Sources of uncertainty in estimation of eelgrass depth limits
- PDF / 617,186 Bytes
- 13 Pages / 547.087 x 737.008 pts Page_size
- 105 Downloads / 177 Views
WATER BODIES IN EUROPE
Sources of uncertainty in estimation of eelgrass depth limits Thorsten J. S. Balsby • Jacob Carstensen Dorte Krause-Jensen
•
Received: 28 February 2012 / Accepted: 29 October 2012 / Published online: 8 January 2013 Ó Springer Science+Business Media Dordrecht 2012
Abstract In coastal areas seagrasses have considerable ecological importance and respond to eutrophication pressures. Seagrasses have, therefore, become an important parameter for assessing ecological status of marine water bodies. In this study we analyzed the sources of uncertainty associated with the monitoring of the maximum depth limit of eelgrass (Zostera marina). Based on a long-term marine monitoring of eelgrass depth limit in Danish coastal waters we estimated the uncertainty contribution of years, divers, transects, and replicates in water bodies and their subareas. For all these components the absolute uncertainty increased with the maximum depth limit. We used either a Spheric or a Gaussian function to describe the relationship between uncertainty and the maximum depth limit for each variable. This parameterization of the depth-specific uncertainty allowed estimation of the total variance associated with monitoring, which can be used to evaluate monitoring
Guest editors: C. K. Feld, A. Borja, L. Carvalho & D. Hering / Water bodies in Europe: integrative systems to assess ecological status and recovery T. J. S. Balsby (&) D. Krause-Jensen Department of Bioscience, Aarhus University, Vejlsøvej 25, 8600 Silkeborg, Denmark e-mail: [email protected] J. Carstensen Department of Bioscience, Aarhus University, Frederiksborgvej 399, 4000 Roskilde, Denmark
designs. The variance components were included in a time budget for optimizing eelgrass monitoring. With a maximum time limit of 100 or 200 h allocated for monitoring, the design that resulted in the lowest variance of the estimated maximum depth limit used 2 or 3 divers, respectively, and involved 2 or 3 years of monitoring and 4–8 transects. Keywords Eelgrass Depth limit Uncertainty Indicator Water Framework Directive
Introduction Eelgrass and other seagrasses are widely distributed in temperate and tropical coastal waters (Short et al., 2011). The meadows provide habitat for a wealth of organisms, some of which complete their lifecycle there, while others use them as hatching and nursery areas. Seagrass meadows also play important roles in the sequestration of carbon and recycling of nutrients, stabilize the seabottom, and protect coastlines against erosion. The many important ecological functions make seagrasses key components of healthy coastal ecosystems (Hemminga & Duarte, 2000). Seagrasses grow in relatively shallow coastal waters with their maximum depth limits potentially extending as deep as light levels allow their growth to balance losses (Dennison, 1987). Seagrass depth limits are, therefore, mainly determined by water clarity (Duarte et al., 2007; Ralph et al., 2007; Krause-Jensen
123
312
et al., 2011). Water clarity is affected by eutrophication (e.g.
Data Loading...
