Impact of drainage and soil hydrology on sources and degradation of organic matter in tropical coastal podzols

In podzols important environmental issues converge, including dissolved organic matter (DOM) transport, DOM-metal binding, and carbon storage in the subsoil. Therefore, it is important to understand the formation and degradation of podzols in relation to (changes in) environmental conditions. For this purpose a Holocene barrier island with coastal sand dunes (Ilha Comprida, SE Brazil) was chosen as study area. The island is build-up of five geomorphic units that have different age (from >5000 to 325 y BP), vegetation (restinga ecosystems), soil hydrology (flat units or units with ridges and swales) and drainage (poorly drained, well-drained, and improved drainage). Representative profiles were studied for each geomorphic unit, resulting in 100 samples from A, E, B, and C horizons, from which soil organic matter (SOM) was isolated by alkaline extraction. To better understand carbon sources and dynamics, we additionally sampled litter from different vegetation types and DOM from various sources. The molecular composition of SOM, DOM and litter was analyzed with pyrolysis gas chromatography mass spectrometry (pyrolysis-GC/MS). Comparing the pyrolysates of all samples (DOM, SOM and litter) factor analysis demonstrated that the major difference in molecular composition (factor 1) was related to the contribution from DOM (phenol, acetic acid, benzofurans, pyridine, benzene and naphthalene) or in-situ root material (straight chain aliphatics and methoxyphenols from the biomacromolecules suberan and lignin, respectively). The contribution from DOM or roots was characteristic for a profile i.e. without much change with depth. Factor 2 reflected decomposition processes, and showed that the predominantly DOM-derived B horizons were relatively enriched in aromatics compared to DOM, indicating selective decay and/or selective precipitation. In geomorphic units with swales and ridges that received DOM via groundwater flow from the catchment area, the B horizon was predominantly DOM-derived; these profiles showed large differences in the contribution from black carbon (BC; (poly)aromatics), with the younger profiles showing a larger contribution from BC in precipitated DOM. B horizons with a relatively large contribution from in-situ root materials were found in well-drained soils and in some of the poorly drained soils without lateral groundwater flow from the catchment area, i.e., the flat geomorphic unit without ridges and swales. Microbial material (N-containing compounds and sugars) was associated with relatively recent SOM and with well-drained conditions at present. i.e., well-drained profiles, and profiles with improved drainage

Podzolisation preserves ichnofossils constructed by ghost shrimp

Ichnofossils of ghost shrimps (e.g., Ophiomorpha nodosa and Callichirus major) are interpreted worldwide as records of sea level fluctuations and provide reliable evidence of sedimentation rate, salinity, and substrate type. The preservation of these ichnofossils was previously ascribed to the polysaccharide mucus produced by ghost shrimps when burrows were built. We found evidence that these ichnofossils were preserved due to the impregnation of the burrow walls by dissolved organic matter (DOM) during podzolisation that took place after the galleries had been abandoned. Our study was conducted on a tropical barrier island in southeastern Brazil with a spatial gradient of podzolisation intensity. We made a detailed macromorphological description of the ichnofossils at the soil profile scale. Then, we used thin sections of undisturbed soils to identify sand grain arrangements and organic matter (OM) accumulation. We detected three macromorphological structures, (i) tubular gallery wall, (ii) sandy infilling of the gallery, and (iii) soil matrix outside the gallery. In the micromorphology analysis, we identified that the tubular wall is impregnated with monomorphic OM also found outside the burrow but in lower concentration. Sand grains in the wall of the gallery are tightly packed, causing a lower porosity than inside and outside the trace fossil. The precipitation of monomorphic OM is due to stagnation of DOM that percolated through the soil. Water with DOM is trapped in the wall of the tubule because of its smaller pores. The ghost shrimps constructed their burrows in marine sediments without podzolisation. Then, with the progradation of the shoreline, the sediments were colonized by restinga forest adding DOM to the soil and podzolisation started. The extent to which DOM is produced depends on vegetation development, therefore, the accumulation of DOM in the B horizon that enables the preservation of the ichnofossils is constrained by vegetation development and progradation of the shoreline.</p

Soil morphology related to hydrology and degradation in tropical coastal podzols (SE Brazil)

