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The top map shows the location of the experimentally restored marshes in the Ebro Delta (Catalonia, Spain). The bottom map shows its detailed location between an active organic rice field and an old restored marsh dominated by Phragmites australis (Cav.) Steudel and Typha latifolia L.
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... Ebro Delta is a vital coastal ecosystem in the western Mediterranean extending ∼330 km 2 ( Fig. 1) and is the second most important special protection area for birds (SPA) in Spain (Seo/BirdLife, 1997). The Ebro Delta possesses a diverse number of ecosystems including coastal lagoons, marshes and seagrasses, which comprise the Ebro Delta Natural Park and are part of the Natura 2000 network of the European Union (EU). Juxtaposed ...
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... carried out the field experiment at an organic rice farm located in the southeast of the Ebro Delta (Catalonia, Spain) (Fig. 1, Fig. 2. Design of the experimentally restored marshes. The two water treatments consisted of 36 experimental units receiving either irrigation or drainage water. Each treatment included the water level factor (10, 20 and 30 cm depth) divided in 3 blocks via a complete randomized block design. top). We established the experiment between an ...
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... units receiving either irrigation or drainage water. Each treatment included the water level factor (10, 20 and 30 cm depth) divided in 3 blocks via a complete randomized block design. top). We established the experiment between an active organic rice field to the West and an old restored marsh to the East separated by a bare soil strip (Fig. 1, bottom). We used a partly nested experimental design to compare plant biomass, vertical accretion and elevation change in response to water type and water level treatments. Water type comprised 2 treatments: riverine irrigation water (IW) and rice field drainage water (DW) applied to 36 experimental units (EUs) for each treatment. The water ...
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... Ebro Delta is a vital coastal ecosystem in the western Mediterranean extending ∼ 330 km 2 ( Fig. 1) and is the second most important special protection area for birds (SPA) in Spain (Seo/BirdLife, 1997). The Ebro Delta possesses a diverse number of ecosystems including coastal lagoons, marshes and seagrasses, which comprise the Ebro Delta Natural Park and are part of the Natura 2000 network of the European Union (EU). Jux- taposed with these natural areas there are 20,000 Ha of rice fields. Rice agriculture is the main economic activity within the Delta comprising up to 60% of the land surface of the Ebro Delta, providing an annual gross income of about D 60 million and a total rice production of 120,000 tons per year (Cardoch et al., 2002). Although rice agriculture development has transformed much of the Ebro Delta over the last two centuries (Cardoch et al., 2002), rice fields provide significant ecosystem services such as seasonal habitat for migratory birds, preven- tion of saline intrusion and nutrient removal (Martinez-Vilalta, 1995). The marshes and rice fields within the Delta receive irrigation water from the Ebro River, which is the largest river of the Iberian Peninsula (flow ca. 400 m 3 s − 1 ). A series of dams ( ∼ 170) were built along the watercourse during the 1960s to support a vari- ety of intensive water uses (Ibá nez ̃ and Prat, 2003). These dams retain an estimated 99% of the sediment that would normally be deposited within the Ebro Delta, thus creating a severe sediment deficit (Ibá nez ̃ et al., 1996). Global eustatic sea-level rise (ESLR) has increased at a rate of 1–2 mm yr − 1 over the last century and it is now higher than 3 mm yr − 1 (FitzGerald et al., 2008). However, predicted relative sea-level rise (RSLR) in Ebro Delta may range from 5 to 8 mm yr − 1 at the end of the present century, due to ESLR and land subsidence (Ibá nez ̃ et al., 2010). Both sediment reduction and RSLR have created an environment where ∼ 40% of the emerged Ebro Delta plain has an elevation lower than 50 cm and ∼ 10% of the delta is below sea level (Ibá nez ̃ et al., 1997). Thus, 50% of the Ebro Delta is vulnerable to flooding impacts and permanent submergence of both marshes and rice fields (DMAiH, 2008; Alvarado-Aguilar et al., 2012). This is not a problem unique to the Ebro Delta as similar systems such as the Ganges, Mississippi, Nile, Rhone and Po Deltas, all suffer from similar sediment deficits (Syvitski et al., 2009). RSLR impacts on worldwide deltaic rice agriculture would have effects on the global market by reduced production and subsequent increases in rice prices, which may have important implications for food security (Chen et al., 2012). Several studies in the Mediterranean and Asian Deltas (e.g. Ebro, Nile, Ganges and Mekong Deltas) also suggest potential population displacements, loss of biodiversity and cultural heritage (Syvitski et al., 2009; Day et al., 2011). One proposed measure to mitigate deltaic impacts is the intro- duction of riverine sediments into marshes as a means of correcting the sediment deficit (e.g. Mississippi Delta, Rhone Delta and Ebro Delta) (Ibá nez ̃ et al., 1997; DeLaune et al., 2003; Day et al., 2007). The reintroduced river water would also provide a source of nutrient input, which theoretically would increase marsh elevation by stimulating autogenic organic contribution via plant growth (McKee and Mendelssohn, 1989; Day et al., 2008). Freshwater inputs also reduce soil stressors such as hyper-salinity, anoxia and toxins that typically inhibit plant growth (Day et al., 2011). Several studies also emphasize that the organic contributions to marsh elevation may be more relevant than mineral contributions in sediment-deficient deltas and estuaries (DeLaune and Pezeshki, 2003; Blum and Christian, 2004; Nyman et al., 2006). However, more data are required to directly link organic contribution to marsh elevation (Cahoon et al., 2006; Day et al., 2011; Fagherazzi et al., 2012). In the Ebro Delta only marshes that maintain significant freshwater and sediment inputs will likely survive predicted RSLR (Ibá nez ̃ et al., 2010). So it is important to understand under which conditions the mineral and organic contributions to marsh elevation can be optimized as a key restoration objective. For example, the use of Paspalum Distichum L. during the establishment of restored marshes may be a viable restoration practice to mitigate RSLR due its ability to capture sediments, it’s tolerances to salinity, water logging, and dry conditions, fast growth, and ability to repro- duce from rhizomes, stolons, or seeds (Anderson and Ehringer, 2000; Carr, 2010; Wanyama et al., 2012). The practice of converting rice fields into marshes in areas of low elevation has been proposed in the Ebro Delta as a way to mitigate the effects of climate change (e.g. by elevation gain and carbon sequestration) and improve the water quality of agricultural runoff (Ibá nez ̃ et al., 1997). Recently, several public efforts have restored rice field land to freshwater marshes in the Ebro ...
