Pore water pressure

About: Pore water pressure is a research topic. Over the lifetime, 11455 publications have been published within this topic receiving 247670 citations. The topic is also known as: pwp.

Miniaturized photometrical methods for the rapid analysis of phosphate, ammonium, ferrous iron, and sulfate in pore water of freshwater sediments

Abstract: Pore water analysis is a challenge for routine analysis methods, because of the small sample volume available and large sample numbers required for a high spatial resolution. To overcome the restrictions of established methods, this study presents a miniaturized photometrical method for the rapid analysis of phosphate, ammonium, ferrous iron, and sulfate in pore water of lake sediments. The method can cope with large sample sets (> 1000) and minimizes the sample volume to about 250 µL. Standard photometric methods were modified for the use of microtiter plates (microphotometry), which allow the simultaneous determination of up to 100 samples by a microtiter plate reader. The advantage of this analytical technique is the minimal sample consumption, which enables new approaches for pore water sampling and analysis on a microscale level. In combination with a 2-dimensional dialysis sampler, it is now possible to obtain spatial patterns of pore water concentrations (SRP, NH4+, Fe2+, SO42−) with a high vertical and lateral resolution (9 mm). This approach shows the common 1-dimensional view of pore water profiles to be insufficient. Furthermore, the application examples yield new insights on lateral heterogeneity as well as nutrient mobilization and redox processes associated with the formation of microzones around biogenic structures, such as roots or macrofaunal burrows.

Effect of macrozoobenthos on two‐dimensional small‐scale heterogeneity of pore water phosphorus concentrations in lake sediments: A laboratory study

Abstract: We used mesocosms equipped with two-dimensional (2D) pore water samplers (24 rows 3 24 columns, 9-mm spatial resolution) to resolve and quantify some of the complex spatial patterns in diagenetic reactions produced by irrigated biogenic structures. The mesocosms were filled with an organic-, iron-, and phosphorus-rich sediment, and chironomids and oligochaetes were added in high densities to three of six mesocosms; the other three mesocosms served as controls. In the mesocosms without macrozoobenthos, a classic redox zonation developed. In the mesocosms with macrozoobenthos, profiles of redox-sensitive dissolved species were less steep in the vicinity of the sediment‐water interface, and more irregular throughout the sediment, than in the mesocosms without macrozoobenthos. Furthermore, pore water P concentrations were decreased overall and showed much more small-scale 2D heterogeneity in the mesocosms with macrozoobenthos than in the controls. A comparison of the calculated heterogeneity indices of pore water P concentrations (the ratio of horizontal to vertical flux components) of this laboratory study with in situ-determined indices of previous studies indicates that the presence of macrozoobenthos is the major factor causing heterogeneity. A conceptual model of the effects of macrozoobenthos on biogeochemistry along with pore water and sediment analysis showed a close coupling of P cycling with iron and sulfur cycling. This led to the conclusion that pore water P concentrations and heterogeneity were mainly redox-controlled by association of P with iron oxyhydroxides precipitating along oxidized burrow walls, and not a consequence of mineralization processes occurring in organic-rich ‘‘hot spots’’ of increased P turnover. Decreased P release rates accompanied addition of macrozoobenthos and indicated that redox control of P release by iron oxyhydroxide precipitation and dissolution was of major importance. Pore water phosphorus (P) concentration gradients in the upper zone of lake sediments are used to estimate the magnitude of internal P loading to lakes. In addition, they provide insight into early diagenetic processes (Urban et al. 1997). Although the existence of microniches (Wilson 1978) and spatial heterogeneity (Rhoads 1974) in sediment was already reported in the 1970s, lake sediments are often still assumed to be one-dimensional (1D) systems with a sequentially layered, laterally uniform redox zonation. For example, in many studies, the time series of soluble reactive P (SRP) pore water concentrations are discussed without considering small-scale spatial variability, which might be more important than temporal variability (e.g., de Vicente et al. 2003). This simplified view has persisted. Previously, an increasing number of authors have shown that most turnover does not occur in sequentially layered zones, but instead occurs in discrete, highly reactive sites (Brandes and Devol 1995; 1