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J M Waddington - One of the best experts on this subject based on the ideXlab platform.
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effect of water table drawdown on peatland nutrient dynamics implications for climate change
Biogeochemistry, 2013Co-Authors: Merrin L Macrae, Maria Strack, K J Devito, J M WaddingtonAbstract:It is anticipated that a lowering of the water table and reduced soil moisture levels in peatlands may increase peat decomposition rates and consequently affect nutrient availability. However, it is not clear if patterns will be consistent across different peatland types or within peatlands given the natural range of ecohydrological conditions within these systems. We examined the effect of persistent drought on peatland nutrient dynamics by quantifying the effects of an experimentally lowered water table position (drained for a 10-year period) on peat KCl-extractable total inorganic nitrogen (ext-TIN), peat KCl-extractable nitrate (ext-NO3 −), and water-extractable ortho-phosphorus (ext-PO4 3−) concentrations and net phosphorus (P) and nitrogen (N) mineralization and nitrification rates at natural (control) and drained Microforms (hummocks, lawns) of a bog and poor fen near Quebec City, Canada. Drainage (water table drawdown) decreased net nitrification rates across the landscape and increased ext-NO3 − concentrations, but did not affect net N and P mineralization rates or ext-TIN and ext-PO4 3− concentrations. We suggest that the thick capillary fringe at the drained peatland likely maintained sufficient moisture above the water table to limit the effects of drainage on microbial activity, and a 20 cm lowering of the water table does not appear to have been sufficient to create a clear difference in nutrient dynamics in this peatland landscape. We found some evidence of differences in nutrient concentrations with Microforms, where concentrations were greater in lawn than hummock Microforms at control sites indicating some translocation of nutrients. In general, the same microtopographic differences were not observed at drained sites. The general spatial patterns in nutrient concentrations did not reflect net mineralization/immobilization rates measured at our control or drained peatlands. Rather, the spatial patterns in nutrient availability may be regulated by differences in vegetation (mainly Sphagnum moss) cover between control and drained sites and possibly differences in hydrologic connection between Microforms. Our results suggest that microform distribution and composition within a peatland may be important for determining how peatland nutrient dynamics will respond to water table drawdown in northern peatlands, as some evidence of microtopographic differences in nutrient dynamics was found.
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do peatland Microforms move through time examining the developmental history of a patterned peatland using ground penetrating radar
Journal of Geophysical Research, 2012Co-Authors: Nicholas Kettridge, Maria Strack, Andrew Baird, Alice M Milner, Andrew Binley, Xavier Comas, Nigel J Cassidy, Angela Harris, Jan Van Der Kruk, J M WaddingtonAbstract:Using ground-penetrating radar (GPR) to map subsurface patterns in peat physical properties, we investigated the developmental history of meso-scale surface patterning of Microforms within a raised bog. Common offset GPR measurements were obtained along a 45-m transect, at frequencies ranging from 100 to 900 MHz. We found that low-frequency (central frequency = 240 MHz) showed a striking pattern of subsurface reflections that dip consistently in a northerly direction. The angle of these dipping reflectors is calculated using a semblance algorithm and was shown to average 3.9 degrees between a depth of 1.0 and 2.5 m. These dipping reflectors may indicate downslope migration of surface Microforms during the development of the peatland. Based on the estimated angle and the rate of peat accumulation, the average rate of downslope propagation of these surface Microforms is calculated at 9.8 mm per year. Further survey work is required to establish whether the downslope migration is common across the peatland.