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... water uses (Ibá nez ̃ and Prat, 2003). These dams retain an estimated 99% of the sediment that would normally be deposited within the Ebro Delta, thus creating a severe sediment deficit (Ibá nez ̃ et al., 1996). Global eustatic sea-level rise (ESLR) has increased at a rate of 1–2 mm yr − 1 over the last century and it is now higher than 3 mm yr − 1 (FitzGerald et al., 2008). However, predicted relative sea-level rise (RSLR) in Ebro Delta may range from 5 to 8 mm yr − 1 at the end of the present century, due to ESLR and land subsidence (Ibá nez ̃ et al., 2010). Both sediment reduction and RSLR have created an environment where ∼ 40% of the emerged Ebro Delta plain has an elevation lower than 50 cm and ∼ 10% of the delta is below sea level (Ibá nez ̃ et al., 1997). Thus, 50% of the Ebro Delta is vulnerable to flooding impacts and permanent submergence of both marshes and rice fields (DMAiH, 2008; Alvarado-Aguilar et al., 2012). This is not a problem unique to the Ebro Delta as similar systems such as the Ganges, Mississippi, Nile, Rhone and Po Deltas, all suffer from similar sediment deficits (Syvitski et al., 2009). RSLR impacts on worldwide deltaic rice agriculture would have effects on the global market by reduced production and subsequent increases in rice prices, which may have important implications for food security (Chen et al., 2012). Several studies in the Mediterranean and Asian Deltas (e.g. Ebro, Nile, Ganges and Mekong Deltas) also suggest potential population displacements, loss of biodiversity and cultural heritage (Syvitski et al., 2009; Day et al., 2011). One proposed measure to mitigate deltaic impacts is the intro- duction of riverine sediments into marshes as a means of correcting the sediment deficit (e.g. Mississippi Delta, Rhone Delta and Ebro Delta) (Ibá nez ̃ et al., 1997; DeLaune et al., 2003; Day et al., 2007). The reintroduced river water would also provide a source of nutrient input, which theoretically would increase marsh elevation by stimulating autogenic organic contribution via plant growth (McKee and Mendelssohn, 1989; Day et al., 2008). Freshwater inputs also reduce soil stressors such as hyper-salinity, anoxia and toxins that typically inhibit plant growth (Day et al., 2011). Several studies also emphasize that the organic contributions to marsh elevation may be more relevant than mineral contributions in sediment-deficient deltas and estuaries (DeLaune and Pezeshki, 2003; Blum and Christian, 2004; Nyman et al., 2006). However, more data are required to directly link organic contribution to marsh elevation (Cahoon et al., 2006; Day et al., 2011; Fagherazzi et al., 2012). In the Ebro Delta only marshes that maintain significant freshwater and sediment inputs will likely survive predicted RSLR (Ibá nez ̃ et al., 2010). So it is important to understand under which conditions the mineral and organic contributions to marsh elevation can be optimized as a key restoration objective. For example, the use of Paspalum Distichum L. during the establishment of restored marshes may be a viable restoration practice to mitigate RSLR due its ability to capture sediments, it’s tolerances to salinity, water logging, and dry conditions, fast growth, and ability to repro- duce from rhizomes, stolons, or seeds (Anderson and Ehringer, 2000; Carr, 2010; Wanyama et al., 2012). The practice of converting rice fields into marshes in areas of low elevation has been proposed in the Ebro Delta as a way to mitigate the effects of climate change (e.g. by elevation gain and carbon sequestration) and improve the water quality of agricultural runoff (Ibá nez ̃ et al., 1997). Recently, several public efforts have restored rice field land to freshwater marshes in the Ebro Delta using river irrigation water or rice field drainage water to feed them (MARM, 2006; Ibá nez ̃ and Bertolero, 2009). However, no previous experimental studies in the Ebro Delta and other Mediterranean deltas have assessed restoration initiatives regarding abiotic and biotic factors controlling vertical accretion and elevation change to keep pace with sediment deficit and RSLR. In this study we hypothesized that: (1) vertical accretion and elevation change in oligohaline restored marshes under low sediment availability conditions are controlled by organic contributions as a function of water type and water level, and (2) oligohaline restored marshes can have rates of vertical accretion and elevation gain higher than RSLR under low sediment availability conditions. To test these hypotheses, we conducted an experimental study during three years in a newly established experimentally restored marshes consisting of 72 experimental units (100 m 2 each). Two different freshwater water input types (riverine irrigation water and rice field drainage water) and three water levels (10, 20 and 30 cm deep) were used. We carried out the field experiment at an organic rice farm located in the southeast of the Ebro Delta (Catalonia, Spain) (Fig. 1, top). We established the experiment between an active organic rice field to the West and an old restored marsh to the East separated by a bare soil strip (Fig. 1, bottom). We used a partly nested experimental design to compare plant biomass, vertical accretion and elevation change in response to water type and water level treatments. Water type comprised 2 treatments: riverine irrigation water (IW) and rice field drainage water (DW) applied to 36 experimental units (EUs) for each treatment. The water level factor consisted of 3 water level treatments of 10, 20, and 30 cm in depth. These water level treatments were applied inside each water type using a complete randomized block design with three blocks. Therefore, each water type included 3 blocks and where each block included 12 EUs; 4 replicate EUs for each three water levels (Fig. 2). We included a block design to account for the variation in our experimental units from plant colonization effects from the active rice field on the West side of the experiment. The cho- sen water types and levels were based on readily available water sources and a realistic range of potential water levels found in rice fields and marshes of the Ebro Delta. Freshwater from both IW and DW favors the development of a helophytic marsh dominated by a Phragmites australis (Cav.) Steudel, Scirpus maritimus L. and Scirpus litoralis Schrad., since the study area is located in an old freshwater marsh area (abandoned distributary), which was transformed to rice cultivation in the previous century (Curcó et al., 1995). We initiated the experiment in August 2009 and ran it for 3 