Accumulation Of Organic Sediments Research Articles

Early afforestation on islands of proglacial Lake Ojibway as evidence of post-glacial migration outposts

At the end of the last glacial period in the northern hemisphere, meltwater from receding ice sheets accumulated into large proglacial lakes, potentially limiting postglacial afforestation. We explored whether former islands of proglacial Lake Ojibway (Canada) (hilltops in the current landscape) could have acted as migration outposts and thus accelerated the postglacial migration. We extracted sediments from two small lakes located on “paleo-islands” and used XRF to detect changes in soil erosion and vegetation biomass. We also used plant macro-remains and wood charcoal to determine if (and which) tree species colonized the sites and to detect local fire events. Organic sediment accumulation started around 9657 and 9947 cal. yr BP at Lakes Perché and Despériers, respectively, before the level of Lake Ojibway started to decrease and liberate parts of the studied landscape ca 9400 cal. yr BP. Lithogenic elements (Ti, K, Sr, Fe, Zr, and Rb) decreased between the beginning of organic sediment accumulation and 8800–8700 cal. yr BP, indicating reduced soil erosion, possibly due to soil stabilization by vegetation. Then, the S/Ti ratio, a proxy of organic matter increased around 8800 and 8400 cal. yr BP. The earliest tree macro-remains ( Larix laricina and Pinus spp.) were found between 9850 and 9500 cal. yr BP. Local fires were detected around 9820 and 8362 cal. yr BP. Early afforestation occurred on the islands of Lake Ojibway, 200 and 450 years before its level started to decrease, confirming that some islands acted as migratory outposts accelerating postglacial migration.

Late Glacial development of lakes and wetland vegetation in a dune area in Central Poland

This study investigated the history of the development of six, paleo-lakes, which are at present filled with sediments, in a dune area in Central Poland, based on multiproxy paleoecological analyses and accelerator mass spectrometry radiocarbon dating. The aims of the paleoecological studies were: i) to determine the initial age of lakes development, ii) to reconstruct the local and regional plant succession, as well as iii) to reconstruct the environmental conditions during the initial stage of the development of lakes and peatlands. The obtained results indicated that: the former lakes in dune depressions were developed during the Bølling and Allerød when sparse vegetation allowed strong aeolian activity. Climate warming in Bølling led to the development of a denser plant cover, inhibition of sand transportation and the formation of mid-dune reservoirs with the accumulation of organic sediments. As indicated by 14C dating, mid-dunes basins were formed between 14 686 ± 60 cal. yr BP and 13 421 ± 60 cal. yr BP. The results of the paleobotanical analysis suggested that the reservoirs were shallow, oligo-mesotrophic, inhabited by pioneer calcicole vascular plant species such as: Chara sp., Hippuris vulgaris, Potamogeton natans, Potamogeton fresii, Potamogeton alpinus and Potamogeton filiformis, and mosses such as: Pseudocalliergon trifarium, Calliergon sp. and Calliergonella cordifolium. The area next to the reservoirs was covered with sparse pine forests combined with birch, which is typical of the Late Glacial period. The open areas were dominated by psammophilic and steppe vegetation, including Poaceae, Artemisia and Hippophae rhamnoides. Geochemical analysis revealed that Ca2+ and Fe3+ were in high concentrations, which could have influenced the presence of taxa preferring soil with high Ca2+ content. The accumulation of calcium in sediments confirms that the reservoirs were fed by groundwater originating from the progressive degradation of permafrost associated with thermal changes.