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differential peat deformation compressibility and water storage between peatland Microforms implications for ecosystem function and development
Water Resources Research, 2010Co-Authors: J M Waddington, Maria Strack, E Kellner, Jonathan S PriceAbstract:[1] Because peat is elastic, the daily to seasonal swelling and shrinking of the peat surface not only affects water storage but also alters peatland hydraulics and the biogeochemical and thermal properties of peat. Due to different botanical origins and degrees of decomposition, we hypothesized that different peatland Microforms (ridges and lawns) display a large variation in peat deformation and compressibility. Here we examined the spatial variation of peat surface movement, peat strength, and volumetric water content at a low lawn (LL), upper lawn (UL), and ridge (R) along a 5 m transect in a peatland in Quebec, Canada. The average seasonal amplitude in peat surface level was 9, 6, and 2 cm at the LL, UL, and R sites, respectively. The surface layers in each of these sites were fairly rigid with the largest changes in peat thickness occurring between 20 and 60 cm depth in the peat profile. Compressibility varied among Microforms but was not correlated to other properties within the layer in individual soil layers. However, when average profile compressibility was considered, it was significantly correlated to peat depth, von Post humification, distance to hollow, and peat strength. The total water storage by dilation below the water table was about the same as the water deficit (precipitation minus evapotranspiration) for LL, while the storage deficit for UL and especially R was lower. Including changes in entrapped gas content over the season reduced estimates of changes in water storage at all sites. Because microform type and position were significant predictors of hydrophysical properties, we argue that this suggests that peatland microtopography is self-reinforcing through ecohydrological feedbacks. Including the variability in these properties in peatland ecohydrological models will be key for predicting the response of peatland ecosystems to disturbance.
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response of vegetation and net ecosystem carbon dioxide exchange at different peatland Microforms following water table drawdown
Journal of Geophysical Research, 2006Co-Authors: Maria Strack, J M Waddington, Line Rochefort, Eeva-stiina TuittilaAbstract:[1] Northern peatlands are significant stocks of terrestrial soil carbon, and it has been predicted that warmer temperatures and lower water tables resulting from climate change will convert these ecosystems into sources for atmospheric carbon dioxide (CO2). However, these predictions do not consider the potential for hydrologically induced ecological succession or the spatial variability of carbon accumulation rates between different Microforms in peatlands. To address these issues, the vegetation community was described, and the rates of gross ecosystem photosynthesis (GEP), ecosystem respiration (Rtot) and net ecosystem CO2 exchange were determined along poor fen microtopographic gradients at a control site and at a site which experienced a water table drawdown of � 20 cm 8 years prior to the study (drained). Sampling plots within these sites were classified as Microforms of hummocks, lawns, or hollows. The coverage of Sphagnum moss declined on drained hummocks, drained lawns were invaded by sedges, and hollows shifted from open water plots at the control site to Sphagnum-dominated plots with sparse vascular plant cover at the drained site. As a result, Rtot was significantly greater at the drained site at all Microforms while maximum rates of GEP declined at drained hummocks and were enhanced at drained lawns and hollows compared to similar control Microforms. These results suggest that predictions about the response of northern peatland carbon exchange to climate change must consider the interaction between ecology and hydrology and the differential responses of Microforms related to their initial ecohydrological conditions.
Maria Strack - One of the best experts on this subject based on the ideXlab platform.
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saturated hydraulic conductivity in sphagnum dominated peatlands do Microforms matter
Hydrological Processes, 2014Co-Authors: Jordanna E Branham, Maria StrackAbstract:Within peatland ecosystems, small deviations in surface elevation result in Microforms that differ in depth to water table, plant type and rate of biogeochemical cycling, possibly leading to differences in peat physical and hydrological properties that could feed back to the whole ecosystem hydrological and biogeochemical function. However, hydrological parameters for peatland Microforms have not been quantified. This study determined bulk density, pore size distribution and saturated hydraulic conductivity (Ksat) at hummocks and hollows of four, Sphagnum-dominated Canadian peatlands. Study sites included both a bog and poor fen in each of Alberta and Quebec allowing for investigation of differences in peat hydrophysical properties between Microforms across a range of Sphagnum-dominated peatlands. Hydraulic conductivity was determined in the laboratory on peat from the surface (0.03–0.08 m) and the saturated zone (0.20 m below the local water table position). Peatland type, climate region, microform and depth of peat were all significant descriptors of variation in Ksat. Deeper peat was less conductive than surface peat. Hummocks generally had higher Ksat than hollows at both surface and saturated zones, although differences between Microforms varied between sites. Differences in Ksat between samples were correlated with bulk density, von Post humification and macroporosity. These results indicate that there are microtopographical differences in peat hydrophysical properties; however, the strong decline in Ksat with depth indicates that differences in the local water table, resulting in a change in depth of water flow, is likely a stronger control on local Ksat than microform type. Copyright © 2014 John Wiley & Sons, Ltd.