years (Appendix 1). The hydroperiod for the experiment (seasonal flooding and draw down periods) was coincident with the regional rice harvest/planting regime. During the first year, the EUs were fully flooded from August to December. In the second and third years, the EUs were flooded from June to December. Targeted water levels were maintained using an average water in-flow rate of 4.5 L s − 1 . The EUs were individually isolated using plastic lined wooden walls to prevent/limit water loss. Physical and chemical parameters were analyzed monthly from 2009 to 2011 for both water type inflows (3 samples per month and water type). Dissolved oxygen (DO 2 ), temperature, conductivity and pH were measured using an YSI 556 multiprobe (YSI Incorporated, Yellow Springs, OH, USA). Three water samples per month were collected for both water type inflows during 2010 and 2011 to measure total suspended solids (TSS), and total inorganic suspended solids (TISS) according to the UNE-EN 872 norm (AENOR, 1996). TSS and TISS analysis quantifies both total and mineral sediment inputs in both water types that may cause vertical accretion and elevation change response. In addition, three water samples per month for both water type inflows during 2010 were analyzed for the following nutrients: total phosphorus (TP) and total nitrogen (TN); inorganic dissolved nutrients; phosphate (P-PO 4 3 − ), nitrate (N-NO 3 − ) and ammonium (N-NH 4 + ), following standard methods (Grasshoff et al., 1999). Water nutrient analysis quantifies nutrient inputs in both water types that may cause a plant growth response. Furthermore, the same physical and chemical parameters were analyzed from a subset of 26 randomly selected EUs (Fig. 2) from the surface and sub-soil (0.5 m depth) from 2009 to 2011 to monitoring water characteristics that may influence plant growth. Superfi- cial soil core samples (above marker horizons) were collected in May 2011 within a 36 EUs subset to analyze soil parameters (i.e. mineral matter content, bulk density and mineral particle size) that may impact vertical accretion. Samples of known vol- ume were weighted to determine wet weight and dried to a constant weight at 60 ◦ C. Soil bulk density was calculated from these data (Page et al., 1982). Organic matter content was measured by loss-on-ignition at 500 ◦ C during 12 h and mineral matter was derived from organic matter percentage following Pont et al. (2002). The determination of particle size distribution in mineral soil material was performed using wet sieving and sedimentation technique (ISO11277, 2002). The following particles sizes classes were measured: clay ( d < 2 m), fine silt (2 m < d < 16 m), medium silt (16 m < d < 45 m), coarse silt (45 m < d < 63 m) and sand (63 m < d < 2000 m). Maximum aboveground biomass (MAB) or peak standing crop was measured to obtain an estimate of plant growth (Cronk and Siobhan Fennessy, 2001) that may affect vertical accretion and elevation change. Accordingly, three random subsamples of 0.25 m 2 were sampled from the previously identified 36 EUs subset in the last growing season of the experiment (August 2011) following a direct method from Schubauer and Hopkinson (1984). Plants were separated by species and dried to constant weight (at 60 ◦ C). Maximum belowground biomass (MBB) was analyzed to ...
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... a severe sediment deficit (Ibá nez ̃ et al., 1996). Global eustatic sea-level rise (ESLR) has increased at a rate of 1–2 mm yr − 1 over the last century and it is now higher than 3 mm yr − 1 (FitzGerald et al., 2008). However, predicted relative sea-level rise (RSLR) in Ebro Delta may range from 5 to 8 mm yr − 1 at the end of the present century, due to ESLR and land subsidence (Ibá nez ̃ et al., 2010). Both sediment reduction and RSLR have created an environment where ∼ 40% of the emerged Ebro Delta plain has an elevation lower than 50 cm and ∼ 10% of the delta is below sea level (Ibá nez ̃ et al., 1997). Thus, 50% of the Ebro Delta is vulnerable to flooding impacts and permanent submergence of both marshes and rice fields (DMAiH, 2008; Alvarado-Aguilar et al., 2012). This is not a problem unique to the Ebro Delta as similar systems such as the Ganges, Mississippi, Nile, Rhone and Po Deltas, all suffer from similar sediment deficits (Syvitski et al., 2009). RSLR impacts on worldwide deltaic rice agriculture would have effects on the global market by reduced production and subsequent increases in rice prices, which may have important implications for food security (Chen et al., 2012). Several studies in the Mediterranean and Asian Deltas (e.g. Ebro, Nile, Ganges and Mekong Deltas) also suggest potential population displacements, loss of biodiversity and cultural heritage (Syvitski et al., 2009; Day et al., 2011). One proposed measure to mitigate deltaic impacts is the intro- duction of riverine sediments into marshes as a means of correcting the sediment deficit (e.g. Mississippi Delta, Rhone Delta and Ebro Delta) (Ibá nez ̃ et al., 1997; DeLaune et al., 2003; Day et al., 2007). The reintroduced river water would also provide a source of nutrient input, which theoretically would increase marsh elevation by stimulating autogenic organic contribution via plant growth (McKee and Mendelssohn, 1989; Day et al., 2008). Freshwater inputs also reduce soil stressors such as hyper-salinity, anoxia and toxins that typically inhibit plant growth (Day et al., 2011). Several studies also emphasize that the organic contributions to marsh elevation may be more relevant than mineral contributions in sediment-deficient deltas and estuaries (DeLaune and Pezeshki, 2003; Blum and Christian, 2004; Nyman et al., 2006). However, more data are required to directly link organic contribution to marsh elevation (Cahoon et al., 2006; Day et al., 2011; Fagherazzi et al., 2012). In the Ebro Delta only marshes that maintain significant freshwater and sediment inputs will likely survive predicted RSLR (Ibá nez ̃ et al., 2010). So it is important to understand under which conditions the mineral and organic contributions to marsh elevation can be optimized as a key restoration objective. For example, the use of Paspalum Distichum L. during the establishment of restored marshes may be a viable restoration practice to mitigate RSLR due its ability to capture sediments, it’s tolerances to salinity, water logging, and dry conditions, fast growth, and ability to repro- duce from rhizomes, stolons, or seeds (Anderson and Ehringer, 2000; Carr, 2010; Wanyama et al., 2012). The practice of converting rice fields into marshes in areas of low elevation has been proposed in