Chemical composition and the nitrogen-regulated trophic state of Patagonian lakes   总被引：5，自引：0，他引：5  

Mnica Diaz  Fernando Pedrozo  Colin Reynolds  Pedro Temporetti 《Limnologica》2007,37(1):17-27

Chemical composition and nutrient concentrations of 39 relatively poorly known Patagonian lakes (38–50°S and from 70° to 68°W) are described and analysed using principal component analysis (PCA). The general relationships between nutrients (total phosphorus, bioavailable phosphorus and dissolved inorganic nitrogen) and plankton biomass are examined.We seek to demonstrate that the extreme oligotrophy characterising many lakes and reservoirs of the Argentine Patagonian region of South America owes more to nitrogen deficiency than to a shortage of available phosphorus. The data show a range of trophic conditions with variable water chemistry characteristics.The first two axes of the PCA ordination explain most of the variance (63%). The first component of the variance in the environmental data is a trophic gradient, with positive correlations with the concentrations of nutrients (TP, SRP, DIN) and electrical conductivity and a negative correlation with transparency. For all the reservoirs considered, the calculated annual, summer and winter chlorophyll-a carrying capacities of the available phosphorus were consistently and significantly (P<0.05) in excess of observations but maximum chlorophyll-a values correlate with DIN availability. Indeed the chlorophyll-a carrying capacities, as an index of the resource-sustainable maximum biomass, of the available nitrogen gives a better predictive yield relationship than does P. Our findings are remarkable in so far as the general expectation that dinitrogen-fixing phytoplankton should thrive in the absence of dissolved inorganic nitrogen, at least to the supportive limits of the available phosphorus, is unfulfilled.  相似文献   

Field report: Sailing around the exhumed roots of the Mesozoic Patagonian paleo-accretionary wedge(Diego de Almagro Island,Chile)     

Samuel Angiboust  Jesus Mu?oz 《地学前缘(英文版)》2018,9(5):1591-1594

We undertook a boat expedition to explore the geological framework of a very remote, lesser-known island, in the Chilean Patagonia: the Diego de Almagro Island(latitude S51°330'). This uninhabited, ca.400 km~2 Island is one of the very rare exposures of the Mesozoic accretionary subduction complex along the Chilean margin. Unstable weather, strong winds, steep topography, and very dense vegetation make an on-land mission difficult. Careful preparation based on high-resolution satellite images is advised to optimize shore access and minimize risks of injury. Despite a relatively important degree of regional reequilibration of metamorphic assemblages due to sluggish exhumation through the forearc crust, our results have shown that the island is composed of a nappe stack of ocean-floor derived slivers of metasedimentary units that exhibit very different pressure-temperature-time paths during burial by subduction under the Chilean margin and subsequent exhumation. These rocks are witness to a complex thermal evolution of the subduction zone between Jurassic and Cretaceous times from granulite facies to blueschist facies conditions as well as multiple episodes of accretion at ca. 35 -40 km in depth for almost100 Ma over the Mesozoic era.  相似文献   

Tidal signature recorded in burrow fill     

Andreas Wetzel  Noelia Carmona  Juan Ponce 《Sedimentology》2014,61(5):1198-1210

The arrangement of sediment couplets preserved in Thalassinoides shafts suggests that tides regulated the passive filling of these trace fossils and, thus, represent tubular tidalites. The thickness variation in individual layers and couplets implies a mixed diurnal, semi‐diurnal tidal signature where packages of either thick‐layered or thin‐layered couplets alternate. Calcarenitic sediment accumulated when tidal current velocity was too high to allow deposition of mud, whereas a marly mud layer is interpreted to have formed during more tranquil times of a tidal cycle (in particular, low‐tide slack water). The tidal record within the burrows covers a few weeks and the corresponding spring–neap cycles. The fill of the Thalassinoides shafts is the only known record to decipher the tidal signature from otherwise totally bioturbated sediments. These deposits accumulated in a lower‐shoreface to upper‐offshore setting during the late Miocene on a shallow shelf extending from the Atlantic Ocean to the west into northern Patagonia. The fill of all investigated burrows started around spring tide and, thus, the behaviour of the burrow producers – probably crustaceans – is speculated to have been affected by tides or the high water level because all studied burrows became abandoned around the same period of a tidal cycle.  相似文献   

Variations in sediment yield over the advance and retreat of a calving glacier, Laguna San Rafael, North Patagonian Icefield     

Michèle Koppes  Richard Sylwester  Bernard Hallet 《Quaternary Research》2010,73(1):84-95

Bathymetric and sub-bottom acoustic data were collected in Laguna San Rafael, Chile, to determine sediment yields during the Little Ice Age advance and subsequent retreat of San Rafael Glacier. The sediment volumes and subaqueous landforms imaged are used to interpret the proglacial dynamics and estimate erosion rates from a temperate tidewater glacier over a complete advance-retreat cycle. Sediment yields from San Rafael Glacier averaged 2.7 × 10⁷ m³/a since the end of the Little Ice Age, circa AD 1898, corresponding to average basin-wide erosion rates of 23 ± 9 mm/a; the highest erosion rates, 68 ± 23 mm/a, occurred at the start of the retreat phase, and have since been steadily decreasing. Erosion rates were much lower during glacial advance, averaging at most 7 mm/a, than during retreat. Such large glacial sediment yields over two centuries of advance and retreat suggest that the contribution of sediments stored subglacially cannot account for much of the sediment being delivered to the terminus today. The detailed sub-bottom information of a proglacial lagoon yields important clues as to the timing of erosion, deposition and transfer of glacigenic sediments from orogens to the continental shelves, and the influence of glacier dynamics on this process.  相似文献   

Assessing land use and land cover influence on surface water quality using a parametric weighted distance function     

《Limnologica》2019

Stream water quality is directly influenced by land use and human practices in the surrounding environment. Understanding such effects and the spatial extent of impacts is essential to generate reliable information for ecosystem-based management of water resources. We identified sources of impact on water quality and characterized indicator-specific landscape influence on samples collected during base flow along the Chubut River (43 °S, 69 °W). We modeled Total Nitrogen (TN), Total Phosphorous (TP), Soluble Reactive Phosphorous (SRP) concentrations and δ¹⁵N of particulate organic matter along the river, as a function of effective contribution areas (A_EC) of Land Use/Land Cover (LULC). A_ECs were calculated by assuming that landscape influence decays exponentially with the Euclidean distance between a given LULC parcel and the sampling point. We calibrated the model to the observations by estimating an indicator-specific decay rate. Agriculture and barren lands were the main sources of phosphate nutrients whereas urban areas were the main source of TN. Radius of landscape influence for SRP (100–180 km) was larger than for TP (10–25 km), reflecting different patterns of mobilization and delivery in the catchment. δ¹⁵N variation was explained by vegetation cover but the influence rapidly decreased (1–4 km) reflecting a mostly autochthonous source of organic matter.  相似文献