Rate Of Wetland Loss Research Articles

Effect of channel morphological changes on wetland transformation

Keeping aside the traditional approaches to investigating floodplain wetland transformation, the current study investigated various aspects of it through changes in river channel morphology and drainage pattern. The study analyzed wetland transformation using satellite image-based machine learning and intensive fieldwork. Ordinary Least Square (OLS) regression was applied to identify dominant influencing factors among 24 contributing factors under six clusters to eight dependent phenomena of transformation. The result showed that 57 % of wetland area lost since 1991, and existing wetland has also experiencing hydrological scarcity. From 1991 to 2021, the area under low water depth (<1 m.) inflated from 18.55 % to 50.54 %, the hydro-period narrowed down, and the appearance of water become inconsistent. The OLS result showed that changes in channel morphology (bottle neck channel, embankment-driven carrying capacity enhancement, etc.), interruptions in river and wetland connecting channels (source closure, breaching the continuity, conversion in to agricultural land, etc.), and changes in flood ambience (regulated by dam construction, erection of embankments, etc.) majorly contributed to wetland transformation. Very high explainability was found in the cases of rate of wetland loss, decreasing water depth under greater depth, narrowing hydro-period (R2 > 0.9). The findings of this work would be a good policy document for floodplain wetland management.

Accelerating Elevation Gain Indicates Land Loss Associated with Erosion in Mississippi River Deltaic Plain Tidal Wetlands

In recent years, the Mississippi River Deltaic Plain (MRDP) has experienced the highest rates of wetland loss in the USA. Although the process of vertical drowning has been heavily studied in coastal wetlands, less is known about the relationship between elevation change and land loss in wetlands that are experiencing lateral erosion and the contribution of erosion to land loss in the MRDP. We quantified relationships of elevation change and land change in ten submerging tidal wetlands and found that, despite significant land loss, elevation trajectories in seven of the land loss study sites were positive. Furthermore, we observed an acceleration in elevation gain preceding the conversion from vegetated marsh to open water.To identify regional contributions of lateral erosion to land loss, we quantified the relationship of elevation change and land change in 159 tidal marsh sites in the MRDP. Approximately half the sites were persistently losing land, and 82% of these sites were vulnerable to erosion, identifying erosion as a dominant mechanism of coastal wetland loss in this region. Notably, the sites that were vulnerable to erosion were experiencing land loss while also gaining elevation, and sites with the highest land loss exhibited accelerating elevation gain. Together, these data illustrate that (1) erosion is a dominant mechanism of wetland loss in the MRDP, (2) accelerated elevation gain is an indicator of erosion, and (3) consideration of elevation change trajectories within the context of land change is critical for providing accurate coastal wetland vulnerability assessments.

Assessment of marsh terrace designs for wave attenuation utilizing a wave model

The northern Gulf of Mexico is facing high rates of wetland loss due to subsidence and sea level–rise, which has encouraged the application of various wetland restoration techniques. Marsh terracing is a restoration technique that has been implemented since the early 1990 s in Texas and Louisiana, yet few studies have been conducted to evaluate its effectiveness. Marsh terraces are segmented berms of soil built in coastal ponds that were once vegetated marshes. Marsh terracing is hypothesized to dissipate wind waves, encourage marsh expansion, and reduce shoreline erosion. This study (1) assessed the effectiveness of the most common terrace shapes (linear, chevron, and square) and spacing (100, 110, and 120 m) at reducing significant wave height (Hs), (2) assessed the effectiveness of alternative terrace designs for reducing Hs during different wind conditions, and 3) estimated the construction costs of alternative terrace designs. The Simulating WAves Nearshore (SWAN) model was used to simulate wind–driven waves in ponds with real and hypothetical terrace designs. Results revealed that: (1) The chevron shape provided the greatest reduction in Hs during all wind conditions, reducing Hs by up to 54%. (2) Hs reduction was not affected by terrace spacings. (3) Based on wave attenuation, the chevron design with a 120 m terrace spacing provided the optimal outcome with an estimated construction cost/ha of $6332 in a 250,000 m2 site compared to the terrace shapes and spacings evaluated in this study. This study will help coastal managers design marsh terraces to address wetland erosion in the Gulf of Mexico and other coastal areas facing similar environmental problems.

