Wetland Loss Research Articles

Predicting the vulnerability of seasonally-flooded wetlands to climate change across the Mediterranean Basin

Wetlands have been declining worldwide over the last century with climate change becoming an additional pressure, especially in regions already characterized by water deficit. This paper investigates how climate change will affect the values and functions of Mediterranean seasonally-flooded wetlands with emergent vegetation. We simulated the future evolution of water balance, wetland condition and water volumes necessary to maintain these ecosystems at mid- and late- 21st century, in 229 localities around the Mediterranean basin. We considered future projections of the relevant climatic variables under two Representative Concentration Pathway scenarios assuming a stabilization (RCP4.5) or increase (RCP 8.5) of greenhouse gases emissions. We found similar increases of water deficits at most localities around 2050 under both RCP scenarios. By 2100, however, water deficits under RCP 8.5 are expected to be more severe and will impact all localities. Simulations performed under current conditions show that 97% of localities could have wetland habitats in good state. By 2050, however, this proportion would decrease to 81% and 68% under the RCP 4.5 and RCP 8.5 scenarios, respectively, decreasing further to 52% and 27% by 2100. Our results suggest that wetlands can persist with up to a 400 mm decrease in annual precipitation. Such resilience to climate change is attributed to the semi-permanent character of wetlands (lower evaporation on dry ground) and their capacity to act as reservoir (higher precipitation expected in some countries during winter). Countries at highest risk of wetland degradation and loss are Algeria, Morocco, Portugal and Spain. Degradation of wetlands with emergent vegetation will negatively affect their biodiversity and the services they provide by eliminating animal refuges and primary resources for industry and tourism. A sound strategy to preserve these wetlands would consist of proactive management to reduce non-climate stressors.

Wetland Loss in Northeastern Italy Documented by Historical Maps

Abstract. Historical landscape and habitat reconstruction can be an important mitigation tool for regional habitat loss, conservation and restoration (NRC 1992; Swetnam et al. 1999; Steiner 2000). Among landscapes and habitats, wetlands play an important role in providing ecosystem services. Any loss of wetland areas may cause serious and sometimes irreparable environmental and habitat damages (Soule, 1991). Wetlands have a paramount importance for ecosystems and are protected by the Ramsar Convention and regulated and valorized, in different ways, by local and/or regional protection agency and laws.Analysing trends of wetlands loss on a regional scale can now be performed using geo-historical approaches and remote sensing and GIS technologies. Many notable examples of wetlands loss studies using a combined geohistorical and GIS approach may be find in the literature. Much of the previous research on wetlands loss has focused on the United States where wetlands are more legally protected and regulated. Little research has focused on wetlands in southern Europe. The focus of this research is on wetland loss in the Southern Venetian-Po Plain (Northeastern Italy) through a comparison of contemporary and historical data with the analysis of remote sensing and historical maps. In particular, this work focuses on the province of Padova, well known for their abundance of inland wetlands in the past although greatly disrupted through drainage and agricultural expansion in the last century.The Southern Venetian Po-Plain is an alluvial plain located between the Lagoon of Venice, the Po river and the Veneto pre-Alps piedmont region. This region is currently characterized by an apparent scarcity of wetlands in comparison to what is represented in many historical maps and described in historical documents. Some studies on wetlands in parts of the Venetian region have been conducted using different approaches. Typical research focused on single portions of larger wetlands or single ponds for the study of current biochemical conditions and ecosystems in the environment (e.g. Serandrei-Barbero et al., 2011; Pappalardo et al., 2016). Research on more extensive wetlands, land reclamations and humans-rivers relationships mostly focus on the analysis of the socio-economical conditions in the Po Delta and the Lagoon of Venice (e.g. Bertoncin, 2002; Novello, 2009). Despite numerous works on singular ponds or studies on larger water bodies in the Venetian area, there is still a poor knowledge of the amount, the extension and the type of wetlands in the Southern Venetian Po-Plain. A comprehensive survey of wetlands for the Venetian area has never been conducted, and the ‘official’ data are notably incomplete.The objectives of this work were: 1) to perform a survey (Figure 1) of both historic and present-day wetlands in the province of Padova (northeastern Italy) using historical cartography (1882 map of the province of Padova by O. Morelli) and recent aerial orthophotos (2015), 2) to provide a first estimation of the extraordinary loss of wetlands in this province due mostly to land reclamation processes of the last century, and 3) to discuss the prospects for further historical wetlands analysis based on additional historic maps (1776, 1801, 1862, 1882, 1980) for a key area called Bassa Padovana (Padova’s lowland). All quantitative analyses were performed through the use of a GIS. This research contributes to the discussion of small isolated wetlands (Figure 2) that have been created in the last century and their unique role in the ecosystems.

