calcretization, and (3) precipitation of palustrine carbonate. It was concluded that Hagul formation has been deposited within the distal part of an alluvial plain during three successive climatic conditions: a humid climate during which alluvial sediments were deposited, a semi-arid climate with episodic precipitation which was favorable for pedogenic calcrete development, and a sub-humid climate during which groundwater level was gradually elevated and groundwater calcrete accumulated. Rising groundwater level continued until shallow wetlands covered the area and palustrine limestone was precipitated. Variations in the thickness and the nature of the host sediment, calcrete and palustrine limestone cycle suggest that each of the sedimentation processes varied from cycle to cycle.  相似文献   

12.
We demonstrate that land reclamation in estuaries is resulting in very large-scale loss of intertidal area and disconnection of stored sediment with the water column. This process is not just causing loss of estuarine ecosystem services, it is also having a major deleterious impact on the ability of estuaries to retain nutrients and trace metals. The global scale of loss of estuarine wetlands and subtidal sediments has reached the point where the impact of this loss of estuarine retention is likely to be affecting coastal seas worldwide and possibly global element cycles.  相似文献   

13.
A middle Eocene Crassostrea sp. reef near Río Turbio, southwestern Patagonia (Argentina), represents the earliest record of an oyster reef associated with estuarine facies in the southern hemisphere, and also one of the few known worldwide occurring in Paleogene rocks. The reef grew in an outer estuary environment subject to periodic changes in salinity and may have reached a maturing phase. The Río Turbio reef – by its dimensions, geometry, and substrate lithology– would have been located in a tidal channel convergence area. This reef provides new evidence suggesting that estuaries served as refuges for Crassostrea populations allowing them to disperse into fully marine environments many times throughout the Cenozoic.  相似文献   

14.
Gillichthys mirabilis population static measurements (abundance, age, and size class structures) and vital rates (growth, mortality, recruitment) were monitored on an annual basis from 2002 to 2007. Population-level metrics were used to gauge habitat quality at two study sites (a contaminated site and a reference site) in two large northern California estuaries (San Francisco and Tomales Bays). San Francisco Bay populations exhibited slower growth and higher mortality rates and contained higher amounts of contaminants than Tomales Bay. Recruitment rates were highest at contaminated sites (Stege Marsh and Walker Creek) in 3 years out of 5 years, suggesting low adult survival. This study suggests that population-level effects on a residential fish may be attributed to estuarine contamination on the US Pacific coast.  相似文献   

15.
Important parameters of estuarine variability include morphology, flushing times, nutrient loading rates, and wetland: water ratios. This variability both reflects and disguises underlying relationships between the physics and biology of estuaries, which this comparative analysis seeks to reveal, using the Gulf of Mexico (GOM) estuaries as a starting point. A question used to focus this analysis is: are the GOM estuaries unique? The GOM receives the Mississippi River, a uniquely large, world-class river, which dominates the freshwater and nutrient inflows to the GOM continental shelf, whose margins include 35 major estuarine systems. These GOM estuaries have 28% and 41% of the U.S. estuarine wetlands and open water, respectively. Within the GOM, estuarine nitrogen, phosphorus, and suspended matter loading varies over 2 orders of magnitude. Anoxic estuarine events tend to occur in estuaries with relatively slow freshwater turnover and high nitrogen loading. Compared to estuaries from other regions in the U.S., the average GOM estuary is distinguished by shallower depths, faster freshwater flushing time, a higher wetland area:open water area ratio, greater fisheries yield per area wetland, lower tidal range, and higher sediment accumulation rates. The average GOM estuary often, but not always, has a flora and fauna not usually found in most other U.S. estuaries (e.g., manatees and mangroves). Coastal wetland loss in the GOM is extraordinarily high compared to other regions and is causally linked to cultural influences. Variations in nutrient loading and population density are very large among and within estuarine regions. This variation is large enough to demonstrate that there are insufficient systematic differences among these estuarine regions that precludes cross-system analyses. There are no abrupt discontinuities among regions in the fisheries yields per wetland area, tidal amplitude and vegetation range, salt marsh vertical accretion rates and organic accumulations, nitrogen retention, or wetland restoration rates. These results suggest that a comparative analysis emphasizing forcing functions, rather than geographic uniqueness, will lead to significant progress in understanding how all estuaries function, are perturbed, and even how they can be restored.  相似文献   

