12 IBÀÑEZ, C., ALCARAZ, C., CAIOLA, N., PRADO, P., TROBAJO, R., BENITO, X., REYES, E., DAY, J.W. & SYVITSKI, J.P.M. 2019. Basin-scale land use impacts on world deltas: human vs natural forcings Global and Planetary Change DOI: 10.1016/j.gloplacha.2018.12.003 Link
A new global database of 86 deltas and river basins was analyzed to investigate the relative importance of deforestation and land use changes versus natural forcingsin determining long-term total delta size. Results show that mean riverflow and shelf slope were the most important variables, whereas population density andsediment load had a much lower importance. Deforestation and other variables related to land-use generally had a very small effect, but were more influential in asubset comprising Mediterranean and Black Sea deltas. As most deltas have developed over thousands of years, the much shorter-lived anthropogenic signals fromdeforestation and other landscape perturbations have had only secondary impact on the total area of deltas. Also, delta progradation is strongly influenced on sanddeposition, whereas anthropogenic impacts on sediment load have more often impacted mostly thefiner sediment being deposited offshore (prodelta deposits) or inthe deltaic plain. These data disproves the hypothesis that delta size and growth is strongly influenced by human forcings, particularly for larger deltas, sinceHolocene delta building is mainly determined by natural forces. However, humans are influencing the geomorphology of deltas, particularly over the last centurywhen the Anthropocene nature of deltas has become manifest. A more precise terminology is proposed to clarify concepts such as“human-made”,“human-en-gineered”or“human-influenced”deltas
11 PRADO, P., ALCARAZ, C., BENITO, X., CAIOLA, N. & IBÁÑEZ, C. 2019. Pristine vs. human-altered Ebro Delta habitats display contrasting resilience to RSLR. Science of the Total Environment DOI: 10.1016/j.scitotenv.2018.11.318 Link
River deltas are ecologically and economically valuable coastal ecosystems but low elevations make them extremely sensitive to relative sea level rise (RSLR), i.e. the combined effects of sea level rise and subsidence. Most deltas are subjected to extensive human exploitation, which has altered the habitat composition, connectivity and geomorphology of deltaic landscapes. In the Ebro Delta, extensive wetland reclamation for rice cultivation over the last 150 years has resulted in the loss of 65% of the natural habitats. Here, we compare the dynamics of habitat shifts under two departure conditions (a simulated pristine delta vs. the human-altered delta) using the Sea Level Affecting Marshes Model (SLAMM) under the 4.5 and 8.5 RCP (Representative Concentration Pathways) scenarios for evaluating their resilience to RSLR (i.e. resistance to inundation). Results showed lower inundation rates in the human delta (~10 to 22% by the end of the century, depending on RCP conditions), mostly due to ~4.5 times lower initial extension of coastal lagoons compared to the pristine delta. Yet, inundation rates from ~15 to 30% of the total surface represent the worst possible human scenario, assuming no flooding protection measures. Besides, accretion rates within rice fields are disregarded since this option is not available in SLAMM for developed dry land. In the human delta, rice fields were largely shifted to other wetland habitats and experienced the highest reductions, mostly because of their larger surface. In contrast, in the pristine delta most of the habitats showed significant decreases by 2100 (~2 to 32% of the surface). Coastal infrastructures (dykes or flood protection dunes) and reintroduction of riverine sediments through irrigation channels are proposed to minimize impacts of RSLR. In the worst RCP scenarios, promoting preservation of natural habitats by transforming unproductive rice fields into wetlands could be the most sustainable option.