Marsh edge erosion and associated carbon dynamics in coastal Louisiana: A proxy for future wetland-dominated coastlines world-wide

Coastal wetland loss through marsh edge erosion is a serious problem in Louisiana. The majority of studies on coastal land loss use aerial and satellite photographic analysis while field and site-specific measurements are limited. The aim of this study was to spatially and temporally measure coastal marsh edge erosion and investigate factors responsible for differences in erosion including shoreline orientation, soil physio-chemical properties, and wind speed and duration. A total of 33 transects across six island sites in northern Barataria Basin, Louisiana were established. Transects on shorelines facing different compass directions were measured for erosion for up to 2 years. Soils were analyzed for physiochemical properties including bulk density, organic matter, total carbon, nitrogen, and phosphorus. Bathymetric surveys were conducted to determine the extent of the erosive bay bottom profile. In addition, 14C dating of the basal organic matter (1.5–1.6 m) was conducted. Erosion rates ranged from 49.27 to 324.85 cm y-1 with a mean value of 141.69 ± 22.45 cm y−1. As expected, erosion rates were significantly different (p < 0.001) between protected and unprotected sites. The erosion rate was not correlated with wind speed (r = -0.07), weakly correlated with compass direction of shoreline (r = 0.25) and water level (r = 0.25) but strongly correlated with duration of wind (r = 0.60). Erosion rate was negatively correlated (r = -0.45) with bulk density and positively correlated with organic matter content (r = 0.42) of the top 40 cm of the soil. Over time, the marsh is eroded down to a depth of 1.5 m, which correlates to annual loss of 1.82 ± 0.29 m3 volume of marsh per meter shoreline length including a loss of organic matter (141.5 ± 22.55 kg m−1) and carbon (63.32 ± 10.09 kg m−1) previously preserved for up to 850 years. As a consequence, annual CO2 emissions for Barataria Basin were estimated to be 1.56 ± 0.26 million tCO2e y−1. Results can inform coastal managers as to the most vulnerable marshes to target restoration efforts. Due to high relative sea level rise in coastal Louisiana, these results can also be used to inform the world's stable coastlines on the relative vulnerability of their coastal marshes in the near future, due to projected eustatic sea level. Consequently, the eroding coastlines across the globe may be a significant source of CO2 emissions in near future, as millennial age stored soil carbon is released in a relatively short time, potentially overwhelming human efforts to slow rising atmospheric CO2 levels.

Impacts of Coastal Reclamation on Natural Wetlands in Large River Deltas in China

Little information is available on the impacts of coastal reclamation on wetland loss in large-river deltas at a regional scale. Using remote sensing data of coastal wetland and reclamation in four deltas in China from 1978 to 2014, we tracked their continuous area changes in four periods: 1978–1990, 1990–2000, 2000–2008, and 2008–2014. The areal relation between wetland loss and reclamation was quantified and used to identify coastal reclamation mode intensity coupled with another three indicators: reclamation rate, accretion rate and land-use intensity of coastal reclamation. The results showed that coastal reclamation driven by economic development reduced, or even reverse the original growth of delta which was determined by the offset between wetland acceleration rate and wetland loss rate. Generally, the area of reclamation showed a positive linear correlation with the area of wetland loss. The findings imply that human activities should control reclamation rate and intensity to alleviate total wetland loss and maintain wetland ‘net gain’. Inappropriate coastal reclamation modes can magnify total wetland loss; therefore, coastal reclamation with a slow increment rate and low impervious surface percent is of great importance for sustainable development in future coastal management.

