Estimation of Submergent Plant Bed Biovolume using Acoustic Range Information

Abstract

1990. Estimation of submergent plant bed biovolume using acoustic range information. Can. J. Fish. Aquat. Sci. 47: 805-81 2.Acoustic nieasurements of the distance between the water surface, top of the aquatic plants, and bottom of the water column were made using chart recording echosounders. The vertical cross sectional area (m2), height (m), biovolume (rn3), of aquatic plant beds and variances were computed for three surveys of Devils Lake, Oregon, in May, July, and September, 1986 when coefficients of variation for the plant bed biovolume estimates were 0.1 8, 0.05, and 0.06, respectively (n = 14). Coefficients of variation for plant biomass estimates (g/m2) computed from SCUBA quadrat samples collected concurrently with the acoustic surveys, were 0.98 (n =48), 0.81 (n = go), and 1.05 (n = 901, respectively. The higher precision of the biovolume estimates allow for a 5-to 18-fold greater capability to detect a change in the mean. -the lower costs of the biovolume estimates allow for a 10-to 33-fold greater precision-for-cost. The plant bed biovolume variable contains ecologically different information than the biomass variable in that it provides a direct estimate of the amount of aquatic habitat in a lake that is influenced by plants; it should prove useful for evaluating plant control practices and possibly for studying plant-fish interactions.Des mesures acoustiques de la distance separant la surface de I'eau et le sorr~met des plantes aquatiques, et le fond de la colonne d'eau ont ete effectuees 2 I'aide d'echosondeurs graphiques. La superficie de la section verticale (m2), la hauteur (m), le volume de vegetaux (m3) et les variations ont ete calcules en mai, juillet et septembre 1986 dans le lac Devils en Oregon, lorsque les coefficients de variation du volume vegetal etaient estimes respectivement 2 0,18, 0,05 et 0,06 (n = 14). Les coefficients de variation des estimations de la biomasse vegetale (g/m2) calcules A partir des echantillons SCUBA de quadrats preleves en meme temps que les releves acoustiques s'elevaient respectivement A 0,98 (n = 48), 2 0,81 (n = 90) et A 1,05 (n = 90) pour les trois releves. La precision plus 6levee de I'estimation du volume vegetal augmente de 5 A 18 fois la capacite de detection d'un changement dans la moyenne. Le coGt inferieur de ces estimations permet d'obtenir un rapport coGt-precision de 10 i 33 fois superieur. La variable du biovolume vegetal donne des informations ecologiques differentes de celles de la variable de la biomasse en ce qu'elle donne une estimation quantitative directe de I'habitat aquatique d'un lac qui est influence par la vegetation; cela devrait se reveler utile pour I'evaluation des methodes de contrale des vegetaux et, eventuellement pour I'etude des interactions vegetaux-poissons.

Quantifying the major sinks and sources of phosphorus in Tabor Lake: implications for management and remediation

“…This greater expense was primarily attributed to the greater labour costs associated with harvesting. Thomas et al (1990) also found the acoustic technique had a higher precision than from quadrat harvests, providing a 5-to-18 fold greater capability to detect a change in the mean. However, the two techniques were comparing slightly different characteristics of the macrophyte community.…”

“…Sparse vegetation included a third variable which was the percent vertical cover of vegetation on the echosound tracings. Thomas et al (1990) compared SCUBA quadrat harvesting to the acoustic method proposed by Maceina and Shireman to determine the relative costs associated with each technique. Over three years of research, the quadrat harvesting method was shown to be 1.9 times more expensive than sampling with an echosounder.…”

“…The acoustic technique estimated biovolume (m3), whereas the quadrat harvest technique estimated biomass (g I m2) . Duarte ( 1987) Maceina and Shireman (1980), Duarte (1987) and Thomas et al (1990) have demonstrated that an echosounder can be used to estimate aquatic biomass (or biovolume) with as much, or greater, precision as quadrat harvesting techniques. In this experiment, an echosounder is used to estimate the biomass of aquatic vegetation in Tabor Lake.…”

“…Thus two models were used depending on the density of macrophytes. Thomas et al (1990) found that sediment was often undetected by the echosounder, especially in dense macrophyte stands. This problem also occurred in the Tabor Lake study.…”

“…The echosound approach introduced by Maceina and Shireman, and modified by Duarte ( 1987) and Thomas et al ( 1990) The problem most frequently encountered during this experiment was the loss of acoustic signals in areas of ultra dense vegetation. Typically, the echosounder would continue to work in these areas until the transducer was engulfed by macrophytes.…”