16.
While it has long been known that Pacific salmon use estuarine habitat, it has proven much harder to establish that the loss of estuarine habitat results in reduced survival. We used coded-wire tagging of hatchery fish to estimate the survival from release until maturity and related this survival to several indicators of estuarine condition. We found a significant relationship between the survival of chinook salmon (Oncorhynchus tshawytscha) and the percentage of the estuary that is in pristine condition, but no significant relationship for coho salmon (Oncorhynchus kisutch). This supports field observations that chinook salmon use estuarine habitat much more than coho salmon and confirms that the loss of estuarine habitat results in lower survival of chinook salmon.  相似文献   

17.
During the transition of juveniles from fresh water to estuarine and coastal environments, the survival of Pacific salmon (Oncorhynchus spp.) can be strongly size selective and cohort abundance is partly determined at this stage. Because quantity and quality of food influence juvenile salmon growth, high rates of prey and energy acquisition during estuarine residence are important for survival. Human activities may have affected the foraging performance of juvenile salmon in estuaries by reducing the area of wetlands and by altering the abundance of salmon. To improve our understanding of the effects of wetland loss and salmon density on juvenile salmon foraging performance and diet composition in estuaries, we assembled Chinook salmon (Oncorhynchus tshawytscha) diet and density data from nine US Pacific Northwest estuaries across a gradient of wetland loss. We evaluated the influence of wetland loss and density on juvenile Chinook salmon instantaneous ration and energy ration, two measures of foraging performance, and whether the effect of density varied among estuaries with different levels of wetland loss. We also assessed the influence of wetland loss and other explanatory variables on salmon diet composition. There was no evidence of a direct effect of wetland loss on juvenile salmon foraging performance, but wetland loss appeared to mediate the effect of density on salmon foraging performance and alter salmon diet composition. Specifically, density had no effect on foraging performance in the estuaries with less than 50 % wetland loss but had a negative effect on foraging performance in the estuaries with greater than 50 % wetland loss. These results suggest that habitat loss may interact with density to constrain the foraging performance of juvenile Chinook salmon, and ultimately their growth, during a life history stage when survival can be positively correlated with growth and size.  相似文献   

18.
Detailed information on semi‐arid, palustrine carbonate–calcrete lithofacies associations in a sheetwash‐dominated regolith setting is sparse. This is addressed by studying the Lower Limestone of the Lameta Beds, a well‐exposed Maastrichtian regolith in central India. The general vertical lithofacies assemblage for this unit comprises: (a) basal calcareous siltstones and marls with charophytes, ostracods and gastropods; (b) buff micritic limestones associated in their upper parts with calcretized fissure‐fill sandstones; (c) sheetwash as fissure‐fill diamictites and thin pebbly sheets, locally developed over a few metres; and (d) sandy, nodular, brecciated and pisolitic calcretes at the top. The sequence is ‘regressive’, with upsection filling of topographic lows by increased sheetwash. Lateral lithofacies change is marked, but there are no permanent open‐water lake deposits. In topographic lows close to the water table, marshy palustrine or groundwater calcretes formed, whereas on better drained highs, brecciation and calcretization occurred. Prolonged exposure is implied, suggesting that shrinkage was the main cause of brecciation. Evidence for rhizobrecciation and other biological calcrete fabrics is sparse, contrasting with the emphasis on root‐related brecciation in many studies of palustrine lithofacies. Stable isotope (δ18O and δ13C) values are consistent with the palustrine limestones being fed from meteoric‐derived groundwater with a strong input of soil‐zone carbon. There is overlap of both δ18O and δ13C values from the various palustrine and calcrete fabrics co‐occurring at outcrop. This suggests that, in groundwater‐supported wetlands, conversion from palustrine carbonate to calcrete need not show isotopic expression, as the groundwater source and input of soil‐zone carbon are essentially unchanged. Cretaceous–Tertiary δ18O and δ13C values from palustrine lithofacies and associated calcretes appear to be strongly influenced by the inherited values from lakes and wetlands. Hydrologically closed lakes and marine‐influenced water bodies tend to result in low negative palustrine δ18O and δ13C values. During brecciation and calcretization, the degree of isotopic inheritance depends on whether or not alteration occurs in waters that are different from those of the original water body or wetland. Marked biological activity (e.g. rhizobrecciation or root mat development) during calcretization may lower δ13C values where C3 plants are abundant but, in shrinkage‐dominated systems, δ13C values will be largely inherited from the palustrine limestones.  相似文献   

