Seasonal Wetlands Research Articles

Agronomic and socio-economic assessment of the introduction of a rice-based mixed cropping system to Cuvelai seasonal wetland system in northern Namibia

ABSTRACT In the semi-arid regions of southern Africa, around the borders of Angola with Namibia, the Cuvelai seasonal wetland system is formed by floods during the rainy season. The objective of the present study was to assess the effects of introduction of a rice-based mixed cropping system to the seasonal wetlands (ondombe in the local language) from agronomic, social, and economic perspectives. For this purpose, we used a simple methodology with a multidisciplinary approach for yield and household survey and scenario analysis in northern Namibia. The yield survey revealed that in ondombe, rice showed a higher yield performance than that of pearl millet and sorghum, even in a drought year. The farm household survey showed that introducing a rice-based mixed cropping to ondombe could help local farmers enhance crop productivity by reducing labour and providing high rice yield. In addition, scenario analysis based on the yield and household surveys conducted in these regions suggested that the introduction of the mixed cropping system to ondombe could compensate for one-fourth of the governmental urgent food import budget even in drought years. Therefore, this system is an effective option for sustainable agricultural production and environmental management in the studied region.

Growth and Productivity Assessment of Short-Duration Rice (Oryza sativa L. and Upland NERICA) Genotypes in Semiarid North-Central Namibia

In semiarid regions, drought is the major threat to crop production, but climate change and variability often bring floods to the regions, forming seasonal wetlands causing damage to local, drought-adapted staple grains and, hence, low yields and food deficit. Introduction of the semiaquatic crop rice (Oryza spp.) to these semiarid wetlands could complement the dryland crop low yields and overcome the food shortage problem. A field experiment was carried out at the University of Namibia-Ogongo Campus during the 2016/2017 and 2017/2018 cropping seasons to assess the growth and yield of rice genotypes. Twelve short-duration rice genotypes, nine from the International Rice Research Institute (IRRI) and three locally grown upland NERICA genotypes, were used. Parametric analysis of variance was performed to test their effects on crop growth and yield characters. The results showed significant genotype by year interaction for days to heading, plant height, the number of tillers per m2, shoot biomass, the number of panicles per m2, 1000-grain weight, harvest index, and grain yield. The IRRI genotypes produced a higher number of tillers, shoot biomass, and grain yield than the NERICA ones, which were early maturing, were taller, and had higher 1000-grain weight across the years. Generally, most of the genotypes had lower grain yield and higher shoot biomass in the first year, due to the prevailing cool, rainy, and seemingly cloudy weather conditions associated with lower temperature and lower solar radiation. Grain yield was positively correlated with most characters but negatively correlated with the 1000-grain weight. These results demonstrate the yield superiority of IRRI genotypes over their early-maturing NERICA counterparts. However, further studies on morphological characters and drought tolerance of the IRRI genotypes are warranted to ascertain production sustainability under semiarid environments.

Mapping Vernal Pools Using LiDAR Data and Multitemporal Satellite Imagery

Seasonal depressional wetlands, or vernal pools, offer critical breeding habitats for diverse species (primarily amphibians and invertebrates) in northeastern America. Their seasonal aspect contributes to their uniqueness. Degradation and loss of these habitats are attributed to human activities such as urban development and some forestry activities. Thus, it is important to map vernal pools to plan conservation measures. We studied topographic depressions derived from airborne LiDAR Digital Elevation Models (3 m) combined with optical multitemporal satellite imagery provided by Pleiades (50 cm) to detect depressional wetlands with the objective of discriminating vernal pools from other small wetlands. We first set a hierarchical identification approach with five criteria to plan the field campaigns, but after using statistical analysis, we were able to reduce these to only one criterion, the temporal difference (May to September) of the Normalized Difference Water Index (NDWI). Our results suggest that vernal pool occurrence is highly correlated with the temporal difference of NDWI. The higher the difference, the higher the observed occurrence. Considering 81 field-validated vernal pools, the user’s accuracy reached 83% and the producer’s accuracy, 59%. Our study presents a simple approach to map vernal pools on large territories while considering their temporary status.

