The influence of the initial humidity of balneological peat on its pharmacological features]

The viscosity of balneological peat got special meaning according to its thermical features. Until now, there has been no answer on the question in how far balneological peat, which is prepared with different degrees of humidity, can vary the pharmacological character. Aim of this work was, on the one hand, to examine which initial degree of peat-humidity is necessary to get the wished viscosity in therapy when diluted with water. On the other hand, how far the pharmacological character of balneological is influenced by the initial degree of humidity. From peat, with initial different degrees of humidity, balneological peat is prepared, fulfilling the demands of the Quentin-Test and therefore the necessary consistence for therapy. Here in this work the in-vitro effect of aqueous peat extract (APE) on the spontaneous contractile activity of the smooth muscle fibres of guinea-pig stomachs was examined. The APE used got initial different degrees of humidity. It was found out, that the ability of peat according to a new water-uptake, with a initial humidity under 60%, was clearly reduced. Because of the reduced water content of balneological peat its thermical features were deteriorated. This goes for peat with a humidity factor < 60%. First, with the Quentin-Test, showing the optimal viscosity of peat before medical use, you can also make statements according its ability of maximum uptake of water, meaning the ability taking up water until it becomes gel-like. Second, the results show that the initial humidity of peat got no influence on the pharmacological features.     

Simulating the development of peat bogs

Summary A dynamic model is developed which simulates changes in peat bogs on different kinds of slopes. The relationships between the elements of the model which include bog plants, fen plants, water, peat and nutrients, are defined based on data from an earlier study of vegetation in the Rothenthurm area in Switzerland, and from published sources.The model is tested for its performance on three types of slope, starting development at a hypothetical state with low amounts of all variables. The development of bogs is traced until a stable state is reached at equilibrium.It is evident from the results that the establishment of a mature stable system takes longest on the flat slope. On all three slopes the peat layer reaches its maximum value before the equilibrium is reached at a slightly reduced peat level. As were observed in the fied, most slope types do not allow a peat bog to persist long under the local climatical conditions, but changes are forced in the vegetation toward a fen type with higher nutrient supply. It was however possible to simulate a stable peat bog when the slope was flat enough (type C in main text). The results of simulation reproduced with reasonable accuracy the shape of the bogs investigated in the field, the abundance of bog and fen plant species, the ground water table, the thickness of peat and the state of nutrient concentrations in the site. The model is rendered to have minimum complexity by assumptions, described in the main text, to reproduce only those properties of peat bogs that were considered primary in importance in the field. The extent to which the model can help to better understand the natural system is discussed.A version of the model described in this paper was developed by the author at the Institute of Geobotany, Swiss Federal School of Technology, Zürich, in 1975–1976. The author expresses his thanks to Prof. Dr. E. Landolt, Director of the Department.     

Mechanisms involved in the re-establishment of Sphagnum-dominated vegetation in rewetted bog remnants

Restoration of peat bog vegetation inhighly degraded peatlands is generallyattempted by improving the hydrology ofthese areas. The present paper discussesand explains various restoration strategiesrelating to peat quality, water chemistryand hydrology. In some cases, (shallow)inundation of bog remnants leads to a rapidredevelopment of (floating) Sphagnumvegetation, usually when poorly humifiedSphagnum peat is still present. Afterinundation, the peat either swells up tothe newly created water table or becomesbuoyant, in both cases creating a favorablesubstrate for Sphagnum mosses. Bulkdensity and methane production rate play animportant role in the buoyancy of floatingpeat, methane providing buoyancy to thesubstrates. The presence of (slightly)calcareous groundwater in the peat base mayenhance the development of floating raftsby stimulating decomposition processes.Alternatively, the growth of submerged Sphagnum species can also lead to thedevelopment of floating rafts. This dependson the penetration of light into the waterlayer and the availability of carbondioxide in the water layer.Many bog remnants, however, only havestrongly humified peat, which does notfavor the redevelopment of Sphagnumcarpets after deep inundation. On the otherhand, most peat moss species appear to dovery well on surface soaked black peat,which is why shallow inundation (< 0.3 m)is to be preferred in such cases.Compartmentalization of the terrain willprobably be necessary to ensure a more orless constant water table.An important prerequisite for thesuccessful restoration of bog remnants isthe development of a hydrologicallyself-regulating acrotelm. Key speciesinvolved in this development are Sphagnum magellanicum, Sphagnumpapillosum and Sphagnum rubellum.These typical hummock and lawn species areusually very slow colonizers compared tohollow species such as Sphagnumcuspidatum and Sphagnum fallax.Introduction of key species in carpetsdominated by hollow species or on baresubstrates appears to be very successful,indicating that the main constraint iscolonization.     

