Inundation Regimes Research Articles

Litter decomposition of Rhizophora stylosa in Sabang-Weh Island, Aceh, Indonesia; evidence from mass loss and nutrients

Dewiyanti I (2010) Litter decomposition of Rhizophora stylosa in Sabang-Weh Island, Aceh, Indonesia; evidence from mass loss and nutrients. Biodiversitas 11: 139-144. Mangrove is an essential coastal ecosystem that provides nutrients to estuarine and its surrounding environments through its litter decomposition. This vegetation can be considered as an important ecosystem in food web along the coast. The research was conducted in mangrove forest in Sabang-Weh Island, Aceh. Rhizophora stylosa was dominant species of mangrove in the study area that still remains after tsunami catastrophe in 2004. This study was conducted from February to April 2008, and the purposes were to obtain the decomposition rate of senescent leaves and to measure mass loss, and nutrient contents of decomposing leaves under different inundation regime. Three plots were established in each site. Decomposition of R. stylosa leaves were studied by using litter bag technique. They were made of synthetic nylon which had size 20x30 cm and mesh size was 1x1.25 mm2. Senescent leaves were used because they present major leaves on the forest floor and started to decay. Remaining leaves decreased during experiment period because decomposition process had been taking place in the study area. Time required for decomposing a half of theinitial material (t50) was 67 days and 63 days for site next to the land and site next to the sea, respectively. The decay rate can be expressed by the decay coefficient (K) and the results of K were 0.010 and 0.011 (d-1). The value of carbon (C), nitrogen (N), C: N ratio and phosphorous (P) during decomposition periods were no significant difference in sites but significant difference in time. The C: N ratio of decomposing leaves decreased in both sites. Low C: N ratio in the last of observation indicated that R. stylosa leaves weredecomposed easier at the end of observation than that in the beginning of observation.Key words: Rhizophora stylosa, leaves litter, mass loss, nutrients, Aceh.

Disturbance-mediated competition: the interacting roles of inundation regime and mechanical and herbicidal control in determining native and invasive plant abundance

Disturbance is a key component of many successful plant invasions. However, interactions among natural and anthropogenic disturbances and effects of these interacting disturbances on invasive plants and desired vegetation are rarely examined. We investigated the effect of anthropogenic disturbance (herbicidal and mechanical) along a natural inundation gradient (20-282 days) on the biomass and resource allocation of the invasive wetland plant, alligator weed (Alternanthera philoxeroides), and two co-occurring competitor plants, the introduced grass, kikuyu (Pennisetum clandestinum), and the native grass, couch (Cynodon dactylon), over a 2-year period. In the absence of additional disturbance, kikuyu biomass was negatively affected, alligator weed biomass was positively affected, and couch biomass was not affected by inundation disturbance. In addition, kikuyu was not affected by the selective removal of alligator weed, while couch increased in wetter habitats where kikuyu was absent due to inundation stress. This suggests that kikuyu is a superior competitor in drier habitats and inundation facilitates the invasion of alligator weed, while couch is an inferior competitor to both kikuyu and alligator weed and is therefore suppressed across its entire niche by these two introduced species. Mowing alone had no effect on the biomass of the species, suggesting the plants are equally tolerant of shoot removal. Selective herbicide reduced alligator weed biomass by 97.5% and the combination of selective herbicide and mowing reduced the biomass of alligator weed significantly more than herbicide alone, by 98.6% compared with un-manipulated controls. To predict community change and prevent sequential exotic plant invasions after weed removal, it is necessary to consider the interacting effects of disturbance and the niche space of invasive species in the local propagule pool.

