Variation of stream metabolism along a tropical environmental gradient

Stream metabolism is affected by both natural and human-induced processes. While metabolism has multiple implications for ecological processes, relatively little is known about how metabolic rates are influenced by land use in tropical streams. In this study, we assessed the metabolic characteristics and related environmental factors of six streams located in a transition area from Cerrado to Atlantic Forest (São Carlos/Brazil). Three streams were relatively preserved, while three were flowing through more agriculturally and/or urban impacted watersheds. Surface water samples were analyzed for biological and physico-chemical parameters as well as discharge and percentage of canopy cover. Metabolism was determined through the single-station method to estimate gross primary production (GPP), ecosystem respiration (ER) and net ecosystem production (NEP) with BAyesian Single-station Estimation (BASE). Nutrient concentrations tended to be higher in impacted versus preserved streams (e.g., average total phosphorus between 0.028-0.042 mg L-1 and 0.009-0.038 mg L-1, respectively). Average canopy cover varied between 58 and 77%, with no significant spatial or seasonal variation. All streams were net heterotrophic (ER exceeded GPP) in all sampling periods. GPP rates were always lower than 0.7 gO2 m-2 d-1 in all streams and ER varied from 0.6 to 42.1 gO2 m-2 d-1.  Linear Mixed-Effect models showed that depth, discharge, velocity and total phosphorus are the most important predictors for GPP. For ER, depth, velocity and canopy cover are significant potential predictors. Canopy cover was the main light limiting factor and influenced stream metabolism. Our findings reinforced the concepts that shifts in the shading effect provided by vegetation (e.g., through deforestation) or changes in discharge (e.g., through land use conversion or water abstractions) can impact freshwater metabolism. Our study suggests that human activities in low latitude areas can alter tropical streams’ water quality, ecosystem function, and the degree of riparian influence. Our data showed that tropical streams can be especially responsive to increases of organic matter inputs leading to high respiration rates and net heterotrophy, and this should be considered to support management and restoration efforts

Integrated hydrologic-economic model for sustainable water resources management in front of climate change. The Tunuyán River basin and the Piave River Basin case studies