10 FRITZ, S., BENITO, X. & STEINITZ-KANNAN, M. 2018. Long-term and regional perspectives on recent change in lacustrine diatom communities in the tropical Andes. Journal of Paleolimnology DOI: 10.1007/s10933-018-0056-6 Link
Understanding and managing the responses of natural systems to climate change requires knowing whether recent changes in ecosystem structure and function are within the bounds of
natural variation or whether the systems are entering new states that are unprecedented. Several recent studies of the fossil diatom record of the last ~150 years in Andean lakes have shown
changes in diatom species composition that suggest changes in lake thermal structure in response to regional climate warming. Yet these paleolimnological records are only a few hundred years
in length, so it is unclear whether the systems have entered new states, with potentially severe consequences for ecosystem structure and function, or whether current trends are within the
natural variability of the systems. Here, we use a recently compiled diatom database from tropical South America to explore the regional distribution and ecological controls of selected
planktic diatom taxa that are associated with warming and changes in the lake thermal structure. We also review published Andean stratigraphic records that span thousands of years to
characterize the long-term dynamics of relevant planktic species in response to past climate change. The contemporary data show that many planktic taxa have broad latitudinal and
elevational distributions. The distributions of several taxa are correlated with surface water temperature, but most also are correlated with pH and/or conductivity. A review of existing
stratigraphic data from Andean lakes demonstrates that rapid changes in diatom abundance, including abrupt increases followed by decades to centuries of near extirpation, are a common
mode of population variation for some planktic taxa. Yet the majority of these published paleolimnological investigations are of lakes that are larger and differ in nutrient status and
conductivity from the small dilute systems where recent species shifts have been observed. We propose that assessing the resilience of contemporary diatom communities and, by inference,
lake ecosystems is best done by generating new records from Andean lakes of varied size and chemistry that span a millennium or more and hence a broader spectrum of climate conditions,
coupled with new ecological and biogeographic studies that build upon new research programs in the tropical Andes.
9 BENITO, X., FRITZ, S., STEINITZ-KANNAN, M., VÉLEZ, M.I. & McGLUE, M.M. 2018. Lake regionalization and diatom metacommunity structuring in tropical South America. Ecology and Evolution DOI: 10.1002/ece3.4305 Link
Lakes and their topological distribution across Earth’s surface impose ecological and evolutionary constraints on aquatic metacommunities. In this study, we group similar lake ecosystems as metacommunity units influencing diatom community structure. We assembled a database of 195 lakes from the tropical Andes and adjacent lowlands (8ºN–30ºS and 58–79ºW) with associated environmental predictors to examine diatom metacommunity patterns at two different levels: taxon and functional (deconstructed species matrix by ecological guilds). We also derived spatial variables that inherently assessed the relative role of dispersal. Using complementary multivariate statistical techniques (Principal Component Analysis, cluster analysis, non-metric multidimensional scaling, Procrustes, variance partitioning), we examined diatom-environment relationships among different lake habitats (sediment surface, periphyton and plankton) and partitioned community variation to evaluate the influence of niche- and dispersal-based assembly processes in diatom metacommunity structure across lake clusters. The results showed a significant association between geographic clusters of lakes based on gradients of climate and landscape configuration and diatom assemblages. Six lake clusters distributed along a latitudinal gradient were identified as functional metacommunity units for diatom communities. Variance partitioning revealed that dispersal mechanisms were a major contributor to diatom metacommunity structure, but in a highly context-dependent fashion across lake clusters. In the Andean Altiplano and adjacent lowlands of Bolivia, diatom metacommunities are niche assembled but constrained by either dispersal limitation or mass effects, resulting from area, environmental heterogeneity, and ecological guild relationships. Topographic heterogeneity played an important role in structuring planktic diatom metacommunities. We emphasize the value of a guild-based metacommunity model linked to dispersal for elucidating mechanisms underlying latitudinal gradients in distribution. Our findings reveal the importance of shifts in ecological drivers across climatic and physiographically distinct lake clusters, providing a basis for comparison of broad-scale community gradients in lake-rich regions elsewhere. This may help guide future research to explore evolutionary constraints on the rich Neotropical benthic diatom species pool.
8 BENITO, X., FRITZ, S., STEINITZ-KANNAN, M., TAPIA, P., KELLY, M.A. & LOWELL, T. 2018. Geo-climatic factors drive diatom community distribution in tropical South American freshwaters. Journal of Ecology 106: 1660-1672 Link
1. Patterns that maintain and generate biodiversity of macro-organisms in the Neotropics are widely discussed in the scientific literature, yet the spatial ecology of microorganisms is largely unknown. The unique character of the tropical Andes and adjacent Amazon lowlands generates a wide gradient of environmental conditions to advance our understanding of what drives community assembly and diversity processes.
2. We analyzed the distribution patterns of benthic diatoms (unicellular siliceous algae) as a model group of microbial passive dispersers, including predictors that describe limnological and geo-climatic gradients for a total of 113 waterbodies (0–28ºS and 58–80ºW), including lakes and streams. Complementary multivariate statistical analyses were performed to correlate i) community composition, and ii) diatom species richness with environmental and spatial factors to infer niche-based and dispersal-based assembly processes, respectively.
