35 years of change in the fauna of Nevada City due to sewer plant upgrades
I was hired to run Nevada City's primative sewer plant in 1982 and to oversee million dollar upgrades. From about 1950, when Nevada City first got a sewer plant (before then just a pipe putting wastes into Deer Creek downstream from town), to 1992, the main treatment was spraying sewage over 9000 square feet of beds of cobbles which served as substrate for sewage-eating bacteria with huge masses of midge fly larva, psychoda flies and other insects and harvestmen living off the bacterial masses. It was a specialized mini ecosystem and food chain. Year round there was always a family of Black Phoebes--always--which built its mud nests on site. That Phoebe family still lives there now in 2014. Two dozen American Robins also lived there year round and did not migrate. Every year 100s or even thousands of swallows showed up to feed, and they (and the bats at night) flew in persistent patterns: they flew eastward low over the trickling beds, swung upwards and back towards the west and then down again for another pass. The swallows and bats lived elsewhere in colonies mostly in or on the buildings in downtown Nevada City. Unpredictably and irregularly, flycatchers and western bluebirds would show up in spring or summer in small flocks--but not every year. There were also warblers and kinglets in their seasons. During heavy snows when the trickling beds were the only snow-free source of food, all kinds of birds showed up from hunger, including the Stellar Jays which in snowless times preferred other food sources. In the evenings, downtown Nevada City squeaked with the sound of waking bats in the upper stories of the old buildings and businesses. People sometimes stood at downtown corners to watch the bats drop down from the eaves.
In 1992, the wastewater plant upgraded to different processes, and the trickling beds were removed. The midges disappeared along with the harvestmen and other insects and arachnids. The Robins stopped coming and presumably took to migrating or to starving. The bats disappeared from downtown Nevada City. The swallows stopped showing up. Only the Phoebe family remained.
Point: the wastewater plant now treats sewage to a high degree, and the water in Deer Creek is clear and clean, but an ecosystem was disrupted and many creatures were put into peril.