the Ebro Delta as a way to mitigate the effects of climate change (e.g. by elevation gain and carbon sequestration) and improve the water quality of agricultural runoff (Ibá nez ̃ et al., 1997). Recently, several public efforts have restored rice field land to freshwater marshes in the Ebro Delta using river irrigation water or rice field drainage water to feed them (MARM, 2006; Ibá nez ̃ and Bertolero, 2009). However, no previous experimental studies in the Ebro Delta and other Mediterranean deltas have assessed restoration initiatives regarding abiotic and biotic factors controlling vertical accretion and elevation change to keep pace with sediment deficit and RSLR. In this study we hypothesized that: (1) vertical accretion and elevation change in oligohaline restored marshes under low sediment availability conditions are controlled by organic contributions as a function of water type and water level, and (2) oligohaline restored marshes can have rates of vertical accretion and elevation gain higher than RSLR under low sediment availability conditions. To test these hypotheses, we conducted an experimental study during three years in a newly established experimentally restored marshes consisting of 72 experimental units (100 m 2 each). Two different freshwater water input types (riverine irrigation water and rice field drainage water) and three water levels (10, 20 and 30 cm deep) were used. We carried out the field experiment at an organic rice farm located in the southeast of the Ebro Delta (Catalonia, Spain) (Fig. 1, top). We established the experiment between an active organic rice field to the West and an old restored marsh to the East separated by a bare soil strip (Fig. 1, bottom). We used a partly nested experimental design to compare plant biomass, vertical accretion and elevation change in response to water type and water level treatments. Water type comprised 2 treatments: riverine irrigation water (IW) and rice field drainage water (DW) applied to 36 experimental units (EUs) for each treatment. The water level factor consisted of 3 water level treatments of 10, 20, and 30 cm in depth. These water level treatments were applied inside each water type using a complete randomized block design with three blocks. Therefore, each water type included 3 blocks and where each block included 12 EUs; 4 replicate EUs for each three water levels (Fig. 2). We included a block design to account for the variation in our experimental units from plant colonization effects from the active rice field on the West side of the experiment. The cho- sen water types and levels were based on readily available water sources and a realistic range of potential water levels found in rice fields and marshes of the Ebro Delta. Freshwater from both IW and DW favors the development of a helophytic marsh dominated by a Phragmites australis (Cav.) Steudel, Scirpus maritimus L. and Scirpus litoralis Schrad., since the study area is located in an old freshwater marsh area (abandoned distributary), which was transformed to rice cultivation in the previous century (Curcó et al., 1995). We initiated the experiment in August 2009 and ran it for 3 years (Appendix 1). The hydroperiod for the experiment (seasonal flooding and draw down periods) was coincident with the regional rice harvest/planting regime. During the first year, the EUs were fully flooded from August to December. In the second and third years, the EUs were flooded from June to December. Targeted water levels were maintained using an average water in-flow rate of 4.5 L s − 1 . The EUs were individually isolated using plastic lined wooden walls to prevent/limit water loss. Physical and chemical parameters were analyzed monthly from 2009 to 2011 for both water type inflows (3 samples per month and water type). Dissolved oxygen (DO 2 ), temperature, conductivity and pH were measured using an YSI 556 multiprobe (YSI Incorporated, Yellow Springs, OH, USA). Three water samples per month were collected for both water type inflows during 2010 and 2011 to measure total suspended solids (TSS), and total inorganic suspended solids (TISS) according to the UNE-EN 872 norm (AENOR, 1996). TSS and TISS analysis quantifies both total and mineral sediment inputs in both water types that may cause vertical accretion and elevation change response. In addition, three water samples per month for both water type inflows during 2010 were analyzed for the following nutrients: total phosphorus (TP) and total nitrogen (TN); inorganic dissolved nutrients; phosphate (P-PO 4 3 − ), nitrate (N-NO 3 − ) and ammonium (N-NH 4 + ), following standard methods (Grasshoff et al., 1999). Water nutrient analysis quantifies nutrient inputs in both water types that may cause a plant growth response. Furthermore, the same physical and chemical parameters were analyzed from a subset of 26 randomly selected EUs (Fig. 2) from the surface and sub-soil (0.5 m depth) from 2009 to 2011 to monitoring water characteristics that may influence plant growth. Superfi- cial soil core samples (above marker horizons) were collected in May 2011 within a 36 EUs subset to analyze soil parameters (i.e. mineral matter content, bulk density and mineral particle size) that may impact vertical accretion. Samples of known vol- ume were weighted to determine wet weight and dried to a constant weight at 60 ◦ C. Soil bulk density was calculated from these data (Page et al., 1982). Organic matter content was measured by loss-on-ignition at 500 ◦ C during 12 h and mineral matter was derived from organic matter percentage following Pont et al. (2002). The determination of particle size distribution in mineral soil material was performed using wet sieving and sedimentation technique (ISO11277, 2002). The following particles sizes classes were measured: clay ( d < 2 m), fine silt (2 m < d < 16 m), medium silt (16 m < d < 45 m), coarse silt (45 m < d < 63 m) and sand (63 m < d < 2000 m). Maximum aboveground biomass (MAB) or peak standing crop was measured to obtain an estimate of plant growth (Cronk and Siobhan Fennessy, 2001) that may affect vertical accretion and elevation change. Accordingly, three random subsamples of 0.25 m 2 were sampled from the previously identified 36 EUs subset in the last growing season of the experiment (August 2011) following a direct method from Schubauer and Hopkinson (1984). Plants were separated by species and dried to constant weight (at 60 ◦ C). Maximum belowground biomass (MBB) was analyzed to obtain information of root growth contribution to vertical accretion and elevation change. MBB was sampled in the last dormant season of the experiment (May 2012) by ...
