Genevieve Ali

Spatial relationships between soil moisture patterns and topographic variables at multiple scales in a humid temperate forested catchment

[1] New tools are needed in hydrology to improve our understanding of process heterogeneity and its relationship to catchment topography. We tested the distance‐based Moran’s eigenvector maps (DBMEM) method, which models patterns using a combination of positively and negatively autocorrelated structures, searching for soil moisture characteristic scales in a temperate humid forested system. We focused on three questions: (1) What are the characteristic spatial scales of shallow soil moisture? (2) Is there a strong relationship between soil moisture patterns and topographic variables at these scales? and (3) Which hydro‐meteorological variables influence soil moisture scales and topographic controls in a significant way? Data consisted of 16 surveys of soil moisture at depths of 5, 15, 30, and 45 cm in the 5.1 ha Hermine catchment (Laurentians, Canada). The global DBMEM model explained 21 to 96% (adjusted R square) of the spatial variations in soil moisture apportioned into decreasing fractions over six spatially nested, additive submodels: very large (0.85–1.4 ha), large (0.54–0.85 ha), meso (0.50–0.54 ha), fine positive (0.22–0.50 ha), fine negative (0.10–0.22 ha), and very fine (0.02–0.10 ha). The effects of catchment topography (e.g., slope and contributing area) on soil moisture were significant at large and very large scales. Moisture patterns at these scales were dependent on previous storm properties and were good predictors of catchment response. The DBMEM approach provided insightful quantitative evidence regarding the temporal dependency of the relationships between dynamic soil moisture content and static topographic variables across scales.

Integrating geographically isolated wetlands into land management decisions

Wetlands across the globe provide extensive ecosystem services. However, many wetlands - especially those surrounded by uplands, often referred to as geographically isolated wetlands (GIWs) - remain poorly protected. Protection and restoration of wetlands frequently requires information on their hydrologic connectivity to other surface waters, and their cumulative watershed-scale effects. The integration of measurements and models can supply this information. However, the types of measurements and models that should be integrated are dependent on management questions and information compatibility. We summarize the importance of GIWs in watersheds and discuss what wetland connectivity means in both science and management contexts. We then describe the latest tools available to quantify GIW connectivity and explore crucial next steps to enhancing and integrating such tools. These advancements will ensure that appropriate tools are used in GIW decision making and maintaining the important ecosystem services that these wetlands support.

Groundwater-Driven Wetland-Stream Connectivity in the Prairie Pothole Region: Inferences Based on Electrical Conductivity Data

This study examined the potential for electrical conductivity (EC) to serve as an indicator of groundwater-driven wetland-stream connectivity in the Prairie Pothole Region. Focus was on the Broughton’s Creek Watershed (Manitoba, Canada) where thirteen wetlands and a creek were monitored in 2013–2014. A connectivity index (CI), computed by incorporating EC data in a hyperbolic solute export model, identified a potential for both shallow and deep groundwater-driven wetland-stream connectivity to occur, although shallower connections were rarer. Both raw EC and CI values were strongly correlated to wetland volume capacity, indicating the importance of storage and flow generation processes for wetland-stream connectivity potential. The proposed CI was instrumental in reaching that conclusion, making it a simple yet physically-based metric of wetland behavior that should be tested in multiple environments to confirm or infirm its validity.

Phosphorus export dynamics and hydrobiogeochemical controls across gradients of scale, topography and human impact

Concentration-discharge (c-Q) plots are routinely used as an integrated signal of watershed response to infer solute sources and travel pathways. However, the interpretation of c-Q data can be difficult unless these data are fitted using statistical models. Such models are frequently applied for geogenic solutes, but it is unclear to what extent they might aid in the investigation of nutrient export patterns, particularly for total dissolved phosphorus (TDP), which is a critical driver of downstream eutrophication problems. The goal of the present study was therefore to statistically model c-Q relations (where c is TDP concentrations) in a set of contrasting watersheds in the Northern Great Plains – ranging in size from 0.2 to 1000+ km2 – to assess the controls of landscape properties on TDP transport dynamics. Six statistical models were fitted to c-Q data, notably (i) one linear model, (ii) one model assuming that c-Q relations are driven by the mixing of end-member waters from different landscape locations (i.e., hydrograph separation), (iii) one model relying on a biogeochemical stationarity hypothesis (i.e., power law), (iv) one model hypothesizing that c-Q relations change as a function of the solute subsurface contact time (i.e., hyperbolic model), and (v) two models assuming that solute fluxes are mostly dependent on reaction rates (i.e., chemical models). Model performance ranged from mediocre (R2 0.9), but the hydrograph separation model seemed most universal. No watershed was found to exhibit chemostatic behavior but many showed signs of dilution or enrichment behavior. A tendency toward a multi-model fit and better model performance was observed for watersheds with moderate slope and higher effective drainage area. The relatively poor model performance obtained outside these conditions illustrates the likely importance of controls on TDP concentrations in the region that are independent of flow dynamics.

