| Título | Autores | Línea de Investigación | Año | DOI | Abstract | Revista | ISSN | Acceso | Páginas | Volumen | Index | Key Words |
|---|---|---|---|---|---|---|---|---|---|---|---|---|
| The southern South American Proteaceae, Embothrium coccineum exhibits intraspecific variation in growth and cluster-root formation depending on climatic and edaphic origins | Zúñiga-Feest, Alejandra; Delgado, Mabel; Bustos-Salazar, Angela; Ochoa, Valeria | Cambio de Uso de Suelo | 2015.0 | 10.1007/s11104-015-2574-6 | Background and aims Cluster root (CR) functioning has been studied mainly in Proteaceae species from (P)-deficient old soils. However, in southern South America, six species occur in young P rich soils. The aims were: i) to study the growth and CR formation of Embothrium coccineum seedlings from populations contrasting in edaphic and climatic conditions and, ii) to study the effect of P availability on CR formation. Methods Seedlings were grown from seeds collected from nine Chilean populations of E. coccineum (36° to 45° S). After 9 months in a nursery, CR formation and growth were determined. Additionally, seedlings from the two populations at the extreme ends of the distribution were maintained on sand and watered with nutrient solutions including or excluding P. Results All seedlings showed CR formation at 4 months old; however, CR allocation differed in that it was lower in plants from the north versus from the south. CR in seedlings from Curacautín (38°) were suppressed when P supply increased, though this was not seen in seedlings from Coyhaique (45°). Conclusions Results suggest local root adaptation related to both climatic and edaphic conditions. We hypothesize that these features could favor Proteaceae persistence in southern South American ecosystems. | Plant and Soil | 0032-079X, 1573-5036 | http://link.springer.com/10.1007/s11104-015-2574-6 | 201-213 | 396.0 | Thomson Reuters ISI | climate conditions, cluster analysis, evergreen tree, growth rate, hypothesis testing, intraspecific variation, persistence, phosphorus, seedling, volcanic soil, aisen, chile, coihaique, embothrium coccineum, proteaceae |
| Physiological and morphological responses to permanent and intermittent waterlogging in seedlings of four evergreen trees of temperate swamp forests | Zúñiga-Feest, Alejandra; Bustos-Salazar, Angela; Alves, Fernanda; Martinez, Vanessa; Smith-Ramírez, Cecilia | Cambio de Uso de Suelo | 2017.0 | 10.1093/treephys/tpx023 | Tree Physiology | 0829-318X, 1758-4469 | https://academic.oup.com/treephys/article/37/6/779/3069384 | 779-789 | 37.0 | Thomson Reuters ISI | acclimation, adventitious root, carbon cycle, evergreen tree, gas exchange, growth, leaf area, metabolism, microhabitat, morphology, photosynthesis, physiological response, seedling, stomatal conductance, swamp forest, temperate environment, tolerance, transpiration, waterlogging, south america, blepharocalyx, drimys winteri, luma apiculata, myrceugenia exsucca, water, drimys, ecosystem, forest, growth, development and aging, myrtaceae, physiology, plant leaf, plant root, seedling, tree, wetland, drimys, ecosystem, forests, myrtaceae, plant leaves, plant roots, seedlings, trees, water, wetlands | |
| Detailed dynamic land cover mapping of Chile: Accuracy improvement by integrating multi-temporal data | Zhao, Yuanyuan; Feng, Duole; Yu, Le; Wang, Xiaoyi; Chen, Yanlei; Bai, Yuqi; Hernández, H. Jaime; Galleguillos, Mauricio; Estades, Cristian; Biging, Gregory S.; Radke, John D.; Gong, Peng | Servicios Ecosistémicos | 2016.0 | 10.1016/j.rse.2016.05.016 | Stretching over 4300 km north to south, Chile is a special country with complicated landscapes and rich biodiversity. Accurate and timely updated land cover map of Chile in detailed classification categories is highly demanded for many applications. A conclusive land cover map integrated from multi-seasonal mapping results and a seasonal dynamic map series were produced using Landsat 8 imagery mainly acquired in 2013 and 2014, supplemented by MODIS Enhanced Vegetation Index data, high resolution imagery on Google Earth, and Shuttle Radar Topography Mission DEM data. The overall accuracy is 80% for the integrated map at level 1 and 73% for level 2 based on independent validation data. Accuracies for seasonal map series were also assessed, which is around 70% for each season, greatly improved by integrated use of seasonal information. The importance of growing season imagery was proved in our analysis. The analysis of the spatial variation of accuracies among various ecoregions indicates that the accuracy for land cover mapping decreases gradually