Influence of surface water variations on VOD and biomass estimates from passive microwave sensors

Vegetation optical depth (VOD) is a remotely sensed indicator characterizing the attenuation of the Earth's thermal emission at microwave wavelengths by the vegetation layer. At L-band, VOD is used to estimate the global biomass, a key component of the Earth's surface and of the carbon cycle. This study focuses on the behaviour of L-band VOD (L-VOD) retrieval algorithm over seasonally inundated areas, as some previous observations have shown an unexpected decline in VOD during flooding events. To analyse such variations, a passive microwave model was used to simulate the signal emitted by a mixed scene composed of soil and standing water. The retrieval over this inundated scene led to an overestimation of soil moisture (SM) and an underestimation of L-VOD. The phenomenon is more pronounced over grasslands than over forests, since low vegetation is mostly submerged under water and becomes invisible to the sensor; and since more standing water is visible to the sensor. The estimated L-VOD is typically reduced by ~10% over flooded forests and up to 100% over flooded grasslands. Such effects can distort the analysis of aboveground biomass (AGB) and aboveground carbon (AGC) dynamics based on L-VOD estimates. We evaluated that AGB can be underestimated by 15/20 Mg ha−1 in the largest seasonal wetlands, which can represent more than 50% of the actual AGB of these fields, and up to higher values during exceptional meteorological years. Consequently, to better estimate the global biomass, surface water seasonality has to be taken into account in passive microwave retrieval algorithms.

Assessing the Long-Term Ecological Sustainability of Dambo Cultivation in Southern Africa: Ten-Year Case Studies from Zambia and Malawi

Internationally, evidence-based assessments of the sustainability of cultivation in seasonal wetlands are lacking despite such areas, including dambos in southern Africa, providing key areas for cultivation. The Striking a Balance project, which supported multiple use, including cultivation, of dambos, was undertaken in Zambia and Malawi between 2006 and 2008. Using the baseline WET-SustainableUse assessments made in 2008 in four of these dambos, the procedures were repeated in 2019 to explore the ecological sustainability of current use based on the concept of Thresholds of Potential Concern (TPC). This concept was applied to the five components of ecological health, namely hydrology, geomorphology, soil organic matter, nutrient retention and vegetation composition. In all four dambos, despite ten years of multiple use including cultivation, the change in ecological health between 2008 and 2019 was generally small, and overall, the ecological health of the four dambos has largely been maintained. However, there are some concerns, particularly with respect to vegetation composition, which had fallen below the TPC for two of the dambos. The methods used and the findings appear to have wider application in Africa for long-term monitoring the ecological health of seasonal wetlands and determining the ecological bounds for wetland cultivation.

Rainfall patterns and geomorphological controls driving inundation frequency in tropical wetlands: How does the Pantanal flood?

The Pantanal is one of the world’s largest freshwater wetlands. The spatial and temporal variability of flooded areas is a key factor for preserving and managing the flora and fauna of this biodiversity hotspot, and thus, its dynamic is crucial to maintain ecosystem services. However, existing inventories of flooded areas with high spatial resolution are scarce or do not represent a continuous time series considering the entire Pantanal wetland. In this study, flooded areas were derived from Landsat and Resourcesat satellite imagery time series for the years 2000 to 2020 through big data analytical tools. Our results show that permanently flooded areas accounted for 3.40% of the total Pantanal wetland and 8.85% of the study area was flooded during only one year, indicating a complex and dynamic fluvial system. In addition, approximately 39% of the basin was composed of non-flooded areas. During the analyzed period (2000–2020), the highest flood event occurred in 2011 covering an area of 57,969 km2, followed by 2014, with 52,500 km2 (respectively 38.55% and 34.91% of the total area of the Pantanal). The year with the smallest flooded area was 2020 (10,668 km2), 83% lower when compared to the period-based average. The Pantanal is a seasonal wetland, thus, rainfall plays a significant role in the flood pulse, accounting for approximately 60% of the total variability of the flooded areas. The flood dynamics is also affected by the morphology of the modern depositional system of the Pantanal, which is composed by large megafans created by several distributive rivers, and by neotectonics that generates differential movements of blocks creating lower areas that will determine how flood pulse moves spatially and temporally. Therefore, the understanding and analysis of this dynamism becomes an indispensable tool for the public government ordering defining policies for the occupation and the economic zoning of the Pantanal.