Citations
... Increasing organic matter input by incorporating all crop residues can increase annual accretion rates; however, maintaining the accretion rate will depend on the stability of the newly incorporated organic matter and SOM (i.e., reducing decomposition rates). Incorporating residues (i.e., organic matter) into cropland soils has not been reported to promote soil accretion, but it does promote adaptation to SLR, as is the case for organic matter production and accumulation in marshes that bears most of the accretion (Calvo-Cubero et al., 2013;Neubauer, 2008). In addition, sediments help stabilize SOM (Neubauer, 2008). ...
... In this sense, it may be advisable to prioritize sediment input in fields that have lower elevation and are more vulnerable to loss of SOC sequestration capacity, such as those closer to the coast and/or those with more organic soils, since the latter especially have lower predicted accretion rates and are more vulnerable to loss of SOC sequestration capacity (Fig. 6). In addition, restoring wetland habitats in the most vulnerable rice fields could be an effective measure to promote SOC sequestration and address SLR, since it has been shown that accretion in rice fields transformed back into wetlands can be as high as 1 cm yr -1 , mainly due to accumulation of organic matter after establishment of plant communities (Calvo-Cubero et al., 2013). Therefore, due to the heterogeneity of the Ebro Delta landscape, application of management measures would be advisable with field-specific planning, for instance considering a field's SOM content, soil physical-chemical properties and elevation. ...
Rice cultivation is popular in low-lying areas such as deltas, but climate change threatens the viability of the crop. In recent decades, the resilience of deltas to sea level rise (SLR) has been influenced by the reduction of sediment load from rivers due to the construction of dams, disrupting natural deposition in deltaic plains. Sediment and organic matter accumulation in wetlands are key to vertical accretion in the face of SLR and soil organic carbon (SOC) sequestration. In this sense, deltaic rice fields can retain sediments as well as wetlands and promote SOC sequestration, which is effective in adapting to SLR. In the Ebro Delta, the sediments that reached the fields through irrigation channels were used to build up and form rice fields in the wetlands of the area. We hypothesize that this sedimentation has been key to vertical accretion and SOC sequestration in rice fields. These processes were simulated by developing a process-based cohort model inspired by accretion in marsh equilibrium models (MEM). The model was able to simulate the soil carbon profile of rice fields in the Ebro Delta, based on the soil-accretion concept and considering the spatial heterogeneity of the area. Its predictions of vertical accretion and carbon content were more accurate for mineral and clay-like soils than for organic and sandy soils. Topsoil decomposition rate and organic matter content were the parameters that most influenced predictions of total vertical accretion and final soil organic carbon stock. Simulations were carried out according to future climate change scenarios, considering restoration of river sediment flux, to evaluate effects on SOC sequestration and vertical accretion in rice fields. Results showed that only with
significant river sediment restoration did rice fields show positive vertical accretion, which facilitates SOC sequestration.
... but their capacity for vertical accretion, carbon sequestration and nutrient removal is still being assessed. In the Ebro Delta, previous results on vertical accretion in constructed wetlands have been obtained in small experimental plots, with accretion rates higher than 1 cm/yr (Calvo-Cubero et al., 2013), which is in balance with a present-day relative SLR rate of 1.1 cm/yr (Church et al., 2013). ...
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.
... The intricate connection between OM, accretion, and subsidence is of particular importance due to the increasing interest in resuming natural processes to restore deltaic plains and related coastal environments. These restoration efforts involve reintroducing mineral sediment to enable land building in areas that have been disconnected from the sediment source, usually due to flood-protection engineering (e.g., Auerbach et al., 2015;Calvo-Cubero et al., 2013;Giosan et al., 2013;Temmerman & Kirwan, 2015;Van der Deijl et al., 2018). To date, little attention has been given to how the loading associated with the introduction of mineral sediment may affect underlying, organic-rich strata in terms of sediment compaction (a notable exception is the study by Nienhuis et al., 2018). ...