Influence of Increased Freshwater Inflow on Nitrogen and Phosphorus Budgets in a Dynamic Subtropical Estuary, Barataria Basin, Louisiana

Coastal Louisiana is currently experiencing high rates of wetland loss and large-scale ecosystem restoration is being implemented. One of the largest and most novel restoration projects is a controlled sediment diversion, proposed to rebuild and sustain wetlands by diverting sediment- and nutrient-rich water from the Mississippi River. However, the impact of this proposed sediment diversion on the nutrient budget of the receiving basin is largely unknown. A water quality model was developed to investigate the impact of the planned Mid-Barataria Sediment Diversion on the nutrient budget of the Barataria Basin (herein referred to as ‘the Basin’). The model results indicate that the planned diversion will increase TN and TP pools by about 38% and 17%, respectively, even with TN and TP loadings that increase by &gt;300%. Water quality model results suggest that the increase of nutrients in the basin will be mitigated by increased advection transport (i.e., decreased residence time from ~170 days to ~40 days, leading to greater flushing) and increased removal via assimilation, denitrification, and settling within the Basin. Advection transport resulted in higher TN removal in the Basin than other processes, such as uptake or denitrification. Approximately 25% of the additional TN loading and 30% of the additional TP loading were processed within the Basin through the assimilation of phytoplankton and wetland vegetation, denitrification, and burial in the sediment/soils. These nutrient budgets help to better understand how the planned large-scale sediment diversion project may change the future ecological conditions within the estuaries of coastal Louisiana and near-shore northern Gulf of Mexico.

Economic and socioecological perspectives of urban wetland loss and processes: a study from literatures.

Existing literatures across the world highlighted the causes and rate of wetland loss; however, so far, no researches tried to analyze how these are guided by the socioeconomic and ecological conditions. The current review work wished to explore how economic and socioecological perspectives could control the rate and drivers of urban wetland loss. Through meta-analysis, this study also intended to explore the changing polarity in research publication and collaborative research. Total 287 original research articles indicating the rates and drivers of wetland loss from 1990 to June 2022 for the first objective and 1500 articles focusing wetland researches from Dimensions AI database for the last objective were taken.Results clearly revealed that the rate of urban wetland loss varies from 0.03 to 3.13% annually, and three main drivers like built-up, agricultural expansions, pollution were identified all across the world. Loss rate was found maximum in the developing and least developed countries. Pollution, built-up expansion, and agriculture expansion, respectively, in developed, developing, and least developed nations were identified as the most dominant drivers of urban wetland loss. Linking loss rate and drivers with socioecological and economic perspectives revealed that human development index (HDI), ecological performance index (EPI), sustainable development goal index (SDGI), and social progress index (SPI) is negatively associated with the rate of urban wetland loss. Contrarily, a poverty rate encouraged higher rate of loss. This study articulated that improving these socioecological and economic conditions could help wetland conservation and restoration to achieve SDGs.

The concept of land bridge marshes in the Mississippi River Delta and implications for coastal restoration

Louisiana has high coastal wetland loss rates due to natural processes such as subsidence and anthropogenic activities such as construction of river levees and dams, pervasive alteration of surface hydrology by local industries such as oil and gas, and navigation. With the exception of the Atchafalaya River discharge area, most of Louisiana's marsh coastline is retreating and coastal marshes are degrading. In the inactive degrading delta regions, there exists a previously uncharacterized landform referred to colloquially as coastal ‘land bridge’ marshes. Land bridge marshes are saline or brackish marshes fronting large estuarine bays or lakes with sufficient fetch and wave energy to supply high levels of resuspended sediments to the marsh surface. They are generally linear features that are oriented parallel to the coast and the shoreline front retreats landward due to erosion from wave energy. These marshes persist over time vertically due to input of resuspended sediments but are experiencing rapid edge erosion due to wave attack. Comparison of data from Louisiana's Coastal Reference Monitoring System (CRMS) sites show that land bridge marshes have a greater frequency of higher soil surface elevation and higher soil bulk density than non-land bridge marshes. Because land bridges are vertically stable relative to other coastal wetlands, identification of measures to sustain these landscape features is important. Simulations using MarshMorpho2D, a process-based reduced-complexity morphology model, suggest that protection barriers installed on the seaward side of land bridge marshes will attenuate wave energy and, thus, edge erosion. Shoreline protection that can reduce wave energy but still allow sediment input to marshes include living shorelines, rock barriers, and/or breakwaters. Periodic thin layer nourishment of the marsh surface may be necessary to help sustain vertical growth. Further, marsh creation projects directly landward of land bridge marshes may benefit from their protection from waves and as a source of sediment. Consideration of land bridge marshes as distinct marsh types in the State Master Plan and integrated modeling could help to identify measures to sustain these landscape features.