Invertebrate assemblages associated with leaf litter in three floodplain wetlands of the Paraná River

We analyzed invertebrate abundance and richness associated with decomposing litter across three riverine wetlands with different inundation regimes located in the alluvial floodplain of the Parana River. Three replicate bags were incubated for different types of leaf litter that were dominant in each wetland for five sampling dates, yielding a total of 165 litterbags. The number of invertebrates per g of remaining leaf litter differed among wetlands and was affected by leaf litter type and incubation date within each wetland. In contrast to abundance, differences in invertebrate composition were more pronounced across wetlands than across leaf litter types within a wetland. Different species dominated in each of the three wetlands. When we compared the number of invertebrates per g remaining of a single litter type (Eichhornia crassipes) across the three wetlands, variability in density was explained by the NH4+ content of the water and dissolved oxygen concentration. Many invertebrates associated with litter may not be directly involved in shredding the material, and collectors dominated invertebrate assemblages at study sites. Although both litter quality and wetland condition affect the invertebrates colonizing leaf litter, our results suggest that spatial heterogeneity, linked to connectivity, plays an important role in determining invertebrate assemblages.

A multitemporal multiple density slice method for wetland mapping across the state of Queensland, Australia

The Australian and Queensland Governments are developing comprehensive wetland maps at a scale of 1:100 000 for the state of Queensland, Australia. Spectral classifications for water features were developed using Landsat Thematic Mapper (TM) and Enhanced Thematic Mapper (ETM+) imagery acquired over a 16‐year period. A multiple density slice/supervised classification method, the Standing Water Body (SWB) method, was developed to separate the main spectral and land cover elements of wetlands (vegetation, water and shadow cast by vegetation and topographic relief) and used rules to combine spectral classes to provide multitemporal (MT) information on wetland extent and water inundation regimes for features of at least 0.25 ha. Accuracy assessment in four trial areas compared the SWB method to the Normalized Difference Water Index (NDWI). The assessments of classified features were scale adjusted to maximum class‐area proportions to enable statistical comparison and to account for the large area of non‐wetland in the four trial areas. The average overall accuracy for wetland classification was 95.9% for the SWB method and 95.3% for the NDWI. The average unadjusted KHAT statistic for the wetland classification was 0.84 and 0.90 for the SWB and NDWI, respectively. The scale‐adjusted KHAT statistic was much lower for both methods, averaging 0.45 for the SWB and 0.39 for the NDWI, mainly due to large omission errors. A method for the implementation of the SWB method for systematic and repeatable mapping of wetland areas is presented. The study recommends enhancement of the SWB classification through the inclusion of the NDWI classification and ancillary data such as vegetation mapping and drainage networks.

Hydrological controls on the transport and deposition of plant propagules within riparian zones

AbstractThe establishment of vegetation in riparian zones is dependent upon the availability of suitable habitat and the presence of viable propagules. Studies have shown that propagules are transported by rivers (hydrochory) and deposited in the riparian zone. However, there has been no detailed integrated study of fluvial propagule transport and deposition in relation to the hydrological regime and relative to other key dispersal mechanisms, such as wind dispersal (anemochory) and direct fall from local riparian vegetation.This paper presents the findings of a 1 year study of the hydrological controls on propagule input, transport and deposition in the riparian zone along two morphologically contrasting reaches of the River Frome (UK) and the potential importance of these processes for the riparian vegetation.Analysis of samples, taken every 6 weeks, shows that aerial seed dispersal delivered relatively few propagules to the riparian zone and was highly spatially and temporally variable. The river transported and deposited large numbers of propagules of high diversity, including many species which were not present in the local vegetation, although this varied with river water levels and with season. Winter high flows were particularly important for depositing diverse propagules into the riparian zone along with local seed production during the summer. Despite contrasts in the planform and cross profile morphology of the two study reaches, they showed great similarity in patterns of propagule deposition, which were largely driven by the inundation regime, the elevation of the sampling site, and the season of sampling. Copyright © 2009 John Wiley & Sons, Ltd.