The Main Drivers of Wetland Changes in the Beijing-Tianjin-Hebei Region

Wetlands are the most threatened ecosystem in China, and wetland conservation is a national priority because of their importance for water security, flood mitigation, and biodiversity conservation. A goal has been established for the Beijing-Tianjin-Hebei Region (BTH) to recover 340 km2 of wetlands by 2020. To guide restoration and protection efforts, policymakers need information on the trends of wetland loss, conversion of wetlands, and their associated human drivers. The main drivers of changes in different wetland types in the BTH were identified and quantified from 2000 to 2015. In 2015, there was 6264.07 km2 less wetland area than in 2000, with the remaining wetlands primarily located in Hebei and Tianjin. Reservoirs/ponds were the most abundant wetland type, followed by herbaceous swamps, rivers, canals and channels, and then lakes as the least represented. There were continuous losses of wetlands from 2000 to 2015, with marked decreases for rivers (30.48%), channels/canals (23.30%), and herbaceous swamps (16.12%). However, there was an increase in the area of lakes and reservoirs/ponds, with increases of 54.96% and 3.47%, respectively. The largest changes in natural wetlands were due to agricultural production followed by artificialization and grassland expansion. The driving forces of the observed changes were specific to each local region. According to an aggregated boosted trees (ABT) analysis, gross farm production, total aquatic products, and irrigated area were the top three drivers of the decrease in natural wetlands, which agreed with the main patterns of change in the BTH. The purpose of this study was to provide guidance for policy makers working to meet the 2020 BTH wetland recovery target. Recommendations were provided at the provincial level, including water transfers across provincial boundaries, the control of agricultural expansion, exploration of species-specific irrigation deficits, a reduction in the artificialization of land surfaces, the development of a sustainable intensified aquaculture model, and the promotion of awareness of wetland importance among local people.

Benefits of Climate-Change Mitigation for Reducing the Impacts of Sea-Level Rise in G-20 Countries

This paper assesses the potential benefits of climate-change mitigation in reducing the impacts of sea-level rise over the 21st century in G-20 countries (excluding the European Union as a whole), using the Dynamic Interactive Vulnerability Assessment model. Impacts of the expected number of people flooded annually and wetland losses were assessed. To assess the benefits of mitigation, it was assumed that defences were not upgraded during the study. Globally, with a sea-level rise of 0.68 m by the 2080s (with respect to 1980–99), representing a potential future with limited climate-change mitigation, and with the Special Report on Emissions Scenarios A1 socio-economic scenario, 123 million additional people could be flooded annually and 39% of present global wetland stock could be lost. For a 0.19-m rise in sea level, associated with a substantial reduction in emissions, the number of people flooded could be reduced to 13 million/y, with 21% of global wetland stock loss, unless new wetlands emerge. Collectively, non-Annex 1 G-20 countries experience a disproportionately higher number of people flooded in their nations compared with the proportion of population flooded globally. The greatest wetland losses for G-20 countries are projected for Australia, Indonesia, and the United States. Thus, G-20 nations with the highest emissions or gross domestic product frequently do not experience the greatest impacts, despite some of these nations being potentially more able to pay for adaptation.

Evaluating Tradeoffs in the Response of Sora (Porzana carolina) and Waterfowl to the Timing of Early Autumn Wetland Inundation

Wetland loss has increased the importance of multi-species management in remaining wetlands, which provide habitat for a multitude of wetland-dependent species. Many public wetlands across the mid-latitude United States are managed as moist soil impoundments with emphasis on migratory waterfowl. However, how the timing of these water management decisions affects rails is still uncertain. Wetland managers identified this as an area of uncertainty regarding timing of alternative water management strategies to benefit waterfowl and rails, which was addressed through a 3-year management experiment. Sora (Porzana carolina) and waterfowl were surveyed on 10 public wetland properties in Missouri, USA from 2014-2016, and their responses to early autumn inundation of managed palustrine wetlands were compared. A total of 558 Sora surveys detected 5,755 birds (20.6 birds/survey ± 30.8 SD), and 1,304 waterfowl surveys detected 1,411,779 birds (15,686.4 birds/survey ± 23,933.9 SD). Sora responded positively (birds/ha) to inundation of moist soil impoundments earlier in autumn migration (August). The top model for Sora included treatment, year and region of Missouri. There was no difference in waterfowl abundance between early or late inundation. Inundating wetlands earlier in autumn migration can provide habitat for migrating Sora without negative effects on waterfowl use of those wetlands, and wetland managers can incorporate this into their decision-making framework.