Morphology of podzol profiles can be used to improve our understanding of soil formation and degradation processes. The morphology of a podzol chronosequence was studied for a 1800 m long cliff perpendicular to the coastline at the southern coast of the Island Ilha Comprida (São Paulo, Brazil). The large variation in hydrological conditions with time (surfaces with ages from 6000 to 300 yrs BP) and space (topography) allowed studying the relation between podzol morphology and drainage conditions, both during soil formation and degradation. On the oldest two surfaces, the podzols formed under poorly drained circumstances. Uplift during their formation resulted in (1) very deep Bh horizons and (2) degradation of the upper B horizon as a result of improved drainage. On the younger surface most podzols were poorly drained, but well-drained podzols and transitions occurred in beach ridges. In the cliffs on the southern coast of the island, improved drainage of the poorly drained podzols resulted in degradation of the B horizon. This degradation exhibits various forms, including (1) complete removal of the B horizon down to an underlying clay layer, (2) degradation of the B horizon along root channels with preferential vertical water transport, (3) degradation of the upper B horizon resulting in a diffuse EB transition, and (4) areas of organic matter (OM) depletion related to microbial activity, sometimes combined with burrowing. Type (2) degradation may result in a convoluted EB transition, the formation of islands of B horizon in the deepening E horizon, and formation of E horizon tongues into the Bh. Recent (post degradation) OM bands were found in E and B horizons. A thorough study of podzol morphology can be used to reconstruct several stages of their formation and degradation in relation to drainage conditions

Soil morphology related to hydrology and degradation in tropical coastal podzols (SE Brazil)

Morphology of podzol profiles can be used to improve our understanding of soil formation and degradation processes. The morphology of a podzol chronosequence was studied for a 1800 m long cliff perpendicular to the coastline at the southern coast of the Island Ilha Comprida (São Paulo, Brazil). The large variation in hydrological conditions with time (surfaces with ages from 6000 to 300 yrs BP) and space (topography) allowed studying the relation between podzol morphology and drainage conditions, both during soil formation and degradation. On the oldest two surfaces, the podzols formed under poorly drained circumstances. Uplift during their formation resulted in (1) very deep Bh horizons and (2) degradation of the upper B horizon as a result of improved drainage. On the younger surface most podzols were poorly drained, but well-drained podzols and transitions occurred in beach ridges. In the cliffs on the southern coast of the island, improved drainage of the poorly drained podzols resulted in degradation of the B horizon. This degradation exhibits various forms, including (1) complete removal of the B horizon down to an underlying clay layer, (2) degradation of the B horizon along root channels with preferential vertical water transport, (3) degradation of the upper B horizon resulting in a diffuse EB transition, and (4) areas of organic matter (OM) depletion related to microbial activity, sometimes combined with burrowing. Type (2) degradation may result in a convoluted EB transition, the formation of islands of B horizon in the deepening E horizon, and formation of E horizon tongues into the Bh. Recent (post degradation) OM bands were found in E and B horizons. A thorough study of podzol morphology can be used to reconstruct several stages of their formation and degradation in relation to drainage conditions

Geomorphological control on podzolisation – An example from a tropical barrier island

We investigated how the geomorphology of coastal barrier islands impacts soil hydrology and drainage at the landscape scale. Ilha Comprida is a Holocene barrier island with a 2.5 km-long cliff that is perpendicular to the coastal shore which provides an ideal condition to study the relation between age, relief, hydrology, and podzol morphology. Five geomorphic units were identified that differed in surface morphology and alignment of ridges and swales. Optical stimulated luminescence (OSL) dating showed that these geomorphic units had growth phases that decreased in age from west to east (Units I-V, from 5250 ± 820 to 325 ± 31 years ago, respectively). The geomorphic units were studied in two parallel 3 km transects on the southern part of the island. Along transect A-B, about 1 km from the southern shore, deep augerings were used to study sedimentary sequence and soil development, while on transect C-D on the southern shore, the continuous cliff exposure allowed more detailed morphological investigation. On all geomorphic units excluding the youngest, podzolisation has been the main soil-forming process. Groundwater level was monitored monthly for two years in 14 deep wells along transect A-B. Groundwater level during the formation of the B horizon was ascertained by determination of Fe. Podzol morphology (color of B horizon and its boundary with the E horizon) generally showed correlation to groundwater levels for both transects, except for the podzols in southwestern part of the island (Unit II). The podzols of Unit II showed an extremely thick (3 m) Bhm horizon devoid of Fe, indicating that they were formed under poor drainage conditions. However, soil morphology (undulating EB horizon boundary) and measured groundwater levels (below the B horizons) demonstrated that drainage has been improved. The extremely thick B horizon (3 m) in those podzols, which was formed in approximately 3000 years, and its genesis is explained by concentrated lateral flow of DOM-loaded groundwater due to the converging ridge alignments found in these units, in combination with a gradual uplift of the southwestern part of the island

Topsoil physico-chemical properties from the UKCEH Countryside Survey, Great Britain, 2020