Seed flotation and germination of salt marsh plants: The effects of stratification, salinity, and/or inundation regime

We examined the effects of cold stratification and salinity on seed flotation of eight salt marsh species. Four of the eight species were tested for germination success under different stratification, salinity, and flooding conditions. Species were separated into two groups, four species received wet stratification and four dry stratification and fresh seeds of all species were tested for flotation and germination. Fresh seeds of seven out of eight species had flotation times independent of salinity, six of which had average flotation times of at least 50 d. Seeds of Spartina alterniflora and Spartina patens had the shortest flotation times, averaging 24 and 26 d, respectively. Following wet stratification, the flotation time of S. alterniflora seeds in higher salinity water (15 and 36 ppt) was reduced by over 75% and germination declined by more than 90%. Wet stratification reduced the flotation time of Distichlis spicata seeds in fresh water but increased seed germination from 2 to 16% in a fluctuating inundation regime. Fresh seeds of Iva frutescens and S. alternflora were capable of germination and therefore are non-dormant during dispersal. Fresh seeds of I. frutescens had similar germination to dry stratified seeds ranging 25–30%. Salinity reduced seed germination for all species except for S. alterniflora. A fluctuating inundation regime was important for seed germination of the low marsh species and for germination following cold stratification. The conditions that resulted in seeds sinking faster were similar to the conditions that resulted in higher germination for two of four species.

Relative influence of habitat fragmentation and inundation on brown shrimp Farfantepenaeus aztecus production in northern Gulf of Mexico salt marshes

MEPS Marine Ecology Progress Series Contact the journal Facebook Twitter RSS Mailing List Subscribe to our mailing list via Mailchimp HomeLatest VolumeAbout the JournalEditorsTheme Sections MEPS 359:185-202 (2008) - DOI: https://doi.org/10.3354/meps07380 Relative influence of habitat fragmentation and inundation on brown shrimp Farfantepenaeus aztecus production in northern Gulf of Mexico salt marshes B. M. Roth1, K. A. Rose1, L. P. Rozas2, T. J. Minello3 1Department of Oceanography and Coastal Sciences, Louisiana State University, Baton Rouge, Louisiana 70803, USA 2NOAA Fisheries, SEFC/Estuarine Habitats and Coastal Fisheries Center, Lafayette, Louisiana 70506, USA 3NOAA Fisheries, Galveston Laboratory, Galveston, Texas 77551, USA *Email: broth2@lsu.edu ABSTRACT: We used a spatially explicit individual-based model to investigate the relative influences of inundation and habitat fragmentation on brown shrimp Farfantepenaeus aztecus production in northern Gulf of Mexico (NGOM) salt marshes. The model simulates the mortality, growth, and movement of a population of brown shrimp from their arrival in Spartina salt marsh as post-larvae in spring to their emigration as sub-adults in summer and fall. We quantified production in terms of sub-adult export, growth production (a measure of total shrimp growth), and trophic transfer (total shrimp mortality). We utilized a factorial design to simulate shrimp on all combinations of 4 maps that represented an idealized progression of habitat fragmentation and 4 inundation regimes from each of 2 locations in the NGOM (Louisiana and Texas). We also quantified the configuration of the marsh landscape to determine if specific metrics could be utilized as a proxy for shrimp production within a single inundation regime. Our results indicate that inundation is more important than habitat fragmentation for determining sub-adult export, growth production, and trophic transfer, but that marsh configuration has a strong influence on shrimp production within a single inundation regime. Inundation affected all 3 measures of shrimp production, primarily due to decreased mortality incurred when shrimp have access to vegetation through marsh flooding. We conclude that simple metrics of marsh configuration are capable of adequate predictions of shrimp production in static landscapes, but future research must consider the dynamic relationship between inundation and marsh fragmentation to fully assess how these forces affect shrimp production. KEY WORDS: Farfantepenaeus aztecus · Fragmentation · Inundation · Production · Spartina · Salt marsh · Gulf of Mexico · Estuaries · Individual-based model Full text in pdf format PreviousNextCite this article as: Roth BM, Rose KA, Rozas LP, Minello TJ (2008) Relative influence of habitat fragmentation and inundation on brown shrimp Farfantepenaeus aztecus production in northern Gulf of Mexico salt marshes. Mar Ecol Prog Ser 359:185-202. https://doi.org/10.3354/meps07380 Export citation RSS - Facebook - Tweet - linkedIn Cited by Published in MEPS Vol. 359. Online publication date: May 05, 2008 Print ISSN: 0171-8630; Online ISSN: 1616-1599 Copyright © 2008 Inter-Research.

