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doi: 10.2136/sssaj2014.08.0330pmid: N/A
Quantitative assessment of frequency and control of preferential flow (PF) across the landscape has been largely lacking. Previous work evaluated PF occurrence at 10 sites along a hillslope in the Shale Hills Catchment using soil moisture response to 175 precipitation events. We expanded the analysis to include (i) 237 additional events to test the temporal consistency and predictability of PF occurrence and (ii) 25 additional sites to upscale to the entire catchment. The results showed considerable temporal consistence in both frequency and main controls of PF at the hillslope scale, attributed largely to statistical stability of precipitation patterns during the 6.5‐yr monitoring and relatively stable subsurface PF paths. Generally, PF tended to occur more often in response to intense rainfalls and favored conditions at dry hilltop or wet valley sites. When upscaling to the catchment, topographic controls became more evident, leading to the identification of a hidden subsurface PF network. Higher frequency of PF occurred at the hilltop (average 46%) and the valley floor (average 41%), while the overall average frequency for swales was 26% and that for planar and convex hillslopes was 18%. Soil‐terrain attributes provided a limited estimation (R2 = 0.43–0.48) of PF occurrence, suggesting complexities involved in PF dynamics. This study confirmed that the initiation and persistence of PF were controlled by interactions among landforms, soils, initial moisture conditions, precipitation, and seasons. Further investigations of these key controls can lead to improved understanding and modeling of PF from pedon to catchment scales.
D'Amore, David V.; Edwards, Rick T.; Herendeen, Paul A.; Hood, Eran; Fellman, Jason B.
doi: 10.2136/sssaj2014.09.0380pmid: N/A
Dissolved organic C (DOC) transfer from the landscape to coastal margins is a key component of regional C cycles. Hydropedology provides a conceptual and observational framework for linking soil hydrologic function to landscape C cycling. We used hydropedology to quantify the export of DOC from the terrestrial landscape and understand how soil temperature and water table fluctuations regulate DOC losses in the C‐rich, perhumid coastal temperate rainforest (PCTR) of Alaska. Land cover in the region is dominated by three major hydropedologic units: poor fen, forested wetland, and upland. We instrumented soils and streams in nine hydropedologic units to quantify DOC fluxes. Stream‐water DOC concentrations varied from 5.7 to 16.7 mg C L−1. Mean area‐weighted DOC fluxes were 24.8, 29.9, and 10.5 g C m−2 yr−1 from the poor fens, forested wetlands, and uplands, respectively. We found that increased soil temperature and frequent fluctuations of soil water tables promoted the export of large quantities of DOC from poor fen and forested wetland units and relatively high amounts of DOC from upland units. The DOC export from the hydropedologic units in the PCTR is among the highest in the world and highlights the importance of terrestrial to aquatic fluxes of DOC as a pathway for C loss in the region.
Millar, Christina M.; Owusu Aduomih, Adiza Ama; Still, Brett; Stolt, Mark H.
doi: 10.2136/sssaj2014.05.0204pmid: N/A
Subaqueous soils have largely been overlooked in soil C accounting studies. Recent work suggests that shallow, subtidal soils along the Atlantic Coast contain soil organic C (SOC) pools that are equal to or greater than comparable upland pools. In this study, we investigated the spatial relationships between SOC pool size and subaqueous soil landscape units in three coastal lagoons in Rhode Island and estimated SOC sequestration rates for these soils. Fifty‐two pedons were sampled to 1 m and analyzed for SOC content and bulk density to calculate SOC pools. Pools varied significantly among soil landscape units and subaqueous soil Great Groups. Average SOC pools for the upper meter ranged from 354 Mg C ha−1 in mainland cove units (which frequently contained buried organic horizons) to 31 Mg C ha−1 in washover fan flat units. Soil organic C pool averages per Great Group ranged from 174 Mg C ha−1 in Sulfiwassents to 40 Mg C ha−1 in Psammowassents. Average sequestration rates ranged from 0.18 to 1.45 Mg C ha−1 yr−1 and were significantly different among soil landscape units. Subaqueous SOC pools and sequestration rates were found to be essentially equivalent to regional forest subaerial mineral soils. These data suggest that estuarine subaqueous soils may be important C sinks and should be included in sequestration studies of estuarine ecosystems. Furthermore, subaqueous soil surveys provide the spatial information needed for SOC accounting of coastal soils.