Physical properties of two-component growth media based on Sphagnum peat and their implications for plant-available water and aeration

The physical properties, in particular the water retention characteristics, of two-component growth media based on low-humified Sphagnum peat were studied. The high water retention of pure peat, which is further increased by shrinkage of the medium at desorption, yielded low air-filled porosity at high matric potentials ( –1 kPa). The addition of coarse perlite to peat decreased the shrinkage markedly and also tended to increase the low saturated hydraulic conductivity of peat, which had initially been rather low. In all media studied, the amount of water that is easily available to plants (water content retained between –1 and –10 kPa matric potential) was relatively high. In peat that contained half repellent rockwool or hydrogel, this water retention was, however, markedly lower. Between –10 and –50 kPa matric potential, water retention was rather low in all media (< 10%). Within the lowest matric potential range studied (–50 to –1500 kPa), water retention was considerably elevated in peat that contained half hydrogel. The implications of the physical properties of the media for plant-available water and aeration in the media are discussed.     

Hydrology,groundwater chemistry and peat chemistry in relation to habitat conditions in a mire on the South – eastern Alps of Italy

The habitat conditions in a mire on the southern Alps of Italy were defined based on data on topography, hydrology, water chemistry, peat chemistry and floristic composition. Water flowed along the main longitudinal axis from the eastern dry sector to the western wet sector of the mire. Along the transverse axes the water table assumed a convex shape during dry periods, which resulted in water flowing towards the margins of the mire. During wet periods the water table assumed a concave shape, determining a flow of water from the margins towards the mire centre. The absence of any vertical groundwater flows enhanced habitat acidification, particularly in the eastern sector of the mire characterised by a smaller peat thickness. Surface water in the central portion of the mire had low calcium concentration and low electrical conductivity, comparable to those found in ombrotrophic bogs. Calcium concentration and electrical conductivity in surface water were higher along the margins, indicating a certain degree of mineral soil water inflow. Total contents of major nutrients (N, P and K) in the peat were rather homogeneous over the mire, while calcium concentrations were slightly higher in the peat layers of the wet portion of the mire. Species distribution was strongly influenced, rather than by surface water chemistry, by water table position and rate of surface water flow.     

Release of inorganic N,P and K in peat soils; effect of temperature,water chemistry and water level

In the Netherlands, fens that are fed by polluted river water are often eutrophic, whereas fens fed by calcium-rich groundwater often are mesotrophic. Differences in trophic status can not always be attributed to differences in the nutrient load of the water. In this paper we try to determine if the inflow of river water in fens, in fact, accelerates the soil nutrient release, thereby creating more eutrophic conditions (‘internal eutrophication’). For this purpose, we compared nutrient release rates (N, P and K) in soil cores fromSphagnum peat andCarex peat saturated with different media, that were artificially created to mimic the three basic water sources: polluted river water, unpolluted calcium-rich groundwater and rainwater. In addition, we studied the effect of temperature and water level on nutrient release rates. The experiments proved thatSphagnum peat released much more P and ammonium thanCarex peat. The strong site effect proved consistent throughout the water chemistry treatments, which indicates that soil quality may be the most important agent determining nutrient release rates. Nevertheless, it was established that water chemistry and water level are of significant influence on nutrient release rates in peat soils. In particular, river water stimulated P release by the peat, most notably in theSphagnum peat. P-release in both soils was only minor when the soils were incubated in clean Ca-rich groundwater. It is suggested that P release is strongly associated with soil chemical processes, and that high P release rates after incubation in river water are due to the high sulphate content of the water. The net release from the soil of ammonium, potassium and phosphate increased with increasing temperature. A freezing treatment significantly increased nutrient availability. The results of the experiments are examined in the context of hydrologic management strategies for the conservation of fens in agricultural landscapes.     