Infrastructure effects on floods in the Mekong River Delta in Vietnam

AbstractThe Mekong River Delta (MRD) is one of two primary rice‐growing areas in Vietnam. Flooding in the Mekong River is a recurrent event and is not only one of the most destructive natural disasters but also a natural resource in this area. The cultivated surface soil layer in the Mekong Delta has a thickness of only about 50 cm, and is heavily polluted by acidic water infiltrating from deeper soil layers during the dry season. The annual floods carry fertile silt to farmland and fresh water to wash away the acidic water and provide the water needed to grow vast rice fields. The flood water carries with it various fish species that facilitate aquaculture development in the area. The floods also wash away polluted water and provide the whole delta with clean water.Owing to these different factors, the flooding in this area has a positive impact on agriculture and a negative impact on regional planning. Recent infrastructural changes designed to mitigate flood damage and protect crops and residents' lives make the inundation regime more complicated. To understand the role of infrastructure in the flood regime in this area as well as the mechanism of the flood regime, it is necessary to apply an integrated method of study including numerical modelling, a geographic information system (GIS), and statistical analyses. This study includes a brief presentation of the measured data analysis of flood variation trends over the 43‐year period from 1961 to 2004 and an analysis of the hydrological effects of infrastructure changes associated with human activities in the period from 1996 to 2001 based on the integrated hydraulic model known as HydroGis. Copyright © 2008 John Wiley & Sons, Ltd.

Effects of cutting Phragmites australis along an inundation gradient, with implications for managing reed encroachment in a South African estuarine lake system

Substantive encroachment of Phragmites australis (common reed) occurred since the 1970s in the Wilderness estuarine lakes, a National Park and Ramsar site. Cutting of reeds in late summer as a means of controlling reed encroachment was investigated under three different inundation regimes, termed ‘wet zone’ (permanently inundated), ‘moist zone’ (infrequently inundated) and ‘dry zone’ (rarely inundated). The effects of a single annual cut were furthermore compared to those of two successive annual cuts. Without cutting, wet zones had thinner and shorter, but more abundant reeds than drier zones. Cutting in dry and moist zones resulted after one year in more, but shorter and thinner reeds, whereas in wet zones reeds were almost eliminated. After two years, reeds in wet zones had not recovered from the first annual cut. In moist and dry zones, a second annual cut did not result in amplified detrimental effects on reeds. Throughout the experiment, moisture zone was the factor with the largest effect, cutting had the second largest impact, and inter-annual variation was relatively unimportant. We have demonstrated that cutting alone has minimal long-term effect on above-ground reed biomass, whereas reed growth and survivorship can be strongly suppressed through cutting in late-summer in conjunction with inundation with moderately saline water (5.0–7.5 g kg−1). Cut reeds must remain completely inundated for at least a four-week period, or else emerging shoots should be re-cut below the water level. Cut material should be removed from the treatment site. Whenever possible, cutting and inundation should be undertaken to coincide with periods when salinity levels of surface waters are higher. It is foreseen that reed management in the Wilderness Lakes would have positive effects on other biota by countering progression towards single species domination of wetland plant communities and reinstating exposed sandbanks which are extensively utilised by resident and migratory waterbirds.