Analysis of hydrological seasonality across northern catchments using monthly precipitation–runoff polygon metrics

Abstract Seasonality is an important hydrological signature for catchment comparison. Here, the relevance of monthly precipitation–runoff polygons (defined as scatter points of 12 monthly average precipitation–runoff value pairs connected in the chronological monthly sequence) for characterizing seasonality patterns was investigated to describe the hydrological behaviour of 10 catchments spanning a climatic gradient across the northern temperate region. Specifically, the research objectives were to: (a) discuss the extent to which monthly precipitation–runoff polygons can be used to infer active hydrological processes in contrasting catchments; (b) test the ability of quantitative metrics describing the shape, orientation and surface area of monthly precipitation–runoff polygons to discriminate between different seasonality patterns; and (c) examine the value of precipitation–runoff polygons as a basis for catchment grouping and comparison. This study showed that some polygon metrics were as effective as monthly average runoff coefficients for illustrating differences between the 10 catchments. The use of precipitation–runoff polygons was especially helpful to look at the dynamics prevailing in specific months and better assess the coupling between precipitation and runoff and their relative degree of seasonality. This polygon methodology, linked with a range of quantitative metrics, could therefore provide a new simple tool for understanding and comparing seasonality among catchments. Editor Z.W. Kundzewicz; Associate editor K. Heal Citation Ali, G., Tetzlaff, D., Kruitbos, L., Soulsby, C., Carey, S., McDonnell, J., Buttle, J., Laudon, H., Seibert, J., McGuire, K., and Shanley, J., 2013. Analysis of hydrological seasonality across northern catchments using monthly precipitation–runoff polygon metrics. Hydrological Sciences Journal, 59 (1), 56–72.

Hydroclimatic influences and physiographic controls on phosphorus dynamics in prairie pothole wetlands

While wetlands are known as long-term storages or sinks for contaminants, not all are equally effective at trapping phosphorus (P). The prevalence of P-sink behavior in prairie pothole wetlands remains unclear, especially across gradients of human disturbance. The objectives of the current study were three-fold: (1) characterize the spatiotemporal variability of wetland hydrology and wetland water P concentration across a range of prairie potholes; (2) establish the propensity of different pothole wetlands to act as sources or sinks of P; and (3) assess the potential controls of climatic conditions, landscape characteristics, wetland soil physiochemical properties and local hydrology on source versus sink dynamics. Ten intact and three consolidated (i.e., drained) wetlands located in southwestern Manitoba, Canada, were monitored for water level fluctuations and water soluble reactive P (SRP) concentration over two years with contrasting antecedent wetness conditions. Soil cores were also collected to measure soil physiochemical properties such as the equilibrium phosphorus concentration (EPC). Water column SRP concentrations were compared to EPC values to infer the time-variable source versus sink behavior of each of wetland. Statistical analyses were then performed to assess whether the source versus sink behavior of individual wetlands could be linked to their physiographic or hydrologic characteristics. Results show that some wetlands persistently acted as P sinks while others switched between source and sink behavior. Persistent P-sink behavior was more common with intact wetlands, as opposed to consolidated wetlands. Wetland soil texture, storage volume and short-term water level fluctuations appeared to control the source versus sink behavior of individual wetlands. The dominant controls on P-sink behavior identified under dry conditions were, however, different from those identified under wetter conditions. This study therefore highlights the importance of considering the non-stationary nature of P-sorption dynamics and their controls, even at sub-annual timescales, in the prairie pothole region.