Abstract The research carried out investigated the structure of the complex system composed by hydrological, economic and climatic variables, with the aim of sustainable water management modelling. Two case studies (the Tunuyán River Basin and Piave River Basin) were investigated, applying different methodologies for data analysis, due to the diverse management objectives and specific site characteristics. In the Tunuyán River Basin case study a correlation analysis on time series data of annual grape yields, sugar rate, monthly temperatures and precipitations was carried on, in order to individuate possible relations between them. Strong correlations were found between annual grape yield and minimum temperature of June, minimum temperature of July, maximum temperature of January, maximum temperature of October and the PVC index of precipitations. Correlations were strong also between sugar rate in grape and minimum temperature of July, minimum temperature of November, Minimum temperature of December, Maximum temperature of February, Maximum temperature of November and the PVC index. A multi-linear regression analysis was then applied to data in order to quantify those relations. A Mann Kendall analysis was applied on time series of meteorological data and the Tunuyán River up flow discharge, to detect significant trends. Significant positive trends were identified on the total annual river flow and on mostly monthly river flows except for July, August, September and December monthly flows, which trends were not significant. The optimum area to be sustainable irrigated with a 12” pump, energy requirements and energy cost for water extraction were estimated using data available from pumping tests. Irrigation water demand as total crop water requirements was estimated using the FAO Penman-Monteith formula. Energy cost variations were examined to evaluate the economic impact of climate warming. The cultivated area increase rate (as a consequence of economic development) was also considered. Finally, all variables were integrated in a whole dynamic system model written in Vensim, to analyse the dynamic of the entire system through time. The objective formula of the integrated model is the maximisation of net benefit minimizing water use. In the Piave River Basin case study a Mann-Kendall trend analysis was carried on to detect trends in time series of monthly precipitations. Significant trends were indentified identified only in September precipitations. An optimization model written in GAMS was applied to estimate the cultivation pattern for optimum water allocation.Abstract La ricerca ha analizzato la sruttura del sistema complesso costitutio da variabili idrologiche, economiche e climatiche, con l’obbiettivo della modellazioneper la gestione sostenibile delle risorce idriche. Due casi studi sono stati approfonditi, il bacino del fiume Tunuyan (Mendoza, Argentina) e il bacino del fiume Piave (Italia). Diverse metodologie di analisi dei dati sono state applicate, a causa di diversi obbiettivi gestionali e seconda della caratteristiche specifiche di ciascuna zona. Nel caso studio del bacino del fiume Tunuyan è stata condotta un’analisi di correlazione tra serie storiche di dati di produzione di uva, tenore zuccherino nell’uva, temperature mensili di precipitazioni, con l’obbiettivo di identificare possibili relazioni tra le variabili. Forti correlazioni sono state identificate tra produzione annuale di uva e temperatura minima di Giugno, temperatura minima di Luglio, temperatura minima di Novembre, temperatura minima di dicembre, temperatura massima di febbraio, temperatura massima di Novembre e l’indice PVC di precipitazioni. Un’analisi di regressione lineare multipla è infine stata applicata ai dati per quantificare tali relazioni. L’analisi delle tendenze delle serie storiche di dati meteorologici e di portata del fiume Tunuyán è stata condotta attraverso il test non parametrico Mann Kendall, che ha permesso di valutare le tendenze significative. Tendenze positive sono state identificate nella portata a monte totale e in quasi tutte le serie storiche delle portate mensili, tranne per Luglio, Agosto, Settembre e Dicembre, le cui tendenze sono risultate non significative. L’area di irrigazione ottimale con una pompa di estrazione di 12” ,le necessità energetiche e i costi di estrazione dell’acqua sotterranea sono stati calcolati attraverso i dati disponibili da test di pompaggio condotti dall’INA (Istituto Nacional del Agua di Mendoza). La domanda irrigua, calcolata come necessità idriche delle colture è stata stimata usando la formula FAO Penman-Monteith. Le variazioni nei costi sono state esaminate per valutare i possibili impatti del riscaldamento globale. L’incremento di area coltivata come conseguenza dello sviluppo economico è stato preso in considerazione. Infine tutte le variabili sono state integrate in un modello olisitco scritto in Vensim, con l’obbiettivo di analizzare la dinamica dell’intero sistema nel tempo. La formula obbiettivo del modello integrato è la massimizzazione dei profitti minimizzando l’utilizzo di risorsa idrica. Nel caso studio del bacino del Piave un’analisi di tendenza Mann-Kendall è stata condotta per individuare le tendenza nelle serie storiche di dati di precipitazione. Tendenze positive sono state identificate solo nelle precipitazioni di Settembre. Un modello di ottimizzazione scritto in GAMS è stato infine applicato per stimare il pattern di coltivazione per l’allocazione ottimale della risorsa idrica

Changing Land Use and Population Density Are Degrading Water Quality in the Lower Mekong Basin

Establishing reference conditions in rivers is important to understand environmental change and protect ecosystem integrity. Ranked third globally for fish biodiversity, the Mekong River has the world’s largest inland fishery providing livelihoods, food security, and protein to the local population. It is therefore of paramount importance to maintain the water quality and biotic integrity of this ecosystem. We analyzed land use impacts on water quality constituents (TSS, TN, TP, DO, NO3−, NH4+, PO43−) in the Lower Mekong Basin. We then used a best-model regression approach with anthropogenic land-use as independent variables and water quality parameters as the dependent variables, to define reference conditions in the absence of human activities (corresponding to the intercept value). From 2000–2017, the population and the percentage of crop, rice, and plantation land cover increased, while there was a decrease in upland forest and flooded forest. Agriculture, urbanization, and population density were associated with decreasing water quality health in the Lower Mekong Basin. In several sites, Thailand and Laos had higher TN, NO3−, and NH4+ concentrations compared to reference conditions, while Cambodia had higher TP values than reference conditions, showing water quality degradation. TSS was higher than reference conditions in the dry season in Cambodia, but was lower than reference values in the wet season in Thailand and Laos. This study shows how deforestation from agriculture conversion and increasing urbanization pressure causes water quality decline in the Lower Mekong Basin, and provides a first characterization of reference water quality conditions for the Lower Mekong River and its tributaries

