What can you do when your pond shows evidence of eutrophication?

During the 2006-2007 school year, before Deppe Pond had a aerator installed a red water fern, most likely a member of the Azolla sp. (possiblly Azolla ruba), would take over the surface of the pond during the spring and fall months. This would generally follow our efforts to remove emergent species such as cattail and bulrush which stirred up sediments. After the pond was drained, dried, refilled, and an aerator was installed during the spring of 2007-2008, the azolla "blooms" disappeared but green filamentous algae began to grow along the bottom and raise to the surface as trapped gasses made it more buoyant. I believe both "blooms" were due to the eutrophication of the pond (its sediments and water). One element that did change between 2006-2007 azolla bloom and the 2007-2008 alga bloom, besides adding aeration in the spring of 2008, was the water source. Before the spring of 2008, Deppe Pond was filled by either urban runoff or with city water. After April 2008, only well water was used. I believe this fact begs that we test the water quality of the well water. More about that later.

It is our contention that fertilizer used on the lawn surfaces adjacent and uphill of Deppe Pond is the major nutrients that seem to be encouraging the increase in algae growth after the Spring on 2008. Plans will be put into place to decrease the application rates of fertilizer (if not stopping that practice altogether) of the “upstream” lawn surfaces. In the meantime the students and I have decided that we can possibly reverse the eutrophication process by harvesting the algal mats (and the nutrients they contain) that collect on the surface of the pond every month and compost the detritus at the greenhouse. Initial, we would rake and pitchfork what we could collect from the side. That proved to be a rather laborious process. So I tasked 4 students to design a tool that we could use both in Deppe Pond and in Tui Slough. The result worked beautifully.

It had to float and be sturdy, so we used closed–ended PVC. It need to be no wider that the narrowest point across Tui Slough, so it is 15 ½ feet long. It needed to be pulled from both sides, so there is a fixed center pull line. The line we used needed to be able to reach across the widest part of Deppe Pond, so the lines are 100 feet long. We needed to have anchored guidelines, so the ends of the 15 ½ foot PVC span have four foot guides, making it look like a wide capital H or I-------------------I, with a pair eye hooks to run two 100 foot anchor lines through. The last addition was a wire mesh (edging used to reinforce dry walled corners in homes) that was zip-tied along the length of the 15 ½ foot cross bar. This mesh provided the needed grabbing ability that our “algae-raker” would need. As you can tell from this slideshow, the device worked wonderfully. The best part of the whole process, however, was all the team work that went into its design (Thanks to Jeff Freed and Ethan Sockwell) and the teamwork that is needed to use our new "scum-raker" (the rest of the Mojave River Conservation class). (Patent Pending :^) ).