Ice‐sheet deglaciation and Loch Lomond Readvance in the eastern Cairngorms: implications of a Lateglacial sediment record from Glen Builg

We present new lithostratigraphic, pollen-stratigraphic and tephrochronological data obtained from a sediment sequence in a small lake basin in Glen Builg, eastern Cairngorms, with mapping of the surrounding glacial geomorphological features. The collective evidence indicates that basin organic sediment accumulation started during the Windermere Interstadial at ~14.3 ka. The new results reaffirm the conclusions of Clapperton et al. (1975), that any occupation of the eastern Cairngorms by Loch Lomond (‘Younger Dryas’) Stadial glacier ice was spatially restricted. The record also suggests that harsh climatic conditions prevailed throughout the Windermere Interstadial, probably due to the relatively high altitude of the site (~460 m) and its proximity to major Cairngorm peaks. Our new, more comprehensive study provides a robust chronology, and reveals several palaeoenvironmental signals congruent with other recently reported Scottish Highlands records. Key similarities with regional records are: (i) a short climatic reversal corresponding to GI-1d in the Greenland stratotype sequence; (ii) a two-phased Loch Lomond Stadial, with a transition around the Vedde Ash, dating to ~12.1 ka; and (iii) a delayed response to Early Holocene climatic warming of ~250 years, before soils were sufficiently stabilised to permit shrub vegetation establishment.

A 14,000 year peatland record of environmental change in the southern Gutland region, Luxembourg

A Late Pleistocene/Holocene paleoenvironmental record was obtained from the Rouer peatland (5°54′E, 49°45′N; 270 m a.s.l.), located in the Gutland area of southern Luxembourg. A total of six sediment samples were AMS radiocarbon-dated to obtain an age-depth model. XRF analyses and analyses of geochemical proxies of organic matter (TOC, TN, δ13C, δ15N) were conducted to identify major paleoenvironmental changes in the record. Pollen analysis reveals insights into the vegetation history throughout the last 14,000 cal. yr BP. The record offers unique insights into the evolution of local organic sediment/peat accumulation, as well as into the environmental history of the Gutland region and beyond. The accumulation of organic sediment and peat started at about 13,800 cal. yr BP before present. Until about 6000 cal. yr BP, periods of apparently stable climatic conditions had been interrupted repeatedly by pronounced episodes with increased input of minerogenic matter into the peat matrix (12,700–11,800 cal. yr BP; 11,500–11,300 cal. yr BP; 11,100–10,800 cal. yr BP; 9300 cal. yr BP; 8200 cal. yr BP), indicated by sudden increases of Ti/coh values. After 6000 cal. yr BP, environmental conditions stabilized. Between 4200 and 2800 cal. yr BP, during the Bronze Age, changes in the pollen spectrum indicate an increasing clearance of woodlands. Since the Roman period, an ongoing intensification of grassland farming and agriculture is evidenced. Lowest tree species abundances are witnessed during the Middle Ages. The Modern Era is characterized by enhanced sediment input due to soil erosion. In short, this record complements the Late Pleistocene/Holocene climatic history of the Gutland area and demonstrates that fen peat deposits can be valuable high-resolution paleoclimate archives.

Coastal wetland response to sea level rise in Connecticut and New York

The persistence of salt marshes in the landscape depends on their ability to accommodate rising sea level and minimize additional flooding stress. We use sediment cores and water level data from 14 marshes in Connecticut and New York to evaluate how marsh accretion, mineral and organic accumulation, carbon storage, and hydroperiod have changed from 1900 to 2012. We observe a regional acceleration in marsh accretion beginning around 1940, although marsh accretion did not reach parity with sea level rise for several additional decades. Despite a rise in marsh accretion from 1.0 mm yr−1 circa 1900 to 3.6 mm yr−1 at present, the marsh surface has lost elevation relative to tidal datums. Declining relative elevations have led to increased tidal flooding, particularly in high marsh settings. As flooding increased, organic matter accumulation accelerated at all marshes. Accelerating mineral deposition was only observed in areas of short-form Spartina alterniflora. Mineral and organic sediment accumulation co-limit accretion, but organic accumulation was the stronger limiting factor, suggesting that marsh response to sea level rise in the region is sensitive to processes affecting rates of belowground production and decomposition. Marsh carbon storage over the period of study averaged 84 g C m−2 yr−1, increasing as accretion accelerated. If marshes remain spatially intact as sea levels rise, these results suggest that marshes have the capacity to become even greater C sinks.

