Dan Pennock

Landform classification and soil distribution in hummocky terrain, Saskatchewan, Canada

This study presents a classification of distinct, three-dimensional landform elements and examines the relationship between these landform elements and selected soil morphological properties of Udic Boroll soils in southern Saskatchewan, Canada. The classification is based on defined ranges of three criteria derived from topographic data: gradient, profile (downslope) curvature, and plan (across-slope) curvature. Seven landform elements are recognized: convergent shoulders, divergent shoulders, convergent backslopes, divergent backslopes, convergent footslopes, divergent footslopes, and level elements. All of the elements are easily identified in the field.rnrnThe thicknesses of A horizons and depths to calcium carbonate of the soils were consistently greater in convergent versus divergent elements in the same profile group (e.g. shoulders), and showed an overall increase in the sequence shoulders<backslopes<level<footslope elements. Distinct groups of elements emerge from a statistical analysis of the differences between individual and bivariate means of soil morphological properties associated with each landform element. The differences in soil properties among the elements can be largely explained by differences in water movement and distribution in hillslope systems. The results of the study highlight the need to consider land-surface morphology during the development of research designs for soil related studies.

Landscape-scale changes in indicators of soil quality due to cultivation in Saskatchewan, Canada☆

Quantitative assessments of the impact of agricultural practises on soil quality have been hindered by the lack of basic spatial units for designing landscape-scale research projects. This paper builds on the relationship which has been demonstrated to exist between small (5 m by 5 m) slope segments and soil distribution in order to define larger landform element complexes in till landscapes of southern Saskatchewan, Canada. Distinctive pedogenic regimes are associated with these complexes. These complexes were then used to stratify the landscape at four conterminous sites with different cultivation histories and to assess changes in indicators of soil quality. Soil redistribution (as assessed by 137Cs redistribution) has had a major impact on these landscapes. The shoulder and level summit complexes have experienced continued high rates of soil loss. The shoulder complexes have lost 55% of their original soil organic carbon (a loss of 64 mg ha−1) over 80 years and 70% of this loss is attributable to net soil export from these positions. The portions of the footslope complexes dominated by Orthic Black Chernozemic soils initially act as sediment deposition sites in the first 22 years of cultivation, but ultimately this soil is removed from these positions and a moderate decline in soil quality occurs. The Gleysolic-dominated portions of the footslopes and the level depressional complexes occupy 15% of the landscape and are the major long-term sediment depositional sites; the biochemical indicators of soil quality (soil organic carbon and total soil nitrogen) show a major and beneficial increase in these positions.

Greenhouse gas emissions and carbon sequestration potential in restored wetlands of the Canadian prairie pothole region

North American prairie pothole wetlands are known to be important carbon stores. As a result there is interest in using wetland restoration and conservation programs to mitigate the effects of increasing greenhouse gas concentration in the atmosphere. However, the same conditions which cause these systems to accumulate organic carbon also produce the conditions under which methanogenesis can occur. As a result prairie pothole wetlands are potential hotspots for methane emissions. We examined change in soil organic carbon density as well as emissions of methane and nitrous oxide in newly restored, long-term restored, and reference wetlands across the Canadian prairies to determine the net GHG mitigation potential associated with wetland restoration. Our results indicate that methane emissions from seasonal, semi-permanent, and permanent prairie pothole wetlands are quite high while nitrous oxide emissions from these sites are fairly low. Increases in soil organic carbon between newly restored and long-term restored wetlands supports the conclusion that restored wetlands sequester organic carbon. Assuming a sequestration duration of 33xa0years and a return to historical SOC densities we estimate a mean annual sequestration rate for restored wetlands of 2.7xa0Mgxa0Cxa0ha−1year−1 or 9.9xa0Mgxa0CO2xa0eq.xa0ha−1xa0year−1. Even after accounting for increased CH4 emissions associated with restoration our research indicates that wetland restoration would sequester approximately 3.25xa0Mg CO2 eq.xa0ha−1year−1. This research indicates that widescale restoration of seasonal, semi-permanent, and permanent wetlands in the Canadian prairies could help mitigate GHG emissions in the near term until a more viable long-term solution to increasing atmospheric concentrations of GHGs can be found.

