Ecosystem-level effects of re-oligotrophication and N:P imbalances in rivers and estuaries on a global scale.

Trends and ecological consequences of phosphorus (P) decline and increasing nitrogen (N) to phosphorus (N:P) ratios in rivers and estuaries are reviewed and discussed. Results suggest that re-oligotrophication is a dominant trend in rivers and estuaries of high-income countries in the last two-three decades, while in low-income countries widespread eutrophication occurs. The decline in P is well documented in hundreds of rivers of United States and the European Union, but the biotic response of rivers and estuaries besides phytoplankton decline such as trends in phytoplankton composition, changes in primary production, ecosystem shifts, cascading effects, changes in ecosystem metabolism, etc., have not been sufficiently monitored and investigated, neither the effects of N:P imbalance. N:P imbalance has significant ecological effects that need to be further investigated. There is a growing number of cases in which phytoplankton biomass have been shown to decrease due to re-oligotrophication, but the potential regime shift from phytoplankton to macrophyte dominance described in shallow lakes has been documented only in a few rivers and estuaries yet. The main reasons why regime shifts are rarely described in rivers and estuaries are, from one hand the scarcity of data on macrophyte cover trends, and from the other hand physical factors such as peak flows or high turbidity that could prevent a general spread of submerged macrophytes as observed in shallow lakes. Moreover, re-oligotrophication effects on rivers may be different compared to lakes (e.g., lower dominance of macrophytes) or estuaries (e.g., limitation of primary production by N instead of P) or may be dependent on river/estuary type. We conclude that river and estuary re-oligotrophication effects are complex, diverse and still little known, and in some cases are equivalent to those described in shallow lakes, but the regime shift is more likely to occur in mid to high-order rivers and shallow estuaries.

Environmental filtering determines metacommunity structure in wetland microcrustaceans.

Metacommunity approaches are becoming popular when analyzing factors driving species distribution at the regional scale. However, until the popularization of the variation partitioning technique it was difficult to assess the main drivers of the observed patterns (spatial or environmental). Here we propose a new framework linking the emergence of different metacommunity structures (e.g., nested, Gleasonian, Clementsian) to spatial and environmental filters. This is a novel approach that provides a more profound analysis of how both drivers could lead to similar metacommunity structures. We tested this framework on 110 sites covering a strong environmental gradient (i.e., microcrustacean assemblages organized along a salinity gradient, from freshwater to brackish water wetlands). First we identified the metacommunity structure that better fitted these microcrustacean assemblages. Then, we used hierarchical variation partitioning to quantify the relative influences of environmental filters and the distance among wetlands on the identified structure. Our results showed that under strong environmental filtering metacommunity structures were non-random. We also noted that even passive dispersers, that are supposed to be poorly spatially filtered, showed spatial signals at a large geographical scale. However, some difficulties arose when inferring biotic interactions at finer-scale spatial signals. Overall, our study shows the potential of elements of metacommunity structure combined with variation partition techniques to detect environmental drivers and broadscale patterns of metacommunity structure, and that some caution is needed when interpreting finer-scale spatial signals.

Genetic and Physiological Diversity in the Diatom Nitzschia inconspicua.

Nitzschia inconspicua is an ecologically important diatom species, which is believed to have a widespread distribution and to be tolerant to salinity and to organic or nutrient pollution. However, its identification is not straightforward and there is no information on genetic and ecophysiological diversity within the species. We used morphological, molecular (rbcL and LSU D1-D3), ecophysiological and reproductive data to investigate whether N. inconspicua constitutes a single species with a broad ecological tolerance or two or more cryptic species with shared or different ecological preferences. Molecular genetic data for clones from upstream and deltaic sites in the Ebro River basin (Catalonia, Spain) revealed seven N. inconspicua rbcL + LSU genotypes grouped into three major clades. Two of the clades were related to other Nitzschia and Denticula species, making N. inconspicua paraphyletic and suggesting the need for taxonomic revision. Most clones were observed to be automictic, exhibiting paedogamy, and so the biological species concept cannot be used to establish species boundaries. Although there were morphological differences among clones, we found no consistent differences among genotypes belonging to different clades, which are definable only through sequence data. Nevertheless, separating the genotypes could be important for ecological purposes because two different ecophysiological responses were encountered among them.

Top ten priorities for global saltmarsh restoration, conservation and ecosystem service research.