Multi-scale spatiotemporal wetland loss and its critical influencing factors in China determined using innovative grid-based GWR

Wetlands serve as a critical habitat for many plants and animals. However, with urban expansion and other processes, the wetlands in China are lost at an alarming rate in recent decades. This study quantifies the pace of wetland loss in the past two decades and investigates the hidden mechanisms of wetland loss via a proposed innovative grid-based geographically weighted regression computing unified device architecture (Grid-GWR-CUDA) method. Also assessed in this study is the relative importance of four natural factors (precipitation, digital elevation model (DEM), slope, evaporation), and four human related factors (distance to city, distance to roads, population, and gross domestic product (GDP)) in wetland loss at both the national and regional levels. The importance of some critical factors is compared across different regions. The results indicated that GDP, population size and DEM are the three most significant factors impacting on the rate of wetland loss at the national level. They are still the most influential factors for most regions at the sub-national level while precipitation is an important factor only in the eastern regions. Therefore, the main causes of wetland loss in China are attributed to human socioeconomic activities. Compared with the traditional geographically weighted regression (GWR) method, the proposed Grid-GWR-CUDA method is innovative enough to handle large data volumes efficiently while retaining all data samples at a fine (e.g., 30 m) spatial resolution because the computational efficiency is significantly improved via graphics processing unit (GPU) acceleration. It improves the accuracy of regression by several folds over traditional ordinary least square and GWR. It has the potential to predict future wetland loss if supplied with the latest land cover data.

Aboveground wetland vegetation growth responses to simulated sediment diversion inundation scenarios

Coastal Louisiana is experiencing extremely high rates of wetland loss, particularly within the Mississippi River Deltaic Plain. Although multiple stressors contribute to this loss, one major driver is decreased wetland elevation stemming from disconnection of recurrent sediment rich influxes of Mississippi River floodwater. The decrease in sediment delivery, in conjunction with natural subsidence processes, reduce marsh elevations and increase flooding stress on vegetation, leading to marsh collapse. River sediment diversions are large-scale restoration techniques intended to rehabilitate Louisiana's degraded coastal wetlands by mimicking historic crevasse splays, thereby stimulating land building and vegetation growth. However, such large-scale restoration techniques require an appropriate knowledge base of vegetation and soil biogeochemical responses to altered environmental conditions. In this research, monospecific sods of three foundational marsh species (Spartina patens, Spartina alterniflora, Typha latifolia) were exposed to inundation depth (20 and 40 cm), duration (8 and 16 weeks), and salinity (0 and 5 psu) treatments consistent with a range of anticipated sediment diversion scenarios in a mesocosm setting. Additionally, sods were monitored through week 20 after being removed from their experimental conditions. Both Spartina alterniflora and Typha latifolia displayed relatively consistent increases in stem densities over time across inundation depth-duration treatments, whereas Spartina patens displayed a sharp decline in stem densities at 40 cm flooding depths. Additionally, both Spartina alterniflora and Spartina patens had the least observed amount of total aboveground biomass at 40 cm flooding depths. Spartina patens sods displayed a significant loss in surface elevation with increased flooding stress through study week 20, whereas Typha latifolia demonstrated a significant gain in surface elevation. These results suggest that restoration projects increasing inundation within the limits of the depths employed herein and the anticipated duration of river diversion induced inundation are unlikely to negatively impact the aboveground growth responses of Spartina alterniflora and Typha latifolia, but could reduce stem densities and aboveground biomass of Spartina patens.

