Raised Water Table Research Articles

Sequential Changes in Coastal Plain Rivers Influenced by Rising Sea-Level

Coastal backwater effects on low-gradient coastal plain rivers extend well upstream of the head of the estuary and propagate upstream as sea-level rises. Hydrological, geomorphological, and ecological indicators can serve as sentinels of the upriver encroachment. Analyzing the along-river spatial distribution of these indicators as a space-for-time substitution allows the prediction of sequential changes. Interpretation of results from 20 rivers in Virginia and the Carolinas shows that backwater effects at the leading edge result in higher river stages, increasing floodplain inundation, and raising water tables. Lower slopes and flow velocities reduce sediment transport, reducing river sediment input and floodplain deposition. This inhibits natural levee development, reducing bank heights. These factors combine to increase the frequency and duration of inundation, resulting in semi-permanently flooded wetlands. Anaerobic conditions limit organic decomposition, and ponding allows transported and suspended organic matter to settle, leading to organic muck and peat floodplain soils. This accumulation, coupled with general valley-filling, buries alluvial terrace remnants. Finally, vegetation changes driven by salinity increases occur, resulting in swamp conversions to brackish marsh. Backwater encroachment is strongly controlled by channel bed slope, with relatively steeper channels experiencing slower rates of tidal extension. With accelerating sea-level rise (SLR), the lowest-sloping channels could experience encroachment rates of >1 km yr−1. Hydrological changes associated with SLR are most rapid at the leading, upriver end—averaging 71 km upstream of the head of the estuary in the study rivers at present—and at the lowermost, downstream end of the fluvial-estuarine transition zone.

Mitigation of Greenhouse Gas Emissions by Optimizing Groundwater Level in Boreal Cultivated Peatland

Optimizing the level of groundwater presents a viable strategy for mitigating the greenhouse gas (GHG) emissions associated with the cultivation of peatlands. This study investigated the impact of soil hydrological conditions on carbon dioxide (CO2) and methane (CH4) emissions. The CO2 and CH4 emissions from bare soil were continuously measured using an automated chamber system throughout the growing seasons from 2021 to 2023 at a boreal cultivated peat soil site. Annual CO2 emissions from soil respiration averaged to 21,600 kg ha-1 (April-November) corresponding to carbon (C) loss of 5890 kg ha-1. The CO2 emissions were highly temperature dependent. Lowering the groundwater level (GWL) was found to increase the CO2 emissions nearly linearly. The soil functioned as a CH4 sink for the majority of the growing season, and the total sink corresponded to 27 and 20 kg ha-1 yr-1 CO2 equivalent in 2022 and 2023, respectively. The CH4 emissions occurred generally when soil water content (SWC) exceeded 0.6 m3 m-3 and when GWL was at the depth of less than 30 cm from soil surface. For optimal climate efficiency the mitigation measures must be implemented during the mid-growing season, and the water table should be brought close to the soil surface. Potentially, this can hamper the operation of machinery on the field and reduce the harvested yield. Thus, comprehensive cost-benefit analysis is necessary before adopting a raised water table level in large-scale crop production.

Trajectories of plant communities in Massachusetts, USA cranberry farms discontinued from agriculture

Retirement of cultivated croplands creates potential for ecosystem and wetland restoration, but vegetation and soil legacies of cropping influence the development of post-agriculture vegetation. In low-lying coastal watersheds of southeastern Massachusetts, cranberries (Vaccinium macrocarpon Aiton) are cultivated in commercial farm units that are diked, leveled and sanded beds created from historic wetlands. Current low cranberry prices and expanding cranberry production elsewhere now increase the likelihood of cranberry farmland retirement. We quantified the trajectories of plant species richness and cover, and plant characteristics (life form, native or non-native, wetland or non-wetland) in a chronosequence of cranberry farm beds that ranged from cultivated units to those retired from cropping and revegetated for 90 years with no post-cropping management. Species richness increased from active beds to 10–20 year-old beds and subsequently decreased. Post-retirement species richness was overwhelmingly dominated by native species. Shrub and tree richness and cover increased steadily over time. The richness of wetland, upland and facultative species all increased quickly after retirement and then declined in the oldest retired beds. The basal area and canopy cover of red maple (Acer rubrum) and pitch pine (Pinus rigida) increased over time. Vegetation followed a relatively consistent successional trajectory and the plant community after five to nine decades was predominantly forest and dominated by non-wetland plants. Encouragement of long-term persistence of greater diversity and cover of wetland plant species on retired cranberry farms will likely require active hydrological and soil modifications that decrease sand depth and raise water tables.