Irruptive White Ibis breeding is associated with use of freshwater crayfish in the coastal Everglades

AbstractAs avian reproductive success is generally prey limited, identifying important prey types or sizes and understanding mechanisms governing prey availability are important objectives for avian conservation ecology. Irruptive White Ibis (Eudocimus albus) nesting at coastal colonies in the southern Everglades numbered over 100,000 nests in the 1930s. A century of drainage and altered hydrologic patterns reduced aquatic prey availability and eliminated large nesting events; nesting activity in recent decades has been typically less than 5% of historical peaks. Hydrologic restoration is expected to increase ibis nesting activity, but which prey types will support high nesting effort is less clear. In 2017 and 2018, we collected food boluses from White Ibis chicks at coastal colonies in Everglades National Park. We also monitored regional nesting activity from 1999 to 2018. In 2017, the region had 1,075 nests, typical of the past several decades; but in 2018, there were 30,420 nests, representing the highest recorded nesting activity in 87 yr. Prey composition varied between years; estuarine crabs dominated nestling boluses in 2017, while crayfish and fish were dominant prey in 2018. Crayfish, especially Procambarus alleni, were heavily exploited by ibis early in the 2018 breeding season, while fish were used more at the end. Crayfish abundances in wetlands near the colonies were higher prior to 2018, and more crayfish-producing short-hydroperiod wetlands remained available for ibis foraging in 2018. Our results support previous studies indicating that crayfish are important prey for breeding ibises and suggest that unprecedented, extensive flooding of seasonal wetlands promoted crayfish production and initiated the irruptive breeding in 2018. Our observations indicate that rehydration of the southern Everglades could restore ibis nesting activity at coastal colonies, but further investigations of hydrologic variation, crayfish production, and ibis foraging and nesting activity will be helpful to understand these dynamics and the importance of short-hydroperiod wetlands.

Beyond the comfort zone: amphibian diversity and distribution in the West Sahara-Sahel using mtDNA and nuDNA barcoding and spatial modelling

Our study seeks to: (1) reduce biodiversity knowledge gaps in amphibians from desert and arid regions; (2) quantify species diversity and detect potential cryptic diversity; (3) identify environmental correlates of amphibian richness distribution, and (4) identify diversity hotspots. DNA barcoding and spatial modelling were integrated to map observed and predicted amphibian richness in Mauritania, Africa. We built two DNA barcoding libraries using one mitochondrial (COI) and one nuclear marker (RAG1). Taxon richness was calculated using species delimitation methods. A generalised linear model was employed to identify environmental correlates of amphibian richness and the distribution of diversity hotspots was predicted. We found a total of 16 anuran taxa with Afrotropic affinities, and two genera and four species were added for the amphibian list of Mauritania. Potential cryptic diversity was detected in Hoplobatrachus occipitalis. Amphibian richness was positively correlated with proximity to savannah, gravel floodplains, and with presence of seasonal wetlands, and negatively with proximity to dunes. Major diversity hotspots were predicted in southern Mauritania. Barcoding methods for both genetic markers successfully identified the taxonomic identity of specimens, also uncovering cryptic diversity in the amphibians of the Sahara-Sahel ecoregions. Amphibian richness in Mauritania increases southwards and it is mostly concentrated in areas under pressure due to habitat conversion, lacking legal protection. The combination of DNA barcoding with spatial modelling can be easily applied to any desert system to address pressing needs for research on biodiversity distribution.

Palaeohydrological changes recorded from a small Moroccan Middle Atlas pond during the last 6000 cal. yr BP: a multi-proxy study

