Riverine Floodplains Research Articles

Hunter-Gatherers in Southeast Asia: From Prehistory to the Present

Anatomically modern hunter-gatherers expanded from Africa into Southeast Asia at least 50,000 years ago, where they probably encountered and interacted with populations of Homo erectus and Homo floresiensis and the recently discovered Denisovans. Simulation studies suggest that these hunter-gatherers may well have followed a coastal route that ultimately led to the settlement of Sahul, while archaeology confirms that they also crossed significant seas and explored well into the interior. They also adapted to marked environmental changes that alternated between relatively cool and dry conditions and warmer, wetter interludes. During the former, the sea fell by up to 120 m below its present level, which opened up a vast low-lying area known as Sundaland. Three principal alignments can be identified: the first involved the occupation of rock shelters in upland regions, the second has identified settlement on broad riverine floodplains, and the last concentrated on the raised beaches formed from about five millennia ago when the sea level was elevated above its present position. This cultural sequence was dislocated about 4 kya when rice and millet farmers infiltrated the lowlands of Southeast Asia ultimately from the Yangtze River valley. It is suggested that this led to two forms of interaction. In the first, the indigenous hunter-gatherers integrated with intrusive Neolithic communities and, while losing their cultural identity, contributed their genes to the present population of Southeast Asia. In the second, hunter-gatherers withdrew to rainforest refugia and, through selective pressures inherent in such an environment, survived as the small-bodied, dark-skinned humans found to this day in the Philippines, Peninsular Malaysia and Thailand, and the Andaman Islands. Beyond the impact of expansive rice farmers in Melanesia and Australia, hunter-gatherers continued to dominate until they encountered European settlement.

Effects of flood timing and livestock grazing on exotic annual plants in riverine floodplains

Summary Riverine floodplains around the world are highly prone to invasions by exotic species. While many processes have contributed to floodplain invasions, two theories have received particular attention: (i) replacement of native perennials by exotic annuals following historical livestock grazing and (ii) ‘terrestrialization’ because of fewer floods following river regulation. We assessed how exclusion of grazers and flooding in different seasons affected established populations of exotic annuals in an 8‐year experiment. We hypothesized that effects of season of flooding would vary depending on timing in relation to annual plant life cycles and that outcomes may be affected by interactions between grazing and flooding. Flooding in any season reduced exotic annuals to <2% cover and converted a dryland flora dominated by exotic annuals to a wetland flora dominated by native perennials. However, flood effects may be short lived, as areas flooded in 1 year supported abundant exotics the next. Grazer exclusion and interactions between grazing and flooding did not affect cover of exotic annuals, although grazing depleted native perennials in recently flooded areas. Synthesis and applications. Consistent with the terrestrialization hypothesis, short‐duration floods provide a practical method for controlling exotic annual plants where river regulation has reduced the frequency of natural floods. As exotic impacts are greatest in dry periods, when exotics are most abundant, ecosystem benefits will be greatest when flooding leads to a protracted decline in exotic annuals during the dry (non‐inundated) years following flood recession. Otherwise, reductions in exotic annuals may be transient and have little positive impact on floodplain ecosystems and processes.

Isotopic signature of nitrate in river waters of the lower Mississippi and its distributary, the Atchafalaya

