Salvador Sánchez-Carrillo

Hydrological and botanical man-made changes in the Spanish wetland of Las Tablas de Daimiel

Man-made change in wetland ecosystems is mainly a 20th century process. Here, we report the changes over the last 55 years in the hydrology and botany of a Spanish semi-arid wetland, Las Tablas de Daimiel, a Ramsar site and a National Park. The landscape is valuable because of interesting waterfowl and plant species (particularly, Netta ruffina and Cladium mariscus) brought about by the fluctuations in water table arising from the interaction of surface flooding due to stream- and groundwater discharges and water retention by watermill dams. However, drainage reduced the wetland area to one seventh of its original value in 8 years between 1965 and 1973, and watermills were destroyed in the 1960s. Water pollution, mainly organic matter, nitrogen and phosphorus, coming from point (towns and agroindustry) and non-point sources (agricultural practices in the watershed) started in the late 1970s and peaked by the middle of next decade, decreasing later as a result of newly-implemented, water treatment plants in the catchment area. Water availability was reduced greatly between the late 1970s and the 1990s because of irrigation programs in the catchment area, which exhausted the groundwater aquifer, and their effects on plants were mediated by decreasing yearly average flooding and its variability. The combined effect of increased eutrophication and decreased water inputs reduced the Cladium cover 10-fold, reduced the extent of Charophyte meadows and three quarters of hydrophyte species were lost. The reed (Phragmites communis) cover increased 22-fold. Later, a sudden increase in water inputs coming from a nearby aquifer raised the number of hydrophytes and the Cladium cover, and reduced the reed cover. Thus, decreases in water quantity and quality have acted together on wetlands over the last 35 years affecting plant species richness and cover. Wetland survival is endangered if no remedial actions, such as those we propose, are implemented.

Export of nitrogen from catchments: A worldwide analysis

This study reviews nitrogen export rates from 946 rivers of the world to determine the influence of quantitative (runoff, rainfall, inhabitant density, catchment area, percentage of land use cover, airborne deposition, fertilizer input) and qualitative (dominant type of forest, occurrence of stagnant waterbodies, dominant land use, occurrence of point sources, runoff type) environmental factors on nitrogen fluxes. All fractions (total, nitrate, ammonia, dissolved organic and particulate organic) of nitrogen export showed a left-skewed distribution, which suggests a relatively pristine condition for most systems. Total nitrogen export showed the highest variability whereas total organic nitrogen export comprised the dominant fraction of export. Nitrogen export rates were only weakly explained by our qualitative and quantitative environmental variables. Our study suggests that the consideration of spatial and temporal scales is important for predicting nitrogen export rates using simple and easy-to-get environmental variables. Regionally based modelling approaches prove more useful than global-scale analyses.

The influence of Procambarus clarkii (Cambaridae, Decapoda) on water quality and sediment characteristics in a Spanish floodplain wetland

This study describes the effects of the American red swamp crayfish, Procambarus clarkii Girard, on water quality and sediment characteristics in the Spanish floodplain wetland, Las Tablas de Daimiel National Park. Our short term enclosure study during a summer drawdown revealed that crayfish acted as a nutrient pump that transformed and translocated sediment bound nutrients to the water column. Water quality impoverishment was mainly due to the increase of dissolved inorganic nutrients (soluble reactive phosphorus and ammonia), and a significant increase of total suspended solids occurred likely as a result of crayfish associated bioturbation. At the same time, crayfish reduced the content of organic matter in the sediment and we observed a slight increase of total sediment phosphorus and nitrogen content as a result of crayfish benthic activity. P. clarkii effects, in terms of internal nutrient loading (229.91 mg TP m−2 d−1), were shown to be important on a local scale, indicating the significance of internal nutrient supply to water column primary producers particularly under low external supply (summer). Extrapolations to the whole ecosystem, however, revealed a negligible crayfish contribution (0.06%) to total internal nutrient loading (0.035 mg TP m−2 d−1). Hence, crayfish spatial heterogeneity patterns are important in global and local matter fluxes and nutrient cycles in wetlands.