Effects of cutting Phragmites australis along a flooding gradient, with implications for managing reed encroachment in a South African estuarine lake system

Substantive encroachment of Phragmites australis (common reed) occurred since the 1970s in the Wilderness estuarine lakes, a National Park and Ramsar site. Cutting of reeds in late summer as a means of controlling reed encroachment was investigated under three different inundation regimes, termed ‘wet zone’ (permanently inundated), ‘moist zone’ (infrequently inundated) and ‘dry zone’ (rarely inundated). The effects of a single annual cut were furthermore compared to those of two successive annual cuts. Without cutting, wet zones had thinner and shorter, but more abundant reeds than drier zones. Cutting in dry and moist zones resulted after one year in more, but shorter and thinner reeds, whereas in wet zones reeds were almost eliminated. After two years, reeds in wet zones had not recovered from the first annual cut. In moist and dry zones, a second annual cut did not result in amplified detrimental effects on reeds. Throughout the experiment, moisture zone was the factor with the largest effect, cutting had the second largest impact, and inter-annual variation was relatively unimportant. We have demonstrated that cutting alone has minimal long-term effect on above-ground reed biomass, whereas reed growth and survivorship can be strongly suppressed through cutting in late-summer in conjunction with inundation with moderately saline water (5.0–7.5 g kg−1). Cut reeds must remain completely inundated for at least a four-week period, or else emerging shoots should be re-cut below the water level. Cut material should be removed from the treatment site. Whenever possible, cutting and inundation should be undertaken to coincide with periods when salinity levels of surface waters are higher. It is foreseen that reed management in the Wilderness Lakes would have positive effects on other biota by countering progression towards single species domination of wetland plant communities and reinstating exposed sandbanks which are extensively utilised by resident and migratory waterbirds.

Синтаксономическое разнообразие растительности устьевой области Днепра. І. Классы Scorzonero—Juncetea gerardii Golub et al. 2001, Festuco-Puccinellietea Soó 1968, Molinio-Arrhenatheretea R. Tx. 1937

The revealed syntaxonomic diversity of meadow vegetation of the Dnieper mouth area comprises 12 associations subordinated to 7 alliances, 5 orders, and 3 classes: Scorzonero—Juncetea gerardii, Festuco-Puccinellietea and Molinio-Arrhenatheretea. For each class, the phytosociological tables are presented together with the summarizing vegetation syntaxa prodromus and the ecological-phytocoenological portraits of the associations described. Meadow commu­nities of the study area have been proved to bear peculiar features of their structure and composition. The spatial distribution of communities is mainly governed by the inundation regime and the degree of soil salinity. The results of the floristic analysis have pointed out notable numbers of rare and endangered plants participating in the community composition. These facts, together with the increasing anthropogenic impact on the vegetation, prompt us to discuss the problems of meadow vegetation conservation.

Impact of a changed inundation regime caused by climate change and floodplain rehabilitation on population viability of earthworms in a lower River Rhine floodplain

River floodplains are dynamic and fertile ecosystems where soil invertebrates such as earthworms can reach high population densities. Earthworms are an important food source for a wide range of organisms including species under conservation such as badgers. Flooding, however, reduces earthworm numbers. Populations recover from cocoons that survive floods. If the period between two floods is too short such that cocoons cannot develop into reproductive adults, populations cannot sustain themselves. Both climate change and floodplain rehabilitation change the flooding frequency affecting earthworm populations. The present paper estimates the influence of climate change and floodplain rehabilitation on the viability of earthworm populations in a Dutch floodplain; the Afferdensche and Deestsche Waarden along the River Waal. This floodplain will be part of major river rehabilitation plans of the Dutch government. In those plans, the floodplain will experience the construction of a secondary channel and the removal of part of its minor embankment. To estimate the impact of these plans and climate change, we used a dataset of daily discharges for 1900-2003 for the River Rhine at the Dutch-German border. We perturbed this dataset to obtain two new datasets under climate change scenarios for 2050 and 2100. From the original and two projected datasets we derived the frequency distributions for the annual periods without inundations for the studied floodplain. We subsequently compared the duration of these inundation-free (dry) periods with the maturation age distribution for L. rubellus as derived from a Dynamic Energy Budget model. This comparison yielded in which parts of our study area and under which climate conditions the populations would still be viable, be able to adapt or become extinct. The results show that climate change has almost no adverse effect on earthworm viability. This is because climate change reduces the flooding frequency during the earthworms growing season. Floodplain rehabilitation, on the other hand, reduces the part of the floodplain area where populations can sustain themselves. Before rehabilitation, only 12% of the floodplain area cannot sustain a viable earthworm population. After rehabilitation, this increases to 59%, 28% of which is due to more frequent flooding. Enhanced exposure to soil contaminants may further suppress earthworm viability. This could frustrate further nature development and the viability of earthworm-dependent species such as the badger (Meles meles) or little owl (Athene noctua vidalli species), which is an objective of the river rehabilitation plans in the Netherlands.