Globally, mineral sediment supply to deltaic wetlands has generally decreased so these wetlands increasingly rely on accretion of organic matter to keep pace with relative sea‐level rise (RSLR). Because organic‐rich sediments tend to be more compressible than mineral‐dominated sediments, deltaic wetland strata are vulnerable to compaction and drowning. Using an unprecedented data set of almost 3,000 discrete bulk density and organic‐matter measurements, we examine organic‐rich facies from coastal Louisiana to quantify the thickness lost to compaction and investigate whether sediments are able to maintain sufficient volume for the associated wetlands to keep pace with RSLR. We find that organic content as well as overburden thickness and density (which together determine effective stress) strongly control sediment compaction. Most compaction occurs in the top 1–3 m and within the first 100–500 years after deposition. In settings with thick peat beds, successions up to 14 m thick have been compacted by up to ∼50%. We apply geotechnical modeling to examine the balance between elevation gained from accretion and elevation lost to compaction due to renewed sediment deposition over a 100‐year timescale. Wetlands overlying mineral‐dominated lithologies may support the weight of deposition and allow net elevation gain. Model results show that reintroduction of sediment to a representative Mississippi Delta wetland site will likely cause another ∼0.35–1.14 m of compaction but leave a net elevation gain of ∼0.01–1.75 m, depending on the sediment delivery rate and stiffness of underlying strata.
... mm/yr) by Fennessy et al. (2019). In a related study, Calvo-Cubero et al. (2013; assessed vertical accretion in abandoned rice fields receiving different water sources (irrigation versus runoff water from rice fields) and found vertical accretion rates of 11.5 ± 0.8 and 15.5 ± 0.6 mm/yr, respectively. The deposited sediment was about 85% of mineral origin with 90% silt and clay content. ...
... In comparison, the Alfacs salt marsh seemed to receive a greater contribution of C from allochthonous sources, given that C sequestration rates based on metabolic rates were lower than vertical soil accretion estimated with marker horizons (Table 15.1; Table 15.2). In coastal marshes, exogenous inputs include fine sediment carrying organic matter from the decomposition of macrophytes (rice plants and algae), while the autochthonous material depends on algae production and a settled plant community (Calvo-Cubero et al., 2013;Ibáñez et al., 2002). The high rates of organic carbon sequestration in these areas, together with the low methane rates (e.g., Alfacs C-CH 4 emissions are 0.48 g C-CH 4 /m 2 /yr; Morant et al. 2020a;Table 15.1) give these sites high C sequestration capacity and a negative GWP (i.e., a net cooling effect on climate). ...
... Today, due to the reduction in riverine sediment loads (Rovira et al., 2015), it is estimated that the sediment inputs in the last 50 years through the irrigation system are virtually nil (Calvo-Cubero et al 2013). Rice fields can function as sediment traps (Slaets et al., 2016) and, like wetlands, can store carbon from crop residues (root, straw, and algae) by burying them and increasing the organic matter content. ...
Coastal and deltaic wetlands are among the most effective ecosystems for climate regulation through carbon sequestration and storage. The Ebro Delta is an example of a landscape that attempts to integrate nature protection with economic development that is threatened by global change. The functionality of Ebro Delta wetlands is deteriorating due to sea‐level rise, subsidence, sediment starvation, limited hydrological connectivity and direct impacts caused by human activities (i.e., agriculture). Here we review studies on natural and agricultural wetlands (i.e., rice fields) with a focus on drivers of carbon (C) dynamics. The evidence supports that natural wetlands keep functioning as C sinks despite the impact of anthropogenic activities in the Delta, while rice fields act as net carbon sources to the atmosphere. Rates of C sequestration are mainly related to hydrological connectivity and salinity that modulate metabolic rates. In coastal lagoons (lower connectivity, lower salinity), autochthonous primary productivity is the main C sequestering process, whereas in salt marshes (higher connectivity, higher salinity) with lower metabolic rates, deposition of allochthonous material dominates. We discuss management options that promote C sequestration and greenhouse gas (GHG) emission reduction under a changing climate. Integrated management both at the local level – mainly of rice fields and adjacent wetlands – and at the regional level – the whole river basin and the delta – is essential to enhance fundamental ecosystem services such as carbon sequestration provided by the Ebro Delta, in order to increase its capacity to mitigate climate change.
... In the microtidal Mediterranean, sediment delivery mostly occurs episodically via freshwater flows during periodic river flooding and salt water flows during marine storm events, rather than through daily tidal inundation (Pont et al., 2017). The input of freshwater and the associated nutrients also lead to increased primary productivity, helping build soil organic matter (Hensel et al., 1999;Craft, 2007;Day et al., 2011;Calvo-Cubero et al., 2013). ...
... Understanding what drives the dynamics of sediment and carbon accumulation, and assessing the ability of wetlands to build vertically and keep pace with SLR will aid in restoration and management activities that promote the resilience of delta ecosystems. While previous studies have investigated this topic in constructed wetlands (Calvo-Cubero et al., 2013 and in other regions with a Mediterranean-climate (Callaway et al., 2012;Morris et al., 2013), this is the first study assessing carbon sequestration rates in coastal wetlands of the Mediterranean basin. ...
... Nitrate also varied from a maximum of 2.9 mg l −1 in 1992 to a low of 2.0 mg l −1 in 2003. Drainage from rice fields also creates a subsidy for plant growth, for example Calvo-Cubero et al. (2013) found phosphate levels of 0.13 mg L −1 and total nitrogen concentrations of 1.1 mg L −1 in agricultural drainage water in the Ebro Delta. ...