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effect of water table drawdown on peatland nutrient dynamics implications for climate change
Biogeochemistry, 2013Co-Authors: Merrin L Macrae, Maria Strack, K J Devito, J M WaddingtonAbstract:It is anticipated that a lowering of the water table and reduced soil moisture levels in peatlands may increase peat decomposition rates and consequently affect nutrient availability. However, it is not clear if patterns will be consistent across different peatland types or within peatlands given the natural range of ecohydrological conditions within these systems. We examined the effect of persistent drought on peatland nutrient dynamics by quantifying the effects of an experimentally lowered water table position (drained for a 10-year period) on peat KCl-extractable total inorganic nitrogen (ext-TIN), peat KCl-extractable nitrate (ext-NO3 −), and water-extractable ortho-phosphorus (ext-PO4 3−) concentrations and net phosphorus (P) and nitrogen (N) mineralization and nitrification rates at natural (control) and drained Microforms (hummocks, lawns) of a bog and poor fen near Quebec City, Canada. Drainage (water table drawdown) decreased net nitrification rates across the landscape and increased ext-NO3 − concentrations, but did not affect net N and P mineralization rates or ext-TIN and ext-PO4 3− concentrations. We suggest that the thick capillary fringe at the drained peatland likely maintained sufficient moisture above the water table to limit the effects of drainage on microbial activity, and a 20 cm lowering of the water table does not appear to have been sufficient to create a clear difference in nutrient dynamics in this peatland landscape. We found some evidence of differences in nutrient concentrations with Microforms, where concentrations were greater in lawn than hummock Microforms at control sites indicating some translocation of nutrients. In general, the same microtopographic differences were not observed at drained sites. The general spatial patterns in nutrient concentrations did not reflect net mineralization/immobilization rates measured at our control or drained peatlands. Rather, the spatial patterns in nutrient availability may be regulated by differences in vegetation (mainly Sphagnum moss) cover between control and drained sites and possibly differences in hydrologic connection between Microforms. Our results suggest that microform distribution and composition within a peatland may be important for determining how peatland nutrient dynamics will respond to water table drawdown in northern peatlands, as some evidence of microtopographic differences in nutrient dynamics was found.
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do peatland Microforms move through time examining the developmental history of a patterned peatland using ground penetrating radar
Journal of Geophysical Research, 2012Co-Authors: Nicholas Kettridge, Maria Strack, Andrew Baird, Alice M Milner, Andrew Binley, Xavier Comas, Nigel J Cassidy, Angela Harris, Jan Van Der Kruk, J M WaddingtonAbstract:Using ground-penetrating radar (GPR) to map subsurface patterns in peat physical properties, we investigated the developmental history of meso-scale surface patterning of Microforms within a raised bog. Common offset GPR measurements were obtained along a 45-m transect, at frequencies ranging from 100 to 900 MHz. We found that low-frequency (central frequency = 240 MHz) showed a striking pattern of subsurface reflections that dip consistently in a northerly direction. The angle of these dipping reflectors is calculated using a semblance algorithm and was shown to average 3.9 degrees between a depth of 1.0 and 2.5 m. These dipping reflectors may indicate downslope migration of surface Microforms during the development of the peatland. Based on the estimated angle and the rate of peat accumulation, the average rate of downslope propagation of these surface Microforms is calculated at 9.8 mm per year. Further survey work is required to establish whether the downslope migration is common across the peatland.
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differential peat deformation compressibility and water storage between peatland Microforms implications for ecosystem function and development
Water Resources Research, 2010Co-Authors: J M Waddington, Maria Strack, E Kellner, Jonathan S PriceAbstract:[1] Because peat is elastic, the daily to seasonal swelling and shrinking of the peat surface not only affects water storage but also alters peatland hydraulics and the biogeochemical and thermal properties of peat. Due to different botanical origins and degrees of decomposition, we hypothesized that different peatland Microforms (ridges and lawns) display a large variation in peat deformation and compressibility. Here we examined the spatial variation of peat surface movement, peat strength, and volumetric water content at a low lawn (LL), upper lawn (UL), and ridge (R) along a 5 m transect in a peatland in Quebec, Canada. The average seasonal amplitude in peat surface level was 9, 6, and 2 cm at the LL, UL, and R sites, respectively. The surface layers in each of these sites were fairly rigid with the largest changes in peat thickness occurring between 20 and 60 cm depth in the peat profile. Compressibility varied among Microforms but was not correlated to other properties within the layer in individual soil layers. However, when average profile compressibility was considered, it was significantly correlated to peat depth, von Post humification, distance to hollow, and peat strength. The total water storage by dilation below the water table was about the same as the water deficit (precipitation minus evapotranspiration) for LL, while the storage deficit for UL and especially R was lower. Including changes in entrapped gas content over the season reduced estimates of changes in water storage at all sites. Because microform type and position were significant predictors of hydrophysical properties, we argue that this suggests that peatland microtopography is self-reinforcing through ecohydrological feedbacks. Including the variability in these properties in peatland ecohydrological models will be key for predicting the response of peatland ecosystems to disturbance.