Integrated hydrologic-economic decision support system for groundwater use confronting climate change uncertainties in the Tunuyan River basin, Argentina

This study presents an integrated hydrologic-economic model as decision support system for groundwater use and incorporates uncertainties of climate change. The model was developed with the Vensim software (Ventana Systems) for system dynamic simulations. The software permitted the integration of economic variables along with hydrologic variables, in a unified format with the aim of evaluating the economic impacts of climate change on arid environments. To test the model, we applied it in one of the upper Tunuyán River sub-basin, located in the Mendoza Province (Argentina), where irrigation comes from groundwater. The model defines the best mix of crops and the total land use required to maximize the total river sub-basin monetary income, considering as a limit the amount of water that does not exceed the natural annual aquifer recharge. To estimate the impacts of climatic changes, four scenarios were compared: the business as usual (with the number of existing wells) in a dry year with a temperature increase of 4 °C; the business as usual in a wet year with an increase in temperature of 1.1 °C; an efficient use of wells in a dry year and a temperature increase of 4 °C and an efficient use of wells in a wet year with a temperature increase of 1.1 °C. Outputs calculated by the model were: land use per crop, total sub-basin net benefit, total sub-basin water extraction, water extraction limit depending on river discharge and total number of wells required to irrigate the entire area. Preliminary results showed that the number of existing wells exceeded the optimized number of wells required to sustainably irrigate the entire river sub-basin. Results indicated that in an average river discharge year, if wells were efficiently used, further rural development would be possible, until the limit of 350 million m3 of water extraction per year was reached (650 million m3 for a wet year and 180 million m3 for a dry year). The unified format and the low cost of the software license make the model a useful tool for Water Resources Management Institutions, particularly in developing countries

Stable Integration of Inducible SPLICS Reporters Enables Spatio-Temporal Analysis of Multiple Organelle Contact Sites upon Modulation of Cholesterol Traffic

The study of organelle contact sites has received a great impulse due to increased interest in the understanding of their involvement in many disease conditions. Split-GFP-based contact sites (SPLICS) reporters emerged as essential tools to easily detect changes in a wide range of organelle contact sites in cultured cells and in vivo, e.g., in zebrafish larvae. We report here on the generation of a new vector library of SPLICS cloned into a piggyBac system for stable and inducible expression of the reporters in a cell line of interest to overcome any potential weakness due to variable protein expression in transient transfection studies. Stable HeLa cell lines expressing SPLICS between the endoplasmic reticulum (ER) and mitochondria (MT), the ER and plasma membrane (PM), peroxisomes (PO) and ER, and PO and MT, were generated and tested for their ability to express the reporters upon treatment with doxycycline. Moreover, to take advantage of these cellular models, we decided to follow the behavior of different membrane contact sites upon modulating cholesterol traffic. Interestingly, we found that the acute pharmacological inhibition of the intracellular cholesterol transporter 1 (NPC1) differently affects membrane contact sites, highlighting the importance of different interfaces for cholesterol sensing and distribution within the cell

Heterogeneity and scaling of photosynthesis, respiration, and nitrogen uptake in three Atlantic Rainforest streams