Coastal saltmarshes provide globally important ecosystem services including 'blue carbon' sequestration, flood protection, pollutant remediation, habitat provision and cultural value. Large portions of marshes have been lost or fragmented as a result of land reclamation, embankment construction, and pollution. Sea level rise threatens marsh survival by blocking landward migration where coastlines have been developed. Research-informed saltmarsh conservation and restoration efforts are helping to prevent further loss, yet significant knowledge gaps remain. Using a mixed methods approach, this paper identifies ten research priorities through an online questionnaire and a residential workshop attended by an international, multi-disciplinary network of 35 saltmarsh experts spanning natural, physical and social sciences across research, policy, and practitioner sectors. Priorities have been grouped under four thematic areas of research: Saltmarsh Area Extent, Change and Restoration Potential (including past, present, global variation), Spatio-social contexts of Ecosystem Service delivery (e.g. influences of environmental context, climate change, and stakeholder groups on service provisioning), Patterns and Processes in saltmarsh functioning (global drivers of saltmarsh ecosystem structure/function) and Management and Policy Needs (how management varies contextually; challenges/opportunities for management). Although not intended to be exhaustive, the challenges, opportunities, and strategies for addressing each research priority examined here, providing a blueprint of the work that needs to be done to protect saltmarshes for future generations.

Evaluating adaptation options to sea level rise and benefits to agriculture: The Ebro Delta showcase.

Sea level rise (SLR) is threatening low-lying coastal areas such as river deltas. The Ebro river Delta (Spain) is representative of coastal systems particularly vulnerable to SLR due to significant sediment retention behind upstream dams (up to 99%), thereby dramatically reducing the capacity for deltaic sediment accretion. Rice production is the main economic activity, covering 66% of the delta area, and is negatively affected by SLR because of flooding and soil salinization. Therefore, appropriate adaptation measures are needed to preserve rice production. We combined Geographic Information Systems and Generalized Linear Models to identify zones prone to flooding and increasing soil salinity, and to calculate the so-called sediment deficit, that is the amount of sediment needed to raise the land to compensate flooding and soil salinization. We modelled SLR scenarios predicted by the IPCC Fifth Assessment Report, and analysed the economic feasibility (not the technical feasibility) of reintroducing fluvial sediments retained in the upstream river dam reservoirs into the delta plain, which can contribute to maintaining land elevation and rice production with SLR. To do this, the costs of the sediment reintroduction measures and their benefits in terms of avoided loss of rice production income were evaluated with an approximate economic cost-benefit analysis. Results predicted that between 35 and 90% of the rice field area will be flooded in the best and worst SLR scenarios considered (SLR = 0.5 m and 1.8 m by 2100, respectively), with a sediment deficit of 130 and 442 million tonnes, with an associated cost of sediment reintroduction of 13 and 226 million €. The net benefit of rice production maintenance was 24.6 and 328 €/ha. The proposed adaptation measure has a positive effect on rice production and can be considered as an innovative management option for maintaining deltaic areas under SLR.

Constraints on the adjustment of tidal marshes to accelerating sea level rise.

Much uncertainty exists about the vulnerability of valuable tidal marsh ecosystems to relative sea level rise. Previous assessments of resilience to sea level rise, to which marshes can adjust by sediment accretion and elevation gain, revealed contrasting results, depending on contemporary or Holocene geological data. By analyzing globally distributed contemporary data, we found that marsh sediment accretion increases in parity with sea level rise, seemingly confirming previously claimed marsh resilience. However, subsidence of the substrate shows a nonlinear increase with accretion. As a result, marsh elevation gain is constrained in relation to sea level rise, and deficits emerge that are consistent with Holocene observations of tidal marsh vulnerability.

Procambarus clarkii as a bioindicator of heavy metal pollution sources in the lower Ebro River and Delta.

In the Ebro River basin, point and diffuse pollution of heavy metals stems mainly from industry and agriculture. Bioaccumulation patterns were examined under different pollution sources (point and diffuse) using levels of heavy metals (As, Cd, Cr, Cu, Hg, Pb and Zn) in abdominal muscle tissue of Procambarus clarkii. P. clarkii captured under point source effects presented the highest concentrations of Hg, Pb and As; and were related with distance to the source of industrial waste sediments. Mean Hg levels in crayfish exposed to point sources of metals significantly exceeded legal allowed values established by the European Union legislation. In the Ebro Delta, high levels of As, Cr, Cu and Zn were associated with traditional agriculture activity (diffuse pollution) as well. These results demonstrate the potential of P. clarkii to bioaccumulate heavy metals from both point and diffuse sources and hence potentially transfer these metals to higher trophic levels.

Ecotoxicological effects of rice field waters on selected planktonic species: comparison between conventional and organic farming.

