Projects

Lower Lakes Aquatic Vegetation Survey Project

Project report in PDF can be viewed here

PROJECT CATEGORY: Aquatic Vegetation Survey

PROJECT LOCATION: Chatcolet, Benewah and Round Lakes

SITE CHARACTERISTICS: Generally shallow water (maximum depth in study area 35 feet) with extensive submersed plant growth

PROBLEM DESCRIPTION: This project has been designed to address significant data gaps on aquatic vegetation present in the three lakes which surround the mouth of the St. Joe River at the south end of Coeur d'Alene Lake: Benewah, Chatcolet and Round Lakes. These lakes are each shallow systems with considerable potential to support submersed plant communities. This study is warranted by the following needs:

• need for biomass and distribution data on which to base harvest plans and effectiveness assessments,
• need for species-specific nutrient content data to develop estimates of nutrient release (loading) to the three lake systems and CDA Lake proper (this also would effect harvest plans), and
• need for surveillance to document the presence or absence of invasive, noxious aquatic species such as Eurasian watermilfoil.

DESCRIPTION OF FINDINGS: Preliminary findings are that there are seven submersed species, or groups of species which are prevalent throughout the study area; these Ceratophyllum demersum, Elodea species, Myriophyllum species, Najas species, Potamogeton praelongis, P. robinsii and other thin-leafed Potamogeton species. Visually, overall, Elodea species and Potamogeton species were the dominant plants. However, the noxious species M. spicatum was found to be widespread with areas of Chatcolet and Round Lakes being dominated by this canopy-forming species. The presence of M. spicatum as well as a M. spicatum-M. sibericum hybrid was verified through DNA sequencing analyses. (Biomass and nutrient content data were not available at the time of this writing).

DESCRIPTION OF RESEARCH METHODS:

1. Survey transects: The quantitative sampling is a modification of a "line intercept" method where samples are collected along a fixed line which is oriented from a start point on shore by a compass heading. Along this line samples are collected using SCUBA techniques at 1.0 foot depth intervals. At an onshore location, all collected plant materials are sorted by species for drying and weighing by a contract laboratory. Biomass and nutrient content analyses (for phosphorus and nitrogen compounds) are performed on selected samples following standard methods (APHA 1992 or more recent). There are 21 transects planned for the first year and several (up to five) transects will be re-sampled the second year as an effort to determine variability. Up to 16 new transects will be laid out and sampled the second year, based on the species distribution seen in the initial 21 transects. Transect sampling will be performed during the July-August period of maximum biomass.
2. Grid sampling: For this effort a grid with 250 meter intervals will be set up across the project area using GIS mapping techniques. Using GPS equipment, each grid point will be located and one toss made with a weighted "rake-on-a-rope". Species present in each toss at each sample site will be recorded. This sampling is to be performed following the transect surveying (i.e. mid August to mid-September). During the second year of the survey a second set of 360 grid nodes will be selected and sampled using the rake-on-a-rope method.
3. Milfoil inspection: This will be a one-time effort which will involve using SCUBA techniques to inspect the area around (within 100 meters radius) of the four existing boat launches for presence of Eurasian watermilfoil or other nuisance species. Two divers and a support boat / operator with GPS capabilities will be complete this work. A sample of any suspect plants will be collected and submitted to expert review if there is any doubt of the specific species.
4. Nutrient Release research: A literature search and communications with university researchers and others will be performed to collect available information on nutrient release from aquatic plant species. This will be performed following the first years sampling and will focus on those species that are found to be present.

PROJECT GOALS & OBJECTIVES: Specific objectives are to perform diver collection of submersed aquatic vegetation species along set transects, and to perform additional sampling at randomly selected grid intersections using remote (rake-on-a-rope) techniques. All diver-collected samples will be sorted by species and each species sample dried to obtain a standard biomass estimate. Sub-samples of diver-collected plants will be analyzed to determine nutrient (phosphorus and nitrogen) content. Samples collected at grid intersection sites will be sorted to identify species present. Based on the nutrient content data and published literature on species specific nutrient release rates, estimated nutrient loading from submersed plants will be calculated.

Project photographs:

Photo 1. Workers preparing for SCUBA sampling of transect, 7/04.

Photo 2. Worker inspecting rake sample for species presence, 8/04.