from central Chile to both north and south. More mapping efforts for those ecoregions are needed. In addition, the training dataset includes sample points spatially distributed in the whole country, temporally distributed throughout the year, and categorically encompassing all land cover types. This training dataset constitutes a universal sample set allowing us to map land cover from any Landsat 8 image acquired in Chile without additional ad hoc training sample collection. | Remote Sensing of Environment | 0034-4257 | http://www.sciencedirect.com/science/article/pii/S0034425716302188 | 170-185 | 183 | Thomson Reuters ISI | biodiversity, mapping, 30 m, enhanced vegetation index, high resolution imagery, land cover mapping, landsat, seasonal dynamics, shuttle radar topography mission, spatial variation of accuracies, image enhancement, accuracy assessment, biodiversity, digital elevation model, ecosystem dynamics, land cover, landsat, satellite imagery, seasonality, spatial variation, vegetation index, vegetation mapping, chile |
| Temporal and spatial evaluation of satellite-based rainfall estimates across the complex topographical and climatic gradients of Chile | Zambrano-Bigiarini, M.; Nauditt, A.; Birkel, C.; Verbist, K.; Ribbe, L. | Dinámica del Clima | 2017.0 | 10.5194/hess-21-1295-2017 | Accurate representation of the real spatio-temporal variability of catchment rainfall inputs is currently severely limited. Moreover, spatially interpolated catchment precipitation is subject to large uncertainties, particularly in developing countries and regions which are difficult to access. Recently, satellite-based rainfall estimates (SREs) provide an unprecedented opportunity for a wide range of hydrological applications, from water resources modelling to monitoring of extreme events such as droughts and floods.This study attempts to exhaustively evaluate – for the first time – the suitability of seven state-of-the-art SRE products (TMPA 3B42v7, CHIRPSv2, CMORPH, PERSIANN-CDR, PERSIAN-CCS-Adj, MSWEPv1.1, and PGFv3) over the complex topography and diverse climatic gradients of Chile. Different temporal scales (daily, monthly, seasonal, annual) are used in a point-to-pixel comparison between precipitation time series measured at 366 stations (from sea level to 4600 m a.s.l. in the Andean Plateau) and the corresponding grid cell of each SRE (rescaled to a 0.25° grid if necessary). The modified Kling–Gupta efficiency was used to identify possible sources of systematic errors in each SRE. In addition, five categorical indices (PC, POD, FAR, ETS, fBIAS) were used to assess the ability of each SRE to correctly identify different precipitation intensities.Results revealed that most SRE products performed better for the humid South (36.4–43.7° S) and Central Chile (32.18–36.4° S), in particular at low- and mid-elevation zones (0–1000 m a.s.l.) compared to the arid northern regions and the Far South. Seasonally, all products performed best during the wet seasons (autumn and winter; MAM–JJA) compared to summer (DJF) and spring (SON). In addition, all SREs were able to correctly identify the occurrence of no-rain events, but they presented a low skill in classifying precipitation intensities during rainy days. Overall, PGFv3 exhibited the best performance everywhere and for all timescales, which can be clearly attributed to its bias-correction procedure using 217 stations from Chile. Good results were also obtained by the research products CHIRPSv2, TMPA 3B42v7 and MSWEPv1.1, while CMORPH, PERSIANN-CDR, and the real-time PERSIANN-CCS-Adj were less skillful in representing observed rainfall. While PGFv3 (currently available up to 2010) might be used in Chile for historical analyses and calibration of hydrological models, the high spatial resolution, low latency and long data records of CHIRPS and TMPA 3B42v7 (in transition to IMERG) show promising potential to be used in meteorological studies and water resource assessments. We finally conclude that despite improvements of most SRE products, a site-specific assessment is still needed before any use in catchment-scale hydrological studies. | Hydrology and Earth System Sciences | 1027-5606 | http://www.hydrol-earth-syst-sci.net/21/1295/2017/ | 1295-1320 | 21 | Thomson Reuters ISI | catchments, clock and data recovery circuits (cdr circuits), developing countries, runoff, sea level, systematic errors, complex topographies, high spatial resolution, meteorological studies, precipitation intensity, precipitation time series, resource assessments, spatiotemporal variability, water resources modelling, rain, catchment, climate conditions, drought, environmental monitoring, extreme event, flood, hydrological modeling, hydrometeorology, precipitation (climatology), precipitation assessment, precipitation intensity, rainfall, satellite data, software, spatiotemporal analysis, time series, topography, water resource, chile |