Rapid expansion of coastal aquaculture ponds in China from Landsat observations during 1984–2016

Aquaculture is one of the fastest growing animal food production sectors mainly developed in fertile coastal areas. Monitoring and mapping of aquaculture ponds are of utmost importance for the sustainable management of coastal ecosystems. In this study, an integrated updating and object-based classification approach was developed to generate maps of coastal aquaculture ponds in China from 1984 to 2016 at 30-m spatial resolution. The current extent and change of coastal aquaculture ponds in China were analyzed over the course of 32 years. In addition, spatial-temporal dynamics of coastal aquaculture ponds were examined by buffer and overlay analyses. The results showed that the total area of coastal aquaculture ponds in China expanded by 10,463 km2, with the largest gain occurring from 1990 to 2000 (4,207 km2). The coastal provinces of Guangdong, Shandong, Jiangsu, Liaoning, and Hebei had significant increases of aquaculture ponds areas, accounting for 83% of totally expanded ponds in the coastal zone of China. Rapid expansion of coastal aquaculture ponds was observed in the 0–10 km inshore buffer and the loss of wetlands and arable land contributed more than 50% to the expansion. Socio-economic factors helped drive the continual increase of coastal aquaculture ponds in China. Scientific environmental regulations and planning and management strategies at the national and international policy levels should be enhanced to consider the ecological impacts of aquaculture expansion.

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.

Geospatial Tools for the Large-Scale Monitoring of Wetlands in the San Francisco Estuary: Opportunities and Challenges

Author(s): Taddeo, Sophie; Dronova, Iryna | Abstract: Significant wetland losses and continuing threats to remnant habitats have motivated extensive restoration efforts in the San Francisco Bay–Delta estuary of California, the largest in the western United States. Consistent monitoring of ecological outcomes from this restoration effort would help managers learn from past projects to improve the design of future endeavors. However, budget constraints and challenging field conditions can limit the scope of current monitoring programs. Geospatial tools and remote sensing data sets could help complement field efforts for a low-cost, longer, and broader monitoring of wetland resources. To understand where geospatial tools could best complement current field monitoring practices, we reviewed the metrics and monitoring methods used by 42 wetland restoration projects implemented in the estuary. Monitoring strategies within our sample of monitoring plans relied predominantly on field surveys to assess key aspects of vegetation recovery while geospatial data sets were used sparingly. Drawing on recent publications that focus on the estuary and other wetland systems, we propose additional geospatial applications to help monitor the progress made toward site-specific and regional goals. These include the use of ecological niche models to target on-the-ground monitoring efforts, the up-scaling of field measurements into regional estimates using remote sensing data, and the analysis of time-series to detect ecosystem shifts. We discuss challenges and limitations to the broad-scale application of remote sensing data in wetland monitoring. These notably include the need to find a venue to store and share computationally intensive data sets, the often cumbersome pre-processing effort needed for long-term analyses, and multiple confounding factors that can obscure the signal of remote sensing data sets.

Impact of urbanization on water resources of Pakistan: A review

This paper summarizes the various dimensions and impacts of urbanization on Pakistan’s water resources in order to provide foundations for future water policy that will lead towards country’s socio-economic development. Urbanization is considered as a major trend of 21st century in many developing countries. Along with urbanization, increase in population growth in recent years has put a pressure on the world’s water resources in terms of water demand and pollution. Various issues related to water sector in urban areas of Pakistan have been identified including contamination of surface and ground water resources through industrial, agricultural and domestic discharge of waste and waste water, increasing floods, loss of wetlands and aquatic biodiversity, sea water intrusion and subsidence, physical reduction in water resources quantity and quality and operational and managerial incapacities. There are some other issues like unequal water distribution which together with population burden, rapid urbanization and growing industrialization are posing a huge challenge for Pakistan’s water management in 21st century. Taken together all the studies, this review suggests that to reduce vulnerability to water resources of Pakistan, there is a need for new systems of urban planning and governance institutions as the core of Pakistan’s water crisis is water management.

The denitrification potential of eroding wetlands in Barataria Bay, LA, USA: Implications for river reconnection