Potential methane production in oligohaline wetlands undergoing erosion and accretion in the Mississippi River Delta Plain, Louisiana, USA

Methane (CH4) is steadily increasing in the atmosphere from different sources including wetlands. However, there is limited landscape level CH4 flux data in deltaic coastal systems where the availability of freshwater is impacted by the combined effect of climate change and anthropogenic impacts. Here we determine potential CH4 fluxes in oligohaline wetlands and benthic sediments in the Mississippi River Delta Plain (MRDP), which is undergoing the highest rate of wetland loss and most extensive hydrological wetland restoration in North America. We evaluate potential CH4 fluxes in two contrasting deltaic systems, one undergoing sediment accretion as result of a freshwater and sediment diversions (Wax Lake Delta, WLD), and one experiencing net land loss (Barataria-Lake Cataouatche, BLC). Short- (<4 days) and long-term (36 days) incubations using soil and sediment intact cores and slurries were performed at different temperatures representing seasonal differences (10, 20, 30 °C). Our study revealed that all habitats were net sources of atmospheric CH4 in all seasons, and CH4 fluxes were generally the highest for the 20 °C incubation. The CH4 flux was higher in the marsh habitat of the recently formed delta system (WLD) with total carbon content of 5–24 mg C cm−3 compared to the marsh habitat in BLC, which had high soil carbon content of 67–213 mg C cm−3. This suggests that the quantity of soil organic matter might not be a determining factor in CH4 flux. Overall, benthic habitats were found to have the lowest CH4 fluxes indicating that projected future conversions of marshes to open water in this region will impact the total wetland CH4 emission, although the overall contribution of such conversions to the regional and global carbon budgets is still unknown. Further research is needed to expand the CH4 flux studies by simultaneously using several methods across different wetland habitats.

Coastal wetland area change for two freshwater diversions in the Mississippi River Delta

Coastal systems around the globe are being re-integrated with adjacent river systems to restore the natural hydrologic connection to riparian wetlands. The Mississippi River sediment diversions or river reconnections are one such tool to combat high rates of wetland loss in coastal Louisiana, USA by providing freshwater, sediment, and nutrients. There has been some disagreement in the published literature whether re-establishing river reconnection is slowing or contributing to coastal wetland loss. This issue is due to the difficulties in the application of remote sensing in low-relief environments where water level changes could indicate either land loss or simply temporary submergence. We analyzed land change at the receiving areas of two existing freshwater river diversions, Davis Pond and Caernarvon, which have been intermittently receiving river water for up to 2+ decades. This study provides a robust analysis of wetland land change rates in proximity these river diversions including years before river reconnection. Our analyses indicate a net land gain since river reconnection operations began at Davis Pond Diversion (+3.42 km2; range: +2.02–4.81 km2) and no statistically significant change at the Caernarvon Diversion. The Davis Pond wetland results are corroborated with data from a decadal field study documenting increased inorganic sedimentation in the soil. It is clear from this study and others, that river reconnection can increase or, in the case of Caernarvon, have no statistical effect on the land change in these systems due to differences in vegetation, hydroperiod, sediment delivery and external factors including hurricane impacts. Our remote sensing analysis was compared with a global water area change analysis mapping tool which also supported our findings.

Wetland Restoration Progress 39 Years After Canal Backfilling

Dredging to create canals and channels in wetlands is widespread and is a major cause of dramatically high wetland loss rates in coastal Louisiana. The dredged material placed alongside the canal forms continuous levees and can be dragged back into the canal to start wetland restoration (backfilling) but is rarely done. Thirty-three canals backfilled in the 1980s as opportunistic permit requirements were examined to determine their re-vegetation after 39 years. Sixteen of the 33 disturbed areas are now mostly restored to wetlands, and seventeen were compromised by re-dredging and other factors such as being surrounded by other canals or embedded within water level control structures. Success occurred where the natural hydrology was not artificially constrained by these structures. The re-vegetation of these 16 canals were compared to backfilled canals in the Barataria Preserve of the Jean Lafitte Historical National Park. The spoil bank was restored wetland habitat within a few years, and the open water of the canal was 70% re-vegetated after 39 years if there was no soil “plug” placed at the canal entrance during backfilling. Backfilling canals can be done on the 27 thousand abandoned canals across this coast for a low cost compared to other restoration strategies.