AbstractPeriodic summer hypoxia occurring in the Northern Gulf of Mexico has been attributed to large nutrient inputs, especially nitrate‐nitrogen, from the Mississippi–Atchafalaya River system. The 2008 Gulf Hypoxia Action Plan calls for river corridor wetland restoration to reduce nitrate loads, but it is largely unknown how effective riverine wetland systems in the lower Mississippi River are for nitrate removal. We carried out an intensive isotope study to address this question by comparing nitrate isotopic signatures of the well‐channelized Mississippi River with those of the Atchafalaya River, which has extensive floodplains and backwater swamps. We investigated changes in δ15NNO3 and δ18ONO3 for water samples collected biweekly to monthly over a 2‐year period at the Atchafalaya River outlets (Morgan City and Wax Lake) and on the Mississippi River at Baton Rouge. In addition, in situ water quality parameters including temperature, dissolved oxygen and pH were recorded for each sampling date. Waters from both rivers showed moderately high nitrate concentration (>1 mg l−1) and undetectable (< 0.01 mg l−1) nitrite throughout the study period. The Mississippi River had slightly, but significantly higher (p=0.01) mean nitrate concentrations (1.5 mg l−1) and higher δ15NNO3 (7.7‰) than the Atchafalaya (1.1 mg l−1, 7.0‰); while no difference in δ18ONO3 (4.6‰) was found between the rivers. Flux‐weighted mean isotope values were overall lower than mean values for both the Mississippi and Atchafalaya Rivers, with a greater difference between the two rivers (7.4‰ versus 6.5‰, respectively). River flooding and hurricane storm surge also appeared to affect nitrate isotopic values. The lack of large difference in isotopic values between the Atchafalaya and Mississippi Rivers suggests that the majority of nitrate is transported through the Atchafalaya River with relatively little processing, and that riverine floodplains and wetlands are not effective sinks for nitrate, as previously assumed, because of insufficient residence time and well‐oxygenated river waters. Copyright © 2012 John Wiley & Sons, Ltd.

Record 2011 Spring Flood of the Mississippi River: How Much Nitrate Was Exported from Its Largest Distributary, the Atchafalaya River, into the Gulf of Mexico?

AbstractThe Mississippi River Flood of 2011 was a record-breaking flood that required the opening of the Morganza Spillway for only the second time since its completion in 1954. The opening brought a large quantity of nitrogen-rich Mississippi River water into the Atchafalaya River, causing widespread inundation in the river corridor wetlands and flood plains. A rapid sampling study was conducted from May 14 through July 20 at the Atchafalaya River’s inflow and outflow locations to determine nitrate transport and retention of the basin during a historic flood event. The goal was to test the hypothesis that riverine wetlands and floodplains in the Lower Mississippi River Basin (LMRB) function as a significant sink for nitrate during an extreme flood event. Based on intensive sampling data, a total nitrate mass of 97,100 Mg entering and 93,500 Mg leaving the Atchafalaya for the 10-week high flood period was estimated. This large quantity of nitrate export represents approximately 54% of the reported long-te...

Large-scale controls on potential respiration and denitrification in riverine floodplains

Restoration measures of deteriorated river ecosystems generally aim at increasing the spatial heterogeneity and connectivity of these systems in order to increase biodiversity and ecosystem stability. While this is believed to benefit overall ecological integrity, consequences of such restoration projects on biogeochemical processes per se (i.e. ecosystem functioning) in fluvial systems are rarely considered. We address these issues by evaluating the characteristics of surface water connection between side arms and the main river channel in a former braided river section and the role and degree of connectivity (i.e. duration of surface water connection) on the sediment biogeochemistry. We hypothesized that potential respiration and denitrification would be controlled by the degree of hydrological connectivity, which was increased after floodplain restoration. We measured potential microbial respiration (SIR) and denitrification (DEA) and compared a degraded floodplain section of the Danube River with a reconnected and restored floodplain in the same river section. Re-establishing surface water connection altered the controls on sediment microbial respiration and denitrification ultimately impacting potential microbial activities. Meta-variables were created to characterize the effects of hydrology, morphology, and the available carbon and nutrient pools on potential microbial processing. Mantel statistics and path analysis were performed and demonstrate a hierarchy where the effects of hydrology on the available substrates and microbial processing are mediated by the morphology of the floodplain. In addition, these processes are highest in the least connected sites. Surface water connection, mediated by morphology regulates the potential denitrification rate and the ratio of N2O to N2 emissions, demonstrating the effects of restoration in floodplain systems.

