Álvaro Cabezas

Macroinvertebrate patterns along environmental gradients and hydrological connectivity within a regulated river-floodplain

Abstract.Flood and flow pulses are primary factors that regulate macroinvertebrate community structure in river-floodplain ecosystems. In order to assess the impacts of these important hydrological events in a regulated Mediterranean river, bimonthly water and macroinvertebrate samples were collected in 2006 in the Middle Ebro River channel and six floodplain wetlands (NE Spain).We found significant differences among the river sites (permanently connected), two constructed wetlands (groundwater seepage) and three natural oxbow lakes (surface connected at 400, 800 and 1200 m3/s). River sites were dominated by aquatic worms (e.g., Naididae) and showed a high degree of eutrophication. Constructed wetlands provided new habitat for predatory insects (e.g.,Coenagrion scitulum and Trithemis annulata) that benefited from the absence of fish. Natural oxbow lakes were dominated by crustaceans (e.g., Atyaephyra desmarestii, Procambarus clarkii) and were highly overlapped in Correspondence Analysis. Canonical Correspondence Analysis, coupled with variance partitioning, showed that hydrological connectivity accounted for 28% of the variability in the invertebrate community, followed by physicochemical (10%) and trophic (7%) factors. Differences in frequency and duration of flood pulses in natural oxbow lakes were not enough to generate distinctive macroinvertebrate assemblages in the different wetlands. Analysis of variance showed that richness and total abundance increased with hydrological connectivity, while diversity showed a rather unimodal distribution. Generalized Additive Models indicated that among the measured environmental variables, nitrate concentration strongly affected the composition, abundance and diversity of aquatic communities. Our data indicate that increasing the diversity of water body types in degraded floodplains enhances biodiversity and aids in the functional and ecological recovery of the riverine landscape.

Effects of hydrological connectivity on the substrate and understory structure of riparian wetlands in the Middle Ebro River (NE Spain): Implications for restoration and management

Abstract.The hydroperiod, flooded sediments and riparian understory were examined for eight riparian wetlands of one Ebro River reach (NE Spain) to relate river-floodplain interactions at different spatio-temporal scales with wetland strucuture. This analysis served as a basis for assessing the ecological status of the study reach and proposing a valid restoration plan. A comparison of water-level fluctuations in riparian wetlands with that in the river channel during an ordinary flood was use to characterize the hydroperiod. This characterization was further linked with the results of a multivariate analysis performed using sediment physico-chemistry. Moreover, different measures of understory diversity were used to estimate the successional stage of eight riparian wetlands located in the same reach of the Ebro River. We described four hydroperiod types from the examined flood, from disconnected oxbow lakes to backflow channels fluctuating in concert with the Ebro River. Also three types of sediment differ in their organic matter content. Both results were closely related reflecting the dominance of endogenous or allogeneous processes. However, such heterogeneity was interpreted as being variable over longer spatiotemporal scales. In addition, the riverscape was found to be homogenous and dominated by wetlands at mature successional stages. Consequently, the lack of erosive floods within the reach seems to make inclusion of ecological restoration of geomorphological dynamics a highly appropriate management objective. Alternative strategies at both reach and site scales are proposed.

The effect of anthropogenic disturbance on the hydrochemical characteristics of riparian wetlands at the Middle Ebro River (NE Spain)

In natural systems, the chemistry of floodplain waters is a function of the source of the water, which is influenced by geomorphic features of riparian wetlands. However, anthropogenic disturbances may alter both geomorphic features and the natural balance of water mixing in the floodplain. The aim of this study was to classify riparian wetlands and characterize their water characteristics in one reach of the Middle Ebro River to assess the hydrochemical functioning of the system. In order to accomplish that goal, water samples were collected at 40 sampling sites during low-water conditions and two floods of different magnitude. Moreover, geomorphic characteristics of riparian wetlands were also analyzed to interpret the results at broader spatio-temporal scales. Three group of wetlands were identified using multivariate ordination: (1) major and secondary channels highly connected to the river by surface water, containing weakly ionized water with high nitrate levels during floods; (2) secondary channels and artificial ponds located in riparian forests near the river, most of which were affected by river seepage during the examined events. This type of sites had high major ions concentrations and elevated spatial variability with respect to nutrient concentrations during floods; (3) Siltated oxbow lakes, whose hydrogeochemical features seemed to be unaffected by factors related to river fluctuations. Total dissolved solids, major ion (sulfate, chloride, sodium, calcium, magnesium, and potassium) and nutrient (nitrate, ammonium and organic nitrogen, and phosphate) depended upon the relationships between surface and subsurface water flows. Seasonal changes and geomorphic characterization indicated that a strong functional dependence of floodplain wetlands close to the main river channel is established, whereas most of the floodplain area remains disconnected from river dynamics. Moreover, the effect of nitrate-enriched agricultural runoff seems to affect water quality and hydrochemical gradients of the system. Based on our results, we propose different types of actions for the management of the Ebro River flow to ensure a more natural ecological functioning of its floodplains.