Exploring Methods for Sharing Wetland Knowledge and Identifying Future Needs and Solutions

Successful management of wetlands is increasingly making more use of traditional and contemporary community knowledge of wetlands in addition to the knowledge obtained from scientific investigations (Ens et al. 2012; Pyke et al. 2018). For this to happen, wetland managers need ways to tap into such knowledge, including respecting protocols around ownership of and access to such knowledge, and appreciating its value. However, at the same time the rapid advancement of science and technology and changes in societal values has led to the loss of valuable traditional knowledge, or such knowledge being ignored in favor of an over-reliance on modern scientific techniques. Mechanisms available through wetland centres (Finlayson 2018; Gevers et al. 2018), education outreach initiatives (Finlayson et al. 2013) and engagement with schools (M. Bartlett 2019, pers. comm.) go some way towards tapping into the value of these knowledge sources. However, much more is needed if the mutual benefits that can come from sharing knowledge are to be realized. This is more the case with the intensification of the threats to wetlands from climate change and sea level rise, invasive non-native species, and pollution. Given the difficulties associated with managing wetlands and ensuring there are sufficient funds to both collect and make use of contemporary scientific information, having access to knowledge provided by local communities may prove invaluable when addressing the harmful outcomes from these phenomena, in addition to assisting with efforts to ensure local communities are effectively engaged in wetland management. There have been many successful cases where traditional and community knowledge have been used alongside contemporary scientific practices for managing wetlands (Carbonell et al. 2001; Ens et al. 2012: Pyke et al 2018), but unless these are extended and expanded in time and space we fear that current high rates of wetland loss and degradation (Darrah et al. 2019; McInnes et al. 2020; Simpson et al. 2021) will continue. One way of contributing to the effort to ensure that these approaches are extended and expanded is to explore and develop effective methods for sharing knowledge between local communities, wetland researchers, and managers. This could start with the increasing sources of knowledge about the values and benefits derived from wetlands as well as that about management responses to the pressing problems for wetland management. The latter are well known, and yet, continue, with steps to stop and reverse wetland loss and degradation being acknowledged as insufficient (Ramsar Convention on Wetlands 2018). As part of ongoing programs run through organizations such as the Sydney Olympic Park Authority in Australia and the Wildfowl and Wetlands Trust in the United Kingdom (UK) a symposium on Methods for Sharing Wetland Knowledge and Exploring Future Needs and Solutions was held at the INTECOL International Wetland Conference in Christchurch, New Zealand in October 2021. The symposium had three objectives, namely to: 1) explore the wealth and usefulness of traditional and community knowledge about wetlands; 2) identify gaps in knowledge-sharing tools, techniques and mechanism; and 3) explore ways forward. The symposium was intended to revisit the effectiveness of current approaches and programs in wetland awareness, education and training, and suggest measures for future improvements. It was further expected that in the future there would also be an emphasis on newer communication approaches, such as webinars and twitter conferences, alongside traditional and local community knowledge, which in themselves are based on having participatory approaches to ensure knowledge is shared in an open way. Provided below is an overview of the key issues that were included in the presentations in the symposium.

Detecting wetland encroachment and urban agriculture land classification in Uganda using hyper-temporal remote sensing.