| Using the Weather Research and Forecasting (WRF) Model for Precipitation Forecasting in an Andean Region with Complex Topography | Yáñez-Morroni, Gonzalo; Gironás, Jorge; Caneo, Marta; Delgado, Rodrigo; Garreaud, René | Agua y Extremos | 2018.0 | 10.3390/atmos9080304 | The Weather Research and Forecasting (WRF) model has been successfully used in weather prediction, but its ability to simulate precipitation over areas with complex topography is not optimal. Consequently, WRF has problems forecasting rainfall events over Chilean mountainous terrain and foothills, where some of the main cities are located, and where intense rainfall occurs due to cutoff lows. This work analyzes an ensemble of microphysics schemes to enhance initial forecasts made by the Chilean Weather Agency in the front range of Santiago. We first tested different vertical levels resolution, land use and land surface models, as well as meteorological forcing (GFS/FNL). The final ensemble configuration considered three microphysics schemes and lead times over three rainfall events between 2015 and 2017. Cutoff low complex meteorological characteristics impede the temporal simulation of rainfall properties. With three days of lead time, WRF properly forecasts the rainiest N-hours and temperatures during the event, although more accuracy is obtained when the rainfall is caused by a meteorological frontal system. Finally, the WSM6 microphysics option had the best performance, although further analysis using other storms and locations in the area are needed to strengthen this result. | Atmosphere | 2073-4433 | http://www.mdpi.com/2073-4433/9/8/304 | 304 | 9 | Thomson Reuters ISI | land use, rain, topography, complex topographies, flash flood, land surface models, meteorological forcing, mountainous terrain, precipitation forecasting, temporal simulation, weather research and forecasting models, weather forecasting, atmospheric modeling, computer simulation, ensemble forecasting, precipitation (climatology), regional climate, temporal analysis, topography, urban atmosphere, weather forecasting |
| Tracing Nitrate-Nitrogen Sources and Modifications in a Stream Impacted by Various Land Uses, South Portugal | Yevenes, Mariela A.; Soetaert, Karline; Mannaerts, Chris M. | Biogeoquímica | 2016.0 | 10.3390/w8090385 | The identification of nitrate-nitrogen (NO3–N) origin is important in the control of surface and ground water quality. These are the main sources of available drinking water. Stable isotopes (15N and 18O) for NO3–N and along with a 1-D reactive transport model were used to study the origin and processes that lead to nitrogen transformation and loss in a major stream that flows into a reservoir within an intensively cultivated catchment area (352 km2) in Alentejo-Portugal. Seasonal water samples (October–November 2008, March 2009 and September 2009) of stream surface water, wells and sediment pore water were collected. The results showed consistently increasing isotope values and decreasing NO3–N concentrations downstream. During winter (wet period, November 2008 and March 2009) slightly higher NO3–N concentrations were found in comparison to early fall (dry period: October 2008) and summer (dry period: September 2009). Isotopic composition of 15N and 18O values in surface water samples from the stream and wells indicated that the dominant NO3–N sources were derived mainly from the soil and fertilizers. There was also significant nitrification in surface water at the head of the stream. Sediment pore waters showed high NO3–N values near the sediment-water interface (reaching 25 mg·N·L−1) and NO3–N concentrations sharply decreasing with sediment depth, suggesting significant NO3–N consumption. Denitrification was also detected using the 15N signature in upstream waters, but not downstream where very low NO3–N levels were measured. In the stream, the calculated isotopic enrichment factor for NO3–N was −2.9‰ for 15N and −1.78 for 18O, this indicates that denitrification accounts for 7.8% to 48% of nitrate removal. | Water | 2073-4441 | http://www.mdpi.com/2073-4441/8/9/385 | art385 | 8 | Thomson Reuters ISI | catchments, denitrification, drought, groundwater, isotopes, land use, nitrates, potable water, reservoirs (water), sediments, water quality, isotopic composition, nitrate nitrogen, nitrogen transformations, reactive transport modeling, sediment water interface, stable isotopes, streams, surface and ground waters, rivers, catchment, denitrification, drinking water, land use change, nitrate, nitrogen, porewater, reactive transport, reservoir, sediment-water interface, stable isotope, streamflow, transformation, water quality, alentejo, portugal |
