title: Impacts of surface water diversions for marijuana cultivation on aquatic habitat in four northwestern California watersheds.
abstract: Marijuana (Cannabis sativa L.) cultivation has proliferated in northwestern California since at least the mid-1990s. The environmental impacts associated with marijuana cultivation appear substantial, yet have been difficult to quantify, in part because cultivation is clandestine and often occurs on private property. To evaluate the impacts of water diversions at a watershed scale, we interpreted high-resolution aerial imagery to estimate the number of marijuana plants being cultivated in four watersheds in northwestern California, USA. Low-altitude aircraft flights and search warrants executed with law enforcement at cultivation sites in the region helped to validate assumptions used in aerial imagery interpretation. We estimated the water demand of marijuana irrigation and the potential effects water diversions could have on stream flow in the study watersheds. Our results indicate that water demand for marijuana cultivation has the potential to divert substantial portions of streamflow in the study watersheds, with an estimated flow reduction of up to 23% of the annual seven-day low flow in the least impacted of the study watersheds. Estimates from the other study watersheds indicate that water demand for marijuana cultivation exceeds streamflow during the low-flow period. In the most impacted study watersheds, diminished streamflow is likely to have lethal or sub-lethal effects on state- and federally-listed salmon and steelhead trout and to cause further decline of sensitive amphibian species.
authors.affiliation: California Department of Fish and Wildlife, Eureka, California, United States of America.
authors.forename: Scott
authors.initials: S
authors.lastname: Bauer
authors.affiliation: California Department of Fish and Wildlife, Eureka, California, United States of America.
authors.forename: Jennifer
authors.initials: J
authors.lastname: Olson
authors.affiliation: California Department of Fish and Wildlife, Eureka, California, United States of America.
authors.forename: Adam
authors.initials: A
authors.lastname: Cockrill
authors.affiliation: California Department of Fish and Wildlife, Eureka, California, United States of America.
authors.forename: Michael
authors.initials: M
authors.lastname: van Hattem
authors.affiliation: California Department of Fish and Wildlife, Eureka, California, United States of America.
authors.forename: Linda
authors.initials: L
authors.lastname: Miller
authors.affiliation: National Marine Fisheries Service, Arcata, California, United States of America.
authors.forename: Margaret
authors.initials: M
authors.lastname: Tauzer
authors.affiliation: California Department of Fish and Wildlife, Eureka, California, United States of America.
authors.forename: Gordon
authors.initials: G
authors.lastname: Leppig
mesh_terms: D000818:Animals; D059001:Aquatic Organisms; D002140:California; D002188:Cannabis / Q000254:growth & development*; D003247:Conservation of Natural Resources; D017753:Ecosystem; D062070:Hydrology; D012621:Seasons; D011795:Surveys and Questionnaires; D014867:Water
chemical_list: D014867:Water