Background: Urbanization is an important indicator of economic growth and social change but is associated with environmental degradation, which threatens the sustainable growth of African cities. One of the most vulnerable ecosystems in urban areas are wetlands. In Uganda, wetlands cover an area of 11% of the country's land area. Half of the wetland areas in Ugandan cities have been converted to industrial and residential areas, and urban agriculture. There is limited information on the extent of wetland conversion or utilization for urban agriculture. The objective of this study was to investigate the extent of wetlands lost in two Ugandan cities, Wakiso and Kampala, in the last 30 years. Secondly, we extracted crop agriculture in the wetlands of Kampala and Wakiso from hyper-temporal satellite image analysis in an attempt to produce a spatial detail of wetland encroachment maps of urban agriculture using a reproducible mapmaking method. Methods: Using a field survey and free remote sensing data from Landsat TM 1986 and Landsat ETM 2016 we classified the rate of wetland loss and encroachment between the years 1986 and 2016. We used MODIS NDVI 16-day composites at a 500-meter spatial resolution to broaden the analysis to distinguish distinctive crops and crop mixtures in the encroached wetlands for urban agriculture using the ISODATA clustering algorithm. Results: Over 30 years, 72,828 ha (73%) of the Wakiso-Kampala wetlands have been lost meanwhile agriculture areas have doubled. Of this 16,488 ha (23%) were converted from wetlands. All cultivated agriculture in Kampala was in the wetlands while in Wakiso, 73% of crop agriculture was in the wetlands. The major crops grown in these urban wetlands were banana (20%), sugarcane (22%), maize (17%), Eucalyptus trees (12%), sweet potatoes (10%), while ornamental nurseries, pine trees, vegetables, and passion fruits were each at 5%.

Wetland conversion risk assessment of East Kolkata Wetland: A Ramsar site using random forest and support vector machine model

East Kolkata Wetland (EKW) is a Ramsar site located adjacent to the Kolkata megacity. EKW is one of the resourceful wetland ecosystems of the world which offers a bundle of direct and indirect ecosystem services to the Kolkata megacity region. The rapid expansion of built-up in the surrounding urban agglomeration of the EKW is putting immense pressure on the EKW and the rate of wetland loss has been highest in recent decades. To ensure that this distinct ecosystem is conserved, an efficient means of identifying wetland conversion risk is needed. This study aims to assess the risk of EKW conversion using two advanced data-driven Machine Learning (ML) models, viz, Random Forest (RF), and Support Vector Machine (SVM). The novelty of the paper is in the fact that ML models have been widely applied to groundwater potential, flood susceptibility, and landslide susceptibility, their applicability to wetland conversion risk assessment has not yet been explored. The advantage of RF and SVM is that both of the ML models can overcome the limitations of pre-assumption based conventional methods of wetland risk assessment. A total of eight factors are selected which can be categorized into ecological, bio-physical, demographic, and physical infrastructure groups. Both results indicate that around 60% area under medium to very high-risk zones. A comparison is also made between these two methods to identify the most precise prediction method for this study area. The results of the models are quantitatively validated applying the Receiver Operating Characteristics (ROC) method, where both of this method identifies SVM as a more precise predictive model for this study with 91.12% accuracy. The spatial pattern of encroachment and shrinkage of EKW triggered by urban expansion is successfully captured by RF and ME. Policy analysts and land-use planners can use the outcome derived from RF and SVM models and associated maps to identify the risk zones, assess the effectiveness of wetland conservation programs, design effective policies to stop further degradation of the wetlands, and adopt long-term sustainable planning for this precious ecosystem.

Detecting level of wetland encroachment for urban agriculture in Uganda using hyper-temporal remote sensing