Tropical alluvial forest fragmentation in the eastern lowlands of Colombia (1939–1997)

AbstractAlluvial forests are under high pressure from human activities because of their value as agricultural, wildlife, timber and recreational land. Despite this, spatial patterns of alluvial forest deforestation are not well known. We studied forest alterations in a 2800 ha alluvial ecosystem using aerial photographs. During the study period (1939–1997), forests with canopy heights greater than 15 m (high canopy mature forest; HCM forest) decreased by 70·4 per cent while forests with canopy heights less than 15 m (low canopy mature forest; LCM forest) forests decreased by 51 per cent, producing a highly fragmented landscape. Factors responsible for forest change included human activities and river dynamics. Although most of the deforestation was related to human disturbance, almost 27 per cent of forest losses were due to channel migration of the Meta River. HCM forests were the most affected land cover since they are easily accessed, viable for logging and occurred on fertile soils, which are valuable for agriculture. LCM forests were less affected since their soil fertilities and inundation regimes were unfavourable to human uses, and thus, less prone to anthropogenic disturbances. Copyright © 2006 John Wiley & Sons, Ltd.

Leaf litter decomposition in three wetland types of the Paraná River floodplain

Leaf decomposition rates of nine types of litter, ranging in lignin content from 1.04 to 25.71%, were measured at three wetlands with different inundation regimes and related to internal and external factors. In these sites (located in the alluvial floodplain along at transect perpendicular to the main channel of the Parana River), 180 litter bags were incubated under water. To test the importance of initial nitrogen, lignin, phosphorus, or L:N content of the litter in predicting decay rates, we analyzed the relationship between leaf quality and dry weight remaining (at 30 days and at the end of the incubation) within each wetland and under uniform environmental conditions. To elucidate the effects of environmental factors (especially hydroperiod) on decomposition processes, we compared the decay coefficient of one of these species (Eichhornia crassipes) across the three wetlands. Our results strongly suggest that under uniform environmental conditions, decomposition rates were best explained by a single internal factor related to litter quality. We found two different situations. 1) In the marsh with riverine forest, where decomposition was rapid and the half-life of the litter ranged from 9.6 to 63 days, the initial nitrogen content of leaves was a good predictor of decay rates both at 30 days and at the end of the incubation. 2) In the oxbow lake and palm swamp forest, where decomposition was lower and the half-life varied between 31.5 and 219 days, the L:N explains the variability on dry weight remaining at the end of the incubation. The decay coefficient of E. crassipes across sites was significantly related to NO3− concentration of water. We concluded that both environmental variables (i.e., the fluvial quotient of connectivity and the number of days in high water) and leaf litter quality (i.e., nitrogen content and L:N) are important factors regulating leaf litter decomposition in Parana River floodplain wetlands.

Microbial diversity in three floodplain soils at the Elbe River (Germany)