Effects of drainage and wood ash fertilization on water chemistry at a cutover peatland

Afforestation is one of many different ways to reclaim cutover peatland areas. Among the treatments often required to obtain successful afforestation are supplementary drainage, fertilization and rotovation. This study presents the effects of drainage and wood-ash fertilization on the chemical composition of water in a cutover peatland area, which constitutes 34 hectares of a minerotrophic mire in SW Sweden. Fourteen hectares of the cutover peatland was amended with 23 tonnes of wood ash, 0.4 tonnes of raw phosphate and 0.25 tonnes of superphosphate per hectare, while different doses of a PK-fertilizer were applied on the remaining 20 hectares. The chemical properties of groundwater and stream water in the wood-ash amended area were compared with those in the PK-fertilized area and a control area. Outflowing groundwater emanating from the mineral subsoil affected the chemical composition of peat groundwater and streamwater. Drainage changed chemical composition more than the wood ash fertilization. Drainage led to increases in SO₄ and decreases in alkalinity in both peat groundwater and in stream water. The pH decreased in peat groundwater, whereas the streamwater pH was not affected because the high alkalinity in the mineral soil groundwater buffered the acid peat groundwater. Fertilization increased contents of K, Ca and Mn in both peat groundwater and stream water. Contents of B, o-P and Tot-P increased in peat groundwater but not in stream water, whereas the reverse was true for Mg. The outflow of P did not increase in spite of the large amount of P applied. The high retention of P was caused by large quantities of sesquioxides, especially Fe-oxides in the peat.     

Cultivating the climate: socio-economic prospects and consequences of climate-friendly peat land management in Germany

About 30% of the world’s soil carbon is stored in peat soils. Peat land’s functional principle of carbon storage greatly depends on management strategies. Therefore, agricultural peat land use becomes a focal point of interest in the current debate on climate protection. Agricultural management demands a drawdown of the water-level that causes degradation of the soils, as well as trace-gas emissions which have a negative impact on greenhouse-gas balance. Climate-friendly peat land management strategies, however, demand enhanced groundwater tables and decreased land-use intensity. Against this background, we analyse ways of re-organising agricultural peat land use within a case study located in Germany, where intensive peat land use accounts for 2.3–5.1% of the country’s overall greenhouse-gas emission. The study takes place in six regions which represent all possible socio-economic and natural conditions with regard to the range of existing peat land types, range of management and cultivation types, as well as the range of land-use intensity. To analyse potentials and effects of re-organising peat land use, stakeholder workshops and extensive farm surveys were carried out. The results indicate that reservations exist as regards a re-organisation of peat land management. Financial compensation for farmers appears necessary. The results also show that the potential of rearrangement throughout the regions varies significantly, mainly according to the existing level of interconnection and cooperation between local stakeholders, the technical feasibility of restoration and water logging and the level of agricultural profitability of peat land cultivation with regard to income, capital commitment and the share of affected peat land area.     

Regeneration of Three <Emphasis Type="Italic">Sphagnum</Emphasis> species

Sphagnum capillifolium var. tenellum, S. magellanicum, and S. recurvum var. brevifolium were regenerated from stem pieces grown in containers to assess their potential for use in peatland restoration projects. The effect of two water levels; peat, peat/sand or peat/clay substrates; and peat decomposition level on the species’ regeneration was evaluated. S. magellanicum attained the greatest cover on the peat or peat/sand mixture using decomposed peat when the growing surface was occasionally inundated. S. recurvum attained the greatest cover grown on the peat or peat/sand mixture using undecomposed peat when the water level was kept below the surface. S. capillifolium showed an affinity for the peat/clay mixture, and overall attained a greater total cover than the other species when grown under the lower water level on all substrate types, with total cover approximately three to five times that of the others. When developing management plans for restoration of mined peatlands, species-specific responses to water level, type and extent of mineral soil mixed with the peat surface, and peat decomposition level should be considered.     

The influence of fulvic and ulmic acids from peat, on the spontaneous contractile activity of smooth muscles.