Urban and wildland herpetofauna communities and riparian microhabitats along the Salt River, Arizona

Metropolitan areas are continually expanding, resulting in increasing impacts on ecosystems. Worldwide, riverine floodplains are among the most endangered landscapes and are often the focus of restoration activities. Amphibians and reptiles have valuable ecological roles in ecosystems, and promoting their abundance and diversity when rehabilitating riparian systems can contribute to reestablishing degraded ecosystem functions. We evaluated the herpetofauna community by measuring abundance, richness, diversity, and species-habitat relations along three reaches (wildland, urban rehabilitated, and urban disturbed reaches) varying in degree of urbanization and rehabilitation along the Salt River in central Arizona. We performed visual surveys for herpetofauna and quantified riparian microhabitat along eight transects per reach. The wildland reach had the greatest herpetofauna species richness and diversity, and had similar abundance compared to the urban rehabilitated reach. The urban disturbed reach had the lowest herpetofauna abundance and species richness, and had a similar diversity compared to the urban rehabilitated reach. Principal Component Analysis reduced 21 microhabitat variables to five factors which described habitat differences among reaches. Vegetation structural complexity, vegetation species richness, densities of Prosopis (mesquite), Salix (willow), Populus (cottonwood), and animal burrow density had a positive correlation with at least one herpetofauna community parameter, and had a positive correlation with abundance of at least one lizard species. Rehabilitation activities positively influenced herpetofauna abundance and species richness; whereas, urbanization negatively influenced herpetofauna diversity. Based on herpetofauna-microhabitat associations, we recommend urban natural resource managers increase vegetation structural complexity and woody debris to improve herpetofauna habitat when rehabilitating degraded riparian systems.

ESTIMATION OF JUVENILE SALMON HABITAT IN PACIFIC RIM RIVERS USING MULTISCALAR REMOTE SENSING AND GEOSPATIAL ANALYSIS

ABSTRACTWe conducted a regional classification and analysis of riverine floodplain physical features that represent key attributes of salmon rearing habitats. Riverine habitat classifications, including floodplain area and river channel complexity, were derived at moderate (30 m) spatial resolution using multispectral Landsat imagery and global terrain data (90 m) encompassing over 3 400 000 km2 and most North Pacific Rim (NPR) salmon rivers. Similar classifications were derived using finer scale (i.e. ≤ 2.4‐m resolution) remote sensing data over a smaller set of 31 regionally representative flood plains. A suite of physical habitat metrics (e.g. channel sinuosity, nodes, floodplain width) were derived from each dataset and used to assess the congruence between similar habitat features at the different spatial scales and to evaluate the utility of moderate scale geospatial data for determining abundance of selected juvenile salmon habitats relative to fine scale remote sensing measurements. The resulting habitat metrics corresponded favorably (p < 0.0001) between the moderate scale and the fine scale floodplain classifications; a subset of these metrics (channel nodes and maximum floodplain width) also were strong indicators (R2 > 0.5, p < 0.0001) of floodplain habitats defined from the finer scale analysis. These relationships were used to estimate the abundance and distribution of three critical shallow water floodplain habitats for juvenile salmon (parafluvial and orthofluvial springs, and shallow shore) across the entire NPR domain. The resulting database provides a potential tool to evaluate and prioritize salmon conservation efforts both within individual river systems and across major catchments on the basis of physical habitat distribution and abundance. Copyright © 2011 John Wiley & Sons, Ltd.

Diversity of soil mesofauna in northern taiga biogeocenosises of the Kamennaya River basin (Karelia)

The population of soil mesofauna in the basin of the small river subzone of the northern taiga (Karelia) has been investigated. It was shown that indexes of the number and mass of soil mesofauna in the landscape-ecological row ofbiogeocenosises are maximal in floodplain soils. The taxonomic composition and structure of domination of the soil mesofauna population depends on the location of biogeocenosis in the landscape: earthworms are dominants in riverine floodplain biogeocenosises, and larvae of elaterids and spiders prevail in the places outside of floodplains. The abundance of saprophytic invertebrates in floodplain biogeocenosises results in formation of humus of the mull type. A group of animals with mixed type of nutrition dominates in the places outside of floodplain soils that are related with humus of the moder-mor type. The population of rove beetles (Staphylinidae) allows the division of biogeocenosises into two groups according to their position in the landscape.