3. Results showed that two gradients structured both diatom assemblages and waterbodies, namely climate and landscape configuration. Variance partitioning revealed that broad-scale spatial variables (distance-based Moran’s Eigenvectors) outperformed the two environmental components (limnological and geo-climatic), suggesting dispersal-assembled communities. However, diatom assemblages were structured by geo-climatic (regional) factors in certain lakes in the northern and central Andes, although their effects were partially manifested via local variables after the geographical distances were factored out. In a similar way, climatic and topographic structuring homogenized lake and stream communities within ecoregions, as indicated by the strong overlap between the two community types and the weak correlation between biota and limnological variables. Notably, a significant increase in diatom species richness was related to increased water connectivity, interpreted to indicate that a decrease in the remoteness of the system increase species number.
4. Synthesis. We emphasize the strength of macroecological gradients (landscape configuration and climatic factors) in affecting both diatom diversity and community composition in the South American tropics. In this context, our results and the commonalities of ecoregion patterning with groups of macroorganisms (vegetation), suggest the need to integrate microbial ecology into a macroecology framework to unravel mechanisms behind diversity gradients.
7 VÉLEZ, M.I., JARAMILLO, C., SALAZAR, F., BENITO, X., FRITZ, S., TAPIA, P., LUBINIECKI, D., KAR., N. & ESCOBAR, J. 2018. Aquatic ecosystems in a newly formed ecospace: Early Pliocene lakes in the Central Andean Altiplano. Palaeogeography, Palaeoclimatology, Palaeoecology 490: 218-226 Link
Uplift of the Altiplano in the Central Andes of South America had profound effects on land, oceans and atmosphere. Very little, however, is known about the ecosystems that developed on the ecospaces first formed once the Altiplano reached its present high altitude. We present a micropaleontological (diatoms and ostracods) and stratigraphic analysis of Pliocene Member C of the El Descanso Formation that outcrops near the town of Yaurí, Perú. Lithofacies analysis indicates that fluvial conditions were eventually replaced by several lacustrine and marsh environments. Diatom and ostracod assemblages indicate that these bodies of water were alkaline, slightly saline and shallow. Lacustrine conditions were favoured by a change in the tectonic regime from compressional to tensional, which led to formation of small isolated basins, and by wet conditions. We hypothesize that a stronger and/or longer rainy season prevailed during that time in the Altiplano, possibly as a consequence of an intensified South American Summer Monsoon, driven by a warmer atmosphere, imposed by high concentrations of atmospheric CO2.
6 CARBALLEIRA, R., TROBAJO, R., LEIRA, M., BENITO, X., SATO, S. & MANN D.G. 2017. A combined morphological and molecular approach to Nitzschia varelae sp. nov., with discussion of symmetry in Bacillariaceae. European Journal of Phycology 52: 342-359 Link
A previously unknown member of the Bacillariaceae was discovered almost simultaneously in four different brackish coastal wetlands on the Atlantic and Mediterranean coasts of the Iberian Peninsula. It appears to tolerate a wide range of salinities but was never common in samples where it occurred. The frustules were consistently hantzschioid (i.e. with the raphe systems always on the same side of the frustule) and the valve outline was asymmetrical about the apical plane, two features that have until recently been considered characteristic of Hantzschia. Molecular phylogenies based on rbcL and LSU rDNA indicated, however, that the new species does not belong in Hantzschia but among the several disparate lineages that comprise the paraphyletic genus Nitzschia. This finding, coupled with the recent discovery of other diatoms with constant hantzschioid symmetry but with a morphology very similar to the type species of Nitzschia, is discussed in relation to the status and characterization of Hantzschia as an independent genus. It is concluded that, while a core of hantzschioid species may exist that can be classified together, corresponding to the traditional understanding of the genus Hantzschia, there is no single morphological feature common to all of them that can be used to diagnose the group and differentiate it from the various hantzschioid lineages that are separate from true Hantzschia and currently placed in e.g. Nitzschia or Cymbellonitzschia. Testing whether a hantzschioid species does or does not belong to Hantzschia will in many cases require molecular evidence. Although the new coastal species does not belong to the same lineage as the type species of Nitzschia, N. sigmoidea, it is described for the moment as N. varelae Carballeira, D.G. Mann & Trobajo, sp. nov., until there is a better understanding of generic limits in the Bacillariaceae following a wider molecular and morphological survey of that family.