The perennial and seasonal wetland diversity of the Moroccan Middle Atlas region provides a valuable “test-bed” for understanding the response of different hydrosystems to climatic variations. A multiproxy study, based on sedimentological descriptions, together with mineralogy, carbonate content, XRF core scanning and biological proxies supported by AMS 14C dates, were applied to the 3-m-long core extracted from “Flowers Marsh”, a small Middle Atlas pond. This approach provides evidence for a continuous paleohydrological and paleoenvironmental record during the Mid- to Late Holocene. The investigated aquatic system evolved from a dry or very shallow waterbody towards a system with a progressively rising water level. The dominance of the detrital fraction with poor preservation of bioindicators and eroded pollen, indicate the existence of an ephemeral waterbody from 6000 cal. yr BP until a transitional phase characterized by new sedimentological facies and the appearance of ostracods around 2300 cal. yr BP. This transition, ending at 2000 cal. yr BP, is interpreted as a flooding phase leading to an ephemeral lake. It is certainly fed by the excess water from the nearby Aguelmam Azigza Lake during its high level period. Afterwards, enhanced organic matter deposition and the appearance of well-preserved diatoms until 1400 cal. yr BP corroborate a high water-level trend. Endogenic carbonate to detrital fraction ratios indicate fluctuating, but generally shallow, water levels from 1400 cal. yr BP until 650 cal. yr BP when a relatively rapid rise in water level occurred. Flowers Marsh data are, generally, consistent with most of the existing regional records. The highstand period recorded between 2000 and 1400 cal. yr is a common feature extending to more distant sites from the northern Mediterranean. It corresponds to the wetter Iberian-Roman period. Fluctuating shallow water levels recorded since 1400 cal. yr BP to now could be linked to drier/wetter phases associated with the Medieval Climate Anomaly and the Little Ice Age (650– 150 cal. yr BP) respectively, in the western Mediterranean realm. The present study demonstrates the ability of Flowers Marsh to record valuable palaeohydrological changes since the Mid-Holocene and confirms the high sensitivity of Middle Atlas hydrosystems to climatic changes.

Contrasting climate controls on the hydrology of the mountainous Cauca River and its associated sedimentary basin: Implications for interpreting the sedimentary record

In coupled “source-to-sink” systems, spatial differences in hydrology and geomorphology influence how processes in the source are recorded in the sink. The catchment of the tropical Cauca River (source) in the northern (Colombian) Andes, and its associated Mojana lowland sedimentary basin (sink), are a model system in which to explore the relationship between climate processes that control runoff and erosion in the upper catchment, and sediment deposition in the lower basin that occurs through avulsion events and seasonal wetland flooding. This study employed historical climate and hydrologic data from the Cauca River watershed and its associated sedimentary basin, along with topographic data and satellite imagery. We discovered that the Cauca River catchment and its associated Mojana Basin are governed by different patterns of intra- and inter-annual climate variability. Biannual passage of the Intertropical Convergence Zone (ITCZ) over the watershed, annual incursion of the Choco Jet, and sub-decadal variability of the El Niño Southern Oscillation (ENSO) all modulate runoff and sediment fluxes that ultimately become fluvial deposits (e.g., crevasse splays, channel and floodplain sediments). Fluctuations in wetland water levels and area, preserved as lacustrine and marsh deposits, are influenced primarily by annual variations in rainfall that are controlled by the yearly northernmost extent of the ITCZ. Long-term erosion in the Cauca River catchment is controlled largely by active tectonism in the northern Central Cordillera. Avulsion events on the Cauca River in 2010 and 2011 occurred as a consequence of levee failure during a period of high runoff associated with the negative phase of the El Niño Southern Oscillation (ENSO) along with higher cross-floodplain than down-valley slopes in the basin.

Stability consistency and trend mapping of seasonally inundated wetlands in Moribund deltaic part of India

The Ganga-Padma moribund deltaic zone contains plenty of small seasonal wetlands. In this paper we mapped the temporal hydrological dynamics of floodplain wetlands in the Ganga-Padma moribund deltaic zone. To evaluate the trend in wetland changes over time we used a time-series of Landsat images from 1987 to 2016 and adopted Water Presence Frequency (WPF), Standard Deviation, and Trend Analysis for stability and trend of water presence and change over time. Normalized Difference Water Index is used for wetland mapping for both pre- and post-monsoon seasons using the 30 years Landsat images. The result shows sequential changes in trend of wetland area and nature of deviation in water availability in wetland over time. More than 85% wetland area is prone to shallowing of depth and out of which 25% area is highly infected to this problem as found from wetland trend analysis. Standard deviation approach and trend analysis approach are used for detecting pixel-wise dynamics of wetland and trend of wetland change over the selected period of time based on the same images. The entire time spectrum is subdivided into three phases for detecting phasal change of water presence frequency (WPF) or stability of wetland. Among the total wetland area, 21.22% appeared as highly stable (high WPF) and 43.71% emerged as instable (low WPF). Only 14.56% wetland area recorded low departure in water availability, and these are usually found in the stable wetland part.