Peatland gully restoration with stone and timber dams (Kinder Plateau, UK)

Blanket peat erosion is widespread in the British Isles. Eroded gullies have formed largely from the action of running water, with anthropogenic influences thought to have initiated and accelerated erosion. Currently, many blanket peatlands are undergoing restoration using aerial applications of lime, seed, fertiliser, and hand spreading of heather mulch (LSFM) on bare peat flats and blocking gullies with dams. Dams help stabilise areas of bare peat, trap sediment, reduce runoff velocities, raise water tables, and promote the re-vegetation of peat-forming plant species. Few studies have examined how gully blocks change over time and what this means for the functions they provide. We randomly sampled 500 of >2500 small stone and timber dams 8–9 years after installation in an eroding blanket peatland. We measured: vegetation cover and abundance, sediment accumulation behind dams, and available water storage capacity in dam pools as determined by gully morphology. On average, 92% and 93% of gully floors and 85% and 95% of gully walls were fully vegetated, while mean sediment depths were 22 and 20 cm, representing 42% and 44% infill for stone and timber dams, respectively. 2% of dams had failed, suggesting that failure is rare within the first decade. Most retained upstream pools, filling 18% (stone) and 44% (timber) of remaining storage. Sediment accumulation depths (and, conversely, available storage) did not differ significantly between stone and timber dams (95% CI) nor with distance down the gully. Results showed broadly consistent storage depth behind blocks independent of gully properties or dam design. These results suggest that sedimentation depths behind dams quickly reach equilibrium with subsequent sediment inputs balanced by the flux over the dam. Runoff attenuation functions from gully blocking were maintained for almost a decade. Therefore, re-vegetated gully blocked systems likely represent a stable equilibrium condition for the restored peatland so that the restored functions are a long-term benefit of peatland restoration.

The effects of hydrologic restoration on carbon budgets and GHG fluxes in southeastern US coastal shrub bogs

The southeastern US coastal plain was originally home to over one million ha of evergreen shrub bogs, locally known as pocosin. More than 70% have been drained for agriculture and forestry. These drained peatlands release GHGs to the atmosphere, mainly as CO2, which has resulted in significant concerns about their impact on climate change. Our long-term study at Pocosin Lakes National Wildlife Refuge (PLNWR) and adjacent private peatlands in North Carolina investigates the effect of drainage, and hydrologic restoration on carbon (C) budgets, including GHG losses, C sequestration rates, soil C respiration, and net ecosystem exchange (NEE). Soil CH4 and N2O emissions were negligible as CO2 emissions made up 99% of their GHG contributions. Carbon budgets indicate that the vast majority of C (>97%) is stored in the peat soil with the drained site having only about 53% of the peat mass found at the restored site. The reference site with the highest biomass produced the highest annual soil GHG loss of 11.3 Mg C ha−1 yr−1 followed by the drained site at 6.8 Mg C ha−1 yr−1 with the restored site having the lowest annual losses at 5.2 Mg C ha−1 yr−1. The drained site exported 0.39 Mg ha−1 yr−1 of TOC through hydraulic transport, a value 15% higher than either the restored or reference site annual mean. Eddy-covariance analyses revealed that restoring peatlands by raising water tables by 30 cm, i.e., by decreasing water table depth (WTD) from −60 to −30 cm, reduces CO2 losses to the atmosphere by >90%. When annual mean WTDs are deeper than a threshold of -30 cm, the drier peatlands generate an annual C loss and if WTDs are shallower (-20 cm) and wetter the peatlands show annual C gains, thus providing restoration guidelines.