Assessment of exotic fish impacts on water quality and zooplankton in a degraded semi-arid floodplain wetland

Abstract. We carried out enclosure experiments to assess the potential deleterious effects of the alien species common carp (Cyprinus carpio L.), mosquitofish (Gambusia holbrookii Gir.), and pumpkinseed sunfish (Lepomis gibbosus L.) on water quality and food web in a severely degraded floodplain wetland, the Spanish National Park Las Tablas de Daimiel. With addition of either carp or pumpkinseed sunfish, chlorophyll a and turbidity levels, as well as concentrations of total phosphorus and total nitrogen increased. The magnitude of this increase depended on fish species and was severest in the carp treatment. Mosquitofish did not significantly affect water quality. In the treatments with fish, cyclopoid copepods and rotifers dominated, while cladocerans were virtually absent. Zooplankton biomass was significantly lower in the carp treatment compared with the control. However, no direct negative effect (predation) of carp was observed. Zooplankton biomass did not differ from the control, neither with pumpkinseed sunfish treatment nor with mosquitofish treatment. Nonetheless, both fish species had a negative impact on zooplankton biomass owing to planktivorous feeding. Ceriodaphnia reticulata Jurine populations increased in the fishless controls. Only this cladoceran species was able to control significantly phytoplankton. Results indicate that biomanipulations could have a high potential for environmental quality improvements of degraded riverine wetlands. A model was built to predict the potential advances and successes of biomanipulations in the wetland.

Sedimentation in the semi-arid freshwater wetland Las Tablas de Daimiel (Spain)

Despite sedimentation being recognized as a very important process in wetlands, very little is known about its dynamics. This study analyzed sedimentation on a short-term scale in the semiarid floodplain wetland Las Tablas de Daimiel National Park (central Spain). In monthly sampling intervals during 1997 and 1998, we measured seasonal and spatial sedimentation patterns of total solids, organic and mineral matter, nitrogen, and phosphorus using sediment traps. The highest mean mass accumulation rates were obtained at the wetland-input site (135±57 g m−2 d−1), but a decrease in sedimentation rates was noted with increasing distance from the inflow (49±39 g m−2 d−1 in the terminal zone of the wetland). Flow and water level explained only 13% of variance in sedimentation. The sedimentation patterns presented clear seasonality, coinciding with the period of vegetation growth. There existed a marked spatial heterogeneity in sedimentation that can be attributed to differences in vegetative cover. In vegetated areas, sedimentation of solids was related with nutrient deposition coming from detritus. Sedimentation of mineral matter dominated over the organic fraction. Autochthonous material comprised a very important fraction of accumulated sediment (between 31–57% of mineral matter and 45–65% of organic matter). Sedimentation of autochthonous total phosphorus made up about 90% of total settling phosphorus. Reed (Phragmites australis) and sawgrass (Cladium mariscus) plant cover significantly explained sedimentation of organic matter in the wetland (R2=0.78 and 0.57, respectively). The contribution of phytoplankton primary productivity to total organic carbon sedimentation was negligible and observed only at the deeper sampling stations. The autochthonous mineral matter of the settlign seston may originate either from primary precipitation of endogenic calcite and/or rapid mineralization of organic matter on the sediment surface. Accretion rates were very high (1.61–3.87 cm yr−1), suggesting that the wetland will silt up within the next century if present rates are maintained. Thus, sedimentation dynamics must be involved in management strategies in order to conserve important wetlands.

A simple method for estimating water loss by transpiration in wetlands

Abstract Estimates of transpiration are often needed for hydrological management in wetlands. A new and simple method, using a portable steady-state porometer, is presented for estimating transpiration in three aquatic emergent macrophytes (reed, cut-sedge, and cattail). The method was established on the basis of the relationships between transpiration, solar radiation, relative humidity and air temperature. By assessing relationships between all variables in piecewise linear regressions with breakpoint, water loss by transpiration can be estimated. The regression equations are calculated from direct observations including daily averages of climatic variables. Other data used in the model are area-defined leaf density of macrophytes and yearly macrophyte cover. The results of this method in comparison with literature transpiration data confirm the importance of transpiration in the water balance in aquatic ecosystems. The advantage of this method relies on the possibility to determine the physiological variability of transpiration in relation to climatic variables determined in situ. This permits a closer approximation of processes taking place in nature. Given that the required information is easily obtainable and that good estimates of transpiration in emergent macrophytes are provided, the method serves as a valuable tool for wetland hydrology management.

Inferring the Relative Resilience of Alternative States

Ecological systems may occur in alternative states that differ in ecological structures, functions and processes. Resilience is the measure of disturbance an ecological system can absorb before changing states. However, how the intrinsic structures and processes of systems that characterize their states affects their resilience remains unclear. We analyzed time series of phytoplankton communities at three sites in a floodplain in central Spain to assess the dominant frequencies or “temporal scales” in community dynamics and compared the patterns between a wet and a dry alternative state. The identified frequencies and cross-scale structures are expected to arise from positive feedbacks that are thought to reinforce processes in alternative states of ecological systems and regulate emergent phenomena such as resilience. Our analyses show a higher species richness and diversity but lower evenness in the dry state. Time series modeling revealed a decrease in the importance of short-term variability in the communities, suggesting that community dynamics slowed down in the dry relative to the wet state. The number of temporal scales at which community dynamics manifested, and the explanatory power of time series models, was lower in the dry state. The higher diversity, reduced number of temporal scales and the lower explanatory power of time series models suggest that species dynamics tended to be more stochastic in the dry state. From a resilience perspective our results highlight a paradox: increasing species richness may not necessarily enhance resilience. The loss of cross-scale structure (i.e. the lower number of temporal scales) in community dynamics across sites suggests that resilience erodes during drought. Phytoplankton communities in the dry state are therefore likely less resilient than in the wet state. Our case study demonstrates the potential of time series modeling to assess attributes that mediate resilience. The approach is useful for assessing resilience of alternative states across ecological and other complex systems.

