Contribution of dust inputs to dissolved organic carbon and water transparency in Mediterranean reservoirs

The Mediterranean reservoirs receive frequent atmospheric Saharan dust inputs with soil-derived organic components mostly during the stratification periods, when run-off inputs are particularly limited. Here, we quantified and optically characterized the water-soluble organic carbon (WSOC) of the (dry and wet) atmospheric deposition in collectors placed near three reservoirs from the western Mediterranean Basin. In addition, we determined the WSOC contribution to the pool of dissolved organic carbon (DOC) in the reservoirs and the influence of dust-derived chromophoric organic components on the water transparency during their stratification periods. We found synchronous dynamics in the WSOC atmospheric inputs among the three collectors and in the DOC concentrations among the three reservoirs. The DOC concentrations and the WSOC atmospheric inputs were positive and significantly correlated in the most oligotrophic reservoir (Quéntar) and in the reservoir with the highest ratio of surface area to mixing water depth (Cubillas). Despite these correlations, WSOC atmospheric inputs represented less than 10% of the total DOC pool, suggesting that indirect effects of dust inputs on reservoir DOC may also promote these synchronous patterns observed in the reservoirs. Chromophoric components from dust inputs can significantly reduce the water transparency to the ultraviolet radiation (UVR). The depths where UVR at λ = 320 nm was reduced to ten percent of surface intensity (Z10%) decreased 27 cm in Béznar, 49 cm in Cubillas, and 69 cm in Quéntar due to the dust inputs. Therefore, the increasing dust export to the atmosphere may have consequences for the water transparency of aquatic ecosystems located under the influence of the global dust belt.This work was funded by the Spanish Ministry of Science and Technology (DISPAR, CGL2005-00076 to IR and CGL2008-06101/BOS to IdV) and by the Spanish Ministry of Education and Science (CICYT grant REN2003-03038 to RM-B)