| Greenhouse gases, nutrients and the carbonate system in the Reloncaví Fjord (Northern Chilean Patagonia): Implications on aquaculture of the mussel, Mytilus chilensis, during an episodic volcanic eruption | Yevenes, Mariela A.; Lagos, Nelson A.; Farías, Laura; Vargas, Cristian A. | Zonas Costeras | 2019.0 | 10.1016/j.scitotenv.2019.03.037 | This study investigates the immediate and mid-term effects of the biogeochemical variables input into the Reloncaví fjord (41°40′S; 72°23′O) as a result of the eruption of Calbuco volcano. Reloncaví is an estuarine system supporting one of the largest mussels farming production within Northern Chilean-Patagonia. Field-surveys were conducted immediately after the volcanic eruption (23–30 April 2015), one month (May 2015), and five months posterior to the event (September 2015). Water samples were collected from three stations along the fjord to determine greenhouse gases [GHG: methane (CH 4 ), nitrous oxide (N 2 O)], nutrients [NO 3 − , NO 2 − , PO 4 3− , Si(OH) 4 , sulphate (SO 4 2− )], and carbonate systems parameters [total pH (pHT), temperature, salinity, dissolved oxygen (O 2 ), and total alkalinity (AT)]. Additionally, the impact of physicochemical changes in the water column on juveniles of the produced Chilean blue mussel, Mytilus chilensis, was also studied. Following the eruption, a large phytoplankton bloom led to an increase in pH T , due to the uptake of dissolved-inorganic carbon in photic waters, potentially associated with the runoff of continental soil covered in volcanic ash. Indeed, high surface SO 4 2− and GHG were observed to be associated with river discharges. No direct evidence of the eruption was observed within the carbonate system. Notwithstanding, a vertical pattern was observed, with an undersaturation of aragonite (Ω Ar < 1) both in brackish surface (<3 m) and deep waters (>10 m), and saturated values in subsurface waters (3 to 7 m). Simultaneously, juvenile mussel shells showed maximized length and weight at 4 m depth. Results suggest a localized impact of the volcanic eruption on surface GHG, nutrients and short-term effects on the carbonate system. Optimal conditions for mussel calcification were identified within a subsurface refuge in the fjord. These specific attributes can be integrated into adaptation strategies by the mussel aquaculture industry to confront ocean acidification and changing runoff conditions. © 2019 Elsevier B.V. | Science of The Total Environment | 0048-9697 | https://linkinghub.elsevier.com/retrieve/pii/S0048969719310150 | 49-61 | 669.0 | Thomson Reuters ISI | alkalinity, aquaculture, biomineralization, carbonation, dissolved oxygen, greenhouse gases, molluscs, nitrogen oxides, nutrients, runoff, sulfur compounds, surface discharges, adaptation strategies, aquaculture industry, chilean patagonian fjord, dissolved inorganic carbon, mussel farming, ocean acidifications, physico-chemical changes, volcanic event, volcanoes, calcium carbonate, carbonic acid, dissolved oxygen, methane, nitrous oxide, sulfate, surface water, carbonic acid, methane, nitrous oxide, sea water, adaptive management, biogeochemical cycle, carbonate system, chemical oceanography, greenhouse gas, mussel culture, nutrient, ocean acidification, volcanic eruption, alkalinity, aquaculture, article, biogeochemical cycle, chilean, estuary, greenhouse gas, mussel, mytilus chilensis, nonhuman, ph, physical chemistry, phytoplankton, priority journal, runoff, salinity, temperature, volcanic ash, volcano, water sampling, analysis, animal, aquaculture, body constitution, chemistry, chile, environmental monitoring, greenhouse gas, mytilus, physiology, season, volcano, calbuco volcano, chile, los lagos, reloncavi fjord, mytilus chilensis, mytilus edulis, animals, aquaculture, body constitution, carbonates, chile, environmental monitoring, greenhouse gases, methane, mytilus, nitrous oxide, nutrients, seasons, seawater, volcanic eruptions |