Landscape-scale peatland rewetting benefits aquatic invertebrate communities

Many northern hemisphere peatlands have historically been drained, but restoration has sought to raise water tables to support peat-forming vegetation and enhance carbon sinks. In the UK alone, millions of new peatland ponds have been created but their biodiversity remains poorly studied and knowledge to guide conservation is lacking. This study advances understanding of aquatic invertebrate responses to peatland restoration from analyses of: (1) pond colonization and development up to 18 months after creation; (2) a pond chronosequence spanning 6 months to 15 years, and; (3) a comparison of restored versus naturally-formed ponds. Invertebrate communities established within 4 months of pond creation, but some initial colonisers were no longer found after 6 months. Diversity and abundance peaked at around 5 years then declined. Older pond environmental conditions and biodiversity were generally similar to natural ponds, highlighting restoration success for aquatic biodiversity gains. Co-ordinated, routine monitoring should be implemented to inform conservation approaches for these habitats and their biodiversity, particularly where other land management activities have the potential to impact aquatic systems.

Oil palm (Elaeis guineensis) plantation on tropical peatland in South East Asia: Photosynthetic response to soil drainage level for mitigation of soil carbon emissions

While existing moratoria in Indonesia and Malaysia should preclude continued large-scale expansion of palm oil production into new areas of South-East Asian tropical peatland, existing plantations in the region remain a globally significant source of atmospheric carbon due to drainage driven decomposition of peatland soils. Previous studies have made clear the direct link between drainage depth and peat carbon decomposition and significant reductions in the emission rate of CO2 can be made by raising water tables nearer to the soil surface. However, the impact of such changes on palm fruit yield is not well understood and will be a critical consideration for plantation managers. Here we take advantage of very high frequency, long-term monitoring of canopy-scale carbon exchange at a mature oil palm plantation in Malaysian Borneo to investigate the relationship between drainage level and photosynthetic uptake and consider the confounding effects of light quality and atmospheric vapour pressure deficit. Canopy modelling from our dataset demonstrated that palms were exerting significantly greater stomatal control at deeper water table depths (WTD) and the optimum WTD for photosynthesis was found to be between 0.3 and 0.4 m below the soil surface. Raising WTD to this level, from the industry typical drainage level of 0.6 m, could increase photosynthetic uptake by 3.6 % and reduce soil surface emission of CO2 by 11 %. Our study site further showed that despite being poorly drained compared to other planting blocks at the same plantation, monthly fruit bunch yield was, on average, 14 % greater. While these results are encouraging, and at least suggest that raising WTD closer to the soil surface to reduce emissions is unlikely to produce significant yield penalties, our results are limited to a single study site and more work is urgently needed to confirm these results at other plantations.

Relocated beaver can increase water storage and decrease stream temperature in headwater streams