Microbial communities in floodplain soils are exposed to periodical flooding. A long-term submerged Eutric Gleysol (GLe), an intermediate flooded Eutric Fluvisol (FLe), and a short-time flooded Mollic Fluvisol (FLm) at the Elbe River (Germany) with similar organic carbon contents (C org) between 8.1% and 8.9% were selected to test the quality of phospholipid fatty acids (PLFA), soil microbial carbon (C mic), basal respiration (BR), metabolic quotient (qCO 2), and C mic/C org ratio to characterize and discriminate these soils with microbial parameters. The three floodplain soils can be differentiated by C mic and by total PLFA-biomass. Due to the different flooding durations and the time since the soils were last flooded C mic and PLFA-biomass increase in the order GLe<FLe<FLm. Both parameters correlate significantly ( r = 0.999 ; p < 0.05 ) . The C mic/C org ratios are low in comparison to terrestrial soils and revealed the same ranking over the three soils like C mic. Contrary, qCO 2 and BR are highest in GLe and lowest in FLm according to inundation regime. The diminished C mic, high BR, and high qCO 2 values in GLe seem to be an unspecific response of aerobic soil microorganisms on the long flooding period and the resulting short time for developing after last flooding as well as the low pH value. Different plant communities and their residues may influence the microbial diversity additionally. The PLFA profiles were dominated by the group of saturated fatty acids that together constituted almost 62–72% of the total fatty acids identified in the soils. In GLe all groups of PLFA, inclusive monounsaturated fatty acids, are lowest and in FLm highest, while in FLe the PLFA fractions show an intermediary amount of the three soils. The FLm had most of the time aerobic conditions and revealed therefore the highest C mic, PLFA-biomass, especially monounsaturated fatty acids, C mic/C org ratio as well as relatively low BR and qCO 2 value. These indicate that microorganisms in FLm are more efficiently in using carbon sources than those in GLe and FLe. All 26 identified PLFA were found in FLe and FLm, while the polyunsaturated fungi biomarker 18:2 ω6,9c could not be detected in GLe. In this long-time submerged soil the environmental conditions which microorganisms are exposed might be disadvantageous for fungi.

Influence of variable inundation regimes on soil collembola

Summary Soil collembola in floodplain habitats are known to react dynamically to inundation, showing direct negative effects of inundation as well as rapid regeneration after flooding. Unknown, however, are how these communities react to variable inundation and the role that spatial and temporal habitat heterogeneity plays. Therefore, the small-scale spatio-temporal dynamics of soil collembolan communities after varying inundation were studied in floodplain habitats in the Upper Rhine Valley in Germany. After frequent flooding, significant differences in density and species richness were found between different floodplain levels of the same location. Due to different species’ responses, major differences occurred in community structure. After infrequent inundation the densities and species richness of the same sites and especially hygrophilous components decreased dramatically. Between neighbouring sites, species exchange occurred and community structures became more similar. The results show that at the same locality soil collembola react dynamically as well as differentially to changes in the hydrological regime. Small-scale landscape heterogeneity allows a mixture of differentially reacting species to occur within the same regional metacommunity. Long-term stability of collembolan communities despite the high spatio-temporal heterogeneity of floodplains is thus maintained by metacommunity dynamics.

The effect of river regulation on floodplain wetland inundation, Murrumbidgee River, Australia

River regulation by headwater dams has altered the flow regime of rivers worldwide. For floodplain rivers, reduced connectivity between the main channel and floodplain wetlands has led to a decline in ecological health. Current river restoration theory advocates a return towards a more natural regime of floodplain wetland inundation. However, for many rivers, a poor understanding of the natural floodplain wetland inundation regime has hampered effective restoration management. This paper describes a technique for quantifying the effect of flow regulation on the inundation regime of floodplain wetlands on an extended reach of the Murrumbidgee River, Australia. A series of Landsat Thematic Mapper (TM) images, captured before and after a set of floods, was analysed to describe the relationship between flow and inundation for a 640 km river reach. These data were combined with historical regulated and modelled natural daily flow data to show that river regulation has reduced the duration and frequency of wetland inundation by ~40%. For the majority of wetlands the capture of small and medium floods in the headwater dams reduced wetland inundation substantially. However, for low connecting wetlands in reaches upstream of the main irrigation off-takes, summer irrigation flows have increased inundation.