Shuster, William D.; Dadio, Stephen D.; Burkman, Caitlin E.; Earl, Stevan R.; Hall, Sharon J.
doi: 10.2136/sssaj2014.05.0200pmid: N/A
Soil morphology and correspondent hydrologic data can contribute to qualifying and quantifying urban soil suitability and capacity to cycle stormwater runoff. We put particular emphasis on the possibility that residential parcels may manage their own stormwater on pervious yard areas. We assessed the morphology of Aridisol pedons (as deep cores to approximately the 3.6‐m depth) via soil taxonomy, performed in situ measurements of infiltration, and measured subsoil hydraulic conductivity in two desert parks, four residential parcels, and three dual‐purpose park–stormwater retention basins in the Phoenix, AZ, metropolitan area. Infiltration rates overall ranged between 0.4 and 1.7 cm h−1. We used borehole hydraulic conductivity as a proxy for drainage, which ranged from a low of 0.0 to 13 cm h−1. Representing a baseline, or set of “natural” hydrologic processes, native desert sites exhibited a relatively high capacity to infiltrate and redistribute rainfall, which, depending on storm intensity, may drain to washes or ephemeral streambeds via subsurface runoff. Simulations of stormwater runoff on residential parcels showed that when rooftop runoff is directed to pervious patches, rainfall is entirely infiltrated and redistributed, which predicts good potential for parcel‐level stormwater management. Our observation of an accumulation of fine sediments in retention basin surface soils was corroborated with local observations that drawdown times in the retention basins had increased with time. Although further assessment is needed on a wider variety of semiarid landscapes, our results suggest a positive role for residential parcels in detaining stormwater on site and perhaps easing the wet‐weather burden on centralized stormwater infrastructure in semiarid urban ecosystems.
Still, Brett M.; Stolt, Mark H.
doi: 10.2136/sssaj2014.09.0366pmid: N/A
In the coastal zone, biological and biogeochemical processes, influenced by anthropogenic inputs, drive pH variability and contribute to coastal acidification. Spatial patterns of these processes across coastal estuaries are unknown. In this study, we used a hydropedological approach to assess the spatial variability of coastal acidification within two coastal lagoons and embayments in Rhode Island by measuring oyster shell dissolution, pH within the water column, and pore water pH within the upper 5 cm of the underlying subaqueous soils. Sampling and monitoring sites were stratified based on submerged soil‐landscape types mapped at the Great Group level as Haplowassents, Sulfiwassents, and Psammowassents. We found that pore water pH varied significantly among soils and with depth. Median pore water pH was significantly greater in sandy, low organic matter content Psammowassents (7.97) than the finer textured, higher soil organic matter content Sulfiwassents (7.35), and the Haplowassents (6.57) that receive groundwater discharge from the surrounding subaerial soils. Juvenile calcifying organisms can experience acidic stress at pH values below 7.6; thus, current pH values within the upper few centimeters of Sulfiwassents and Haplowassents may be low enough to impact recently set juvenile calcifying organisms inhabiting these soils. Consequently, mean shell loss during a 4‐wk period was significantly greater in the Sulfiwassents (1.54) than the Psammowassents (0.96%), with the greatest shell loss (18.62%) in one of our Haplowassent sites with groundwater discharge. Our research suggests that measures of pore water pH and shell dissolution may be helpful in developing soil interpretations regarding the effects of coastal acidification on calcifying organisms.
Sherrod, Lucretia A.; Erskine, Robert H.; Green, Timothy R.
doi: 10.2136/sssaj2014.05.0222pmid: N/A
Soil erosion and deposition impact the sustainability of agricultural lands within the semiarid Great Plains in the United States. Temporal differences between high‐resolution digital elevation maps provide physical estimates of spatial erosion or deposition, and the depth to a calcic horizon is a chemical indicator. We hypothesized that soil surface layer CaCO3 concentration is inversely correlated with the change in surface elevation (Δz). We studied a 109‐ha field in northeastern Colorado under winter wheat (Triticum aestivum L.)–fallow rotation in alternating strips perpendicular to the prevailing wind. Soil samples (top 30 cm) collected from 185 landscape positions in 2001 and 2012 were analyzed for CaCO3 using a modified pressure‐calcimeter method. The change in CaCO3 (ΔC) was significantly correlated with large‐scale erosional and depositional areas (west and east blocks, respectively) and with soil units, whereas Δz was correlated with management strips and blocks. The west block had an average ΔC of 3.2 g kg−1 with 2.0 cm of erosion, whereas the east block decreased by 4.4 g kg−1 with 4.2 cm of deposition. Summit positions had the highest CaCO3, and toeslope positions had the lowest. We found inverse relationships between Δz and ΔC in summit and toeslope positions at both erosional (Δz < −5 cm) and depositional (Δz > 5 cm) areas, but Δz was not correlated significantly with ΔC overall. High values of CaCO3 (>100 g kg−1) decreased with time. A high‐resolution map of Δz showed complex spatial patterns across scales, which inferred water and wind erosion and deposition affected by terrain and management.