The distribution of benthic biomass in hadal trenches: A modelling approach to investigate the effect of vertical and lateral organic matter transport to the seafloor

Most of our knowledge about deep-sea habitats is limited to bathyal (200–3000m) and abyssal depths (3000–6000m), while relatively little is known about the hadal zone (6000–11,000m). The basic paradigm for the distribution of deep seafloor biomass suggests that the reduction in biomass and average body size of benthic animals along depth gradients is mainly related to surface productivity and remineralisation of sinking particulate organic carbon with depth. However, there is evidence that this pattern is somewhat reversed in hadal trenches by the funnelling of organic sediments, which would result in increased food availability along the axis of the trenches and towards their deeper regions. Therefore, despite the extreme hydrostatic pressure and remoteness from the pelagic food supply, it is hypothesized that biomass can increase with depth in hadal trenches. We developed a numerical model of gravitational lateral sediment transport along the seafloor as a function of slope, using the Kermadec Trench, near New Zealand, as a test environment. We propose that local topography (at a scale of tens of kilometres) and trench shape can be used to provide useful estimates of local accumulation of food and, therefore, patterns of benthic biomass. Orientation and steepness of local slopes are the drivers of organic sediment accumulation in the model, which result in higher biomass along the axis of the trench, especially in the deepest spots, and lower biomass on the slopes, from which most sediment is removed. The model outputs for the Kermadec Trench are in agreement with observations suggesting the occurrence of a funnelling effect and substantial spatial variability in biomass inside a trench. Further trench surveys will be needed to determine the degree to which seafloor currents are important compared with the gravity-driven transport modelled here. These outputs can also benefit future hadal investigations by highlighting areas of potential biological interest, on which to focus sampling effort. Comprehensive exploration of hadal trenches will, in turn, provide datasets for improving the model parameters and increasing predictive power.

Typha latifolia plant performance and stand biomass in wetlands affected by surface oil sands mining

Stand productivity of the dominant macrophyte Typha latifolia may be constrained by salinity and pollution in the oil sands wetlands of northern Alberta. We compared the performance and stand biomass of T. latifolia plants established in oil sands industrial wetlands (directly exposed to byproduct processed materials), on-site indirectly-affected, and off-site natural wetlands. We studied T. latifolia physiology (gas exchange, leaf fluorescence), morphology, leaf chemistry, and stand biomass. Oil sands plants had lower stomatal conductance than plants in natural wetlands resulting in lower transpiration but unaffected net photosynthesis rates. Oil sands plants had smaller and lower numbers of green leaves than natural wetlands plants. T. latifolia stands established in oil sands wetlands had lower aboveground and total biomass compared to natural wetlands. Despite water chemistry differences, T. latifolia plant performance did not differ between oil sands wetlands types. However, there was a lower total stand biomass in industrial than in indirectly-affected wetlands. T. latifolia had an unaltered photosynthetic activity in the oil sands wetlands allowing for the maintenance of persistent plant stands. However, T. latifolia growth restrictions and a lower stand biomass in the oil sands wetlands probably compromise long-term reclamation objectives focused on the accumulation of organic sediment and peat.

Living with sand: A record of landscape change and storminess during the Bronze and Iron Ages Orkney, Scotland

Palaeoenvironmental analyses of an exposed sequence of interbedded sand and peat overlying glacial till on Stronsay, Orkney, has revealed evidence of dynamic landscape change during the Holocene. AMS radiocarbon and OSL dating are used to identify periods of minerogenic and organic sediment accumulation. A lengthy period of stability during the early Holocene is inferred from the development of a deeply weathered till surface with pollen and soil micromorphological evidence suggesting prolonged woodland cover. During the mid to late Holocene phases of wind-blown sand that inundated the landscape are defined from the sedimentary record and are interpreted as periods of increased storminess between c. 3400–3100 cal. BP and c. 2800–2260 cal. BP. The palaeoecological evidence points to continuity of human exploitation, despite the phases of increased storminess during the Bronze Age and into the Iron Age. Rising sea levels and a severe storm event at c. 650 years BP inundated the site with massive sands and truncated the record. These storm events recorded on Stronsay are part of a regionally synchronous record for periods of increased storminess across the North Atlantic region during the Holocene.