Drivers of aquatic macrophyte community structure in a Neotropical riverine lake

We explored the hypothesis that flood events and connectivity interact with local factors (biotic and abiotic) to drive changes in aquatic vegetation in a typical backwater lake connected to the River Paraná, Brazil. Over three years, we conducted quarterly surveys to analyse macrophyte composition and abundance, and environmental variables. In total 34 macrophyte species were recorded, with strong dominance of Eichhornia azurea. During periods of low water level, the lake vegetation was primarily structured by distance from the river. Total community abundance and emergent species diversity increased from the outer to the inner lake, while the opposite occurred for submersed and floating species. These changes were strongly associated with gradients of depth, slope, water transparency, oxygen and phosphorus. Two summer flood periods had different effects upon plants depending on flood features (e.g. intensity, duration) and location. Flood-pulses tended to reset the community, both in terms of species abundance and richness, and disrupt competitive processes. Flood disturbances likely governed interactions among facilitation and competition processes. While recovering from the major flood disturbance, E. azurea invested strongly in stem horizontal growth, but less so in leaf production. In this situation the physical structure of E. azurea facilitated colonization by several other macrophyte species, resulting in substantial and rapid increase in species richness. Under a more stable hydrology E. azurea displaced less competitive species by forming dense stands. Connectivity and flood-pulses were the main factors responsible for sustaining high diversity of aquatic macrophytes in the lake, but these drivers interact, in both time and space, with local environmental and biotic drivers to structure the temporally and spatially shifting mosaic of lake vegetation. Our results show the fundamental importance of natural variability of hydrological connectivity and flood disturbances for biodiversity conservation in tropical riverine floodplains.

Heterogeneity of soil carbon pools and fluxes in a channelized and a restored floodplain section (Thur River, Switzerland)

Abstract. Due to their spatial complexity and dynamic nature, floodplains provide a wide range of ecosystem functions. However, because of flow regulation, many riverine floodplains have lost their characteristic heterogeneity. Restoration of floodplain habitats and the rehabilitation of key ecosystem functions, many of them linked to organic carbon (C) dynamics in riparian soils, has therefore become a major goal of environmental policy. The fundamental understanding of the factors that drive the processes involved in C cycling in heterogeneous and dynamic systems such as floodplains is however only fragmentary. We quantified soil organic C pools (microbial C and water extractable organic C) and fluxes (soil respiration and net methane production) in functional process zones of adjacent channelized and widened sections of the Thur River, NE Switzerland, on a seasonal basis. The objective was to assess how spatial heterogeneity and temporal variability of these pools and fluxes relate to physicochemical soil properties on one hand, and to soil environmental conditions and flood disturbance on the other hand. Overall, factors related to seasonality and flooding (temperature, water content, organic matter input) affected soil C dynamics more than soil properties did. Coarse-textured soils on gravel bars in the restored section were characterized by low base-levels of organic C pools due to low TOC contents. However, frequent disturbance by flood pulses led to high heterogeneity with temporarily and locally increased C pools and soil respiration. By contrast, in stable riparian forests, the finer texture of the soils and corresponding higher TOC contents and water retention capacity led to high base-levels of C pools. Spatial heterogeneity was low, but major floods and seasonal differences in temperature had additional impacts on both pools and fluxes. Soil properties and base levels of C pools in the dam foreland of the channelized section were similar to the gravel bars of the restored section. By contrast, spatial heterogeneity, seasonal effects and flood disturbance were similar to the forests, except for indications of high CH4 production that are explained by long travel times of infiltrating water favoring reducing conditions. Overall, the restored section exhibited both a larger range and a higher heterogeneity of organic C pools and fluxes as well as a higher plant biodiversity than the channelized section. This suggests that restoration has indeed led to an increase in functional diversity.

