Benthic animals and plants and what they do to sediments

This chapter explores the interactions of plants and animals with their immediate sedimentary environment. Plants and animals fundamentally change the physical and chemical characteristics of their sedimentary environment. The changes they effect are dependent on their size, living position, feeding mode and mobility. The types of changes are discussed as well as the resultant ability of plants and animals to actually create seafloor habitats and contribute to sediment heterogeneity at both small and large scales. Seafloor habitats are therefore best defined by a mix of physical and biology rather than physical descriptors alone. But the differences between how different animals feed and move and their ability to create structures such as tubes and burrows that influence the flows of oxygen and porewater within the sediments and across the sediment–water interface mean that there are not only a variety of vegetated seafloor habitats but a variety of non-vegetated ones.

Influence of Streambed Heterogeneity on Hyporheic Flow and Sorptive Solute Transport

The subsurface region where river water and groundwater actively mix (the hyporheic zone) plays an important role in conservative and reactive solute transport along rivers. Deposits of high-conductivity (K) sediments along rivers can strongly control hyporheic processes by channeling flow along preferential flow paths wherever they intersect the channel boundary. Our goal is to understand how sediment heterogeneity influences conservative and sorptive solute transport within hyporheic zones containing high- and low-K sediment facies types. The sedimentary architecture of high-K facies is modeled using commonly observed characteristics (e.g., volume proportion and mean length), and their spatial connectivity is quantified to evaluate its effect on hyporheic mixing dynamics. Numerical simulations incorporate physical and chemical heterogeneity by representing spatial variability in both K and in the sediment sorption distribution coefficient ( K d ). Sediment heterogeneity significantly enhances hyporheic exchange and skews solute breakthrough behavior, while in homogeneous sediments, interfacial flux and solute transport are instead controlled by geomorphology and local-scale riverbed topographies. The hyporheic zone is compressed in sediments with high sorptive capacity, which limits solute interactions to only a small portion of the sedimentary architecture and thus increases retention. Our results have practical implications for groundwater quality, including remediation strategies for contaminants of emerging concern.

Comparison of DET, DGT and conventional porewater extractions for determining nutrient profiles and cycling in stream sediments

Passive samplers measurements, especially DET, contributed to understanding of nitrogen transformations and sediment heterogeneity influenced by benthic microalgae, rooted aquatic plants and/or diel light cycles. Measurement capabilities varied considerably, especially for NH4–N.

Subsurface heterogeneity in the geological and hydraulic properties of the hummocky Paris Moraine, Guelph, Ontario

The advance and retreat of ice lobe margins of the Laurentide Ice Sheet formed moraines that are a prevalent feature throughout southwestern Ontario. In contrast to the well-studied stratified moraine complexes, recessional and end moraines have largely been ignored in the context of hydrogeological studies. Recent urban growth has led to development pressures on these moraines and a need to better understand their hydrogeology. This study presents data sets from the Paris Moraine near Guelph, Ontario, to examine its geomorphology, internal composition, and the corresponding hydraulic properties of these ice-marginal features. The moraine’s geomorphic elements were mapped using high-resolution Global Positioning System transects, aerial photograph analysis, and ground truthing. Nine continuous sediment cores were recovered to determine the nature and distribution of subsurface sedimentary units and their relation to the regional stratigraphic framework. Cores were described in detail using standard sedimentological techniques, and significant sediment heterogeneity was observed in cross sections. Grain-size analyses of over 150 samples provide site-specific estimates of saturated hydraulic conductivity. In addition, saturated hydraulic conductivity was measured on 104 samples using the falling head permeameter method. This study found that different scales of sediment heterogeneity occur across the moraine and the associated till plain and outwash. In contrast, the hydraulic conductivity varies much less. It is expected that certain sedimentary units at specific depths will impact groundwater flow at the centimetre to hundreds of metres scale, which is significant in environmental site assessments or for understanding contaminant hydrogeological problems.