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response of vegetation and net ecosystem carbon dioxide exchange at different peatland Microforms following water table drawdown
Journal of Geophysical Research, 2006Co-Authors: Maria Strack, J M Waddington, Line Rochefort, Eeva-stiina TuittilaAbstract:[1] Northern peatlands are significant stocks of terrestrial soil carbon, and it has been predicted that warmer temperatures and lower water tables resulting from climate change will convert these ecosystems into sources for atmospheric carbon dioxide (CO2). However, these predictions do not consider the potential for hydrologically induced ecological succession or the spatial variability of carbon accumulation rates between different Microforms in peatlands. To address these issues, the vegetation community was described, and the rates of gross ecosystem photosynthesis (GEP), ecosystem respiration (Rtot) and net ecosystem CO2 exchange were determined along poor fen microtopographic gradients at a control site and at a site which experienced a water table drawdown of � 20 cm 8 years prior to the study (drained). Sampling plots within these sites were classified as Microforms of hummocks, lawns, or hollows. The coverage of Sphagnum moss declined on drained hummocks, drained lawns were invaded by sedges, and hollows shifted from open water plots at the control site to Sphagnum-dominated plots with sparse vascular plant cover at the drained site. As a result, Rtot was significantly greater at the drained site at all Microforms while maximum rates of GEP declined at drained hummocks and were enhanced at drained lawns and hollows compared to similar control Microforms. These results suggest that predictions about the response of northern peatland carbon exchange to climate change must consider the interaction between ecology and hydrology and the differential responses of Microforms related to their initial ecohydrological conditions.
Dong Hun Choi - One of the best experts on this subject based on the ideXlab platform.
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correction of minor form and microform cleft lip using modified muscle overlapping with a minimal skin incision
Archives of Plastic Surgery, 2017Co-Authors: Dong Hun ChoiAbstract:In treating minor-form or microform cleft lip, obtaining an optimal result is a challenge because of the visible scarring caused by traditional surgery. We present a refined method using muscle overlapping with a minimal skin incision in patients younger than 3 years, a group characterized by thin muscle.The surgical technique involves restoration of the notched vermillion using Z-plasty, formation of the philtral column using overlapping of an orbicularis oris muscle flap through an intraoral incision, and correction of the cleft lip nasal deformity using a reverse-U incision and V-Y plasty. A single radiologist evaluated ultrasonographic images of the upper lip.Sixty patients were treated between September 2008 and June 2014. The age at the time of operation ranged from 6 to 36 months (mean, 26 months). The follow-up period ranged from 8 to 38 months (mean, 20 months) in minor-form cases and from 14 to 64 months (mean, 37 months) in microform cases. A notched cupid's bow was corrected in 10 minor-form cases and 50 microform cases. Ultrasonographic images were obtained from 3 patients with minor-form cleft lip and 9 patients with microform cleft lip 12 months after surgery. The average muscle thickness was 4.5 mm on the affected side and 4.1 mm on the unaffected side.The advantages of the proposed procedure include the creation of an anatomically natural philtrum with minimal scarring. This method also preserves the continuity and function of the muscle and provides sufficient augmentation of the philtral column and nostril sill.