A study of seed dispersal by flood flow in an artificially restored floodplain

Riverine floodplains play many important roles in river ecosystems. However, many floodplains have suffered degradation or loss of ecological function due to excessive river improvements or through changes in agricultural systems. As a result, many floodplain restoration projects are being conducted worldwide. One of the many methods being implemented to restore floodplain vegetation is flood water seed dispersal. In this technique, precisely estimating the effect of seed dispersal by flood water is important in order to achieve successful floodplain revegetation. Here, we focus our attention on sediment transport by flood water into the Azamenose Swamp, a restored floodplain. We attempt to estimate the function of seed deposition in the restored floodplain and explain how the seeds are deposited in the floodplain by flood water. The result suggests that the restored floodplain functions as a more appropriate deposition site for seeds than the riverbanks of the main river. It was also found that the distance from the inflow site and the weight of the sediment were related to seed deposition.

Taphonomy of the Lamy amphibian quarry: A Late Triassic bonebed in New Mexico, U.S.A.

Located in Santa Fe County, New Mexico, USA, the Lamy amphibian quarry is a Late Triassic (Adamanian) bonebed stratigraphically low in the Garita Creek Formation of the Chinle Group. Well known for its mass accumulation of metoposaurid amphibians, it was initially interpreted as a drought-induced death assemblage. Based on microstratigraphic and sedimentological studies, additional and extensive collecting at the quarry and a revised understanding of the bonebed, we provide a detailed taphonomic analysis of the Lamy amphibian quarry that identifies it as a low diversity multitaxic and monodominant bonebed in pedogenically modified floodplain mudstone. The Lamy bonebed shows no evidence of drought and is characterized by a high density of completely dissociated bones that show clear alignment by current and sorting (enrichment of Voorhies Group II and III elements). The bones show no significant abrasion or weathering (stage 0), preserve virtually no evidence of scavenging and show no evidence of trampling. Based on skull lengths, the metoposaurid assemblage has a type I survivorship curve and lacks juveniles. We thus posit that the following sequence of events formed the Lamy amphibian bonebed: (1) aggregation (cause unknown) of a large number of metoposaurid amphibians at a site different from the location of the bonebed, though not distant; (2) catastrophic mass mortality; (3) complete disarticulation and disassociation of the skeletons; and (4) rapid transport of the disarticulated bones onto a floodplain surface that was undergoing pedogenesis. The Lamy amphibian bonebed is representative of the Late Triassic metoposaurid bonebeds from Morocco and the western USA, which are monodominant and nearly monotaxic. They indicate that aggregation (probably of breeding populations) and mass death of metoposaurids were relatively common across the riverine floodplains of Late Triassic Pangea.

Multiple stressors in coupled river–floodplain ecosystems

Summary1. Riverine floodplains are highly complex, dynamic and diverse ecosystems. At the same time they are among the world’s most threatened ecosystems because of the pervasiveness of dams, levees and other factors such as rapid spreading of non‐native species. Hence, floodplains are ideal systems to study ecological impacts of multiple stressors at the local, regional and catchment scale.2. Concepts such as the subsidy‐stress hypothesis and the stress‐induced community tolerance concept have been formulated to study the effect of stressors on aquatic and terrestrial ecosystems, as well as on their functional linkages.3. Riverine floodplains are pulsed ecosystems with distinct flow, sediment, resource and thermal pulses – thereby creating distinct ‘windows of ecological opportunity’. Human modifications that truncate or amplify theses pulses will have cascading effects on river–floodplain interactions by shifting the thresholds of connectivity, resilience or resistance – causing drastic regime shifts.4. Most aquatic insects and pond‐breeding amphibians have complex life cycles with aquatic and terrestrial stages. They are exposed to different stressors in their aquatic and terrestrial realm. Because most life history functions of aquatic insects are restricted to a short terrestrial period, we need to fully integrate the ‘airscape’ into the future management of river–floodplain ecosystems.5. Riverine floodplains integrate and accumulate multiple stressors at the catchment level, as reflected by distinct catchment fingerprints. Based on the European Catchment Data Base we provide spatially explicit information on multiple stressors; a key prerequisite for setting priorities in conservation and management planning.6. Thematic implications: the management of stressed river and floodplain ecosystems is a major challenge for the near future and water managers worldwide. Management approaches need to be adaptive and embedded within a catchment‐wide concept to cope with upcoming pressures originating from global change.

