by Terry McNabb, CLM
Aquatic Biologist/Certified Lake Manager, Aquatechnex
This Kitsap Lake bathymetry map helped us develop treatment recommendations.
Us “old” lake managers have seen significant shifts in our ability to accurately and remotely obtain the data we need to make decisions. Before GPS/GIS mapping, we created bathymetry maps by doing soundings along a line and connecting the dots. We used dot grids over air photos to estimate acres. We used shoreline landmarks to apply products. Things have come a long way, although it is nice to know how to do it the old way just in case.
Hydro-acoustic mapping and remote monitoring are two effective tools we have adopted in our work.
This is the Kitsap Lake sediment hardness map. The HEAT map and color ramp show conditions of sediment. Lighter colors equal organic soft sediments.
Hydro-acoustic mapping uses a sonar data logger to take readings along transects the boat drives across the lake surface. The unit collects a DGPS (differential global positioning system) location every two seconds along with the sonar reading. This data is uploaded to a cloud server with algorithms that process the data creating three types of maps. This technology creates high-resolution bathymetry maps and calculates exact water volume. It creates an aquatic plant biovolume map that shows the location, shape and density of submerged aquatic plant communities. It creates a sediment composition map that shows variations from rock substrate to soft organic fluff.
Aquatechnex’s Kitsap Lake project is a case in which bathymetry and bottom hardness helped us develop a phosphorus management plan that has led to stunning results. Kitsap Lake had experienced several years of summer-long closures due to toxic conditions from excessive cyanobacteria. The hydroacoustic bathymetry map helped us calculate the exact water volume of the lake, which was used to determine dosing rates for phosphorus-sequestering technologies. The bathymetry map was also used in conjunction with a dissolved oxygen/temperature profile to map the water locations and volume under the thermocline. The cost to map this 250-acre lake was $1,500.
Our data suggested that an early summer water column stripping application of EutroSORB (a lanthanum modified clay) would help suppress the blooms, while a second application in late summer before fall turnover would target the sediment-released phosphorus accumulating in the hypolimnion.
The results have been impressive. Water clarity has improved dramatically with summer Secchi disk readings of 15 feet or better. Hypolimnion late summer phosphorus levels have dropped dramatically as well. See a video of this project at: https://vimeo.com/757177417
This Osoyoos aquatic plant biovolume map shows the location and shape of aquatic plant beds. The HEAT map color ramp shows no vegetation (blue) to 100% of water column filled (red). Note that much of this area does not need to be reviewed as no plants are present.
Our Eurasian milfoil control work at Lake Osoyoos has also been sharpened by hydroacoustic mapping. This lake, which straddles the United States-Canada border, has over ten miles of shoreline and littoral area in the US. Water clarity is also often poor.
We performed an initial hydroacoustic survey to map the location and extent of aquatic plant communities. The survey work to cover the entire littoral area of the lake took most of a day. The hydroacoustic data was uploaded and processed to create maps locating vegetation in the lake. This map was then used to “ground truth” as we traveled to known aquatic plant beds, determined species present and created treatment maps. Much of the littoral zone was rocky and free of milfoil; this helped us avoid using more time-consuming techniques looking at locations with no plant growth. Using Procellacor herbicide, we have selectively targeted and removed this invasive weed from large portions of the US side. Procellacor received Canadian registration in April 2023 and we are looking forward to getting after the feeder crop north of the border.
This Algaetracker buoy reports conditions to a web page, which we review daily to determine which lakes need attention.
Remote monitoring tools that report wirelessly to cloud computing systems are also playing a more important role in our work. The Algaetracker buoy is a technology we have deployed in a number of our urban lakes that require frequent algae treatments to combat cyanobacteria. Before working with the Algaetracker, we had to visit these lakes regularly through the summer to monitor conditions. The Algaetracker measures chlorophyll a and phycocyanin (a pigment unique to cyanobacteria) and reports to the cloud-based web page every 15 minutes. Now our teams can review a significant number of lakes each morning, see which lakes need attention and which are just fine. We dispatch crews based on this information.
The last example would be Laguna Niguel Lake in Southern California. This lake has had periodic fish kills attributed to low dissolved oxygen levels. In 2014 and 2017, a paramecium bloom occurred almost overnight and these organisms consumed oxygen to the point of significant fishkill. This past year we deployed a remote probe system in the lake attached to a buoy with a wireless data transfer system. We have probes deployed at a number of depths under the buoy and can now see trends and detect problems remotely and investigate when conditions start to deteriorate.
Technology is bringing information to lake managers that allows them to make better decisions and protect the water resources they work with. For more information, contact us through our website at www.aquatechnex.com
Kitsap Lake reduction in hypolimnetic phosphorus from three years of EutroSORB treatments