Microinvertebrate and plant beta diversity in dry soils of a semiarid agricultural wetland complex

The relationship between environmental features and the β diversity of the propagule bank of dry soils of temporary wetlands has relevance to ecological theories of community structure and to the conservation of wetland biodiversity. The correlation of β diversity of microinvertebrates and macrophytes derived from propagules in dry soils with wetland habitat characteristics, catchment land-use, and the distance between wetlands in a remnant pond complex in central Spain was assessed. Redundancy analyses showed that β diversity of both groups correlated with habitat characteristics, whereas associations with catchment agricultural practices were weaker. Nestedness analyses showed that species-poor communities from degraded sites tended to form nested subsets of less degraded ponds with higher species richness. Distance between the ponds had no significant association with community similarity, suggesting that fragmentation did not shape β diversity at the scale of our study area. To maintain high β diversity in this area, ponds with species-rich propagule banks should receive conservation priority. Given the functional dependence by much wildlife on these propagule banks once these wetlands rewet, conservation of this hidden biodiversity is crucial for providing ecosystem services to humans and wildlife.

Phytoplankton community similarity in a semiarid floodplain under contrasting hydrological connectivity regimes

In this study we compare phytoplankton community similarity between sites in a semiarid floodplain wetland over a 6-year period with variable hydroperiod and connectivity regimes. Phytoplankton communities showed a relatively high site idiosyncrasy during most parts of the study; however, during situations of low connectivity when individual sites were highly fragmented, phytoplankton communities occasionally became more similar between sites. This suggests that mass effects related to dispersal-mediated processes could be important. Viewed from a metacommunity perspective, phytoplankton community assembly at the wetland scale involves complex hierarchical processes that can act independently at different spatial extents. The main conclusion of this study is that the well-known effects of environmental variability associated with hydrological disturbance alone may not be sufficient for explaining, and by extension predicting, community assembly in this wetland. Other processes, perhaps involving overland dispersal, may eventually add a new dimension to, and complicate our understanding of, community processes in fluctuating wetlands.

Freshwater wetland eutrophication

The traditional perception of wetlands as nutrient sinks has led them to be used as wastewater disposal areas for a long time, resulting in a severe alteration of the structure and function by eutrophication. Nutrient loading is usually linked to hydrological alterations which encompass shifts in vegetation patterns and nutrient cycling. The eutrophication process in wetlands accelerates primary productivity and increases net accumulation of organic matter and nutrients but also enhances organic matter decomposition, microbial activity, and soluble nutrients in sediments. Internal loading becomes the main nutrient source to the wetland, even in the years of low external inputs, controlling the nutrient dynamics. Since soil phosphorus microbial biomass responds positively to phosphorus enrichment in wetlands, mineralized phosphorus in wetland soils appears as the most responsive microbial indicator to nutrient enrichment in wetlands. Therefore, phosphorus internal loading is the critical factor in regulating eutrophication status of wetlands. N2O and N2 emissions by wetlands can be enhanced in the future as nitrate availability in wetlands continues to be high due to increased pollution. The biological symptoms of wetlands degraded by eutrophication differ little from those observed in shallow lakes, these changes being consistent with predictions made by alternative state theory. The turbid state shows phytoplankton dominance and elevated biomass of planktivorous and benthivorous fish. Zooplanktivorous fish contribute to eutrophication chiefly via food web-mediated effects. Benthivorous fish increase the nutrient availability to phytoplankton chiefly by transferring sediment-bound nutrients to the water column during bottom foraging. Little of the methodology found to be useful in shallow lake restoration has been applied to wetland management. Whereas catchment nutrient management programs may be insufficient because of substantial storage of nutrients in wetland sediments, recent studies indicate that biomanipulation of fish standing stocks could contribute significantly to wetland eutrophication abatement. Therefore, biomanipulation, when appropriately timed in accordance with low water levels, combined with sediment dredging and other interventions, may be a low cost–high benefit tool for wetland eutrophication abatement.