AbstractMany areas are experiencing increasing stream temperatures due to climate change, and some are experiencing reduced summer stream flows and water availability. Because dam building and pond formation by beaver can increase water storage, stream cooling, and riparian ecosystem resilience, beaver have been proposed as a potential climate adaption tool. Despite the large number of studies that have evaluated how beaver activity may affect hydrology and water temperature, few experimental studies have quantified these outcomes following beaver relocation. We evaluated changes in temperature and water storage following the relocation of 69 beaver into 13 headwater stream reaches of the Skykomish River watershed within the Snohomish River basin, Washington, USA. We evaluated how beaver dams affected surface and groundwater storage and stream temperature. Successful relocations created 243 m3of surface water storage per 100 m of stream in the first year following relocation. Dams raised water table elevations by up to 0.33 m and stored approximately 2.4 times as much groundwater as surface water per relocation reach. Stream reaches downstream of dams exhibited an average decrease of 2.3°C during summer base‐flow conditions. We also assessed how dam age, condition, maintenance frequency, and pond morphology influenced stream temperature at naturally colonized wetland complexes. Our findings demonstrate that dam building can increase water storage and reduce stream temperatures in the first year following successful beaver relocation. Fluvial and floodplain morphology of candidate reaches for relocation is an important consideration because it determines the type and magnitude of response. Relocation to reaches with existing small, abandoned ponds may address thermal criteria by conversion from warming to cooling reaches, whereas relocation within large, abandoned complexes or vacant habitat may result in greater water storage. Although beaver relocation can be an effective climate adaptation strategy to retain more stable hydrologic regimes and water quality in our study area, there appear to be regionally specific environmental and geomorphic factors that influence how beaver affect water storage and temperature. More research is needed to investigate how and why these regional differences affect water storage and stream temperature response in beaver‐influenced systems.

Viewpoints on Cooperative Peatland Management: Expectations and Motives of Dutch Farmers

The European Union (EU) is globally the second highest emitter of greenhouse gases from drained peatlands. On the national level, 15% of agricultural peat soils in the Netherlands are responsible for 34% of agricultural emissions. Crucial to any successful policy is a better understanding of the behavioral change it will bring about among the target groups. Thus, we aim to explore farmers’ differing viewpoints to discuss how policy and planning can be improved to ensure landscape-scale climate mitigation on agriculturally used peatlands. Q methodology was used to interview fifteen farmers on Dutch peat soils, whereby 37 statements were ranked in a grid according to their level of agreement. Factor analysis revealed three main viewpoints: farmers with a higher peat proportion show an urgency in continuing to use their land (‘cooperative businesspeople’), while ‘independent opportunists’ are wary of cooperation compromising their sense of autonomy. Farmers who are ‘conditional land stewards’ are open to agriculture without drainage but require appropriate payments to do so. Future policy design must focus on providing support to farmers that go beyond compensation payments by providing information about funding sources as well as potential business models for peatland uses with raised water tables.

Geochemical Characterization of the Eocene Coal-Bearing Source Rocks, Xihu Sag, East China Sea Shelf Basin, China: Implications for Origin and Depositional Environment of Organic Matter and Hydrocarbon Potential

Eocene coal-bearing source rocks of the Pinghu Formation from the W-3 well in the western margin of the Xihu Sag, East China Sea Shelf Basin were analyzed using Rock-Eval pyrolysis and gas chromatography–mass spectrometry to investigate the samples’ source of organic matter, depositional environment, thermal maturity, and hydrocarbon generative potential. The distribution patterns of n-alkanes, isoprenoids and steranes, high Pr/Ph ratios, abundant diterpanes, and the presence of non-hopanoid triterpanes indicate predominant source input from higher land plants. The contribution of aquatic organic matter was occasionally slightly elevated probably due to a raised water table. High hopane/sterane ratios and the occurrence of bicyclic sesquiterpanes and A-ring degraded triterpanes suggest microbial activity and the input of microbial organisms. Overwhelming predominance of gymnosperm-derived diterpanes over angiosperm-derived triterpanes suggest a domination of gymnosperms over angiosperms in local palaeovegetation during the period of deposition. The high Pr/Ph ratios, the plot of Pr/n-C17 versus Ph/n-C18, the almost complete absence of gammacerane, and the distribution pattern of hopanes suggest that the samples were deposited in a relatively oxic environment. Generally, fluctuation of redox potential is coupled with source input, i.e., less oxic conditions were associated with more aquatic organic matter, suggesting an occasionally raised water table. Comprehensive maturity evaluation based on Ro, Tmax, and biomarker parameters shows that the samples constitute a natural maturation profile ranging from marginally mature to a near peak oil window. Hydrogen index and atomic H/C and O/C ratios of kerogens suggest that the samples mainly contain type II/III organic matter and could generate mixed oil and gas.