Expressions of eutrophication have led to increased stress on coastal ecosystems around the world. The nitrogen (N) removal potential of coastal wetland ecosystems is important due to increased loading of N to the coast. In Louisiana, there is rapid coastal wetland loss due primarily to the presence of river levees, which have isolated the coastal basins, and a high relative sea level rise. Ecosystem managers are planning to construct the Mid-Barataria sediment diversion which will reconnect the Mississippi River with Barataria Basin to build new wetlands and nourish existing marsh. The sediment diversion will deliver large amounts of nitrate into the surface waters of Barataria Bay. This research sought to quantify the nitrate removal potential of three bay zones; vegetated marsh, submerged peat fringe, and bay-bottom muddy estuarine sediment in intact soil cores incubated with a 2 mg L−1 N-NO3 water column. We noted: i) The areal nitrate reduction rates for the marsh, fringe, and estuary zones were 29.29 ± 3.28, 18.83 ± 1.31, and 10.83 ± 0.62 mg N m−2 day−1, respectively; ii) the majority (~93%) of NO3 was converted to N2O, indicating denitrification was the major NO3 reduction pathway; iii) the submerged, eroded marsh soils (peat fringe zone) will play a large role in nitrate reduction due to increased contact time with the surface water. These findings can inform the predictive numerical models produced and utilized by ecosystem managers to better quantitatively understand how the coastal basin will respond to nutrient loading from river reconnection. In a broader context, the current relative sea level rise in coastal Louisiana is within the range of eustatic sea level rise that most stable coastlines will experience within the next 65–85 years. Therefore, these findings can serve as an example of potential future impacts to coastal wetland systems, globally, within the next century.

Safe places: Increasing Finnish waterfowl resilience through human-made wetlands

Loss of boreal wetlands in Finland has negative consequences for waders, ducks and local socio-ecological systems. These changes result from over 70-years of human-made alterations to land and waterscapes. Climate change and associated extreme events are expected to be further drivers of negative change. In order to build resilience and seek answers to these challenges, a five-year monitoring of Linnunsuo, a 120-ha human-made wetland was conducted. Wood sandpiper (Tringa glareola) and Northern pintail (Anas acuta) were the indicator species. Analysis of co-management complemented the review. Results indicate that the creation of well-designed wetlands has the potential to increase resilience of these socio-ecological systems. They are cost-effective and can be replicated across the boreal region to address the need of habitat loss and climate impacts.

The value of coastal wetland flood prevention lost to urbanization on the coastal plain of the Gulf of Mexico: An analysis of flood damage by hurricane impacts

Wetlands provide ecosystem services such as flood prevention; however, their transformation to housing developments limits the provision of these services. When tropical storms and hurricanes occur where coastal wetlands have undergone land use change (LUC), socioeconomic disaster results. Our objective was to estimate the economic value of flood prevention service provided by coastal wetlands. We quantified LUC and the loss of water retention capacity as a wetlands loss function and estimated the economic cost of flooding to households (lost appliances). The Veracruz-Boca del Rio-Medellin conurbation in Veracruz, Mexico, was used to evaluate these parameters during the floods caused by hurricane Karl in 2010. The total economic cost of losses to households was $150.85 million USD/2007. Between 1980 and 2010, the urban zone grew by 1,437.41 ha, resulting in the loss of 16.34 ha of water bodies, 455.41 ha of agriculture, and 965.66 ha of coastal wetlands (25.36 ha of mangroves, 152.95 ha of freshwater marshes and 787.35 ha of flooded grasslands). These results were used to obtain the economic value of flood prevention service and expressed as indirect-avoided cost. The economic values of flood prevention were: flooded grassland at $148,277 USD/ha/2007, freshwater broad-leaved marsh at $190,863 USD/ha/2007, and mangroves at $193,674 USD/ha/2007. The results of this study highlight the importance of protecting coastal wetlands and can be used by urban planning decision-makers when drawing up public policies in regional coastal contexts to protect human settlements and infrastructure.

Toward a mechanistic understanding of "peat collapse" and its potential contribution to coastal wetland loss.