The aim of this study was to assess the ecotoxicological effects of water coming from untreated organic and conventional rice field production areas in the Ebro Delta (Catalonia, Spain) treated with the herbicides oxadiazon, benzofenap, clomazone and bensulfuron-methyl and the fungicides carbendazim, tricyclazole and flusilazole. Irrigation and drainage channels of the study locations were also included to account for potential toxic effects of water coming in and out of the studied rice fields. Toxicity tests included four species (Pseudokirchneriella subcapitata, Desmodesmus subcapitatus, Chlorella vulgaris and Daphnia magna), three endpoints (microalgae growth, D. magna mortality and feeding rates), and two trophic levels: primary producers (microalgae) and grazers (D. magna). Pesticides in water were analyzed by solid phase extraction-liquid chromatography-electrospray-tandem mass spectrometry (LC-ESI-MS/MS). Negative effects on algae growth and D. magna feeding rates were detected mainly after application of herbicides and fungicides, respectively, in the conventional rice field. Results indicated that most of the observed negative effects in microalgae and D. magna were explained by the presence of herbicides and fungicides. The above mentioned analyses also denoted an inverse relationship between phytoplankton biomass measured as chlorophyll a and herbicides. In summary, this study indicates that in real field situations low to moderate levels of herbicides and fungicides have negative impacts to planktonic organisms and these effects seem to be short-lived.

Carbon metabolic rates and GHG emissions in different wetland types of the Ebro Delta.

Deltaic wetlands are highly productive ecosystems, which characteristically can act as C-sinks. However, they are among the most threatened ecosystems, being very vulnerable to global change, and require special attention towards its conservation. Knowing their climate change mitigating potential, conservation measures should also be oriented with a climatic approach, to strengthen their regulatory services. In this work we studied the carbon biogeochemistry and the specific relevance of certain microbial guilds on carbon metabolisms of the three main types of deltaic wetlands located in the Ebro Delta, north-eastern Spain, as well as how they deal with human pressures and climate change effects. We estimated the metabolic rates of the main carbon-related metabolisms (primary production and respiration) and the resulting carbon and global warming potential balances in sites with a different salinity range and trophic status. With the results obtained, we tried to define the influence of possible changes in salinity and trophic level linked to the main impacts currently threatening deltaic wetlands, on the C-metabolisms and GHG emissions, for a better understanding of the mitigating capacity and their possible enhancement when applying specific management actions. Metabolic rates showed a pattern highly influenced by the salinity range and nutrients inputs. Freshwater and brackish wetlands, with higher nutrient inputs from agricultural runoff, showed higher C-capture capacity (around 220-250 g C m-2 y-1), but also higher rates of degradative metabolisms (aerobic respiration and CH4 emissions). Contrastingly, the rates of C-related metabolisms and C-retention of Salicornia-type coastal salt marshes were lower (42 g C m-2 y-1). The study of the microbial metacommunity composition by the16S RNA gene sequencing revealed a significant higher presence of methanogens in the salt marsh, and also higher metabolic potential, where there was significantly more organic matter content in sediment. Salinity inhibition, however, explained the lower respiration rates, both aerobic and anaerobic, and prevented higher rates of methanogenesis despite the major presence of methanogens. Conservation measures for these wetlands would require, overall, maintaining the sediment contributions of the river basin intending to overcome the regression of the Delta and its salt marshes in a climate change scenario. Particularly, for reducing degradative metabolisms, and favour C-retention, nutrient inputs should be controlled in freshwater and brackish wetlands in order to reduce eutrophication. In salt marshes, the reduction of salinity should be avoided to control increases in methanogenesis and CH4 emissions.

Pristine vs. human-altered Ebro Delta habitats display contrasting resilience to RSLR.

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.

Neglecting the fallow season can significantly underestimate annual methane emissions in Mediterranean rice fields.

