Detection of total water mass changes in the Patagonian glaciers area by satellite gravimetry

Despite present efforts to better understand glacier changes and their trends, the satellite gravimetry is a powerful tool still not applied in depth to study relatively large areas in the Andes of Argentina and Chile. In this work the mass variations of the Patagonian Icefield are analyzed together with the decrease trends of the ice layer in the region. The purpose of this study is to demonstrate the GRACE satellite mission (Gravity Recovery and Climate Experiment) ability to detect the water storage changes over the glaciers area. Furthermore, the variations of the hydrometric level of some Patagonian lakes were monitored by combining satellite altimetry data and in situ measurements with the observed water mass variations. Data from GRACE was used to estimate gravity trends, and high-resolution CSR GRACE RL05 mascon solutions were used to analyze the water storage change of the icefields in the region under study for the 2002-2017 period. Virtual stations from satellite altimetry obtained from a lake database and also hydrometric height data from in situ stations, located at Patagonian lakes in Argentina and Chile, were also used in order to compare the TWS from GRACE to the water level of the specific lakes. Additionally, correlation coefficients were determined at each station. The results show a significant water storage decrease in the Icefield area, and they also demonstrate that the ice melt in southern Patagonia (of about 6 cm/year) tends to be more pronounced than in the northern region.

Crustacean zooplankton communities, mixotrophic cililates, and optical properties in North Patagonian lakes, investigated by remote sensing

North Patagonian lakes are characterized by their oligotrophic or oligo-mesotrophic status. These conditions bring with them, respectively, the presence of abundant mixotrophic ciliates and a low species number of crustacean zooplankton under oligotrophic status, and low numbers of mixotrophic ciliates and a high species number of zooplankton under oligo-mesotrophic status. The aims of the present study are, (1) to use remote sensing techniques for determining abundances of mixotrophic ciliates and crustacean zooplankton, and (2) to characterize these mixotrophic and zooplankton communities by using null models. The sensing was accomplished from a satellite, i.e., by measuring the reflectance of the sunlight on a waterbody, which result will vary according to the contents of the water column. The results of Principal Component Analysis (PCA) revealed that sites with low reflectance of all bands have a high abundance of Stentor accompanied by low zooplankton absolute abundance, whereas a markedly opposite situation was observed under high reflectance, where Stentor has low abundance in conjunction with high zooplankton absolute abundances. The null models revealed that the communities in the studied sites do not have structured species associations, and that there is an overlap of niches. These results obtained agree with similar observations for Argentinean Patagonian lakes.

Daily vertical distribution of zooplankton in two oligo-mesotrophic north Patagonian lakes (39° S, Chile).

The zooplankton communities often exhibit daily vertical migrations to avoid natural ultraviolet radiation and/or fish predation. However there is no information on this topic in Chilean North Patagonian lakes up to date. Therefore, this study deals with a first characterization of plankton crustacean daily vertical migration in two temperate, oligotrophic lakes (Villarrica and Panguipulli lakes, 39°S) in Southern Chile. Zooplankton were collected at different depths intervals (0-10m, 10-20 m, 20-30m, 30-40m) at early morning, middle day, evening and night in the studied site. The results revealed that zooplankton species (Daphnia pulex, Ceriodaphnia dubia, Neobosmina chilensis, Mesocyclops araucanus, and Tropocyclops prasinus) are abundant in surface zones at night, early morning and evening, whereas at middle day the zooplankton abundances are high at deep zones. The results agree with observations for Argentinean and North American lakes where these daily migration patterns in crustacean zooplankton species were reported due mainly natural ultraviolet radiation exposure, whereas for northern hemisphere lakes the vertical migration is due to combined effect of natural ultraviolet radiation and fish predation exposure.

First fecundity observations on female copepods from three northern Patagonian lakes (Pellaifa, Calafquén, Panguipulli; Chile)

The crustacean zooplankton in Chilean Patagonian lakes is characterized by a marked dominance of calanoid copepods when under an oligotrophic status. The aim of the present study was to analyse the number of eggs and the relation of that feature with the total length of females of calanoid and cyclopoid copepods reported in three northern Chilean Patagonian lakes. The calanoid copepods found were Boeckella gracilipes in Lake Pellaifa and Tumeodiaptomus diabolicus in the lakes Panguipulli and Calafquén, whereas the cyclopoid Mesocyclops araucanus was found in the lakes Pellaifa and Calafquén. For calanoid copepods, high egg numbers were found and thus also a high value for the ratio of egg number per female length in Lake Panguipulli, whereas for M. araucanus a high value was found in Lake Pellaifa. These differences would presumably be associated with community structure, specifically predator-prey relationships and possibly other interactions, as, e.g., potential interspecific competition.

Observations on crustacean zooplankton in two connected north Patagonian lakes (Calafquén-Pellaifa, 39°S, Chile)

The northern Patagonian lakes (38-41°S), are characterized by their location in catchment basins that have been markedly altered through human intervention. In those basins, the original native, perennial forest has been replaced by towns, villages and agricultural zones. The present study was done in two interconnected north Patagonian lakes (the lakes Calafquén and Pellaifa), where the species composition of the crustacean zooplankton community was compared, using a biodiversity index and size-structure null models. The results denoted the presence of marked differences between both sites, Calafquén lake being inhabited by less species and in general showing lower abundances of individuals in comparison to Pellaifa lake. The results of size-structure null models revealed the absence of interspecific competition for both sites. The obtained results would agree with similar observations for other northern Patagonian lakes in Argentina and Chile.