Contributions of sea weeds to the natural water-purification in a shallow coastal area Matsukawa-ura
Abstract
It has been accepted that seaweeds make a significant contribution to water purification in a shallow coastal area by taking up nutrients from water column. Contributions of seaweeds were examined quantitatively based on field surveys and in situ experiments carried out in the summer and the winter seasons of FY 1999 in Matsukawa-ura, a lagoon located at the northeastern-part of Fukushima Prefecture, Japan. Ulva pertusa (Ana-aosa) and Zostera marina (Amamo) were the dominant species there during the summer season, and their standing crops were estimated to be 291 t and 199 t, respectively over Matsukawa-ura. Monostroma latissimum (Hitoegusa) has been cultured there during the winter season, and its standing crop was estimated to be 370 t. The DlN (dissolved inorganic nitrogen) uptake rate was determined for U. pertusa and Z. marina by in situ experiments to be 4.32 μg・g-wet wt-1・h-1 and 4.99 μg・g-wet wt-1・h-1, respectively at 21℃ during the summer season. The rate was also determined for M.latissimum to be 1.71 μg・g-wet wt-1・h-1 at 10℃ during the winter season. The DIN removal from water column during one tidal cycle (12.5 h) was calculated by multiplying the uptake rate by the standing crop to be 15.7 kg for U. pertusa and 12.4 kg for Z. marina. A tentative one-box model calculation showed that total DIN removal in Matsukawa-ura was 915 kg during the same period, indicating the contribution of the sea weed species was ca. 3% of total DIN removal.