The aim of the presented studies was to evaluate which classes of compounds of peat ingredients could be responsible for the partial agonistic effect of aqueous peat extract on the alpha2 adreno and D2 dopamine receptors of smooth muscles, which we have reported from former investigations. Based on the different solubility of peat ingredients, water-soluble components of fulvic and ulmic acids were separated according to the pH-value and chemical structure of the solvent. The biological activity of these acids was examined in peat baths using smooth muscle fibers of guinea pig stomach. The results demonstrate that the water-soluble components of fulvic and ulmic acids have a partially agonistic effect on the alpha2 adreno and D2 dopamine receptors, but at the same time quite different effects in terms of their influence on the spontaneous contractile activity (SCA) of smooth muscles have to be noted. From these investigations, we can conclude that aqueous peat extract and the water-soluble components of fulvic acid exhibit similar partial agonistic effects on the alpha2 adreno and D2 dopamine receptors. Therefore it is likely that the mentioned effects of the peat extract derive from the fulvic- and ulmic acids only. The water-soluble component of ulmic acid also showed partial agonistic effects on alpha2 adreno and D2 dopamine receptors. In this case, another substance group is involved, which has a faster blocking effect on these receptors, but was barely soluble in water at a normal pH-value (pH 7).     

North American approach to the restoration of Sphagnum dominated peatlands

Sphagnum dominated peatlands do not rehabilitate well after being cutover (mined) for peat and some action needs to be taken in order to restore these sites within a human generation. Peatland restoration is recent and has seen significant advances in the 1990s. A new approach addressing the North American context has been developed and is presentedin this paper. The short-term goal of this approach is to establish a plant cover composed of peat bog species and to restore a water regime characteristic of peatland ecosystems. The long-term objective is to return the cutover areas to functional peat accumulating ecosystems. The approach developed for peatland restoration in North America involves the following steps: 1)field preparation, 2) diaspore collection, 3) diaspore introduction, 4) diaspore protection, and 5) fertilization. Field preparation aims at providing suitable hydrological conditions for diaspores through creation of microtopography and water retention basins, re-shaping cutover fields and blocking ditches. It is site specific because it depends largely onlocal conditions. The second step is the collection of the top 10 centimetres of the living vegetation in a natural bog as a source of diaspores. It is recommended to use a ratio of surface collected to surface restored between 1: 10 and 1: 15 in order to minimize the impact on natural bogs and to insure rapid plant establishment in less than four years. Diaspores are then spread as a thin layer on the bare peat surfaces to be restored. It has been demonstrated that too scant or too thick a layer decreases plant establishment success. Diaspores are then covered by a straw mulch applied at a rate of 3 000 kg ha^-1 which provides improved water availabilityand temperature conditions. Finally, phosphorus fertilization favours more rapid substrate colonization by vascular plants, which have been shown to help stabilize the bare peat surface and act as nurse plants to the Sphagnum mosses.     

Carbon fluxes from a tropical peat swamp forest floor

A tropical ombrotrophic peatland ecosystem is one of the largest terrestrial carbon stores. Flux rates of carbon dioxide (CO₂) and methane (CH₄) were studied at various peat water table depths in a mixed‐type peat swamp forest floor in Central Kalimantan, Indonesia. Temporary gas fluxes on microtopographically differing hummock and hollow peat surfaces were combined with peat water table data to produce annual cumulative flux estimates. Hummocks formed mainly from living and dead tree roots and decaying debris maintained a relatively steady CO₂ emission rate regardless of the water table position in peat. In nearly vegetation‐free hollows, CO₂ emission rates were progressively smaller as the water table rose towards the peat surface. Methane emissions from the peat surface remained small and were detected only in water‐saturated peat. By applying long‐term peat water table data, annual gas emissions from the peat swamp forest floor were estimated to be 3493±316 g CO₂ m^?2 and less than 1.36±0.57 g CH₄ m^?2. On the basis of the carbon emitted, CO₂ is clearly a more important greenhouse gas than CH₄. CO₂ emissions from peat are the highest during the dry season, when the oxic peat layer is at its thickest because of water table lowering.     

Mobility of Pb in Sphagnum-derived peat

One important assumption in applying²¹⁰Pb-dating is that atmospherically deposited Pb is immobilized in the peat or sediment column. This assumption has been challenged widely, but has never been evaluated experimentally. We evaluated Pb mobility and the chemical forms in which Pb is stabilized in peat profiles by adding either soluble or particulate Pb to intact peat cores that were maintained under different water level regimes (permanently high, permanently low, fluctuating between high and low) and were subjected to simulated precipitation over a five month period. By analyzing the behavior of stable Pb we made inferences about the expected behavior of²¹⁰Pb. Results indicate that added soluble Pb²⁺ was retained in the peat through physiochemical binding to organic matter, and as such Pb²⁺ was largely immobile in peat even under conditions of a fluctuating water table. Added particulate Pb was largely (most likely by physical entrapment), but not completely, immobilized in peat. In none of the water table treatments was there evidence to support mobility of Pb by alternating formation and oxidation of Sulfides, or by any other mechanism. The binding of Pb²⁺ with organic matter at the peat surface, and the absence of Pb mobility lend credence to²¹⁰Pb-dating ofSphagnum-dominated peat deposits, which are over 90% organic matter throughout, and have high cation exchange capacities.     

