RiverWatch October 2023: A Sea of Green
For months now, river park ponds have been turning green. Atmospheric rains early this year brought an unprecedented level of runoff, including water that took a trip through historic agricultural areas on the way here. Clearly, this runoff brought nutrients with it, because ever since then we have been growing a crop of our own.
So what are we looking at? DUCKWEED. Ducks in duckweed, below right. Not algae, not slime, not scum, at least not so far. We are looking at millions of tiny aquatic plants that are edible to fish and wildlife and may actually improve the water.
Not so happy are other plants or animals who would like more sunlight to reach into the pond; duckweed truly does take over. And dissolved oxygen in the water is a concern, potentially leading to the die-off of fish if oxygen levels get too low.
But in sunny conditions duckweed produces more oxygen than it consumes, it removes minerals from water such as lead, copper, zinc, and aresenic, it removes excess nutrients and fixes carbon dioxide. Around the world, duckweed (Lemna minor) has been cultivated and used to treat wastewater, to feed livestock, and to produce biofuel. The ducks tell us it is high in protein.
So for the moment at the river park we are letting nature take its course, keeping an eye on the ponds and watching for ill effects. The birds so far are supremely unbothered; today there were fifteeen egrets and two blue herons swanning about.
The San Diego River still flows underneath, and we have small areas of surface flow that might keep the wetlands sufficiently fresh. As we head into another fall and winter with possible rain, we are as curious as anyone to see what will happen next.
Speaking of exuberant invasives, the photo above shows both a problem and a solution. The sneaky yellow flowers in front are the mustards that have been blooming non-stop this year, and the tarp on the ground is the low-tech, herbicide-free method we are testing out to address them. Mustards do tend to crowd out native species, and in selected areas we are looking to eradicate not just the plants but the seeds on the ground as well. Will report back when we are ready to re-plant!
San Diego Gives
Sincere thanks again to everyone who participated in San Diego Gives and our Day of Service in September! Volunteers and staff pulled a literal ton of trash out of the river bed, it was truly work well done - and generous donors gave $6,600 in support of the river park. Our team could not be more grateful!
Lakeside's River Park Conservancy is a private 501(c)(3) non-profit organization, which means that we raise our own funds for operations. Project grants allow us to do work that fulfills our mission, but individual donations literally help to keep the lights on. Please consider donating today! Thank you.