Sacramento River - Ecology

Ecology

The Sacramento River and its drainage basin were originally abundant in multiple avian and aquatic species, but modern-day development has thinned populations of many species, especially riverine. The river's once-ample stretches of riparian zones and marshes, supported by its wide variations in flow, as well as the wetlands downstream in the Delta, have mostly been replaced by agricultural lands. The Sacramento supports 40–60 species of fish, and 218 types of birds. The basin is relatively abundant in endemic amphibian and fish species. It is surmised that between four and five million years ago, the Sacramento and Snake-Columbia River systems were somehow connected by a series of now-dry wetlands and river channels. Many of the fish in the present-day river are similar to those of the other, indicating a possible link sometime in the past. The Sacramento and San Joaquin also have the southermost runs of five species of anadromous fish.

Wildlife along the Sacramento has been hurt severely by the heavy usage of Sacramento River water for agriculture and urban areas, and pollution caused by pesticides, nitrates, mine tailings, acid mine drainage and urban runoff. Located along the Pacific Flyway, the sprawling marshlands of the Sacramento Valley were originally an important stop for migratory birds; only a few wetlands remain today, either preserved or artificially constructed. Native bird populations have been declining steadily throughout the 19th, 20th and 21st centuries. Species that were once common but now are gone or endangered include the Southwestern Willow Flycatcher, Western Yellow-billed Cuckoo, Least Bell's Vireo, and Warbling Vireo. Another reason for dropping numbers are the introduction of non-native species, such as the "parasitic" cowbird, which steals the nests of other birds to use as its own.

There were once 9 species of amphibians that used the Sacramento River, but some have become extinct and the population of the others are declining drastically due to the loss of their habitat. Amphibians originally thrived in the marshes, sloughs, side-channels and oxbow cutoffs because of their warmer water, abundance of vegetation and nutrients, lower population of predators, and slower current. Encroachment of agricultural and urban land has eliminated most of this habitat. This population once included several species of frogs and salamanders; the foothill yellow-legged frog and western spadefoot are listed as endangered species.

The riparian areas along the Sacramento once totaled more than 500,000 acres (2,000 km2); today only about 10,000 acres (40 km2) remains. Much of it consists of restored stretches, and there is also a significant amount of artificial wetland in the watershed. River control has prevented the Sacramento from its natural flooding, braiding and course-changing patterns, which are important for the maintenance of existing wetlands and the creation of new ones. Since the 1860s, the river has been mostly locked in its channel, which once could shift hundreds of feet or even several miles in a year because of floods. These wetlands originally flooded every winter and spring, but levee construction, agricultural encroachment and the construction of dams upstream have also eliminated the flooding process. Today about 100 miles (160 km) of the river’s riparian forests are undergoing active restoration.