Late Glacial and Early Holocene development of lakes in northeastern Poland in view of plant macrofossil analyses

The Late Glacial history of the development of seven extant or former, now sediment-filled, lakes in northeastern Poland was investigated based on high-resolution plant macrofossil analyses and AMS radiocarbon dating. According to palaeobotanical data and AMS dating, the accumulation of organic sediments began during the Bölling period. The bottom sediments of all studied lakes contain plant macrofossils typical of Late Glacial vegetation, such as Betula nana, Dryas octopetala, Potamogeton filiformis, and Potamogeton alpinus. The first plants to occur in the lakes were Chara sp., P. filiformis and Batrachium sp. The Late Glacial sediments included rarely encountered macrofossils of Sphagnum teres. At the beginning of the Holocene, the water level in the studied northeastern Polish lakes decreased significantly. This was manifested in a change in the type of sediment, transformation of small lakes into peatland in places, and expansion of typical (indicator) plants of shallow waters.

Woody vegetation, fuel and fire track the melting of the Scandinavian ice-sheet before 9500 cal yr BP

New studies indicate the presence of early Holocene ice-free areas far north in Scandinavia. Post-glacial fire and vegetation were investigated based on sedimentary charcoal and pollen from two small lakes in northern Sweden. Accumulation of organic sediment started around 10,900 and 9200calyrBP, showing that both lake valleys were ice-free extremely early given their northerly location. Fire events started after 9600calyrBP and became less common around the ‘8.2-ka event’. Woody vegetation provided fuel that contributed to fires. The first vegetation in our pollen record consisted of Hippophae, Dryas, grasses and sedges. Subsequently broadleaved trees (Betula, Salix) increased in abundance and later Pinus, Alnus, ferns and Lycopodium characterized the vegetation. Pollen from Larix, Picea and Malus were also found. The change in vegetation composition was synchronous with the decrease in lake-water pH in the region, indicating ecosystem-scale processes; this occurred during a period of net global and regional warming. The changes in fire frequency and vegetation appear independent of regional trends in precipitation. The reconstructed fire history and vegetation support the scenario of early ice-free areas far north in Scandinavia during early Holocene warming, creating favorable conditions for woody plants and wildfires.

In Situ Characterization of Resuspended-Sediment Oxygen Demand in Bubbly Creek, Chicago, Illinois

Sediment oxygen demand (SOD) can be a significant oxygen sink in various types of water bodies, particularly slow-moving waters with substantial organic sediment accumulation. In most settings in which SOD is a concern, the prevailing hydraulic conditions are such that the impact of sediment resuspension on SOD is not considered. However, in the case of Bubbly Creek in Chicago, the prevailing slack water conditions are interrupted by infrequent intervals of very high flow rates associated with pumped combined sewer overflow (CSO) during intense hydrologic events. These events can cause resuspension of the highly organic, nutrient-rich bottom sediments, resulting in precipitous drawdown of dissolved oxygen (DO) in the water column. To address this issue, a new in situ experimental apparatus designed to achieve high flow velocities was implemented to characterize SOD, both with and without sediment resuspension. In the case of resuspension, the suspended sediment concentration was analyzed as a function of ...

Stratigraphy of a Cretaceous Coastal-Plain Fluvial Succession: The Campanian Masuk Formation, Henry Mountains Syncline, Utah, U.S.A.