Background: Urbanization is an important indicator of economic growth and social change but is associated with environmental degradation. In Uganda, wetlands cover an area of 11% of the country’s land area, of which half have been converted to industry and residential areas, and urban agriculture. Here, we investigate the extent of wetlands lost in two Ugandan cities, Wakiso and Kampala, in a period of 30 years. Secondly, we demonstrate a simple methodology to monitor agriculture on encroached wetlands. Methods: Using a field survey and free remote sensing data from Landsat TM 1986 and Landsat ETM 2016 we classified the rate of wetland loss and encroachment from 1986 to 2016. Using MODIS NDVI 16-day composites at 500-meter spatial resolution, we generated distinctive crops and crop mixtures in the encroached wetlands for urban agriculture using the ISODATA clustering algorithm. Results: Over 30 years, 72,828 ha (73%) of the Wakiso-Kampala wetlands have been lost. Agriculture areas have doubled, of which 16,488 ha (23%) were reclaimed from wetlands. All cultivated agriculture in Kampala was in the wetlands while in Wakiso, 73% of crop agriculture was in the wetlands. Major crops grown in these urban wetlands were banana (20%), sugarcane (22%), maize (17%), Eucalyptus trees (12%), sweet potatoes (10%). Conclusions: The Kampala-Wakiso wetlands have been disappearing at a rate of 2500 ha annually for the last 30 years. At this rate, there will be no wetlands left by 2029. Policy recommendations should promote wetland reclamation programs so as to restore and reconstruct lost and fragmented wetlands; should mandate food security and poverty eradication to convene with ministries regulating wetlands to merge conflicting policies; and should develop polices that are inclusive of challenges faced by the urban poor while at the same time minimize the pressures on urban environments.

What did China's National Wetland Conservation Program Achieve？Observations of changes in land cover and ecosystem services in the Sanjiang Plain

China implemented the National Wetland Conservation Program (NWCP) from 2002 to protect and rehabilitate wetlands. Under the background of sustainable development, assessment on the effectiveness of the NWCP is important to ecosystem management, especially in the Sanjiang Plain, the largest marsh distribution area and hotspot area with wetland loss. To achieve this aim, this study examined the changes in land cover and ecosystem services (ESs) from 1990 to 2000 and from 2000 to 2015 in the Sanjiang Plain as well as the nine national nature reserves for wetlands (NNRWs) by means of Landsat series images and the InVEST model. Results reveal that the NWCP played critical roles in reducing wetland loss and improving regional ESs. The shrinkage rate of wetlands in the Sanjiang Plain has been decreased remarkably, with a declined rate of wetland loss from 750 km2 yr−1 to 189 km2 yr−1. The reduction rate of habitat area in good suitable grade and ecosystem carbon stock declined notably during the period 2000–2015 compared to the period 1990–2000. The amount of water retention increased by 5.4%, while the grain production capacity was enhanced by nine times from 1990 to 2015. Specifically, since 2000, the reduction rate of wetland area in NNRWs (33 km2 yr−1) was obviously lower than that in the entire Sanjiang Plain, whilst various ESs in NNRWs were better than that in the whole Sanjiang Plain. This study is expected to provide an example for evaluating the effectiveness of the NWCP at other regions and support regional wetland conservation management.

Coastal Watershed Forested Wetland Change and Opportunities for Enhanced Collaboration with the Forestry Community

U.S. Fish and Wildlife Service National Wetlands Inventory (NWI) Wetlands Status and Trends reports have documented greater net wetland loss rates in U.S. coastal watersheds than in the rest of the contiguous U.S., and this loss rate has increased through time. Atlantic and Gulf of Mexico coastal watersheds contain 30% of the country’s forested wetlands. Although forested wetlands in this region have a long history of supplying substantial benefits to society, a portion of these habitats are currently being transformed into different land cover types – including both uplands and other types of wetlands. Drivers of forested wetland change in this region are complex, but some loss of area appears to be associated with plantation forestry. Improved understanding of this relationship is necessary to better support informed management of this critical resource. This will require close collaboration between the wetland and forestry communities. Unfortunately, communication between these two communities has been hampered by misconceptions about how wetland and forestry data are collected, and differences in the way key terms are defined. This article summarizes recent Wetlands Status and Trends data, seeks to clarify definitions and current misconceptions involving this dataset, and describes opportunities for future collaboration between the forestry and wetland communities.