Rates of biogeochemical phosphorus and copper redistribution in young floodplain soils

Abstract. Nutrients and trace metals in river-floodplain systems may originate from anthropogenic activities and/or geogenic sources. Here, we analyze a soil chronosequence (2 to approximately 600 years) on a floodplain at the Danube River (Austria) to quantify the rates of P and Cu redistribution among biogeochemical pools during early soil formation under temperate continental climate. While bulk and clay mineralogy remained unchanged over the studied age gradient, we found considerable (mostly non-linear) redistribution of P and Cu among biogeochemical pools. The calcium-associated P and Cu fractions decreased rapidly during the initial decades of soil formation. The dissolution of calcium-associated P was mirrored by marked accumulation of organic P. Copper incorporated within resistant minerals showed a relative enrichment with soil age. The mean dissolution rates of calcium-associated (primary mineral) P decreased exponentially with increasing soil age from ~1.6 g m−2 yr−1 over ~15 years to ~0.04 g m−2 yr−1 over ~550 years, and were almost an order of magnitude higher than rates reported for tropical environments. Our study demonstrates that on riverine floodplains, rapid biogeochemical transformations can occur within the first centuries of soil formation under temperate climatic conditions.

Rapid carbon accretion and organic matter pool stabilization in riverine floodplain soils

The importance of wetlands in the global C budget has been recognized in recent years, and the high biomass productivity of riverine floodplains is widely acknowledged. However, soil C dynamics in these ecosystems are still poorly understood and rarely quantified. In this study, we quantify organic C accretion and examine changes of organic matter pools across an age gradient of riverine floodplain soils under different land uses in a warm temperate climate. We find rapid C accumulation during the initial 100 years of soil formation, with rates exceeding 100 g m−2 a−1. We show that floodplain land use strongly affects soil C sequestration and organic matter pool allocation and find that the distribution of different soil organic matter pools reaches a steady state within a few decades of soil development. Our results demonstrate that continually rejuvenated soils on riverine floodplains are strong C sinks but also show that intensive cultivation severely compromises their high C sequestration potential.

Fifty‐five years of soil development in restored freshwater depressional wetlands

Wetland restoration is increasingly used as a strategy both to address historical wetland losses and to mitigate new wetland impacts. Research has examined the success of restored wetlands for avifaunal habitat, plant biodiversity, and plant cover; however, less is known about soil development in these systems. Soil processes are particularly important as soil organic matter (SOM), cation exchange capacity (CEC), and other properties are directly linked to wetland functions such as water quality improvement. This research compared soil development processes and properties of 30 palustrine depressional wetlands of four different age classes (approximately 5, 14, 35, and 55 years since restoration) located in central New York (USA). Five natural wetlands were used as references. This chronosequence included wetlands 27 years older than previously conducted studies, making it the longest reported database available. Replicated soil cores from each site were analyzed for SOM, bulk density (D(b)), CEC, and concentrations of nutrients and other chemical constituents. Decomposition rate and aboveground plant and litter biomass were measured as key contributors to soil development. The results indicate that some soil properties critical for water quality functions take decades or centuries to reach natural reference levels. Of particular importance, in the top five centimeters of soil, SOM, D(b), and CEC achieved <50% of reference levels 55 years after restoration. Soil development processes in these depressional wetlands appear to be driven by autochthonous inputs and by internal processes such as litter decomposition and are not accelerated in the initial phase of development by allochthonous inputs as has been documented in coastal salt marshes and riverine floodplains. While monitoring generally focuses on the initial establishment phase of restored ecosystems, our findings indicate that the later autogenic phase strongly influences development trajectories for important wetland soil properties. Therefore, the role of different successional phases in determining long-term trajectories of ecosystem development should be considered in restoration design, research, and monitoring. This research highlights areas for improving the field of restoration through understanding of successional processes, increased efforts to jump-start soil development, longer-term monitoring programs, and greater focus on soil components of restored wetlands.