Bourgault, Rebecca R.; Ross, Donald S.; Bailey, Scott W.
doi: 10.2136/sssaj2014.05.0190pmid: N/A
Classical podzolization studies assumed vertical percolation and pedon‐scale horizon development. However, hillslope‐scale lateral podzolization also occurs where lateral subsurface water flux predominates. In this hydropedologic study, 99 podzols were observed in Watershed 3, Hubbard Brook Experimental Forest, New Hampshire. Soil horizon samples were extracted with citrate–dithionite (d) and acid ammonium oxalate (o) to quantify Fed, Mnd, Alo, and Feo. Optical density of oxalate extract (ODOE) was measured to assess spodic C. Amorphous organometallic complexes (AOC) were observed in thin section, for which Al, Fe, Mn, and C were quantified using scanning electron microscopy–energy dispersive X‐ray spectroscopy. Porosity and AOC/mineral ratio were calculated for thin section images using ImageJ. Laterally developed spodic horizons were twice as thick as vertically developed spodic horizons and contained higher concentrations of Al and Mn but lower Fe and C. Vertically developed spodic horizons had crumb microstructure with higher porosity, while laterally developed spodic horizons were more infilled. Aluminum + 0.5Fe and ODOE in the surface of laterally developed podzols were high and lacked contrast with the spodic horizon, making Spodosol classification problematic. Vertically developed spodic horizons form by solutional translocation and precipitation of AOC under unsaturated conditions. However, laterally developed spodic horizons could form via lateral translocation of solutes or physical transport and deposition of colloidal AOC with unsaturated or saturated flow. This study demonstrates the importance of lateral podzolization in producing soils with distinctive morphology, composition, and classification. Future studies or mapping efforts in podzolized catchments should incorporate these different pedogenic processes.
Gillin, Cody P.; Bailey, Scott W.; McGuire, Kevin J.; Gannon, John P.
doi: 10.2136/sssaj2014.05.0189pmid: N/A
A hydropedologic approach can be used to describe soil units affected by distinct hydrologic regimes. We used field observations of soil morphology and geospatial information technology to map the distribution of five hydropedologic soil units across a 42‐ha forested headwater catchment. Soils were described and characterized at 172 locations within Watershed 3, the hydrologic reference catchment for the Hubbard Brook Experimental Forest, New Hampshire. Soil profiles were grouped by presence and thickness of genetic horizons. Topographic and bedrock metrics were used in a logistic regression model to estimate the probability of soil group occurrence. Each soil group occurred under specific settings that influence subsurface hydrologic conditions. The most important metrics for predicting soil groups were Euclidean distance from bedrock outcrop, topographic wetness index, bedrock‐weighted upslope accumulated area, and topographic position index. Catchment‐scale maps of hydropedologic units highlight regions dominated by lateral eluviation or lateral illuviation and show that only about half the catchment is dominated by podzolization processes occurring under vertical percolation at the pedon scale. A water table map shows the importance of near‐stream zones, typically viewed as variable source areas, as well as more distal bedrock‐controlled zones to runoff generation. Although the catchment is steep and underlain by soils developed in coarse‐textured parent material, patterns of groundwater incursion into the solum indicate that well‐drained soils are restricted to deeper soils away from shallow bedrock and the intermittent stream network. Hydropedologic units can be a valuable tool for informing watershed management, soil C accounting, and understanding biogeochemical processes and runoff generation.
doi: 10.2136/sssaj2014.11.0470pmid: N/A
The introduction of information and communication technology (ICT) has fundamentally changed the flow and role of data and information in our increasingly digital society and this also strongly affects soil science. Stakeholders become more knowledgeable and critical. This issue paper raises the question as to how the scientific community, and particularly soil science, can best deal with the implications of the ICT revolution. Problems are evident when studying sustainable development, presenting ”wicked” environmental problems that defy simple, straightforward solutions because many stakeholders are involved with contrasting opinions and interests, only allowing development of alternative options. A suggestion is made to establish Communities of Scientific Practice that interact with societal partners and the policy arena in a long‐duration joint learning mode, promote and safeguard science quality and offer broad career perspectives for soil scientists.
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