Light attenuation in Southern Iberian Peninsula reservoirs

[EN] This study evaluates the extinction coefficient of light (Kd) and the Secchi disk depth (SD) in 12 reservoirs located in the southern Iberian Peninsula. These systems show differences in landscape, physical, chemical and trophic properties. The relationships found were analyzed to evaluate the utility of the SD as predictor of the photic zone (Zeu) measured with Kd.The, a new equation is proposed here as a better estimation for the photic zone in these reservoirs: Zeu (m)≈ 2·SD (m)+6. The influence of the chlorophyll-a, turbidity and dissolved organic carbon (DOC) concentration on the water transparency is studied. Both DOC concentration and turbidity affect water transparency. Finally, the capacity of SD as a Kd predictor is also assessed.[ES] Este trabajo estudia de forma pareada los valores del coeficiente de extinción vertical de la luz (Kd) y de la profundidad de visión del disco de Secchi (SD) en un conjunto de 12 embalses del sureste de la Península Ibérica que difieren en sus características de paisaje, físicas, químicas y tróficas. Se analizan las relaciones encontradas para evaluar la utilidad del SD como predictor de la zona fótica (Zeu) calculada mediante Kd y se propone la expresión Zeu(m) ≈ 2·SD (m)+6 como una mejor estima de la zona fótica en estos embalses. Además se investiga la influencia de la clorofila-a, turbidez y carbono orgánico disuelto (DOC) sobre la transparencia del agua de los embalses. Tanto la concentración de DOC como la turbidez afectan a dichas propiedades. Finalmente, se analiza la capacidad de SD como predictor de Kd.La financiación para el presente trabajo fue obtenida del Ministerio de Economía y Competitividad, referencia: CGL2014-52362-R y fondos FEDER. E.L-P. cuenta con un contrato predoctoral de Formación del Profesorado Universitario (FPU014/02917). Los autores agradecen a los revisores los comentarios recibidos sobre el texto original al que han ayudado a mejorar.León-Palmero, E.; Reche, I.; Morales-Baquero, R. (2019). Atenuación de luz en embalses del sur-este de la Península Ibérica. Ingeniería del Agua. 23(1):65-75. https://doi.org/10.4995/ia.2019.10655SWORD6575231APHA. 1998. Methods for the Examination of Water and Wastewater. American Public Health AssociationBorowiak, D., Borowiak, M. 2016. Comparative studies of underwater light regimes in lakes of the East-Suwałki Lakeland. Limnological Review, 16(4), 173-183. https://doi.org/10.1515/limre-2016-0019Canteras, J.C., Pérez, L., León, P., Lorda, T. 1999. Efecto de la radiación luminosa en la desaparición de Escherichia coli (T90) en medio acuático. Estudio experimental. Ingeniería del Agua, 6(3), 269-274. https://doi.org/10.4995/ia.1999.2791Carlson, R.E. 1977. A trophic index for lakes. Limnology and Oceanography, 22, 361-369. https://doi.org/10.4319/lo.1977.22.2.0361Devlin, M.J., Barry, J., Mills, D.K., Gowen, R.J., Foden, J., Sivyer, D., Greenwood, N., Pearce, D., Tett, P. 2009. Estimating the diffuse attenuation coefficient from optically active constituents in UK marine waters. Estuarine, Coastal and Shelf Science, 82, 73-83. https://doi.org/10.1016/j.ecss.2008.12.015Dzieszko, P., Zwoliński, Z. 2015. Trophic diversity of Poznań Lakeland lakes. Limnological Review, 15(2), 61-69. https://doi.org/10.2478/limre-2015-0007French, R.H., Cooper, J.J., Vigg, S. 1982. Secchi disk relationships. Water Resources Bulletin, 18, 121-123. https://doi.org/10.1111/j.1752-1688.1982.tb04538.xHolmes, R.W. 1970. The Secchi disk in turbid coastal waters. Limnology and Oceanography, 15, 688-694. https://doi.org/10.4319/lo.1970.15.5.0688Koenings, J.P., Edmundson, J.A., 1991. Seechi disk and photometer estimates of light regimes in Alaskan lakes: effects of yellow color and turbidity. Limnology and Oceanography 36, 91-105. https://doi.org/10.4319/lo.1991.36.1.0091Ma, J., Song, K., Wen, Z., Zhao, Y., Shang, Y., Fang, C., Du, J. 2016. Spatial Distribution of Diffuse Attenuation of Photosynthetic Active Radiation and Its Main Regulating Factors in Inland Waters of Northeast China. Remote Sensing, 8, 964. https://doi.org/10.3390/rs8110964Morales-Baquero, R., Conde-Porcuna, J., Pérez-Martínez, C., Cruz-Pizarro, L. 1991. Vertical light attenuation in four reservoirs of Genil River (Granada, Spain). Proceedings of the 17th International Congress on Large Dams (ICOLD) (Q64, R9), 137-148.Morris, D.P., Zagarese, H., Williamson, C.E., Balseiro, E.G., Hargreaves, B.R., Modenutti, B., Moeller, R., Queimalinos, C. 1995. The attenuation of solar UV radiation in lakes and the role of dissolved organic carbon. Limnology and Oceanography, 40(8), 1381-1391. https://doi.org/10.4319/lo.1995.40.8.1381Poikane, S. 2009. Water Framework Directive.Intercalibration Technical Report. Part 2: Lakes. Office for Official Publications of the European Communities. Luxemburgo.Poole, H.H., Atkins,W.R. 1929. Photo-electric measurements of submarine illumination throughout the year. Journal of Marine Biological Association U.K. 16, 297-394. https://doi.org/10.1017/S0025315400029829Prats-Rodríguez, J., Morales-Baquero, R., Dolz-Ripollés, J., Armengol-Bachero, J. 2014. Aportaciones de la limnología a la gestión de embalses. Ingeniería del Agua, 18(1), 83-97. https://doi.org/10.4995/ia.2014.3145Rodríguez, J. 2016. Ecología. Pirámide. Madrid.Reche, I., Pace, M.L., Cole, J.J. 2000. Modeled Effects of Dissolved Organic Carbon and Solar Spectra on Photobleaching in Lake Ecosystems. Ecosystems, 3, 419-432.Scully N.M., Lean, D.R.S. 1994. The attenuation of ultraviolet light in temperate lakes. Ergebnisse der Limnologie, 43,135-144.Tundisi, J.C., Matsumura-Tundisi, T. 2011. Limnology. CRC Press, Boca-Ratón.USA

Climate change and Saharan dust drive recent cladoceran and primary production changes in remote alpine lakes of Sierra Nevada, Spain