Heterogeneity in mycorrhizal inoculum potential of flood-deposited sediments

Riparian areas are diverse systems where flooding creates new sites for establishment of vegetation. Symbioses with soil microorganisms, such as mycorrhizal fungi, affect vascular plant growth and community composition. It is unknown, however, how mycorrhizal fungi are dispersed along rivers and what potential they have to inoculate roots of plants establishing on recently deposited sedimentary surfaces of flood plains. We measured AMF inocula in sediment deposited by an average spring flood along an expansive riverine flood plain in Montana, USA, to determine whether AMF inocula were present in sediments and what types of propagules (spores, hyphae, or colonized root fragments) contribute to AMF infectivity. Flood-deposited sediments contained sufficient inocula for AMF to colonize host plants (Sorghum sudanense) grown in a greenhouse, and both AMF hyphal lengths and spore densities were correlated with infectivity. Availability of mycorrhizal inocula, which is patchily distributed in this system, may lead to microsites that differ in ability to support establishment and growth of early-successional plants.

Is there a commercially viable market for crop insurance in rural Bangladesh?

The study aims to assess the commercial viability of a potential crop insurance market in Bangladesh. In a large scale household survey, agricultural farm households were asked for their preferences for a hypothetical crop insurance scheme using double bounded (DB) contingent valuation (CV) method. Both revenue and production cost based indemnity payment approaches were applied to assess the commercial viability of a crop insurance program assuming a partner-agent (PA) model of insurance supply. Crop insurance is found marginally commercially viable in riverine flood plain areas. The expected indemnity payable consistently exceeds the expected insurance premium receivable by the insurer for the households living in wetland basin and coastal floodplain. We conclude that a uniform structure of crop insurance market does not exist in Bangladesh. The nature of the disaster risks faced by the farm households and the socio-economic characteristics of the rural farm communities need to be taken into careful consideration while designing such an insurance scheme.

Hydrological complexity supports high phytoplankton richness in the Doñana marshland (SW Spain)

Two hundred and twenty-four phytoplanktonic taxa were recorded in a riverine floodplain on the NE side of the Doñana marshland from September 2002 to 2004. This collection of 11 samples included 80 Bacillariophyceae (Diatoms), 71 Chlorophyta, 39 Cyanophyta, 19 Euglenophyta, 6 Chrysophyceae, 5 Cryptophyta, and 4 Dinophyceae. Fifty-five percent of the total taxa had a very low frequency of appearance (<5%), while only three species appeared with a frequency >90% (Monoraphidium contortum Komárková-Legnevorá, Cyclotella atomus Hustedt, and Nitzschia palea W. Smith). According to multivariate analyses, both temporal and spatial factors produced a pattern in the phytoplankton assemblages dominated by freshwater inputs during winter flooding, tidal inputs in summer, and transitional stages during the rest of the year. Spatial segregation of phytoplankton was likely due to differences in retention time and distance to water input. The main taxa involved in this segregation were Chrysidalis sp. 1 (June 2003 and 2004), Chlamydomonas sp. 4 (September 2003), C. atomus (December 2003), and Tetradesmus aff. crocini (February 2004). The hydrologic complexity of the study area could account for this high taxa richness by promoting replacement and colonization episodes following seasonal changes in water source (freshwater versus tidal inputs).

Livelihoods Pattern of “Negede Weyto” Community in Lake Tana Shore, Bahir Dar Ethiopia.

Livelihoods is function of location, certain locations possessed resources (physical and human) and provides better opportunities to inhabitants than others. People living in marginal lands such as deserts, delta and riverine areas, flood plains and mountainous area with high slope gradient have problems in sustaining their livelihoods. This Paper examined the livelihoods pattern of “Negede Weyto” community, a small tribe living in the marginal land along the Lake Tana shore line, Bahir Dar Ethiopia. Using 123 respondents and 4 FGD groups for the survey and analyzed with simple statistical methods and regression; the study revealed that their livelihoods is seriously exposed to vulnerability factors which are external and beyond what they can address by their limited capacities. It thus calls for intervention by Government and NGOs to rescue the vulnerable community. Keywords : Negede Weyto, Lake Tana, Livelihoods, Vulnerability. Ethiopian Journal of Environmental Studies and Management Vol. 1 (1) 2008: pp. 19-30