From satellites to frogs: Quantifying ecohydrological change, drought mitigation, and population demography in desert meadows

Increasing frequency and severity of droughts have motivated natural resource managers to mitigate harmful ecological and hydrological effects of drought, but drought mitigation is an emerging science and evaluating its effectiveness is difficult. We examined ecohydrological responses of drought mitigation actions aimed at conserving populations of the Columbia spotted frog (Rana luteiventris) in a semi-arid valley in Nevada, USA. Abundance of this rare frog had declined precipitously after multiple droughts. Mitigation included excavating ponds to increase available surface water and installing earthen dams to raise water tables. We assessed responses of riparian vegetation to mitigation using a 30-year time series of satellite-derived Normalized Difference Vegetation Index (NDVI) and gridded weather data. We then analyzed a 23-year mark-recapture dataset to evaluate the effects of drought mitigation and NDVI on the probability of frog survival and rates of recruitment. After accounting for interannual precipitation variability, we found that NDVI increased significantly from before to after drought mitigation, suggesting that mitigation influenced the hydrology and vegetation of the meadows. Frog survival increased with NDVI, but mitigation had a stronger effect than NDVI suggesting that excavated mitigation ponds were particularly important for frog survival during drought. In contrast, frog recruitment was associated with NDVI more than mitigation, but only in meadows where NDVI was dependent on precipitation. At meadows with available groundwater, recruitment was associated with mitigation ponds. These findings suggest that mitigation ponds are critical for juvenile frogs to recruit into the adult population, but recruitment can also be increased by raising water tables in meadows lacking groundwater sources. Lagged recruitment (i.e., effects on larvae and juveniles) was negatively associated with NDVI. This study illustrates the ecohydrological complexity of drought mitigation and demonstrates novel ways to assess the effectiveness of drought mitigation using time series of readily available satellite imagery and organismal data.

Drain blocking has limited short-term effects on greenhouse gas fluxes in a Molinia caerulea dominated shallow peatland

Drained peatlands dominated by purple moor grass (Molinia caerulea) are widespread in the UK and Western Europe. Although substantial carbon stores may be present in these peatlands, in this degraded state they are not currently acting as carbon sinks. Therefore, M.caerulea dominated peatlands have been identified as potential sites for ecohydrological restoration to tackle the current climate emergency. However, at present little is known about whether ditch blocking can raise water tables and promote the recovery of bog plant species, and the subsequent effects on carbon sequestration in these peatlands.To investigate the potential for restoration, we measured changes in water table depth, vegetation composition, photosynthesis at 1000 μmol Photons m−2 s−1 (PG1000), ecosystem respiration (REco) and partitioned below-ground respiration in two M.caerulea dominated peatlands in which drainage ditches had been blocked located in Exmoor National Park, southwest England. Measurements were made in two headwater catchments at ⅛, ¼ and ½ of the distance between adjacent drainage ditches at four control-restored paired sites, during the growing seasons pre- (2012) and post- (2014, 2016 & 2018) restoration.Restoration had a small but significant (p = 0.009) effect on water table depths however, this did not result in a significant change in vegetation composition (p > 0.350). Ecosystem respiration increased in both the control and restored locations following restoration however, this increase was significantly smaller (p = 0.010) at the restored locations, possibly due to a similarly reduced increase in photosynthesis, although this change was not significant (p = 0.116). Below-ground respiration showed no significant changes following restoration.This research illustrates how degraded these shallow peatlands are, and raises concerns that ditch blocking alone may not bring about the high and stable water tables required to perturb the existing Molinia caerulea-dominated ecosystem and substantially alter the carbon balance. Additional restoration measures may be required.

On the potential for saturated buffers in northwest Ohio to remediate nutrients from agricultural runoff.