DNA barcoding of Smiliogastrinae (Teleostei: Cypriniformes) of Bangladesh based on cytochrome c oxidase subunit I (COI) sequences

This study aims to molecularly characterize the phylogenetic relationship of small barbs under the Subfamily Smiliogastrinae (Cypriniformes: Cyprinidae) in Bangladesh using a fragment of the mitochondrial gene cytochrome c oxidase subunit I (COI). Samples were collected from rivers, haors (a seasonal wetland), baors (an oxbow lake), beels (perennial waterbody), and floodplains. A total of eleven species under five genera were confirmed based on both morphological and molecular approaches. The average Kimura two-parameter (K2P) distances for intraspecies and interspecies were 0.0058 and 0.1538, respectively. The mean GC content was markedly low (44.03%) in the COI sequences of the smiliogastrin species compared to the mean AT content (55.97%). In addition to the barcode-based species identification, phylogenetic relationships among the species were also explored. Phylogenetic (neighbor-joining, parsimony, and maximum likelihood) as well as species delimitation (ASAP and mPTP) analyses of all the eleven species revealed distinct clusters in concurrence with the taxonomic status of the species.

Plant trait-environment trends and their conservation implications for riparian wetlands in the Yellow River

Determining the relationship between plant functional traits and the environment are key for the protection and sustainable utilization of riparian wetlands. In the middle and lower reaches of the Yellow River, riparian wetlands are divided into seasonal floodplain wetlands (natural) and pond-like wetlands or paddy fields (artificial). Here, species composition differences were catalogued based on plant functional traits including origin, life history, and wetland affinity in natural and artificial wetlands. Wetland physicochemical characteristics and regional socio-economic parameters collected as indicators of environmental variables were used to analyze the plant functional trait-environment relationship. The results reveal that plant functional traits in the seasonal floodplain wetland are impacted by physicochemical characteristics of habitat. The abundance of annual plants tends to decrease with concentration of heavy metals, while species diversity is mainly determined by soil physical and chemical properties, especially soil pH and temperature. Specifically, wetland-obligate species (not in water) are more resistant to heavy metal content in water than species with other types of wetland affinity. Life history strategies of species in artificial sites tend to be significantly associated with animal husbandry and artificial populations, while the wetland affinity of species is mainly determined by regional agriculture, especially the installation of agricultural covered areas. Furthermore, water quality and nutrients in suspended sediments from the Yellow River affected species diversity and life history strategies by affecting water and soil conditions of surrounding wetlands, especially conductivity and phosphorus levels.

Understanding Volumetric Water Storage in Monsoonal Wetlands of Northeastern Bangladesh

AbstractThe volume of water stored in seasonal wetlands is a fundamental but difficult to measure variable for developing a physical understanding of wetland behavior. For seasonal wetlands that are a major source of water for rice and fish production, this physical understanding is key to planning for water‐food security and ecosystem services. This study quantified variations in volumetric storage for the numerous seasonal wetlands of northeastern Bangladesh, locally known as “haors.” These haors receive transboundary runoff from densely vegetated and mountainous terrain in India and face persistent monsoonal cloud cover as they become full. We estimated volumetric storage for 13 haors by using extensive remote sensing data on water surface extent and elevation that was complemented with citizen‐contributed gauge data. Assuming a trapezoidal bathymetry, an area‐volume relationship was developed for selected haors. This relationship was assumed to be valid for extrapolating volumetric estimations over all the haors in the region. Results suggested that as haors get filled with the onset of monsoon rains, total estimated storage relative to the lowest observable level varied from 6.5 (±0.4) km3 in May to 30.9 (±2.0) km3 in July (peak of monsoon). Choosing a rectangular bathymetry can lead to 47% higher estimates compared to trapezoidal cross section. Estimating this intra‐annual/interannual increase in storage is important for the region to plan water management policies that balance the human and ecosystem needs. Our analytical approach has potential for application to wetlands worldwide in light of the upcoming Surface Water and Ocean Topography (SWOT) mission.