5 BENITO, X., CEARRETA, A., TROBAJO, R. & IBÁÑEZ, C. 2016. Benthic foraminifera as indicators of habitat in a Mediterranean delta: implications for ecological and palaeoenvironmental studies. Estuarine, Coastal and Shelf Science 180: 97–113 Link
The ecology and modern distribution of benthic foraminiferal assemblages were analysed in the Ebro Delta (NW Mediterranean Sea). Foraminiferal distributions were from 191 sediment surface samples covering a wide range of deltaic habitats and adjacent open sea areas. According to similarity in species composition, cluster analysis identified four habitat types: (1) offshore habitat, (2) nearshore and outer bays, (3) salt and brackish marshes and (4) coastal lagoons and inner bays. Canonical Correspondence Analysis identified water depth, salinity and sand content as the main environmental factors structuring living foraminiferal assemblages. Partial Canonical Correspondence Analysis revealed water depth as the most statistically significant associated with the distribution of modern foraminifera in the Ebro Delta. Thus, a transfer function for water depth using Weighted Average Partial Least Squares regression was successfully developed. Although depth per se is unlikely to affect the foraminifera directly but will exert its effects via various environmental variables that co-vary with depth in the deltaic habitats (e.g. hydrodynamics, oxygen, food availability, etc), the resulting model (r2 = 0.89; RMSEP = 0.32 log10 m) suggested a strong correlation between observed and foraminifera-predicted water depths, and therefore provided a potentially useful tool for water-depth reconstructions in the Ebro Delta. This work indicated the potential role of modern foraminifera as quantitative indicators of water depth and habitat types in the Ebro Delta. This complementary approach (transfer function and indicator species) will allow reconstruction of the palaeoenvironmental changes that have occurred in the Ebro Delta based on the benthic foraminiferal record.
4 CEARRETA, A., BENITO, X., TROBAJO, R., IBÁÑEZ, C. & GIOSAN, L. 2016. Holocene palaeoenvironmental evolution of the Ebro Delta (Western Mediterranean Sea): an early formation based on the benthic foraminiferal record. The Holocene 26(9): 1438–1456 Link
Major Mediterranean deltas began to develop during a period between 8000 and 6000 yr BP when the rate of fluvial sediment input overtook the declining rate of sea-level rise. However, different authors have argued that the Ebro Delta primarily formed during the late Middle Ages as a consequence of increased anthropogenic pressure on its river basin and these arguments are supported by the scarcity of previous geological studies and available radiocarbon dates. To reconstruct the environmental evolution of the Ebro Delta during the Holocene, we used micropalaeontological analysis of continuous boreholes drilled in two different locations (Carlet and Sant Jaume) on the central delta plain. Different lithofacies distributions and associated environments of deposition were defined based on diagnostic foraminiferal assemblages and the application of a palaeowater-depth transfer function. The more landward Carlet sequence shows an older and more proximal progradational delta with a sedimentary record composed of inner bay, lagoonal and beach materials deposited between 7600 and >2000 yr BP under rising sea-level and highstand conditions. This phase was followed by a series of delta plain environments reflected in part by the Carlet deposits that formed before 2000 yr BP. The Sant Jaume borehole is located closer to the present coastline and contains a much younger sequence that accumulated in the last 2.0 ka during the development of three different deltaic lobes under highstand sea-level conditions. The results of this study reinforce the idea that the Ebro Delta dates to the early Holocene, similar to other large Mediterranean deltas.
3 BENITO, X., CEARRETA, A., TROBAJO, R., IBÁÑEZ, C. & BRUNET, M. 2015. Benthic foraminifera as indicators of habitat changes in anthropogenically impacted deltaic wetlands: the Ebro Delta (NE Iberian Peninsula). Marine Pollution Bulletin 101: 163–173 Link
Present-day habitats of the Ebro Delta, NE Iberian Peninsula, have been ecologically altered as a consequence of intensive human impacts in the last two centuries (especially rice farming). Benthic foraminiferal palaeoassemblages and sediment characteristics of five short cores were used to reconstruct past wetland habitats, through application of multivariate DCA and CONISS techniques, and dissimilarity coefficients (SCD). The timing of environmental changes was compared to known natural and anthropogenic events in order to identify their possible relationships. In deltaic wetlands under altered hydrological conditions, we found a decrease in species diversity and calcareous-dominated assemblages, and a significant positive correlation between microfaunal changes and organic matter content. Modern analogues supported palaeoenvironmental interpretation of the recent evolution of the Delta wetlands. This research provides the first recent reconstruction of change in the Ebro Delta wetlands, and also illustrates the importance of benthic foraminifera for biomonitoring present and future conditions in Mediterranean deltas.