This dataset consists of measures of topsoil (0-15cm) physico-chemical properties from soils sampled from 49 1km squares across Great Britain in 2020 as part of a rolling soil and vegetation monitoring program of 500 1km squares, repeated every 5 years. The properties included are: soil organic matter (loss on ignition (LOI)), derived carbon concentration, total soil organic carbon (SOC), nitrogen, Olsen-phosphorous, pH, electrical conductivity, soil bulk density of fine earth and fine earth volumetric water content. The UKCEH Countryside Survey is a unique study or 'audit' of the natural resources of the UK's countryside. The sample sites are chosen from a stratified random sample, based on a 15 by 15 km grid of GB. Surveys have been carried out in 1978, 1984, 1990, 1998 and 2007 by the UK Centre for Ecology & Hydrology (UKCEH) and predecessors, with repeated visits to the majority of squares. The countryside is sampled and surveyed using rigorous scientific methods, allowing us to compare new results with those from previous surveys. In this way we can detect the gradual and subtle changes that occur in the UK's countryside over time. In addition to soil data, vegetation species data are also gathered by the current phase of Countryside Survey

Topsoil physico-chemical properties from the UKCEH Countryside Survey, Great Britain, 2019

This dataset consists of measures of topsoil (0-15cm) physico-chemical properties from soils sampled from the first 100 1km squares across Great Britain in 2019 as part of a rolling soil and vegetation monitoring program of 500 1km squares repeated every 5 years. The properties included are: soil organic matter (loss on ignition (LOI)), derived carbon concentration, total soil organic carbon (SOC), nitrogen, Olsen-phosphorous, pH, electrical conductivity, soil bulk density of fine earth and fine earth volumetric water content. The UKCEH Countryside Survey is a unique study or 'audit' of the natural resources of the UK's countryside. The sample sites are chosen from a stratified random sample, based on a 15 by 15 km grid of GB. Surveys have been carried out in 1978, 1984, 1990, 1998 and 2007 by the UK Centre for Ecology & Hydrology (UKCEH) and predecessors, with repeated visits to the majority of squares. The countryside is sampled and surveyed using rigorous scientific methods, allowing us to compare new results with those from previous surveys. In this way we can detect the gradual and subtle changes that occur in the UK's countryside over time. In addition to soil data, vegetation species data are also gathered by the current phase of Countryside Survey

Topsoil physico-chemical properties from the UKCEH Countryside Survey, Great Britain, 2020, v2

This dataset consists of measures of topsoil (0-15 cm) physico-chemical properties from soils sampled from 48 x 1-km squares across Great Britain in 2020 as part of a rolling soil and vegetation monitoring program of 500 1-km squares repeated every 5 years. The properties included are: pH, soil organic matter (loss on ignition, LOI), derived carbon concentration and carbon stock (SOC), soil group, soil bulk density of fine earth, soil moisture of wet soil, fine earth volumetric water content (dry), nitrogen concentration and stock, and Olsen-phosphorus concentration. The UKCEH Countryside Survey is a unique study or 'audit' of the natural resources of the UK's countryside. The sample sites are chosen from a stratified random sample, based on a 15 by 15 km grid of GB. Surveys have been carried out in 1978, 1984, 1990, 1998 and 2007 by the UK Centre for Ecology & Hydrology (UKCEH) and predecessors, with repeated visits to most of the squares. The countryside is sampled and surveyed using rigorous scientific methods, allowing us to compare new results with those from previous surveys. In this way, we can detect the gradual and subtle changes that occur in the UK's countryside over time. In addition to soil data, vegetation species data are also gathered by the current phase of the UKCEH Countryside Survey. This work was supported by the Natural Environment Research Council award number NE/R016429/1 as part of the UK-SCAPE programme delivering National Capability

Topsoil physico-chemical properties from the UKCEH Countryside Survey, Great Britain, 2018-2019

This dataset consists of measurements of topsoil (0-15 cm) physico-chemical properties from soils sampled from the first 106 1-km squares across Great Britain in 2018 and 2019 as part of a rolling soil and vegetation monitoring program of 500 1-km squares repeated every 5 years. The properties included are: pH, soil organic matter (loss on ignition, LOI), derived carbon concentration and carbon stock (SOC), soil group, soil bulk density of fine earth, soil moisture of wet soil, fine earth volumetric water content (dry), nitrogen concentration and stock, and Olsen-phosphorus concentration. The UKCEH Countryside Survey is a unique study or 'audit' of the natural resources of the UK's countryside. The sample sites are chosen from a stratified random sample, based on a 15 by 15 km grid of GB. Surveys have been carried out in 1978, 1984, 1990, 1998 and 2007 by the UK Centre for Ecology & Hydrology (UKCEH) and predecessors, with repeated visits to most of the squares. The countryside is sampled and surveyed using rigorous scientific methods, allowing us to compare new results with those from previous surveys. In this way, we can detect the gradual and subtle changes that occur in the UK's countryside over time. In addition to soil data, vegetation species data are also gathered by the current phase of the UKCEH Countryside Survey. This work was supported by the Natural Environment Research Council award number NE/R016429/1 as part of the UK-SCAPE programme delivering National Capability