Monitoring aids control of ag-related stream-temperature increases

C only has so much water to go around and using it in one place can have unintended — and undesirable — consequences in another. Take the Klamath River, where large-scale water diversions for agriculture contributed to low flows and warm waters in 2002, which in turn are blamed for this summer’s dive in chinook salmon stocks. Likewise, salmon and other cold-water fish can suffer when warm irrigation water is discharged into streams. While the impacts are small individually, they can add up over an entire watershed, particularly in California where temperatureimpaired streams and at-risk salmon populations overlap considerably. In response to pressure from environmental groups over the salmon decline, agricultural discharge regulations for stream temperatures are now in the works. To help ranchers and other stakeholders comply with these upcoming temperature regulations, UC Cooperative Extension (UCCE) researchers are developing ways to monitor and mitigate stream temperatures (see pages 153, 161). “Our goal is to help ranchers and other stakeholders figure out what’s going on in their creeks, and start seeing how management affects stream temperature,” says UCCE rangeland watershed specialist Kenneth Tate. California has 10 populations of chinook, coho and steelhead that are federally listed as threatened or endangered. Fish in the salmon family depend on cold water for all stages of their life cycle, from migration to spawning to rearing. While the temperature requirements vary with species and age, the preferred ranges for growth and survival are generally 45 ̊F to 58 ̊F (see figure, page 150). “Higher temperatures are usually less than optimal and those above the upper seventies are usually lethal,” says UCCE anadromous and inland fisheries specialist, Lisa Thompson. Irrigation systems can raise stream temperatures to the suboptimal or even lethal range. For example, flood-irrigation water can heat up as it crosses pastures, thus adding warm runoff to streams. Other types of land use that can increase stream temperatures include logging and grazing, which can reduce the riparian vegetation that shades and so keeps streams cool. Until recently, such agricultural discharges were allowed under a statewide waiver granted by the State Water Resources Control Board. Now, however, the regulations for agricultural discharge are in flux. In addition, the particulars vary from region to region because they are set individually by local water-quality control boards. For example, the Central Valley region (from Modoc County to Kern County) has adopted a conditional discharge waiver tied to a compliance process. In contrast, the North Coast region (from Del Norte/Siskiyou counties to Sonoma County) does not currently grant irrigation waivers. “We have no plans for a waiver,” says Catherine Kuhlman, executive officer of the North Coast Water Quality Control Board (NCWQCB). “It is reasonable to forecast that at some point in the future, anyone in the state discharging pollutants that affect water quality will need to be covered by a waiver or permit. That said, it is going to take us awhile to get there.”