Comparative study of the thermal properties of mud and peat solutions applied in clinical practice.

Different peloids as e.g. mud and peat have been traditionally used for therapeutic purposes successfully, especially of there thermal actions. It was the aim of the experimental study to compare the thermal properties of two peloids, mud and peat, with a view to assessing their thermal effects when they are applied in clinical practice. The studies were carried out using peat of the marsh type of peats (Hochmoor), and curative Pomorie (Bulgaria) mud. As important parameters were determined the specific thermal capacity at constant pressure (Cp), the density of solutions (rho), the cooling rate (m), the coefficient of temperature transfer (a) of solutions and the coefficient of thermal conductivity (lambda) of solutions of peat and curative mud, compared to water bath. The comparative studies of the thermal properties of water and water solutions of peat and curative mud show that the thermal effect of the water bath is substantially smaller than that of the peat and mud applications. This difference is due to a greater extent to the high values of the dynamic viscosity, not allowing cooling by convection and protecting the surface of the skin upon applications of peloid solutions with a higher temperature.     

Land use increases the recalcitrance of tropical peat

Tropical peat carbon compound composition (CCC) is a highly understudied subject. Advanced understanding of peat CCC and carbon dynamics in differing conditions is desperately needed due to large-scale utilization of these peatlands. We studied the CCC—i.e. the hemicellulosic carbohydrate and uronic acid composition and concentrations of extractives, cellulose, acid-soluble lignin and acid-insoluble lignin—in association with peat profile depth and physical structure of peat, under representative, common land uses. Samples were gathered from an undrained forest and three sites altered 20–30 years prior to the study, which in aggregate form a continuum of increasing land-use intensity (drainage-affected forest; drained and deforested degraded open site; drained and deforested site under cultivation) in Central Kalimantan, Indonesia. Peat samples were taken from depths between 10 and 115 cm that covered mostly oxic, frequently waterlogged and permanently waterlogged, anoxic conditions. Our results demonstrated greater modification of peat properties when both vegetation and hydrological conditions were altered. The differences between sites were mainly present in the topmost peat and decreased with depth. Peat located at the surface contained more labile compounds (hemicelluloses, extractives, uronic acids, cellulose) on forest sites than at the most intensively altered open sites, where peat was enriched with recalcitrant acid insoluble lignin. The effect of drainage was evident in the drained forest site, where at the approximate median water table depth peat more closely resembled open sites in terms of the peat properties. The increased recalcitrance of peat in reclaimed areas has been a result of enhanced decomposition, reduced litter input rates and, at open sites also by repeated fires.     

Development of Sphagnum fallax diaspores on bare peat with implications for the restoration of cut-over bogs

1. The growth of Sphagnum fallax was studied in a glasshouse experiment. Capitulum diaspores of S. fallax were cultivated on five different types of bare peat core, representing a gradient of increasing disturbance. Increases in length and weight were measured. Three microclimates were simulated by protecting the bare peat with a shading mesh and a plastic cover in combination with two water levels.
2. Significant differences in the growth of S. fallax were observed in relation to microclimate changes. Protection techniques such as shading mesh and perforated plastic film allowed a better development of the diaspores compared to bare peat. A plastic cover caused the best growth and compensated for a low water table level.
3. Peat properties are critical when diaspores grow in direct contact with decomposed peat. The porosity, and especially its vertical pattern in the peat profile, proved to be an important factor. A particular combination of microclimate conditions at the surface of the bare peat, and physical properties of the upper peat layers, may favour the growth of S. fallax diaspores even where there is a low water
Table 4 . Restoration of Sphagnum species on cut-over bogs needs to consider both the microclimate conditions at the surface of the bare peat and the peat properties themselves. These factors are important for the diaspores, particularly in periods of climatic and hydrological stress. In such situations, commensalism with some vascular plants may be a useful trigger for Sphagnum growth.     