Paddy rice fields are one of the most important sources of anthropogenic methane. Improving the accuracy in the CH4 budget is fundamental to identify strategies to mitigate climate change. Such improvement requires a mechanistic understanding of the complex interactions between environmental and agronomic factors determining CH4 emissions, and also the characterization of the annual temporal CH4 emissions pattern in the whole crop cycle. Hence, both the growing and fallow seasons must be included. However, most of the previous research has been based on single-factor analyses that are focused on the growing season. In order to fill this gap, a study was conducted in a Mediterranean rice agrosystem (Ebre Delta, Catalonia) following a farm-to-farm approach with the purpose of 1) evaluating the cumulative and temporal pattern of CH4 emission, and 2) conducting a multi-variate analyses to assess the associative pattern, relative contribution and temporal variation of the main explanatory variables concerning the observed CH4 emissions. Measurements of CH4 emissions and agronomic and environmental parameters in 15 commercial rice fields were monitored monthly, during a whole crop field cycle. The temporal pattern of CH4 emission followed a bi-modal distribution peaking in August and October. The cumulative annual CH4 emissions from rice fields amounted 314 kg CH4 kg ha-1, of which ca. 70% were emitted during the fallow season. The main controlling factors of the CH4 emission rate in the growing season were positive related to water level and plant cover, while soil redox was negatively related. The main controlling factors in the fallow season were water level (negatively related, conversely to the growing season), as well as straw incorporation and soil temperature (positively related). The results of this study highlight the importance of the often neglected fallow season in the accurate estimation of CH4 emissions and, thus, the necessity of measurement programs that cover the whole crop field cycle. This information is the first step for setting effective mitigation strategies based on straw and water management.

Correction: Neglecting the fallow season can significantly underestimate annual methane emissions in Mediterranean rice fields.

[This corrects the article DOI: 10.1371/journal.pone.0198081.].

The impact of two large floods (1993-1994) on sediment deposition in the Rhône delta: Implications for sustainable management.

In October 1993 and January 1994, two large floods with peak discharge of 9800 and 10,980m3/s and total suspended solid transport of 10.7×106 and 9.7×106 tons, respectively, occurred on the Rhône River. Both floods led to multiple levee breeches in the Northern part of the delta resulting in the introduction of 131×106 and 54.9×106m3 of river water, respectively. In both cases, the flood water drained to the southern lagoons and was partly pumped directly back to the Rhône or to the sea. Most of the 390,000 tons of sediment introduced remained in the Northern inundated area with accretion ranging from 70mm near the breaches to 4mm 6-8km away. This last value is close to the mean accretion value (3.7mm) inferred from the water budget and the estimation of the total quantity of sediment introduced in the flooded area. In a small area near the mouth of the Rhône river still receiving natural overflow from the river, total deposition during both floods was as high as 10cm. The Rhône delta is facing an uncertain future with projected sea-level rise. The results of this study show that large introductions of river water can help sustain the delta in the face of climate change. Controlled introductions of river water using riverside closable structures, as in being done in other deltas, could be done in a way that delivers water and sediments to the places where it is needed most and at the same time protect important infrastructure.

Effects of enhanced hydrological connectivity on Mediterranean salt marsh fish assemblages with emphasis on the endangered Spanish toothcarp (Aphanius iberus).

The hydrological connectivity between the salt marsh and the sea was partially restored in a Mediterranean wetland containing isolated ponds resulting from former salt extraction and aquaculture activities. A preliminary assessment provided evidence that ponds farther from the sea hosted very large numbers of the endangered Spanish toothcarp, Aphanius iberus, suggesting that individuals had been trapped and consequently reach unnaturally high densities. In order to achieve both habitat rehabilitation and toothcarp conservation, efforts were made to create a gradient of hydrologically connected areas, including isolated fish reservoirs, semi-isolated, and connected salt marsh-sea areas that could allow migratory movements of fish and provide some protection for A. iberus. The fish community was monitored prior to, and for three years after rehabilitation. Results showed an increase in the number of fish species within semi-isolated areas (Zone A), whereas areas adjacent to the sea (Zone B) increased the number of marine species and decreased that of estuarine species (ES). Yet overall differences in fish assemblages were much higher between zones than among study years. Generalized linear models (GLMs) evidenced that distance to the sea was the most important variable explaining the local diversity of the fish community after restoration, with occasional influence of other factors such as temperature, and depth. The abundance of A. iberus was consistently higher in semi-isolated areas at greater distances from the sea, but a decline occurred in both zones and in isolated reservoir ponds after restoration efforts, which may be attributable to interannual differences in recruitment success and, to a lesser extent, to dispersal into adjacent habitats. A negative effect of restoration works on fish population cannot be excluded, but the final outcome of the intervention likely needs a longer period.

Sea level rise impacts on rice production: The Ebro Delta as an example.