Nutrient loading from nonpoint source runoff in the Midwest has emerged as one of the largest threats to water quality as the frequency of harmful algal blooms, hypoxic zones, and issues associated with human-resource interactions have risen abruptly over the past several decades. In this study, a saturated buffer ~500 m in length located in the western basin of the Lake Erie watershed was evaluated for its potential to reduce edge of field runoff and nutrient loading. Saturated buffers reduce runoff by routing subsurface tile drainage water into the riparian zone, providing an opportunity for drainage volume as well as nutrient reduction of runoff waters. Over a 12-month study period, controlled drainage was used to redirect nearly 25% of the total tile flow into the riparian zone from a subwatershed in corn/soybean rotation with near complete reductions of dissolved nitrogen and phosphorus from tile inflows averaging 4.7 and 0.08 mg/L, respectively, as well as total reduction of suspended sediments (average 10.4 mg/L). This study provides additional evidence that riparian areas are an important part of nutrient reduction strategies as they can act as both controlled drainage points by raising water tables in fields as well as nutrient sinks which couple to help mitigate nutrient runoff in the region.

Sediment storage and shallow groundwater response to beaver dam analogues in the Colorado Front Range, USA

AbstractEnthusiasm for using beaver dam analogues (BDAs) to restore incised channels and riparian corridors has been increasing. BDAs are expected to create a similar channel response to natural beaver dams by causing channel bed aggradation and overbank flow, which subsequently raise water tables and support vegetation growth. However, lack of funding for monitoring projects post‐restoration has limited research on whether BDAs actually cause expected channel change in the Front Range and elsewhere. Geomorphic and hydrologic response to BDAs was monitored in two watersheds 1 year post‐restoration. BDAs were studied at Fish Creek, a steep mountainous catchment, and Campbell Creek, a lower gradient piedmont catchment from May to October 2018. At each restoration site, the upstream‐ and downstream‐most BDAs were chosen for intensive study in comparison with unrestored reference reaches. Monitoring focused on quantifying sediment volumes in BDA ponds and recording changes to stream stage and riparian groundwater. Despite differences in physical basin characteristics, BDA pools at both sites stored similar volumes of sediment and stored more sediment than reference pools. Sediment storage is positively correlated to BDA height and pool surface area. However, BDAs did not have a significant influence on shallow groundwater. The lack of groundwater response proximal to BDAs could indicate that local watershed factors have a stronger influence on groundwater response than restoration design 1 year post‐restoration. Systematic, long‐term studies of channel and floodplain response to BDAs are needed to better understand how BDAs will influence geomorphology and hydrology.

Earthquake-triggered 2018 Palu Valley landslides enabled by wet rice cultivation

The death toll and economic impact of an earthquake can be greatly exacerbated if seismic ground shaking triggers landslides. Earthquake-triggered landslides typically occur in two different contexts: localized failure of steep slopes and resulting landslides that pose a major threat to life in areas below; and lateral spreading of nearly flat sediment plains due to shaking-induced liquefaction, which can damage large areas of critical infrastructure. Unexpected catastrophic landsliding triggered by the 28 September 2018 earthquake at Palu, Indonesia did not occur in either typical context, but produced both destructive outcomes. Here, we show that alluvial ground failure in the Palu Valley was a direct consequence of irrigation creating a new liquefaction hazard. Aqueduct-supported cultivation, primarily of wet rice, raised the water table to near ground level, saturating sandy alluvial soils that liquefied in response to strong ground shaking. Large-displacement lateral spreads occurred on slopes of 1°. Slopes steeper than 1.5° sourced long-runout landslides and debris flows that swept through villages occupying the gentler slopes below. The resulting damage and loss of life would probably not have occurred in the absence of a raised water table. Earthquake-triggered landsliding of gentle, irrigated alluvial slopes is an under-recognized, but avoidable, anthropogenic hazard. Aqueduct-supported cultivation of rice resulted in liquefaction of the alluvial soils that led to the landslides triggered by the Palu 2018 earthquake, according to satellite analyses.

