This site - that is being scarified - is one of our Spawning Study Sites in the Winters Putah Creek Parkway. We had numerous pairs of salmon that spawning at this site in 2016. I will be measuring the degree of "cementation" which is the percent of the cobble that is locked by a condition called sedimentation.
Cementation is caused by a chemical reaction with sediment and minerals in the water. The process can totally entrap cobble and make it so hard that aquatic invertebrates cannot seek harbor in the spaces between the cobble. Salmon and trout cannot dig effective redd (nests) for protection of their eggs. Much of the riparian ecology can be interrupted by the condition.
Aquatic invertebrates, such as the stonefly nymph on the left, cannot seek safety from predators when the cobble is cemented. Invertebrate popularizations then to decrease in density and diversity. Fish and many riparian wildlife are impacted by the decreased prey base of aquatic insects.
Successful female salmon dig their redds (nests) in areas where their eggs will be safe from hungry trout and other animals. When they choose sites which do not have open gravel (non-cemented), the eggs can be eaten by other fish or simply perish. After hatching, the Alevin (newly hatched salmon) also require protection within open spaces between the cobble.
Part of the ongoing study is to determine if female salmon in 2016 selected spawning sites dependent on ideal substrate or flow regime.
The Fix: An expert operator, using a mid- or long-reach excavator can easily penetrate the hard crust caused by sedimentation. Once the crust is broken, it appears that Chinook salmon can maintain the open cobble condition. One control site was originally scarified in 2014. It appears that three years of spawning salmon have doubled the size of the original spawning site by digging at the edges. No additional scarification has been needed. We will continue to monitor the site, the redds, and the percent of cementation in the spawning areas and in control areas.
Thirteen scarification sites, several control sites and two former scarification sites will be monitored on a regular basis. We will be measuring the depth of salmon redds, the percent of sedimentation, and benthic macroinvertebrate density and diversity. Reports of the monitoring will be available on this site.
Check back for Monitoring Documents