Recent anthropogenic climate change and the exponential increase over the past few decades of Saharan dust deposition, containing ecologically important inputs of phosphorus (P) and calcium (Ca), are potentially affecting remote aquatic ecosystems. In this study, we examine changes in cladoceran assemblage composition and chlorophyll-a concentrations over the past ~150 years from high-resolution, welldated sediment cores retrieved from six remote high mountain lakes in the Sierra Nevada Mountains of Southern Spain, a region affected by Saharan dust deposition. In each lake, marked shifts in cladoceran assemblages and chlorophyll-a concentrations in recent decades indicate a regional-scale response to climate and Saharan dust deposition. Chlorophyll-a concentrations have increased since the 1970s, consistent with a response to rising air temperatures and the intensification of atmospheric deposition of Saharan P. Similar shifts in cladoceran taxa across lakes began over a century ago, but have intensified over the past ~50 years, concurrent with trends in regional air temperature, precipitation, and increased Saharan dust deposition. An abrupt increase in the relative abundance of the benthic cladoceran Alona quadrangularis at the expense of Chydorus sphaericus, and a significant increase in Daphnia pulex gr. was a common trend in these softwater lakes. Differences in the magnitude and timing of these changes are likely due to catchment and lake-specific differences. In contrast with other alpine lakes that are often affected by acid deposition, atmospheric Ca deposition appears to be a significant explanatory factor, among others, for the changes in the lake biota of Sierra Nevada that has not been previously considered. The effects observed in Sierra Nevada are likely occurring in other Mediterranean lake districts, especially in softwater, oligotrophic lakes. The predicted increases in global temperature and Saharan dust deposition in the future will further impact the ecological condition of these ecosystemsMinisterio de Educación y Ciencia (MEC), Grant/Award Number: AP2007-00352; Programa Nacional de Movilidad de Recursos Humanos de Investigaci on (MICINN); Ministerio de Medio Ambiente (MMA), Grant/Award Number: 87/2007; Ministerio de Econom ıa, Industria y Competitividad (MINECO), Grant/Award Number: CGL2011-23483; Natural Sciences and Engineering Research Council of Canad

Dust inputs and bacteria influence dissolved organic matter in clear alpine lakes

Remote lakes are usually unaffected by direct human influence, yet they receive inputs of atmospheric pollutants, dust, and other aerosols, both inorganic and organic. In remote, alpine lakes, these atmospheric inputs may influence the pool of dissolved organic matter, a critical constituent for the biogeochemical functioning of aquatic ecosystems. Here, to assess this influence, we evaluate factors related to aerosol deposition, climate, catchment properties, and microbial constituents in a global dataset of 86 alpine and polar lakes. We show significant latitudinal trends in dissolved organic matter quantity and quality, and uncover new evidence that this geographic pattern is influenced by dust deposition, flux of incident ultraviolet radiation, and bacterial processing. Our results suggest that changes in land use and climate that result in increasing dust flux, ultraviolet radiation, and air temperature may act to shift the optical quality of dissolved organic matter in clear, alpine lakes

Alpine bogs of southern Spain show human-induced environmental change superimposed on long-term natural variations

Recent studies have proved that high elevation environments, especially remote wetlands, are exceptional ecological sensors of global change. For example, European glaciers have retreated during the 20th century while the Sierra Nevada National Park in southern Spain witnessed the first complete disappearance of modern glaciers in Europe. Given that the effects of climatic fluctuations on local ecosystems are complex in these sensitive alpine areas, it is crucial to identify their long-term natural trends, ecological thresholds, and responses to human impact. In this study, the geochemical records from two adjacent alpine bogs in the protected Sierra Nevada National Park reveal different sensitivities and long-term environmental responses, despite similar natural forcings, such as solar radiation and the North Atlantic Oscillation, during the late Holocene. After the Industrial Revolution both bogs registered an independent, abrupt and enhanced response to the anthropogenic forcing, at the same time that the last glaciers disappeared. The different response recorded at each site suggests that the National Park and land managers of similar regions need to consider landscape and environmental evolution in addition to changing climate to fully understand implications of climate and human influence.This study was supported by the project P11-RNM 7332 of the “Junta de Andalucía”, the projects CGL2013-47038-R and CGL2015-67130-C2-1-R of the “Ministerio de Economía y Competitividad of Spain and Fondo Europeo de Desarrollo Regional FEDER” and the research group RNM0190 and RNM309 (Junta de Andalucía). A.G.-A. was also supported by a Marie Curie Intra-European Fellowship of the 7th Framework Programme for Research, Technological Development and Demonstration of the European Commission (NAOSIPUK. Grant Number: PIEF-GA-2012-623027) and by a Ramón y Cajal Fellowship RYC-2015-18966 of the Spanish Government (Ministerio de Economía y Competividad). J.L.T. was also supported by a Small Research Grant by the Carnegie Trust for the Universities of Scotland and hosted the NAOSIPUK project (PIEF-GA-2012-623027). M. J. R-R acknowledges the PhD funding provided by Consejería de Economía, Innovación, Ciencia y Empleo de la Junta de Andalucía (P11-RNM 7332)

The effect of atmospheric acid processing on the global deposition of bioavailable phosphorus from dust