Delta wetlands are increasingly recognized as important sinks for ‘blue carbon,’ although this and other ecosystem services that deltas provide are threatened by human activities. We investigated factors that affect sediment accretion using short term (3 years using marker horizons) and longer-term measures (∼50 year using ¹³⁷ Cs soil core distribution and ∼100 year using ²¹⁰ Pb distribution), the associated carbon accumulation rates, and resulting changes in surface elevation in the Ebro River Delta, Catalonia, Spain. Fifteen sites were selected, representing the geomorphological settings and range of salinities typical of the delta's wetlands. Sediment accretion rates as measured by ¹³⁷ Cs distribution in soil cores ranged from 0.13 to 0.93 cm yr ⁻¹ . Surface elevations increased at all sites, from 0.10 to 2.13 cm yr ⁻¹ with the greatest increases in natural impoundments with little connection to other surface waters. Carbon accumulation rates were highly spatially variable, ranging from 32 to 435 g C m ⁻¹ yr ⁻¹ with significantly higher rates at bay sites (p = 0.02) where hydrologic connectivity is high and sediment resuspension more intense. Sites with high connectivity had significantly higher rates of carbon accumulation (averaging 376 ± 50 g C m ⁻¹ yr ⁻¹ ) compared to sites with moderate or low connectivity. We also found high rates of carbon accumulation in brackish sites where connectivity was low and biomass production was characteristically higher than in saline sites. A stepwise regression model explained 81% of variability in carbon accumulation rates across all sites. Our data indicate deltaic wetlands can be important sinks for blue carbon, contributing to climate change mitigation.
... Rice fields provide an important seasonal habitat for aquatic birds, and fresh water inputs contribute to preventing the saline intrusion among other ecosystem services (e.g. sediment accretion; Calvo-Cubero et al., 2013). However, rice fields may display altered patterns of connectivity due to the presence of irrigation ditches and other man-made structures (Katano et al., 2003) as well as differential rates of vertical accretion (Ibáñez et al., 1997) due to seasonal extraction of ca. ...
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.
... 188 E. C. van der Deijl et al.: Sediment budget in the "Kleine Noordwaard" cesses are restored and the system becomes multifunctional. Examples include the Tidal River Management project in Bangladesh (Khadim et al., 2013), the diversion projects in the Mississippi deltaic plain (DeLaune et al., 2003;Day et al., 2007;Paola et al., 2011), the Plan Integrale de Protección del Delta Ebro in the Ebro Delta (Calvo-Cubero et al., 2013), and the Room for the River initiative in the Netherlands (Rijke et al., 2012). Paola et al. (2011) defined river delta restoration as diverting sediment and water from major channels into adjoining drowned areas, where the sediment can build new land and provide a platform for regenerating wetland ecosystems. ...
Many deltas are threatened by accelerated soil subsidence, sea-level rise, increasing river discharge, and sediment starvation. Effective delta restoration and effective river management require a thorough understanding of the mechanisms of sediment deposition, erosion, and their controls. Sediment dynamics has been studied at floodplains and marshes, but little is known about the sediment dynamics and budget of newly created wetlands. Here we take advantage of a recently opened tidal freshwater system to study both the mechanisms and controls of sediment deposition and erosion in newly created wetlands. We quantified both the magnitude and spatial patterns of sedimentation and erosion in a former polder area in which water and sediment have been reintroduced since 2008. Based on terrestrial and bathymetric elevation data, supplemented with field observations of the location and height of cut banks and the thickness of the newly deposited layer of sediment, we determined the sediment budget of the study area for the period 2008–2015. Deposition primarily took place in channels in the central part of the former polder area, whereas channels near the inlet and outlet of the area experienced considerable erosion. In the intertidal area, sand deposition especially takes place at low-lying locations close to the channels. Mud deposition typically occurs further away from the channels, but sediment is in general uniformly distributed over the intertidal area, due to the presence of topographic irregularities and micro-topographic flow paths. Marsh erosion does not significantly contribute to the total sediment budget, because wind wave formation is limited by the length of the fetch. Consecutive measurements of channel bathymetry show a decrease in erosion and deposition rates over time, but the overall results of this study indicate that the area functions as a sediment trap. The total contemporary sediment budget of the study area amounts to 35.7×103 m3 year-1, which corresponds to a net area-averaged deposition rate of 6.1 mm year-1. This is enough to compensate for the actual rates of sea-level rise and soil subsidence in the Netherlands.
... Under natural conditions, deltas are dynamic, riverdominated systems, which drown or aggradate in response to changes in environmental conditions (Giosan et al. 2013). Both sedimentation and organic soil formation by vegetation contribute to elevation gain and delta aggradation (Reddy and DeLaune 2008;Calvo-Cubero et al. 2013;Kirwan and Megonigal 2013;Schile et al. 2014). However, many deltas are threatened by drowning due to sea-level rise, human-induced accelerated soil subsidence, sediment starvation due to upstream land use and river management, or increased river discharge (Ibáñez et al. 1997; Content courtesy of Springer Nature, terms of use apply. ...
... Paola et al. (2011) defined river delta restoration as "diverting sediment and water from major channels into adjoining drowned areas, where the sediment can build new land and provide a platform for regenerating wetland ecosystems." This type of river delta restoration is currently considered or implemented in the Tidal River Management project in Bangladesh (Khadim et al. 2013), the diversion projects in the Mississippi deltaic plain (DeLaune et al. 2003;Day et al. 2007;Paola et al. 2011) or in the Atchafalaya subdelta (Roberts et al. 2015;DeLaune et al. 2016), and the Plan Integrale de Protección del Delta Ebro for the Ebro Delta (Calvo-Cubero et al. 2013). ...
Purpose
A thorough understanding of mechanisms controlling sedimentation and erosion is vital for a proper assessment of the effectiveness of delta restoration. Only few field-based studies have been undertaken in freshwater tidal wetlands. Furthermore, studies that measured sediment deposition in newly created wetlands are also sparse. This paper aims to identify the factors controlling the sediment trapping of two newly created freshwater tidal wetlands.
Materials and methods
Two recently re-opened polder areas in the Biesbosch, The Netherlands are used as study area. Field measurements of water levels, flow velocities, and turbidity at both the in- and outlet of the areas were carried out to determine the sediment budgets and trapping efficiencies under varying conditions of river discharge, tide, and wind in the period 2014–2016.