Grazing and microhabitat interact to affect plant–plant interactions in subtropical seasonal wetlands

AbstractAimsThe stress gradient hypothesis predicts that competition will be important in productive environments while facilitation will be common in environments with high stress or consumer pressure. However, abiotic stress and grazing may vary independently and even occur simultaneously. Here we examine the outcome of plant interactions in grazed wetlands where consumer pressure and abiotic stress occur concurrently. We hypothesized that cattle grazing and microhabitat would alter the outcome of plant interactions. Given that wetland edges are drier and less productive than wetland centers we expected that facilitation would be greatest in drier wetland edges due to greater abiotic stress regardless of cattle presence.LocationArchbold Biological Station's Buck Island Ranch (BIR), south‐central Florida, USA (27°09′ N, 81°11′ W).MethodsWe conducted an experiment for two growing seasons in ten wetlands, five exposed to cattle grazing and five fenced. Two wetland obligate plants were included (Panicum hemitomon and Alternanthera philoxeroides), and plots were assigned to three treatments (a) all neighbors removed; (b) all neighbors removed except Juncus effusus, a dominant, unpalatable plant; and (c) all neighbors intact (control), in both wetland centers and edges. Differences in survival, change in height and number of leaves were assessed.ResultsIn ungrazed wetlands, plant survival was higher in wetland edges vs centers, while it did not differ between microhabitats in grazed wetlands. Survival in wetland edges was further increased by the presence of Juncus effusus. Positive interactions under grazed conditions were clear when plant height was assessed, but negative interactions affected leaf production in both ungrazed and grazed wetlands.ConclusionsGrazing interacts with wetland microhabitat to alter plant survival. Facilitative interactions on plant height were apparent in grazed wetlands. Understanding how plant interactions change under different biotic and abiotic contexts is important for informing ecosystem restoration and management.

The "minute diving beetles" of southern Australia - taxonomic revision of Gibbidessus Watts, 1978, with description of six new species (Coleoptera, Dytiscidae, Bidessini).

Morphology and mitochondrial DNA sequence data are used to reassess the taxonomy of Australian diving beetles previously assigned to the genera Uvarus Guignot, 1939 and Gibbidessus Watts, 1978. Gibbidessus was described as a monotypic genus for Gibbidessus chipi Watts, 1978. The genus is significantly extended here. Based on molecular systematic evidence, Uvarus pictipes (Lea, 1899) is transferred to Gibbidessus. Gibbidessus chipi and Gibbidessus pictipescomb. nov. are redescribed, and six new species are described: Gibbiddessus atomussp. nov. (SW Australia, Northcliffe area) [the smallest epigean diving beetle in Australia], G. davidisp. nov. (SW Australia), G. drikdrikensissp. nov. (Victoria), G. kangarooensissp. nov. (SA Kangaroo Island), G. pederzaniisp. nov. (SW Australia, Nannup area), and G. rottnestensissp. nov. (SW Australia). Species are delineated using characters such as male genital structure and beetle size, shape and colour pattern. Mitochondrial Cox1 data for 27 individuals, representing five species, were generated, and revealed clusters congruent with the morphological evidence. Gibbidessus occur in southern Australia, with the centre of diversification in the isolated peat- and wetlands of SW Australia. All species occur in very shallow water of seasonal, exposed or half-shaded wetlands and flooded meadows.

Assisted colonisation trials for the western swamp turtle show that juveniles can grow in cooler and wetter climates

Species with restricted ranges and long generation times are vulnerable to climate change due to limited opportunity to disperse or adapt. Australia’s rarest reptile, the western swamp turtle Pseudemydura umbrina, persists naturally in only one seasonal swamp that holds water in the Austral winter and spring. A marked reduction in winter rainfall in recent decades has shortened the swamp hydroperiod, restricting when turtles are able to feed, grow and reproduce. To mitigate possible future loss of reproductive capacity in the native habitat, assisted colonisation was trialled in 2016 using 35 captive-bred juveniles. Here, we report the outcomes of this 6 mo trial, which compared the growth of turtles released approximately 300 km south of the species’ indigenous range with growth of turtles released at an existing northern translocation site. We showed that growth rates comparable to those at warmer northern translocation sites can be achieved in the south, even in an atypically cool spring as occurred in 2016. Microclimates available to P. umbrina at 2 southern sites were suitable for foraging and growth in late spring and early summer, but juvenile growth at one southern site was significantly better than at the other, likely due to higher prey biomass when water temperatures were suitable for foraging. These early results suggest that introduction of P. umbrina to seasonal wetlands near the south coast of Western Australia could be considered in the immediate future, but further trials are recommended to assess growth and survivorship over longer periods.