Leaves, epilithon, macrophytes, and fine benthic organic material are central ecosystem compartments to food webs and mediate nutrient fluxes in streams. Most estimates of gross primary production (GPP) and ecosystem respiration (ER) are made at a reach scale, averaging across compartments. Thus, there is little information on how individual compartments contribute to and scale up to whole-stream estimates across watersheds. We compared estimates of GPP, ER, and nitrogen (N) uptake of individual ecosystem compartments (dm) and stream reaches (similar to 100 m) in three sizes of streams in a preserved Atlantic Rainforest watershed. The smallest stream had dense forest canopy cover, whereas the largest was more open. We measured substratum-specific rates of GPP and ER, as well as ammonium and nitrate N-15 uptake in recirculating chambers. We compared these decimeter-scale measurements to whole-stream estimates, using single-station dissolved oxygen (GPP and ER) and pulsed N uptake methods. Epilithon and macrophytes (when present) were the dominant GPP and N uptake compartments in open-canopy sites, and leaves contributed strongly to ER at all sites, even though they covered <3 percent of the stream bottom. Ammonium and nitrate uptake per unit N content varied significantly among substrata and streams. Upscaled inorganic N uptake per unit area was greater when macrophytes were present. Chamber measurements overestimated metabolic rates in the larger streams, but not in the smallest one. The smallest transient storage zone streams were more active than the biggest one, and this influenced the mismatch between whole-stream and chamber nutrient uptake estimates. We conclude that scaling to the whole watershed requires information on location in the watershed (e.g., where canopy cover is dense), rates of individual compartments, and reach-specific hydrodynamic information as influenced by large-scale geomorphic details (i.e., the size and activity of the transient storage zones)

Effects of riparian deforestation on benthic invertebrate community and leaf processing in Atlantic forest streams

Riparian deforestation may strongly affect stream functioning, with consequences for biodiversity and ecosystem services. These effects can be assessed using bioindicators relating to biotic community structure and ecosystem functioning. We evaluated the effects of riparian deforestation on 1. measures of community structure using aquatic benthic invertebrates, and 2. an aspect of ecosystem functioning, aquatic leaf processing. We selected sites along gradients of riparian land use in four Atlantic rainforest streams and measured physical and chemical properties for their association with riparian deforestation. We sampled benthic invertebrates and calculated metrics of community structure at each site. We measured rates of leaf processing using leaves of a common riparian tree, Guarea guidonia. Riparian deforestation was accompanied by increasing concentration of ammonia, water current and temperature and decreasing nightly oxygen saturation. Invertebrate diversity decreased and community metrics changed with deforestation as expected of negative impacts. Leaf processing decreased with deforestation. Although there were significant differences in physical and chemical measurements among streams, the gradients in community and ecosystem responses were similar, thus suggesting that both types of bioindicators were useful for monitoring changes and relating them to loss of biodiversity and ecosystem function

Nitrogen and Phosphorus Uptake Dynamics in Tropical Cerrado Woodland Streams

Pollution abatement through phosphorus and nitrogen retention is a key ecosystem service provided by streams. Human activities have been changing in-stream nutrient concentrations, thereby altering lotic ecosystem functioning, especially in developing countries. We estimated nutrient uptake metrics (ambient uptake length, areal uptake rate, and uptake velocity) for nitrate (NO3-N), ammonium (NH4-N), and soluble reactive phosphorus (SRP) in four tropical Cerrado headwater streams during 2017, through whole-stream nutrient addition experiments. According to multiple regression models, ambient SRP concentration was an important explanatory variable of nutrient uptake. Further, best models included ambient NO3-N and water velocity (for NO3-N uptake metrics), dissolved oxygen (DO) and canopy cover (for NH4-N) and DO, discharge, water velocity, and temperature (for SRP). The best kinetic models describing nutrient uptake were efficiency-loss (R-2 from 0.47-0.88) and first-order models (R-2 from 0.60-0.85). NO3-N, NH4-N, and SRP uptake in these streams seemed coupled as a result of complex interactions of biotic P limitation, abiotic P cycling processes, and the preferential uptake of NH4-N among N-forms. Global change effects on these tropical streams, such as temperature increase and nutrient enrichment due to urban and agricultural expansion, may have adverse and partially unpredictable impacts on whole-stream nutrient processing

Changing Land Use and Population Density are Degrading Water Quality in the Lower Mekong Basin