19.
Wetlands constitute a part of human heritage. It has played a significant role in the development of human culture and society. More over it contains very rich components of biodiversity of local, national, and regional significance. They also provide habitat for a variety of resident and migratory waterfowl, a significant number of endangered species, and a large number of commercially important species. Mangrove wetlands are unique environments of floral-faunal assemblages, providing a complex detritus-based food-web for a number of marine and brackish water organisms. Wetlands in Bangladesh have great importance for the country’s economic, industrial, ecological, socioeconomic, and cultural aspects. There are five types of wetlands available in Bangladesh, such as saltwater wetlands, freshwater wetlands, palustrine wetlands, lacustrine wetlands, and manmade wetlands. There are 43 designated wetlands, and some are under threat from indiscriminate utilization, encroachments and reclamation, urbanization and drawbacks from agricultural development, and flood control. Almost 50% of the country’s people are directly dependent on wetlands resources. The vast majority of the poor people in the wetlands areas are dependent on wetlands resources for their nourishment. Wetlands have potential and have been recognized as a driving force for biodiversity conservation and rural socioeconomic improvement. Smart-use of wetlands can solve the ecosystems problems in the floodplain areas. A comprehensive analysis of the various issues leading to wetlands degradation is made in this study. The country needs an adequate interdisciplinary policy and political will to implement it for sustainable management and protection of wetlands and ecologically sensitive ecosystems in Bangladesh. Therefore, a reliable data bank is provided in this study to enhance the conservation measures initiated by the Government.  相似文献   

20.
As an essential nutrient for diatoms, silica plays a key role in the estuarine and coastal food web. High concentrations of dissolved silica (DSi) were found in the seepage water of tidal freshwater marshes, which were therefore assumed to contribute to the silica supply to estuarine waters in times of silica limitation. A comprehensive budget calculation for European salt marshes is presented in this study. Earlier, salt marshes were considered to have even higher silica recycling rates than tidal freshwater marshes. Between 2009 and 2011, concentrations, pools and fluxes of silica in two salt marshes at the German Wadden Sea coast were determined (in soil, pore water, aboveground vegetation, freshly deposited sediments and seepage water). Subsequently, a budget was calculated. Special emphasis was placed on the influence of grazing management on silica cycling. Our results show that the two salt marshes were sinks for silica. The average import of biogenic silica (BSi) with freshly deposited sediments (1,334 kmol km?2 year?1) largely exceeded the DSi and BSi exports with seepage water (80 kmol km?2 year?1). Grazing management can affect silica cycling of salt marshes by influencing hydrology and vegetation structure. Abandoned sites had larger DSi export rates than grazed sites. One third of all BSi imports occurred in only one major flooding, underlining the relevance of rare events in the silica budget of tidal marshes. This aspect has been widely neglected in earlier studies, what might have led to an underestimation of silica import rates to tidal marshes hitherto.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号