The role of dust as a source of bioavailable phosphorus (Bio-P) is quantified using a new parameterization for apatite dissolution in combination with global soil data maps and a global aerosol transport model. Mineral dust provides 31.2 Gg-P yr-1 of Bio-P to the oceans, with 14.3 Gg-P yr-1 from labile P present in the dust, and an aditional 16.9 Gg-P yr from acid dissolution of apatite in the atmosphere, representing an increase of 120%. The North Atlantic, north west Pacific, and Mediterranean Sea are identified as important sites of Bio-P deposition from mineral dust. The acid dissolution process increases the fraction of total-P that is bioavailable from ~10% globally from the labile pool to 23% in the Atlantic Ocean, 45% in the Pacific Ocean, and 21% in the Indian Ocean, with an ocean global mean value of 22%. Strong seasonal variations, especially in the North Pacific, northwest Atlantic, and Indian Ocean, are driven by large-scale meteorology and pollution sources from industrial and biomass-burning regions. Globally constant values of total-P content and bioavailable fraction used previously do not capture the simulated variability. We find particular sensitivity to the representation of particle-to-particle variability of apatite, which supplies Bio-P through acid-dissolution, and calcium carbonate, which helps to buffer the dissolution process. A modest 10% external mixing results in an increase of Bio-P deposition by 18%. The total Bio-P calculated here (31.2 Gg-P yr-1) represents a minimum compared to previous estimates due to the relatively low total-P in the global soil map used

Nucleic Acid Content in Crustacean Zooplankton: Bridging Metabolic and Stoichiometric Predictions

Metabolic and stoichiometric theories of ecology have provided broad complementary principles to understand ecosystem processes across different levels of biological organization. We tested several of their cornerstone hypotheses by measuring the nucleic acid (NA) and phosphorus (P) content of crustacean zooplankton species in 22 high mountain lakes (Sierra Nevada and the Pyrenees mountains, Spain). The P-allocation hypothesis (PAH) proposes that the genome size is smaller in cladocerans than in copepods as a result of selection for fast growth towards P-allocation from DNA to RNA under P limitation. Consistent with the PAH, the RNA:DNA ratio was >8-fold higher in cladocerans than in copepods, although ‘fast-growth’ cladocerans did not always exhibit higher RNA and lower DNA contents in comparison to ‘slow-growth’ copepods. We also showed strong associations among growth rate, RNA, and total P content supporting the growth rate hypothesis, which predicts that fast-growing organisms have high P content because of the preferential allocation to P-rich ribosomal RNA. In addition, we found that ontogenetic variability in NA content of the copepod Mixodiaptomus laciniatus (intra- and interstage variability) was comparable to the interspecific variability across other zooplankton species. Further, according to the metabolic theory of ecology, temperature should enhance growth rate and hence RNA demands. RNA content in zooplankton was correlated with temperature, but the relationships were nutrient-dependent, with a positive correlation in nutrient-rich ecosystems and a negative one in those with scarce nutrients. Overall our results illustrate the mechanistic connections among organismal NA content, growth rate, nutrients and temperature, contributing to the conceptual unification of metabolic and stoichiometric theories.This research was supported by the Spanish Ministries of Science and Innovation (CGL2011-23681/BOS), and Environment, Rural and Marine Affairs (OAPN2009/067); ‘Consejería de Innovación, Ciencia y Empresa – Junta de Andalucía’ (Excelencia CVI-02598; P09-RNM-5376); The Swedish Research Council for Environment, Agricultural Sciences and Spatial Planning (FORMAS) and Stockholm University’s strategic marine environmental research program ‘Baltic Ecosystem Adaptive Management’, and a Spanish government ‘Formación de Profesorado Universitario’ fellowship to F.J. Bullejos

Rising nutrient-pulse frequency and high UVR strengthen microbial interactions

Solar radiation and nutrient pulses regulate the ecosystem’s functioning. However, little is known about how a greater frequency of pulsed nutrients under high ultraviolet radiation (UVR) levels, as expected in the near future, could alter the responses and interaction between primary producers and decomposers. In this report, we demonstrate through a mesocosm study in lake La Caldera (Spain) that a repeated (press) compared to a one-time (pulse) schedule under UVR prompted higher increases in primary (PP) than in bacterial production (BP) coupled with a replacement of photoautotrophs by mixotrophic nanoflagellates (MNFs). The mechanism underlying these amplified phytoplanktonic responses was a dual control by MNFs on bacteria through the excretion of organic carbon and an increased top-down control by bacterivory. We also show across a 6-year whole-lake study that the changes from photoautotrophs to MNFs were related mainly to the frequency of pulsed nutrients (e.g. desert dust inputs). Our results underscore how an improved understanding of the interaction between chronic and stochastic environmental factors is critical for predicting ongoing changes in ecosystem functioning and its responses to climatically driven changes.This study was supported by the Ministerio de Economía y Competitividad and Fondo Europeo de Desarrollo Regional (FEDER) (CGL2011-23681 and CGL2015-67682-R to PC), Ministerio de Medio Ambiente, Rural, y Marino (PN2009/067 to PC) and Junta de Andalucía (Excelencia projects P09-RNM-5376 and P12-RNM-327 to PC and JMMS, respectively). M.J.C. was supported by the Spanish Government “Formación de Profesorado Universitario” PhD grant (FPU12/01243) and I.D.-G. by the Junta de Andalucía “Personal Investigador en Formación” PhD grant (FPI RNM-5376). This work is in partial fulfillment of the Ph. D. thesis of M.J.C

