Submerged plant data: answering the what, where and why
Mary de Winton
A database of submerged plant records can be used as a tool to describe lakes and to identify major influences on the composition and distribution of lake vegetation.
Plants growing within lakes integrate changes in environmental conditions over time, and so can tell us a lot more about a water body than “snapshot” measurements of physical or other biological parameters. Moreover, our understanding of how plants relate to lake condition is increasing. In order to improve access to ecological information on submerged plants in New Zealand water bodies, NIWA is developing the NIWA Aquatic Plant Database. This will enable a wealth of information on submerged plants to be accessed and analysed for use by water body managers and researchers alike.
The NIWA Aquatic Plant Database
NIWA currently maintains the database containing over 12,000 plant records from 113 different lakes. These records have been collected over the last 20 years, using a SCUBA survey technique (see “Plumbing the depths”).
To identify surveyed lakes, the database includes unique codes for 988 New Zealand water-bodies. As lakes are often surveyed more than once, a visit number is also assigned for each survey date. Records are then entered by code for each plant species, at each lake site, and associated ecological data are listed. This information can then be retrieved and analysed based on any combination of the identity codes.
Future developments
It is planned to provide web page access to summary information from the database. Soon it will be possible for web users to view maps showing the distribution of New Zealand’s worst water-weeds, or a list of the submerged plants found in a selected lake, their depth range and a measure of abundance. These data can be used for inventories of local flora, State-of-the-Environment reporting, or for assessing weed risk.
NIWA’s database also provides a tool for researchers to discover how plants and lake conditions are inter-related (see “Data for diversity” and “Predicting plant patterns”).
Interpreting data
Teachers: this article can be used for Biology L7 A.O. 7.3. See other curriculum connections at www.niwa.co.nz/pubs/wa/resources
Submerged plants are sensitive indicators for changing water quality, hydrology or aquatic biodiversity. Plants respond to influences over time frames of months to years, so they time-integrate the prevailing lake conditions. Also, they cannot move to escape from unfavourable influences! Therefore, significant changes in the composition and distribution of vegetation mirror change in the state of a lake.
Submerged plants survive short-term reductions in water clarity, but they die if they don’t receive enough light over the long-term. Survey data that show changes in the abundance and depth range of submerged plants can alert water managers to significant water clarity changes in a lake. In response, actions to identify the direction and degree of change (for example, intensified water quality monitoring) can be initiated.
Invasive, introduced water-weeds out-compete native submerged plants, leading to uniform beds of a single species. This has repercussions for lake habitat diversity – for example, see Claustrophobic fish: how do aquatic plants affect fish that feed on invertebrates? With knowledge of the current distribution of a weed species and recent spread, managers can assess the risk of weed introduction to a lake.
We’ll keep you posted!