Results and discussion
Short-term sediment fluxes of the two study areas varied due to river discharge, tide, and wind. A positive sediment budget and trapping efficiency was found for the first study area, which has a continuing supply of river water and sediment. Sediment was lost from the second study area which lies further from the river and had a lower sediment supply. The daily sediment budget is positively related to upstream river discharge, and in general, export takes place during ebb and import during flood. However, strong wind events overrule this pattern, and trapping efficiencies decrease for increasing wind strengths at mid-range river discharges and for the highest river discharges due to increased shear stress.
Conclusions
Delta restoration, based on sedimentation to compensate for sea-level rise and soil subsidence, could only be effective when there is a sufficient supply of water and sediment. Management to enhance the trapping efficiency of the incoming sediment should focus on directing sufficient river flow into the wetland, ensuring the supply of water and sediment within the system during a tidal cycle, creating sufficiently large residence time of water within the polder areas for sediment settling, and decreasing wave shear stress by the establishment of vegetation or topographic irregularities.
... Therefore, since recently, river delta management has been shifting from the implementation of these strong regulations towards the control of a more natural system where dynamic processes are restored and the system becomes multifunctional. Examples 5 include the Tidal River Management project in Bangladesh (Khadim et al., 2013), the diversion projects in the Mississippi deltaic plain (DeLaune et al., 2003;Day et al., 2007;Paola et al., 2011), the Plan Integrale de Protección del Delta Ebro in the Ebro Delta (Calvo-Cubero et al., 2013) and the Room for the River initiative in the Netherlands (Rijke et al., 2012). Paola et al. (2011) defined river delta restoration as diverting sediment and water from major channels into adjoining drowned areas, where the sediment can build new land and provide a platform for regenerating wetland ecosystems. ...
Many deltas are threatened by accelerated soil subsidence, sea level rise, increasing river discharge, and sediment starvation. Effective delta restoration and effective river management require a thorough understanding of the mechanisms of aggradation, erosion, and their controls. Sediment dynamics has been studied at floodplains and marshes, but little is known about the sediment dynamics and budget of newly created wetlands. Here we take advantage of a recently opened tidal freshwater system to study both the mechanisms and controls of aggradation and erosion in newly created wetlands. We quantified both the magnitude and spatial patterns of aggradation and erosion in a former polder area in which water and sediment have been reintroduced since 2008. Based on terrestrial and bathymetric elevation data, supplemented with field observations of the location and height of cut banks and the thickness of the newly deposited layer of sediment, we determined the sediment budget of the study area for the period 2008–2015. Aggradation primarily took place in channels in the central part of the former polder area, whereas channels near the inlet and outlet of the area experienced considerable erosion. At the intertidal flats, sand aggradation especially takes place at low lying locations close to the channels. Mud aggradation typically occurs further away from the channels, but sediment is in general uniformly distributed over the intertidal area, due to the presence of topographic irregularities and micro topographic flow paths. Cut bank retreat does not significantly contribute to the total sediment budget, because wind wave formation is limited by the length of the fetch. Consecutive measurements of channel bathymetry show a decrease in erosion and aggradation rates over time, but the overall result of this study indicate that the area functions as a sediment trap. On average, the area traps approximately 46 % of the sediment delivered to the study area, which is approximately 3 % of the sediment load of the River Rhine at the Dutch-German border. The total sediment budget of the study area amounts to 29.7 × 10³ m³ year−1, which corresponds to a net area-averaged aggradation rate of 5.1 mm year−1. This is enough to compensate for the actual rates of sea level rise and soil subsidence in The Netherlands.
... Similarly, Mugu Lagoon has experienced loss of open-water habitat due to a large sediment deposition during El Niño events (Onuf 1987). However, some Mediterranean-climate salt marshes in other regions, such as Venice Lagoon, Italy (Day et al. 1998), San Francisco Bay Area, California (Callaway et al. 2012), and Ebro Delta, Spain (Calvo-Cubero et al. 2013), have been highly modified due to agriculture and urban uses, and consequently have highly variable sedimentation rates. Watershed-level comparisons in non-Mediterranean-climate zone marshes show that watershed sediment availability is a key component of future resilience to accelerated sea-level rise (Day et al. 2011). ...
Salt marsh resilience to sea-level rise depends on marsh plain elevation, tidal range, subsurface processes, as well as surface accretion, of which suspended-sediment concentration (SSC) is a critical component. However, spatial and temporal patterns of inorganic sedimentation are poorly quantified within and across Salicornia pacifica (pickleweed)-dominated marshes. We compared vertical accretion rates and re-examined previously published suspended-sediment patterns during dry-weather periods at Seal Beach Wetlands, which is characterized by a mix of Spartina foliosa (cordgrass) and pickleweed, and for Mugu Lagoon, where cordgrass is rare. Mugu Lagoon occurs higher in the tidal frame and receives terrigenous sediment from an adjacent creek. Feldspar marker horizons were established in winter 2013–2014 to measure accretion. Accretion rates at Seal Beach Wetlands and Mugu Lagoon were 6 ± 0.5 mm/year (mean ± SE) and 2 ± 0.3 mm/year. Also, the estimated sediment flux (g/year) across the random feldspar plots was 3.5 times higher at Seal Beach Wetlands. At Mugu Lagoon, accretion was higher near creeks, although not statistically significant. Dry-weather SSC showed similar concentrations at transect locations across sites. During wet weather, however, SSC at Mugu Lagoon increased at all locations, with concentrations decaying farther than 8 m from tidal creek edge. Based on these results from Mugu Lagoon, we conclude accretion patterns are set by infrequent large flooding events in systems where there is a watershed sediment source. Higher accretion rates at Seal Beach Wetlands may be linked to lower-marsh elevations, and thus more frequent inundation, compared with Mugu Lagoon.