The role of timing, duration, and frequency of inundation in controlling leaf litter decomposition in a river-floodplain ecosystem (Tagliamento, northeastern Italy)

Despite growing recognition of the importance of a natural flow regime in river-floodplain systems, researchers struggle to quantify ecosystem responses to altered hydrological regimes. How do frequency, timing, and duration of inundation affect fundamental ecosystem processes such as leaf litter decomposition? Along the semi-natural Tagliamento River corridor, located in northeastern Italy, we employed in situ experiments to separate effects of different inundation components on breakdown rates of black poplar (Populus nigra). We used a litter-bag method with two different mesh sizes to investigate how fungi and macroinvertebrates influence leaf breakdown rates. Ten treatments, each representing a specific combination of duration and frequency of inundation, were deployed in two seasons (summer, winter) to mimic complex inundation patterns. After 30 days of exposure, mean percentage of remaining leaf litter (ash free dry mass) ranged between 51% (permanent wet) and 88% (permanent dry). Leaf breakdown was significantly faster in winter than in summer. Duration of inundation was the main inundation component that controlled leaf breakdown rates. Leaf-shredding macroinvertebrates played only a role in the permanent wet treatment. Fungal parameters explained the faster leaf breakdown in winter. Our study suggests that modifications of the inundation regime will directly modify established decomposition processes. Factors reducing duration of inundation will decelerate leaf breakdown rates, whereas a decrease in flow variation will reduce leaf breakdown heterogeneity.

Safeguarding the Pantanal Wetlands: Threats and Conservation Initiatives

Abstract: The Pantanal, one of the largest wetlands on the planet, comprises 140,000 km2 of lowland floodplain of the upper Rio Paraguai basin that drains the Cerrado of central Brazil. The diverse mosaics of habitats resulting from the varied soil types and inundation regimes are responsible for an extraordinarily rich terrestrial and aquatic biota, exemplified by the bird richest wetland in the world—463 birds have been recorded there—and the largest known populations of several threatened mammals, such as Pampas deer (Ozotoceros bezoarticus), marsh deer (Blastocerus dichotomus), giant otter (Pteronura brasiliensis), and jaguar (Panthera onca). Until recently, deforestation of the adjoining Brazilian central plateau was considered the major threat to this area, but now deforestation is a critical problem within the floodplain itself. More than 40% of the forest and savanna habitats have been altered for cattle ranching through the introduction of exotic grasses. And there are other threats that lead to large‐scale disruption of ecological processes, severely affecting biodiversity. Although the Pantanal wetland is a Biosphere Reserve and is considered a Wetland of International Importance, only 2.5% of the upper Paraguai River basin is formally protected. To date, protected areas have been created opportunistically and as such, although of undoubted value, protect only a fraction of the Pantanal's wildlife and habitats. Among the conservation initiatives in the area, the private sector is increasingly participating in the establishment of private reserves. The prospects are far from optimistic, however, and the major challenge is to find alternative socioeconomic models that allow for conservation and economic uses of the land in association with the development of specific environmental legislation that reflects the unique characteristics of the region.

Gallery forest types and their environmental correlates in a Colombian savanna landscape

Savanna regions may contain significant areas of forest, usually in riparian environments. We described forest composition and quantified environmental variables for 80 plots in the watershed of the Yucao River (2550 km2), a tributary to the Meta River (Orinoco basin) in the eastern plains of Colombia. The total sampled area of 3.2 ha contained 147 tree species (110 genera and 45 families) with diameter at breast height &gt;5 cm. The families represented by most species were Leguminosae (15 species), Arecaceae (11 species), Rubiaceae (9), Chrysobalanaceae (7), Euphorbiaceae (7), Melastomataceae (7) and Myrtaceae (7). Although most of the tree species have wide distribution ranges in humid neotropical forests, and few are endemic to the region, comparison with other neotropical forests suggests that the combination of taxa is characteristic for neotropical gallery forests. Cluster analysis allowed the definition of five forest types. They show important differences in a number of environmental variables, especially those related to inundation regimes and soil properties. Canonical correspondence analysis indicates good correlation of the first ordination axis with the size of the stream with which the forest is associated, the height to which the water rises during floods and variables related to soil fertility. The second ordination axis differentiates between soils with high or low water content in the dry season, high or low organic matter content and low or high bulk density. The results demonstrate the role of spatial variability and interactions of floodplain morphology, hydrological regime, and soil properties in structuring this important riparian community.