Coastal wetlands are susceptible to loss in both health and extent via stressors associated with global climate change and anthropogenic disturbance. Peat collapse may represent an additional phenomenon contributing to coastal wetland loss in organic‐rich soils through rapid vertical elevation decline. However, the term “peat collapse” has been inconsistently used in the literature, leading to ambiguities regarding the mechanisms, timing, and spatial extent of its contribution to coastal wetland loss. For example, it is unclear whether peat collapse is distinct from general subsidence, or what biogeochemical changes or sequence of events may constitute peat collapse. A critical analysis of peer‐reviewed literature related to peat collapse was supplemented with fundamental principles of soil physics and biogeochemistry to develop a conceptual framework for coastal wetland peat collapse. We propose that coastal wetland peat collapse is a specific type of shallow subsidence unique to highly organic soils in which a loss of soil strength and structural integrity contributes to a decline in elevation, over the course of a few months to a few years, below the lower limit for emergent plant growth and natural recovery. We further posit that coastal wetland peat collapse is driven by severe stress or death of the vegetation, which compromises the supportive structure roots provide to low‐density organic soils and shifts the carbon balance of the ecosystem toward a net source, as mineralization is no longer offset by sequestration. Under these conditions, four mechanisms may contribute to peat collapse: (1) compression of gas‐filled pore spaces within the soil during dry‐down conditions; (2) deconsolidation of excessively waterlogged peat, followed by transport; (3) compaction of aerenchyma tissue in wetland plant roots, and possibly collapse of root channels; and (4) acceleration of soil mineralization due to the addition of labile carbon (dying roots), oxygen (decreased flooding), nutrients (eutrophication), or sulfate (saltwater intrusion). Scientists and land managers should focus efforts on monitoring vegetation health across the coastal landscape as an indicator for peat collapse vulnerability and move toward codifying the term “peat collapse” in the scientific literature. Once clarified, the contribution of peat collapse to coastal wetland loss can be evaluated.

A synthesis of three decades of hydrological research at Scotty Creek, NWT, Canada

Abstract. Scotty Creek, Northwest Territories (NWT), Canada, has been the focus of hydrological research for nearly three decades. Over this period, field and modelling studies have generated new insights into the thermal and physical mechanisms governing the flux and storage of water in the wetland-dominated regions of discontinuous permafrost that characterises much of the Canadian and circumpolar subarctic. Research at Scotty Creek has coincided with a period of unprecedented climate warming, permafrost thaw, and resulting land cover transformations including the expansion of wetland areas and loss of forests. This paper (1) synthesises field and modelling studies at Scotty Creek, (2) highlights the key insights of these studies on the major water flux and storage processes operating within and between the major land cover types, and (3) provides insights into the rate and pattern of the permafrost-thaw-induced land cover change and how such changes will affect the hydrology and water resources of the study region.

Assessment of the temporal evolution of storm surge across coastal Louisiana

The co-evolution of wetland loss and flood risk in the Mississippi River Delta is tested by contrasting the response of storm surge in coastal basins with varying historical riverine sediment inputs. A previously developed method to construct hydrodynamic storm surge models is employed to quantify historical changes in coastal storm surge. Simplified historical landscapes facilitate comparability while storm surge model meshes developed from historical data are incomparable due to the only recent (post-2000) extensive use of lidar for topographic mapping. Storm surge model meshes circa 1930, 1970 and 2010 are constructed via application of land to water (L:W) isopleths, lines that indicate areas of constant land to water ratio across coastal Louisiana. The ADvanced CIRCulation (ADCIRC) code, coupled with the Simulating WAves Nearshore (SWAN) wave model, is used to compute water surface elevations, time of inundation, depth-averaged currents and wave statistics from a suite of 14 hurricane wind and pressure fields for each mesh year. Maximum water surface elevation and inundation time differences correspond with coastal basins featuring historically negligible riverine sediment inputs and wetland loss as well as a coastal basin with historically substantial riverine inputs and wetland gain. The major finding of this analysis is maximum water surface elevations differences from 1970 to 2010 are 0.247 m and 0.282 m within sediment-starved Terrebonne and Barataria coastal basins, respectively. This difference is only 0.096 m across the adjacent sediment-abundant Atchafalaya-Vermilion coastal basin. Hurricane Rita inundation time results from 1970 to 2010 demonstrate an increase of approximately one day across Terrebonne and Barataria while little change occurs across Atchafalaya-Vermilion. The connection between storm surge characteristics and changes in riverine sediment inputs is also demonstrated via a sensitivity analysis which identifies changes in sediment inputs as the greatest contributor to changes in storm surge when compared with historical global mean sea level (GMSL) rise and the excavation of major navigation waterways. Results imply the magnitude of the challenge of preparing this area for future subsidence and GMSL rise.