Terrain controls on depressional soil distribution in a hummocky morainal landscape

In hummocky morainal landscapes, soil distribution in well-drained landscape positions tends to follow a consistent pattern. Soils in depressions, however, are more difficult to predict reliably. This study had two objectives: (1) to determine the parent material and landscape properties controlling the formation of the different depressional soils; and (2) to use these controls to identify quantitative, terrain-based predictors of soil type in depressions. Only two terrain attributes, specific dispersal area (SDA) and elevation relative to open water bodies, were required to distinguish three main soil groups: Gley Recharge, Non-gley Recharge, and Discharge soils. n nSpecific dispersal area is the downslope area draining flow from a given grid cell. Gley Recharge soils occur primarily at points with SDA of less than 2 m2 m−1, regardless of elevation within a given site, because most of the runoff flowing to a point with very low SDA values will pond or infiltrate vertically rather than flow downslope. Non-gley Recharge soils and Discharge soils both occur at points with SDA of greater than 2 m2 m−1. The majority of the Non-gley Recharge soils occur above 5-m elevation relative to an open water body and the majority of the Discharge soils occur below 5-m elevation relative to an open water body, reflecting the importance of solute cycling in the development of discharge conditions. Buried and depositional soils could not be predicted from current terrain attributes because their profile characteristics were derived from the paleosurface.

Designing field studies in soil science

Field research in soil science ranges from modal profile descriptions in support of soil survey to elaborate manipulative experimental designs. All of these field approaches make a valuable contribution to soil science, but researchers who do not use either classical manipulative experimental or geostatistical designs have little guidance (or encouragement) available to them. Well-designed field research of any type requires a clear definition of the research question; a thorough review of the literature to establish the state of knowledge; definition of the population under study and the elements that comprise it; and choice of appropriate scales for sampling support, spacing, and study extent based on an understanding of the underlying processes. For studies where hypothesis testing is appropriate, the hypotheses should be based on sound biological or physical reasoning, and sufficient replicates should be taken to ensure a reliable test. The major challenge in field research design is the development o...

Dissipation of glyphosate and aminomethylphosphonic acid in water and sediment of two Canadian prairie wetlands

Glyphosate [N-(phosphonomethyl)glycine] is the active ingredient of several herbicide products first registered for use in 1974 under the tradename Roundup. The use of glyphosate-based herbicides has increased dramatically over the last two decades particularly in association with the adoption of glyphosate-tolerant crops. Glyphosate has been detected in a range of surface waters but this is the first study to monitor its fate in prairie wetlands situated in agricultural fields. An ephemeral wetland (E) and a semi-permanent wetland (SP) were each divided into halves using a polyvinyl curtain. One half of each wetland was fortified with glyphosate with the added mass simulating an accidental direct overspray. Glyphosate dissipated rapidly in the water column of the two prairie wetlands studied (DT50 values of 1.3 and 4.8 d) which may effectively reduce the impact of exposure of aquatic biota to the herbicide. Degradation of glyphosate to its major metabolite aminomethylphosphonic acid (AMPA) and sorption of the herbicide to bottom sediment were more important pathways for the dissipation of glyphosate from the water column than movement of the herbicide with infiltrating water. Presently, we are not aware of any Canadian guidelines for glyphosate residues in sediment of aquatic ecosystems. Since a substantial portion of glyphosate entering prairie wetlands will become associated with bottom sediments, particularly in ephemeral wetlands, guidelines would need to be developed to assess the protection of organisms that spend all or part of their lifecycle in sediment.

Trace level determination of selected sulfonylurea herbicides in wetland sediment by liquid chromatography electrospray tandem mass spectrometry

Sulfonylurea herbicides are widely used in crop production on the Canadian prairies and a portion of these herbicides applied to cropland are inevitably lost to surrounding aquatic ecosystems. Little is known regarding the presence of sulfonylurea herbicides in wetlands located amongst cropland. This paper describes a new analytical method for the extraction and the determination of seven sulfonylurea herbicides (thifensulfuron-methyl, tribenuron-methyl, ethametsulfuron-methyl, metsulfuron-methyl, rimsulfuron, nicosulfuron and sulfosulfuron) in wetland sediment. The method provided > 85% analyte recovery from fortified sediment for six of the seven sulfonylurea herbicides with a limit of quantification (LOQ) of 1.0 μ g kg− 1. Tribenuron-methyl had significantly lower recovery compared to the other six sulfonylurea herbicides (LOQ = 2 μ g kg− 1). Mean recovery standard deviations were < 10%. This methodology was used to quantify sulfonylurea herbicide residues in sediment samples collected from prairie wetlands situated within the agricultural landscape of Saskatchewan and Manitoba, Canada. This is the first-known detection of sulfonylurea herbicide residues in prairie wetland sediments. Ethametsulfuron-methyl, sulfosulfuron and metsulfuron-methyl, the three most environmentally persistent of the seven sulfonylurea herbicides monitored in the surveillance component of this study, were most frequently detected in wetland sediment with mean concentrations ranging from 1.2 to 10 μ g kg− 1.