Abundance of arthropods as food for meadow bird chicks in response to short- and long-term soil wetting in Dutch dairy grasslands.

BackgroundThroughout the world, intensive dairy farming has resulted in grasslands almost devoid of arthropods and birds. Meadow birds appear to be especially vulnerable during the chick-rearing period. So far, studies have focused mainly on describing population declines, but solutions to effectively stop these trends on the short-term are lacking. In this study at a single farm, we experimentally manipulated soil moisture through occasional irrigation, to mitigate against early season drainage and create favorable conditions for the emergence of above-ground arthropods during the meadow bird chick rearing phase.MethodsTo guarantee the presence of at least a sizeable arthropod community for the measurement of effects of wetting, we selected a farm with low intensity management. The land use and intensity of the study site and surroundings were categorized according to the national land use database and quantified using remote sensing imagery. From May 1 to June 18, 2017, we compared a control situation, with no water added, to two wetting treatments, a “short-term” (3 weeks) treatment based on wetting on warm days with a sprinkler system and a “long-term” treatment next to a water pond with a consistently raised water table from 2010. We measured soil temperature, soil moisture and resistance as well as the biomass of arthropods at 3-day intervals. Flying arthropods were sampled by sticky traps and crawling arthropods by pitfall traps. Individual arthropods were identified to Order and their length recorded, to assess their relevance to meadow bird chicks.ResultsThe land use analysis confirmed that the selected dairy farm had very low intensity management. This was different from most of the surrounding area (20 km radius), characterized by (very) high intensity land use. The experiments showed that irrigation contributed to cooler soils during midday, and that his happened already in the early part of the season; the differences with the control increased with time. In the short- and long-term treatments, soil moisture increased and soil resistance decreased from the mid-measurement period onward. Compared with the control, cumulative arthropod biomass was higher in the long-term treatment, but showed no change in the irrigation treatment. We conclude that small-scale interventions, such as occasional irrigation, favorably affected local soil properties. However, the effects on above-ground arthropod abundance currently appear limited or overridden by negative landscape-scale processes on arthropods.

The full carbon balance of a rewetted cropland fen and a conservation-managed fen

On a global scale, the release of greenhouse gases (GHG) from peatland drainage and cultivation are believed to account for ∼5% of estimated anthropogenic GHG emissions. Drainage generally leads to peat subsidence and extensive soil loss, resulting in a diminishing store of soil carbon (C). This is a challenge for maintaining drainage-based agriculture, as such practices will eventually lead to the loss of organic soils that arable cultivation depends on. The conversion of croplands on peat to semi-natural grasslands, alongside raising water tables, is one possible way to reduce the loss of these valuable C stores. Here, we report the net ecosystem carbon balances (NECB) of two lowland peatlands in East Anglia, south-east UK. One site is a relic conservation-managed fen on deep peat, subject to active hydrological management to maintain water levels, and dominated by Cladium and Phragmites sedge and reed beds, whilst the other is a former cropland that has been converted to seasonally-inundated grazed grassland. Despite occasionally experiencing severe water table drawdown, the conservation-managed fen was a strong C sink of -104 g C m−2 yr−1. In contrast, the grassland was a C source of 133 g C m−2 yr−1, with gaseous carbon dioxide (CO2) emissions being the main loss pathway, due to low water tables exposing the soil profile in summer. At each site, ditch emissions of CO2 were moderately large (22 and 37 g C m−2 yr−1), whilst ditch methane (CH4) emissions (0.2 and 1.8 g C m−2 yr−1) made a negligible contribution to the NECB, but are important when considering the ecosystem GHG balance in terms of CO2 equivalents. Excluding dissolved inorganic carbon (DIC), fluvial C losses were 6 g C m−2 yr−1 for the conservation-managed fen and 12 g C m−2 yr−1 for the former cropland, and were dominated by dissolved organic carbon (DOC). The small fluvial C loss is the result of both sites being hydrologically isolated from the surrounding agricultural landscapes. Although the partially re-wetted cropland was still acting as a net C source, our estimates suggest that seasonal rewetting has reduced net annual C losses to ∼20% of their former cropland values. Maintaining high water tables year round would potentially further reduce C losses, and shallow inundation might allow the return of wetland species such as Phragmites and Typha, perhaps as floating rafts.