Abstract The internal architecture and genetic-stratigraphic analysis of coastal-plain fluvial successions has applications to both academic understanding of continental-margin stratigraphy and to the economic evaluation of subsurface hydrocarbon and water reservoirs. Despite the abundance of exposed ancient examples of such coastal-plain to shallow marine transitions, however, the lateral facies changes and stratigraphic stacking patterns of such transitions remain largely unresolved in detail. This study presents a sedimentological and stratigraphic analysis of the Campanian Masuk Formation in the Henry Mountains syncline of Utah, western USA, and proposes a sequence-stratigraphic model to explain the geometries of fluvial-channel lithosomes found in the unit. At its type section, the Masuk Formation is an ~ 220-m-thick succession of interbedded sandstone, mudstone, and coal with minor intraformational breccias. Six facies are defined: Facies 1, coal and carbonaceous shale, records accumulation of organic sediments in coastal-plain mires; Facies 2, mudrock, records coastal-plain floodbasin settings; Facies 3, thinly interbedded sandstone and siltstone, represents estuarine-basin deposits with one interval of marine flooding; Facies 4, admixed siltstone-sandstone with intraformational breccia, represents chaotically filled coastal plain channels; Facies 5, interbedded sandstone-siltstone with inclined heterolithic stratification (IHS), records deposits of coastal-plain channels with variable sediment supply; and Facies 6, trough-cross-bedded sandstone, records sand-dominated coastal-plain channel deposits. Facies 4, 5, and 6 all show evidence of coastal and tidal influence on sediment accumulation (IHS, low-diversity trace-fossil assemblages, bimodal to bipolar paleocurrent distributions, mud drapes on small-scale sedimentary structures) to varying degrees. Facies analysis and tracing of key surfaces such as regionally extensive erosion surfaces (sequence boundaries) and flooding surfaces suggest that the entire Masuk Formation (and the uppermost part of the underlying Muley Canyon Sandstone) is a single depositional sequence. The typically multilateral channel bodies are traceable in a depositional strike direction over distances much greater than empirically calculated estimates of channel-belt width. This pattern suggests an allogenic control on stacking patterns. Multistory and multilateral channel bodies typically have a Facies 4 unit at the base, overlain by one or more stories of Facies 5, and in turn capped by Facies 6. This stacking pattern could reflect cycles of incision, initial lowstand channel filling, and subsequent backfilling of estuarine channels during transgressions. This pattern further hints at the possibility of preservation of high-frequency sequences nested within the longer-term sequence. This study provides new insights into the stacking patterns of coastal-plain fluvial successions and their interpretation.

Limnology of Macrobrachium amazonicum grow-out ponds subject to high inflow of nutrient-rich water and different stocking and harvest management

We evaluated the water characteristics and particle sedimentation in Macrobrachium amazonicum (Heller 1862) grow-out ponds supplied with a high inflow of nutrient-rich water. Prawns were subject to different stocking and harvesting strategies: upper-graded juveniles, lower-graded juveniles, non-graded juveniles+selective harvesting and traditional farming (non-grading juveniles and total harvest only). Dissolved oxygen, afternoon N-ammonia and N-nitrate and soluble orthophosphate were lower in the ponds in comparison with inflow water through the rearing cycle. Ponds stocked with the upper population fraction of graded prawns showed higher turbidity, total suspended solids and total Kjeldahl nitrogen than the remaining treatments. An increase in the chemical oxygen demand:biochemical oxygen demand ratio from inlet (4.9) to pond (7.1–8.0) waters indicated a non-readily biodegradable fraction enhancement in ponds. The sedimentation mean rate ranged from 0.08 to 0.16 mm day−1 and sediment contained >80% of organic matter. The major factors affecting pond ecosystem dynamic were the organic load (due to primary production and feed addition) and bioturbation caused by stocking larger animals. Data suggest that M. amazonicum grow-out in ponds subjected to a high inflow of nutrient-rich water produce changes in the water properties, huge accumulation of organic sediment at the pond bottom and non-readily biodegradable material in the water column. However, the water quality remains suitable for aquaculture purposes. Therefore, nutrient-rich waters, when available, may represent a source of unpaid nutrients, which may be incorporated into economically valued biomass if managed properly.