Differing Modes of Biotic Connectivity within Freshwater Ecosystem Mosaics

Abstract We describe a collection of aquatic and wetland habitats in an inland landscape, and their occurrence within a terrestrial matrix, as a “freshwater ecosystem mosaic” (FEM). Aquatic and wetland habitats in any FEM can vary widely, from permanently ponded lakes, to ephemerally ponded wetlands, to groundwater‐fed springs, to flowing rivers and streams. The terrestrial matrix can also vary, including in its influence on flows of energy, materials, and organisms among ecosystems. Biota occurring in a specific region are adapted to the unique opportunities and challenges presented by spatial and temporal patterns of habitat types inherent to each FEM. To persist in any given landscape, most species move to recolonize habitats and maintain mixtures of genetic materials. Species also connect habitats through time if they possess needed morphological, physiological, or behavioral traits to persist in a habitat through periods of unfavorable environmental conditions. By examining key spatial and temporal patterns underlying FEMs, and species‐specific adaptations to these patterns, a better understanding of the structural and functional connectivity of a landscape can be obtained. Fully including aquatic, wetland, and terrestrial habitats in FEMs facilitates adoption of the next generation of individual‐based models that integrate the principles of population, community, and ecosystem ecology.

Supply and Transport Limitations on Phosphorus Losses from Agricultural Fields in the Lower Great Lakes Region, Canada

Phosphorus (P) mobilization in agricultural landscapes is regulated by both hydrologic (transport) and biogeochemical (supply) processes interacting within soils; however, the dominance of these controls can vary spatially and temporally. In this study, we analyzed a 5-yr dataset of stormflow events across nine agricultural fields in the lower Great Lakes region of Ontario, Canada, to determine if edge-of-field surface runoff and tile drainage losses (total and dissolved reactive P) were limited by transport mechanisms or P supply. Field sites ranged from clay loam, silt loam, to sandy loam textures. Findings indicate that biogeochemical processes (P supply) were more important for tile drain P loading patterns (i.e., variable flow-weighted mean concentrations ([]) across a range of flow regimes) relative to surface runoff, which trended toward a more chemostatic or transport-limited response. At two sites with the same soil texture, higher tile [] and greater transport limitations were apparent at the site with higher soil available P (STP); however, STP did not significantly correlate with tile [] or P loading patterns across the nine sites. This may reflect that the fields were all within a narrow STP range and were not elevated in STP concentrations (Olsen-P, ≤25 mg kg). For the study sites where STP was maintained at reasonable concentrations, hydrology was less of a driving factor for tile P loadings, and thus management strategies that limit P supply may be an effective way to reduce P losses from fields (e.g., timing of fertilizer application).

Hydrological dynamics of prairie pothole wetlands: Dominant processes and landscape controls under contrasted conditions

Department of Geological Sciences, University of Manitoba, Winnipeg, Manitoba, Canada Watershed System Research Program, University of Manitoba, Winnipeg, Manitoba, Canada Center for Earth Observation Science, University of Manitoba, Winnipeg, Manitoba, Canada 4 Institute for Wetland and Waterfowl Research, Ducks Unlimited Canada, Stonewall, Manitoba, Canada Correspondence Aminul Haque, Department of Geological Sciences, University of Manitoba, 125 Dysart Road (Wallace Building), Winnipeg, Manitoba R3T 2N2, Canada. Email: haquema@myumanitoba.ca

Evaluating the Effects of Tracer Choice and End‐Member Definitions on Hydrograph Separation Results Across Nested, Seasonally Cold Watersheds

Isotope-based hydrograph separation (IHS) is a widely used method in studies of runoff generation and streamflow partitioning. Challenges in choosing and characterizing appropriate tracers and end-members have, however, led to presumably highly uncertain IHS results. Here we tested the effects of end-member definitions and tracer choices on IHS results in nested Prairie watersheds of varying size and landscape characteristics. Specifically, the consideration of eight potential “new” water end-members, eight potential “old” water end-members, and two stable water isotope tracers led to 80 potential IHS results for each stream water sample. IHS-related uncertainty was evaluated using a Gaussian error propagation method. Results show that choosing an appropriate “new” water end-member is most challenging during the freshet: highly variable “old” water fractions associated with high uncertainties were attributed to changing conditions from melting snow only to rain-on-snow. In summer and fall, it was rather the choice of an appropriate “old” water end-member that was most problematic. IHS results obtained using δ18O versus δ2H as a tracer were significantly different except in the flattest and most wind-sheltered watersheds examined. Overall, δ2H-based IHS results were more uncertain than their δ18O-based counterparts. Recommendations are therefore made toward careful selection of a tracer and a sampling strategy aimed at characterizing the most appropriate end-members for IHS, especially when dealing with seasonally cold watersheds.