2 BENITO, X., TROBAJO, R. & IBÁÑEZ, C. 2015. Benthic diatoms in a Mediterranean delta: ecological indicators and a conductivity transfer function for paleoenvironmental studies. Journal of Paleolimnology 54: 171–188 Link
The contemporary distribution of benthic diatoms and their use as ecological indicators were examined in a coastal wetland, the Ebro Delta, as a representative of environmental conditions in Mediterranean coastal wetlands. A total of 424 diatom taxa were identified across 24 sites encompassing a wide range of wetland habitat types (coastal lagoons, salt and brackish marshes, shallow bays, microbial mats and nearshore marine waters) and conductivities. Canonical correspondence analysis showed that water conductivity and water depth were the main factors structuring the diatom assemblages. Cluster analysis identified five habitat types according to the similarity in diatom species composition: salt marshes, brackish marshes, brackish coastal lagoons and bays, coastal lagoons with fresher conditions, and nearshore open sea. For each wetland habitat, diatom indicator species were identified. Partial canonical correspondence analysis showed that water conductivity, a proxy for salinity, was the most statistically significant and independent variable for explaining the distribution of benthic diatoms in the study area. A transfer function, using a weighted average regression model, was developed for conductivity and displayed reasonable performance (r 2 = 0.64; RMSEP = 0.302 log10 mS/cm). Our study in the Ebro Delta provides a basis for using diatom assemblages to make quantitative conductivity inferences, and for using diatom indicator species to identify wetland habitats. These approaches are complementary and may be valuable for paleoenvironmental studies of (1) effects of large-scale, natural changes in the Delta (e.g. sea-level fluctuations), and (2) impacts of short-term anthropogenic changes, such as the introduction and development of rice agriculture.
1 BENITO, X., TROBAJO, R. & IBÁÑEZ, C. 2014. Modelling habitat distribution of Mediterranean coastal wetlands: the Ebro Delta as case study. Wetlands 34: 775–785 Link
Manuscripts under review
Present-day altered distribution of the natural habitats in the Ebro Delta is consequence of intensive human settlement in the last two centuries. We developed spatial predictive models of potential natural wetland habitats of the Ebro Delta based on ecogeographical predictors and presence/pseudo-absence data for each habitat. The independent variables (i.e. elevation, distance from the coast, distance from the river and distance from the inner border) were analysed using Generalized Additive Models (GAMs). Elevation and the distance from the coast appeared as key predictors in most of the coastal habitats (coastal lagoons, sandy environments, Salicornia-type marshes and reed beds), whereas distances from the river and from the inner border were relevant in the most terrestrial or inland habitats (salt meadows, Cladium-type marshes and riparian vegetation). Our findings suggest that the most inland habitats (i.e. Cladium-type marshes, salt meadows and riparian vegetation) would have undergone a severe reduction (higher than 90 %), whereas in the most coastal habitats (coastal lagoons, sandy environments, Salicornia-type marshes) the reduction in relation to their potential distribution would be around 70 %. This modelling approach can be applied to other deltaic areas, since all them share a similar topography.
Benito, X., Feitl, M., Fritz, S.C., Mosquera, P., Schneider, T., Hampel., H., Quevedo, L. & Steinitz-Kannan, M. A diatom metacommunity perspective on limnological change over the last 150 in the tropical Andes. Under review in Journal of Biogeography
Manuscripts in preparation
Benito, X., Schneider,T., Fritz, S.C, Ruhi, A. Climate fluctuations and continental-scale synchrony in lake regime shifts. To be submitted to Nature Ecology and Evolution
Benito, X., Fritz, S.C. Diatom diversity and biodiversity across tropical South America. Book chapter for Neotropical Diversification (Ed Rull, V. & Carnaval, A.C.) Springer