Coos Bay
[5] The bay was formed when sea levels rose over 20,000 years ago at the end of the Last Glacial Maximum, flooding the mouth of the Coos River.
[7][8] Dredging, deepening, river diversion and spoil disposal has led to physical, biological, and chemical changes to the system over time.
[9] The Empire Formation, on which Coos Bay lies, is mainly composed of sedimentary rock created by marine sediments that were deposited offshore before being pushed onshore over millions of years.
[13] In addition, sea level rise 20,000 years ago drowned the prior river mouth, creating Coos Bay estuary as we know today.
[4] The higher organic content of mudflats is composed of plant and animal tissues and wastes, diatoms, bacteria, and flocculants, chemicals that pull suspended particles out of the water to form into sediment.
[4] The environment a few centimeters below the sediment doesn't have enough oxygen, so sulfate-reducing bacteria live there, breaking down organic matter and producing hydrogen sulfide, giving the mudflats the classic "rotten egg" smell.
[17] For an estuary, this involves the tributaries and their flow rates, bottom topography, water discharge and the drainage basin, and sedimentation and deposition.
[22] In the summer, wind primarily comes from the North along the Oregon coast, bringing up nutrient-rich deep water and boosting primary production.
[28] Temperature, salinity, and dissolved oxygen levels vary according to wind forcing, river discharge and tides, with a variety of timescales from daily (tidal) to yearly.
[23][4] Lowest dissolved oxygen levels are found in the mouth in the spring and at the riverine end in late summer and early fall.
[23] Overall, there is minimal likelihood of hypoxia due to rapid tidal exchange and shallow waters, based on the established dissolved oxygen content of the estuary throughout the year.
[4] South Slough did not exhibit any distinct seasonal pattern in pH at any of the monitoring sites, instead remaining within 7.5 and 8.2 year round at Valino Island.
[3] Historically, Coos Bay has been subject to a range of pollutants from different sources from logging mills, boat manufacturing, and runoff.
The area is also particularly vulnerable to any oil or chemical spills at the International Port of Coos Bay, due to its strong tidal currents.
[30] After sample results showed toxic levels of TBT, the two shipyards worked with the DEQ to clean up contaminated sediments and implement more environmentally conscience practices, which allowed Coos Bay to avoid being listed as a superfund site.
The forested regions of Coos Bay have been logged at least once in the past century, and some of these areas were replanted solely with Douglas fir trees.
[3] Sitka spruce, western hemlock, and Port Orford cedar trees can also be found in Coos Bay watershed, ranging from 15- to 75-years of age.
[34] Over the course of the study, which includes the transition from El Niño to La Niña, leading to warmer winters and cooler summers, eelgrass density, biomass, and flowering all increased.
[4] Z. japonica converts unvegetated mudflats into eelgrass beds, leading to significant changes in the species composition and abundance of invertebrate communities of the area.
[31] In a typical year, there is a small bloom of diatoms in the late winter and early spring before heavy grazing pressure by the zooplankton limits overall abundance.
[2][3] Surveys in the South Slough, the most commonly studied portion of Coos Bay, have shown that Shiner perch are the most abundant fish in the estuary.
Commonly found plants include Triglochin maritirh, Scirpus robustus, Carex, Jaumea, Spergularia, Juncus lescurii, and Cotula coronopifolia.
Commonly found plants include Carex, Deschampsia, Hordeum, Juncus lesccurii, Potentilla pacifica, Distichlis, Artiplex natula, and Agrostis alba.
Commonly found plants include Remex occidentalis, Grindelia stricta, Trifolium wormskjoldii, Vicia gigantea, and Lathyrus japonicus.
[37] However, South Slough was rated higher than average for adaptive capacity because there is a lot of space for marsh migration as sea levels rise; recommendations for management include protecting these surrounding areas.
[42] Additionally, boats and ships have accidentally introduced terrestrial plant species such as gorse, English ivy, reed canary grass, and Spartina spp.
[3][38] The South Slough Research Reserve is aware of these species and, according to its 2017-2022 Management Plan, is "motivated to minimize their damaging effects early.
[8] In 1976, the Coos Bay was dredged as part of the Deep-Draft Navigation Project, a campaign by the US Army Corps of Engineers to increase channel depth and width for vessel usage.
[8] A harbor and bridge were constructed in the entrance of South Slough, and the entry point of Coos River into the estuary has been redirected to the west, partially separating it from the east-estuary flats.
[46] Coupled with the Coos Bay Rail Line, which threads through the Oregon Coast Range to Eugene, the port could see increased usage in coming years.