Water Table Drawdown Alters Soil and Microbial Carbon Pool Size and Isotope Composition in Coastal Freshwater Forested Wetlands

Loss of coastal wetlands is occurring at an increasingly rapid rate due to drainage of these wetlands for alternative land-uses, which also threatens carbon (C) storage in these C-rich ecosystems. Wetland drainage results in water table drawdown and increased peat aeration, which enhances decomposition of previously stabilized peat and changes stable C isotope profiles with soil depth. The effect of water table drawdown on the pool size and δ13C signature of plant C, soil organic C (SOC) and microbial biomass C (MBC) across a range of organic and mineral soils has not previously been reported in coastal freshwater forested wetlands. To this end, litter, roots, and soils were collected from organic and mineral soil horizons in two coastal freshwater forested wetlands in North Carolina with different hydrological regimes: 1) a natural bottomland hardwood forest (natural); and 2) a ditched and drained, intensively-managed wetland for loblolly pine silviculture (managed). We found that hydrology and soil horizon, and to a lesser degree micro-topography, was important in shaping observed differences in size and 13C signature of soil and microbial pools between the natural and managed wetland. The natural wetland had higher SOC and MBC concentrations in the litter, surface organic, and mineral horizons compared to the managed wetland. In the managed wetland, 13C of SOC was enriched across most of the soil profile (Oa and mineral soil horizons) compared to the natural wetland, suggesting enhanced decomposition and incorporation of microbially-derived inputs to soils. Root C concentration decreased with soil depth, while root 13C signature became enriched with soil depth. In the litter and Oe horizon of the natural wetland, MBC was higher and 13C of MBC and SOC was enriched in hummocks compared to hollows. The 13C of MBC and SOC tended to be enriched in upper soil horizons and depleted in lower soil horizons, particularly in the managed wetland. We conclude that drainage of these coastal wetlands has enhanced the breakdown of previously stabilized C and has the potential to alter regional C storage, feedbacks to climate warming, and ecosystem responses to changing environmental conditions.

Beaver‐created successional gradients increase β‐diversity of invertebrates by turnover in stream‐wetland complexes

Abstract Beavers are ecosystem engineers known to modify the environment primarily via dam building. Beaver wetlands are complexes of newly created, mature, and abandoned beaver constructions within a stream network. Invertebrate dynamics across all habitats derived from these successional stages remains poorly explored. Here, we test how this natural successional gradient created by beaver affects invertebrate β‐diversity and its components (turnover and nestedness). Invertebrates were sampled in the Piedmont region of Georgia (U.S.A.) in two seasons (autumn and spring) in each of four stages of habitat succession: natural stream channels, forested wetlands created by newly formed beaver dams, mature open wetland marshes, and abandoned wetland meadows. In autumn, invertebrate communities were different among successional stages, apart from new versus abandoned wetlands and new versus mature wetlands, which were only marginally different, and streams versus abandoned wetlands. In spring, only the mature beaver wetland communities were unique, differing from both streams and from newly formed or abandoned wetlands. Beta‐diversity was nearly twice as high for the overall study‐system than any individual successional stage, which all had similar diversity. Additionally, turnover was significantly higher than nestedness in all stages. Community differences combined with high turnover among successional stages indicates that beaver wetland communities are not merely a subset of more stable mature wetlands or streams; instead, each stage has a different taxonomic make‐up. Our results strengthen the idea that beaver activity can be an important conservation tool by contributing substantially to diversity in areas where they are present. Beaver wetlands have the potential to help stabilise β‐ and regional diversity in the face of wetland loss from climate change and other human impacts.

Effects of cropland encroachment on prairie pothole wetlands: numbers, density, size, shape, and structural connectivity

Agricultural expansion is the greatest source of wetland loss in the Prairie Pothole Region (PPR) of North and South Dakota, a critical waterfowl production area in North America. It is unknown how wetland losses from grassland conversion may alter structural connectivity in the prairie pothole network, however. We examined how agricultural expansion over the period 2001–2011 altered the number, size, shape, and structural connectivity of PPR wetlands. We hypothesized that the loss of wetlands or wetland area would decrease structural connectivity on the landscape. We analyzed a published raster database that quantified 2001–2011 agricultural conversion of wetlands in the Dakotas. A suite of structural connectivity metrics was computed using the igraph R package. Wetland area decreased by 25% within the study area, density decreased by 16%, and average size decreased from 2.41 to 2.16 ha with no increase in perimeter:area ratios, thus indicating changes more from the splitting of larger wetlands (accounting for 23% of area lost) and “nibbling” at patch area (38%) than from complete wetland elimination (39%). Despite loss of wetlands and wetland area to cropland, however, the network did not display constrained structural connectivity. Structural connectivity has not been significantly affected by wetland losses because of the large number of remaining wetlands, but wetlands will continue to be lost with ongoing grassland conversion and climate shifts. It is unknown where the tipping point of wetland losses lies in the PPR that will incur ecological costs.