| Seasonal drought effects on the water quality of the Biobío River, Central Chile | Yevenes, Mariela A.; Figueroa, Ricardo; Parra, Oscar | Zonas Costeras | 2018.0 | 10.1007/s11356-018-1415-6 | Quantifying the effect of droughts on ecosystem functions is essential to the development of coastal zone and river management under a changing climate. It is widely acknowledged that climate change is increasing the frequency and intensity of droughts, which can affect important ecosystem services, such as the regional supply of clean water. Very little is understood about how droughts affect the water quality of Chilean high flow rivers. This paper intends to investigate the effect of an, recently identified, unprecedented drought in Chile (2010–2015), on the Biobío River water quality, (36°45′–38°49′ S and 71°00′–73°20′ W), Central Chile. This river is one of the largest Chilean rivers and it provides abundant freshwater. Water quality (water temperature, pH, dissolved oxygen, electrical conductivity, biological oxygen demand, total suspended solids, chloride, sodium, nutrients, and trace metals), during the drought (2010–2015), was compared with a pre-drought period (2000–2009) over two reaches (upstream and downstream) of the river. Multivariate analysis and seasonal Mann-Kendall trend analyses and a Theil-Sen estimator were employed to analyze trends and slopes of the reaches. Results indicated a significant decreased trend in total suspended solids and a slightly increasing trend in water temperature and EC, major ions, and trace metals (chrome, lead, iron, and cobalt), mainly in summer and autumn during the drought. The reduced variability upstream suggested that nutrient and metal concentrations were more constant than downstream. The results evidenced, due to the close relationship between river discharge and water quality, a slightly decline of the water quality downstream of the Biobío River during drought period, which could be attenuated in a post-drought period. These results displayed that water quality is vulnerable to reductions in flow, through historical and emerging solutes/contaminants and induced pH mobilization. Consequently, seasonal changes and a progressive reduction of river flow affect the ecosystem functionality in this key Chilean river. The outcomes from this research can be used to improve how low flow conditions and the effects of a reduction in the river volume and discharge are assessed, which is the case under the scenario of more frequent drought periods. | Environmental Science and Pollution Research | 0944-1344, 1614-7499 | http://link.springer.com/10.1007/s11356-018-1415-6 | 13844-13856 | 25 | Thomson Reuters ISI | climate change, drought, ecosystem function, ecosystem service, river discharge, river flow, river management, seasonal variation, water quality, water supply, water temperature, biobio river, chile, analysis, chemistry, chile, drought, environmental monitoring, river, season, water pollutant, water quality, chile, droughts, environmental monitoring, rivers, seasons, water pollutants, chemical, water quality |
| Spatial Distribution of Nitrous Oxide (N2O) in the Reloncaví Estuary–Sound and Adjacent Sea (41°–43° S), Chilean Patagonia | Yevenes, Mariela A.; Bello, Estrella; Sanhueza-Guevara, Sandra; Farías, Laura | Biogeoquímica | 2016.0 | 10.1007/s12237-016-0184-z | Fjords and estuaries exchange large amounts of solutes, gases, and particulates between fluvial and marine systems. These exchanges and their relative distributions of compounds/particles are partially controlled by stratification and water circulation. The spatial and vertical distributions of N2O, an important greenhouse gas, along with other oceanographic variables, are analyzed from the Reloncaví estuary (RE) (~41° 30′ S) to the gulf of Corcovado in the interior sea of Chiloé (43° 45′ S) during the austral winter. Freshwater runoff into the estuary regulated salinity and stratification of the water column, clearly demarking the surface (<5 m depth) and subsurface layer (>5 m depth) and also separating estuarine and marine influenced areas. N2O levels varied between 8.3 and 21 nM (corresponding to 80 and 170 % saturation, respectively), being significantly lower (11.8 ± 1.70) at the surface than in subsurface waters in the Reloncaví estuary (14.5 ± 1.73). Low salinity and NO3 −, NO2 −, and PO4 3− levels, as well as high Si(OH)4 values were associated with low surface N2O levels. Remarkably, an accumulation of N2O was observed in the subsurface waters of the Reloncaví sound, associated with a relatively high consumption of O2. The sound is exposed to increasing anthropogenic impacts from aquaculture and urban discharge, occurring simultaneously with an internal recirculation, which leads to potential signals of early eutrophication. In contrast, within the interior sea of Chiloé (ISC), most of water column was quasi homohaline and occupied by modified subantarctic