Proving a landslide: ground behaviour problems at Pissouri, Cyprus

The residential area of Limnes in Pissouri, SW Cyprus has experienced significant ground behaviour problems since heavy winter rainfall in 2011/2012. These problems have comprised cracking and displacement to the ground, pavements, roads, walls and buildings, leading to the abandonment of the most seriously-affected houses. Nicosia marl comprises the underlying lithology, a material that is associated with volume change upon wetting and drying and has led to foundation problems elsewhere in the country. Various explanations have been given to account for the observed phenomena at Limnes, including the effects of underground water , settlement, slope instability, cyclical shrink–swell, seepage erosion and dissolution. Raised water tables, caused by residential waste-water discharges, applied loads from residential buildings, and inadequate ground investigation and foundation design, are other contributory or causal factors that have been cited. A geomorphological study was undertaken in 2017 and early 2018 that combined field observations with aerial photograph interpretation, and a review of available ground investigation data, to yield an explanation and develop a preliminary ground model. The conclusion drawn was that the Limnes area had been affected by ancient (possibly late Pleistocene–early Holocene) deep-seated failure and that slope instability had subsequently been reactivated at a shallower depth within the failed material as a result of loss of material strength and high water tables. The properties of the Nicosia marl, while important in controlling the behaviour of the ground on a site-by-site basis, were considered to be aggravating factors in the context of the landslide displacement(s) affecting the slope as a whole. InSAR satellite movement monitoring data were analysed for the Limnes area and the outcome vindicated the geomorphological interpretation and helped strengthen the ground model that embodied slope failure as the underlying cause of damage.

The concept of water storage on agriculture lands: Exploring the notion in South Florida

Lands in the Everglades Agricultural Area (EAA) can be used for increased water storage in order to relieve coastal estuaries of excess runoff in the rainy season. The goals of this study were: (1) to quantify the environmental and economic tradeoffs of different water storage scenarios using water tolerant sugarcane cultivars; and (2) to quantify the amount of water storage possible in the EAA under different water storage scenarios. A mathematical model was developed to calculate soil depth, soil subsidence, depth to the water table, and water storage for three different sugarcane cultivars with different water tolerances. The results showed raising water tables on farmlands did have the environmental benefits of reduced soil subsidence, extended farm life and increased years of water storage. In addition, raising water tables in the EAA to increase water storage is overall more costly, but yearly costs are very low. Therefore, water storage on farmlands is an affordable interim method of water storage.

Beaver‐mediated water table dynamics in a Rocky Mountain fen

AbstractBeaver dams are known to raise water tables in mineral soil environments, but very little is known about their impact in wetlands, such as peatlands. Peatlands tend to have shallow water tables, and the position and tendency of the water table to fluctuate (i.e., stability) is a factor controlling the system's ability to store carbon and water. Many peatland environments, especially fens, offer ideal habitat for beaver, and the potential for beaver dams to influence this link by manipulating water tables requires investigation. Our objective was to determine the influence of beaver dams on the water table dynamics of a Rocky Mountain fen. We monitored water tables in the peatland for 4 years while beaver dams were intact and 2 years after they were breached by an extreme flood event. We found that, because of the unique way in which dams were built, they connected the peatland to the stream and raised and stabilized already high water tables within a 150‐m radius. Beaver‐mediated changes to peatland water table regimes have the potential to enhance carbon sequestration and the peatland's ability to respond to external pressures such as climate change. Furthermore, beaver dams increased surface and groundwater storage, which has implications for regional water balances, especially in times of drought.