Establishing reference conditions in rivers is important to understand environmental change and protect ecosystem integrity. Ranked third globally for fish biodiversity, the Mekong River has the world’s largest inland fishery providing livelihoods, food security, and protein to the local population. It is therefore of paramount importance to maintain the water quality and biotic integrity of this ecosystem. We analyzed land use impacts on water quality constituents (TSS, TN, TP, DO, NO3−, NH4+, PO43−) in the Lower Mekong Basin. We then used a best‐model regression approach with anthropogenic land‐use as independent variables and water quality parameters as the dependent variables, to define reference conditions in the absence of human activities (corresponding to the intercept value). From 2000–2017, the population and the percentage of crop, rice, and plantation land cover increased, while there was a decrease in upland forest and flooded forest. Agriculture, urbanization, and population density were associated with decreasing water quality health in the Lower Mekong Basin. In several sites, Thailand and Laos had higher TN, NO3−, and NH4+ concentrations compared to reference conditions, while Cambodia had higher TP values than reference conditions, showing water quality degradation. TSS was higher than reference conditions in the dry season in Cambodia, but was lower than reference values in the wet season in Thailand and Laos. This study shows how deforestation from agriculture conversion and increasing urbanization pressure causes water quality decline in the Lower Mekong Basin, and provides a first characterization of reference water quality conditions for the Lower Mekong River and its tributaries

Smoke from regional wildfires alters lake ecology

Wildfire smoke often covers areas larger than the burned area, yet the impacts of smoke on nearby aquatic ecosystems are understudied. In the summer of 2018, wildfire smoke covered Castle Lake (California, USA) for 55 days. We quantified the influence of smoke on the lake by comparing the physics, chemistry, productivity, and animal ecology in the prior four years (2014?2017) to the smoke year (2018). Smoke reduced incident ultraviolet-B (UV-B) radiation by 31% and photosynthetically active radiation (PAR) by 11%. Similarly, underwater UV-B and PAR decreased by 65 and 44%, respectively, and lake heat content decreased by 7%. While the nutrient limitation of primary production did not change, shallow production in the offshore habitat increased by 109%, likely due to a release from photoinhibition. In contrast, deep-water, primary production decreased and the deep-water peak in chlorophyll a did not develop, likely due to reduced PAR. Despite the structural changes in primary production, light, and temperature, we observed little significant change in zooplankton biomass, community composition, or migration pattern. Trout were absent from the littoral-benthic habitat during the smoke period. The duration and intensity of smoke influences light regimes, heat content, and productivity, with differing responses to consumers.Fil: Scordo, Facundo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto Argentino de Oceanografía. Universidad Nacional del Sur. Instituto Argentino de Oceanografía; Argentina. University Of Nevada; Estados UnidosFil: Chandra, Sudeep. University Of Nevada; Estados UnidosFil: Suenaga, Erin. University Of Nevada; Estados UnidosFil: Kelson, Suzanne J.. University Of Nevada; Estados UnidosFil: Culpepper, Joshua. University Of Nevada; Estados UnidosFil: Scaff, Lucia. University of Saskatchewan; CanadáFil: Tromboni, Flavia. University Of Nevada; Estados UnidosFil: Caldwell, Timothy J.. University Of Nevada; Estados UnidosFil: Seitz, Carina. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Instituto Argentino de Oceanografía. Universidad Nacional del Sur. Instituto Argentino de Oceanografía; ArgentinaFil: Fiorenza, Juan Esteban. Consejo Nacional de Investigaciones Científicas y Técnicas. Oficina de Coordinación Administrativa Parque Centenario. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura. Universidad de Buenos Aires. Facultad de Agronomía. Instituto de Investigaciones Fisiológicas y Ecológicas Vinculadas a la Agricultura; ArgentinaFil: Williamson, Craig E.. Miami University; Estados UnidosFil: Sadro, Steven. University of California at Davis; Estados UnidosFil: Rose, Kevin C.. Rensselaer Polytechnic Institute; Estados UnidosFil: Poulson, Simon R.. University Of Nevada; Estados Unido