Wetland Restoration: Integrating Scientific-Technical, Economic, and Social Perspectives

ECOLOGICAL RESTORATION 23:3 ■ SEPTEMBER 2005 Ecological Restoration, Vol. 23, No. 3, 2005 ISSN 1522-4740 E-ISSN 1543-4079 ©2005 by the Board of Regents of the University of Wisconsin System. Wetlands are being restored around the world using a wide spectrum of different approaches from the application of well-grounded scientific knowledge to obtain a precise objective to trial-and-error practices just to have water for some time on a piece of land. Whatever the methodology, wetland restoration projects can provide good theoretical and practical knowledge because, compared to other ecosystems, wetland ecosystems react relatively soon to manipulations (Mitsch and Gosselink 2000, Zentner and others 2003). Given this range of approaches, it must also be noted that the success of an ecological restoration project depends on many factors that should be taken into account when planning and developing a project. These can be grouped into three types: 1) technical failures or lack of scientific information, 2) economic constraints, and 3) social disagreements. The integration of these three perspectives— scientific-technical, economic and social —is important to obtain all the values of an ecological restoration project (Comín 2002, Winterhalder and others 2004). In this article, we present a number of wetland restoration experiences developed under different conditions in northeastern Spain in order to look for common recommendations for planning future, highvalue projects.

Relationship between invertebrate traits and lateral environmental gradients in a Mediterranean river-floodplain

The aim of the present study was to describe the relationships between macroinvertebrate traits and lateral hydrological and environmental gradients in a Mediterranean river-fl oodplain, from the main river channel to three disconnected fl oodplain wetlands. Bimonthly water and macroinvertebrate samples were collected from an array of riverine wetlands in the Ebro River in northeast Spain. Our analysis of trait structures in wetlands aligned along a lateral hydrological gradient showed that community composition changed from a rich and abundant inver- tebrate community dominated by generalist species adapted to disturbance at the river site to a more trait-diversifi ed community of specialist species adapted to stability and biotic interaction in hydrologically disconnected fl oodplain sites. The diversity of functional groups peaked at intermediate-connected sites, where both generalist and spe- cialist species coexist. The highest richness of functional groups was found in the river site, refl ecting its highest habitat heterogeneity. The main environmental variables shaping the structure of invertebrate traits extracted after Redundancy Analysis were fl ood duration and frequency (surrogates of hydrological disturbance), dissolved solids (surrogate of confi nement) and nitrate concentration (surrogate of agricultural pressure). These environmental vari- ables explained 43 % of the existing variability in invertebrate traits. Because groups with similar traits responded in different ways to the main gradients, we conclude that the functional grouping of invertebrates provides an adequate and simple tool to assess changes in functionality and the effect of lateral gradients across a fl oodplain. Our results highlight the need to integrate the study of rivers and their fl oodplains to better account for their close interaction.

Autochthonous Versus Allochthonous Organic Matter in Recent Soil C Accumulation Along a Floodplain Biogeomorphic Gradient: An Exploratory Study

Abstract The mechanisms controlling soil succession in floodplains remain much less studied than in uplands due to the complexity that flooddriven erosion and sedimentation bring into soil development processes. The amount of organic matter and C generally grows with soil ageing and is controlled by multiple and interacting allogenic and autogenic factors, but to what extent the production of organic matter by in situ vegetation contributes to soil formation in floodplains remains unknown. The objective of this work was to explore the importance of autochthonous organic matter versus allochthonous organic matter in organic C accumulation of floodplain forest soils along a vegetation succession and hydrogeomorphic connectivity gradient. Physicochemical analyses of sediment collected after one single flood event in a large Mediterranean floodplain (Middle Ebro, a 9th order regulated river reach in NE Spain) were used to estimate the proportion of organic C found in the topsoil (first 10 cm) samples of young (<25 yr), mature (25-50 yr) and old (>50 yr) floodplain forests that had an allochthonous (i.e., % of organic C deposited by floods) or autochthonous (i.e., % of organic C produced in situ by vegetation) source. Results of this exploratory study showed that the accumulation of autochthonous organic C in the floodplain topsoil only occurred in floodplain forests older than 50 year-old, but even then, it was more than six-fold less abundant than that with an allochthonous origin. Moreover, a linear mixed effect model showed that, although autochthonous organic C accumulation was mainly explained by the forest structure, a small proportion of it was also controlled by an allogenic factor, the groundwater table depth. Then, groundwater table depth variations could be partly controlling autochthonous organic matter production and decomposition in this Mediterranean floodplain. Although flow regulation and embankment has dramatically limited the hydrogeomorphic dynamics of the river, allogenic overbank sedimentation during flood events still controls floodplain soil succession and organic C accumulation in the floodplain.