I will be sampling for larvae of the intertidal insect species that I study, and I am hoping to collect some environmental variables for each sampling site. The larval habitat for my species consists of a matrix of sediment and macroalgae that grows on rocks in the lower intertidal zone (see photos for examples). Since the habitat is exposed during low tides, I would like to know how hot, dry, and saline the larval habitat can get in order to understand what conditions the larvae must withstand. My idea so far was to use a soil moisture probe, soil salinity probe, and a laser thermometer, but maybe there is a better way to get these data. Any advice would be greatly appreciated! Thanks!
You could potentially obtain pore water from the sediment at location or laboratory. Yet, this depends on the sediment composition is it soft or "rock hard". For soft sediment rhizons are my preference (https://www.rhizosphere.com/). It costs around 10 per piece, reusage is possible till some extend although this is likely not advised on the website.
Simply, insert the rhizon in the sediment, place a vacuum over it, extract the pore water, freeze for further analysis (ICP or IC). In this case soil salinity and a plurality of other components can be analysed. Depending on the sediment this extraction takes a few minuts for sand, and a few hours for mud/silt. In the later case leave it over night. After usage clean the rhizon on the outside in a bit of water and hang it in demineralized water with a vacuum over it to extract the remaining dirt and water through the filter.
Sticking cores in the field and taking it to the lab is also possible, take a wide pvc (i.e. 15 cm in diameter) stick it into the sediment and place the content in a small bucket. Let is calm down for a day in the laboratory and the insert the rhizon and extract the pore water as the above.
Otherwise taking sediment and centrifuging it in the laboratory is also performed. It is a bit tricky considering you "swing" all substrate down and the pore water up, mixing oxygen in mostly anoxic soil. This might potentially disturb microbial and biogeocheical processes. Yet, it is unclear to me how fast the chemical composition of NH4, NO2, NO3, SO4 changes due to this. It might not be and issue if you are only interseted in the elements . Ca, Fe, P and S do not change so elemental analysis is not affected. Note that Fe concentration can be high and perciptiation of stored porewater is often vissible, this will defenitely be the case in tidal pools, so for ICP acidifying is definitely needed.
Perhaps brings in more ideas
Best,
Is it possible to log the electrical conductivity (proxy for salinity) and temperature of the water in small pools that may remain liquid-filled even if the main part of the sediment surface is exposed? Perhaps the installation of small probes is possible if the data logger is placed above the high tide level.
This could possibly allow the detection of fluctuations in water salinity and water temperature due to short-term evaporation, or does only the long-term mean matter for these algae?
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