water (MSAAW), which was relatively rich in N2O (12.6 ± 2.36 nM) and NO3 − (18.3 ± 1.63 μM). The relationship between salinity, nutrients, and N2O revealed that water from the open ocean, entering into ISC (the Gulf of Corcovado) through the Guafo mouth, was the main source of N2O (up to 21 nM), as it gradually mixed with estuarine water. In addition, significant relationships between N2O excess vs. AOU and N2O excess vs. NO3 − suggest that part of N2O is also produced by nitrification. Our results show that the estuarine and marine waters can act as light source or sink of N2O to the atmosphere (air–sea N2O fluxes ranged from −1.57 to 5.75 μmol m−2 day−1), respectively; influxes seem to be associated to brackish water depleted in N2O that also caused a strong stratification, creating a barrier to gas exchange. | Estuaries and Coasts | 1559-2723 | http://link.springer.com/10.1007/s12237-016-0184-z | 1-15 | published online | Thomson Reuters ISI | coastal zone, estuarine environment, fjord, inland sea, nitrous oxide, nutrient budget, shelf sea, spatial distribution, chilean margin, pacific ocean, patagonia, chilo |
| Unravel biophysical factors on river water quality response in Chilean Central-Southern watersheds | Yevenes, Mariela A.; Arumí, José L.; Farías, Laura | Biogeoquímica | 2016.0 | 10.1007/s10661-016-5235-1 | Identifying the key anthropogenic (land uses) and natural (topography and climate) biophysical drivers affecting river water quality is essential for efficient management of water resources. We tested the hypothesis that water quality can be predicted by different biophysical factors. Multivariate statistics based on a geographical information system (GIS) were used to explore the influence of factors (i.e., precipitation, topography, and land uses) on water quality (i.e., nitrate (NO 3 − ), phosphate (PO 4 3 − ), silicate (Si(OH)4), dissolved oxygen (DO), suspended solids (TSS), biological oxygen demand (DO), temperature (T), conductivity (EC), and pH) for two consecutive years in the Itata and Biobío river watersheds, Central Chile (36° 00′ and 38° 30′). The results showed that (NO 3 − ), (PO 4 3 − ), Si(OH)4, TSS, EC, and DO were higher during rainy season (austral fall, winter, and spring), whereas BOD and temperature were higher during dry season. The spatial variation of these parameters in both watersheds was related to land use, topography (e.g., soil moisture, soil hydrological group, and erodability), and precipitation. Soil hydrological group and soil moisture were the strongest explanatory predictors for PO 4 3 − , Si(OH)4 and EC in the river, followed by land use such as agriculture for NO 3 − and DO and silviculture for TSS and Si(OH)4. High-resolution water leaching and runoff maps allowed us to identify agriculture areas with major probability of water leaching and higher probability of runoff in silviculture areas. Moreover, redundancy analysis (RDA) revealed that land uses (agriculture and silviculture) explained in 60 % the river water quality variation. Our finding highlights the vulnerability of Chilean river waters to different biophysical drivers, rather than climate conditions alone, which is amplified by human-induced degradation. | Environmental Monitoring and Assessment | 0167-6369 | http://link.springer.com/10.1007/s10661-016-5235-1 | 264-281 | 188 | Thomson Reuters ISI | agricultural runoff, agriculture, biochemical oxygen demand, biophysics, dissolved oxygen, geographic information systems, land use, leaching, moisture, multivariant analysis, rivers, runoff, silicates, silicon, soil moisture, soils, topography, water management, water quality, watersheds, biological oxygen demand, biophysical factors, efficient managements, human-induced degradations, multivariate statistics, redundancy analysis (rda), river water quality, spatial variations, water resources, dissolved oxygen, nitrate, phosphate, river water, silicate, fresh water, nitric acid derivative, rain, soil, anthropogenic effect, climate effect, gis, land use, leaching, river water, runoff, topographic effect, water quality, watershed, article, biochemical oxygen demand, chile, controlled study, electric conductivity, environmental factor, land use, leaching, ph, physical chemistry, precipitation, seasonal variation, topography, water quality, water temperature, watershed, agriculture, chemistry, environmental monitoring, hydrology, river, season, soil, standards, water quality, chile, itata, agriculture, biological oxygen demand analysis, chile, environmental monitoring, fresh water, hydrology, nitrates, rain, rivers, seasons, soil, water quality |