Mangroves as an agent of rapid coastal change in a tidal-dominated environment, Gulf St Vincent, South Australia: implications for coastal management

The northeastern shore of Gulf St Vincent, South Australia is a mesotidal, low-wave-energy coastline, characterised by tidal-dominated bioclastic carbonate sedimentation. Distinctive assemblages of subtidal, intertidal and supratidal marine plants and invertebrate animals have resulted in well defined, adjacent bio- and litho-facies that lie parallel to each other across broad areas of coastal sedimentation. At Port Gawler, the intertidal zone is bounded by a landward high-tide beach and a subtidal Posidonia australis seagrass meadow seaward. Thirty years ago, within the immediate study area, this intertidal zone comprised an inner sandflat and an outer muddy seagrass meadow dominated by Zostera muelleri, the two areas separated by a shallow tidal distributary. Avicennia marina is a species of mangrove that has colonised much of the protected, tidal-dominated coasts of South Australia. Propagules of this tree readily take root in intertidal mud, with a natural ecological succession of Z. muelleri followed by A. marina. Over the time of observation, juvenile mangroves have progressively colonised a narrow zone along the landward side of the muddy seagrass meadow; they appear unable to colonise a sandy substrate. Juveniles advanced rapidly southward from mature woodland in the north towards equally mature woodland in the south. From the initial tap root, juvenile plants send out radial roots from which project, snorkel-like, an array of vertical pneumatophores. Redistributed algal, seagrass and other organic flotsam collect around these vertically protruding pneumatophores, promoting accumulation of organic sediment. Within the newly forming mangrove woodland, there has been pronounced sediment aggradation of >0.5 m, greatly altering the dynamics of tidal flow. Tidal flow is now largely constrained to a channel between the mature southern woodland and that formed most recently. Higher velocity flows through this channel have exhumed populations of infaunal bivalves, and floodtide and ebbtide deltas of coarse bioclastic sediments are a consequence. The aggraded sediment of the new woodland shelters the area landward. Consequently, more muddy sediments are now covering what was formerly bare sandflat, thus providing new areas for mangrove colonisation. Migration of mangroves towards the high-tide beach is inevitable and will be limited only by their need for regular flushing of accumulated salt from their roots by seawater at high tide. Thus, A. marina drives rapid geomorphic change in the tidal-dominated coasts of the South Australian gulfs. In similar coastal areas of southeast Asia, where intertidal muddy sediments predominate, this species appears to be an ideal candidate for reforestation projects. Juvenile plants should grow successfully and rapidly, so preparing coastal environments for the establishment of more ecologically diverse mangrove communities.

Paleohydrology of Lake Nhaucati (southern Mozambique), ∼400 AD to present

This paper investigates the correlations between lake level change, rainfall variability and general atmospheric forcing in southern Africa. The analysis of fossil diatom assemblages in a sediment sequence from the small, rain-fed Lake Nhaucati, southern Mozambique, is presented and discussed in relation to regional palaeoclimate data. The accumulation of organic sediments in Lake Nhaucati began 1,600 years ago when the lake level was rising. Lithology and pollen suggest a low stand at 800 AD, which correlates with other climate proxies from the summer rainfall region of southern Africa. The diatom assemblage suggests that lake levels were high between 900 and 1300 AD, with shorter low stands at c.1100 and 1200 AD. The period after 1400 AD was marked by a slow rate of accumulation and consequently a low temporal resolution. The correlation with other climate proxies in the summer rainfall region, written sources, and pollen data suggests repeated droughts corresponding to the Little Ice Age, though the driest periods may have caused complete desiccation of the lake. Higher lake levels are suggested after 1800 AD, though written sources suggest droughts in the beginning of the twentieth century. The analysis shows a good correlation with palaeoclimate data from the summer rainfall region and confirms the presence of an anti-phase relationship between the summer rainfall region of southern Africa and the bi-modal rainfall region of east tropical Africa. It also supports the general hypothesis that variation in the intensity of the Inter Tropical Convergence Zone is the main agent modulating rainfall over southern and eastern Africa on centennial timescales.

