Effects of sampling time and depth on phytoplankton metrics in irrigation ponds

Authors: SMITH, JACLYN - Orise Fellow; Stocker (ctr), Matthew; WOLNY, JENNIFER - Food And Drug Administration(FDA); Pachepsky, Yakov

Submitted to: Journal of Phycology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 3/30/2024
Publication Date: 4/4/2024
Citation: Smith, J., Stocker, M.D., Wolny, J., Pachepsky, Y.A. 2024. Effects of sampling time and depth on phytoplankton metrics in irrigation ponds. Journal of Phycology. 11(4): Article e74. https://doi.org/10.3390/environments11040074.
DOI: https://doi.org/10.3390/environments11040074

Interpretive Summary: Monitoring microscopic organisms comprising phytoplankton is essential for irrigation water quality assessment, especially with regard to the harmful algae blooms. Cell count and photosynthetic pigment concentration measurements present two approaches to characterizing phytoplankton communities. The objective of this work was to find out if time and depth of sampling water may affect phytoplankton monitoring results in a predictable way. The study was carried out at two irrigation ponds in Maryland. Depth was the significant factor of photosynthetic pigment variations during the first half of the day, and time of day was significant in about 50% of cases. Algae cell counts did not show significant dependence on depth, and were dependent on time of the day in 30% of cases. Results of this work can be useful for water quality monitoring professionals in that they indicate the need and direction on standardizing water sampling for phytoplankton monitoring.

Technical Abstract: Water quality of irrigation ponds is affected by phytoplankton. Spatiotemporal variation of phytoplankton population needs to be accounted for to assess the role of phytoplankton as the water quality factor. Cell accounts and photosynthetic pigment concentrations are two major types of metrics used to characterize the phytoplankton populations in water bodies. The objective of this work was to evaluate depth and time of the day as factors affecting the phytoplankton population in irrigation ponds. Cell counts of green alga, diatoms , cyanobacteria., and dinoflagellates as well as chlorophyll A and phycocyanin concentrations were determined in samples taken at the surface and at depth with 0.5 m increments in five spatial replications at 9 am. 12 pm, and 3 pm in two irrigation ponds in Maryland. Twelve water quality parameters were measured in water samples. Depth was the significant factor for photosynthetic pigments variation photosynthetic pigment concentrations in both ponds on most of sampling dates. Time of the day was significant in half of daily datasets. Depth was not a significant factor of variation of cell counts for any of the algae functional groups; time of day was a significant factor in 30% of daily datasets. Two distinctly different patterns in the normalized pigment concentration daily variation were observed. The first one featured a continuous decrease with depth and another included maximum concentrations as surface in the morning changing to maximum at 0.5 m at noon and at 3 PM. Differences in morning solar irradiance values corresponded to difference in patterns in pond 2. Depth as a significant factor of photosynthetic pigments has to be standardized in the phytoplankton monitoring designs.