Dissolved oxygen under water hyacinth following herbicide application

Authors: MISKELLA, JOHN - University Of California, Davis; Madsen, John; LLABAN, ANGELA - Department Of Fish And Wildlife; HARD, EDWARD - California Department Of Boating And Waterways

Submitted to: Journal of Aquatic Plant Management
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/12/2020
Publication Date: 8/31/2021
Citation: Miskella, J.J., Madsen, J.D., Llaban, A., Hard, E. 2021. Dissolved oxygen under water hyacinth following herbicide application. Journal of Aquatic Plant Management. 59s:82-89.

Interpretive Summary: Natural resource agencies have the commonly held opinion that treating aquatic plants with herbicides will likely result in a depression of dissolved oxygen in the water. This opinion does not have data to substantiate the claim, but it is an assumption that has translated into specific application language on many herbicide labels. To test this hypothesis, we treated floating waterhyacinth with the systemic herbicides glyphosate, 2,4-D, and imazamox, and compared it to an untreated reference plot and to an open water plot. These tests were done in three areas each of channel-side treatments and backbay slough treatments. Our results indicated that typically, the dissolved oxygen grew progressively worse in the untreated plots, while treated plots did not have a reduction in dissolved oxygen. Channelside areas typically had adequate dissolved oxygen for fish, while the backbay areas typically had stressfully low concentrations of dissolved oxygen.

Technical Abstract: The California State Parks Division of Boating and Waterways (CDBW) manages water hyacinth in the Sacramento-San Joaquin River Delta to ensure navigation and fish habitat. Decreasing the amount of water hyacinth in the Delta should increase the proportion of oxygenated water for fish habitat and migration. However, some water resource management personnel are concerned that plant decomposition following herbicide treatment could temporarily lower the dissolved oxygen in the water under the plant canopy. The USDA-ARS and the CDBW conducted an experiment in the summer of 2016 to monitor dissolved oxygen following herbicide treatment relative to untreated water hyacinth canopies and open water. The experiment was conducted in two Delta environments, the first was channels subject to tidal fluctuations and mass flow, and the second was in backend sloughs where there was minimal water movement. Three channel-side sites were chosen and three 30.5m by 9.1m plots per site were randomly assigned to be treated with glyphosate, 2,4-D, or remain untreated. Three backend slough sites were chosen and four 30.5m by 9.1m plots per site were randomly assigned to be treated with imazamox, glyphosate, 2,4-D, or remain untreated. A miniDO2T datalogger measuring dissolved oxygen every 30 minutes was deployed under the canopy in each plot. Data was collected two week prior to treatment through six WAT. MiniDO2T dataloggers were deployed in the open water, away from water hyacinth canopy, in the channels and in the backend sloughs. The dissolved oxygen levels PRE and POST treatment were compared for each treatment, using ANOVA (p = 0.05). For the channel-side trial, there was no significant difference in dissolved oxygen levels for any of the treatments (p > 0.18). In the backend sloughs, there was no significant difference in dissolved oxygen levels for any of the treatments (p > 0.92 for all comparisons). Herbicide treatments did not result in a significant deline in dissolved oxygen after treatment relative to pretreatment levels.