Plant Settlement Patterns and Their Effects on Breeding Sites of Little Terns (Sterna albifrons) on Sand Bars on Ganwol Lake

We analyzed soil characteristics, soil seed banks, and plant communities in a small islet in Ganwol Lake from May 2005 to August 2006 to examine the forces driving plant settlement on sand bars and the effects of plant settlement patterns on nesting sites of little terns (Sterna albifrons). The soil nutrients contents in a site where the feces of wintering birds accumulate (N: 15.4 mg/kg, P: 10.5 mg/kg, LOI: 0.51 %, pH: 6.8) and a site where organic sediments accumulate (N: 20.7 mg/kg, P: 16.4 mg/kg, LOI: 0.40%, pH: 6.6) were much higher those of a control site which was not affected by bird feces and organic sediments (N: 4.1 mg/kg, P: 5.4 mg/kg, LOI: 0.41%, pH: 6.7). However, a seed bank was formed only on the site with accumulated organic sediments. Plant settlement was accelerated by feces from wintering birds and organic sediment accumulation on sand bars in Ganwol Lake. The percentage of area disturbed by human activities increased from 0.2% in May 2005 to 13.9% in August 2006, and the percentage of annual communities increased from 27.5% to 43.3%, but the percentage of open area decreased from 55.2% to 28.0% from May 2005 to August 2006. These increases in disturbed area and annual communities decreased the open area for breeding of little terns. The enlargement of P. communis and T. angustata communities was suppressed by irregular flooding. These results provide useful information for the management of little tern breeding sites for conservation purposes.

Characteristics of reeds on Lake Peipsi and the floristic consequences of their expansion

The reeds of Lake Peipsi (surface area 3555 km 2, mean depth 7.1 m, max. depth 15.3 m, not-regulated) have increased through the last 30 years. The most significant increase has taken place in the larger formerly mesotrophic northern part where the mean air-dry biomass of reed shoots has increased from 20 g m −2 in 1970 through 789 g m −2 in 1989 to 1563 g m −2 in 2002. The data of 34 transects for 2001–2002 along the Estonian coast and aerophotos made in 2001 showed that in places reeds reach a water depth of 1 m (mean 0.64 m) and a width of more than 200 m (mean 89.5 m). Their area of 9.3 km 2 accounts for about 0.6% of the Estonian territory of the lake. The longer and thicker shoots grew in the lakeward and intermediate zones of reeds. Near villages the shoots were weaker and their biomass lower. Phosphorus content of shoots, being higher near settlements, was generally low; in some cases content of phosphorus was ≤0.001%. The monotonous reed belt occupies the growth area of shallow-water submergent and shorter emergent species and favours the accumulation of organic sediments. The frequency of several species demanding light and sandy bottom has decreased, as well has the overall diversity of the macrovegetation. The main reasons for expansion of the reed could be eutrophication, combined with low-water periods, and the decline of cattle breeding in the shore areas. Some suppressed species have reappeared on stretches cleaned from reeds.

Late quaternary vegetation dynamics and human impact on Alexander Selkirk Island, Chile