Multi-site assessment of cultivation-induced soil change using revised landform segmentation procedures

The range of soil properties associated with soil taxonomic class results from natural soil formation and soil-changing effects of human activity. My goal was to assess cultivation effects on soil formation and soil organic carbon (SOC) at four cultivated and two native hummocky till sites from the same climatic region of Saskatchewan. A revised landform segmentation procedure was used for comparisons across sites. Neither A horizon thickness nor SOC was related to topographical attributes at the native sites, but both had significant relationships (P = 0.001) with profile curvature (Pearson r= −0.53 and −0.57 for A horizon thickness and SOC, respectively), specific dispersal area (r = −0.40 and −0.54) and plan curvature (r = −0.24 and −0.34) at the cultivated sites. The greatest decreases in A horizon thickness (16 cm) and SOC (56 Mg ha-1) at the cultivated sites occurred in divergent shoulder elements, which have high rates of tillage-induced soil loss. Increases in soil thickness (including depth to ca...

Land Use and Riparian Effects on Prairie Wetland Sediment Properties and Herbicide Sorption Coefficients

Sorption of commonly used herbicides by wetland sediment can provide important information for herbicide fate modeling. The influence of sediment properties on herbicide sorption as a result of different land uses in the wetland catchment is unclear. We examined the effects of land use on the physiochemical properties of wetland sediments and the associations between these sediment properties and herbicide sorption characteristics. Bottom sediments were sampled in 0- to 5- and 5- to 10-cm sections from 17 wetlands under five different land use classes: (i) ephemeral wetlands with no riparian vegetation in a cultivated catchment (ECNR), (ii) ephemeral wetlands with riparian vegetation in a cultivated catchment (ECR), (iii) ephemeral wetlands in a grassland catchment established 4 yr ago (E4G), (iv) ephemeral wetlands in a brome grass catchment established 20 yr ago (E20G), and (v) semi-permanent (SP) wetlands in a multiple-land-use catchment. Sediments were analyzed for total organic carbon (TOC), total inorganic carbon (TIC), pH, electrical conductivity, exchangeable cations (EXCAT), total cation exchangeable capacity (CEC), and percent clay (%clay). Sediment herbicide sorption partition coefficient (Kd) was measured for trifluralin, atrazine, 2,4-D, and glyphosate. The sorption of the herbicides in the sediment increased in the order of 2,4-D < atrazine < glyphosate < trifluralin. The sorption of 2,4-D, atrazine, and trifluralin was positively correlated to TOC, EXCAT, and CEC but negatively correlated to %clay. Glyphosate sorption was negatively correlated to pH, TIC, EXCAT, and %clay. Overall, wetland sediments that were recently cultivated (ECNR and E4G) had lower TOC, TIC, EC, EXCAT, CEC, and Kd values (2,4-D, trifluralin, and atrazine) than sediments that had not been recently cultivated (ECR, E20G, and SP). The ECR wetland sediments had the largest Kd for all four herbicides, suggesting that land use and riparian vegetation have a significant impact on herbicide sorption.

Dissipation of six acid herbicides in water and sediment of two Canadian prairie wetlands

In the present study, an ephemeral (E) and a semipermanent (SP) wetland were divided into halves using a polyvinyl curtain and one-half of each wetland was treated with dicamba (3,6-dichloro-o-anisic acid), bromoxynil (3,5-dibromo-4-hydroxy-benzonitrile), MCPA [(4-chloro-2-methylphenoxy)acetic acid], 2,4-D [(2,4-dichlorophenoxy)acetic acid], mecoprop-P (R)-2-(4-chloro-o-tolyloxy)propionic acid], and dichlorprop [(RS)-2-(2,4-dichlorophenoxy)propionic acid] such that concentrations in the water simulated an overspraying event, thus representing a worst-case scenario for wetland contamination. Water and sediment samples were taken over the 77-d study period to monitor herbicide concentrations. The dissipation of all six herbicides could be described by first-order reaction kinetics. In water, the field half-life (DT50) values ranged from 2.3 d (bromoxynil) to 31 d (dichlorprop). All six herbicides were detected in sediment samples from both wetlands. Overall, the phenoxypropionic acids (mecoprop-P and dichlorprop) were more persistent than the phenoxyacetic acids (2,4-D and MCPA) in both sediment and water. Use of bromide ion as a conservative tracer indicated that infiltration through sediment was an important route of water loss in both wetlands, especially in wetland E. Because strong correlations were found between the mass of each herbicide and bromide ion mass in wetland SP (r(2) u2009= 0.59-0.76) and wetland E (r(2) u2009= 0.80-0.95), it is likely that herbicide dissipation was due, in part, to mass lost by way of infiltration through sediment.