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Correction of Minor-Form and Microform Cleft Lip Using Modified Muscle Overlapping with a Minimal Skin Incision
Korean Society of Plastic and Reconstructive Surgeons, 2017Co-Authors: Min Chul Kim, Dong Hun Choi, Sung Gun Bae, Byung Chae ChoAbstract:BackgroundIn treating minor-form or microform cleft lip, obtaining an optimal result is a challenge because of the visible scarring caused by traditional surgery. We present a refined method using muscle overlapping with a minimal skin incision in patients younger than 3 years, a group characterized by thin muscle.MethodsThe surgical technique involves restoration of the notched vermillion using Z-plasty, formation of the philtral column using overlapping of an orbicularis oris muscle flap through an intraoral incision, and correction of the cleft lip nasal deformity using a reverse-U incision and V-Y plasty. A single radiologist evaluated ultrasonographic images of the upper lip.ResultsSixty patients were treated between September 2008 and June 2014. The age at the time of operation ranged from 6 to 36 months (mean, 26 months). The follow-up period ranged from 8 to 38 months (mean, 20 months) in minor-form cases and from 14 to 64 months (mean, 37 months) in microform cases. A notched cupid's bow was corrected in 10 minor-form cases and 50 microform cases. Ultrasonographic images were obtained from 3 patients with minor-form cleft lip and 9 patients with microform cleft lip 12 months after surgery. The average muscle thickness was 4.5 mm on the affected side and 4.1 mm on the unaffected side.ConclusionsThe advantages of the proposed procedure include the creation of an anatomically natural philtrum with minimal scarring. This method also preserves the continuity and function of the muscle and provides sufficient augmentation of the philtral column and nostril sill
Andrew Binley - One of the best experts on this subject based on the ideXlab platform.
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impact of Microforms on nitrate transport at the groundwater surface water interface in gaining streams
Advances in Water Resources, 2014Co-Authors: Andrew Binley, C M Heppell, Katrina Lansdown, Xiaomin MaoAbstract:Abstract Small streambed structures (or Microforms, 0.01–1 m in length) exist ubiquitously in riverbed systems. Small-scale topography is potentially important in controlling hyporheic exchange flow and transport of conservative and reactive solutes at the groundwater–surface water interface. The role of Microforms on NO 3 - transfer in a riffle-scale (macroforms of >1 m length) hyporheic zone within a gaining river setting is investigated using a 2-D flow and transport model which accounts for both nitrification and denitrification. Results show that t he short pathlines caused by Microforms lead to more NO 3 - discharge to the river compared with a macroform-only condition due to shortened residence times of both surface water and groundwater in mixing zones. Short hyporheic exchange flow pathways caused by Microforms could remain oxic along their entire length or switch from nitrate producing to nitrate consuming as oxygen concentrations decline. Microforms affect net NO 3 - flux by the combined effect of introducing more stream mass flux and reducing their residence time in mixing zones under different hydrological and biogeochemical conditions. Our findings underscore that ignoring Microforms in river beds may underestimate NO 3 - load to the river and have practical implications for pore water sampling strategies in groundwater–surface water studies.
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on the importance of considering channel Microforms in groundwater models of hyporheic exchange
River Research and Applications, 2013Co-Authors: D H Kaser, Andrew Binley, A L HeathwaiteAbstract:The infiltration of stream water in the sediment and its return to the stream—a process known here as hyporheic exchange flows (HEF)—is a critical control of the structure and functions of the stream ecosystem. River restoration programmes will increasingly require quantitative methods for evaluating this influence. Previous studies have already shown the potential of numerical groundwater models to characterize HEF and compare restoration scenarios. Although various sources of uncertainty are acknowledged, the potential effect of small streambed structures (or Microforms), such as grains or ripples, embedded in channel-unit scale structures (or macroforms), such as riffle-pool sequences, is commonly ignored. Here, a simple conceptualization through a 2-D vertical model is used to test whether (i) ignoring Microforms in groundwater models at the macroform scale can impact estimations of residence times; (ii) Microforms can influence HEF patterns driven by macroforms; and conversely (iii) the uncertainty of head measurements in stream piezometers can affect our understanding of HEF patterns. Results show that (i) residence times and flux estimations can be strongly affected by the modeller's choice to represent microform-induced HEF or not; (ii) the interaction of the microform and macroform scales can induce various subsurface flow patterns; and (iii) the perceived significance of microform-induced HEF is highly sensitive to the uncertainty of in-stream measurements of subsurface heads. Little is known about the relative efficiency of these microform and macroform scales, which are effectively influencing exchange at different depths and interacting with each other. Future studies that consider biogeochemical cycling or streambed ecology should be placed in this context. It is also necessary to find ways of including this source of uncertainty in groundwater models of HEF. Copyright © 2012 John Wiley & Sons, Ltd.