An expert system model for mapping tropical wetlands and peatlands reveals South America as the largest contributor

Wetlands are important providers of ecosystem services and key regulators of climate change. They positively contribute to global warming through their greenhouse gas emissions, and negatively through the accumulation of organic material in histosols, particularly in peatlands. Our understanding of wetlands’ services is currently constrained by limited knowledge on their distribution, extent, volume, interannual flood variability and disturbance levels. We present an expert system approach to estimate wetland and peatland areas, depths and volumes, which relies on three biophysical indices related to wetland and peat formation: (1) long‐term water supply exceeding atmospheric water demand; (2) annually or seasonally water‐logged soils; and (3) a geomorphological position where water is supplied and retained. Tropical and subtropical wetlands estimates reach 4.7 million km² (Mkm²). In line with current understanding, the American continent is the major contributor (45%), and Brazil, with its Amazonian interfluvial region, contains the largest tropical wetland area (800,720 km²). Our model suggests, however, unprecedented extents and volumes of peatland in the tropics (1.7 Mkm² and 7,268 (6,076–7,368) km³), which more than threefold current estimates. Unlike current understanding, our estimates suggest that South America and not Asia contributes the most to tropical peatland area and volume (ca. 44% for both) partly related to some yet unaccounted extended deep deposits but mainly to extended but shallow peat in the Amazon Basin. Brazil leads the peatland area and volume contribution. Asia hosts 38% of both tropical peat area and volume with Indonesia as the main regional contributor and still the holder of the deepest and most extended peat areas in the tropics. Africa hosts more peat than previously reported but climatic and topographic contexts leave it as the least peat‐forming continent. Our results suggest large biases in our current understanding of the distribution, area and volumes of tropical peat and their continental contributions.     

Mineralization rates of peat from eroding peat islands in reservoirs

Reservoirs are sources of greenhouses gases to the atmosphere, primarily due to organic carbon mineralization in flooded plants and soils to carbon dioxide (CO₂) and methane (CH₄). Floating peat islands are common in reservoirs that inundated peatlands. These islands can decompose on mass, or small pieces of peat can erode from islands to decompose in the water column or on the bottom of reservoirs. Here we used large 450 liter sealed enclosures to measure mineralization rates of small peat pieces and larger peat blocks collected from floating peat islands. Mineralization rates were calculated by quantifying dissolved inorganic carbon (DIC), CO₂ and CH₄ accumulation within the water and headspace of the enclosures over time. We found that peat did decompose under water, but rates of mineralization of peat pieces were not different than rates of mineralization of larger peat blocks. Mineralization rates ranged between 59 and l40 g C g^–1 d^–1. Peat pieces acidified the water, shifting the bicarbonate equilibrium to almost exclusively dissolved CO₂, which was then readily able to flux to the atmosphere. We estimated that 2.4–5.6% of peat carbon was mineralized annually, suggesting that fluxes of CO₂ and CH₄ from reservoirs that flood peatlands could last at minimum 18–42 years from this carbon source alone.     

Recognition of peat-forming plant communities from their peat deposits in two south Swedish bog complexes

Peat samples, 3 015 from 103 boring points, on two mires (Åkhult mire, Store Mosse mire) south Sweden, have been subjected to macrofossil analysis. Based on plant remains, 9 peat groups were distinguished in the field. A further classification using phytosociological methods revealed 29 peat types. The affinities between the peat types were determined from TABORD classification and a Reciprocal Averaging ordination. The primary floristic differentiation is correlated with a gradient from treeless-to wooded stands, which coincides largely with the mire expanse-mire margin gradient. The poor-rich gradient seems to parallel the treeless-wooded gradient as well and may reflect the natural conditions in this mire before it was affected by man. The hummock-mud-bottom gradient is easy to distinguish in peat, formed by bog communities, but is not distinct in peat formed by fen communities and impossible to detect in peat dominated by wood remains. The amount of identifiable remains depends on the decomposition, which is determined by (1) the period of time the plant litter stays in the acrotelm, and (2) the nutrient status. The decomposition is greatest in fen-peat with abundant wood remains. This probably depends on a good supply of oxygen caused by greater horizontal water movements and better nutrient status.