AbstractAim To reconstruct the history of vegetation and environments using pollen, charcoal and sediment analysis, and to identify the timing and nature of climate change and human impact on the vegetation of a remote Pacific island.Location Cerro de Los Inocentes, 1000 m above sea level, Alexander Selkirk Island (33°45′S, 80°45′W), Chile. The westernmost island of the Juan Fernandez Archipelago, south‐east Pacific Ocean.Methods A 150‐cm long sediment core comprising 87 cm dark brown peat overlying 63 cm of yellow grey clay was extracted from a shallow depression on the southern slopes of Cerro de Los Inocentes. Pollen, charcoal, sediment and accelerator mass spectrometry radiocarbon analyses were used to construct a record of vegetation change through time. Numerical analysis of multispecies data allowed the classification of fossil assemblages into distinct pollen zones.Results Pollen and spores are preserved throughout the sediment with high concentrations coinciding with the beginning of organic sediment accumulation at around 8000 14C yr BP. Prior to 8000 14C yr BP, the deposition of clays, presumably from upslope erosion, occurred in a landscape sparsely vegetated by grasses, ferns and Pernettya rigida heath, including several plants that are only found 100–200 m above the site today (Zone CI‐1). After 8000 14C yr BP, a P. rigida heath was the dominant vegetation (Zone CI‐2). A shift to a wet heath–shrubland (Zone CI‐3) occurred at 6000 14C yr BP and was followed by a transition to a treefern–shrubland mosaic accompanied by periodic burning (Zone CI‐4) after 4500 14C yr BP. The impact of human occupation is evident in Zone CI‐5 at 450 14C yr BP with the loss of forest species, increased burning and invasion of the exotic plant Rumex.Main conclusions The pollen and charcoal record provides the first evidence of vegetation changes spanning at least the last 8000 14C yr BP from the high altitude environment of Alexander Selkirk Island. Prior to 8000 14C yr BP, the altitudinal ranges of different plant species may have been suppressed by a cooler and drier climate. Increasing precipitation and temperatures at the end of the last glacial period may have mobilized exposed sediments in a sparsely vegetated upland environment, altering local drainage patterns, eventually leading to slope stabilization and deposition of organic detritus under an increasing density of heath and shrub vegetation. The subalpine heath–shrubland persisted until 4500 14C yr BP when first evidence for sustained burning is found in association with the establishment of a more open treefern–shrubland vegetation pattern. In the absence of human occupation at this time, the influence of increased climatic variability associated with more frequent El Niño‐Southern Oscillation events during the mid to late Holocene is considered one of the main driving forces behind increased vegetation disturbance during this period. The record provides evidence that island vegetation patterns have been highly dynamic over millennial to decadal time‐scales and that the flora has persisted through periods of rapid and major climate change. This changed with the discovery of the island by European explorers in the late sixteenth century and the subsequent introduction of goats and exploitation and burning of forests, which resulted in the progressive destruction of native vegetation and the invasion of introduced plants. There is evidence that reduced burning and control of the goat population within the last 50 years has resulted in marginal recovery of some high altitude native plant species.

Shrimp and fish pond soils: processes and management

Abstract The pond bottom soil and the accumulated sediments are integral parts of ponds. Concentrations of nutrients, organic matter and microorganism density in the pond bottom are several orders of magnitude greater than in the water. The accumulation of organic sediments may limit pond intensification. The intensive organic matter degradation at the pond bottom and high sediment oxygen demand exceeds the oxygen renewal rate. This leads to the development of anoxic conditions in the sediments and at the sediment–water interface. A series of anaerobic processes, affected by the redox potential of the system, are taking place. A large number of potentially toxic materials are generated. Among those are organic acids, reduced organic sulfur compounds, reduced manganese and sulfides. Shrimp, as animals that normally live on or near the bottom, are exposed to conditions on the pond bottom. Exposure to toxic materials endanger the well being of the cultured shrimp. Reduced feeding, slower growth, mortality and possibly higher sensitivity to disease are reported. The rational use of aerators to minimize the area of sludge accumulation, construction of ponds to trap sludge, stirring sediments, chemical poising of the redox system and environmentally accepted treatment and reuse of drained sediments are means to control the conditions at the pond bottom.

Modern and historic accumulation rates of phosphorus in Lake Okeechobee, Florida

Phosphorus accumulation rates in depositional zone sediments of Lake Okeechobee were determined in 11 mud-zone cores and two peat-zone cores dated by 210Pb. Although difficulties were encountered in interpreting 210Pb data from some sites, reliable dating of sediments from the mud zone of this shallow lake is possible. Sediment accumulation rates in this zone have increased during the present century by an average of about twofold, and accumulation of organic sediments in the lake during pre-settlement times apparently was much slower than during the past century. Concentrations of all forms of sedimentary P but especially nonapatite inorganic-P and organic-P also have increased since pre-settlement times and especially since about 1940. Annual P accumulation rates in the lake's sediments have increased about fourfold during the 1900s, with most of the increase occurring in the past 40–50 years. The recent accumulation rate of sedimentary P (past ~ 10 years) agrees within a factor of 1.5 with the net retention of P in the lake calculated from published input-output mass balances.