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do peatland Microforms move through time examining the developmental history of a patterned peatland using ground penetrating radar
Journal of Geophysical Research, 2012Co-Authors: Nicholas Kettridge, Maria Strack, Andrew Baird, Alice M Milner, Andrew Binley, Xavier Comas, Nigel J Cassidy, Angela Harris, Jan Van Der Kruk, J M WaddingtonAbstract:Using ground-penetrating radar (GPR) to map subsurface patterns in peat physical properties, we investigated the developmental history of meso-scale surface patterning of Microforms within a raised bog. Common offset GPR measurements were obtained along a 45-m transect, at frequencies ranging from 100 to 900 MHz. We found that low-frequency (central frequency = 240 MHz) showed a striking pattern of subsurface reflections that dip consistently in a northerly direction. The angle of these dipping reflectors is calculated using a semblance algorithm and was shown to average 3.9 degrees between a depth of 1.0 and 2.5 m. These dipping reflectors may indicate downslope migration of surface Microforms during the development of the peatland. Based on the estimated angle and the rate of peat accumulation, the average rate of downslope propagation of these surface Microforms is calculated at 9.8 mm per year. Further survey work is required to establish whether the downslope migration is common across the peatland.
Eeva-stiina Tuittila - One of the best experts on this subject based on the ideXlab platform.
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microform related community patterns of methane cycling microbes in boreal sphagnum bogs are site specific
FEMS Microbiology Ecology, 2015Co-Authors: Heli Juottonen, Devin Robinson, Mirkka Kotiaho, Päivi Merilä, Hannu Fritze, Eeva-stiina TuittilaAbstract:Vegetation and water table are important regulators of methane emission in peatlands. Microform variation encompasses these factors in small-scale topographic gradients of dry hummocks, intermediate lawns and wet hollows. We examined methane production and oxidization among Microforms in four boreal bogs that showed more variation of vegetation within a bog with microform than between the bogs. Potential methane production was low and differed among bogs but not consistently with microform. Methane oxidation followed water table position with microform, showing higher rates closer to surface in lawns and hollows than in hummocks. Methanogen community, analysed by mcrA terminal restriction fragment length polymorphism and dominated by Methanoregulaceae or ‘ Methanoflorentaceae’ , varied strongly with bog. The extent of microform-related variation of methanogens depended on the bog. Methanotrophs identified as Methylocystis spp. in pmoA denaturing gradient gel electrophoresis similarly showed effect of bog, and microform patterns were stronger within individual bogs. Our results suggest that methane-cycling microbes in boreal Sphagnum bogs with seemingly uniform environmental conditions may show strong site-dependent variation. The bog-intrinsic factor may be related to carbon availability but contrary to expectations appears to be unrelated to current surface vegetation, calling attention to the origin of carbon substrates for microbes in bogs.
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response of vegetation and net ecosystem carbon dioxide exchange at different peatland Microforms following water table drawdown
Journal of Geophysical Research, 2006Co-Authors: Maria Strack, J M Waddington, Line Rochefort, Eeva-stiina TuittilaAbstract:[1] Northern peatlands are significant stocks of terrestrial soil carbon, and it has been predicted that warmer temperatures and lower water tables resulting from climate change will convert these ecosystems into sources for atmospheric carbon dioxide (CO2). However, these predictions do not consider the potential for hydrologically induced ecological succession or the spatial variability of carbon accumulation rates between different Microforms in peatlands. To address these issues, the vegetation community was described, and the rates of gross ecosystem photosynthesis (GEP), ecosystem respiration (Rtot) and net ecosystem CO2 exchange were determined along poor fen microtopographic gradients at a control site and at a site which experienced a water table drawdown of � 20 cm 8 years prior to the study (drained). Sampling plots within these sites were classified as Microforms of hummocks, lawns, or hollows. The coverage of Sphagnum moss declined on drained hummocks, drained lawns were invaded by sedges, and hollows shifted from open water plots at the control site to Sphagnum-dominated plots with sparse vascular plant cover at the drained site. As a result, Rtot was significantly greater at the drained site at all Microforms while maximum rates of GEP declined at drained hummocks and were enhanced at drained lawns and hollows compared to similar control Microforms. These results suggest that predictions about the response of northern peatland carbon exchange to climate change must consider the interaction between ecology and hydrology and the differential responses of Microforms related to their initial ecohydrological conditions.