Demographic consequences of habitat loss and crowding in large carnivores: A natural experiment

AbstractHabitat loss is one of largest threats to the persistence of large carnivore populations. However, because most large carnivores are long‐lived, cryptic and wide‐ranging, few studies examine the demographic consequences of habitat loss, and the resultant crowding that ensues, on these species. We used long‐term data to examine the demographic responses of an African lion (Panthera leo) population to flooding‐induced habitat loss in a seasonal wetland, the Okavango Delta, during a transition from low to high annual flooding patterns. We found that intraspecific competition reduced cub survival and that this effect was exacerbated by habitat loss and consequent crowding. The proportion of cubs recorded in the population also declined as crowding increased, and both the survival of cubs and proportion of cubs recorded declined as prey abundance decreased. Apparent sub‐adult survival declined with increasing pride size, but this likely reflects emigration rather than mortality. Adult survival remained relatively constant throughout the study period, a population response which is important in buffering populations against short‐term fluctuations in ecological conditions. As many large carnivore populations face future habitat loss, it is important that we understand the demographic consequences of habitat loss in order to better mitigate its effects in the future.

Vegetation Affects Timing and Location of Wetland Methane Emissions

AbstractCommon assumptions about how vegetation affects wetland methane (CH4) flux include acting as conduits for CH4release, providing carbon substrates for growth and activity of methanogenic organisms, and supplying oxygen to support CH4oxidation. However, these effects may change through time, especially in seasonal wetlands that experience drying and rewetting, or change across space, dependent on proximity to vegetation. In a mesocosm study, we assessed the impacts ofTyphaon CH4flux using clear flux chamber measurements directly overTyphaplants (“whole‐plant”), adjacent toTyphaplants (where roots were present but no stems; “plant‐adjacent”), and plant‐free soils (“control”). During the establishment phase of the study (first 30 days), the whole‐plant treatment had ~5 times higher CH4flux rates (51.78 ± 8.16 mg‐C m−2day−1) than plant‐adjacent or control treatments, which was primarily due to plant‐mediated transport, with little contribution from diffusive‐only flux. However, porewater CH4concentrations were relatively low directly below whole‐plant and in neighboring plant‐adjacent treatments, while controls accumulated a highly concentrated reservoir of porewater CH4. When the water table was drawn down to simulate seasonal drying, reserve porewater CH4from control soil was released as a pulse, equaling the earlier higher CH4emissions from whole‐plants. Plant‐adjacent treatments, which had neither plant‐mediated CH4transport nor a concentrated reservoir of porewater CH4, had low CH4flux throughout the study. Our findings indicate that in seasonal wetlands, vegetation affects the timing and location of CH4emissions. These results have important mechanistic and methodological implications for understanding the role of vegetation on wetland CH4flux.

Net landscape carbon balance of a tropical savanna: Relative importance of fire and aquatic export in offsetting terrestrial production

The magnitude of the terrestrial carbon (C) sink may be overestimated globally due to the difficulty of accounting for all C losses across heterogeneous landscapes. More complete assessments of net landscape C balances (NLCB) are needed that integrate both emissions by fire and transfer to aquatic systems, two key loss pathways of terrestrial C. These pathways can be particularly significant in the wet-dry tropics, where fire plays a fundamental part in ecosystems and where intense rainfall and seasonal flooding can result in considerable aquatic C export (ΣFaq ). Here, we determined the NLCB of a lowland catchment (~140km2 ) in tropical Australia over 2years by evaluating net terrestrial productivity (NEP), fire-related C emissions and ΣFaq (comprising both downstream transport and gaseous evasion) for the two main landscape components, that is, savanna woodland and seasonal wetlands. We found that the catchment was a large C sink (NLCB 334MgCkm-2 year-1 ), and that savanna and wetland areas contributed 84% and 16% to this sink, respectively. Annually, fire emissions (-56MgCkm-2 year-1 ) and ΣFaq (-28MgCkm-2 year-1 ) reduced NEP by 13% and 7%, respectively. Savanna burning shifted the catchment to a net C source for several months during the dry season, while ΣFaq significantly offset NEP during the wet season, with a disproportionate contribution by single major monsoonal events-up to 39% of annual ΣFaq was exported in one event. We hypothesize that wetter and hotter conditions in the wet-dry tropics in the future will increase ΣFaq and fire emissions, potentially further reducing the current C sink in the region. More long-term studies are needed to upscale this first NLCB estimate to less productive, yet hydrologically dynamic regions of the wet-dry tropics where our result indicating a significant C sink may not hold.