Climate change and sea level rise (SLR) are global impacts threatening the sustainability of coastal territories and valuable ecosystems such as deltas. The Ebro Delta is representative of the vulnerability of coastal areas to SLR. Rice cultivation is the main economic activity in the region. Rice fields occupy most of the delta (ca. 65%) and are vulnerable to accelerated SLR and consequent increase in soil salinity, the most important physical factor affecting rice production. We developed a model to predict the impacts of SLR on soil salinity and rice production under different scenarios predicted by the Fifth Assessment Report of the Intergovernmental Panel on Climate Change by coupling data from Geographic Information Systems with Generalized Linear Models. Soil salinity data were measured in agricultural parcels and rice production from surveys among farmers. The correlation between observed and soil salinity predicted values was high and significant (Pearson's r=0.72, P<0.0001), thus supporting the predictive ability of the model. Soil salinity was directly related to distances to the river, to the delta inner border, and to the river old mouth, while clay presence, winter river flow and surface elevation were inversely related to it. Surface elevation was the most important variable in explaining soil salinity. Rice production was negatively influenced by soil salinity, thus the models predict a decrease from higher elevation zones close to the river to the shoreline. The model predicts a maximum reduction in normalized rice production index from 61.2% in 2010 to 33.8% by 2100 in the worst considered scenario (SLR=1.8m), with a decrease of profit up to 300 € per hectare. The model can be applied to other deltaic areas worldwide, and help rice farmers and stakeholders to identify the most vulnerable areas to SLR impacts.

Benthic macrofaunal dynamics and environmental stress across a salt wedge Mediterranean estuary.

The spatial distribution of benthic macroinvertebrate community in relation to environmental factors was studied along the Ebro Estuary (NE Iberian Peninsula), a salt wedge Mediterranean estuary. Both ordination methods and generalized additive models were performed to identify the different benthic assemblages and their relationship to abiotic factors. Our results showed a strong relationship between macrofaunal assemblages and the predominant environmental gradients (e.g. salinity); thus revealing spatial differences in their structure and composition. Two different stretches were identified, namely the upper (UE) and the lower Ebro Estuary (LE). UE showed riverine characteristics and hence was colonized by a freshwater community; whereas LE was influenced by marine intrusion and sustained a complex marine-origin community. However, within each stretch, water and sediment characteristics played an important role in explaining species composition differences among sampling stations. Moreover, outcomes suggested a total species replacement pattern, instead of the nestedness pattern usually associated with well-mixed temperate estuaries. The sharp species turnover together with the estuarine stratification point out that the Ebro Estuary is working, in terms of ecological boundaries, under an ecotone model. Finally, despite obvious differences with well mixed estuaries (i.e. lack of tidal influence, stratification and species turnover), the Ebro Estuary shares important ecological attributes with well-mixed temperate estuaries.

Low intramuscular fat (but high in PUFA) content in cooked cured pork ham decreased Maillard reaction volatiles and pleasing aroma attributes.

The influence of intramuscular fat content (high - HI versus low - LI) and fatty acid composition on pork cooked cured ham flavour was analysed by gas chromatography-olfactometry using nasal impact frequency (GC-O/NIF) and quantitative descriptive analysis (QDA). Potential relationships were studied by principal component analysis (PCA). Sixteen and fourteen odourants were identified by GC-O/NIF in LI and HI cooked hams, respectively. The two ham types differed in lipid oxidation odourants: polyunsaturated fatty acid (PUFA) derivatives hexanal, 1-octen-3-one and (E,E)-2,4-decadienal were higher in LI ham; while monounsaturated fatty acid (MUFA) derivative decanal was higher in HI. HI samples resulted in higher values for odour-active aroma compounds from Maillard reaction, which are related to roast flavour and a higher overall flavour liking. In summary, our results suggest that Maillard derived odour-active aroma compounds were partially inhibited in LI samples (high in PUFA), resulting in lower positive sensory ratings.

Benthic foraminifera as indicators of habitat change in anthropogenically impacted coastal wetlands of the Ebro Delta (NE Iberian Peninsula).

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.

Optimisation of stir-bar sorptive extraction (SBSE), targeting medium and long-chain free fatty acids in cooked ham exudates.

The purpose of our research was to optimise the extraction conditions of the stir-bar sorptive extraction (SBSE) targeting the identification of lipid compounds particularly medium and long-chain free fatty acids in cooked cured pork ham exudates. The analytical conditions of extraction (including sample volume, extraction time, stirring speed, pH and dilution of the sample) were checked using the Simplex method approach. As a result of the SBSE optimisation, improved detection limits and linear ranges for hexanoic, heptanoic, octanoic, nonanoic, decanoic, dodecanoic and tetradecanoic fatty acids were obtained. When comparing results with those obtained by the commonly used SPME methodology, optimisation of SBSE achieved better results for volatile compounds of low volatility, such as medium and long-chain free fatty acids, whereas compounds with high volatility and polarity were only detected by SPME. SBSE also confirmed its potential as a tool to help identify undesirable contaminants/residues in meat products.