A high‐resolution pore water sampler for sandy sediments

Abstract

In this paper, we present a new technique for collecting pore‐water samples in coarse‐to fine‐grained sandy sediments. We have used the technique both for in situ sampling and for pore‐water extraction from sediment cores brought back to the laboratory, in both cases with a depth resolution as fine as 1 cm. The key device is a long, thin (~2 mm) stainless steel tube with a specially designed tip that functions as a filter. Pore‐water samples are collected by inserting the tube into the sediment at the desired depth and applying a light suction from a syringe connected to the tube. The sample is injected immediately into a vial through a syringe filter and stored for later analysis. The technique has some clear advantages over other methods that are used commonly in sandy sediments. In comparison with lysimeters or sippers, it gives pore‐water samples with a much higher depth resolution, which often is needed to accurately estimate fluxes across the sediment‐water interface or transformation rates of solutes within the sediments. In comparison with dialysis cells or peepers, the new technique gives measurements that truly represent the time of collection. This can be crucial when non‐steady‐state systems are studied. Furthermore, disturbance of the sediment is minimal because of the small dimension of the tube. This is especially important in vegetated sediments, in which the deployment of larger conventional samplers is likely to cause significant disturbance. Finally, sample extraction is less laborious than other techniques, requiring only one site visit and typically <1 min of sampling time per sample. In laboratory tests using a dye tracer, we showed that pore water was drawn evenly toward the tube tip from all directions in the surrounding sediment. On the basis of these results, we provide guidelines for choosing the appropriate sampling depth intervals as a function of the sample size. Data from representative pore‐water profiles are presented for PO432 from vegetated coarse‐grained carbonate sediments in the Bahamas and NH4+1 from fine‐grained unvegetated sands in a temperate coastal lagoon in Virginia.

Genetic diversity enhances the resistance of a seagrass ecosystem to disturbance

“…nigricans) migrated into our study site and consumed a significant amount of the eelgrass in our plots (see Results). At the end of the fourth month (just before grazing by the geese) and the end of the 10th month (after the plots had recovered to predisturbance shoot density), we sampled sediment porewater ammonium concentration (23,24) and epiphyte biomass (25), following standard procedures. Ammonium concentrations were used as a measure of resource availability, because ammonium can be a limiting nutrient for Zostera growth (25).…”

Nitrogen Uptake by Native and Invasive Temperate Coastal Macrophytes: Importance of Dissolved Organic Nitrogen

“…The porewater volume of the core was estimated to be 1.55 l using the porosity of marsh soils (∼0.85) near this field site (Thomas 2004). During the falling tide, all cores were amended with either 25 μmols of combined amino acid-N (1:1; 15 N, 13 C glycine: 15 N, 13 C glutamic acid), 65 μmols of 15 NH 4 Cl, or deionized water using a highresolution water sampler (Berg and McGlathery 2001) to distribute the tracer uniformly. The cores were inserted on August 2, 2004, and the plant + core remained intact for 4 days, after which the entire plant + core was carefully removed for subsequent analysis.…”

“…On August 16, 2005 bulk porewater at approximately 10 cm in depth was sampled from five S. alterniflora and five introduced Phragmites locations in the OM marsh using the high-resolution porewater sampler (Berg and McGlathery 2001). Samples were filtered (GHP Pall, 0.45 μm) and frozen for subsequent porewater N determination.…”

Submersible‐operated porewater sampler for permeable sediments

“…Alternatively, the sediment probe could be constructed from a set of thin stainless-steel tubing or needles used to collect porewater from specific depths (e.g., Duff et al 1998;Berg and McGlathery 2001;Burdige and Zimmerman 2002). However, the small sampling ports of such needle probes are prone to clogging in less than well-sorted sands (i.e., those with an appreciable amount of silt).…”