Loss of wetlands due to the expansion of polder in the Dongting Plain, China, AD 1368–1980

The Dongting Plain is an area characterized by wetland losses because of long-term polder construction. The study of historical polder expansion provides an opportunity to better understand the loss of wetlands covered by polders. To reconstruct the polder expansion over time, the polder patches extracted though remote sensing were marked with the names obtained from maps and the times of construction obtained from local gazetteers, and shown in the chronological order of turning points. Then, the distribution and changes in the wetlands covered by polders during 1368–1980 were reconstructed. The following are the major findings: (1) the current polders (2010s) accumulated over many centuries. There were 5.7% of the current polder area in 1644, 14.0% in 1735, 23.4% in 1850, 55.0% in 1911, 73.6% in 1949, and 100% in 1980; (2) the wetlands were mostly lost in the northern part of the region and declined rapidly over the past two centuries. The wetland area in 1850 was 6635 km2, which in 1911, 1949 and 1980 were 73.9%, 62.7% and 40.6% of that in 1850, respectively; (3) there were differences in the rate of wetland loss. The fastest time of wetland area disappearance was in 1949–1980, and 45.8 km2 of the wetlands had been lost each year; and (4) there was a spatial difference in wetland losses caused by polder expansion. In the northern part of the area, the wetland loss was mainly in 1851–1980, and the polders constructed in this period covered 89.5% of the polder area. In contrast, in the southern part of the area, the change in the wetland area was relatively small in each period, and the polder constructed before and after 1850 covered 48.3% and 52.7% of the polder area, respectively.

Canals, backfilling and wetland loss in the Mississippi Delta

Canals and spoil banks have contributed significantly to high rates of wetland loss in the Mississippi Delta. There has been relatively little research on management of canals and spoil banks and this needs to be a significant component of restoration of the delta. We analyze research on the role of backfilling canals in the context of delta restoration with special reference to Turner and McClenachan (2018) who state that if all canals were backfilled, it could significantly reduce or even reverse wetland loss and that most wetland loss is caused by canals. We agree with Turner and McClenachan that canals have been a significant cause of wetland loss in the Mississippi Delta and that removing spoil banks and backfilling canals should be an integral part of delta restoration. However, a number of factors need to be considered when choosing which canals to backfill including possible enhanced erosion due to exposure to wave action for newly created and remnant marsh, the current and future production history of oil and natural gas wells associated with canals, and other restoration activities in oil and gas fields. Turner and McClenachan's analysis using wetland loss patterns in 15-min quadrangles suggesting that canal density can explain most wetland loss in coastal Louisiana is flawed because of scale problems and other impacts of oil and gas activity. These impacts include subsurface induced subsidence and the impact of produced water and toxins on wetlands that are largely unrelated to surface alteration due to canals and spoil banks.

Multiscale effects of wetland availability and matrix composition on wetland breeding birds in Minnesota, USA

Abstract The increasing intensity of wetland stressors in the Upper Midwestern United States hastens the need to understand how matrix composition influences wetland bird occurrence and abundance. The optimal spatial scale for assessing species–habitat relationships is not always apparent, but may affect inference about wetland use and suitability. We developed occupancy and abundance models, accounting for imperfect detection, for 9 wetland bird species breeding in Minnesota. We evaluated land cover associations at 3 spatial scales (12.6 ha, 50.3 ha, and 4,000 ha), quantified species-specific sensitivity to wetland availability and matrix habitat composition (agricultural and developed land covers), and assessed ecoregional variation in occupancy and abundance. Amount of wetland cover was positively associated with occupancy of 89% of species and with abundance of 67% of species, but the spatial scale of support differed among species. American Bittern (Botaurus lentiginosus), Pied-billed Grebe (Podilymbus podiceps), and Wilson’s Snipe (Gallinago delicata) in particular were negatively impacted by anthropogenic land uses within the surrounding matrix, indicating a need to shift wetland conservation planning from the site scale to the landscape scale to capture pertinent drivers of wetland bird habitat use. Mean expected occupancy across all species was greatest in the Prairie Pothole Region (PPR), suggesting that restoration efforts within this ecoregion are likely to maintain wetland bird diversity. However, given the minimal total wetland availability and predominantly agricultural matrix in the PPR, protecting wetlands and upland buffers in the Aspen Parklands or Boreal ecoregions may represent a better investment for agricultural-sensitive species such as American Bittern, Sandhill Crane (Antigone canadensis), and Wilson’s Snipe. Our modeling approach provides a multi-species framework for identifying habitat management priorities; future applications at broader spatial extents can continue to improve wetland bird conservation in a region with high rates of wetland loss and degradation.