Maximum in the Middle: Nonlinear Response of Microbial Plankton to Ultraviolet Radiation and Phosphorus

The responses of heterotrophic microbial food webs (HMFW) to the joint action of abiotic stressors related to global change have been studied in an oligotrophic high-mountain lake. A 2×5 factorial design field experiment performed with large mesocosms for >2 months was used to quantify the dynamics of the entire HMFW (bacteria, heterotrophic nanoflagellates, ciliates, and viruses) after an experimental P-enrichment gradient which approximated or surpassed current atmospheric P pulses in the presence vs. absence of ultraviolet radiation. HMFW underwent a mid-term (<20 days) acute development following a noticeable unimodal response to P enrichment, which peaked at intermediate P-enrichment levels and, unexpectedly, was more accentuated under ultraviolet radiation. However, after depletion of dissolved inorganic P, the HMFW collapsed and was outcompeted by a low-diversity autotrophic compartment, which constrained the development of HMFW and caused a significant loss of functional biodiversity. The dynamics and relationships among variables, and the response patterns found, suggest the importance of biotic interactions (predation/parasitism and competition) in restricting HMFW development, in contrast to the role of abiotic factors as main drivers of autotrophic compartment. The response of HMFW may contribute to ecosystem resilience by favoring the maintenance of the peculiar paths of energy and nutrient-mobilization in these pristine ecosystems, which are vulnerable to threats by the joint action of abiotic stressors related to global change.This research was supported by Junta de Andalucía (Excelencia P07-CVI-02598 to PC, and P09-RNM-5376 to JMMS), the Spanish Ministries of Medio Ambiente, Rural y Marino (PN2009/067 to PC) and Ciencia e Innovación (GLC2008-01127/BOS and CGL2011-23681 to PC), the ERC Advanced Grant project number 250254 “MINOS” (to GB), and two Spanish government grants (to JADM and FJB)

Differential Response of High-Elevation Planktonic Bacterial Community Structure and Metabolism to Experimental Nutrient Enrichment

Nutrient enrichment of high-elevation freshwater ecosystems by atmospheric deposition is increasing worldwide, and bacteria are a key conduit for the metabolism of organic matter in these oligotrophic environments. We conducted two distinct in situ microcosm experiments in a high-elevation lake (Emerald Lake, Sierra Nevada, California, USA) to evaluate responses in bacterioplankton growth, carbon utilization, and community structure to short-term enrichment by nitrate and phosphate. The first experiment, conducted just following ice-off, employed dark dilution culture to directly assess the impact of nutrients on bacterioplankton growth and consumption of terrigenous dissolved organic matter during snowmelt. The second experiment, conducted in transparent microcosms during autumn overturn, examined how bacterioplankton in unmanipulated microbial communities responded to nutrients concomitant with increasing phytoplankton-derived organic matter. In both experiments, phosphate enrichment (but not nitrate) caused significant increases in bacterioplankton growth, changed particulate organic stoichiometry, and induced shifts in bacterial community composition, including consistent declines in the relative abundance of Actinobacteria. The dark dilution culture showed a significant increase in dissolved organic carbon removal in response to phosphate enrichment. In transparent microcosms nutrient enrichment had no effect on concentrations of chlorophyll, carbon, or the fluorescence characteristics of dissolved organic matter, suggesting that bacterioplankton responses were independent of phytoplankton responses. These results demonstrate that bacterioplankton communities in unproductive high-elevation habitats can rapidly alter their taxonomic composition and metabolism in response to short-term phosphate enrichment. Our results reinforce the key role that phosphorus plays in oligotrophic lake ecosystems, clarify the nature of bacterioplankton nutrient limitation, and emphasize that evaluation of eutrophication in these habitats should incorporate heterotrophic microbial communities and processes